AIVC, Air Infiltration Review, Volume 22, No 1, December 2000

21st AIVC Annual Conference - Report

Innovations in Ventilation Technology

Introduction

The 21st AIVC Annual Conference took place recently in The Netherlands at the Kurhaus Hotel, located in The Hague. Nearly 80 participants from 17 different countries attended the conference, which spanned four days and consisted of 56 paper and poster presentations. It focused on innovations in ventilation technology and their effects on the provision of ventilation in buildings. Included among the wide range of subjects discussed were ventilation strategies, calculation, measurement and design methods, standards, energy impact and occupant response. Summaries of a selection of the papers may be found below.

Keynote Address

The Keynote Speaker at the 21st AIVC Conference, Prof ir Hans Cauberg from the Technical University of Delft, explored the main driving forces behind recent changes in the Dutch Building Regulations. Principally, he thought, these contain a greater emphasis on sustainable development, energy performance standards and life cycle cost assessments, all of which have been or are currently being addressed in the Regulations. The Building Regulations and associated standards have all stemmed from research conducted on specific building elements over time. In the past this research has mainly focused on the reduction of energy use. However the concept of sustainability, including healthy indoor air quality and environmental impact, has become the key issue in ventilation research. This trend will affect the ventilation systems used in modern buildings. He foresaw that in the near future there would be a major shift away from developing components individually towards whole system concepts. Central to this shift, he proposed, would be the advance of hybrid ventilation concepts with an integrated approach for both commercial and residential buildings.

Innovative Strategies and Hybrid Ventilation

Several innovative strategies were presented and in particular, hybrid ventilation was a key topic. Peter Wouters (BBRI, Belgium) examined the major characteristics of hybrid ventilation systems, considering such systems as a whole range of associated strategies as opposed to a single concept. He suggested that future ventilation systems would inevitably be composed of hybrid solutions containing technologies such as low pressure ductwork, fans, and static heat exchangers, and would operate within current or improved energy and environmental targets. From The Netherlands, Willem de Gids (TNO) discussed the development of energy efficient and sustainable air distribution systems for mechanical ventilation (LeVent) as part of the EU TIPVENT project. The research dealt with the development of low resistance ductwork, fittings and air terminal devices, better controls and more efficient fans. He reported that the fan energy use in domestic ventilation could be decreased by a factor of between two and five. However, the costs of such improvements presently result in unrealistic payback periods.

A Japanese test house containing a full-scale hybrid ventilation system was described on behalf of the author. Results indicate that the addition of an electric fan for mild weather situations can augment any under ventilation with the airflow rate being fixable. Over ventilation can also be minimised with an additional damper control in cold weather. Mark Bassett (BRANZ, New Zealand) identified the need to develop such hybrid systems in New Zealand. While their building codes still allow residential ventilation provision based on openable window areas, these buildings are becoming increasingly more airtight, with a decreasing reliance on window opening. Thus, new ventilation strategies are required to ensure adequate ventilation is maintained. It is envisaged that a combination of natural and simple mechanical ventilation will provide an efficient and cost effective answer.

Implications of Demand Controlled Ventilation

Another important issue examined by several authors was the effectiveness of demand controlled ventilation (DCV). Helmut Weinläder (ZAE Bayern, Germany) compared the indoor air quality within classrooms ventilated by a DCV exhaust system and a natural ventilation system. The DCV system provided lower peak CO2 levels (>2500ppm) than those measured in the classrooms ventilated naturally (4000ppm). The higher air exchange rates associated with exhaust ventilation causes no measurable increases in heating demand and no noise or draught problems were experienced.

Jeffrey Huang presents his poster "Modelling contaminant exporusre and indoor air quality in a single family house".

Two different DCV systems installed into meeting rooms were investigated by Anne-Marie Bernard (CETIAT, France). The first system was controlled via a movement sensor located on terminal units and the second system incorporated a CO2 detector attached to the fan. Energy savings of over 70% were seen based on intermittent occupation and maintaining CO2 levels. The payback time for the French market and electrical power cost would be 2 years. In a study involving Danish dwellings, Niels Bergsoe (Danish Building Research Institute) examined the energy saving potential for DCV, in which the indoor humidity is the most important IAQ problem. Simulations indicate that basic ventilation in a typical Danish apartment under normal conditions can be reduced by 20%-30% without compromising the indoor air quality.

