Optimum Ventilation and Air Flow Control in Buildings

Proceedings of the 17th Annual AIVC Conference, held Gothenburg, Sweden, September 1996

1996, ISBN 0 946075 90 5, 2 Vols plus supplement, Code CP17

Optimum ventilation and airflow control in buildings?
Malmstrom T-G
Air quality, air flows in buildings, and ventilation are most important topics. Good air quality is however critically dependent also on other things than ventilation, eg source strengths, as is well known. The theme of our conference could also lead to the assumption that there is a simple connection between ventilation and air quality. As the public tend to see ventilation systems as responsible for bad air quality, it is important to state that there is no general criterion for good air quality possible to use in practice to control ventilation processes. Automatic ventilation control is still possible in specific cases only. The ventilation process depends on the total air exchange in the building, which is difficult to control. A related question is: what is acceptable as ventilation air? Is air leaking in through the outer wall acceptable? Is air supplied through the staircases acceptable? To answer such questions air quality criteria are needed too.

Computerised methods for balancing ventilation systems.
Larsen B T
Adequate ventilation with the "right amount of air, to the right place and at the right time" are important factors for achieving a good indoor climate. Thus it is of prime importance that the ventilation system is working properly. Using traditional methods, it is a very time consuming, and some times even impossible, task to balance ventilation systems to achieve correct air distribution. In most countries the growing concern about Indoor Air Quality has resulted in Building Codes demanding increased ventilation rates. This makes it even more critical that ventilation systems are correctly balanced. Otherwise the effort of solving one problem: "inadequate ventilation", may create two new problems: "draught and noise". This paper describes the "DPM method which is a new method for balancing ventilation systems. The balancing "starts at the designer's desk" by doing a comprehensive computerised pressure loss analysis. The results from this analysis are then input to a PC connected with an electronic instrument. The PC/instrument may be used for balancing when the air terminals are already installed in the building. However, there is a much larger potential for time and cost savings when using the DPM method for pre-setting air terminals at the factory. For this purpose a "DPM machine" has been designed for computerised pre-setting and bar code labelling of air terminals. With impressive results the ventilation systems in a number of buildings have been balanced in the last two years using the described innovative technology.

The effect of recirculation on air-change effectiveness.
Federspiel C C
The effect of recirculation on the age of air is described. A new effectiveness measure called the relative air-change effectiveness is defined in such a way that the air distribution pattern in a room may be quantitatively characterized even when the age of the supply air is non-zero. This admits the evaluation of air distribution patterns in single-zone systems that recirculate air, and also multizone systems with or without recirculation. It is shown that the relative air-change effectiveness may be calculated either solely from age of air measurements of from age of air measurements and flow rate measurements. Re-evaluation of previously published experimental data demonstrates how knowledge of the relative air-change effectiveness may change conclusions drawn from experiments in working buildings.

How effective is natural ventilation? A study of local mean age of air by modelling and measurement.
Walker R R, Hayes S D, White M K
A condition often assumed when designing a naturally ventilated building is where air enters at low level and leaves at high level due to the stack effect. It then follows that, at upper levels, the air may be relatively 'stale' since it has previously passed through the lower storeys. An analogous situation may arise when wind is blowing, in which the air entering through the windward face becomes stale as it passes through the building to the downwind sections. It is not well understood how ventilation may, in reality, be affected by this. To address these issues, this report describes a modelling approach using BREEZE and complimentary measurements using the Passive Tracer Gas technique to study local ventilation rates in multiroomed office buildings. Calculations show that simple ventilation flow rates, as conventionally calculated at the design stage, cannot be relied upon to indicate the true 'freshness'. Measurements show that effective ventilation can be less than current minimum occupancy requirements.

The effect of external atmospheric pollution on indoor air quality.
Kukadia V, Palmer J
This paper reports the findings of a pilot field study carried out to investigate the internal and external air pollution levels of two adjacent buildings, one naturally-ventilated and the other air-conditioned in an urban area, to investigate their relative attenuation of external pollution levels and to compare internal levels with existing air quality guidelines. Concentration levels of sulphur dioxide, nitrogen oxides, carbon monoxide and carbon dioxide were monitored, Simultaneously, measurements of ventilation rates within the buildings and periodic video recordings of the traffic were also carried out. As expected the concentration of external pollutants in the buildings followed the daily external variation, but at reduced levels. Generally, pollutant levels were higher in the naturally ventilated building than in the air-conditioned building. However, on a number of occasions, combustion products from heating boilers were entrained into the air-conditioned building via the high level air intake of the ventilation system raising the levels of nitrogen oxides, sulphur dioxide and carbon dioxide inside the building to higher than those found externally. A comparison of the results with existing air quality guidelines or standards for exposure showed that in both buildings the level of contamination was less than the relevant standard, except during a limited period at the weekend when combustion products were possibly entrained into the air-conditioned building. There is thus no clear distinction between the two types of ventilation strategies in terms of providing adequate indoor air quality to the occupants of the buildings.

Comparison of indoor levels of radon between workplaces and homes located nearby in different parts of Finland.
Korhonen P, Kokotti H, Kalliokoski P
The aim of this study was to compare the radon levels at workplaces and in homes located nearby. Homes (number of 57) and partly or fully underground workrooms (number of 55) have been studied at the four workplaces in southern Finland and one workplace in northern Finland. Radon concentrations both at workplaces and in homes seemed to be at the same level in the same district. The mean radon concentration in workrooms was 406 Bq.m-3, and in homes concentration was 398 Bq.m-3. At the workplaces having mere exhaust ventilation the mean radon concentration was higher (arithmetic mean of 677 Bq.m-3 n=14), than the places having mechanical exhaust and supply ventilation (arithmetic mean of 207 Bq.m-3, n=33). In an average the naturally ventilated workplaces (n=8) had the lowest level of indoor radon (arithmetic mean of 133 Bq.m-3). The highest radon level, both in the workrooms (2937 Bq.m-3) and in the homes (3080 Bq.m-3), was found in the northern Finland. The high values of indoor radon might be partly explained by the hill-construction of buildings without sealed constructions against soil, and partly by depressurisation caused by mechanical exhaust ventilation.

Particulate pollution interactions with indoor surfaces: measurement and modelling for risk assessment and contaminant control.
Byrne M A, Goddard A J H, Lockwood F C, Nasrullah M
In the urban environment, there is strong evidence that fine particulates associated with vehicular emissions are linked with respiratory problems and an increase in mortality. The population sector most at risk is the elderly who spend much of their time indoors; consequently, the infiltration of these particles and their subsequent behaviour indoors is of primary concern. The deposition of aerosol particles in the respiratory system and on indoor surfaces is a process governed by particle size; in addition to providing risk assessment data, an understanding of the interaction of particles with indoor surfaces can be applied to the design of systems for enhancing indoor aerosol deposition and thus inhibiting inhalation exposure. This paper describes experiments using tracer-labelled aerosols, in a range of monodisperse size distributions representative of real particulate pollutants, to study aerosol deposition on surfaces with representative roughness. Some preliminary data, exhibiting electrostactically-enhanced aerosol deposition are also presented. In order to make these data widely accessible, the experimental results are used to aid in the development of a CFD code by providing validation data. Simulations are described for a room-sized enclosure with representative indoor surfaces, to illustrate the influence of internal building surface characteristics on indoor aerosol concentration modification.

