AIVC, Air Infiltration Review, Volume 18, No 1, December 1996

Optimum Ventilation and Air Flow Control in Buildings

17th AIVC Conference Report

17th-20th September 1996, Hotel 11, Gothenburg, Sweden
Conference Report by Malcolm Orme

The 17th Annual AIVC Conference was convened this year at Hotel 11 in Gothenburg, in western Sweden. For the first time, an invitation was extended to all participating countries of the IEA Energy Conservation in Buildings and Community Systems Programme . This resulted in over 100 delegates attending 4 sessions of oral presentations based on submitted papers and a further 3 poster sessions, a total of 59 presentations from 15 countries. Topics covered included:

Keynote Speaker and the Opening Session

The Keynote Speaker at the Conference, Bertil Pettersson, Director General of the Swedish Board for Building Research, stated in his address that much of the world's energy is obtained and used in a non-sustainable way. He continued by stressing that existing energy supplies must be used more efficiently and renewable energy sources should be further exploited. Citing the example of Sweden, he indicated that while the total floor area of the Swedish residential and service sector building stock had increased by about 40% from 1970 to 1995, the total energy consumption had remained roughly constant. This implied that the specific energy consumption (energy used per unit of floor area) had decreased by approximately 25% during the same period. Furthermore, he also outlined the benefits of International Energy Agency collaborative research with the aim of decreasing total energy consumption. The benefits that he observed included:

  • shared costs,
  • pooled resources,
  • the avoidance of mistakes and duplicated efforts, and
  • the development of a common understanding of technical methods.

The first paper in the opening session, called "Optimum ventilation and air flow control in buildings? ", examined the overall theme of the Conference, and was presented by Tor-Göran Malmström (Royal Institute of Technology , Sweden). In this paper he explained the factors affecting indoor air quality. In particular, he emphasised that internal pollutant sources should first be controlled and then the quality of the air entering the room should be verified. He then continued by discussing how air flow control can be used to determine the quality and rate of air exchange.

This session also included a paper by Bjørn Larsen (The Vekst Foundation, Norway) explaining his computerised method ( Figure 1 ) for balancing ventilation systems, a practical demonstration of which was also given at the Conference. The method he described makes it possible to pre-set ventilation terminals at the factory to desired pressure loss characteristics (achieved by damper positioning). In this way, mechanical ventilation systems can be balanced before they have been installed.

Figure 1 A 'DPM' machine for pre-setting air terminals


Offices and Other Non-Residential Buildings

Two contributions from the UK Building Research Establishment focused on office buildings. Martin White discussed the efficiency of single-sided and cross ventilation in office spaces, while Brian Webb considered summer cooling for office-type buildings by night ventilation. Although not restricted in application to non-residential buildings, Matheos Santamouris (University of Athens, Greece) reported on the progress of the natural ventilation studies made within the European PASCOOL project. This included single-sided and cross ventilation, as well as flow through large internal openings in the context of natural ventilation for cooling. The project has resulted in the development of several applicable calculation tools. Passive cooling was also the subject of other presentations from Greece , Sweden and Switzerland ( Figure 2 ).

Figure 2 Cooling improvement for night cooling system


Mikko Suokas (Fincoil-teollisuus Oy, Finland) advised on how to reduce draught problems in cooled working rooms. His view was that the 'throw' from air-cooling devices should stay close to the ceiling for as long as possible, without interference from either beams, light fittings, or walls. In this way, the cooled air mixes better with the existing room air, without causing draughts in the occupied zone.

Peter Wouters from Belgium (BBRI) expanded on the subject of non-residential ventilation. In "Ventilation requirements in non-domestic buildings and energy efficiency ", voted as the Best Paper at the Conference, he proposed that ventilation rate requirements for non-domestic buildings may vary by up to a factor of 10 depending on whether or not the levels of emissions from the building materials are taken into account. This, he argued, could potentially have a large consequent effect on energy consumption. Anders Nilson (Bengt Dahlgren AB, Sweden) also considered energy efficiency, specifically in office buildings, with an energy and system analysis study.

