AIVC, Air Infiltration Review, Volume 19, No 1, December 1997

18th AIVC Conference "Ventilation and Cooling"

Conference Report by Malcolm Orme

This year the 18th Annual AIVC Conference was held in Greece, from 23rd - 26th September, at the Astir Palace Vouliagmeni Complex south of Athens. More than 100 delegates from 16 different countries attended the various sessions featuring 65 presentations on the conference theme.

Energy Conservation Measures in Greece

The keynote speaker, Dr Nomidis, explained the energy conservation measures which have been adopted in Greece for the building sector, summarised as follows:

  • A law concerning the insulation of buildings.
  • The preparation of another law, which will provide for:
    • the submission of an integrated energy study for each building,
    • energy certification of new and existing buildings,
    • energy auditing of buildings in the industrial and tertiary sectors,
    • improvement of the existing law for insulation by setting stricter standards and enforcing the actual implementation of the law, and
    • incentives for the realisation of energy conservation in existing buildings (mainly by tax reduction).
  • High rates of subsidies (40% - 55%) for energy conservation investments in the industrial and tertiary sectors, according to the criteria that:
    • renewable energy sources (RES) are promoted,
    • substitution of electricity or fuel oil by fuel gases, treated waste products, RES, or waste heat recovery, and
    • energy savings are higher than 10%.
  • The Operational Energy Programme, jointly funded by the European Community and the Greek Government, including a sub-programme for RES investments. Examples of applications include:
    • co-generation of heat and power,
    • substitution of electricity or conventional fuels by natural or liquefied petroleum gas,
    • active or passive solar systems, and
    • passive systems for heating, cooling and lighting and bioclimatic systems.
  • European energy efficiency legislation (from the SAVE programme), in particular minimum energy efficiency standards for non-industrial boilers.
  • European directives for energy labelling of domestic appliances, in particular labelling for packaged air-conditioners is under preparation.

Ventilation and Energy Efficient Cooling

A large number of presentations strongly reflected the Conference theme, “Ventilation and Cooling”. Topics covered included night cooling, minimising heat gains and non-refrigerative cooling and dehumidification technologies. In fact, the subject of the Best Paper at the Conference, by Gary Hunt (University of Cambridge, UK), was an examination of passive cooling by natural ventilation, investigated using salt bath modelling of combined wind and buoyancy forces.

Session one opened with an explanation from Fritz Steimle (University of Essen, Germany) of how requirements for cooling and dehumidification of ventilation air depend on human thermal comfort. This, in turn, is fixed by activity level, clothing, air temperature, humidity and velocity, and wall temperature. He continued by giving the advantages for the separation of cooling and ventilation air, in air conditioning systems. The principal reason for this separation is that it is more effective to transport cooling energy by using water systems than to use only air. Ventilation rates can then be reduced, ensuring dehumidification needs are also minimised. Sensible cooling of the conditioned space can then be achieved using water as the energy transport medium. Another example of the separation of the cooling and dehumidification processes was provided by Gunther Mertz (FGK, Germany), who discussed a sorption-supported air conditioning system in a printing-office. (In this instance, evaporative air cooling was used.)

Night Cooling

There is currently much interest in using night-time ventilation to achieve air cooling during the daytime (particularly in office buildings). The key to the technique is to use external air to cool the building structure at night, which subsequently re-absorbs heat during the day, thus cooling the internal air. Vassilis Geros (University of Athens, Greece) gave the results of measurements made in three real office buildings, in which night ventilation had been in use. Both ‘free floating’ (i.e. no additional temperature control) and air conditioned operation were studied. It was found that night ventilation had a particularly significant impact in the building of highest thermal mass, with a daytime temperature reduction up to 2.5 ºC under free floating conditions, and 1 ºC under air conditioned operation.

The design of low energy office buildings combining mechanical ventilation for indoor air quality (IAQ) control and night time natural ventilation for thermal comfort was commented upon by Peter Wouters (BBRI, Belgium). Amongst other things, his conclusions took the view that natural ventilation for IAQ control requires completely different provisions than natural ventilation for thermal comfort control in summer. Furthermore, he proposed that the attainment of an optimum balance between IAQ and energy use is not evident with the natural ventilation devices presently available, although self-regulating devices may in future remedy this situation.