Checking of ventilation rates by CO2 monitoring.
Ekberg L E, Strindehag O
The present paper presents results from measurements of outdoor airflow rates and air change rates carried out simultaneously with measurements of the indoor concentration of carbon dioxide (CO2). The measurements were made both under controlled laboratory conditions and in the field. The field experiments were performed in a conference room, an assembly hall and an office room, and laboratory investigation was carried out in a 19 m3 test chamber. CO2 measurements can be successfully used to estimate the outdoor airflow rate in occupied rooms, but it is vital that the methodology takes into consideration a number of possible sources of errors. For example, it can not be presupposed that steady-state conditions prevail. However, inaccuracies due to non steady-state conditions may be reduced by a thorough analysis of the measurement results. Furthermore, it is demonstrated how the air change rate can be determined using a method based on analysis of the CO2-concentration decay in a room.

Reducing draught problems in the cold working rooms.
Suokas M
This study is done by order of a Finnish air cooler manufacturer and it is founded to a master's thesis of the same subject matter. The company produces eg unit air coolers with electric fans and so the aim of the study was to reduce draught problems caused by cold air jets. The desired values were: Because there are two different ways to reach and maintain low temperatures in cold working rooms we first compare the advantages and disadvantages of both methods and then get acquainted with cold air jets and reducing draught problems they can cause. The cooling coil can be mounted in the ventilating unit in which case the cold air has to be blown into rooms through ducts and conventional air outlets. Cooling coils can also be mounted directly to the ceiling in cold rooms. In that case there is often used forced convection which is carried out with electric fans. The forced convection improves heat transfer and so it is possible to make coils of compact size. The installation with cooler coils and electric fans is called unit air cooler. The former method makes it possible to have silent cold rooms with good and even distribution. The air distribution can be still improved by using porous textile ducts and let the cold air flow through the cloth into the room. However, there can be some hygienic problems. Hygienic problems can be minimised with the latter method, unit air coolers, because they are quite easy to maintain and keep clean. The disadvantage is that there can be some noise and draught problems. Noise problems can be solved by using fans with low RPM, but the draught problem still remains. It can be reduced with air deflectors which intensify the so-called Coanda effect. The results of this study are utilised in a novel series of air coolers.

AIOLOS: Creation of an educational structure on the use of passive cooling ventilation techniques for buildings.
Santamouris M, Dascalaki E, Priolo C, Vandaele L, Wouters P, Alvarez S, Allard F, Limam K, Maldonado E, Guaraccino G, Bruant M
AIOLOS is a project partly financed by the European Commission, DG XVII for Energy, within the frame of the ALTENER programme. The purpose of the project is the creation and dissemination of educational material on the use of passive ventilation cooling systems and techniques as applied in buildings. All information will be coupled with the problems of passive solar heating, daylighting and visual comfort. The project is oriented to South European but also North European countries with moderate climate presenting cooling problems. Existing information and knowledge together with recent European research results will be compiled into an educational package. The package will include brochures of case studies, slides, didactic software, technical manuals, guidelines and a handbook with basic and up-to-date knowledge acquired by recent research projects in the field. The aim of the project is to provide building professionals with all necessary knowledge and tools on the efficient use of passive ventilation in buildings. All material will be in a flexible form so that it can be updated on a regular basis. Dissemination will be achieved by seminars attended by building professionals. The overall duration of the project is 18 months.

Design guidelines for ventilation system for pollution control in large, semi-enclosed bus terminus.
Yiu J, Yik F, Burnett J
In response to complaints about poor air quality in bus termini, the Hong Kong Government is considering imposing legislative control over ventilation system design and operation of bus termini in Hong Kong. However, there are, as yet, no relevant air quality criteria and ventilation system design guidelines for Hong Kong. In this paper, measured air quality data for 5 semi-enclosed bus termini are reviewed. This provides a picture of the prevalent air quality in bus termini. To establish a design guide for ventilation systems for Hong Kong, a number of overseas design guides are examined and a ventilation system design method is proposed. The significance of design parameters, such as bus engine emission rates, utilization of the terminus, ventilation effectiveness, etc, are discussed.

Cooling and ventilation of a high-speed ground transportation system.
Rosemann P, Moser A
This paper presents the special needs and difficulties concerning cooling and ventilation of the SwissMetro high-speed ground transportation system. SwissMetro is based on four complementary technologies: a complete underground infrastructure, a partly evacuated tunnel system to reduce the aerodynamic drag of the vehicle with a maximum speed between 400 and 500km/h, linear electric motors and a magnetic levitation and guiding system. Due to high internal and external heat loads permanent cooling and air-conditioning of the vehicle is required. Additional thermal problems may occur in the case of an emergency. The pressure level inside the tunnel has to be raised within a short period of time to guarantee the safety of the passengers and to avoid any health risks. This repressurisation of long tunnel sections may cause shock waves and high temperatures inside the tunnel. The aim of the project is to analyse the spatial and temporal temperature evolution in the SwissMetro tunnels under different conditions and in emergency situations.

Experiments in natural ventilation for passive cooling.
Flourentzou F, van der Maas J, Roulet C-A
A naturally ventilated three level office building has been used to study basic stack ventilation configurations and the interaction between ventilation and the subsequent cooling of the building structure in summer. The research was performed in the framework of a European project on passive cooling of buildings and the objective was to validate simple ventilation algorithms and to give an experimental basis to design guidelines for night cooling techniques. The multilevel office allowed the studying of the influence of openings (size and position) on the neutral pressure level (NPL) and on airflow rates. Various cross-ventilation situations have been studied. A single flow path configuration was obtained by closing all windows and doors in the building envelope with the exception of the roof exhaust and one office window as the ventilation air inlet. Air flow patterns were traced with smoke and tracer gas. In a first set of experiments, where the only driving force is stack pressure, air velocities and the position of the NPL have been measured, and contraction and velocity coefficients as used in the Bernoulli model have been observed. In a second set of experiments, the resulting effective area of a combination of two openings in series was studied. Air flow rates derived from velocity measurements in the open doorways were found to be in agreement with the flow rates obtained with a constant injection tracer gas technique, with an uncertainty of +/-20%. Overall agreement was found between the velocity measurements and simplified models based on the Bernoulli equation. In order to cool multiple levels of a building with outside air, the position of the neutral pressure level should be controlled. The restrictions on opening size and position are discussed.

Modelling the influence of outdoor pollutants on the indoor air quality in buildings with airflow rate control.
Kraenzmer M
Low emitting building materials have contributed to the reduction of indoor air contaminants, and in many countries gas ranges and gas cookers are rarely used. As a result, in buildings located in urban environments, a considerable part of the contaminants in the indoor air may originate from the outdoor air. In urban areas buildings are exposed to high concentrations of a large number of contaminants, especially during traffic peak hours. Often, the air intakes are located on the facades, and if there are no filters, the supply air will have the same content of contaminants as the outdoor air adjacent to the buildings. Where if possible, it is advantageous to place the air intakes on the roofs of the buildings (1). The higher the air intakes are placed, the better is the air quality in most cases. To avoid exposure to high concentrations indoors due to concentration peaks of contaminants in the outdoor air, it is possible to decrease the airflow rate temporarily (2). This could be done by monitoring the concentration of carbon dioxide (CO) adjacent to the air intake. When the outdoor concentration of CO exceeds a preset limit, the fans are simply switched off, or the speed of the fans are decreased to a more suitable level.