Energy Implications

Based on the different ventilation rates stated in various European regulations, Vitor Leal (IDMEC-Pólo FEUP, Portugal) has identified their energy impacts. In fact, by using variable DCV based on CO2 and free cooling, large energy savings can be made. In terms of fan power use, the energy saving potential can be large and further enhanced by combing several techniques, representive energy savings of up to 70% can be made compared to a typical system.

Dipak Shah (Honeywell, USA) examined various residential ventilation methods required to achieve the ASHRAE recommended minimum ventilation level of 0.35ach, using dynamic computer simulations. Results showed that single direction ventilation, partially compensates for high natural infiltration levels and saves half the energy cost of ventilating with a direction method without heat recovery. Continuous exhaust fan operation to provide 0.35ach mechanical ventilation results in the lowest annual energy cost. In particularly airtight homes, two direction ventilation may be required. Simulation also shows that heat recovery ventilators significantly reduce the annual energy cost of two directional ventilation. Additionally, Augustino Binamu (Tampere University of Technology, Finland) has derived an equation making it possible to recalculate air change energy use to alternative base temperatures and hence make comparisons among different countries, using differing heating degree day base temperatures.

Technologies for Improved Thermal and Acoustical Comfort

The supply air ventilated window concept was examined by two authors. The first, Ryan Southall (University of Cambridge, UK) explained the principle whereby external air enters through a vent at the base of the window and this relatively cold air is heated by convection and conduction from the warmer inner pane. It then enters the room through a vent at the window top. The second author, Dolf van Paassen (Technical University of Delft, The Netherlands) discussed similar technology for double façades. The principle includes several different ventilation strategies and ways of interaction between the cavity, the interior and the exterior of the building. In a further contribution, Ian Matthews (University of Portsmouth, UK) examined how using fuzzy logic models, occupant preferences can be modelled to predict their preferred thermal and environmental conditions.

On the subject of acoustical comfort, Steve Sharples (Sheffield Hallam University, UK) presented a paper examining techniques for improving the acoustic properties of a natural ventilation opening located in an external wall. Maintaining typical air flow rates and natural pressure differentials, up to 9 dBA greater sound reduction index could be obtained by the insertion of a simple screen in front of the aperture, compared with a wall containing a single acoustic louvre. Preliminary application of active control has suggested that attenuation in excess of 7.5 dB to 8.5 dB can be achieved for traffic noise.

Innovative Technologies

A novel low maintenance, compact and energy efficient domestic ventilation heat recovery heat pump system was discussed by Mark Gillott (University of Nottingham, UK). This uses revolving heat exchangers instead of a fan impeller. The prototype system has a COP of up to 5 and an average of 2.5 over a range of conditions. A typical system provides 2kW of heating for air supplied at 250 m3/h. The system can also be used for cooling by switching the air flows over the evaporator and condenser.

Olivia Noël (Gaz de France, France) outlined a ventilation system, developed under the JOULE III programme (NAVAIR project). This system can be installed at the end of existing ducts providing both ventilation and evacuation of combustion products from a natural gas boiler, and is therefore particularly relevant for retrofitted dwelling applications.

A new process to separate dehumidification and cooling by the utilisation of liquid desiccants was by explained by Sönke Biel (University of Essen, Germany). In this system the outdoor air is dehumidified by a liquid desiccant which is cooled by circulating water from the evaporative cooling system. Dehumidification and regeneration are separate and do not have to be carried out simultaneously. Its advantage is a clear reduction of electrical power input in the summer and reduced energy requirement in relation to systems with a compression refrigeration cycle.