Two papers from French authors were also concerned with night cooling of office buildings. One of these extended the theme to consider the effect of increased ventilation air flow rate during the daytime for cooling purposes, while the other additionally described tools dealing with evaporative cooling. Also, Maria Kolokotroni (BRE, UK) provided an introduction to her pre-design tool for night ventilation of office buildings. This tool allows the prediction of a weekly internal temperature profile for an office space. It also allows energy consumption and peak cooling capacity requirements (i.e. relative to a reference system without night cooling) to be assessed.

Nien-Tzu Chao (Chung-Hua Polytechnic, Taiwan) presented a study, conducted with flow simulations, of window location and furniture layout to maximise cooling effect for an urban apartment by night ventilation. This was also the theme of experimental work conducted in Greece (with natural cross ventilation) that was reported at the Conference.

Minimising Heat Gains

One method of lowering cooling-related energy use is to reduce the heat gains to the conditioned space. Aris Tsangrassoulis (University of Athens, Greece) gave clarification of the ventilation and daylight efficiency of various solar shading devices, which are installed to prevent solar heat gains. Under-roof air cavities are often used in large enclosures such as atria and auditoria, because they allow an effective increase of the thermal insulation of the building, without a great increase of the structure weight. Marco Perino (Politecnico di Torino, Italy) reported that solar gains (and hence cooling loads) may be reduced by means of such constructions, especially with ventilated roof cavities, which may lower solar gains by up to 50% compared with closed cavities.

Non-Refrigerative Cooling and Dehumidification Technologies

An account of the possibilities and limitations for evaporative and desiccant cooling technologies was made by Torbjörn Lindholm (Chalmers University of Technology, Sweden). Furthermore, Sönke Biel (University of Essen, Germany) discussed how he has made an economic comparison of three non-industrial air-conditioning plants, principally to investigate the pricing of a new dehumidification unit.

Retrofit of Buildings

It is sometimes more economic, or otherwise desirable, to retrofit or refurbish existing buildings, rather than to construct new ones, so extending their useful lives. In the future, this may become an increasingly important course of action. Two poster presentations at this year’s Conference were specifically concerned with this activity. The first, describing work undertaken in Finland, involved measurements of the airtightness of apartments before and after renovation. In this, Keijo Kovanen (VTT) concluded that renovation measures (in this case including changing the windows and refurbishing the interior surfaces) usually led to an increase in the airtightness. Exceptions were observed to occur under conditions of poor workmanship in the renovation work. The second poster, presented by Peter Op’t Veld (Cauberg-Huygen Consulting Engineers, The Netherlands), gave an insight into how multi-functional appliances can be installed beneficially when retrofitting certain residential buildings. These appliances combine the provision of ventilation air, hot water and heating, and include a heat recovery heat exchanger.

Energy Recovery

Jørn Brunsell (Norwegian Building Research Institute, Norway) explained the advantages and disadvantages of various approaches to heat recovery systems for naturally ventilated office buildings. (See Figure 1.) Moreover, he argued that the frequency distribution of natural driving forces for a range of European locations indicated a need for assisting fans in the spring and autumn.

Figure 1 Example of natural ventilation with heat recovery

Other contributions were made from Finland relating to energy recovery. Kai Sirén (Helsinki University of Technology) examined solar assisted natural ventilation with heat pipe heat recovery, complementing another paper that investigated heat pipe heat recovery for passive stack ventilation. Furthermore, Esa Marttila (Lappeenranta University of Technology) suggested that the performance of series connected heat exchangers with a looped liquid circuit could be optimised by following a given procedure.

IEA Project - “Evaluation and Demonstration of Domestic Ventilation Systems”

The International Energy Agency’s ECBCS Annex 27, “Evaluation and Demonstration of Domestic Ventilation Systems” is a collaborative project, closely associated with the work of the AIVC. A number of presentations were made by Annex 27 participants, who discussed the progress of certain aspects of the Annex work, now entering the last few months of its programme. Lars-Göran Månsson (LGM Consult AB, Sweden) gave an introduction to the simplified tools, which are being developed to evaluate domestic ventilation systems. In order to assist with the development of a thermal comfort tool, Takao Sawachi (Building Research Institute, Japan) has been undertaking experiments to assess the thermal comfort impact of direct fresh air supply in winter, making a comparison of different air supply inlets for exhaust only ventilation. His poster illustrated the measurement results and also introduced the simplified thermal comfort tool.