Comparison of different methods of incorporation of stochastic factors into deterministic models of indoor air quality.
Sowa J
The paper will discuss problems connected with incorporation of stochastic factors into deterministic models of indoor air quality. Three different methods: * quasi dynamic multi-zone modelling with generating of input data time series, * multi-zone modelling based on the theory of stochastic differential equations, * Monte-Carlo simulation with independent random generating of stochastic parameters, will be shortly presented. Described methods are compared on the base of computer simulation of CO2 concentration in simple two compartment office. The comparison of simulation outcomes shows that the way of stochastic disturbances incorporation into indoor air quality models does not have an important influence on mean value of predicted concentration. At the same time the analysis of standard deviations indicates that the method of disturbances generation and its later incorporation have a great influence on probability distribution of estimated concentrations. The author would like to highlight that differences. The conclusions include also subjective opinion of the author on main advantages and disadvantages of each of proposed methods.

Residential mechanical ventilation systems: performance criteria and evaluations.
Dorer V, Breer D
The performance of mechanical ventilation systems has been checked in several innovative residential houses in the frame of Swiss research as well as pilot and demonstration projects. This paper gives a list of performance criteria for the ongoing comparison and evaluation of these mechanical ventilation systems. For some criteria, target values are proposed. In the second part, this paper shortly describes four residential buildings with mechanical ventilation systems where such evaluations were performed and highlights interesting design features and results from the measurements. It then focuses on discrepancies between the design goals and what has been encountered in reality during the evaluation campaign. Problem items were, among others, commissioning, occupant acceptance and window opening behaviour as well as sealing of ducts and heat exchangers.

French ventilation system performances in residential buildings.
Millet J-R, Villenave J G, Riberon J
The comparison of the performance of ventilation systems must take into account different issues. For indoor air quality, different kinds of pollutant sources have to be defined. To make an evaluation of the results, the best approach is to consider the people exposure. Four generic pollutants are taken into account: rooms components or furniture, human metabolism, cooking activities, passive smoking. As the definition of the unit for each pollutant is free, it is useful for their comparison to press them on a common "normalised" basis. This enables to make a distinction between the simulations based on generic pollutants and their interpretation which could be derived for many kinds of pollutants without having to do additional calculations as far as the considered pollutant follows the conventional patterns. The pressure difference, for example can be related to radon issues as to running of some heat appliances. The room parameters are mainly related to humidity issues as condensation, mould growth or house dust mites. For energy issues, a distinction has to be made between the direct energy use (fans) and the heat needs due to ventilation. Such a methodology has been defined within the IEA annex 27 project. After a presentation of the different parameters taken into account, we describe the computer code SIREN95 developed at CSTB in order to obtain the required results and we present a sensitivity analysis for the basic ventilation system used in France (mechanical exhaust).

Efficiency characterisation of various ventilation configurations.
Hanrion M-L, Barles P, Marchal D
The study concerns the ventilation of a parallelepiped shaped room by means of several systems whose supplying and extracting methods differ, so the different thermic conditions applied to limits. To qualify the efficiency of each of these systems in relation with the various current criteria, we carried out measurements by means of a tracer gas, both with a transitory and a permanent flow. At the same time, numerical simulations were carried out by means of a CFD code which solves the equations of the fluids mechanic, material and heat transfers associated with flows. These calculations results, after measurements validation, enable to accurately know the air movements in the ventilated room as well as the tracer gas concentrations distribution in the tested configurations. From these calculation results, was also demonstrated how the complex behaviour of each of these ventilation systems can be characterised owing to the possibility of identifying it to a simple model, using a reduced number of parameters. These typical parameters can in turn be used to implement the system performance evaluation criteria. These criteria allow to compare the various studied ventilation systems and class them in performance order. It can be seen that this classification can be modified depending on the selected criterion as well as the chosen ventilated area. The study results equally show the interest of the use of numerical simulation together with experiments, thus extending the range of results in order to generalise conclusions.

Ventilation in houses with distributed heating systems.
Parent D, Stricker S, Fugler D
The LTEE laboratory of Hydro-Quebec, in collaboration with Canada Mortgage and Housing conducted an indoor air quality study involving 30 single family detached houses heated with electric baseboard heaters in the vicinity of Trois Rivieres during the 1993-94 heating season. The houses were selected according to the measured air leakage at 50 Pa. so as to have a sample distribution similar to the distribution of air leakage of houses in the province of Quebec. The "source strength" of several air pollutants were calculated from measurements of ambient pollutant levels and total ventilation during a one-week test. In addition, the indoor CO2 and humidity levels were recorded in eight of the houses continuously during the heating season. The level of CO2 in the master bedroom was found to follow fairly closely the CO2 level in other parts of the building including the basement (within about 200 ppm) except when the bedroom door was closed. With the room occupied and the door closed, CO2 levels in the bedroom increased steadily during the night until morning, when the door was opened, to levels in excess of 3 500 ppm with one person, and in excess of 4 500 ppm with two persons. Model studies using the measured pollutant source strengths and measured equivalent leakage areas of the buildings indicated that the recommended health guidelines for airborne respirable solid particles (RSP's), CO2 and formaldehyde are exceeded during periods of low total ventilation, coinciding with mild outdoor temperatures and low wind conditions. It was observed that kitchen and bathroom fans originally installed in some of these houses were not operated by the occupants for sufficiently long times to affect the quality of indoor air. Various different methods of ventilating some of the houses were tested, including quiet replacement exhaust fans, mixing fans for indoor air, and a fresh air intake and mixing system. The effects of operating various air handling systems were monitored by keeping track of indoor CO2 and relative humidity in the master bedroom, and occupancy in person-hours per day. Quiet replacement fans noticeably improved indoor air quality when these were operated over 50% to 100% of the time. An area of remaining concern is the fact that exhaust only systems accentuate the negative pressure in the basement by raising the level of the neutral pressure zone in the building, and may enhance the flow of soil gases into the basement. A system which mixed indoor air between the basement and the main floor also reduced the average level of indoor pollutants. The system was designed to create a pressure difference between the main floor and the basement, causing a slight pressurization of the basement. A system designed to introduce 5L/s of outdoor air and to mix it with 55L/s of indoor air for tempering was installed to draw air from the hallway and deliver the mixed air into each of three bedrooms. This system was capable of maintaining CO2 levels in the master bedroom below 1000 ppm with two occupants in the room and the door closed.

Residential ventilation and energy characteristics.
Sherman M H, Matson N E
The role of ventilation in the housing stock is to provide fresh air and to dilute internally-generated pollutants in order to assure adequate indoor air quality. Energy is required to provide this ventilation service, either directly for moving the air or indirectly for conditioning the outdoor air for thermal comfort. Different kinds of ventilation systems have different energy requirements. Existing dwellings in the United States are ventilated primarily through leaks in the building shell (ie infiltration) rather than by mechanical ventilation systems. This report ascertains, from best available data, the energy liability associated with providing the current levels of ventilation and to estimate the energy savings or penalties associated with tightening or loosening the building envelope while still providing ventilation for adequate indoor air quality. Various ASHRAE Standards (eg 62 119 and 136) are used to determine acceptable ventilation levels and energy requirements. Building characteristics, energy use, and building tightness data are combined to estimate both the energy liabilities of ventilation and its dependence on building stock characteristics. The average annual ventilation energy use for a typical dwelling is about 61 GJ (roughly 50% of total space conditioning energy usage); the cost-effective savings potential is about 38 GJ. The national cost savings potential, by tightening the houses to the ASHRAE Standard 119 levels while sill providing adequate ventilation through infiltration or mechanical ventilation, is $2.4 billion. The associated total annual ventilation energy use for the residential stock is about 4.5EJ (ExaJoules).