Demonstrating the Minneapolis Blower Door

Modelling and Measurement

It is clear that prediction through modelling and measurement plays a key role in the development of new, and the improvement of existing, ventilation systems and their components. In a case study simulation and comparison against field measurements, Konstantia Papakonstantinou (University of Athens, Greece) outlined a study of an industrial building with displacement ventilation and a high thermal load. The main ventilation design problem is to ensure that the interface between fresh air zone and the hot air zone is located above the occupied region of the room. Also, Eoin Clancy (Coventry University, UK) outlined the development of a simple ventilation and thermal model, derived from experimental data for predicting ventilation rates and internal temperatures within an auditorium.

Hans Stymne (University of Gävle, Sweden) reported on a new homogenous pulse tracer gas technique which has not previously been experimentally validated. Pulses of tracer gas are injected into different zones, in proportion to the zone volumes, allowing pulses to be injected at any time path and making it possible to utilise integrating air samplers. His experiments have shown that this technique compares well against the decay method.

Confirming earlier theoretical predictions, Alice Andersen (Windowmaster, Denmark) has found experimentally that under certain circumstances, a particular building geometry with a given heat source and a fixed wind speed may lead to more than one stable ventilation mode and, consequently, air flow rate. Depending on the initial conditions, she found that displacement flow or mixing flow may occur.

A physical model has been used by Gary Hunt (University of Cambridge, UK) to explain what happens at high Reynolds numbers as flow contract through a square edged opening. A small scale water tank using saline solutions to generate buoyancy forces was used. With this model, he observed that a discharge of buoyant fluid from a horizontal opening produces a plume-like flow, which may initially contract considerably in cross section as it rises. This contraction effectively reduces the usable area of the opening and gives rise to reduced values of discharge coefficient. Gary Hunt received the Conference "Best Paper" award for his paper.

Design Criteria

The nature and quality of the source ventilation air should be the determining factor for the sizing of, for instance, fans sizes or ducts, proposed Mats Persson (Chalmers University of Technology, Sweden). In consequence, they should not be sized on the minimum ventilation rate requirements in standards. These may only result in the provision of minimum ventilation, which sometimes proves insufficient. Furthermore, Rik Vollebregt (Bureau Kent, Netherlands) suggested that as a consequence of improved airtightness and the use of self-regulating air vents, the design pressure difference in the Netherlands building regulations should be increased from 1Pa to 2Pa for new buildings. This should be regarded as a minimum level. The aforementioned changes have resulted in decreased energy losses, better ventilation patterns, improved air quality and occupant comfort.

John Zhai: "Integration of indoor and outdoor airflow study for natural ventilation design using CFD".

Environmental and Occupant Surveys

An on-going survey of French ventilation and energy use within homes was presented by Marie-Claude Lemaire (ADEME, France). Her results indicated that the installation of a ventilation system had little bearing on the opening of windows, although in buildings with balanced systems, windows appeared to be opened for less time, compared to buildings with a simple mechanical system. Occupants in the latter open windows less often than those with natural ventilation systems. Whilst mechanical ventilation does appear to limit problems with mould, moisture and odours it does suffer from noise related problems.

In a paper that won the "Best Poster" award at the Conference, Jerzy Sowa (Warsaw University of Technology, Poland) compared 28 real classroom environments in Warsaw, against accepted requirements and standards. He found the main problem was overheating, with controls compensating for high heat gains, thus leading to excessive energy use and thermal discomfort. Also, inefficient ventilation causes high CO2 concentrations. Moreover, window opening is hindered in noisy urban areas. He proposed the only solution to this problem, while keeping to energy conservation and air quality requirements, would be the general application of more sophisticated (but easily still operated) ventilation systems with heat recovery and effective filtration.

Summing-Up

In his final duty as Head of the AIVC, Martin Liddament summed up the conference. In this, he observed how the work presented at the Conference related to the changes that have occurred in ventilation research and practice over the past 30 years.

Acknowledgements

The AIVC would like to thank the exhibitors, Blower Door GmbH (who demonstrated the Minneapolis Blower Door™) and Alusta (who exhibited their Vent-o-System® automatic natural ventilation system). Appreciation is also extended to all participants and contributors, who made the Conference so successful.

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