Moisture and Condensation Problems in Buildings
#NO 12381 Building pressurisation can affect possibility of mould growth.
USA, IEQ Strategies, August 1999, pp 8-13, 9 figs.
Describes case studies which demonstrate the various ways that forced-air systems can significantly affect building pressures. In each case the authors were contacted to determine the cause of mould growth on interior drywall. In each case also, mould growth was determined to be caused by moisture accumulation in the drywall, primarily from the uncontrolled flow of outside air into the building envelope. The case studies concern: 1. Central exhaust system; 2. Building air chases used as a distribution system; 3. Leakage at guest room fan coil units. Concludes that moisture related damage in commercial buildings can result in millions of dollars in damage annually and can come from five possible sources of moisture: bulk moisture intrusion; internally generated moisture; vapour moisture diffusion; capillarity; air leakage. A primary cause of air leakage is depressurisation of the building by the HVAC system, although many HVAC designs have the opposite intent - to pressurise the building. Unfortunately current HVAC commissioning procedures are unable to accurately determine if the HVAC design intent has been accomplished. This is because current commissioning techniques are based on measurement of airflows at delivery and extraction points, such as a supply registers and exhaust grilles. Airflow measurements at these points alone cannot properly assess the performance of the HVAC system or its impact on the characteristics of a building because they fail to fully consider air distribution. The startup sequence of HVAC forced air systems is also a critical aspect of commissioning a building. An improper startup sequence will prevent a forced air system from performing according to the design intent. If this condition occurs during hot, humid weather, moisture accumulation and mildew can occur within several weeks.
mould, building pressurisation, air flow
#NO 12403 Why HVAC commissioning doesn't work in hot, humid climates.
DuBose G, Odom J D, Fairey P
USA, IEQ Strategies, August 1999, pp 4-7.
Moisture-related damage in commercial buildings is a pervasive problem in hot, humid climates. Excess moisture in buildings can stem from failure to control moisture sources, including rain, groundwater, moisture diffusion, and airflows. A growing body of evidence indicates that the most problematic of these climatic moisture sources in hot, humid climates is the uncontrolled flow of outdoor air within the building envelopes. Solving this problem is difficult because current commissioning techniques cannot accurately predict airflows because they do not measure their driving force. As a result, owners cannot identify potential moisture-control problems prior to acceptance of new buildings. Also air -transported moisture is invisible and can travel long distances through interstitial cavities in buildings before accumulating and manifesting in such problems as mould, mildew or corrosion. Thus moisture control problems are not easily diagnosed. The case studies cited in the article illustrate the complexity of the problem and identify common sources of uncontrolled airflows in commercial buildings.
commissioning, hot climate, humid climate, air flow
#NO 12420 Alaska craftsman home program. Design and installation manual for residential mechanical ventilation systems.
Canada, Alaska Craftsman Home Program, Inc (ACHP).
Construction details used to reduce energy consumption and moisture damage to the building structure in modern houses greatly reduce natural air leakage. Without mechanical ventilation, normal activities such as laundry, cooking and showers can cause excessive humidity levels resulting in occupant discomfort, condensation on cool walls and windows and bacterial or fungal growth. There is also a concern with occupant health. Furthermore, as building envelopes become tighter, there is increased competition for air among the various systems, equipment, and appliances. The designer and installer of ventilation systems need to know about mechanical system design and installation guidelines that meet the Canadian standard CSA F326. Heating, Refrigeration and Air Conditions Institute of Canada (HRAI) has developed this manual and training program to provide those involved in the design, installation and inspection of mechanical ventilation systems for residences the training and documentation necessary for them to understand the requirements of and comply with the standard. Chapters cover ventilation; definitions; ventilation and distribution; ventilation system design; ventilation system installation; and system commissioning.
mechanical ventilation, system design
#NO 12438 Defying all skeptics, Steve Lentz's homes work great.
USA, Energy Design Update, October 1999, pp 6-9.
Describes the work of a home builder who has successfully incorporated airtight techniques in his new homes, without suffering indoor air quality or condensation problems, or prohibitive extra costs. The builder charges $1 extra per square foot for a package of airtightening and insulation measures, which meet the US Energy Star rating. The ten measures taken are: Use 2-inch extruded polystyrene on the exterior basement wall instead of the 1 inch specified in the Wisconsin energy code; Wrap all footings with 3-mil cross-laminated polyethylene instead of ordinary poly; Locate all ductwork inside the envelope (within conditioned spaces) and seal it with silicone mastic; Use 1-inch extruded polystyrene (R-5) under the basement floor versus none; Use 1 inch of polyisocyanurate on the exterior instead of 1 inch of extruded polystyrene; Use R-64 blown cellulose insulation in the attic versus R-38; Use cross-laminated 3-mil polyethylene as your air-vapour barrier instead of ordinary poly; Create a continuous air-sealed envelope; Make the attic hatch tight and well insulated; Install a radon-approved sealed sump pump.
low energy buildings, air tightness, cost effectiveness, energy rating, residential building
#NO 12441 Your mobile home. Energy and repair guide for manufactured housing.
USA, Saturn Resource Management, 1998, 224 pp.
The most important feature of manufactured homes for their customers is their low cost - about one third that of the average site-built home. Many metal-sided and metal-roofed mobile homes from the 1960s and 1970s are still in good repair in the United States. Most older mobile homes can be cost-effectively renovated and weatherized. Manufacturing defects, including ineffective insulation and duct air leakage can cause moisture problems, and inadequate insulation is also a major energy problem, along with excessive air leakage. Some new US mobile homes can be very energy efficient. This book describes how the homeowner can upgrade the energy efficiency of the older mobile home, reducing heating and cooling cost by up to 40%. Covers foundations, landscaping, health matters, air leakage, insulation, floors, walls, doors and windows, roofs and ceilings, heating, cooling, water heating, plumbing and electrical matters.
low income housing, retrofitting
#NO 12443 The application of dynamic insulation in buildings.
Taylor B J, Imbabi M S
Pergamon, Elsevier Science Ltd, 1998, proceedings of "Renewable Energy: Energy Efficiency, Policy and the Environment", World Renewable Energy Congress V, 20-25 September 1998, Florence, Italy, edited by A A M Sayigh, Volume 1, pp 377-382, 2 figs, 2 tabs, refs.
Dynamic insulation, a form of 'Breathing Wall' construction which allows the movement of air and moisture through the external walls of a building, was seen as one possible method for reducing building envelope heat losses and achieving high indoor air quality. A research investigation was conducted to provide a firm scientific understanding of dynamic insulation. An important outcome of the work will be the development of building envelope designs which effectively and economically employ dynamic insulation in cold climates. This paper presents some general conclusions, confirming that the energy saving produced by dynamic insulation alone is small relative to that obtained in conjunction with conventional air heat recovery methods.
cold climate, building envelope
#NO 12474 Solving a chimney moisture problem.
USA, Home Energy, September/October 1999, pp 40-47.
Describes a case study of a diagnostic problem regarding a chimney moisture problem, which proved to derive both from rainwater leakage around the chimney, due to a flashing problem, and a chimney obstruction that led to considerable condensation. Also discusses the usefulness of diagnostic tools for such a problem, including manometer, blower door, camera, chemical smoke, data logger, CO detector, static pressure probes, etc.
#NO 12476 Measurements to solve indoor air problems: Part 1: Tools of the trade.
USA, Heating, Piping and Air Conditioning, July 1999, pp 23-28, 5 refs.
Describes tools that can be useful for IAQ investigations, including thermal comfort and moisture problems. Considers occupant-related techniques, including interviewing; measurements and equipment including contaminant tools and transport mechanisms; the personal tool box and its likely contents for every case, frequently needed items and for specific cases.
instrumentation, diagnostic tools
#NO 12515 Evaluating active desiccant systems for ventilating commercial buildings.
Harriman L G, Witte M J, Czachorski M, Kosar D R
USA, ASHRAE Journal, October 1999, pp 28-37, 7 figs, 2 tabs, 9 refs.
States that over the last 15 years, active desiccant systems have become a common component of HVAC systems in commercial buildings needing lower-than-usual humidity levels. Ice arenas, supermarkets and refrigerated warehouses all contain refrigeration systems which cool air more effectively when most of the building's moisture load is removed by an active (heat-reactivated) desiccant system. Cost savings, comfort improvements and "process benefits" of extended-season operation for ice rinks, lower product temperature for supermarkets and improved safety for warehouses are usually enough to make the desiccant component a useful addition to such buildings.
#NO 12559 Indoor Air 99. The 8th International Conference on Indoor Air Quality and Climate. Volume 1.
Raw G, Aizlewood C, Warren P (eds.)
UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 1, 940 pp.
The papers in this volume are in the following sections: ventilation and energy; studies of sick building syndrome; IAQ standards and regulations; indoor air biologi: non-domestic buildings; ventilation guidelines, operation and comfort; VOC sources and sinks; IAQ codes and guidelines; thermal comfort; modelling, simulation and prediction: temperature, air flow and moisture; sick building syndrome research methods; indoor air biology: homes.
indoor air quality
#NO 12560 Indoor Air 99. The 8th International Conference on Indoor Air Quality and Climate. Volume 2.
Raw G, Aizlewood C, Warren P (eds.)
UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 2, 980 pp.
The papers in this volume are in the following sections: ventilation modelling and simulation; thermal comfort and multi-factor studies; indoor air biology: HVAC; risk and IAQ indices; ventilation systems and strategies; VOCs in non-domestic buildings; moisture and mould; odour and sensory irritation; air cleaning and filtration; measurements, methods and portable devices; pollutant mixtures and exposures; radon and ETS.
indoor air quality
#NO 12565 Measured airtightness of an installed skylight.
Shaw C Y, Magee R J, Poirier G F
USA, ASHRAE Transactions, Winter Meeting 2000, Dallas, 6 pp, 7 figs, 1 tab, refs.
An art gallery building had problems with moisture. Inspections using thermographic techniques suggested that air leakage through the skylights could be the main cause of the problem. The air leakage rate of an installed metal frame skylight, 26 m long x 8.5 m wide, was measured, using the balanced fan depressurisation method. Also, fan depressurisation tests were performed on the glazing/upstand interface on the south side of the skylight. The air leakage rates were measured through the full interface and on the west and east halves separately. The methods used for field testing of such components and the test results are discussed.
air tightness, roof, window, public building, moisture, air leakage rate
#NO 12576 Simplified tools for evaluating domestic ventilation systems.
Mansson L-G, Orme M
USA, ASHRAE Transactions, Annual Meeting 1999, Seattle, 1 fig, 6 tabs, refs.
Within an International Energy Agency (IEA) project, Annex 27, experts from 8 countries (Canada, France, Italy, Japan, The Netherlands, Sweden, UK, and USA) have developed simplified tools for evaluating domestic ventilation systems during the heating season. Tools for building and user aspects, thermal comfort, noise, energy, life cycle cost, reliability and indoor air quality (IAQ) have been devised. The results can be used both for dwellings at the design stage and after construction. The tools lead to immediate answers and indications about the consequences of different choices that may arise during discussion with clients. This paper presents an introduction to these tools. Examples applications of the indoor air quality and energy simplified tools are also provided. The IAQ tool accounts for constant emission sources, CO 2 , cooking products, tobacco smoke, condensation risks, humidity levels (i.e., for judging the risk for mould and house dust mites), and pressure difference (for identifying the risk for radon or land fill spillage entering the dwelling or problems with indoor combustion appliances). An elaborated set of design parameters were worked out that resulted in about 17000 combinations. By using multivariate analysis it was possible to reduce this to 174 combinations for IAQ. In addition, a sensitivity analysis was made using 990 combinations. The results from all the runs were used to develop a simplified tool, as well as quantifying equations relying on the design parameters. A computerized energy tool has also been developed within this project, which takes into account air tightness, climate, window airing pattern, outdoor air flow rate and heat exchange efficiency.
ventilation system, residential building
#NO 12596 Wrap it up: building houses with the skin on the outside.
USA, Home Energy, November/December 1999, pp 13-17, 3 figs.
Describes how one simple way of sealing the building envelope to eliminate air and moisture seepage is by putting the insulation and the air/vapour barrier on the outside of the house's frame, minimising penetrations that cause holes and thermal bridging. The method uses the Pressure Equalised Rain Screen Insulated Structure Technique (PERSIST).
exterior cladding, thermal insulation
#NO 12640 Residential pollutants and ventilation strategies: volatile organic compounds and radon.
Grimsrud D T, Hadlich D E
USA, ASHRAE Transactions, Annual Meeting 1999, Seattle, 15 pp, 3 tabs, refs.
This paper reviews literature that reports investigations of residential ventilation and indoor air quality. Two important residential pollutant classes, volatile organic compounds and radon, are examined. A companion paper (Hadlich and Grimsrud 1999) examines moisture and combustion pollutants. Control strategies recommended from the review include appropriate building design to prevent or limit the sources of the pollutants within the space, proper operation and maintenance to prevent adverse conditions from developing during the building's life and appropriate use of ventilation. The characteristics of these pollutant sources suggest that ventilation systems in residences should have several properties. They should have the extra capacity available to reduce short bursts of pollution, be located close to the expected source of the contamination, and be inexpensive. Mitigation of radon is technically a major success using a form of task ventilation. Whole house ventilation is, at best, a secondary form of control of excess radon in residences.
VOC, radon, building design, maintenance, residential building
#NO 12643 Residential pollutants and ventilation strategies: moisture and combustion products.
Hadlich D E, Grimsrud D T
USA, ASHRAE Transactions, Annual Meeting 1999, Seattle, 16 pp, refs.