Ventilation requirements in non-domestic building and energy efficiency.
Wouters P, Vandaele L, Ducarme D, Demeester J
The research community as well as the design and construction practice is spending a lot of efforts and investments in developing systems which optimise the energy use for achieving certain specified air flow rates. For example, improvements in efficiencies of 10 % in heat recovery systems would be considered as remarkable. At present, one observes a tremendous difference in the ventilation requirements in various countries as well as at the European level. Variation of a factor 10 of the ventilation rate requirement can be found in the proposal for European standard CEN prENV 1752 depending on the 'cleanness'of the building. The present paper develops these problems and makes a comparison with the situation in other areas like thermal comfort and lighting requirements.

IEA Annex 27: Evaluation and demonstration of domestic ventilation systems. Assessments on noise.
Op't Veld P, Passlack-Zwaans C
The acceptance and appreciation of ventilation systems is mainly determined by the perceived indoor air quality, thermal comfort and noise. Noise in relation to ventilation systems can be divided into three categories: * outdoor noise (entering the dwelling through ventilation openings, cracks, mechanical supply and exhaust openings etc); * noise generated by components of the ventilation system; * the impact of ventilation systems on sound reduction of partitions (between dwellings, rooms etc). Depending on the type of ventilation system, one or more of these aspects are of concern. Noise related to the ventilation system and components, can result in turning off the ventilation system or closing vents etc. This can have a negative influence on ventilation and indoor air quality. In the framework of IEA ANNEX 27 several noise aspects of domestic ventilation systems have been evaluated. Outdoor noise: In noise loaded areas the selection and the applicability of different types of ventilation systems are determined by the noise level on the facades. A simplified tool is developed to select ventilation systems as a function of the required noise reduction of the facade, room dimensions and design and construction of the facade. System noise: Controlling noise levels caused by ventilation systems is in practice one of the most important factors to contribute to the satisfaction with a ventilation system. Air duct systems in dwellings transport noise generated by fans and aerodynamic noise generated by bends, control valves, grilles etc. ANNEX 27 gives basic formulas to estimate sound power levels of fans and grilles, indication of sizes for silencers and guidelines for design. Impact on noise reduction of partitions: The composite sound reduction is the result of different sound channels from one room to the other. One of these sound channels may be the ventilation system (cross-talk). Cross-talk can be brought about through the air duct system, overflow grilles and ventilation openings in partitions, duct transitions etc. ANNEX 27 provides guidelines for sound reductions of partitions and insertion losses for ducts to eliminate the influence of cross-talk.

Modelling and assessing ventilation efficiency in an imperfectly mixed ventilated air space.
Janssens K, Berckmans D, De Moor M
To ensure indoor air quality an efficient ventilation system should provide fresh air in those parts of a room where it is required. To assess whether the ventilation system fulfils the main objective, different definitions of local ventilation efficiency (the local mean age of air, the local ventilation rate, the local purging flow rate and the local air exchange rate) are reported in literature. Tracer gas techniques (step up method, step down method and pulse method) and CFD-models are mostly used in research to identify the 3-D distribution of these ventilation parameters in a ventilated space. In our laboratory the 'local volumetric concentration of fresh air flow rate' (m3/s.m3) was introduced as a new ventilation parameter. A total amount of 90 step up experiments was performed in a laboratory test installation with a volume of 9 m3 (3x2x1.5m) to model the 3-D distribution of this ventilation parameter in relation to different values of the ventilation rate (120-300 m3/h) and the heat supply (0-400 Watt) as control inputs. In the main part of the paper some results are given of the modelled 3-D distribution of the 'volumetric concentration of fresh air flow rate' in the test installation. This distribution of fresh air flow rate is assessed in relation to the air flow pattern which is visualised by smoke experiments and quantified by image analysis and the Archimedes number.

Practical experiences with IR controlled supply terminals in dwellings and offices.
Ducarme D, Wouters P, Jardinier M, Jardinier L
Ventilation is necessary to provide a good indoor air quality to occupants in office buildings but is however a major energy consumer. In that manner, ventilation in itself can contribute to much more than 50% of the energy consumption for heating in well insulated office buildings. Likewise, the general trend in standards to augment ventilation requirements would still increase its energy costs. Thus, it seems obvious that an intelligent control of ventilation in office building allows to obtain substantial reductions of energy consumption. To a certain extent this is also true for dwellings even if in general ventilation represents a smaller contribution to the energy consumption for heating than in office buildings. In this connection, it should be noted that the increasing requirements regarding insulation of dwellings has for effect to augment this proportion. Demand controlled ventilation in dwellings appears therefore also as an interesting way to achieve energy consumption reduction.

The influence of outdoor air vents and airtightness on natural ventilation - calculations based on measurements.
Blomsterberg A
Many modern buildings in the Nordic countries have mechanical ventilation. Passive stack ventilation is, however, an accepted ventilation system in the Nordic countries according to the current building codes. The building authorities need to be able to supply guidelines on natural ventilation systems in modern buildings, in order to fulfill the requirements on a healthy indoor climate at a reasonable energy cost. Therefore a project was initiated by the Nordic committee on building regulations. The aim of the project was to present functional and technical requirements on natural ventilation systems. The paper discusses the influence of outdoor air vents and airtightness on passive stack ventilation for Nordic dwellings. Calculations, based on measurements, were performed for a one storey one-family house, a 11/2-storey one-family house and two apartments in a three-storey building. Cumulative distributions of ventilation rates for a year were calculated, using a multi-zone air flow model, for individual rooms. It is shown that the ventilation rate will vary very much, without any interaction from the occupants or an automatic control system. A modern system for passive stack ventilation must include a system for control of the air flows in order to avoid excessive use of energy and inadequate indoor air quality.

Maximum velocity of return flow close to the floor in a ventilated room - experimental and numerical results.
Karimpanah M T, Sandberg M
The problem of sensation of draught in ventilated spaces is connected to inappropriate velocities in the occupied zone. In Scandinavia, velocities higher than 0.15 m/s are said to be an indicator of that occupants are likely to feel discomfort. Therefore knowledge of the flow field (both mean velocities and fluctuations) is necessary. Both experimental and numerical analysis of the flow field in a full scale room ventilated by a slot inlet, with two inlet Reynolds numbers 2440 and 7110, have been carried out. Results from both approaches show that the location of the maximum velocity near the floor is nearly independent of the Reynolds number. For a two-dimensional room, the maximum velocity at the floor level occurred at about 2/3 room length from the supply. The distance from the floor level is dependent on the inlet Reynolds number. The velocity profiles far away from the wall opposite to the inlet device have the same character as a wall jet profile. However, close to the corners they are transformed. The relative turbulence intensities measured in the return flow region are questionable, because of a hot wire's inability to record large fluctuations at low mean velocities. These turbulence intensities close to floor level vary from 15 to 80% and as the authors have pointed out previously hot wires do not indicate the real value of the turbulence intensities beyond 20%. Difficulties appear in numerical predictions of return flow properties. Comparison between predicted values and experimentally obtained values show a reasonable agreement. This is promising for future CFD-predictions. However, there is a need for an appropriate measurement technique that can cope with reversing flow.