Public Assembly Buildings

Findings from measurements made in a cinema (with a downwards mixing ventilation system) were reported by Yonghui Jin (Narvik Institute of Technology, Norway). 'Step-up' and 'step-down' tracer gas measurements enabled the calculation of local and room air change efficiencies, which indicated that close to perfect mixing was occurring. Carbon dioxide concentrations were found to vary linearly with the number of occupants. The design of another type of public assembly building, in this case a naturally ventilated concert hall (Figure 3 ), was discussed by Robert Cohen (HGA Consulting Engineers Ltd, UK). This project used computational fluid dynamics to decide the size and locations of the ventilation openings. In addition, a dynamic thermal model was used to confirm that the likely number of hours per year above a certain temperature level was acceptable.

Figure 3 Building section


Ventilation of Transportation-Related Structures

Certain presentations at the Conference examined ventilation of structures intended for transportation-related purposes. Willem de Gids (TNO , Netherlands) described how a dynamic ventilation model had been used to improve the design of a ventilation system in a train tunnel with a shopping centre above (Figure 4 ), thus improving air quality in the centre and reducing cleaning costs. The problems associated with the cooling and ventilation of a high speed underground transportation system were outlined by Peter Rosemann (Swiss Federal Institute of Technology , Switzerland). This major project plans to link the major Swiss cities with a train network involving partially evacuated tunnels (to reduce aerodynamic drag). In addition, design guidelines for ventilation systems for pollution control in large semi-enclosed bus terminals were presented. Concerning this work, Joanna Yiu (Hong Kong Polytechnic University, Hong Kong) indicated that industrial occupational exposure limits were the most applicable existing guidelines to deal with the pollutants contained in diesel fuel exhausts. However, she did not consider them to be ideal, because they are based on working conditions only for healthy adults.

Figure 4 Tunnel with fans


Statistical Analysis

In his poster, Jerzy Sowa (Warsaw University of Technology, Poland) compared different methods of incorporating stochastic factors into deterministic models of indoor air quality. Approaches taken used time series data as inputs to contaminant dispersal models, Monte-Carlo analysis, and a stochastic differential equation model. The mean values of pollutant concentration found with all three methods were very similar. However, the spread of the results as measured by the standard deviation showed a wide variation. Related work was described by Krystyna Pietrzyk (Chalmers University of Technology , Sweden). She explained how probability density functions of the air change rate in a single family house had been derived, with two-parameter Weibull distributions assumed for the wind velocity. The air change rates were found to approximately follow either normal or log-normal distributions depending on the wind direction.

Johnny Kronvall (J&W Consulting Engineers, Sweden) has been investigating system safety analysis as a method of finding "the probability that a ventilation system provides certain required air flow rates in each occupied part of a building during the time between scheduled maintenance occasions." He suggested that this is a promising technique for judging the reliability of mechanical ventilation systems. But, he cautioned that data for the mechanical reliability of individual components would need to be collated for it to be practical.

Applicability of Crack Flow Equations

Two of the fundamental assumptions concerning the applicability of crack flow equations have been investigated by researchers in the UK and the USA. An experimental study of crack flow with varying pressure differentials was the subject of a presentation given by Steve Sharples (University of Sheffield , UK). He proposed that the results confirmed the often assumed view that it is acceptable to consider average steady-state pressure differentials in place of time-varying differentials. Another important issue discussed at the Conference was that the application of experimentally measured airtightness data (typically measured at greater than 10 Pa pressure difference) to numerical models often relies on an extrapolation down to the pressure differences (typically less than 10 Pa) encountered due to natural driving forces. The power law is an appropriate method for extrapolating from measured airtightness data to lower pressure differences was the conclusion reached by Max Sherman (Lawrence Berkeley National Laboratory , USA).

Measures of Ventilation Performance

Lars Ekberg (Chalmers University of Technology , Sweden) spoke about how he has been checking ventilation rates by carbon dioxide monitoring. Again from Sweden, Björn Hedin (Lund Institute of Technology) introduced a new model to extract more information from standard tracer gas measurements of ventilation air flows. The effect of recirculation on air change effectiveness (sometimes called the coefficient of air change performance) was the subject of a contribution by Clifford Federspiel (Johnson Controls Inc, USA). He proposed a relative measure of air change effectiveness that can be used to take into account the age of supply air when the fraction of recirculated air is greater than zero. An advantage of this measure, he argued, is that it can identify systems in which 'short-circuiting' is occurring.

Karl Janssens from Belgium (Catholic University of Leuven) gave an account of laboratory tests for the determination of 'local specific fresh air flow rates' in an imperfectly mixed ventilated air space. In addition, work from France and the UK reported on measurements and modelling respectively for calculating the pollutant removal effectiveness and air change efficiency for various ventilation strategies.