Johnny Kronvall (AB Jacobson and Widmark, Sweden) outlined the quantitative approach to system safety analysis of the performance of mechanical ventilation systems, on which a reliability tool has been established. Also presented was a simplified tool for the assessment of life cycle costing (LCC), by Peter Op’t Veld (Cauberg-Huygen Consulting Engineers, The Netherlands). An indoor air quality simplified tool is currently being finalised. Work carried out for this purpose, relating to numerical simulations (by the COMIS model) of IAQ and energy need was presented. In addition, Willem de Gids (TNO, The Netherlands) has made a comparison of the performance of different ventilation systems in similar dwellings. These results will be used to evaluate the IAQ tool at a later stage.

Although not part of the Annex 27 programme, a paper from the USA was concerned with a strongly related topic, in which ventilation strategies for new energy-efficient production homes were assessed and recommendations made about the choice of systems, for cold, hot humid, mixed and hot arid climatic regions of the USA.

Building Airtightness

Karin Adalberth (AB Jacobson and Widmark, Sweden) summarised practical guidance she has produced in the form of a manual for designers and contractors for constructing airtight buildings. During his presentation, Earle Perera (BRE, UK) demonstrated a spreadsheet-based tool for predicting envelope air leakage in large commercial buildings before construction (which uses data from the AIVC’s Numerical Database, summarised in AIVC Technical Note 44). In addition, building airtightness and ventilation in 20 recently constructed Belgian dwellings were the subject of a further contribution.

Duct Leakage

There appears to be a lack of duct leakage measurements in Europe (apart from in Sweden), according to Francois Rémi Carrié (Ecole Nationale des Travaux Publics de l’Etat, France) in his account of the impact of air distribution system leakage in Europe. However, on the basis of existing data, he judged that the ventilation and energy use implications of leaky ducts are large. Continuing this topic, Johnny Andersson (Scandiaconsult, Sweden) summarised the status of Swedish duct leakage.

Tracer Gas Techniques

Effective ventilation rate measurements have been made in real time for entire floors of buildings by Mark Bassett (BRANZ, New Zealand). His measurements were made in five separate mechanically ventilated buildings. (An example is shown in Figure 2.) He explained how the equipment measures tracer gas concentrations at a large number of locations (30 to 50 positions, using a gas chromatograph working in real time) while the tracer gas itself is released constantly and uniformly within the ventilated space. Also, Hans Stymne (Royal Institute of Technology, Sweden) related how he has found the homogeneous emission tracer gas technique using passive tracer gas sources and integrating diffusive samplers to be a convenient and satisfactory method for measuring the average local mean ages and their distribution. (However, care must be taken when mechanical ventilation is intermittent or varied.)

Figure 2 Approximate contours of effective ventilation rate in the breathing zones of a building

Natural Ventilation Design

Delegates from both Sweden and the UK have produced tools for natural ventilation design. David Etheridge (University of Nottingham, UK) explained his non-dimensional graphs for natural ventilation design. These allow manual calculation of both bouyancy, including stack, and wind driven ventilation rates for summer and winter conditions. From Sweden, Charlotte Svensson (AB Jacobson and Widmark) displayed a computer based design tool for natural ventilation.

Søren Aggerholm (SBI, Denmark) discussed the barriers that exist to natural ventilation design of office buildings. He put forward the view that general knowledge about natural ventilation has to be improved and that standards and guidelines must also be refined to provide a better technical and legal background for the design of naturally ventilated office buildings. By a macroscopic formulation and solution of ventilation design problems, Jim Axley (Yale University, USA) offered feasible combinations of design criteria in order to achieve thermal comfort objectives.

Awards for Best Paper and Best Poster Presented at the Conference Dinner

Delegates at the Conference Dinner enjoyed an after-dinner speech by Professor D. N. Asimakopoulos, Director of the Group Building Environmental Studies at the University of Athens, closely followed by the presentation of the Best Paper and Poster Awards by Ms. Elsa Papadimitriou, Member of the Greek Parliament. The Best Written Paper Award went to Gary Hunt (University of Cambridge, UK) for his description of his salt bath modelling work, and Best Poster was awarded to Kai Sirén (Helsinki University of Technology, Finland) for his modification of the power-law equation to account for large scale wind turbulence. The Conference was summed up and closed by Martin Liddament, Head of the AIVC.


 

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