Full-scale measurements of indoor air flow.
Handa K, Pietrzyk K
Full scale measurements of air flow velocities, temperature, intensity of turbulence and air exchange rate are carried out on two rooms with different types of ventilation located in the department of architecture at Chalmers University of Technology. The measurements have shown that mixed ventilation gives variable mean flow velocities with a high risk of draught as compared to the room provided with displacement ventilation. Air exchange rate for the room with displacement ventilation is obtained from tracer gas monitor by employing decay and constant emission methods. The measurements give similar results for both the methods.

Application of a passive tracer gas technique in naturally and mechanically ventilated school buildings.
Stymne H, Boman C-A
The homogeneous emission passive tracer gas technique is described. This technique relies on an even distribution of constant tracer gas emission rate within the object to be measured, so that the emission rate per volume unit is constant. The local steady state concentration of the tracer gas is directly proportional to the mean age of air and the emission rate per volume unit. The technique was applied in 10 school buildings, of which 4 were newly constructed naturally ventilated buildings, 2 were old naturally ventilated buildings, 2 were old mechanically ventilated buildings and 2 were newly constructed supply and exhaust ventilated buildings. The result shows that the ventilation rates in naturally ventilated schools are relatively low compared to required standards. It demonstrates the importance of not only relying on the naturally induced ventilation rate, but also to use other means for improving the air quality during or between lessons, like window opening.

Developing tracer gas technique to determine interzonal air exchange rate.
Niu J L, Burnett J, van der Kooi J, van der Ree H
The use of local exhaust is considered to be the most effective way to control pollutant dispersion from intense sources, such as in kitchens, in toilets, as well as in copy machine rooms. The optimum air exhaust rate required to prevent pollutants from escaping into the major occupant areas very much depends on the natural air exchange rate (AER) between the hooded room and the major room space. This paper presents a mathematical model and a test procedure of using tracer gas technique to quantify the AER. In this study, the mathematical model analyzes the balance the balance of a tracer gas in two adjacent zones, and establishes two correlations between the dimensionless increase/decay rates of the gas concentrations and the AER. The mathematical model reveals two alternative ways to determine the AER: a). Tracer gas concentrations in both rooms involved be monitored; b). Tracer gas concentration in one of the two spaces be monitored. The latter method was validated in a test for AER quantification between ceiling void and room in a test chamber. Finally the proper use of the two methods is discussed, and it is suggested that the techniques developed in this study can be used for estimating minimum exhaust rate requirement for ventilation system renovation in existing buildings.

Application of the tracer gas techniques for the assessment of ventilation indexes in real buildings.
Aleo F, Vitale S
The work presented in this paper is aimed at the definition of tracer gas experimental procedures for measuring the air change rate, the age of air and the air change efficiency in real buildings under mechanical ventilation conditions. The measurement procedures, based on the decay method, were validated in a special experimental chamber and implemented in two rooms of a building under real operating conditions. Measurements of volumetric flow rate through the air ducts of two buildings, performed by means of the constant emission rate method, will be shown and commented. Results of some measurements obtained by tracer gas technique have been compared with values measured by using other traditional methods.

Zonal model to predict air distribution and dynamic concentration of pollutant in ventilated rooms.
Cocora O
The first part of the paper will show some aspects of experimental research on air distribution in ventilated rooms. The study has been carried out to get an understanding of the air movement and the ventilation effectiveness by means of tracer gas measurements. It has been investigated the velocity and the distribution of the concentration in a two-dimensional isothermal flow issue of a linear supply opening. The second part of the paper will describe a proposed zonal model in 9 zones. This model is able to predict the steady-state behaviour of ventilated rooms and the dynamic evolution of a possible pollutant concentration in such environment. The theoretical model is based on the flow element method according to the throw of an isothermal jet and on a typical configuration of a zonal model. Comparison between experimental measurements and the zonal model show a good agreement on the range of usual air change rate in the ventilated rooms.

Measurement of ventilation air flows.
Hedin B
The common way to determine air infiltration, exfiltration and interzonal flows from tracer gas measurements in multizoned buildings is to rely upon the standard single or multizone model, Vc(t) = Qc(t)+p(t). Here c, p are zonal tracer concentrations and injections, t is time and V, Q are the sought volumes and flows. This model may work well provided that all zones are sufficiently well mixed and all flows really are constant during the measurements. The latter can be doubtful in naturally ventilated buildings, especially as the measurements may require several hours. This paper discusses one single question: What could be gained if the flows of the model are allowed to vary in time?, ie we will consider a (bilinear) model:Vc(t) = Q(t)+p(t). The variation of Q(t) will, however, be restricted to be piecewise linear. This extension will complicate the identification procedure, ie the computations, somewhat. On the other hand it does not alter the tracer gas measurements needed. The idea is rather to pick out more information from the standard tracer gas measurements. To test the extended model, single-tracer gas measurements have been carried out in a natural ventilated row house. Some basic concepts are introduced with one and two zone models and the house is modelled with a nine zones model. As intended, the extended model matches the measurements better. However, as demonstrated in the paper, this does not guarantee that the model found actually is better.

Subfloor and house ventilation rates: comparing measured and predicted values.
Hartless R P
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.

Experimental study of crack flow with varying pressure differentials.
Sharples S, Thompson D
Existing experimental techniques for calculating air flow through building cracks are usually based upon relationships derived from experimental studies employing relatively simple procedures. Typically, a fixed pressure difference, DELTA P, is established across the crack of interest and then the air flow Q through the crack is determined. Most crack flow equations take the pressure differential DELTA P to be steady-state. In reality, the wind forces which generate much of the driving pressures represent highly fluctuating signals. A basic problem is to know what effect a fluctuating DELTA P has on the overall air flow through building cracks. The basic aim of this study was to determine the impact of these fluctuating pressures on crack flow equations. Experimental techniques generated sinusoidal pressure fluctuations across a range of fabricated, straight-through cracks, ranging from 1 to 5 mm thickness. Fluctuation frequencies from 0.5 to 2.0 Hz were used in the investigations. The results suggest that the average flow under conditions of fluctuating pressure differentials does not differ significantly from the flow which would occur if the mean pressure differential were imposed. This implies that the instantaneous flow at any fluctuating value of the pressure differential is that corresponding to the pressure differential on the steady-state flow-pressure curve.

Ventilation performance evaluation using passively-generated carbon dioxide as a tracer gas.
Federspiel C C
Tracer gases are commonly used to evaluate the performance of ventilation systems. One way to reduce the time, complexity, and cost of such experiments is to use the carbon dioxide generated by occupants as a tracer gas. In this paper, a method for using the carbon dioxide generated by occupants as a tracer gas for determining the effective supply air flow rate to a zone or the relative air-change effectiveness of a zone is described. The approach is to make use of a model of the accumulation dynamics and a model of the way that occupants generate carbon dioxide. The carbon dioxide accumulation dynamics are modeled as a first-order perfect-mixing process with bypass. The rate at which occupants generate carbon dioxide is modeled as an integrated random process. Sudden changes in the rate at which carbon dioxide is generated in a zone that occur when occupants enter and leave are detected using statistical techniques. The detector is used to adjust the gains of an estimator that determines either the effective supply air flow rate or the relative air-change effectiveness and also the rate at which occupants generate carbon dioxide. This can be done even when the rate at which occupants generate carbon dioxide changes with time and when the concentration of carbon dioxide in the supply air changes with time. The performance of the strategy is demonstrated with experimental results on a room in a working building.

