AIVC - Air Infiltration and Ventilation Centre

Search form

EBC

You are here

Home  |  LL

LL 28: Ventilation problems in crawlspaces

AIVC, 2001
AIVC | LL
Bibliographic info: LL28
Languages: English

Ventilation problems in crawlspaces

#NO 6669 Indoor radon reduction in crawl-space houses: a review of alternative approaches.

AUTHOR Hanschel D B

BIBINF Denmark, Indoor Air, No 2, 1992, pp 272-287, 2 figs, 2 tabs, refs. #DATE 00:00:1992 in English

ABSTRACT An analysis has been completed of the performance, mechanisms, and costs of alternative technologies for preventing radon entry into the living areas of houses having crawl-space foundations. Sub-membrane depressurization (SMD) is consistently the most effective technique, often providing radon reductions of 80-98% in the living area. It has a relatively high installation cost, but a moderate annual operating cost. Forced crawl-space depressurization is the second most effective, giving reductions of 70-96%. Crawl-space depressurization is less well demonstrated than is SMD, and performance will vary with crawl-space tightness and weather, but it will be a primary option when large radon reductions are needed in buildings with crawl spaces which are inaccessible for installation of SMD. Crawl-space depressurization has a lower installation cost than SMD, but its operating cost may be three times higher. Natural crawl-space ventilation and forced crawl-space pressurization each typically provides roughly 50% reduction or less in the living area. The lack of a clear benefit of crawl-space pressurization in most installations probably indicates that the crawl space is in fact not being pressurized. Crawl-space sealing and barriers (as stand-alone methods) usually give little or no reduction

KEYWORDS crawlspace, radon, residential building

#NO 6922 Temperatures and relative humidities in heated and ventilated crawl spaces.

AUTHOR Tobin L

BIBINF Proceedings of the ASHRAE/DOE/BTECC Conference, December 7-10, 1992, 'Thermal Performance of the Exterior Envelopes of Buildings', Clearwater Beach, Florida. #DATE 00:12:1992 inEnglish

ABSTRACT Temperature and relative humidity in a crawl space beneath a well-insulated house, ventilated by the outdoor air, vary with the season. During the summer, warm, moist outdoor air enters the relatively cool crawl space with the result that the relative humidity becomes so high that mildew can become establised. This sometimes gives rise to an unpleasant smell in the crawl space, and the smell can find its way into the house. Although this is a recognized problem in Sweden, many houses are still built with this type of foundation structure. It is preferable to avoid the use of outdoor-air-ventilated crawl spaces in their entirety and to raise the temperature of the ground beneath the building, either by means of the heat in the house's ventilation exhaust air or by a floor heating system. If so, the foundations must be designed to suit the system to be used. This paper describes a number of designs that are theoretically suitable and for which calculations have been made and presents measured results from houses built on a number of different types of foundations. The results from the calculations and the actual measurements both indicate that heated foundations are also dry foundations. Even if moisture is trapped in the structure as a result of rain during the construction period, it need not result in damage; the heated foundation system accelerates drying out.

KEYWORDS temperature, humidity, crawlspace, outdoor air

#NO 7102 Effectiveness of ventilation improvements as a protective measure against radon.

AUTHOR Hoving P, Arvela H

BIBINF Finland, Helsinki, Indoor Air '93, proceedings of the 6th International Conference on Indoor Air Quality and Climate, 1993, Vol 4, pp 615-620. #DATE 00:07:1993 in English

ABSTRACT Radon reduction rates for ventilation improvement measures vary considerably. In 70% of the cases studied, further mitigation is needed to reach a level of 400 Bq/m3. Ventilation measures in crawl spaces and basements have resulted in reduction rates of up to 90%, though more typically 30-70%. Installating new mechanical systems in dwellings has resulted in 20-80% reduction rates. If fan use or fan efficiency is increase, radon levels can be reduced as much as when new systems are installed. Increasing fresh-air supply through vents or window gaps reduces radon concentrations 10-40%. Low ventilation rates, measured after mitigation using the passive perfluorocarbon tracer gas method, seem to be accompanied by also low radon reduction rates. Multiple zone tracer gas measurements were conducted in order to reveal radon entry from the soil and radon transport between zones.

KEYWORDS radon, crawlspace, basement, mechanical ventilation

#NO 7153 Measured performance of relocated air distribution systems in an existing residential building.

AUTHOR Guyton M L

BIBINF USA, Ashrae Transactions, 1993, Vol 99, Part 2, Preprint, 9pp, 7 figs, 2 tabs, refs. #DATE 00:07:1993 in English

ABSTRACT A study was conducted to determine savings in electric energy use and demand for a heat pump air-distribution system when it is located inside a building's conditioned space versus an identical system located in the attic and crawlspace. The comparison was made in a two-storey apartment building with two identically sized apartments on both the first and second floors. Data obtained show that the "inside" test apartments used 33.8% less energy for heat and 71.4% less energy for cooling and saved 59% demand at the utility's winter peak in January. Compressor run time was 38% less than the control units.

KEYWORDS air distribution, residential building, heat pump, attic, crawlspace, apartment building, cooling

#NO 7171 Temperature and moisture conditions in a crawl-space ventilated by indoor air.

AUTHOR Hagentoft C-E, Harderup L-E

BIBINF Proceedings of the 3rd Symposium on Building Physics in the Nordic Countries: Building Physics '93 (Bjarne Saxhof, editor), Thermal Insulation Laboratory, Lyngby, Denmark, 1993, vol 1, pp261-268, 5 figs, refs. #DATE 00:09:1993 in English

ABSTRACT A single-unit dwelling built according to the Optima concept has been thoroughly investigated by field measurements. One recognition in the concept is a specially designed crawl-space, ventilated by indoor air. Temperature and relative humidity in different parts of the crawl-space have been measured every hour ince August 1992. The moisture content mass by mass in the sills and other wooden parts in the foundation have been measured approximately every third week since March 1992. In this paper the measurements from November and December 1992 are specially examined. The measurements are compared with calculated values based on computer models. Differences between measurements and calculations are discussed at the end of the paper.

KEYWORDS temperature, heat loss, crawl-space, field monitoring, calculation technique

#NO 7179 CICS: calculations in crawl spaces.

AUTHOR Aberg O

BIBINF Proceedings of the 3rd Symposium on Building Physics in the Nordic Countries: Building Physics '93 (Bjarne Saxhof, editor), Thermal Insulation Laboratory, Lyngby, Denmark, 1993, vol 1, pp579-586, 6 figs, refs. #DATE 00:09:1993 in English

ABSTRACT The crawl space foundation is a common ground construction in Sweden. The floor framing is placed on a low foundation wall that forms an enclosed space. Most of the crawlspaces are ventilated with outdoor air, but some are unventilated or ventilated with indoor air. Cics (Calculations In Crawl Spaces) is a new calculation program for PC computers that works with the DOS system. With Cics it is possible to calculate the ventilation rate, temperature, relative humidity, and make a risk analyse of mould growth. The program is easy to use and the calculation time is short.

KEYWORDS crawlspace, temperature, moisture, mould, calculation techniques

#NO 7181 Humidity of wooden structures in the subfloor spaces of churches.

AUTHOR Rantamaki J

BIBINF Proceedings of the 3rd Symposium on Building Physics in the Nordic Countries: Building Physics '93 (Bjarne Saxhof, editor), Thermal Insulation Laboratory, Lyngby, Denmark, 1993, vol 1, pp595-602, 6 figs. #DATE 00:09:1993 in English

ABSTRACT The subfloor spaces of 38 wooden churches in Finland were examined and the humidity of their wooden structures measured. An attempt was made to perform the measurements in autumn so as to ensure that the conditions would be more or less uniform. Features measured in the spaces were construction area, height of subfloor space, size of ventilation holes, capillary rise and soil humidity, and attention was also paid to whether the holes were covered by a mesh or not. The in-situ wind conditions were evaluated visually. The amount of water flowing from the roof into the subfloor space was examined by inquiring and looking for possible signs of such flowing.