This paper reviews literature that reports investigations of residential ventilation and indoor air quality. Two important residential pollutant classes, moisture and combustion pollutants, are examined. A companion paper (Grimsrud and Hadlich 1999) examines volatile organic compounds and radon. Control strategies recommended from the review include appropriate building design to prevent or limit the sources of the pollutants within the space, proper operation and maintenance to prevent adverse conditions from developing during the building's life and appropriate use of ventilation. The characteristics of these pollutant sources suggest that ventilation systems in residences should have several properties. Moisture control puts significant restrictions on a ventilation system. The system should function continuously (averaged over days) and distribute ventilation throughout the habitable space. Combustion sources require task ventilation that functions reliably.
moisture, combustion products, residential building
#NO 12653 Effect of duct-cleaning detergents and disinfection substances on mould growth.
Pasanen P, Pasanen A L, Luoma M, Kalliokoski P
Operating and maintaining buildings for health, comfort and productivity. Proceedings IAQ '93, Philadelphia, November 1993, Teichman K Y Ed., ASHRAE, 139-142, 3 tabs, refs, ISBN 1 883413 13 3
The accumulation of dust including fungi in ventilation ducts may diminish comfort or cause health problems. If moisture is available in ducts, microrganisms may proliferate rapidly in dust. Therefore, air ducts are usually cleaned periodically to diminish these problems. In addition to detergents, disinfectants are often used to enhance the cleaning efficiency. In this study, the effects of seven commercial cleaning and disinfecting agents were tested against the growth of Penicillium verrucosum, Aspergillus veriscolor, Cladosporium sphaerospermum, and Aureubasidium pullulans on agar. Three dilutions of each substance were made for the test; one or two of the dilutions were adjusted to the concentration range recommended by manufacturers. Ethyl alcohol (70%) and distilled water were used as controls. The diameters of inhibition areas were measured after four and ten days from the addition of substances. The inhibition effect of the substances varied with different strains. Penicillium verrucosum was the most tolerant fungus and none of the tested products had a long-term effect (10 days) on its growth. A. pulllulans was the weakest fungus against the substances. The effect of the highest concentration of six substances was stronger than that of ethanol (70%), but even their inhibition effect decreased with time. The lowest concentration of two substances had only a slight influence on mould growth. Thus, duct-cleaning agents seem to provide only short-term protection against fungal growth in ducts.
duct cleaning, chemical cleaners, mould, fungus
#NO 12660 The ten main reasons why HVAC systems get dirty.
DucTales, July/August 1998, Vol 10, No 4, pp 24-26, 1 ref.
Reports the findings of survey of foremen by a duct cleaning company to discover why HVAC systems get dirty in the first place. The top 10 reasons were - 1) No filters, 2) Gapped or poorly-fitted filters, 3) Poor filters, 4) Filters not changed or cleaned regularly, 5) Neglect of the units, 6) Dirty environment, 7) Duct leakage, 8) Poor or no condensation drainage, 9) Deteriorated fibreglass insulation, 10) Leaks in air handlers, such as worn seals around doors or holes in cabinets. Discusses each of these points.
ventilation duct cleaning, maintenance, design
#NO 12684 Unventing attics in cold climates.
USA, Home Energy, November/December 1999, pp 27-28, 2 figs.
Explores the possibility of constructing a cold climate attic with no vents, and achieving large improvements in performance and energy savings. Venting can cause problems in cold dry climates such as allowing snow to blow in, as well as problems with the design of complex geometry roofs. If the roof sheathing is kept above the dew point temperature of the interior air vapor mix, condensation and moisture accumulation will not occur. So the ventless design will depend on installing a continuous ceiling vapour diffusion retarder/air retarder and thick ceiling insulation.
attic, cold climate, sealing, moisture
#NO 12709 Health house cold climate standards keep occupants warm and dry.
Farnsworth C B
USA, Home Energy, November/December 1999, pp 34-38.
Describes the American Lung Association's latest Health House development, which sets new standards for affordable, healthy, and energy efficient construction at the Meskwaki Indian Settlement in Tama County, Iowa. The community is investing revenues generated by Indian gaming to improve their housing. The earlier housing programmes had built tight, energy efficient houses, but all the houses suffered badly from condensation and moisture problems. The new houses do not have moisture problems, mainly due to thorough air sealing and to mechanical ventilation. The ALA standards are modified to work for the specific climate zone that the house is located in.
health, cold climate, condensation, energy efficiency, low income housing
#NO 12716 Impact of ASHRAE Standard 62-1989 on Florida retail stores.
Chasar D A, Shirey D B
in: USA, ASHRAE, 1999, "IAQ and Energy 98: Using ASHRAE Standards 62 and 90.1", pp 99-113, 6 figs, 9 tabs, refs.
Increased outdoor air ventilation rates will greatly increase dehumidification loads to be met by air-conditioning (AC) systems in most humid climate applications. In this study, building energy simulation software was used to investigate the impacts of increased ventilation as specified by ASHRAE Standard 62-1989 on a typical Florida retail store. Detailed evaluation of indoor humidity was accomplished through modelling of moisture transport and storage in common building materials. In addition, a model to predict the effect of continuous supply fan operation on air-conditioner latent capacity was included.
Annual simulations of the modelled retail store were performed using hourly weather data for Miami, Orlando and Jacksonville. Heating, ventilating and air-conditioning (HVAC) system performance was evaluated and compared for a conventional direct expansion (DX) system as well as several commercially available alternative technologies. Cost-effective options for meeting the new ventilation requirements were identified through analysis of the installed first cost and life-cycle cost for each system.
Simulation results indicate that conventional rooftop package DX air conditioners with a sensible hear ration (SHR) of 0.75 would be made unable to maintain acceptable indoor humidity throughout the year under the new ventilation standard. While elevated ventilation rates increase both sensible and latent loads on HVAC systems, the ventilation load can be over 90% latent in humid climates. Several of the alternative HVAC systems evaluated in this study were able to offset the increased ventilation loads, including the heat pipe-assisted air conditioner, chilled water system with ice storage, and three pre-treatment technologies in conjunction with a conventional air conditioner (100% outside air DX unit, gas-fired desiccant system, and enthalpy wheel). While all of these systems provided enhanced humidity control, the enthalpy recovery wheel system did so while minimizing the energy impacts of increased ventilation. In addition, the enthalpy wheel system offered the lowest first cost and life-cycle cost of any of the other alternative technologies.
standard, commercial building, humidity
#NO 12717 The impact of part-load air-conditioner operation on dehumidification performance: validating a latent capacity degradation model.
Henderson H I
in: USA, ASHRAE, 1999, "IAQ and Energy 98: Using ASHRAE Standards 62 and 90.1", pp 115-122, 9 figs, refs.
Constant-volume air-conditioning systems provide space conditioning in many residential and commercial buildings. In these applications, the compressor typically cycles on and off to meet the cooling load, while the supply fan operates constantly to ensure the zone is well mixed. Under this scenario, it has been demonstrated that the dehumidification capacity of an air-conditioning system degrades at part-load conditions because moisture on the cooling coil surface evaporates back into the airstream when cooling is deactivated. Henderson and Rengarajan (1996) developed and engineering model of this phenomenon suitable for use in hourly building simulations as well as other types of analysis. The model considers conditions entering the coil, thermostat cycling rates, air-conditioner transient performance, and the moisture-retaining characteristics of the cooling coil.
Previous laboratory measurements have shown that during the OFF cycle, the cooling coil essentially acts as an evaporative cooler, adiabatically providing both sensible cooling and moisture addition. This paper uses that knowledge to determine the moisture evaporation characteristics of a cooling coil installed in a residence with relatively simple temperature measurements. Field-monitored data for a residential water-to-air heat pump are used to determine required parameters for the latent degradation model. The model was able to properly predict the measured latent degradation effects measured over the cooling season. The paper also discusses the other types of experimental data that would be required to further validate the model for various classes of cooling coils and operating scenarios.
#NO 12719 Monitoring ventilation performance.
Bearg D W
in: USA, ASHRAE, 1999, "IAQ and Energy 98: Using ASHRAE Standards 62 and 90.1", pp 139-146, 8 figs, refs.
The ongoing development of systems for continual, multi-point monitoring of key IAQ parameters is expanding the ways that can be used to optimise building performance by reducing uncertainties associated with the ventilation component of the HVAC system. The monitoring data provide specific details, not only on ventilation, but also on related areas that permit improved operation for both IAQ and energy consumption. The specific information provided on ventilation performance includes.
1. determination and evaluation of the adequacy of the ventilation rates achieved.
2. performance of the ventilation system relative to the distribution of people.
3. determination of the percentage of outdoor air in the supply air as a function of the mechanical system components
involved, including the outdoor air damper position.
4. effectiveness of the overnight purge of the building in its elimination of air contaminants of human origin.
5. identification of indoor sources of moisture.
6. identification of potential energy savings in areas that are significantly over-ventilated.
7. identification of the magnitude and frequency of re-entrainment of building exhaust and the presence of vehicle
exhaust at the outdoor air intakes.
8. discovery of other ventilation problems, and
9. rapid evaluation of the effectiveness of corrective measures to correct these problems.
#NO 12752 Ventilation design in animal research facilities using static microisolators.
USA, ASHRAE Transactions, Winter Meeting 2000, Dallas, 8 pp, 11 figs, 1 tab, refs.
This paper presents the key conclusions from an extensive research project on ventilation design in animal research facilities using static microisolators. This study, which is presented in full in Memarzadeh (1998), considered both experimental and numerical aspects using the computational fluid dynamics (CFD) technique. As well as a summary of various gaseous generation rates for mice, this paper contains conclusions on the effects of changing various parameters within an animal research room on conditions in the cages and in the main room volume itself. These parameters include, but are not limited to, supply type, exhaust location and number, room ventilation rate, and supply air temperature and moisture content.
animal house, instrumentation
#NO 12757 Passive ventilation for residential air quality control.
USA, ASHRAE Transactions, Annual Meeting 1999, Seattle, 13 pp, 10 figs, refs.
Infiltration has long served the residential ventilation needs in North America. In Northern Europe it has been augmented by purposeprovided natural ventilation systems-socalled passive ventilation systems-to better control moisture problems in dwellings smaller than their North American counterparts and in a generally wetter climate. The growing concern for energy consumption, and the environmental impacts associated with it, has however led to tighter residential construction standards on both continents and as a result problems associated with insufficient background ventilation have surfaced. Recognizing the energy penalty of uncontrolled natural ventilation, building researchers and practitioners in North America are turning to mechanical systems to provide the necessary ventilation for air quality control. Northern Europeans are following suit but have not completely abandoned the passive ventilation methods that have served them for the past century. Research programs have been initiated in Britain, Belgium and France, in particular, to improve the understanding and performance of these traditional and largely empiricallybased ventilation methods in the hope that they can more reliably provide basic background ventilation while avoiding the energy penalty associated with uncontrolled overventilation. This state of affairs begs, then, a simple question: Can European passive ventilation systems be adapted for use in North American dwellings to provide general background ventilation for air quality control? This paper attempts to answer this question. The configuration, specifications and performance of the preferred European passive ventilation system-the passive stack ventilation (PSV) system-will be reviewed; innovative components and system design strategies recently developed to improve the traditional PSV system performance will be outlined; and alternative system configurations will be presented that may better serve the climatic extremes and more urban contexts of North America. While these innovative and alternative passive ventilation systems hold great promise for the future, a rational method to size the components of these systems to achieve the control and precision needed to meet the conflicting constraints of new ventilation and air tightness standards has not been forthcoming. Such a method will be introduced in this paper and an application of this method will be presented.
residential building, indoor air quality, moisture
#NO 12782 Combined simulation of airflow, radiation and moisture transport for heat release from a human body.
Murakami S, Kato S, Zeng J
Building and Environment, No 35, 2000, pp 489-500, 16 figs, 2 tabs, 31 refs.
This paper described a combined numerical simulation method of airflow, thermal radiation and moisture transport for predicting heat release from a human body. A human thermo-physiological model was included to examine the sensible and latent heat transfer from the human body. Flow, temperature and moisture fields were investigated with three-dimensional Computational Fluid Dynamics (CFD). We used a low-Reynolds-number type k-e turbulence model, with the generalized curvilinear coordinate system to represent the complicated shape of the human body. The thermal radiation was calculated by means of Gebhart's absorption factor method, and the view factors were obtained by the Monte Carlo method. We adopted Gagge's two-model to simulate the metabolic heat production and the thermoregulatory control processes of the human body. The predicted results were very close to those of an actual human body in a similar situation.
air flow, moisture transport, occupancy effects
#NO 12790 Impact of added insulation on air leakage patterns.
Derome D, Fazio P, Desmarais G
Canada Mortgage and Housing Corporation, External Research Program Research Report, January 2000, 71 pp.
Adding insulation to exterior walls may worsen the original wall performance. Depending on the amount and geometry of air leakage in the original wall, added insulation may actually increase the potential for condensation, letting water accumulate in the wood structure and leading to rot.
An experiment was set up to compare the performance of different leaky walls and to investigate their behaviour with insulation added on one side or other of the wood studs. The experiment also maps the path of air leakage. The test conditions represented winter and late spring weather in Montreal,
It was found that the first measure to be considered remains the sealing and air tightening of the existing walls, with special care given to junctions and to punctures. If not sealed, leaky walls were found to accumulate moisture, especially when insulated on the outside.
external insulation, air leakage, wall
#NO 12791 Conception de joints durables entre les fenetres et les murs. Creating durable bonds between windows and walls.
Rousseau M J (ed.)
Canada Mortgage and Housing Corporation, Research Report, July 1999, 72 pp, in French.
Poor bonding details between a window (door) and the building shell cause many problems, the most significant of which are:
* rain penetration around the window;
* air infiltration or exfiltration around the window frame; and
* superficial condensation on the interior components of the window frame.