Energy efficiency in office buildings. An energy and system analysis study.
Nilson A, Hjalmarsson C, Uppstrom R
In order to study the use of electricity in Swedish office buildings in detail, the Swedish Council for Building Research initiated four monitoring and building simulation projects in 1989. The project buildings represent different ages and different HVAC technologies. Based on a combination of hourly monitored data during four years, building simulations using the DOE2 program have been carried out. In two of the buildings, energy conservation measures have been implemented too. An interesting aspect in our study is the so called load factor. Load factors for lighting and other electric loads are evaluated. Taking this into account, you can optimize the design of the air flow rates and the cooling systems and reduce the investment and operational costs for the HVAC systems. Thanks to a correct HVAC design you may also reduce the negative impact on the environment by less use of CFCs etc. The studies indicate that the load factor variation in Swedish office buildings, during a day or a week, diverge substantially from the schedules for lighting and office machines etc according to the ASHRAE 90.1-1989 Standard. Regarding office machines etc, the installed power density also diverges to a great extent.

Calculation methods for the determination of air flow rates in dwellings.
Cripps A
Ad Hoc Group 4 of Working Group 2 of CEN TC156 (Ventilation) was set up to put forward standardised techniques for estimating ventilation rates in dwellings. The purpose of the standard is to ensure that different people carrying out calculations with the same input data will obtain the same result. This will allow the use of these results in energy, heating load, IAQ or other calculations. The methods proposed use two different techniques, an explicit and an implicit one. The explicit one involves more approximations, but can be carried out with a hand calculator. The implicit one requires the use of a computer. This paper explains the methods used, justifies the approximations made and gives examples of the use of the explicit method. These show that the explicit method gives results in good, but not perfect, agreement with experiment, and also that the method is simple to use.

Probabilistic analysis of air infiltration in a single family house.
Pietrzyk K, Handa K
A Probabilistic model of air change rate in a single family house based on full-scale measurements has been developed. The probability of air change rate exceeding certain prescribed limits (risk of improper ventilation or excessive heat flow) is evaluated by utilising the distribution function based on calculated air flow rate. In this way the results are expressed in terms of the R-S model generally used in the safety analysis of structures. In particular, the probability of excessive and/or insufficient air infiltration can be expressed in terms of safety index BETA to describe the reliability of the building with respect to natural ventilation. The probability density functions for the air change rate have been established for different wind directions. Two methods of reducing the risk of unhygienic conditions have been studied. The first one is based on introducing extra small openings uniformly distributed over the building envelope and providing a fully naturally ventilated system. The second method consists in introducing mechanical exhaust ventilation system coupled with natural ventilation. Probability distributions of air change rates have been analysed for these two cases.

System safety analysis on the performance of mechanical ventilation systems.
Kronvall J
System safety of the performance of mechanical ventilation systems can of course be analysed by means of general methods for system safety analysis. Such methods are used a lot in industrial practice, especially in manufacturing industry. However applications on ventilation systems are more or less non-existing today. This paper summarises today's methods for system safety analysis and shows possible future ways of applying the methods on performance analyses of mechanical ventilation systems.

Does the power law rule for low pressure building envelope leakage?
Walker I S, Wilson D J, Sherman M H
Although the power law has been broadly accepted in measurement and air infiltration standards, and in many air infiltration calculation methods, the assumption that the power law is true over the range of pressures that a building envelope experiences has not been well documented. In this paper, we examine the validity of the power law through theoretical analysis, laboratory measurements of crack flow and detailed field tests of building envelopes. The results of the theoretical considerations, and field and laboratory measurements indicate that the power law is valid for low pressure building envelope leakage.

Improve train tunnels. A dynamical ventilation model.
Phaff H J C, de Gids W F
Train tunnels and subways are an interesting field of ventilation. Trains move air through tunnels at rates of 600 m3/s which is much more than flow rates in buildings. Air pressures can vary up to some 3000 Pa leading to air velocities in the range of 10 to 50 m/s. This can lead to unsafe situations and thermal discomfort. The development of high speed trains causes more concern for better tunnel design. Modern stations often house small shops and restaurants, that require lower air velocities for thermal comfort. A dynamical ventilation model has been made to study effects of improvements. An array of controlled fans seems to be a very effective draught remover. The dynamical model is programmed to serve as a demo to give insight in the matter and can be shown in just a couple of minutes from a PC. A copy can be requested via e-mail to J.Phaff@bouw.tno.nl Subject: Train Demo. This demo version is just intended for demonstration purposes and must not be used for the design of real tunnels.

Multizone calculations and measurements of air flows in dwellings.
Blomsterberg A, Carlsson T, Svensson C
A study of the reliability of systems by considering the ability of different systems to maintain a required air flow rate over time is included in a subtask of IEA Annex 27 "Evaluation and Demonstration of Domestic Ventilation Systems". Measurements and calculations were performed to determine the variation in ventilation rates due to variation in climate and variation in performance of the ventilation system. Dwellings with passive stack, mechanical exhaust and mechanical exhaust-supply ventilation, representative of the Swedish housing stock, were studied. Diagnostic tests were carried out, to discover if the installed ventilation system was functioning as designed and to determine certain values eg characteristics of inlets and outlets. The airtightness was tested. The air flows in mechanical ventilation were measured. The continuous monitoring included measurements in dwellings of overall and local (individual rooms) ventilation rates, and measurements of boundary conditions, during three different monthly periods. The ventilation rates were monitored using tracer gas; passive techniques for monthly averaging and constant concentration for hourly averaging. The measured ventilation rates were simulated using COMIS, a multi-zone air flow network model. The simulated and measured average total outdoor ventilation rates agree reasonably well, while there can be disagreement for hourly rates and individual rooms. This paper presents and discusses the measurements and the calculations and compares the two.

Reduction of flow loss due to heat recovery in PSV systems by optimum arrangement of heat-pipe assemblies.
Riffat S B, Shao L
Natural ventilation is being applied to an increasing number of new buildings to minimise reliance on mechanical ventilation and so reduce emission of greenhouse gases. However, passive stack ventilation (PSV) systems are currently designed without incorporating heat recovery leading to significant wastage of energy. Heat recovery systems have not been used in naturally-ventilated buildings because the pressure loss caused by a conventional heat exchanger is large compared to the stack pressure and could cause the ventilation system to fail. In addition, the stack pressure decreases owing to reduction of the temperature difference associated with the heat exchange, although this problem can be lessened by appropriate siting of the heat exchanger to maximise the effective stack height. In this study, natural convective flow through PSV stacks were computed using CFD to determine the effect of the layout of heat-pipe assemblies as well as the effects of spacing and length of fins on reduction of flow rate through the stack. Among the layout patterns examined, the arrangement where the assemblies are placed in a pattern of an arrow facing the flow direction produced the least insertion flow loss. The flow loss due to the insertion of the heat pipe assemblies (IFL) was found to increase sharply with the number of fins and reached over 30% when only 4 fins were used. IFL also increased with fin length but the rate of increase reduced for larger fin lengths. Therefore, for a given total surface area of fins, using fins with a larger length causes less flow loss than fins with a smaller spacing.