KEYWORDS crawlspace, humidity, wood, public building, soil

#NO 7266 A review of the regulatory and technical literature related to crawl space moisture control.

AUTHOR Rose W B.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, 1994, (preprint), 12pp, 3 figs, refs. #DATE 00:00:1994 in English

ABSTRACT The aim of this paper is to present historical background material on practices and regulations regarding moisture control in crawl spaces. Prior to World War II, crawl space construction in the northern United States was limited primarily to foundations for building accessories, such as porches, sheds, and outbuildings. In the southern U.S., crawl spaces were common, given the common use of pier foundations and open skirting. During the war, the"basement less house" was introduced in the interest of developing low-cost solutions to the housing crisis. Also during the war, the first description of ventilation requirements for the basement less house appeared in Federal Housing Administration documents. During the 1940's, work was conducted by the Housing and Home Finance Agency on ground covers, ventilation, moisture loads, and connections to the rest of the structure. Current code guidelines for crawl space construction reflect strongly the work of that time. In this paper, the results of that period of research are presented in detail and regulatory documents that arose are analyzed. As crawl space construction became more widespread in the mild climatic regions of the U.S., several case studies and surveys appeared that documented a strong correlation between crawl space construction and moisture problems in houses. These articles are summarized. From the 1950's to the present, research has been conducted to determine the effectiveness of various moisture control techniques. Summaries of that research are presented.

KEYWORDS crawlspace, moisture, building regulations.

#NO 7267 Comparison of ambient conditions and wood moisture contents in crawl spaces in a California condominium complex.

AUTHOR Flynn K A, Quarles S L, Dost W A.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, 1994 (preprint), 11pp 10 figs, 1 tab, refs. #DATE 00:00:1994 in English

ABSTRACT This paper describes a study conducted between October 1990 and April 1992 in which the conditions within four crawl spaces were monitored in a six-unit building in a condominium complex in Petaluma, California. Wood moisture contents and ambient conditions were periodically monitored in the crawl spaces of two end and two interior units in the building chosen for this study. The moisture content of the beams in each monitored crawl space was determined using a resistance-type moisture meter, and equilibrium conditions were estimated throughout the study by periodically weighing small wood sections that were suspended from the joists. Ambient conditions were monitored using a fan-aspirated psychrometer, a hygrothermograph, or temperature/relative humidity probes linked to a data acquisition system. The objective of this study was to determine the change in wood moisture content and ambient conditions in a field situation before and after a ground-cover membrane was installed in the crawl spaces of selected units in this building. When installed, the ground-cover membrane was used on one interior and one end unit. The ground-cover membrane was found to reduce humidity levels in the crawl space and allowed previously wet and decayed wood members to dry out.

KEYWORDS wood, moisture, crawlspace, apartment building.

#NO 7268 Reduction of moisture in wood joists in crawl spaces - A study of seventeen houses in southern New Jersey.

AUTHOR Stiles L, Custer M.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, 1994, (preprint), 11pp, 10 figs, 2 tabs, refs. #DATE 00:00:1994 in English

ABSTRACT A study of crawl space moisture of 17 single-family houses in southern New Jersey indicates that a combination of adding a moisture barrier (polyethylene) to the bare soil and foundation walls, closing foundation vents, and sealing air leaks at the rim joist reduces moisture content of exposed floor joists by 3% to 5%, while just applying the moisture barrier reduces moisture content by about one-half that amount. Moisture content in the joists varied between 10% and 23% during the year-long study. Seven houses served as controls, while five were treated with the moisture barrier alone and five as just described. Effective air leakage area between the crawl space and outside, the house and the crawl space, and the house and outside were determined for the latter group. A strong correlation was found between moisture content and effective air leakage area between the crawl space and outside.

KEYWORDS moisture, wood, crawlspace, residential building.

#NO 7269 Crawl space moisture conditions in new and existing northwest homes.

AUTHOR Tsongas G A.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, (preprint), 8pp, refs. #DATE 00:00:1994 in English

ABSTRACT As part of three major field moisture studies, the crawl spaces of numerous homes were inspected during winter for moisture problems. The sample of homes inspected includes 29 older homes in Portland, Oregon, 37 older homes in Spokane, Washington, and 55 relatively new and energy-efficient homes in the metropolitan area of Seattle/Olympia (38), the Washington coast (13), and Montana (4). Some of the older homes did not have a ground cover in the crawl space, and standing water was noted in some of the crawl spaces with and without a ground cover. Both open and closed vents were observed, although open vents were the most common. Mold and mildew in the form of very minor surface staining were only occasionally observed in the crawl spaces, and generally there were no noticeable musty odours. The moisture content of randomly selected wood members was almost always observed to be below 20%. Relative humidities in the crawl spaces generally were not measured, so the impact of the crawl space conditions on the conditions inside the homes is not known. However, the homes had what is considered to be fairly high indoor relative humidities and numerous indoor moisture problems probably due mostly to lack of adequate indoor moisture control. Finally, no wood decay was observed except in a very few cases where plumbing leaks existed or where wood members were improperly in direct contact with the earth. Generally the crawl spaces were almost completely devoid of moisture-related problems. The possible reasons for this are explored, as are code ramifications. Differences in moisture conditions in northwestern and southeastern U.S. crawl spaces are discussed.

KEYWORDS crawlspace, moisture, residential building.

#NO 7270 Investigation of crawl space performance in British Columbia.

AUTHOR Fugler D W, Moffatt S D.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, 1994, (preprint), 9pp, 3 figs, 3 tabs, refs. #DATE 00:00:1994 in English

ABSTRACT Crawl space construction in new Canadian houses is largely limited to the warmer coastal climate of British Columbia (BC). Building inspectors in that area were having trouble applying the somewhat vague requirements in the building code. Crawl space ventilation was being mandated in some cases even when the space contained uninsulated ducting for forced-air furnaces. An investigation of current BC crawl spaces was funded in 1990-91. A contractor inspected ten houses and tested the crawl space moisture levels and air leakiness, both to the outside and the house above. The contractor also summarized the construction details of BC crawl spaces: as designed, as built, and as an ideal. This study showed that current crawl space construction practice often led to an excessive amount of moisture entry and ventilation of conditioned house air. The research results were used to promote code changes in both provincial and national building codes. The contractor revisited some of the test houses in 1993 to investigate the long-term success of remedial measures and canvassed the BC inspectors and builders to see how code changes had affected crawl space construction practice. Application of new code clauses varied between municipalities.

KEYWORDS crawlspace, ventilation system, air leakage.

#NO 7271 Moisture control in crawl spaces.

AUTHOR Samuelson I.

BIBINF USA, Ashrae Transactions, Vol 100,Pt 1, 1994, (preprint), 7pp, 13 figs, 2 refs. #DATE 00:00:1994 in English

ABSTRACT With increasing thermal insulation of the ground floor of a building having an outdoor-air-ventilated crawl space foundation structure, the temperature and relative humidity in the crawl space are dependent on the ventilation provided by the external air. This is the case for well-insulated ground structures in a cold winter and temperate, humid summer climate. During the summer, the relative humidity can become so high that growth of microorganisms can become established. Various steps can be taken to improve conditions. Plastic sheeting on the ground is essential; thermal insulation of the ground or of the perimeter provides more marginal improvement. Measures such as dehumidification or heating of the foundation area, in combination with one or more of the above measures, are considerably more effective. The principle for the design of heated foundations in new buildings is described in this paper together with measured data from such structures in old buildings and present-day outdoor-air-ventilated foundations and heated foundations.