The problems stated above result in:
* a deterioration of interior finishes (peeling of paint and varnishes, lifting of floor finishes, mould, rotting, etc);
* a degradation of the building envelope components (corrosion of anchors, loss of structural properties for hygroscopic materials (wood, drywall), rotting of wood or rusting of steel);
* the presence of mould and a danger of infection for the occupants;
* a reduction in the thermal insulation properties of the materials, leading to greater energy consumption for heating and air conditioning;
* many drawbacks for the occupants of such a building (worry, frequent maintenance, discomfort, etc.); and
* an increase in the transmission of external noises towards the interior of he building due to the poor airtightness of the bond.
In general, the causes of the problems are mainly due to the design and production of the joints or the interface between the components.
window, wall, sealing, joints
#NO 12792 The parameters of the ventilation system of uninsulated cow shed.
Energy and Buildings, No 32, 2000, pp 1-4, 2 figs, 1 tab, 3 refs.
According to the equations of the balances of heat and moisture, the experimental and the analytical data, the mathematical model is created to ground the temperature regime and to calculate the parameters of the ventilation system of the uninsulated cow shed and that with the insulated roof. The suggested countable difference of the value between the internal and external temperatures is 3oC, the greatest permitted meaning is 6oC, and is does not depend on the other parameters of the building in the damp climate zone (in winter, the average dampness of the air is 85%), when the heat transmission coefficient of the external barriers of the cow shed is k = 3.0 W /(m2K). When the roof is insulated (kr + 0.3 W / (m2K)), the countable value of the temperature differences rises up to 7 - 11oC.
animal house, temperature difference, openings
#NO 12797 Building science 101: air barriers.
Canada, Solplan Review, January 2000, pp 3-7.
Air movement is the major factor in transporting moisture through building envelope assemblies. Many building envelope problems can be attributed to inadequate or failed air barriers. The National Building code of Canada has required air barrier systems since 1960. Unfortunately, there is considerable confusion between what is an air barrier and what is a vapour barrier. The two are distinct functions that, in some situations, may be satisfied by the same material components. In 1990, the wording of Part 9 of the Code was modified to clarify and separate the functional requirements for air barrier systems and vapour barriers. The Code now requires that the air barrier system provide an effective barrier to air exfiltration under differential air pressure due to stack effect, mechanical systems and wind. Discusses essential features of an air barrier, tightness, and air barrier joint materials. States that silicone based sealants and adhesive tape achieved the best performance under all conditions. Spun bonded olefin paper and acrylic base sealants should not be used at connections where the temperature may be hot. Staples to attach the spun bonded olefin should be avoided. Because of their high air permeability, open cell gaskets, mineral wool and perforated polyethylene membranes should not be used. The use of closed cell gaskets is not recommended because of problems with long-term performance.
air barrier, air movement, moisture, building envelope
#NO 12799 Dynamic insulation in multistorey buildings.
Taylor B J, Imbabi M S
Building Serv Eng Res Technol, Vol 20, No 4, 1999, pp 179-184, 1 fig, 4 tabs, 13 refs.
Dynamic insulation permits the movement of air and moisture through the external walls of a building to reduce heat loss and achieve high indoor air quality. The present paper details a pilot study carried out to examine the influence of fire safety requirements and external wind on the performance of naturally ventilated multistorey buildings in which the external envelope is dynamically insulated. The theoretical foundation is outlined for a spreadsheet model used to simulate prototype 3-,4-,5- and 10-storey buildings all sharing the same rectangular floor plan, with fresh air drawn into the building through the envelope by depressurisation using a fan-driven, ducted extract system. From the analysis, the effects of wall porosity, depressurisation level, extract system deployment, occupant density and distribution, and building orientation have been quantified, confirming the practical feasibility of such a system.
dynamic insulation, high rise building
#NO 12817 Be on your guard against tobacco smoke, moisture, pollen, radon and pets!
Swedish Building Research, No 1, 2000, pp 10-12.
Describes the conclusions and recommendations drawn from a workshop held last autumn on risk assessment and risk management. The aim of the workshop was to promote transboundary discussions between researchers in the medical, chemical, biological, occupational and environment medical and the building related sciences. The goal was to focus on available knowledge and techniques for the assessment of health hazards in the indoor environment caused mainly by chemical compounds, and to make this knowledge available to different groups. Discusses how Western lifestyle increases the risk, how the indoor environment of the home is most important, the significance of airborne pollutants, that a poorly cleaned, warm and moist environment is worst, smoke sources outdoors, radon, using buildings in the correct way, and the upkeep of the buildings.
health, indoor air quality
#NO 12839 Particle-bound benzene from Diesel engine exhaust.
Muzyka V, Veimer S, Shmidt N
Scand J Work Environ Health, Vol 24, No 6, 1998, pp 481-485, 1 fig, 1 tab, 17 refs.
The large surface area of the carbon core of diesel exhaust particles may contribute to the adsorption or condensation of such volatile carcinogenic organic compounds as benzene. the attention of this study focused on determining the distribution of benzene between the gas and particulate phases in the breathing zone of bus garage workers. Benzene and suspended particulate matter were evaluated jointly in the air of a municipal bus garage. Personal passive monitors were used for benzene sampling in the breathing zone of the workers. Active samplers were used for sampling diesel exhaust particles and the benzene associated with them. The benzene levels were measured by gas chromatography. Diesel engine exhaust from buses was the main source of air pollution caused by benzene and particles in this study. The concentration of benzene in the gas and particulate phases showed a wide range of variation, depending on the distance of the workplace from the operating diesel engine. Benzene present in the breathing zone of the workers was distributed between the gas and particulate phases. The amounts of benzene associated with particles were significantly lower in summer than in winter. The particulate matter of diesel exhaust contains benzene in amounts comparable to the concentrations of carcinogenic polycyclic aromatic hydrocarbons (PAHs) and the usually found nitro-PAH. The concentration of benzene in the gas phase and in the suspended particulate matter of air can serve as an additional indicator of exposure to diesel exhaust and its carcinogenicity.
vehicle exhaust, particulates, garage, workplace
#NO 12855 Moisture content of different new and used air filter media under static climatic conditions.
Bock R, Schleibinger H, Ruden H
paper from "Healthy Buildings/IAQ '97", proceedings of a conference held Natcher Conference Center at National Institutes of Health, Bethesda, USA, September 27-October 2, 1997, Vol 1, pp 593-598, 5 figs, 1 tab, 5 refs.
Microorganisms are able to colonize and amplify on different building materials if sufficient moisture and nutrients are present. Moisture may become available e.g. through sorption processes from the ambient air or from condensation. The moisture content (MC) required is often not large to enable supporting of moulds and/or bacteria growth.
This study describes the MC (or water binding capacity) of different commercial new and used air filter media determined under controlled static climate conditions. Measuring method was gravimetry by a precision scale, which has been a suitable method for the determination of MC of porous and lightweight materials. The collective data of this study show that moisture content of new filter media depends mainly on the textile structure of the medium, whereas the amount of atmospheric dust load is mainly responsible for the revealed MC of used filter media.
moisture, filter, building materials, microbiological pollutant
#NO 12859 Direct measurements of temperature and humidity in dust mite microhabitats.
Cunningham M J
Clinical and Experimental Allergy, Vol 28, 1998, pp 1104-1112, 4 figs, 1 tab, 21 refs.
Background - Up to 70% of atopic asthmatics have a positive skin test to the dust mite allergen Der p 1. Reduction of dust mite numbers by lowering room humidity control is one suggested technique for reducing dust mite allergen levels to clinically acceptable levels. Trials of this technique in temperate climates have reported mixed results. It has been speculated that one reason for this is that humidity changes in room ambient air are not tightly linked to humidity changes in the dust mite microenvironment (in the base of carpets, bedding, furniture etc.).
Objective - To directly measure humidities and temperatures in dust mite microenvironments and compare these to ambient conditions, and so gather on how the microclimates are influenced by room conditions and moisture and heat sources, such as an occupant in a bed.
Methods - A special small humidity device has been developed which can discriminate humidity changes over distances of millimetres. With these devices microclimates have been measures in the base of carpets, in layers through bedding, and in furniture.
Results - Measured base-of-carpets humidities were significantly higher than room humidities . Bedding relative humidities show complex behaviour according to the distance separation between the measuring point and the occupant. Immediately below the occupant, bed relative humidities fall when the person enters the bed. Similar behaviour is observed in a sofa.
Conclusion - Some dust mite microclimates have been shown to be very different from room conditions. Consequently, reduction of dust mite numbers and allergen levels cannot be guaranteed by controlling of room humidities.
temperature, humidity, dust mites
#NO 12860 Improved health after intervention in a school with moisture problems.
Ahman M, Lundin A, Musabasic V, Soderman E
Indoor Air, No 10, 2000, pp 57-62, 2 figs, 1 tab, refs.
In a school with floor moisture problems, the personnel had complaints consistent with the sick-building syndrome (SBS). Interventive measures including the laying of a ventilated floor were undertaken to eliminate the emissions. To examine if the intervention resulted in positive health effects, 34 personnel and 336 pupils were interviewed just before the intervention and also 7 months after. Also were interviewed 21 personnel and 224 pupils at an adjacent school serving as a control. Compared with the control school, the problem school showed more complaints, more general symptoms and more symptoms from the eyes, air-ways and skin, both among the personnel and the pupils. In the post-intervention examinations, the excess of symptoms among the personnel had almost disappeared. Among the pupils, the frequency of eye irritation was reduced but a general improvement of other symptoms was not obvious. However, after adjustment for a recent common cold, atopy and stress among the pupils, only one symptom ("stuffy nose") remained significantly elevated. In conclusion, the intervention was followed by positive health effects, supporting the hypothesis that emissions from building material had contributed to the excess of symptoms. A recent common cold was highly related to the symptoms and should be considered in future SBS studies.
health, school, moisture
#NO 12861 Orifices de ventilation, assechement par ventilation et moderation de la pression. Ventilation openings, ventilation drying and regulation of pressure.
Burnett E, Straube J
Canada Mortgage and Housing Corporation, December 1995, in French.
The orientation, size, and nature of vents in screened exterior wall systems are important to wall performance because these characteristics affect venting, ventilation and pressure moderation. The ventilation of screened wall systems has received very little attention in Canadian building research. An experimental and theoretical study of vents and venting in screened walls was undertaken. The objective of this study was to define the problems and potentials, develop upper and lower bounds of likely performance, and provide some theory and complementary experimental measurements as a precursor to future more detailed and directed studies. Considers literature review, theoretical considerations, the forces driving ventilation flow, ventilation flow rates, ventilation drying rates, laboratory vent flow tests, field pressure measurements, and gives conclusions and recommendations. Concludes that ventilation, even small amounts, can provide significant benefits to wall performance, mostly by contributing to the removal of moisture from behind the screen. If unobstructed cavities and several strategically located large vents are provided in a screened wall, significant ventilation air flow can occur, even with the very small driving pressures that typically occur in service. The same measures will allow for the moderation of wind-induced pressure differences across the screen. Laboratory testing of air flow through proprietary masonry vent inserts show that these inserts greatly reduce ventilation flow. The flow of air through vents driven by dynamic pressure variations is greater, sometimes significantly so, than when driven by a static pressure difference. Designing new or the retro-fit of existing wall systems that encourage ventilation flow can greatly increase the drying potential of a wall assembly. In masonry veneer construction, it is recommended that minimum venting, i.e., an open head joint every 600 mm o.c. at the top and bottom of a 2.5 m high cavity or 0.2% of the wall area, should be provided. To achieve significant benefits from pressure moderation and ventilation drying, at least three times this area (0.6% of wall area) should be provided. To ensure clear cavities (which encourage good ventilation and allow drainage), the minimum width of the air space should be 30 mm, preferably a width of 40-50 mm should be provided. Despite the benefits of ventilation flow, very little is known and it is recommended that a judicious mix of theoretical modelling, lab experiments, and field monitoring should be undertaken.
#NO 12862 Crawl space air change, heat and moisture behaviour.
Energy and Buildings, No 32, 2000, pp 19-39, 22 figs, 6 tabs, 15 refs.
The effect of ventilation on moisture behaviour in the traditional outdoor-air ventilated crawl space of flats with uncovered and moist ground surface is discussed in this paper. The objectives were to compare in real conditions the mechanical supply and mechanical extract ventilation, to determine the rate of ground moisture evaporation, and to test the reduction of humidity with plastic sheet cover. The study was made between April 1997 and October 1998 when the conditions in naturally and mechanically ventilated crawl spaces of the test building were monitored. The air change rate in the crawl space was monitored continuously, as were temperature and humidity. This made it possible to assess the moisture evaporation rate from the ground soil. Additionally, evaporation from some types of soil, crushed stone, gravel and granulated clay was measured in laboratory tests. The reported results account for the behaviour of air change and moisture balance, and give certain validity to arguments for optimum ventilation and the reduction of ground moisture evaporation. It was demonstrated that air change is only one important parameter affecting humidity in crawl spaces. Ground moisture evaporation was related to air change rate and pressure conditions: a higher air change led to higher moisture evaporation. Pressure conditions in the crawl space affected humidity notably; these were varied by using supply and extract fans and were monitored continuously during the measurements. Supply ventilation led to the lowest relative humidity, and extract ventilation brought about even higher humidity than did the natural. No high relative humidity level with natural ventilation and uncovered ground was less than 85%., and with ground cover or with balanced ventilation it did not exceed 80%. It seems that with supply or balanced ventilation at 1-3 ach and with ground cover applied it is possible to maintain the relative humidity level under 80% in the outdoor- air ventilated crawl spaces of blocks of flats.
crawl space, air change rate, humidity, moisture
#NO 12864 Ryomintatilan kosteus ja mikrobit. Crawl space moisture and microbes.