External Contaminants and the Internal Distribution of Pollutants

Vina Kukadia, (Building Research Establishment , UK) presented the outcome of a pilot study designed to find the effect of external atmospheric pollution on indoor air quality. Another external pollutant, radon, is of continuing concern and in connection with this, Pirjo Korhonen (University of Kuopio, Finland) has compared indoor levels of radon between workplaces and homes located nearby in different parts of Finland. Certain features of particulate pollution interactions with indoor surfaces were explained by Miriam Byrne (Imperial College , UK), who has been carrying out measurements and modelling for risk assessment and contaminant control. Also at the Conference, George Walton (NIST , USA) demonstrated the latest version of his multizone airflow and contaminant dispersal model, CONTAM96, which includes a graphical user interface.

Dwellings

The work of members of the European Standards Committee CEN TC156 (Ventilation) was reported by Andrew Cripps (Building Research Establishment , UK) with his paper on calculation methods for the determination of air flow rates in dwellings. Two delegates from Sweden each talked about residential ventilation. One of these was Per Levin (Royal Institute of Technology , Sweden), who outlined the development of a simple occupancy-controlled exhaust air ventilation system. The other was Åke Blomsterberg (Swedish National Testing and Research Institute, Sweden), who discussed the influence of outdoor air vents and airtightness on natural ventilation.

Max Sherman (Lawrence Berkeley National Laboratory , USA) proposed the most appropriate types of residential ventilation systems for the different regions of the USA. This was based on modelling for various levels of airtightness of the dwelling stock to predict resultant energy consumption while still meeting ventilation requirements. On a connected subject, Don Stevens (Stevens and Associates, USA) identified the evolution of ventilation in manufactured housing in the north-western United States. The findings from a measurement survey of the indoor air quality of 30 houses with distributed heating systems in Quebec were given by Denis Parent (Hydro-Québec, Canada). He concluded that during the milder part of the heating season only the minority of the tested houses had adequate ventilation, with an improvement during the colder part. Also, there didn't seem to be a significant correlation between building airtightness and indoor air quality.

IEA ECBCS Annex 27

Other contributions on dwellings concerned products of the continuing work of IEA ECBCS Annex 27 "Evaluation and Demonstration of Domestic Ventilation Systems". Peter Op't Veld (Cauberg-Huygen Consulting Engineers, Netherlands) gave an overview of his assessment of aspects of noise and ventilation systems. This covered the transmission of outdoor noise, noise generated by ventilation system components and the impact of a system on sound transmission in or between dwellings. His work for this Annex has produced a simplified tool for the selection of ventilation systems based on the criteria of noise. Also as part of Annex 27, Lars-Göran Månsson (LGM Consult AB, Sweden) outlined the progress made in developing a simplified tool for evaluating domestic ventilation systems' ability to provide an acceptable indoor air quality.

Multi-zone calculations of air flows and tracer gas measurements in dwellings were compared by Charlotte Svensson (J&W Consulting Engineers, Sweden). This forms part of the Swedish contribution to Annex 27. The study highlighted the good agreement that can be obtained between measurements and calculations when the input parameters of the model are consistent with the experimental configuration. Along similar lines, Jacques Riberon (CSTB , France) gave an account of a comparison of ventilation systems performances in residential buildings made with the model SIREN.

Innovative Technologies

Conventionally, air dehumidification has been achieved by refrigerative systems. However with current environmental concerns, alternative approaches are being sought. As part of an investigation of dehumidification by absorption, Jürgen Röben (University of Essen , Germany) described a theoretical model of an open cycle dehumidification process using hygroscopic materials to absorb the moisture.The Best Poster at the Conference was awarded to Peter Hansson (Royal Institute of Technology , Sweden) for his poster, "A technique to improve the performance of displacement ventilation during cold climate conditions ". He has devised a method of using warm air extracted at ceiling level to heat cold surfaces and so improve ventilation efficiency and thermal comfort by reducing downdraught.

Guest Speaker and Close of Conference

The Guest Speaker at the Conference Banquet was Professor Enno Abel of Chalmers Institute of Technology, who in addition presented the Best Paper and Best Poster awards. Willem de Gids (TNO , Netherlands) and Martin Liddament (AIVC, UK) summed-up and closed the Conference. The AIVC would like to extend thanks to the Conference Participants and also to the companies who exhibited their products (LHG Kanalflakt, Boverket, Scandfilter, Pentiaq AB and Stifab AB).

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