KEYWORDS moisture, crawlspace, foundation, humidity, thermal insulation.

#NO 7272 Three surveys of subfloor moisture in New Zealand.

AUTHOR Trethowen H A.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, 1994, (preprint), 11pp, 10 figs, 3 tabs, refs. #DATE 00:00:1994 in English

ABSTRACT This paper outlines three surveys relating to moisture in house crawl spaces in a cool temperate climate and conclusions drawn from them. The surveys were: - Atwo-year survey of 10 houses, monitoring moisture conditions in crawl spaces and roof spaces where the two were coupled by air leakage paths. Three different remedial treatments were tested, including covering the ground with polyethylene film. This ground cover was assessed later as at least 70% and possibly up to 95%effective. - A pilot study on measurement of subfloorground evaporation using lysimeters, leading to a one-year survey on ground evaporation under 60 houses in three towns. Average evaporation was approximately 400 g/2.day (1.3 oz/ft2.day). - A small survey on subfloor natural ventilation rates and the interchanges between the subfloor and other parts of the building. This survey showed that a NIST model correlated well with observed air exchange.

KEYWORDS survey, floor, moisture, crawlspace, ventilation rate.

#NO 7273 Airflow through crawlspace foundation vents.

AUTHOR DeWitt C A, Bunn J M.

BIBINF USA, Ashrae Transactions, Vol 100, Pt 1, 1994, (preprint), 13pp, 6 figs, 4 tabs. #DATE 00:00:1994 in English

ABSTRACT Pressure/flow relationships of crawl space foundation vents were determined and used in evaluating crawl space ventilation of three houses. Vent effective leakage area (ELA) ranged from 8% greater than net free area (NFA) for the smallest NFA vent to an ELA of 50% less than NFA for some larger NFA vents. Vents with low NFA provide more ventilation "per gross ventilation area" than vents with high NFA; two 24 in2.(.015 m2) NFA vents supplied the same ventilation as one 75 in2.(.048 m2) NFA vent. Vents installed according to building code requirements using state NFA may be providing up to 50% less ventilation than calculated by ELA. Fan pressurization tests on three houses indicated that the ELA of the crawl space with existing vents closed and sealed was greater than 1/1500 of the gross floor area in all test cases. When existing vents were opened, ELA increased 100% to 350%. ELA of the existing vents indicated less ventilation compared to NFA.

KEYWORDS air flow, crawlspace, foundation, vent.

#NO 7298 Radon reduction in buildings; the case of two Belgian schools.

AUTHOR Cohilis P, Wouters P, Voordecker P.

BIBINF USA, Ashrae, 1993, "Building design technology and occupant well-being in temperate climates". International conference, held February 17-19, 1993, Brussels, Belgium, pp 265-273, 4 figs, 5 tabs, refs. #DATE 00:02:1993 in English

ABSTRACT Various investigations were performed in two Belgian schools with high radon concentrations in order to define appropriate remedial actions. These investigations included a visual inspection of the buildings, tracer gas experiments, pressurization experiments, and carbon dioxide and radon concentration measurements. Afterward, a mitigation system was proposed for each school. Their use was completely successful in achieving radon reduction. For the first school, the room pressurization method was preferred to other methods because of its ability to improve the general indoor air quality of the classrooms. For the second school, the crawlspace ventilation method was chosen because of its simplicity. When possible, this type of argument should be taken into account while defining a mitigation method for a building, but, of course, the most important argument is a high probability of success for radon reduction. From this point of view, the present study indicates that the knowledge of the airtightness characteristics of the building, and of some particular rooms. is an important point.

KEYWORDS radon, school, carbon dioxide, crawlspace.

#NO 7377 The new monster in the basement.

AUTHOR Treidler B.

BIBINF USA, Home Energy, September/October 1993, pp 37-39, 1 fig. #DATE 00:09:1993 in English

ABSTRACT Basements differ from houses where the equipment is located in attics or crawlspaces in several significant ways: - Some of the energy "lost" by ducts in basements is recovered. The recovered energy reduces the heating and cooling load on the house above. In contrast, energy lost to an attic or crawlspace is not recovered because these spaces are well-vented. - Sheet metal ducts, which usually leak more that flex ducts, and may be uninsulated, are common in basement houses. For two-story houses, ducts and sometimes located outside conditioned space. This lowers the efficiency of these ducts relative to those in interior walls and floor spaces. - How ducts perform in basements depends on how the basements are used. If the basement is conditioned, then a basement home is similar to homes where the equipment is in a furnace closet and the ducts are in the conditioned space. Houses with unconditioned basements are more complex because the basement is a "buffer zone" between the house and its exterior. - The cooling performance of ducts in basements is usually higher than attic ducts. Attics get hot in summer, so attic ducts are least efficient for cooling just when the highest cooling loads occur. Summer cooling in basement houses contributes less to peak loads on electrical utilities.

KEYWORDS basement, furnace, duct.

#NO 7454 Investigation of a domestic heating system with ventilation heat recovery: performance and integrity.

AUTHOR Serive-Mattei L, Babawale Z, Littler J.

BIBINF Germany, Stuttgart, Fraunhofer Institut fuer Bauphysik, 1993, proceeding, International Symposium Energy Efficient Buildings, Leinfelden - Echterdingen, Germany, March 9-11, 1993. #DATE 00:03:1993 in English

ABSTRACT Domestic heating systems with a heat exchanger are generally assessed for efficiency by the ratio of primary energy input / delivered energy output. In practice, performance depends on all the components in the heat delivery system and on their matching. In the air heating system addressed here, the components include: the gas burning air heater, supply ducts, return ducts, heat recovery system, controls, fans, filters and pumps. This paper describes experiments conducted on a test house in Bath during the years 1991 to 1993. The house has been retrofitted with an air heating system and a ventilation heat recovery unit which also recovers heat from flue gases. The aim of these experiments was to characterize the house and the retrofit system in terms of ventilation and energy performance. In particular, airflows throught he heat exchanger, the heat losses occurring in the ducts and the air leakage from the ducts to the crawl space were investigated. To match the real values most of the experiments were conducted with the settings of the house as used by the occupants. This included the thermostat, the position of the delivery grilles and the window openings. Tracer gases have been used extensively to measure air change rates and an original method to assess air leakage from ducts has been developed.

KEYWORDS heating system, heat recovery, heat exchanger, air heating.

#NO 7473 A comprehensive yardstick for residential thermal distribution efficiency.

AUTHOR Modera M P, Andrews J, Kweller E

BIBINF Paper presented at the ACEEE 1992 Summer Study, Pacific Grove, CA, August 30 - September 5, 1992, 18pp, 5 tabs, refs.#DATE 00:00:1992 in English

ABSTRACT Thermal Energy Distribution (TED) systems provide the critical link between heating and cooling equipment and the conditioned areas of buildings. TED systems have also been shown to have a large potential for efficiency improvement, particularly in residences. This paper discusses the issues associated with characterizing the performance of TED systems in residential buildings. A possible framework for a universal figure of merit for residential TED systems that takes into account interactions between the TED system and the building envelope, interactions with the heating/cooling equipment, as well as the weather-dependence of TED efficiencies, is proposed. The proposed efficiency characterization framework incorporates the TED/envelope interactions that have been extensively studied in crawlspace and slab-on-grade houses over the past several years, as well as some of the findings of ASHRAE Special Project 43(SP43), which focused on air distribution systems in basement houses. This framework is designed to allow for compatibility with existing equipment and envelope characterizations (e.g. Annual Fuel Use Efficiency (AFUE), Seasonal Energy Efficiency Ratio (SEER), Heating Seasonal Performance factor (HSPF), Effective Leakage Area (ELA)), and to allow for comparison of forced-air hydronic and refrigerant distribution systems, including the impacts of zoning. The proposed backbone for most of the supporting analyses required to develop a practical yardstick is a combined simulation model based upon DOE-2, COMIS (a multi-zone airflow network model) and a combined heat and mass transfer model for duct systems. Efficiency calculations made with this model for a typical attic duct system are included as an example. Two applications identified for this figure of merit are utility DSM programs and building energy codes.