Kurnitski J, Pasanen P, Matilainen M, Hyttinen M, Asikainen V
Finland, Helsinki University of Technology, Laboratory of Heating, Ventilating and Air Conditioning, Report B62, Espoo 1999, 63 pp, in Finnish.
In this research project "Crawl space moisture and microbes", decreasing the humidity in crawl spaces with ground cover and a dehumidifier was tested and microbiological conditions were measured. The aim of the study was to test the behaviour of lightweight aggregate (LWA) and crushed stone ground cover and a dehumidifier by field measurements and computer simulations. Another objective was to measure microbe concentrations in crawl spaces and to find out whether the microbes and VOCs drifted from crawl spaces into apartments by leakage air flows through the base floor. Field measurement of temperature and humidity behaviour were carried out over ten months in six crawl spaces of apartment buildings and a day care centre with wooden or stone base floors. The effect of air change and ground cover on crawl space humidity was studied by computer simulations. Mould and VOC concentrations were measured from air and material samples in winter and summer. It was found that the LWA effectively reduced ground moisture evaporation. Used in layers 10-20 cm thick, the LWA cut the capillary rise completely, so that on the surface the relative humidity was almost the same as in the crawl space air. Crushed stone used as a reference had no effect, emphasising the importance of using the correct material. States that an air change of 0.5 ach is sufficient in the to dehumidify the crawl space, although it should be increased to 3-5 ach from May to September for wooden insulated floors. Mould concentrations in the crawl spaces were over the limits for indoor air quality, and the high levels were shown to affect the indoor air quality of the buildings themselves, due to the underpressure created by the mechanical exhaust ventilation system.
crawl space, moisture, microbiological pollutant
#NO 12865 Ryomintatilan ratkaisut ja rakennusfysiikka. Kosteustekninen suunnittelu. Crawl space types and building physics.
Matilainen M, Jerkku I, Kurnitski J
Finland, Helsinki University of Technology, Laboratory of Heating, Ventilating and Air Conditioning, Report B63, Espoo 1999, 61 pp, in Finnish.
Different types of crawl spaces are listed and their physical behaviour including heat, moisture and air change is discussed. The objective was to collect information on the behaviour of crawl spaces, especially concerning moisture control and optimum air change. In addition, the results of two other reports are given in the form of preliminary guidelines for crawl spaces. The behaviour of ordinary crawl spaces ventilated naturally or mechanically by outdoor air as well as heated crawl spaces, unventilated crawl spaces and crawl spaces ventilated by indoor air are discussed. Preliminary guidelines are given for crawl spaces ventilated by outdoor air. Ground moisture evaporation and the crawl space temperature are the most critical factors affecting the moisture behaviour of a crawl space. If the ground moisture evaporation is not reduced by ground cover, the humidity of the crawl space will rise over the limits of mould growth. Properties of ground cover and calculation methods to assess moisture evaporation are given. Air change will affect both humidity and temperature in crawl space. The need for air change is discussed based on results from previous and the present research and some guidelines for optimum ventilation are given. The given guidelines are specific and include the control of roof-, surface- and ground water as a part of crawl space design. The guidelines are preliminary and will be revised in the second stage of the project. Publishing of preliminary guidelines is considered to be useful, as even a small improvement of the current situation might be a notable step ahead towards properly functioning crawl spaces.
crawl space, guidelines, ventilation strategy
#NO 12866 A new algorithm to calculate the isothermal moisture penetration for periodically varying relative humidity at the boundary.
Sweden, Acta Physica Aaedificiorum, Vol 2, 2000
The paper presents a method to calculate the moisture penetration depth and the undisturbed moisture level, inside the region of periodic variation, in a porous material subjected to a periodic relative humidity variation at the boundary. The moisture properties may be highly non-linear. The method is strictly valid for a semi-infinite material. The theory to determine the undisturbed moisture level is given in detail, and a calculation method to determine the penetration depth is presented. A specially designed computer program has been developed. Results for six different building materials subjected to daily and annual periodic relative humidity at the boundary are given.
mathematical modelling, moisture, calculation techniques
#NO 12867 How builders and homeowners can identify and limit fungal contamination in new homes.
USA, IEQ Strategies, April 2000, pp 4-6.
Gives an overview of research carried out on eight homes under construction in North Carolina, USA, aimed at identifying building practices and materials that promoted fungal infestations in new homes. At the end of the two year research period, there was documented evidence to show architectural flaws, construction errors, and negligence by contractors and new homeowners that gave a very high probability of causing serious fungal contamination inside the homes. The research emphasised the need to educate all stakeholders in simple practices that help produce healthier indoor environments.
mould, residential building, moisture, fungal contamination
#NO 12869 Tools to know for home diagnostics.
USA, Home Energy, March/April 2000,k pp 32-37.
Overview of the tools necessary for a building performance contractor to carry out high quality diagnostic work, and solve home performance problems. Includes among others the blower door, duct tester, flow hood, pressure pan, digital manometer, APT data logger, APT software, other data loggers, laptop computer, infrared scanner, infrared thermometer, dual temperature gauge, moisture meter, relative humidity meter, carbon monoxide monitor, Watt meter, and digital camera.
measurement technique, building diagnostics
#NO 12875 Bouwregelgeving en ventilatie. Building regulations and ventilation.
van Overveld M
Netherlands, TVVL Magazine, No 4, 2000, pp 44-45, in Dutch.
The Building Decree, with various objectives in mind, contains a number of regulations on the ventilation of spaces in buildings. There are, for example, regulations for areas where people work ad for traffic areas (and lifts). There are also regulations applicable to the removal of smells and hazardous substances from places such as waste storage areas, garages and meter rooms. Lastly, there are regulations on the removal of smoke in the event of a fire. The secondary objectives of ventilation include the supply of air for combustion and the removal of smoke (when using a gas cooker, for example), t he removal of moisture (which may cause mould to form) and limiting radiation (such as radon) and undesirable substances (for example formaldehyde and asbestos). The issue of specific regulations for these various aspects assumes the real-time availability of the minimum prescribed ventilation capacity.
building regulations, ventilation system
#NO 12880 Moeglichkeiten der passiven Klimagestaltung in Raeumen. Possibilities of passive conditioning in spaces.
Germany, KI Luft- und Kaeltetechnik, No 3, 2000, pp 128-132, 9 figs, 6 refs.
On the basis of the thermodynamic description of wet air, solutions for a passive climatic conditioning are stated for the humidity condensation on cool surfaces and the absorption of humidity in materials. By a direct selection of the surface materials it is possible to reduce technical and energetic measure for the active climatisation.
air conditioning, temperature gradient, humidity
#NO 12898 Positive input ventilation.
Stephen R, Bradley J
UK, Building Services Journal, April 2000, pp 59-60, 2 tabs, refs.
Considers whether positive input ventilation systems for dealing with dampness in dwellings really reduce condensation. In the monitored houses, input ventilation was not consistently effective in reducing relative humidity, the extremes for house average values being a reduction of 5.5% rh to an increase of 1.4% rh. Even in the same house there could be a reduction in one room and an increase in another. Input ventilation was found to be effective in the most humid houses, but did relatively little in the dryer houses. While the measured humidity performance of input ventilation was somewhat disappointing, the occupants were more enthusiastic about the effectiveness of input ventilation than the results would suggest. Those who previously had the highest humidity in their houses were the most impressed, citing a general improvement in indoor conditions, lack of streaming condensation on windows, and condensation on walls. Several of the householders were very reluctant to allow the input ventilation fan to be turned off during the monitoring exercise. Some occupants also claimed relief from severe respiratory illness but these claims could not be substantiated under the project.
moisture, humidity, condensation
#NO 12914 Risk of indoor condensation related to thermal insulation standards.
Ponterio L, Rizzo G, Rodono G, Scaccianoce G
in: PLEA '99 "Sustaining the Future - Energy, Ecology, Architecture", proceedings of a conference held Brisbane, Australia, September 22-24, 1999, edited by Steven V Szokolay, published by PLEA International, in conjunction with the Department of Architecture, The University of Queensland, Brisbane, Volume 2, pp 753-758, 2 figs, tab, refs.
Condensation phenomena on internal surfaces of buildings are becoming recurrent eventualities in contemporary buildings, particularly in residential buildings. Despite the general belief, this accumulation of water on walls is not mainly due to mass migration from outdoor to indoor, but to a modification of behavioural approaches of people, air changes established in buildings are strongly affected by new thermal insulation standards that call for more insulated and sealed buildings and, consequently, for less heat loss by ventilation. Both these causes generate a tendency to an increase in the air vapour concentration inside buildings: this turns into a rise of dew point temperature and, finally, in the risk of condensation on colder indoor surfaces of the envelope.
standard, insulation, condensation, moisture
#NO 12991 Selecting whole house ventilation strategies to meet proposed ASHRAE standard 62.2: energy cost considerations.
Wray C P, Matson N E, Sherman M H
in: ASHRAE Annual Meeting 2000, proceedings of a conference held Minneapolis, USA, June 24-28, 2000.
ASHRAE Standard 62.2P is being proposed to address residential ventilation issues. As housing, especially new housing, gets more airtight and better insulated, it has become clear that many homes are underventilated. The standard contains requirements that provide minimum ventilation rates and source control measures necessary for acceptable indoor air quality. This paper uses previously reported analytical techniques to compare the energy costs of various ventilation strategies for a wide variety of climates and housing types. For new construction, we conclude that mechanical ventilation is needed. In new houses with gas heating, the cheapest whole-house system is a central exhaust fan. The marginal energy costs to provide such ventilation are on the order of 50¢ per day. However, other systems can be more appropriate when depressurization, filtration, moisture, and more expensive heating issues are considered. For most of the existing housing stock, we conclude that infiltration provides adequate ventilation.
ventilation strategy, standard
#NO 13026 Ventilation and IAQ for the hospitality industry.
Turner W A
Heating Piping and Air Conditioning, July 2000, pp 36-44, 8 refs.
Designers of HVAC systems for the hospitality industry are faced with the challenge of providing suitable indoor environments for both an establishment's customers and its workers at an affordable price. This involves consideration of first and operational costs, system maintainability, and degree of environmental control, which includes: temperature control; interior moisture management; pollutant control; interzonal pressure control and the influence of adjoining facilities. This article explores these environmental control challenges and discusses ways to meet them. Concludes that many advanced ventilation designs can address most, if not all, of the environmental challenges described. It is especially important to implement these designs inclimates that are hot and humid, very cold, or both, which can be found throughout much of the continental United States. In many ways, the environmental challenges found in the hospitality industry are no greater than those found in health care facilities and semiconductor manufacturing. However, in general, HVAC capital equipment and operational costs are expected to be lower in hospitality industry applications than in either of the other tow types of applications. All of the advanced solutions noted here require an investment in capital equipment beyond packaged, off the shelf rooftop units; however, in most cases, the costs canbe recovered in a relatively short period of time. It would be useful for ASHRAE to develop more information regarding these advanced equipment approaches. This expanded section on the control of tobacco smoke emissions as a point source or mobile point source in the American Conference of Governmental Industrial Hygienists' Industrial Ventilation: A Manual of Recommended Practice' would help designers to more unformly address these issues.States that until sufficient educational material is available, the development of advanced solutions that work well will depend on the talents of engineers and designers who create them through research efforts.
duct, maintenance, residential building
#NO 13029 Hygrothermal performance of attics.
J. Thermal Env. & Bldg. Sci, Vol 22, October 1998, pp 132-146, 9 figs, 2 tabs, refs.
This paper describes the results of measurements of temperature and relative humidity in six different attics (roof spaces) under controlled conditions. All six attics have the same dimensions and have been constructed adjacent to each other in a single line, but with different insulating materials and ventialted in different ways. Using this fund of measured data, a number of researchers have attempted to apply their mathematical models and, starting from the basis of measured ambient climatic conditions, have calculated expected values of temperature, relative humidity, and in one case, the moisture ratio in the attics. The results of these calculations showed difficulties in matching the performance of the models to real conditions. Notes that there is some degree of moisture buffering in hygroscopic insulation materials (cellulose materials) compared with non hygroscopic insulation (mineral wool). However, the difference is not particularly large; there are considerable differences in moisture and temperature variations in roofs with high and low ventilation rates. The higher the amount of ventilation using outdoor air, the greater the variations; The climate in the attic becomes drier the less it is ventilated. States that moisture can be introduced during the building stage or in normal use. Building moisture must be allowed to dry out before it can cause damage. During the subsequent use stage, convection of moist air up into the attic must be prevented. This is done by ensuring that the structure is airtight in combination with an internal negative pressure.
#NO 13031 Air to air energy recovery.
Besant R W, Simonson C J
USA, ASHRAE Journal, May 20000, pp 31-42, 6 figs, 11 refs.
Auxiliary energy loads for supply air heating or cooling sometimes can substantially reduce the need for dehumidifying or humidifying by using air to air heat or energy exchangers. The most important factors in reducing HVAC capital and operating costs are ventilation airflow requirements, climatic parameters, exchanger recovery system performance factors and duration of operation. This article provides guidance on the types of heat or energy recovery devices and how to select one, how such a device should be integrated into an HVAC system, what one can expect for performance factors, sizing, and likely payback period. Concludes that applying air to air heat/energy exchangers in buildings is a cost effective and reliable way of conditioning outside ventilation air. For many climates and applications an energy wheel is favoured, while sensible heat exchangers are favoured in others. The article shows that air to air heat/energy recovery can reduce significantly the capital costs and energy consumption of auxiliary heating and cooling equipment. For a retrofit, the payback on investment may be several years. In new applications the payback may be immediate because a carefully designed HVAC system, which includes energy recovery, will often have as low or lower initial costs as a system without energy recovery. In this case, the energy savings that accrue will result from essentially no investment. Air to air heat and moisture exchange for ventilation air is important for HVAC design and operation because it can: reduce peak auxiliary energy rates and annual loads as well as capital and operating costs; permit higher ventilation rates to create better IAQ at minimum auxiliary energy costs.
air to air heat recovery, indoor air quality, air flow rate
#NO 13035 Code of Practice for ventilation principles and designing for natural ventilation.