The effect on ventilation parameters of various ventilation strategies.
Simons M W, Waters J R
The work described in this paper is aimed at predicting the local values of the ventilation effectiveness parameters of large industrial buildings by a technique which involves the use of computational fluid dynamics and multizonal modelling. A modelling technique is described and applied to a typical modern industrial building equipped with both, mixing and displacement ventilation systems. The results of modelling each of the above systems are presented and discussed. They provide an interesting insight into magnitude and spatial variations in local air change index that occur in the occupied space. The results also demonstrate how differences in ventilation strategy can result in distinctly different variations of ventilation effectiveness parameters. It is concluded that the modelling technique described may be used to provide important information about the air movement characteristics of buildings in terms of local air change index and also that it could prove to be a very useful design aid.

Natural ventilation design for a concert hall.
Cohen R R, Davies R M, Standeven M A
This paper describes the ventilation analysis undertaken during the design of a new music centre for which it was desired to avoid the use of air conditioning and conventional ducted mechanical ventilation. The main objective was to predict the thermal comfort of occupants in the centre's main auditorium during summertime performances. The analysis was done using computational fluid dynamics (CFD) and a dynamic thermal model. The CFD results were used to decide the size and location of openings for natural ventilation, which led to the final design having a much better distribution of incoming fresh air than the initial design. The peak fresh air ventilation rate was reduced, but this did not significantly increase the risk of summertime overheating. The dynamic thermal analysis predicted that the time when the temperature would be over 25 degrees C ranged from 0.3 performance hours/year with a dense concrete roof construction and an orchestra of 30 to 3.5 performance hours/year with a lightweight roof and an orchestra of 100. Given that the larger orchestra would not be formal and so could wear lighter clothing, it was concluded that natural ventilation should be a viable strategy for controlling the risk of summertime overheating. However, given uncertainties regarding the usage of the space and UK summertime temperatures in the future, it was recommended that provision was made in the design to enable mechanical cooling to be added at a later date.

A technique for controlling air flow through modified Trombe walls.
Pitts A C, Craigen S
This paper describes an experimental investigation into the operation of a modified Trombe wall. The construction has been altered to include a layer of insulation material; two alternative positions for this insulation layer have been considered and tested. Air flow from the top of the Trombe wall has also been enhanced by the inclusion of a low power axial flow fan which was controlled to function dependent on measured temperature in the wall cavity. The construction with exposed concrete facing into the air cavity has a slower response than that with exposed insulation facing the cavity. The concrete option also produces higher outlet temperatures, though the fan was found to operate for longer periods with the insulation option. The controller used could be developed for employment in more sophisticated control strategies.

The efficiency of single-sided and cross ventilation in office spaces.
White M, Walker R
This paper reports on work carried out at BRE to address the need for guidance on designing for natural ventilation via single-sided and cross-ventilation in office spaces and the limits of application on terms of plan depth. Present guidance suggests that natural ventilation will be adequate up to 6 m from the ventilating facade. This leads to the conventional design of offices up to 6 m deep on either side of a central corridor, giving as a rule of thumb a width of 15 m for a building with natural cross-ventilation. The present work looks at the opportunities for going beyond these rules of thumb. The implications for thermal comfort and draught risk are also assessed. In the conclusions issues such as, local ventilation rates, ventilating air penetration from a facade, the use of artificial mixing (eg ceiling fans) on hot days, the position of windows, and means of enhancing internal air speeds and air change rates are discussed.

The evolution of ventilation in manufactured housing in the Northwestern United States.
Stevens D, Lubliner M, Davis B
Electric utilities in the Pacific Northwest have spent over $100 million to support energy efficiency improvements in the HUD-code manufactured housing industry in the Pacific Northwest over the past several years. Over 65,000 manufactured housing units have been built since 1991 that exceed the new HUD standards for both thermal performance and mechanical ventilation that became effective in October, 1994. All of these units included mechanical ventilation systems that were designed to meet or exceed the requirements of ASHRAE Standard 62-1989. This paper addresses the ventilation solutions that were developed and compares the comfort and energy considerations of the various strategies that have evolved in the Pacific Northwest and nationally. The use and location of a variety of outside air inlets will be addressed, as will the acceptance by the occupants of the ventilation strategy.

Evaluation of ventilation system in very low energy houses.
Pittomvils J, Hens H, van Bael F
Since 1985 more than 170 very low energy houses, all of the same type and structure, were built in the Flemish Region, Belgium. Because conduction losses are very low, ventilation losses become very important, up to 45% of the heat losses if no heat recovery is utilised. Three of the houses were monitored in detail for energy consumption, energy and ventilation efficiency. All houses are equipped with the same ventilation system: balanced mechanical ventilation with heat recovery. Tracer gas measurements, pressurisation tests, multipoint temperature measurements and on site and laboratory tests of the heat recovery system, give us a complete scope of the ventilation system and its energy and ventilation efficiency. Pressurisation and depressurisation tests revealed the main air leaks in the construction: the different connections wall-floor and wall-roof, the window perimeter, even the sockets. Extra care in construction practice changed the n50-value from an average of 4.5 AC/h to 3.5AC/h, still high for a house with controlled ventilation. After testing the airtightness, we carried out tracer gas measurements in whole dwellings and between the different zones. Real ventilation rates and interzonal flows were derived. Questions like: Are the airflows in accordance with the design values? Do they match the requirements? How can we measure interzonal flows with one tracer? were answered. The paper gives a mathematical description of the tracer gas flow patterns (solution of the differential flow equations) and compares the results with the measured data. To complete the evaluation we carried out laboratory tests and field measurements on the heat recovery system. In laboratory the flat plate cross-flow heat exchanger showed a thermal efficiency up to 65% under specific climate conditions. In the dwellings, insulation and airtightness of the ducts appeared to be very important. The temperature efficiency decreased to values less than 45%. As a conclusion, one may stress that a global evaluation of the ventilation efficiency has to include different tests. The medium or poor airtightness has the greatest impact on the energy efficiency of heat recovery and on the ability to control the system. Detailed testing also showed some flaws in the ventilation system and in the building construction.

A technique to improve the performance of displacement ventilation during cold climate conditions.
Hansson P, Stymne H
Ventilation by displacement is a type of ventilation where the air flow is thermally driven. By this arrangement one obtains two zones in the room - a lower zone with supply air conditions and an upper recirculation zone with extract air conditions. Cold climate causes downdraught from windows and external walls and results in a mixing of air from the upper into the lower zone. To avoid this problem during cold climate a new principle for ventilation by displacement is tested. Excess heat from the upper zone of the room is used for heating cold surfaces. The principle involves creation of a narrow space in front of the exterior wall, separating the cold wall from direct contact with room air. Extract air from the ceiling level is forced down through this space by an extraction fan. This method can advantageously by applied in large buildings where an external wall mainly consists of glass panes. In this case it might be appropriate to utilise the space between the inner couple of glasses for extract air. Tracer gas and temperature measurements were carried out in a test-room. The result shows that the ventilation efficiency improves when using the new principle. The thermal climate also improves due to less down-draught and higher surface temperatures.