KEYWORDS Thermal performance, duct, building design.

#NO 7724 Conversion of a crawl space ventilated by cold air and one ventilated by warm air. Ombyggnad av kalluftsventilerad krypgrund till varmluftvertilerad

AUTHOR Larsson T

BIBINF Sweden, Rimbo, Bygg & Energiteknisk Utveckling, 1992 #DATE 00:00:1992 in Swedish

ABSTRACT This project was carried out on a housing estate a Ekero. Three crawling spaces were converted. In two of these the ground beams and the ground were insulated, while in the third on only the cat flaps were closed. Before the repairs were made, a computer simulation was carried out. Measurements show that in the spaces where the ground and ground beams had been insulated the temperature rose by about 4C and humidity decreased by about 10%. No negative effects were noted. Energy saving has been calculated at about 3%. It is difficult to verify such a small saving, but the measurements indicate that this saving is possible

KEYWORDS crawlspace, ventilation strategy, humidity insulation

#NO 7844 Sick building syndrome (SBS) in office workers and facial skin symptoms among VDT - workers in relation to building and room characteristics: two case- referent studies

AUTHOR Sundell J, Lindvall T, Stenberg B, Wall S

BIBINF Denmark, Indoor Air, No 4, 1994, pp 83-94, 6 tabs, refs# DATE 00:00:1994 in English

ABSTRACT IN two case-referent studies the associations between questionnaire symptom reports, expressed as SBS (Sick building Syndrome) in office workers or facial skin symptoms among VDT-workers, and physical data from offices in 160 buildings were investigated. The results show that low outdoor airflow rate and presence of certain pollution sources, such as copying machines, tended to be associated with an elevated prevalence of SBS. Buildings built to remodelled between 1977 and 1986, low-rise buildings with a horizontal roof and a foundation of the type "concrete slab on the ground" as well as rooms with fluorescent tube lighting with metal shields were also associated with an overrepresentation of skin symptoms among VDT-workers such as type of foundation (concrete slab on the ground and crawlspace), the frequency of floor cleaning and type of lighting (fluorescent tubes with glass/plastic shields). It has not been possible to establish conclusive explanations for these associations. The difference in associations between building factors and SBS, and between building factors and skin symptoms among VDT-workers points to different etiologies

KEYWORDS sick building syndrome, office building, questionnaire

#NO 8009 Flow paths in a Swedish single family house - a case study.

AUTHOR Hedin B

BIBINF UK, Air Infiltration and Ventilation Centre, 1994, "The Role of Ventilation", proceedings of 15th AIVC Conference, held Buxton, UK, 27-30 September 1994, Volume 2, pp593-614.

ABSTRACT The ventilation of a Swedish single family house is investigated by means of tracer gas and pressurization techniques. The ventilation flow plays an important role in this house as it enters through a dynamic loft insulation and exits via the crawl space. This design is said to give preheated and clean supply air, warm floors and good energy efficiency. But to meet these promises, it is essential that the air really flows in the intended paths. A single tracer gas technique is used to determine the air flow rates. The measurements show that actually too much of the supply air by-passes the dynamic insulation by direct infiltration. The measurements also detect an unintended flow from the crawl space to the living area. If there exists radon in the ground such a flow must be avoided. Pressurization tests are used to build a pressure drop-flow model. This model describes intended flows, i.e. supply air through dynamic insulation, extract air to crawl space and exhaust air from crawl space to the outside, as well as the unintended flows, i.e. infiltration to living area and the two leakages from outside to crawl space and from crawl space to living area. The model is used to explain the present flows and then to tell how to change them. This is done by simulating the model when one of the parameters (e.g. a size of a leakage) is changing. One conclusion is that the crawl space must be made considerably more airtight.

KEYWORDS (air flow, residential building, tracer gas, pressurization, attic, insulation, crawlspace, air tightness)

#NO 8017 Measuring subfloor ventilation rates.

AUTHOR Hartless R, White M K

BIBINF UK, Air Infiltration and Ventilation Centre, 1994, "The Role of Ventilation", proceedings of 15th AIVC Conference, held Buxton, UK, 27-30 September 1994, Volume 2, pp687-696.

ABSTRACT This paper reports on ventilation measurements taken beneath a suspended floor of a BRE/DoE energy and environment test house. Sulphur hexafluoride was introduced into the subfloor void at a constant rate and the resulting concentration measured. Wind speed, wind direction, and internal, external and subfloor temperatures were also recorded. A range of air brick locations were used for each run which lasted two to three days. Analysis of the data shows that subfloor ventilation rates in this test house fluctuated widely, ranging from about 3 air changes per hour (ach) to over 13 ach. Also, the subfloor ventilation rate for this house seems to be heavily influenced by the subfloor/external temperature difference rather than the wind speed, particularly when air bricks are located on sheltered subfloor walls. The main reason for this stack dependence is that there is a significant leakage path at the wall/floor junction with air moving from the subfloor void to the gap behind the plasterboard lining.

KEYWORDS (crawlspace, ventilation rate, measurement technique, floor, wall, air leakage)

#NO 8026 The air lock floor.

AUTHOR Phaff H J C, de Gids W F

BIBINF UK, Air Infiltration and Ventilation Centre, 1994, "The Role of Ventilation", proceedings of 15th AIVC Conference, held Buxton, UK, 27-30 September 1994, Volume 2, pp779-785.

ABSTRACT The Air Lock Floor and the Pressure Ring are two effective measures for control of air flow directions between rooms or zones in buildings. They create a pressure hierarchy that controls spread of pollutants. Here an example has been given for radon from a crawl space, odours from a bakery into a dwelling above and an isolation chamber with a leaky facade. The Air Lock floor can operate with a 7 W fan and at the same time extract the normal dwelling ventilation flow rate. Used in the ground floor, the Air Lock Floor results in a warmer floor and contributes to energy savings. The now well ventilated, warmer and dryer crawl-space would make the use of wooden (plywood) floors possible with less risk of wood rot and mould growth.

KEYWORDS (floor, air flow, pollutant, radon, crawlspace, odour)

#NO 8146 Mechanical crawlspace ventilation.

AUTHOR Anon

BIBINF USA, Energy Design Update, August 1994, pp 14-15.

ABSTRACT Describes how a US ventilation system company has teamed up with a production builder to demonstrate a simple and practical variation of a technique for using the crawlspace under a house as an exhaust medium for the whole house ventilation system, by using a central exhaust ventilation system to provide crawlspace ventilation. This can eliminate the need for conventional "passive" vents.

KEYWORDS (crawlspace, mechanical ventilation, exhaust)

#NO 8535 Gas flow rates into voids below timber floors, theory and experiment 

AUTHOR Cripps A 

BIBINF UK, Building Research Establishment, August 1993, paper presented at the 1993 AAR ST/EPA Radon conference, Denver, Colorado, September 20-23, 1993. 