UK, British Standards Institute (BSI), BS 5925:1991, 40 pp.
This standard supercedes BS5925:1980, which is withdrawn. This revision takes into account research on ventilation and indoor air quality that has taken place since the publication of BS 5925:1980. In particular, under section 2, the ventilation requirements for the dilution and removal of airborne pollutants have been updated and account taken of the guidance given in BS 5250. Under section 3, a new clause dealing with air infiltration has been introduced. Recent increased awareness of the need for efficient use of energy in the design and management of buildings, as recommended in BS 8207, has led to greater insulation levels and reduced ventilation rates in both new and existing builidngs. However, it is essential that a balance is struck between the needs for low ventilation rates commensurate with saving energy and the needs for higher ventilation rates required to ensure good indoor air quality and to reduce the risk of mould growth. Ventilation rates in different parts of a building may differ, depending on both the levels of occupancy and the occupant's activities in those parts. It is important to remember the complex interrelationship of factors affecting condensation and to take particular care when designing new buildings or considering changes or attempting to remedy problems in existing buildings.
natural ventilation, building design, standard
#NO 13058 On ventilation needs - towards demand controlled ventilation in dwellings.
Bergsoe N C
UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 8
Ventilation needs in dwellings must be determined on the basis of both requirements to the indoor air quality and necessary control of moisture conditions. As a first step towards development of energy efficient ventilation strategies for demand controlled ventilation in future dwellings, theoretical analyses comprising a literature study and mathematical simulations have been carried out. In view of the provisions in the current Danish Building Regulations, and based on existing knowledge on contaminants and contaminant sources in the indoor climate, the humidity conditions are regarded as the determining factor for the ventilation requirements in future dwellings. The mathematical simulations indicate that the basic ventilation in a typical apartment under normal use can be reduced by 20-30 percent, compared with provisions in current building regulations, without compromising the indoor climate. Thus, through suitable control of the ventilation, on average, energy savings can be achieved on the energy consumption for ventilation in multi-storey buildings.
demand controlled ventilation, residential building, ventilation needs, moisture, humidity
#NO 13062 "Humid Air" and cooled walls.
Trogisch A, Franzke U
UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 12.
The humidity of room air is a necessary influence of design under the aspects of thermal behavior, technology and conservation.
The moisture absorption in the walls through sorptive materials or dehumidification on the cold window surface by dew point condensation is low because of the new thermal characteristics of these components.
The moisture load of a room briefly or also continuously, caused by technological processes or the users can't be compensated.
Today, the walls are used like a floor heating system. New developments refer to the fact that in the near future the wall will be used like a chilled ceiling system.
The authors would like to show the danger of downward air streams and the condensation of water caused by chilled walls.
The distribution of temperature, velocity and humidity of room air, calculated with a three-dimensional mathematical program, is shown. It becomes clear, that it is necessary to realize an integral process of design by co-working of architects, users and engineers to avoid problems of humidity and to give the guarantee of thermal comfort.
humidity, wall, chilled walls, condensation, mathematical modelling
#NO 13064 Design of ventilation systems in industrial buildings. A computational approach
of displacement ventilation in paper industry.
Papakonstantinou K A, Kiranoudis C T, Markatos N C
UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 14.
In this paper, the ventilation of a "crˆpe" paper-processing workshop containing dryers, which generate a high thermal load, is considered. Displacement ventilation has been used for many years in industries with high thermal load. The main ventilation design problem is to find the appropriate ventilation flow that guarantees that the interface between the fresh air zone and the hot air zone is located above the occupied region of the room. The paper presents a mathematical model, implemented in a general computer code that can provide detailed information on the velocity, temperature and moisture fields in three-dimensional buildings of any geometrical complexity.
The simulation results could be used as a base for further analysis for ventilation design for other industrial processes producing high levels of thermal loads and moisture, leading to a proper ventilation system selection for a more healthy and comfortable environment in a building.
industrial building, displacement ventilation, mathematical modelling
#NO 13085 Impact of ventilator parameters on system energy consumption.
Shah D J
UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 36.
The operation and performance of forced-air ventilation systems with the aid of a dynamic modeling and simulation computer program are presented. The functions and features of GEMS (Generalized Engineering Modeling and Simulation), a dynamic modeling and simulation software tool, are briefly described. Using GEMS, the effects of different ventilation airflow rates and sensible and moisture efficiencies on the thermal comfort environment within the conditioned space were analyzed. The impact of these ventilator parameters on the indoor air humidity levels and annual energy requirements for two cities-one cooling dominated and one heating dominated-was studied. Simulation results from the cooling-dominated region are presented.
air quality, human comfort, energy consumption, building controls, mechanical ventilation
#NO 13090 A novel ventilation heat pump system.
Riffat S B, Gillott M C
UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 41.
The move towards improving building air-tightness to save energy has increased the incidence of poor indoor air quality and associated problems, such as condensation on windows, mould, rot and fungus on window frames. Mechanical ventilation heat recovery systems (MVHR) combined with heat pumps offer a means of significantly improving indoor air quality as well as providing heating and cooling required in buildings.
This paper is concerned with the testing and performance of a novel ventilation heat pump system developed for the domestic market. The novel system uses revolving heat exchangers with both impel air and transfer heat. Low grade heat recovered from the exhaust air is upgraded by a heat pump and used for heating the fresh supply air. The prototype system has a heating coefficient performance (COP) of up to 5 and an average system COP of 2.5 over a range of conditions. The system typically provides 2kW of heating for air supplied at 250m3/hr. The system can also be used for cooling by switching the air flows over the evaporator and condenser. The prototype system requires very little maintenance and is compact and energy efficient.
heat pump ventilation, mechanical ventilation, indoor air quality
#NO 13111 Thermal performance of the exterior envelopes of buildings VII proceedings.
Geshwiler M (ed.)
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, 874 pp.
The papers of this conference are divided into subject areas as follows: roofs and attics - principles; whole building performance; moisture analysis - principles; whole building performance - practices; moisture assessments - principles; indoor air quality and sustainability - practices; moisture surveys - principles; walls - practices; window design and performance - practices; roof and attic issues - heat, moisture, ventilation - practices; window modelling at the University of Massachusetts - principles; moisture - practices; thermal analysis of building systems - principles; fenestration and energy costs - practices; wall systems - principles; infiltration - practices; building systems - principles; performance of air barrier systems - practices; airtightness and airflow in buildings - principles; materials and foundations - practices.
thermal performance, building envelope
#NO 13112 Application of a new type of air and vapour retarder in a self drying dloped roof with a cathedral ceiling.
Hens H, Janssens A
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 15-27, 8 figs, 8 tabs, refs.
In cool and cold climates, sloped roofs with cathedral ceilings are quite sensitive to moisture damages caused by built in moisture and prolonged concealed condensaton of water vapour produced inside. Conventional solutions are to leave a cavity between the thermal insulation and the sheathing and vent it with outdside air and/or to include a vapour barrier below the insulation layer. An alternative, however is the self-drying roof. This concept was evaluated experimentally. For that purpose, three well insulated roof sections, all covered with shingles and lined inside with a gypsum board, were tested in a hot box. The first had an airflow and vapour tight polyethylene film between the glass fibre insulation and the gypsum board internal lining. The second had the gypsum board only as an airflow retarder, and the third has a new type of organic, glass fibre fabric reinforced felt as airflow and vapour retarder. The plywood deck under the shingles contained a known amount of built in moisture. The sections were exposed to a sunny period first, followed by a steady state cold period afterwards. Section I remained wet, with the moisture moving from the plywood to the polyethylene during the sunny period and back to the plywood during the cold period. Section 2 dried during the sunny period; however, it got less than roof 2. Apparently, roof 3 came closest to the concept of self-drying. In order to evaluate to what extent simple engineering tools and simplified models could predict the measured response, the tests were also simulated using three such models.
air barrier, vapour retarder, roof, cold climate
#NO 13114 Mouldy houses - building science lessons from the Wallaceburg Project.
Lawton M D
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 67-79, 2 figs, 4 tabs, refs.
Thirty nine houses with high levels of biologically active contaminants in Wallaceburg, Canada, and twenty houses with low levels of bioligically active contaminants, were subjected to field inspections and testing, monitoring of indoor environmental conditions, and simulation to predict the condensation formation potential in winter. Occupant health was evaluated through questionnaires and blood sampling from an index child (closest to age ten) for analyses of T-lumphocyte and B-lymphocyte structure. We found that low air leakage and natural ventilation were not associated with higher measures of mould growth. Analyses found that moisture sources in the houses were a more significant factor in mould and dust mite antigen levels than relative humidity. Visible mould area was not a good predictor of ergosterol concentrations, indicating that hidden mould growth may be a factor. This paper addresses the influence of house and construction characteristics on the levels of mould growth and the building science lessons provided by this project.
mould, residential building, questionnaire, moisture
#NO 13118 Experimental setup for the study of air leakage patterns.
Desmarais G, Derome D, Fazio P
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 99-108, 10 figs, refs.
A research project has been conducted to investigate the impact of the initial air leakage characteristics on the hygrothermal performance of the insulated walls retrofitted with rigid insulation added either on the warm side or the cold side of the wood studs. This paper presents the experimental setup developed to study and document the air leakage patterns. The research project involves the construction of a test hut inside and environment chamber where winter, and then spring, steady-state conditions are simulated. The methods used to assess the impact of the air leakage characteristics are the three-dimensional monitoring of temperatures and the two-dimensional monitoring of moisture contents within the assemblies. Temperature monitoring results are presented using isotherms for the assemblies with no rigid insulation added.
air leakage, insulation, retrofitting, test chamber, seasonal changes
#NO 13119 Organic insulation materials: effect on indoor humidity and necessity of a vapour barrier.
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 109-121, 15 figs, refs.
Examples of organic insulation products are cellulose fiber, other plant fibers, and animal wool. These materials, which are all very hygroscopic, are associated with certain assumptions about their building physical behavior that needed to be verified. Examples are "A vapor barrier is not needed when using organic insulation materials" and "Organic insulation materials have a stabilizing effect on the indoor humidity."
This paper presents numerical analyses of the hygrothermal behavior of wall constructions and the occupied spaces they surround when an organic insulation material is used. The following problems are analyzed:
The risk of interstitial condensation is typical building construction with different vapor retarders when either conventional or organic insulation materials are used.
The influence on diurnal and seasonal indoor humidity variations when using either inorganic or organic insulation materials in the surrounding walls.
insulation, building materials, humidity, vapour barrier, hygrothermal analysis, numerical modelling
#NO 13120 Temperature and moisture performance of wall assemblies with fibreglass and cellulose insulation.
Rose W B, McCaa D J
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 133-144, 12 figs, 5 tabs, refs.
A three year study in Champaign, Illinois, was designed to measure the thermal and moisture performance of various typical wall assemblies, especially OSB sheathing, under field conditions. The variables that were studied included.
Insulation material (fiberglass and cellulose),
Vapor barriers (none, polyethylene, and facing material),
Means of attachment of facing material, and
Location within the wall cavity.
Measurements of temperature and moisture content, using Duff probes, were gathered at hourly intervals over three winters, and plugs made of the OSB sheathing material were regularly weighed for gravimetric moisture content measurements. The interior was maintained at constant humidity - 50%-55% for one year and 40% for two subsequent years. Following the study, the walls were disassembled and inspected for sheathing condition and mold growth.
Two samples with no vapor diffusion protection, one cellulose and one fiberglass, showed unacceptably high levels of mold growth. All of the samples with vapor barriers or encapsulation remained at a safe level of moisture content. Some of the samples with encapsulation and faced materials showed mold growth at the tops of the cavities, particularly where cabling pierced the interior dry wall.
The construction and building pressure management for this study were such that the moisture performance is a consequence of the diffusion/capillary regime, not the air leakage regime. The cases that were unacceptably bad in this study were affected by diffusion and capillary moisture, not air leakage, under the interior and exterior loads imposed by the test.
insulation, building materials, moisture
#NO 13121 EIFS hygrothermal performance due to initial construction moisture as a function of air leakage, interior cavity insulation, and climate conditions.
Salonvaara M H, Karagiozis A N
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 179-188, 15 figs, 1 tab, refs.
The drying capability of an EIFS wall system with initial construction moisture critically depends on the climatic conditions in which it is placed. The drying rate mechanisms with which walls redistribute and transport moisture away from the envelope may affect the service life of the wall system. Potential moisture-inducted damage becomes important when the wall is not properly designed with adequate drying capacity.
This paper investigates the drying performance of a particular EIFS (exterior insulation and finish system) clad wall. A state-of-the-art two-dimensional hygrothermal model, developed by the authors, was employed to determine the hourly spatial temperatures, moisture content, and air velocity distributes within wall systems as a function of real climate conditions.
In the parametric investigation, the performance of a particular EIFS clad wall as a function of two stud cavity insulation materials was studied. Two cavity insulation walls were investigated: fiberglass and cellulose insulation. Two climatic conditions were chosen in the moisture analysis, representing cold and mild climates: these were Chicago, Illinois and Wilmington, North Carolina respectively.
The effect of wall drying and wetting in the presence of a particular air flow path (cracks) was investigated for all cases. The air leakage path was assumed to be present due to an electrical outlet close at the interior, an opening present between oriented strand panels, and a conduit in the stucco layer. Initial OSB moisture content was assumed to be very high. The influences of wind-driven rain, solar radiation and air movement were included in the simulation analysis on an hourly basis.