Evaluation of a controlled natural ventilation system.
Carlsson T
The project described in this paper has performed simulations using a multi-zone air flow model (4(COMIS)) of three different passive stack ventilation systems. The objective of the simulation calculations was to evaluate system performances and to make suggestions for possible improvements of the systems.

The development of an occupancy-controlled exhaust air ventilation system.
Levin P
Many dwellings with natural or gravity ventilation systems suffer from poor airchange rates. In Sweden, especially houses built in the 1960-ies and 1970-ies heated with electric resistance heating and thus without chimneys, are at risk. Improving the airchange rate in these houses is to some extent performed to decrease Radon gas concentrations where appropriate. For comfort, most homeowners learn to live with low airchange rates, accepting eg odours or window condensation and trying to compensate this with increased airing. They are often reluctant to install mechanical ventilation systems. This paper describes a new concept for an occupancy-controlled exhaust air ventilation system. The system features bedroom night-time ventilation, wet-room day-time ventilation and variable total air flow at a low installation cost. The system has since autumn 1994 been successfully installed in four houses and evaluated by air flow measurements, tracer gas tests, multizone airchange calculations etc. The homeowners are very pleased with the performance of the systems and the improved airchange rates.

Air dehumidification by absorption. (A model for numerical calculation)
Steimle F, Reckzuegel M, Roeben J
Especially in modern buildings with small capacity of humidity storage it is necessary to reduce the humidity in the supply air. Normally this was done by using a refrigeration system mostly with CFC's. There are some alternative fluids available, but mostly they show a high global warming potential. All these systems need electrical energy to be driven and therefore it is necessary to consider other possibilities with alternative systems. The most promising systems are sorptive systems that are used now in open cycles. In these systems the air is dehumidified by a liquid sorbent and cooled indirectly by evaporating water in an open circuit. In order to calculate the process of absorption on several conditions, computer based calculations are required. A model that describes the dehumidification process is introduced.

A control system that prevents air from entering an air-handling unit through the exhaust air.
Seem J E, House J M
Traditional air-handling unit (AHU) control systems link the position of the exhaust air damper, recirculation air damper, and outdoor air damper. Tests at the National Institute of Standards and Technology (NIST) on a variable-air-volume (VAV) AHU have shown that air can enter the AHU through the exhaust air damper. This can negatively impact indoor air quality if the exhaust air duct is located near a pollution source. This paper presents a new control system for variable air volume AHU's that use volume matching to control the return fan. The new control system links only the position of the exhaust air damper and recirculation air damper. During occupied times, the outdoor air damper is in the fully open position. Simulation and laboratory results are presented to compare the new control system and a traditional control system. Several cases are simulated to examine the effect of damper sizing and system load on airflow in AHU's. The simulations demonstrate that the new control system can prevent air from entering the AHU through the exhaust air damper for conditions that the traditional control system cannot. A case demonstrating the limits of the new control system to prevent this phenomenon is included in the simulation results. The laboratory results provide further evidence that the new control system prevents air from entering the AHU through the exhaust air damper for conditions that cause the phenomenon with the traditional control system.
The effects of building form on the natural ventilation of commercial buildings.
Alexander D K, Jenkins H G, Jones P J
Wind pressures can significantly affect ventilation performance. However often they are overlooked in the design of a naturally ventilated building, with buoyancy forces presumed to offer the worst case scenario for design. The result is that airflow patterns and the ventilation performance of the building is often different from the design intent. Successful natural ventilation design requires careful consideration of the building form, and so must involve the architect at the early stages of fabric development. Whilst devices and features may be used to enhance the performance of ventilation outlets, the wind flows at inlets are more likely to be affected by the form of the building, and less amenable to improvement by small devices. Performance may be improved by larger features that in effect become part of the building form itself. Therefore the designer requires a greater awareness of the effect of wind on natural ventilation. They may require access to targeted design information and design tools that are as yet generally unavailable.

Novel methods of inducing air flows within buildings.
Campbell D P, Webb R S
Water use is distributed throughout building structures. Energy used to pump the water to higher levels in the building is not currently recovered, and is dissipated by performing work on air in the ventilation system which is vented to the atmosphere, when the water is discharged into the drainage stack. This energy can be utilised productively, however, by strategically placing the air inlet for the drainage stack inside the building, thereby utilising the potential energy stored in the water to draw air through the building. Airflow induction by falling water films is a well known problem in the drainage industry, and airflow rates of 10-20 times the water flow rate are common. Basic analysis of the ventilation requirements for typical large buildings suggest that this may contribute between 1 and 7.5% of the total ventilation requirement. Air admittance valves would be effective at isolating the habitable space from the waste water.

Summer cooling for office-type buildings by night ventilation.
Kolokotroni M, Webb B C, Hayes S D
The suitability of night ventilation for cooling for the UK is first assessed by presenting plots of summer weather data on the bioclimatic chart for three locations within the country. These indicate that most of the external weather conditions lie within the thermal mass and ventilation effectiveness areas of the charts. To confirm this, thermal simulations of a typical office module under a variety of internal conditions and summer weather data were performed. Predictions have shown that internal temperatures can be maintained below the external values for solar and internal gains of up to about 50W/m2. Field measurements in a refurbished natural ventilated office have confirmed that temperatures in night ventilated spaces are generally lower during the following day, especially during the early hours of the working day. Finally, the development of a pre-design tool in the context of IEA Annex 28 on 'Low Energy Cooling Systems' is discussed. The main aim of the tool is to increase the awareness of designers for the energy benefits and the range of parameters for the application of night ventilation as the first means of cooling so that the need for artificial cooling is minimised or avoided altogether.

Natural ventilation studies within the frame of PASCOOL project.
Santamouris M, Dascalaki E, Allard F
Natural ventilation studies were carried out within the frame of PASCOOL EC Research Project. Research on this topic included experimental and modelling work aiming to fill the existing gaps in our knowledge of indoor air conditions in naturally ventilated buildings. Experiments were carried out in full scale and test cell facilities during the summer period. Single sided and cross ventilation as well as air flow through large internal openings were the basic topics that were studied. Existing models were validated and new ones were developed. A new computational tool for ventilation prediction was developed, based on the airflow network modeling. An intermediate approach, between network and CFD was proposed to take into account the impact of non-homogeneity on the indoor air motion.

Wind towers - old technology to solve a new problem.
Harris D J, Webb R S
Wind towers (scoops situated on the roofs of buildings to catch the wind) have been in use for centuries in the Middle east and Pakistan, to provide ventilation and cooling with minimal mechanical plant. In Europe, the problem of cooling buildings has generally not been significant, but in recent years there has been a trend towards substantial increases in internal heat gains from IT equipment etc and overheating in summer has become one of our major concerns. This has been dealt with by the use of air conditioning, but in many instances this could be avoided by making better use of natural ventilation through wind towers. This paper reviews the use of wind towers for cooling spaces, and reports on work currently being carried out, using wind tunnel tests on scale models, to examine the adaptation of these principles for use in modern office buildings, in order to avoid expensive air conditioning.

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Optimum Ventilation and Air Flow Control in Buildings

Proceedings of the 17th Annual AIVC Conference, held Gothenburg, Sweden, September 1996

Contents