ABSTRACT This paper reports on analytical and experimental studies of the rate of flow of gas into a timber floored test hut at the Building Research Establishment. The analytical results give insight into the nature of the flow through bare soil and will prove useful in verifying computational models. The experimental work took place at the BRE radon pit. The flow rates through the sand produced by different pressures in the under floor space were measured. The analytical solution gives good agreement with the measured flow rate and will in future be compared with the measured pressure field. The analytical solutions enable the flow to be predicted from the soil permeability, the driving pressure and a constant factor which can fairly easily be calculated from the geometry of the building. A detailed calculation of the pressure field is not needed, but the methods used enable it to be found if desired. The mathematics used is fairly difficult and is not included in detail; contact the author for full details. The analytical results will be useful in understanding the effectiveness of remedial measure for this type of floor structure. They will be applicable to heat flow problems, since they are solutions to Laplaces's equation, which also governs heat flow under some conditions. The experiments allow the main predictions of the modelling work to be examined, and show agreement within an order of magnitude. They will be reported on more fully at a later date, when the pressure field in the sand at the radon pit has been measured more carefully. 

KEYWORDS floor, air flow, soil, modelling, radon, crawlspace.

#NO 8677 Aerosol-based duct Sealing Technology 

AUTHOR Modera M, Carrie F R. 

BIBINF USA , Center for Building Science News, Winter 1995, pp 8-9, 4 figs. 

ABSTRACT During the past five years, research has quantified the impacts of residential duct system leakage on HVAC energy consumption and peak electricity demand. A typical house with ducts located in the attic or crawlspace wastes approximately 20% of heating and cooling energy through duct leaks and draws approximately 0.5 KW more electricity during peak cooling periods. A 1991 study indicated that sealing leaks could save close to one Quadrillion Btus per year. Because the major cost of sealing leaks in existing air distribution systems is the labor for the location and sealing process, reducing the labor could greatly improve the cost-effectiveness of such a retrofit. Field studies of duct sealing programs performed by HVAC contractors show that labor costs vary between three and six times material costs. Another conclusion of these studies is that in many instances it is virtually impossible to get to the leaky ductwork. Between 1992 and 1994, we obtained laboratory proof-of-concept of a technique to seal duct systems remotely using an internally injected aerosol. Our tests have shown that holes in the ducts, as well as leaks between duct joints, can be sealed remotely and that even those leaks beyond bends and junctions in the ductwork can be sealed. 

KEYWORDS aerosol, duct, sealing

#NO 8714 The energy demand from cradle to grave for three single family houses in Sweden. 

AUTHOR Adalberth K. 

BIBINF UK, Building Research Establishment, proceedings of the first international conference on Buildings and the Environment, 16-20 May 1994, Session: Case Study Buildings, Paper 4, 5 pp, 6 figs, 4 tabs, 4 refs. 

ABSTRACT Scientists from four different Swedish universities have planned 26 healthy and energy efficient single family houses. The houses have been built in a town west of Stockholm, Sweden. The detached houses have different types of building constructions, for example slab on the ground, indoor or outdoor ventilated crawl space. They have also different thicknesses of mineral wool in the attics and external walls. There are three different heating systems in the 26 houses. These are; warm air space-heating integrated with the ventilation system, radiator consisting water and finally under floor heating with low temperature. All the 26 houses have a balanced ventilation with a heat exchanger. During two years, 1993-1994, the houses will be examined in many different ways. About 20 projects are associated to the 26 healthy and energy efficient houses. The aim of one project is to environmentally classify the houses. The reason for this is that buildings have a great affect on the environment. As a start in this project, three of the dwelling s energy demand during the life cycle have been evaluated. 

KEYWORDS residential building, health, energy efficiency, heat exchanger.

#NO 9153 Modelling and simulation of the crawlspace heat pump. 

AUTHOR Wasserman D, Reid R 

BIBINF (ASHRAE Trans) 1984. vol.90. part 1A, 312-334, 15 figs, 3 tabs, 

ABSTRACT A simple and inexpensive way to increase the efficiency of heat pumps used with houses built with crawlspaces is to use the soil beneath the crawlspace as a heat source or heat sink for the outdoor unit of the heat pump. Air is preconditioned by the crawlspace soil before passing over the outdoor unit coil. A model of heat transfer in a crawlspace was developed, and a computer program written to calculate time dependent soil and air temperatures in a crawlspace containing a heat pump. Latent heat transfer resulting from soil vapour diffusion was included in the model. Various assumptions regarding vapour diffusion in soils were made in order to match simulated soil and air temperatures. This model, together with the seasonal performance factor heat pump model, was compared with data from an instrumented house and then used to predict heating season crawlspace heat pump performance for crawlspaces different from the experimentally evaluated crawlspace. Results included, a single pass system is not suited for winter operation, adding insulation to the walls of an above-grade crawlspace only improves performance slightly, a crawlspace heat pump in a northern region of the United States could significantly reduce heating season purchased energy compared to a conventionally installed heat pump. 

KEYWORDS heat pumps, crawl spaces 

#NO 9324 Dry basements through the selective use of thermal insulation and moisture-resistant materials. 

AUTHOR Timusk J, Pressnail K D, Chisholm W P 

BIBINF USA, Energy Efficient Building Association, EEBA, 1995, proceedings of the 1995 Excellence in Housing conference, Innovations for Performance , held Minneapolis Hilton and Towers, Minnesota, USA, March 8-11, 1995, pp A57-A87. 

ABSTRACT There are many building science problems related to basements including problems associated with heat and moisture movement. This paper examines the soil thermal and moisture regimes which vary with the season and depth below grade. Considering these changes, this paper proposes straightforward solutions involving the selective use of basement thermal insulation and moisture resistant materials. In addition, solutions to insulating crawl spaces are presented together with a discussion of the potential for frost-heave and adhesion freezing problems. The proposed solutions offer the promise of lower building and operating costs while improving the indoor environment. 

KEYWORDS basement, moisture, building material

#NO 9486 Identification of advective entry of soil-gas radon into a crawl space covered with sheets of polyethylene foil. 

AUTHOR Andersen C E, Koopmans M, de Meijer R J 

BIBINF Denmark, Riso National Laboratory, April 1996, 125pp. 

ABSTRACT To assess the effectiveness of mitigative measures against radon (222Rn) entry into houses, experiments were conducted in crawl-space house where the dirt floor of the crawl space was covered with sheets of 0.23 mm polethylene foil fixed to the walls. The radon concentration was measured below the foil and in the crawl space together with environmental variables such as indoor-outdoor pressure differences. The sub-foil region was small compared with the crawl space and in direct contact with the soil, and because the influence of ventilation and radon emerging from building materials was largely suppressed. The experimental data was analyzed using various types of models including a simplistic mass-balance model, a regression model, and a two-dimensional numerical model based on Darcy flow of soil gas and combined diffusive and advective transport of radon. The main outcome of the work was that :(i) The soil-gas entry rate per Pascal depressurization was at the order of 1 m3 h-1 corresponding to an effective soil permeability of 5.10-10m2, (ii) the stack-related part of the depressurization of the crawl space (approx. 0.1 PaoC-1)was controlled by the temperature difference between the living room of the house and the outdoors (not by the difference between the crawl space and the outdoors), (iii) that part of the wind-related depressurization that was measured by the pressure transducers seemed to force radon into the crawl space in the same proportion as the stack-related part of the depressurization, (iv) the ratio of advective and diffusive entry was approx. 0.7, when the crawl space was depressurized 1.5 Pa,(v) the effective diffusivity of the foil was found to be three orders of magnitude larger than that measured in the laboratory (the enhanced diffusivity was most likely caused by leaks in the foil and by mixing fans located in the crawl space), and (vi) there was no measurable mitigative impact of having the sheets of foil on the crawl-space floor even if the crawl space was artificially pressurized or depressurized. 

KEYWORDS radon, crawlspace

#NO 9487 The effect of a foil on the floor of a crawl space in relation to radon entry. 