Results showed that air leakage through a particular EIFS clad wall in Wilmington produced a net drying effect for a wall system with an initially wet OSB layer, while air leakage developed a net seasonal moisture accumulation in Chicago. The effect of stud cavity insulation was found to be critical, as the storage capacity for moisture increased in the cellulose case, compared to the fiberglass insulation case. The distinct effect is present when comparing the two insulation systems. The cellulose insulation case retained higher amounts of moisture. Solar driven moisture was also more critical in the cellulose insulation case than in the fiberglass case. The thermal and moisture results were then linked to a state-of-the-art mold growth model to assess the risk of moisture-induced damage. Results were developed in the form of mold growth indexes. Results showed the probable mold growth index as a potential as a function of climate conditions and as a function of cavity insulation. Higher risks of mold growth is present in the cellulose case than in the fiberglass case. If there is a high mold growth index and the underlying material is maintained at high moisture content, there is potential for developing decay (if the wood is already infected internally). Since boric acid is added in cellulose insulation as a treatment for fire, mold, insect and rodent control, as wet blown cellulose comes in contact with other materials, some of the chemical will treat these surfaces. For the same wall system, Wilmington exhibited slightly worse conditions that Chicago for mold growth. The development of mold growth indexes permits one to perform a moisture engineering analysis and extended current moisture assessment analysis of building envelopes' long-term performance.
hygrothermal performance, building construction, cavity insulation, air leakage
#NO 13122 Drainage, ventilation drying, and enclosure performance.
Straube J F, Burnett E F P
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 189-198, 8 figs, refs.
This paper explores the influence and role of both drainage and ventilation drying on the ability of enclosure assemblies to control moisture. Drainage is often the most direct method of removing water from within a wall (i.e., from exfiltration condensation or rain penetration), but it is often not sufficient to provide moisture control. Design approaches that rely solely on drainage to remove moisture from behind the outer layers or cladding ignore the significant quantities of moisture that can be stored in the outer layers of most enclosure walls.
Most cladding systems have relatively low vapor permeability and therefore tend to restrict diffusive drying. Moisture trapped in or behind the cladding can be transported into the enclosure by solar-driven diffusion, especially in air-conditioned buildings. Rather than control vapor diffusion, a 6 mile vapor retarder close to the interior may, in many instances, exacerbate wetting and greatly retard drying.
The role of ventilation within walls, especially for North America conditions, has not been well researched and there does not appear to be any consensus with respect to the effect of ventilation on drying. We have found that airflow behind the cladding (ventilation) can be an important means of removing moisture stored within and behind vapor impermeable cladding. Calculations, lab experiments, field monitoring, and anecdotal evidence all show than ventilation can not only be improve the drying capacity of wall assemblies, it is sometimes necessary for proper performance.
Several years of temperature, humidity, and moisture data collected from full-scale wall assemblies in a natural exposure and test facility are used to demonstrate these points.
moisture, wall, cladding, ventilated wall
#NO 13123 Condensation risk assessment.
Janssens A, Hens H
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 199-206, 8 figs, 7 tabs, refs.
The methodology of risk analysis and assessments is reviewed and applied to study the reliability of condensation control measures in lightweight building envelopes. It is generally recognized that airtight construction is an essential part of condensation control. Nowadays, different air barrier systems are developed and documented to prevent air leakage and moisture accumulation in the envelope. But does this mean that the condensation risk is sufficiently minimized and that the protective system is reliable? Considering the high occurrence of human error in the building process, the possibility of air barrier defects during the service life of a building envelope may be high.
To define the reliability of the condensation control system, the consequences of air barrier failure are quantified using a two-dimensional numeric control volume model for the calculation of combined heat, air, and vapor transfer in multi-layered building envelope parts. A set of failure modes and design calculation conditions is defined for an exemplary wood frame insulated roof, and a failure effect analysis is performed in order to predict the condensation risk as well as a result of air barrier defects. The effectiveness of redundant design measures to improve the reliability of the condensation control system is studied.
condensation, building envelope, air tightness, model
#NO 13126 Computer simulation of window condensation potential.
McGowan A G, Wright J L
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 229-235, 7 figs, 1 tab, refs.
Condensation on windows creates obscured view, can cause building damage, and may lead to mold growth and poor indoor air quality. The Canadian Standards Association (CSA) has developed new procedures to evaluate window condensation potential, using a combination of computer simulation and testing. The paper summarizes results of a study into various aspects of computer simulation related to the evaluation of condensation potential. These findings were to assist in the development of the CSA procedures.
window, condensation, mould
#NO 13129 Decision making on the indoor environment and building envelope of Canada's Library of Parliament.
Hoffman S P, Lawton M D
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 425-434, 8 figs, refs.
A year-long monitoring program was undertaken at Canada's Library of Parliament to answer the following:
What indoor environmental conditions are currently being maintained in the library with its existing temperature and humidity control systems?
What seasonal indoor environmental conditions can the existing building envelope support without distress or long-term durability problems?
What improvements could be gained with various levels of intervention?
The goal of the monitoring program was to provide specific recommendations for indoor temperature and humidity conditions and required interventions that would provide for the long-term durability of the building envelope and functional, archival, and heritage conservation needs.
The work included monitoring of:
Hydrothermal conditions at key indoor locations and interstitial spaces in the envelope,
Indoor/outdoor pressure differences,
Surface condensation and moisture content of building assemblies including stone walls, and
Surface temperatures to establish the condensation resistance of the existing window systems.
This paper focuses on how monitoring data, visual observations, and assessments of moisture collection potential by analysis and simulation were used to define recommendations for the conservation of both library and its collection.
large building, building envelope
#NO 13130 Case study - ice dam remediation for Northeast ski area condominiums.
Fennell H C
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 445-463, 11 figs, refs.
This is a case study describing the procedures for locating, prioritizing and repairing the causes of ice dam formation at a complex of over one hundred Northeast ski-area condominiums. The testing, performed on four typical units, as commissioned by the Owner's Association to prove the feasibility of preventing ice dam formation without replacing all of the existing roofs and to determine the costs of this approach.
Ice dam formation is one of the predominate problems for building in cold climates. The causes for such formations are often misunderstood by building owners and construction industry professionals alike. Consequently, because the heat-loss sources usually cannot be visually detected, solutions to the problem are more apt to be attempts at limiting damage from the symptoms rather than preventing damage to the building by eliminating the root causes of the ice dams. In addition to roof leaks, hazards from falling ice and potential structural damage to the building are additional reasons to prevent ice formation rather than just addressing leakage. Systems for limiting damage and preventing the intrusion of water from ice dams into the building envelope can be successful but are often more expensive and do not improve the energy performance of the structures. Eliminating the actual causes of ice dams i.e., excessive warming of the roof surfaces in subfreezing weather, always saves energy. This case study looks at a complex of buildings where it was possible to utilize conservation measures to remediate ice dams. It is broad in the scope of its examples because these multi-family buildings with their complicated construction details included many warm air leakage and conductive heat loss problems that have led to ice formation during extreme winter conditions.
condensation, eaves, cold climate, roof
#NO 13131 Moisture in the roofs of cold storage buildings.
Tobiasson W N, Greatorex A R, Fabian B A
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 465-467, 2 figs, refs.
The low-slope on roofs of ten cold storage buildings in the Dallas area visually and thermographically (Tobiasson and Korhonen 1985) from above and below. Two inch (51mm) diameter cores were taken to verify infrared findings and to determine moisture contents for estimating wet thermal resistance (Tobiasson et al. 1991). Twelve inch (0.3 m) square specimens of much of the insulation was removed for laboratory studies of their thermal properties and structure. Types of Insulation encountered included fibrous glass, fiberboard, perlite, woodfiber, expanded and extruded polystyrene, isocyanurate, and phenolic. Six of the ten roofs had suffered problems and had new single-ply membranes. Of the six, all but one has insulation added above their old bituminous membranes.
Visually, all ten roofs appeared to be in good condition. However, areas of wet insulation were found in eight of them. Some moisture was associated with infiltration of warm, moist outdoor air at roof-wall intersections without effective air seals. Figure 1 shows photographic and thermographic images taken within a freezer of a corner suffering such problems. Frost has formed there as warm moist outdoor air infiltrated into the freezer. The bright portion of the thermogram is the area warmed by infiltrating air. The adverse effects of air infiltration on the thermal performance of freezer roofs deserves further study. Of all the insulation examined, permeable fibrous glass was the most susceptible to wetting by air infiltration. While fibrous glass insulation may be able to be dried out (by warming up freezers), the rapidity at which cancers of wet insulation can grow in it make it somewhat ill-suited for use in freezers and coolers where vapor drive and air movement are both usually inward. Some wetness was due to leaks caused by flaws in the roofing membranes and their flashings. Figure 2 shows photographic and thermographic images of a ballasted roof that contained wet phenolic insulation due to and inch (25 mm) long cup in the EPDM rubber roofing membrane there. The phenolic insulation has lost almost all of its insulating ability and thus the surface of the roof appeared colder (darker) in the thermogram than does the roof of surrounding area where the phenolic insulation was dry and effective.
Nighttime on-the-roof infrared moisture surveys were more valuable than daytime indoor infrared surveys, but the indoor surveys and indoor visual inspections helped define the nature and extent of the moisture problems in these roofs.
Since the undersides of these roofs do not contain deliberate vapor retarders, it may be possible to recover some of the insulating ability lost to wetting of fibrous glass insulation by warming each freezer for a few days to allow ice to melt and the meltwater to drain our of the roof at seams in the decks. However, the other insulations cannot be dried this way since they take much longer to dry. Thus, a cost-effective, easy, reliable way of drying most of the wet insulation in these roofs is not available. Flaws in the new single-ply membranes caused wetting of new expanded polystyrene insulation placed between the old bituminous membrane and the new single-ply membrane. Unfortunately there is no way to dry such "trapped" insulation. One roof with a steel deck contained several areas of wet phenolic insulation. Had that deck not been cold, the wet phenolic probably would have rusted through. Being cold, the rate of rusting has been quite slow, but a safety hazard is developing there. As long as a roof membrane and its flashings keep water and moist air away from the insulation in the roofs of cold storage buildings, almost any insulation will stay dry and perform well. However, sustained one-way vapor drive, the sealing-in of moisture at the base of insulation in roofs of freezers by freezing, and the limited opportunities for wet insulation in such roofs. Provide incentives to use insulation that is very resistant to wetting. Its very low rate of moisture gain by vapor diffusion and its resistance to wetting in the presence of freeze-thaw cycles (Tobiasson et al. 1997) makes extrude polystyrene insulation particularly appealing for the use in the roofs of freezers and coolers. The Cold Regions Research and Engineering Laboratory (CRREL) Special Report 98-13 "Moisture in the Roofs of Cold Storage Buildings" documents the details of this study. Copies are available from CRREL, 72 Lyme Road, Hanover, NH 03755-1290
moisture, roof, insulation, air infiltration, air sealing, cold store
#NO 13138 Air pressures in wood frame walls.
Ten Wolde A, Carll C G, Malinauskas V
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 665-675, 13 figs, 3 tabs, refs.
Wind pressures can play an important role in the wetting of exterior walls (driving rain). In response, the rain screen concept, including compartmentalization and air spaces, has been developed to provide pressure equalization and limit water entry into the wall. However, conventional construction such as wood lap siding has not been evaluated as to its ability to function as a rain screen. As part of a two-year project assessing the performance of hardboard lap sliding, we measured air pressure differences across the siding over extended periods of time in two single-story wood-frame buildings, specially constructed for this study in southern Florida. Three different wall constructions were included in the study. We found that the conventionally installed lap sliding provided substantial air pressure equalization. Inward air pressure differences across the siding did not appear strong enough or long enough in duration, to raise concern about significant water penetration through the siding overlaps, even during windy days.
Air leakage has been recognized as an important mode of water vapor transport, and airtight construction is therefore recognized as an important ingredient of designing for high moisture tolerance. As part of the same study, we monitored air pressure across the siding, sheathing, and gypsum board in two of the walls. We found that wind-induced air pressures across the exterior walls were predominantly exfiltrative, even on the windward side of the building. Infiltration pressures only occurred near windward corners of the building during short periods of time. We also found significant air leakage past the top plate into the wall cavity. This paper also presents a method for coordinating the design for airtightness (airflow readers) with the design for control of vapor diffusion (vapor retarders). The calculations show that a vapor retarder of 1 perm (57 ng/Pa.s.m squared) should be complemented with an air barrier system (ABS) with an ELA of 0.003 in. squared /ft squared (2*10 -5 m squared/m squared) or less. Specifying lower-perm vapor retarders (e.g., 0.1 perm, or 5.7 ng/Pa.s.m squared) would require specifying an extraordinary level of airtightness.
air pressure, wood frame wall, water leakage
#NO 13147 The pressure response of buildings.
Lstiburek J W
USA, Atlanta, American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1998, proceedings of "Thermal performance of the exterior envelopes of buildings VII" a conference held Sheraton Sand Key Hotel, Clearwater Beach, Florida, 6-10 December 1998, pp 799-817, 21 figs, refs.
Airflow in buildings is one of the major factors that governs the interaction of the building structure with the mechanical system, climate, and occupants. If the airflow at any point within a building or building assembly can be determined or predicted, the temperature and moisture (hygrothermal and psychometric) conditions can also be determined or predicted. If the hygrothermal conditions of the building or building assembly are known, the performance of materials can also be determined or predicted. This paper shows that airflow in buildings is complex, time dependant and multidirectional. The understanding of airflow through and within buildings has been based on the requirement for continuity of mass and momentum caused by wind forces, thermal effects (stack action), and forces associated with the operation of mechanical cooling, heating, exhaust and other ventilation systems.