AUTHOR Andersen C E, Koopmans m, Berger H, de Meijer R J 

BIBINF In: L Morawska, N S Bofinger and M Maroni (eds): Indoor air, an integrated approach, Elsevier 1995. 

ABSTRACT Experiments were conducted in a crawl-space house where the dirt crawl-space floor was covered by sheets of 0.23mm polythylene foil fixed to the walls. Effective system parameters were identified using a two-dimensional numerical model. The effective foil diffusivity was found to be three orders of magnitude larger than the one measured for the bulk material. Under natural conditions 2 to 3% of the total crawl-space ventilation flow seemed to come from the soil. This flow accounted for 1/3 of the total radon entry from the soil. The model was used to predict the effectiveness of using different foils in combination with slight over- or underpressures of the crawl space. 

KEYWORDS radon, crawlspace

#NO 9717 Heat loss from suspended timber floors.

AUTHOR Harris D J, Dudek S J-M

BIBINF France, Ecole Nationale des Travaux Publics de l'Etat, November 1994, proceedings of the European Conference on Energy Performance and Indoor Climate in Buildings, held Lyon, France, 24-26 November 1994, Vol 3, pp 968-973, 5 figs, 5 refs.

ABSTRACT Suspended timber ground floors are often used on new houses, [1], and are also typical of a large number of houses built before 1940, which represent a substantial building stock that now needs refurbishment with improved insulation levels. While the thermal performance of walls and roofs has been improved in recent years through loft and cavity wall insulation, the heat loss from the ground floor has been overlooked. This may constitute up to 25% of the total heat loss from an otherwise well-insulation house. Ventilation of the under-floor space is required to present a build-up of moisture and subsequent rotting of the timbers, and this serves to increase the heat loss. Earlier work showed that the heat loss may increase by 40% at a ventilation rate of 1.5 air changes per hour[2]. The under-floor void may range in height from a few centimetres to as much as half a metre, and moisture enters mainly by evaporation of water from exposed earth and from construction water drying out. If the moisture content of the timbers exceeds 20% for only a few days, various types of mould may begin to grow, which cause rapid deterioration of the timbers through wet or dry rot. Ventilation is normally used to prevent this, by means of air bricks in the outer walls. This ventilation inevitably results in an increase in the heat loss from the floor, and is dependent on the wind speed and the degree of exposure of the site.

KEYWORDS heat loss, floor, underfloor crawlspace, ventilation rate, insulation

#NO 9861 Subfloor and house ventilation rates: comparing measured and predicted values.

Hartless R P

UK, Air Infiltration and Ventilation Centre (AIVC), 1996, proceedings of 17th AIVC Conference, "Optimum Ventilation and Air Flow Control in Buildings", Volume 1, held 17-20 September 1996, Gothenburg, Sweden, pp 331-342.

This paper reports on the use of BRE's domestic ventilation model, BREVENT, to predict subfloor and whole house ventilation rates in a BRE/DoE test house. Before the model could be used though some minor adjustments were necessary because one of its underlying assumptions was that the subfloor temperature was equal to the external temperature. Temperature measurements over a number of months showed this assumption to be false and so an extra stack term was introduced into the model. However, the overall difference this makes is still quite small, only a few percent at most. The predicted subfloor ventilation rate matched the calculated value well, particularly when it was stack dominated. When wind played a significant part though the level of agreement deteriorated, particularly when subfloor air bricks were located on unsheltered walls. However, both the subfloor and whole house ventilation rate of the test house appears to be heavily influenced by the stack effect because the suspended floor and ceiling are leaky in comparison to the walls. As a result, subfloor ventilation will be stack dominated about 61% of the time. To improve the prediction of wind affected subfloor ventilation better pressure coefficient data is required. In a similar vein BREVENT can predict whole house ventilation rates best when the flow is stack dominated. Analysis of the separate stack and wind effects show that the ventilation in the test house will be stack dominated for about 86% of the time. When wind speed does influence ventilation then wind direction also has an effect: winds blowing from the East and West generally give ventilation rates 25% lower than those blowing from the North and South.

underfloor crawlspace, ventilation rate, prediction, modelling

#NO 10123 Cardboard box demonstration of series leakage. The Energy Conservatory ACEEE '96.

Anon

USA, The Energy Conservatory, ACEEE '96, 1996.

A simple model consisting of a box on top of another box can be used to demonstrate the measurement of series leakage paths. Series leaks are leaks which are not directly connected to the outside, but pass through an intermediate zone (for example a crawl space, attic or garage) on their way into or out of a building. A number of simple pressure diagnostic techniques have been developed allowing us to estimate the leakage areas of series leaks.

air leakage


#NO 10235 A demonstration of new automated equipment and techniques for easier and more precise measurement of pressures and airflow in buildings.

Anon

USA, The Energy Conservatory, [1996].

Describes a multifunctional data acquisition and fan control system which significantly improves the precision of pressure and airtightness measurements in buildings. The Automated Performance Testing (APT) system includes two onboard precision auto-zeroing pressure channels and eight analog voltage channels for optional sensors. An analog output signal allows the APT system to control the speed of a calibrated blower door or duct pressurisation testing system. Improves the measurement of building depressurisation or pressurisation due to exhaust fans, imbalanced duct leakage or imbalanced distribution systems; pressures in building zones (e.g. attics, crawlspaces, garages) which are used to estimate zonal leakage rates and prioritise airsealing activities; airtightness measurements of buildings and ducts; simultaneous monitoring of key building pressures and other parameters for diagnosing performance problems in buildings (backdrafting combustion appliances, CO levels etc).

air flow, pressurisation, measurement technique


#NO 10270 Modeled and measured infiltration in ten single family homes. 

Francisco P W, Palmiter L 

USA, Washington DC, American Council for an Energy Efficient Economy (ACEEE), Proceedings of the 1996 Summer Study on Energy Efficiency in Buildings, "Profiting from Energy Efficiency" 

Real-time ventilation and infiltration measurements were made on ten single-family homes. Seven of these had crawlspaces and were in the Pacific Northwest. Two had daylight basements and were also in the Pacific Northwest. The other is an energy efficient demonstration ``smart'' house built in Rocklin, CA, and was built on a crawlspace. All of the homes were tested under heating season conditions. The home in Rocklin was also tested under cooling conditions. Each house was divided into multiple zones, including buffer spaces, and each test period lasted about a week. Tests were conducted to compare ventilation and infiltration during periods when the forced-air distribution system was on to those times when it was off. Special one-time tests were also done with exhaust fans operating. Detailed data was collected in each house using a real-time multi-tracer measurement system. This paper presents the results of testing on these ten buildings. Blower door test results are compared, and the ability of various models to predict infiltration for the different foundation types are analyzed. 

field monitoring, ventilation rate, infiltration rate, blower door


#NO 10942 Study on humidity environment in crawl space of dwelling house.

Iwamae A, Matsumoto M

Belgium, Proceedings of Clima 2000 Conference, held Brussels, August 30th to September 2nd 1997, paper 304, 15 figs.

Many houses in Japan have crawl space between the lowest floor and the earth ground which is about 50 cm in height. This is considered as protection against corrosion of wood materials in the floor. Japanese building codes recommend ventilation with outdoor air in this space. In our field research, we found condensation in the crawl space in summer. This is due to low temperature of the ground and high humidity of the outdoor air which is typical of the Asian climate. To prevent this condensation and ensure long-term durability, we estimated the effect of a humidity-controlling soil cover which absorbs moisture into itself and desorbs during the dry season. The estimation is performed by field experiments and numerical analysis based on simultaneous heat and moisture transport process, which is validated by experimental results. The numerical analysis also clarifies the effect of ventilation. 

humidity, residential building

#NO 11171 The Optima - house. Air quality and energy use in a single family house with counterflow attic insulation and warm crawl space foundation.

Elmroth A, Fredlund B

Sweden, Lund University, Lund Institute of Technology, Department of Building Science, Report TABK-95/3033, translated by L J Gruber, 1996, 157pp.

The firm Skanska AB has produced a special design concept for the construction of healthy single family houses of low energy consumption - the "Optima" house. It uses the principle of counterflow insulation in the attic floor and a crawl space foundation ventilated by indoor air. Air to the house is supplied through the ceiling insulation with the intention that the air should be filtered by the insulation material. An extract fan creates negative pressure inside the house. The extract air which is passed into the foundation through the floor construction contributes to keeping the floor warm. The results of a year-long evaluation indicated that counterflow insulation works as theoretically calculated on the basis of measured air flow rates through the insulation. Supply air appears to be well filtered on its passage through the loose fill insulation. On the whole, the indoor air ventilated foundation was found to work well, but measurements and analyses clearly showed that the construction is sensitive to excess moisture and leakage of air into the foundation.

attic, crawlspace, retrofitting

#NO 11358 High efficiency houses: moving markets, updating codes.

Rider Allen D

USA, Home Energy, May/June 1998, pp 35-39.

Describes a demonstration house intended to show builders that energy efficient design can be economic. The house promotes the Virginia Power Energy Saver Home Plus program. Innovative features included an unvented crawlspace, flow-through walls, dense-pack cellulose insulation, mechanical ventilation, round metal ductwork, air sealed drywall, and efficient HVAC equipment housed within partially conditioned space.

residential building, energy efficiency, retrofitting

#NO 11714 Crawl space: how to avoid moisture and soil gas problems.

CMHC

Canada Mortgage and Housing Corporation, 1998, 9 pp.

Crawl spaces often do not get adequate inspections and there is a general lack of appreciation by the housing industry for the elements that make up a effective moisture control strategy. Moisture related problems occur in many crawl spaces despite the fact that building codes require vents. Moisture from the crawl space can move into the living area or even into the attic, causing mould growth problems. Houses with high levels of air leakiness will move crawl space air into the house regardless of the type of heating system. Many problems found in crawl spaces are related to a misunderstanding of how crawl spaces work. The insulation, air and vapour barriers are typically not well integrated with the rest of the house. Many crawl spaces are built over an exposed dirt floor, rather than incorporating a ground cover, floor drain and perimeter drainage similar to a properly constructed basement. Recent research has illustrated alternative crawl space construction techniques. Passive ventilation may often be unnecessary or ineffective. The purpose of this publication is to explain the latest understanding of crawl spaces, and how they should be built to avoid problems.

building design, air leakage

#NO 11799 Carpet staining.

Anon

Canada, Solplan Review, July 1998, p 8.

Discusses the problem of staining on light coloured carpets which can be ascribed to the increased use of decorative candles in residential buildings. The staining is caused as a result of pressure differences set up in the house due to air leakage. Suggestions to avoid the problem include the following: heated crawl spaces should have a relief vent to keep them in a negative pressure in relation to the rest of the house. The balance of the house should be kept at an even pressure; ducts should be sealed, especially if they run in a crawl space or basement; penetrations in the envelope should be air sealed; air sealing of the house should be done carefully; lifestyle practices may have to be modified (especially the use of inappropriate candles).

floor coverings, stains, particulates

#NO 11869 Field validation of algebraic equations for stack and wind driven air infiltration calculations.

Walker I S, Wilson D J

USA, ASHRAE, 1998, in: the ASHRAE Transactions CD, proceedings of the 1998 ASHRAE Annual Meeting, held Toronto, Canada, June 1998, 20 pp, 7 figs, 5 tabs, refs.

Explicit algebraic equations for calculation of wind and stack driven ventilation were developed by parametrically matching exact solutions to the flow equations for building envelopes. These separate wind and stack effect flow calculation procedures were incorporated in a simple ventilation model, AIM-2, with empirical functions for superposing wind and stack effect, and for estimating wind shelter. There were three major improvements over previous simplified ventilation calculations: a power law pressure-flow relationship is used to develop the flow equations form first principles, the furnace or fireplace flue is included as a separate leakage site, and the model differentiates between houses with basements, slab-on-grade, and crawlspaces. Over 3400 hours of measured ventilation rates from the test houses at the Alberta Home Heating Research Faculty were used to validate the predictions of ventilation rates and to compare the AIM-2 predictions to those of other ventilation models. The AIM-2 model has bias and scatter errors of less than 15% for wind-dominated ventilation, and less than 7% for buoyancy (stack-effect) dominated cases.

calculation techniques, air infiltration, wind effects

#NO 11922 Distribution system leakage impacts on apartment building ventilation rates.

Walker I S

USA, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc (ASHRAE), 1999, in: the ASHRAE Transactions CD, proceedings of the 1999 ASHRAE Winter Meeting, held Chicago, USA, January 1999, 13 pp, 5 figs, 8 tabs, refs.

Forced air distribution systems in residential buildings are often located outside the conditioned space, for example, in attics, crawl spaces, garages, and basements. Leaks from the ducts to these unconditioned spaces or outside can change flows through the registers and change the ventilation rates of the conditioned spaces. In this study, duct leakage flows were measured in several low-rise apartment buildings. The leakage flow measurements and other data about the apartments were used to develop a prototype apartment building, The multizone airflow model COMIS was then used on this prototype building to determine internal flows within the building, airflows through the building envelope, and the impacts of the duct leakage on the ventilation rates. The effects of sealing the duct leaks were also examined in order to determine changes in infiltration rates resulting from duct retrofits. The simulation results showed that for the prototype tested here, the excess return leakage tended to decrease envelope infiltration flows by about 20%, but the total infiltration load, including return duct leaks, more than doubled during system operation.

duct leakage, apartment building, ventilation rate

#NO 11935 Measured energy penalties from crawl space ventilation.

Hill W W

USA, American Council for an Energy Efficient Economy (ACEEE), 1998, in: proceedings of "Energy Efficiency in a Competitive Environment", the 1998 ACEEE Summer Study on Energy Efficiency in Buildings, CD format, pp 1.135-1.146, 4 figs, 3 tabs, refs.

While there is no convincing technical basis for current code requirements for crawl space ventilation, most codes still require operable vents and the practice is well established among builders and architects. While the evidence against venting is compelling to many if not most in the research community, builders and code officials apparently want to see hard evidence. In this research project I measured weekly energy consumption for space heating for a 1150 square foot home in a climate with 5900 heating degree days. The house was built to meet the 1992 Model Energy Code and the perimeter of the crawl space was insulated with R-10 foamboard. The supply ducts of the gas-fired, forced air system are located in the crawl space and were carefully sealed and pressure tested. Utilizing a "flip flop" research design, with the crawl space vents open one year and closed the next, I measured the "energy penalty" resulting from leaving crawl space vents open during the winter. This measured penalty or, conversely, the savings from closing and insulating the vents was 21% (12 MMBtu/yr) in year two of the research. Savings were 32% (19 MMBtu/yr) in the most recent winter, in which the crawl space access cover was insulated and made airtight in addition to closing and insulating the vents.

crawl space, energy efficiency, ventilation system

#NO 12014 Ryomintatilan tuuletus ja kosteuskayttaytyminen. Crawl spaces air change and moisture behaviour.