Interstitial airflow and interstitial air pressure fields are not often considered. Building analysis typically develops the building pressure field from the airflow field. In doing so, exterior and interior walls, floors, and roof assemblies are either considered as monolithic or having openings resulting in flow across the specific assemblies.
This paper shows that many problems associated with pollutant transfer and the spread of smoke and fire cannot be explained by cross-assembly (one-dimensional) airflow as well as such moisture effects as microbial contamination, corrosion and biological decay. Even the analysis of energy consumption and comfort within buildings needs to be considered in terms of multidirectional airflow. This paper shows that buildings typically comprise multi-layer envelope assemblies with numerous air gaps or void spaces that are often connected to service chases. Complex three-dimensional flow paths and intricate air pressure relationships must be considered.
This paper also introduces an alternative pattern of analysis: developing the flow field, the leakage areas, and the flow relationships from the measured building pressure field - the air pressure regime within and surrounding the building. This approach accounts for interstitial air pressure fields and resulting interstitial airflows. It provides a powerful diagnosis tool for solving many of the problems related to direct and indirect effects of airflows.
#NO 13174 Moisture damage in schools - symptoms and indoor air microbes.
Meklin T, Husman T, Vepselainen A, et al
Finland, SIY Indoor Air Information Oy, 2000, proceedings of "Healthy Buildings 2000", held 6-10 August 2000, Espoo, Finland, paper 161.
The association of moisture damages of school buildings with microbial indoor air quality and health status of school children was studied. To determine the association the school buildings (N=32) were divided into the moisture damaged (index) and non-damaged(reference) schools according to technical inspection data. Children's health surveys were made by questionnaires. Microbes were determined from indoor air of school buildings using a six-stage impactor. Children in the index schools reported more respiratory symptoms compared to children in the reference schools. No significant differences in total concentrations of airborne viable fungi between the damaged and non-damaged schools could be shown. However, some differences in microbial flora were found.
moisture, schools, mould, bacteria, symptoms, fungi
#NO 13205 Effectiveness of energy refurbishment measures applied to high-rise dwellings.
Barbour D, Galbraith G H, McLean R C
UK, Building Serv En Res Technol, Vol 21, No 2, 2000, pp 117-123, 5 figs, 5 tabs, 8 refs.
From 1953 to 1975, some half a million high-rise flats were constructed in the UK in response to the need at that time for the rapid provision of substantial numbers of affordable dwellings. For a variety of reasons, including environmental and social problems, many of these building were subsequently demolished. However, many housing authorities still own a considerable number of high-rise developments which, while structurally sound, will require to be upgraded if they are to continue in service for rental purposes. In Scotland alone, there are over 52,000 high rise flats, representing about 8% of the total available public sector housing. This paper reports on an environmental monitoring exercise carried out to assess the effectiveness of an extensive refurbishment, which included thermal over-cladding and heating system replacement, to a development of 24-storey building in Glasgow, Scotland. Monitoring of temperature and relative humidity was carried out in flats in a pre-and post-refurbishment block over a three-year period to evaluate the effect on occupant comfort levels and condensation risk. A limited energy use comparison ws also carried out. An analysis of the monitored data indicates that the refurbishment has been successful in achieving its objectives, namely improved environmental conditions at a reduced overall energy cost to the tenants.
building refurbishment, high rise building, apartment building
#NO 13207 A farmhouse renovation.
USA, Home Energy, September/October 2000, pp 40-46.
Describes the energy efficient refurbishment of a Vermont, USA farmhouse, built in the 1920s. The house was bought in a poor state of repair with possible ant infestation, loose single pane windows and evidence of high space heating fuel consumption. The owner's aim was to approach US Energy Star requirements cost effectively. There were problems with cavity wall insulation because the gap was narrow due to back plastering, and only allowed 1.5 inches of dense packed cellulose insulation, which contributes to the airtightness of the house, decreases the air transport of moisture in to the wall, and seemed to stop the pest problem. The old windows were removed including frame and new energy efficient glazing installed with air sealing around the frame. The attic was insulated by dense packing the rafter bays and applying rigid foam to the bottom of the rafters, from floor to ceiling, bringing the attic into the thermal envelope of the house. The number of south facing windows was increased from two to six, increasing solar gain and daylight. Attention was also paid to low energy lighting and appliances. An exhaust-only ventilation strategy was adopted, providing about 40 CFM of continuous background ventilation. Intermittent spot ventilation is provided in a first floor bathroom. A kitchen exhaust fan is used whenever the gas cooker is in use. The humidity levels in the house are maintained at a reasonable level. The first results were promising; space heating costs were reduced by 50% in the first two winters, with a 50% increase in conditioned area. Costs are expected to decrease further with new basement insulation and a new furnace. The owner expects to qualify for the Energy Star rating when the work is complete. States that the three biggest obstacles to renovating the house were lighting, proper sizing and installation of the HVAC equipment and financing.
building refurbishment, residential building, old house, insulation
#NO 13228 Moisture conditions of outdoor air ventilated crawl spaces in apartment buildings in a cold climate.
Kurnitski J, Matilainen M
Energy and Buildings, No 33, 2000, pp 15-29, 16 figs, 1 tab, 16 refs.
The effects of air change and ground covers on crawl space moisture balance in a cold climate are discussed in this paper. The objectives were to assess the suitability of outdoor air ventilation in the crawl spaces of apartment buildings, to determine the optimum air change rate with and without ground covers, and the effect of the ground covers' thermal insulation on moisture behaviour. Measured data from the test building was used to develop the crawl space model in a modular simulation environment, where the parametric simulations were carried out. The air change rate was varied between 0-10 ach to study moisture behaviour with covered and uncovered ground surface. Moisture evaporation was included in the moisture balance, but moisture storage in the constructions and in the ground was not. The results show that evaporation and thermal behaviour are the key elements determining the resulting relative humidity in crawl spaces. If moisture evaporation is entirely prevented, the crawl space may be left unventilated. In other cases, ventilation is always required to remove the moisture. The higher air change rates increased moisture evaporation from 2.4 to 4.9 g/m2h and decreased the highest monthly average of relative humidity from 81 to 74%. For the uncovered ground the lowest relative humidity was achieved at 2-3 ach air change in winter, but in the summer, the higher the air change the lower the relative humidity. Ground covers made it possible to decrease relative humidity and to increase temperature significantly due to reduced moisture evaporation. Ground cover with thermal insulation was in principle more effective than without insulation as it provided a slightly higher temperature rise in summer. The studied 5 cm expanded polystyrene layer reduced moisture evaporation to 0.3-0.4 g/m2h, increased crawl space temperature by 2-3 deg C and decreased relative humidity below the 60% level when air change was 0.5-1 ach. In general, outdoor air ventilation demonstrated very high performance in the crawl space of the studied apartment buildng when a ground cover was applied.
crawlspace, moisture, air change, ground covers
#NO 13230 Reexamining roof ventilation.
USA, Home Energy, November/December 2000, pp 14-18.
Discusses the problem of wet attics and how roofers, following the correct procedure for ventilation, and installing ventilation in a previously unventilated attic were making the problem worse. In a cold climate, ventilating a previously unventilated attic has the effect of making the attic colder. If nothing is done to stop warm, moist air from entering the attic space from the living space, condensation on the now cooler surfaces is a certainty. Mould, mildew and eventually leakage into the living space will follow. Insulating the attic floor makes the attic colder in the same way, and if contractors don't seal as well as insulate, warm moist air will penetrate the space. Describes where and how to seal attic leaks.
roof, cold climate, attic moisture, sealing
#NO 13232 Inferring ventilation and moisture release rates from field psychrometric data only using system identification techniques.
Cunningham M J
Building and Environment, No 36, 2001, pp 129-138, 5 figs, 3 tabs, 8 refs.
System identification techniques are developed allowing room or building ventilation and moisture release rates to be inferred from field psychrometric data only. The techniques have been developed primarily to allow the surveying of a large number of houses so that statistical properties can be compiled, in which high accuracy of individual results is not required. This system provides an alternative to PFT tubes, with some economic advantages. These techniques give rise to two parameters (describing the hygroscopic properties of the room) from which ventilation and moisture release rates can be calculated given indoor and outdoor psychrometric data only. Results within 30% of measured values have been obtained, except for the case of moisture release rates under airtight conditions where results seem unreliable.
moisture, perfluorocarbon tracer
#NO 13233 After remediation, unique fan coils are key to keeping mould, mildew away at Hawaiian hotel.
USA, IEQ Strategies, August 2000, pp 8-12.
Describes indoor air quality problems experienced at a new 12 storey addition to a hotel in Hawaii. The facilities are designed as leisure facilities for all active military and retired military members of the US Armed Forces and their families. Part of the cost of construction included an extensive program to ensure quality construction, but despite this the building developed high humidity that triggered mould growth and mildew, making the room air feel damp and degrading the room wall covering. The services of CH2M Hill, a large environmental engineering firm based in the US were employed to solve the problem. The engineers studied the building for a year and pinpointed three key factors that promoted the indoor moisture, mould and mildew problems. First, the HVAC fan-coil units didn't adequately dehumidify the guestrooms. Second, the bathroom-exhaust system caused unconditioned outdoor air to infiltrate the building, boosting humidity, and finally the vapour retarder - a vinyl wall covering - was deployed in the wrong place and ended up promoting mould growth in guestrooms. The renovations were expected to produce a building envelope and HVAC system that would properly dehumidify the air as well as prevent condensation within wall cavities. The building commissioning techniques demonstrated that the renovations would minimize moisture, prevent the return of mould, and maintain a comfortable temperature and relative humidity for guests. Hybrid fan-coil units and modified bathroom exhaust systems keep the dew points below 60 Deg F and maintain positive pressure in the hotel rooms. Two recommendations to increase energy efficiency were that hotel staff member should set room thermostats to 74 Deg F rather than 70 Deg F as previously instructed, and that they should put a message in each guestroom that explains that leaving the thermostat on a single setting produces the most comfortable temperatures and relative humidity. The project cost $5.2 million.
moisture, mould, hotel, fan
#NO 13275 Computational investigation of ventilation strategies to reduce exposure to NO2 and CO from gas cooking.
Ross D I
UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 1, pp 83-88, 3 figs, 3 tabs, refs.
Gas cooking in the home can release high levels of nitrogen dioxide (NO2) and carbon monoxide (CO). This study investigated the effect of various ventilation strategies to reduce personal exposure to these pollutants. It considered the effectiveness of windows, a kitchen extract fan and trickle ventilators for different dwellings, occupant behavior, environmental conditions etc. Strategy selection was based on the need to minimize both personal exposure and energy loss. These strategies were simulated using BRE's BREEZE multi-zonal computer code. The results showed that it is best to ; (a) use a window/ windows (where energy-loss acceptable) or a kitchen fan, and, (b) open all internal doors. However, whilst opening kitchen doors maybe be the best option for NO2 and CO, it may not be appropriate for other combustion products, such as moisture and odours.
Gas cooking, residence, nitrogen dioxide, carbon monoxide, muliti-zonal, modeling, ventilation.
#NO 13318 Development of a ductless air supply system using low temperature air.
Hashimoto Y, Tsubota Y, Nakano Y, Urabe W, Oka T, Kaneko M, Hazama Y, Imai T
UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 1, pp 553-558, 5 figs, refs.
This paper proposes a new ductless air supply system with a ceiling plenum chamber using low temperature air as a secondary HVAC system for an ice thermal storage system. The proposed air supply system mixes low temperature air with return air from a room using the mixing fan unit (MFU), pressurizes a plenum chamber with the mixed air and supplies the air to occupied room from diffusers on the ceiling. The purpose of this study is to develop a new HVAC system to utilize low temperature air, to prevent cold draught and dew condensation, to keep thermal comfort in the room and to save fan energy consumption. Room temperature is fed back to controllers that regulate fan motors of an air handling unit and an MFU with inverters. Low temperature air from an air-handling unit is controlled at 10 deg C by regulating flow rate of chilled glycol. A 7m and 10m and 3m height room is provided to evaluate the proposed system. 24-hour time series data are obtained by data loggers. Vertical temperature distribution is within setpoint +/- 1K and horizontal temperature is controlled between 25.7 and 26.2 deg C at 1.5m height above floor. Time-averaged PMV at the centre of the room is +0.24 and PPD is 6.2%. 24-hour time-averaged temperature is 26.2 deg C at the sensor for control and the root mean square error is 0.18K. Temperature difference between mixed and room air is averaged to 9K. It prevents cold draught due to low temperature air supplied directly to the room from ceiling-mounted air diffusers. Air velocity at the centre of the room is averaged to 0.22m/s and turbulence intensity is 8.6%. The results meet ISO7730-1994. This system is also expected to reduce the fan energy consumption by 70%. In addition, use of night electric power for ice storage systems saves energy cost of a chiller. The ductless air supply system using low temperature air is appreciated satisfactory for thermal comfort and energy saving.
Ductless, ice storage systems, air supply, large temperature difference, energy saving, variable-air-volume (VAV), ceiling plenum chamber, low temperature air, PMV, PPD
#NO 13335 CFD and multi zone modelling of fog formation risk in a naturally ventilated industrial building.
Li Y, Chen L, Delsante A, Hesford G
UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 2, pp 767-772, 3 figs, 5 tabs, refs.
Natural ventilation systems for industrial buildings have traditionally been designed using empirical engineering models, which often require the designer to 'over-engineer' the design to achieve a 'guaranteed' level of ventilation performance. This paper describes an application of computational fluid dynamics (CFD) and multi-zone thermal and airflow modelling to analyse the effectiveness of natural ventilation in removing moisture from a red mud filtration building used in the alumina industry in Australia. Our modeling work was divided into three stages: estimation of heat and moisture sources; modeling flow patterns and moisture distributions in the existing system; and finally modeling of the flow patterns and fog formation risk in a proposed new system. It is concluded that the CFD and multi-zone modeling approaches can be applied for ventilation design of industrial buildings, but great efforts are needed to collect crucial data such as heat and moisture sources in a realistic building.