Kurnitski J, Kettunen A-V, Matilainen M, et al

Finland, Helsinki University of Technology, HVAC-Laboratory & Laboratory of Structural Engineering and Building Physics, Espoo 1998, LVI-tekniikan laboratorio, raportti B 59, Talonrakennustekniikan laboratorio, julkaisu 88, 186 pp.

in Finnish

In the research project the design criteria for crawl spaces were developed and physical mechanisms concerning air change and moisture behaviour of the ground were analysed. Special attention was paid to examining the performance of mechanical ventilation. Field measurements over a period of one and a half years were made in naturally and mechanically-ventilated crawl space of a test building, where mechanical supply and mechanical extract ventilation was compared to natural ventilation. The reduction of the moisture supply from the ground surface by laying a PVC sheet on the ground was tested both in naturally and mechanically-ventilated crawl spaces. Moisture supply from the ground surface was measured by laboratory tests. The evaporation rate of moisture was measured for various types of soil, gravel, crushed stone, expanded clay and some other materials. The effects of the ventilation rate, the insulation layer on the ground and the type of ground soil were studied by computer simulation. According to the results of field measurements, the fact that a portion of the intake air is taken from the crawl space to the apartments should be considered in the design of crawl spaces. The underpressure in apartments, caused by exhaust ventilation, was the main reason for air change in naturally ventilated crawl space, where the extract air escaped through the leakage of the ground floor. The best way to reduce humidity in crawl space by ventilation is to use the mechanical supply (or balanced) ventilation that blocks air flows from the ground soil. The optimal ventilation rate is 1-2 l/h, however 0.5 l/h is usually enough. In the warm season there is no upper limit to air change, but in winter the high air change (>2 l/h) cools down crawl space and the humidity will rise. It is reasonable to use the two-stage ventilation that is controlled by outdoor temperature: 0.5 l/h with half speed and 1-2 l/h with full speed. As a rule uncovered ground surface should be avoided in crawl spaces. In the case of moist ground surface, higher air change leads to higher moisture evaporation, and the humidity of the crawl space will be reduced only within small limits. Thus, moisture production should be reduced. This can be brought about by using approx. 10 cm layer of gravel, crushed stone, expanded clay or a PVC sheet that has been made penetrable by water, i.e. any water flowed into the crawl space should have an exit route. It is important to cut a capillary rise in the surface layer. For example moisture production from clay can be reduced by 50 times by using 10-15 cm of gravel layer with a low capillary rise on the clay. The best way to verify the suitability of the employed gravel or crushed stone is to perform laboratory tests. For example, the capillary rise in crushed stone, used in the test building, was 30 cm, when the capillary rise in washed crushed stone is almost zero. Using an insulation layer on the ground surface is not recommended according to computational results, because even if the insulation cuts off evaporation completely, the crawl space will cool down in the summer (in the heating season crawl space remains warm and dry), and the outdoor air will become the moisture supply, thus raising humidity in the summertime. This result was calculated for the test building with 5 cm cell-plastic insulation. In future the effect of insulation layer on the behaviour of heat and moisture should be studied by field measurements. The monthly average of the relative humidity in crawl spaces will not exceed 80% in summertime when the supply (or balanced) ventilation 1-2 l/h is used and the evaporation from ground surface is suitably reduced (the effect is about 10% RH), and in the heating season the relative humidity will remain at a 70% level.

crawlspace, moisture, air change rate

#NO 12862 Crawl space air change, heat and moisture behaviour.

Kurnitski J

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 13093 Air flow and thermal analysis of a forced air heating and ventilation system.

Levin P

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 44.

The prediction of energy use, air flows and temperatures in different rooms of a building and at different climatic conditions is very important, especially when evaluating new concepts for heating and ventilation systems in combination with different building envelope constructions. A thorough system analysis considering coupled air flow and thermal calculations becomes very complex if e.g. thermal bridges and dynamic conditions are considered. The substance of this paper is to describe a relatively simple methodology for system analysis that has been applied to a house and to compare obtained results from measurements and calculations. 

The methodology consists of initial calculation of air flows using the multi-zone model IDA-MAE for different configurations and climatic conditions. The air flows are then included in a TSBI3 computer model for temperature and energy use calculations. 

User-friendly computer tools that combine multi-zone air flow and thermal calculations are desired to simplify a sensitivity analysis, and this will also increase the precision in the predictions. This development is in progress internationally. Further development of field methods to measure the air leakage characteristics of building components and individual air leakage paths would be useful to increase the knowledge of, in particular, interior air leakage paths in buildings.

The evaluated building concept, called TEEG, uses a heated crawlspace to distribute ventilation and heating air through gaps in the floors along the external walls. As the system relies on distribution of warm air through gaps in the floors, it becomes very sensitive to uncontrolled air leakage paths. Measurements of air leakage become an important quality control tool for buildings using this concept.

forced air heating, air flow, building envelope, multizone modelling, crawlspace

#NO 13103 Ventilation in US manufactured homes: requirements, issues and recommendations.

Lubliner M, Gordon A

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 54.

In the United States 15-20% of new single family dwellings are built in manufactured housing plants on permanent metal chassises in sections and transported to a building site. Once at the site, the axles and wheels are removed, the home sections connected, and typically set on top of vented crawlspaces. The construction and "installation" of these manufactured homes must meet requirements contained in the U.S. Department of Housing and Urban Development's (HUD) Federal Manufactured Housing Construction Safety Standards (FMHCSS). In addition to addressing structural, fire safety and energy efficiency issues the HUD FMHCSS, most recently issued in 1994, contains requirements for providing outdoor air ventilation. In the same time frame, an energy efficient construction program for manufactured homes has been implemented in the Pacific Northwest region of the U.S. This program, Super Good Cents(tm)/Natural Choice(tm) (SGC/NC), resulted in the construction of 90,000 homes. Finally, the National Fire Protection Association (NFPA) adopted the 1994 FMHCSS as NFPA Standard 501and is in the process of revising their standard to reflect new information and new approaches to ventilating manufactured homes.

This paper discusses the activities of HUD, SGC/NC and NFPA as they relate to the issue of ventilation requirements in manufactured homes and the means of implementing these requirements. This discussion focuses on how these requirements relate to energy consumption, thermal comfort and indoor air quality. The various ventilation approaches being used or proposed to meet these requirements are reviewed and a number of issues relating to these approaches are discussed. These issues include the use of outdoor air intake ducts on forced-air system returns, whole house exhaust fans, inlet vents, and interzone communication. Other building and system issues are also addressed, including envelope airtightness, duct leakage, HVAC system oversizing, forced-air fan motor energy and humidity control. This discussion is based largely on experience in the SGC/NC program and on a simulation study conducted at the National Institute of Standards and Technology. This study employed the multizone airflow and indoor air quality program CONTAM to simulate airflow in a double-section home under several different ventilation scenarios. These scenarios included envelope infiltration only, infiltration plus the effects of local exhaust and forced-fan operation, an outdoor air intake duct installed on the forced-air return, and whole house exhaust with and without passive inlet vents. Simulations were performed to predict outdoor ventilation rates into the house due to infiltration and mechanical ventilation, interzone airflow rates between the rooms, building air pressures, and ventilation air distribution. The results show that despite the assumption in the HUD standards that infiltration contributes 0.25 h-1, the predicted infiltration rates are lower than this value for many hours of the year. The supplemental ventilation systems investigated in this study provide ventilation rates that meet or exceed the total ventilation requirement of 0.35 h-1, but the impact of such systems is dependent on the operating schedules of the supplemental systems. In addition to summarizing the results of this study, this paper makes a number of recommendations for these standards, for occupant education and for additional research.

mobile home, ventilation system


Related publications

23 May 2019 | New Perspectives on Kitchen Ventilation
INIVE eeig,
25 April 2019 | Ductwork airtightness measurements: protocols
INIVE eeig,
This project deals with reviewing EBC's Annex 5: "Air Infiltration and Ventilation Cent
AIVC,