Moisture transport, ventilation, CFD, multi-zone modeling, fog formation, condensation
#NO 13361 On controlling indoor thermal and moisture content for an occupied building.
Lu X S, Viljanen M
UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 2, pp 951-956, 5 figs, refs.
The focus of this paper is on controlling ventilation rate to provide acceptable temperature and relative humidity in the space being ventilated. To this end, a system of heat and moisture balance equations for building indoor and components is described. The system is solved numerically. Based on a series of indoor temperature and moisture measurements for our experimental house and well-mixed air distribution in room, moisture generation rate is estimated. The model is validated by simulating the experimental house. Good agreement between the simulated and measured results is obtained. The effects on ventilation controlling and indoor relative humidity of the moisture generation rate and surface moisture resistance of building material are also demonstrated by simulation.
Heat, moisture, mathematical model, indoor temperature, indoor relative humidity, ventilation control
#NO 13370 Efficiency of ventilation systems with heat recovery as a function of the air tightness of the building envelope.
Binamu A H, Lindberg R
UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 2, pp 1061-1066, 1 fig, 1 tab, refs.
The process by which heat energy is recovered from exhaust air for re-use within buildings is termed ventilation heat recovery. Among other factors, air infiltration can greatly impair the total energy performance of a system and in some cases, the recovery process could expend more energy than actually recovered. Moisture problems and severe contamination of the indoor air can also result from air leakage through the building envelope. An investigation on the impacts of the envelope air tightness to ventilation heat recovery system performance can be carried out. The performance evaluation took into consideration other factors such as hourly climatic data in form of statistical relationship between wind speed and direction, temperature differences (inside and outside) and heat gain from solar radiation. The tests were carried out in three experimental houses built of different building materials and having different degree of air tightness. The air tightness of these buildings was determined by using tracer gas method. Balanced mechanical ventilation system with air-to-air heat recovery was implemented. Heat recovered from the exhaust air, wind speed and direction, indoor and outdoor temperatures, and heat gain from solar radiation were continuously recorded and the total thermal energy consumption within two heating months was evaluated. The research is on going but initial results have indicated that the air tightness of the building envelope has a significant impact on the heat energy performance of the system. It was noted that for an airtight building, the wind speed and direction has no great influence on the air change rate of the building. However, excessive air infiltration resulting from poor envelope air tightness leads to uncontrolled energy loss. The colder the outdoor climate the greater the need for ventilation heat recovery.
Air change rate, air infiltration, building air tightness, heat energy, indoor air quality, performance, temperature difference, ventilation heat recovery
#NO 13380 On-site exterior wall monitoring methods for air leakage, condensation and rain penetration control problems
Canada Mortgage and Housing Corporation, 1999, 36pp.
Covers various monitoring protocols which aim to explain the basics of field monitoring and the interpretation of monitoring data. The monitoring protocol includes three specific methods. These are the Air Leakage Detection and Analysis Method, the Condensation Detection and Analysis Method and the Rain or Melt Water Detection and Analysis Method.
cladding, exterior wall, air leakage, condensation, rain water, melt water
#NO 13395 Home performance contractors.
Home Energy Magazine
Home Energy Magazine Online at http://homeenergy.org/
Home performance contractors analyse the house as an integrated whole. They are trained and equipped to find and fix these problems at the source. Gives general information about the work of the home performance contractor.
house system, moisture damage, health hazards, heating and cooling, insulation
#NO 13397 A recessed can of worms.
Armanda L, McCarthy S
USA, Home Energy, January/February 2001, pp 42-46.
High energy bills and ice dam problems in a residential building in Pennsylvania, USA were found to be partly due to recessed-can lighting. Most of the recessed features were found to leak air, the first floor ones directly to the attic. Thermal insulation may not be installed in contact with a recessed-can light if it is rated "non-IC". The lights were protected in the attic by metal enclosures open at the top, which created a large uninsulated attic floor area and large air leakage factor. Air leakage into the attic is a frequent cause of moisture problems. The building code recommends the installation of a sealed insulated box over the light fitting in the attic, but there are concerns about dangerous overheating. After experiments carried out in the lab, the authors recommend the following precautions for safety and energy efficiency: Use only PAR (reflector-type) bulbs or CFLs; Do not use any bulb that exceeds 75 Watts; Make sure the airtight drywall boxes maintain a minimum of 3 inches of clearance to all parts of the fixture, including the terminal or junction box; Do not place insulation over the top of the drywall enclosure.
recessed can lighting, air leakage test, infrared scan, airtight box
#NO 13441 Radon transport modelling: user's guide to RnMod3d.
Andersen C E
Denmark, Roskilde, Riso National Laboratory, August 2000, Riso-R-1201(EN), 116 pp,
RnMod3d is a numerical computer model of soil-gas and radon transport in porous media. It can be used, for example, to study radon entry from soil into houses in response to indoor-outdoor pressure differences or changes in atmospheric pressure. It can also be used for flux calculations of radon from the soil surface or to model radon exhalation from building materials such as concrete.
The finite-volume model is a technical research tool, and it cannot be used meaningfully without good understanding of the involved physical equations. Some understanding of numerical mathematics and the programming language Pascal is also required. Originally, the code was developed for internal use at Riso only. With this guide, however, it should be possible for others to use the model.
Three-dimensional steady-state or transient problems with Darcy flow of soil gas and combined generation, radioactive decay, diffusion and advection of radon can be solved. Moisture is included in the model, and partitioning of radon between air, water and soil grains (adsorption) is taken into account. Most parameters can change in time and space, and transport parameters (diffusivity and permeability) may be anisotropic.
This guide includes benchmark tests based on simple problems with known solutions. RnMod3d has also been part of an international model intercomparison exercise based on more complicated problems without known solutions. All test show that RnMod3d gives results of good quality.
#NO 13450 Humidity control in outdoor-air-ventilated crawl spaces in cold climate by means of ventilation, ground covers and dehumidification.
Finland, Helsinki University of Technology, Department of Mechanical Engineering, Laboratory of Heating, Ventilating and Air Conditioning, A, Espoo, 2000.
The study shows that acceptable moisture conditions in cold climate outdoor-air-ventilated crawl spaces may be achieved by the optimal selection of ground covers and ventilation. The objectives were to find out which ground covers are suitable to use in relatively warm or cold crawl spaces of buildings and houses, which material properties of the ground covers are important for the reduction of crawl space relative humidity and for increasing temperature, to determine optimum air change rates, and to test dehumidification. Measured data were used to develop a new crawl space model in a modular simulation environment, which was used for parametric simulations, where air change rates and ground covers were varied in relatively warm or cold crawl spaces. The model took into account ground moisture evaporation, moisture flows carried by ventilation and moisture transfer in the base floor and ground cover. The acceptability of moisture conditions was assessed by mould growth analyses based on the cumulative time of wetness and the time needed to start mould growth.
crawlspace, humidity, outdoor air
#NO 13451 Diagnosing wall moisture.
USA, Home Energy, January/February 2001, pp 13-14.
Pinpointing where water or air has leaked into an exterior wall - and why - are critical diagnostic steps to take before beginning remedial repairs. Summarises a report which describes three onsite exterior wall monitoring protocols for determining the occurrence and cause of air leakage, condensation and rain and melt water penetration. Successful diagnostics can identify a problem and give a fix more of a chance of succeeding than treating symptoms alone.
moisture, water leakage
#NO 13452 Mould, moisture and mildew in attics: prevention and cure healthier homes, energy savings and new business.
Canada, Solplan Review, September 2000, pp 5-7.
Covers the latest developments on how roofers and other interested parties are co-operating with home performance contractors for the first time on issues of liability, technical rethinking and customer service. It also describes repairs and preventive measures that are being carried out, and how a new business opportunity is being created in cold climate areas as a result.
humidity, attic, cold climate
#NO 13453 Ventilating an attic.
Polson M E
USA, Remodeling Online at https://www.remodeling.hw.net/
States that when the attic is poorly ventilated, insulation can't compensate effectively for temperature extremes, or handle the potentially damaging moisture buildup that is likely to ensue. Even older houses today are much tighter than they used to be, and modern households use a lot more water than before. As a result, a lot of moisture migrates to the attic, where it condenses on rafters and roof decking. Left unchecked, the condensation can saturate the roof, attic floorboards, insulation and even walls and ceilings. Goes on to outline ventilation methods.
attic, ventilation system, thermal insulation
#NO 13454 Improving humidity control for commercial buildings.
Harriman III L G, Lstiburek J, Kittler R
USA, Ashrae Journal, November 2000, pp 24-32.
Covers moisture load data, humidity related problems in buildings, including water intrusion, cold-climate condensation, hot climate condensation, and the new ASHRAE humidity control design guide. The authors state that better and more cost effective humidity control demands a holistic, multidisciplinary approach.
humidity, commercial building, whole building approach
#NO 13455 Through the roof.
USA, Remodeling Online at https://www.remodeling.hw.net/
Describes a solution for a home with severe mould and mildew problems, with the crawl space as its source, and the soil having a chronically high moisture content. Suggests ventilating the crawl space with conditioned air from the home. A vent stack in installed from the crawl space through the roof. A standard inline fan in the attic runs continuously, exhausting the crawl space air and putting the crawl space under negative pressure. The make up air enters the house in the living space, then passes into the crawl space through the "leaky" (non-air-sealed) floor assembly.
humidity, crawlspace, ventilation strategy
#NO 13456 Mold, a poltergeist.
USA, Home Energy, January/February 2001, pp 19-23, 2 figs.
Case study of a severe mould-odour problem in the bedroom of a house in Jacksonville, Florida. The room had been sealed shut by the owners to prevent the odour penetrating the rest of the home. The remedy covered relocation of garden sprinklers, elimination of a negative indoor pressure caused by ductwork supply leaks, correction of the air flow, creation of return air pathways, correction of the refrigerant charge of the air conditioner, provision of constant air flow to the troubled rooms, and application of a brick coating to reduce the water absorbancy of the brick. The problems subsequently cleared up completely.
mould, odour, moisture, wall, water leakage, ventilation strategy
#NO 13457 Mold growth and IAQ woes at three-year-old school spark lawsuits by school district, students, and staff in Texas towns.
USA, IEQ Strategies, December 2000, pp 2-4.
Allergy complaints about a three year old school building prompted remedial action. The classrooms were found to be collecting water condensate from dripping ceilings in garbage cans. The cellulose ceiling tiles were sagging in the middle due to the weight of water they had soaked up. The water was coming from the heating, ventilation and air conditioning air handling units above the drop-down ceiling. It was found that there was no slope on the drain lines from the air handlers, causing the condensation. Mould grew on pipe insulation around the chilled water lines. Mould was also growing on the ceiling tiles and on athletic shoes stored in locker rooms, and the locker rooms had mould growing on exterior surfaces. The CO2 levels were also very high. The remediation costs proved high.
mould, school, indoor air quality
#NO 13474 Energy answers.
Canada, Solplan Review, September 2000, pp 16-17.
Comments on Canada's current residential ventilation regulations. Claims that the standards is too complicated, and requires too much exhaust air flow, which can readily backdraft chimneys in many new houses. Fans specified in the interests of improving indoor air quality are too powerful. States that while most new houses basically have very poor ventilation, a simple, continuous ventilation system with modest air flow will greatly improve the air quality in the house. New houses are prone to indoor air quality problems because they are tighter, many newer furnaces reduce the air exchange (newer furnaces do not have the naturally vented chimneys that used to serve as exhaust ventilators), and greater quantities of synthetic materials (plastics, composites, new paints, etc) are present in them. With less natural air exchange and more indoor pollutant sources, air quality suffers, especially in new homes. Suggestions include: minimise the sources of volatile organic compounds (VOC) emissions; run the ventilation system continuously; provide adequate, but not excessive, amounts of ventilation; do not, under any circumstances, cause fuel burning appliances to backdraft; draw the exhaust air continuously from the odour and moisture producing areas; do not rely on the ventilation system to remove odours or smoke caused by burnt toast, or other unusual events; make the system quiet and reliable; remember that "the best is the enemy of the good."
residential building, building regulations
#NO 13519 Comfort conditioning for large spaces.
Simmonds P, Holst S, Reuss S, Gaw W
in: "Dublin 2000: 20 20 Vision", UK, Chartered Institution of Building Services Engineers (CIBSE), 2000, proceedings of a conference held 20-23 September 2000, Royal College of Surgeons, Dublin, Ireland, Abstracts in printed form and papers on CD.
This paper describes the development of a hybrid conditioning system that creates a comfortable indoor environment in a building. The operation of a variable volume displacement conditioning system and a radiant cooled floor have been optimised to reduce the building load. Control strategies were developed that optimise energy consumption and contain moisture levels within specified limits. The development of conditioning only occupied zones is shown and how the over all energy consumption is reduced. Its application in a large airport is described.
large building, human comfort, energy consumption
#NO 13529 Designing for air to air heat and moisture exchange in HVAC applications.
Besant R, Simonson C, Wei Shang
in: "Dublin 2000: 20 20 Vision", UK, Chartered Institution of Building Services Engineers (CIBSE), 2000, proceedings of a conference held 20-23 September 2000, Royal College of Surgeons, Dublin, Ireland, Abstracts in printed form and papers on CD.
Air-to-air heat and moisture exchange between exhaust and supply airflows can substantially reduce HVAC costs. This paper outlines the design considerations that should be included when selecting a type of exchanger and shows how the performance of each recovery device can be determined. Energy wheels, which transfers both heat and water vapor, are given special consideration. The HVAC design for heat and moisture exchanger sizing is presented as a least life-cycle cost design problem.
air to air heat exchanger, heat recovery