Balanced ventilation in apartment buildings

Transcription

1 Indoor Air 2008, August 2008, Copenhagen, Denmark - Paper ID: 981 Balanced ventilation in apartment buildings Kari Thunshelle * and Mads Mysen SINTEF Building and Infrastructure, Norway * Corresponding kari.thunshelle@sintef.no SUMMARY Use of balanced ventilation in apartment buildings is supposed to improve indoor climate and reduce energy use for heating. On the other hand use of balanced systems can result in user dissatisfactions and complains. Overheating is one not foreseen problem; noise and not satisfactory exhaust from kitchen hoods are common problems. The last years the number of new apartment buildings per year has nearly been doubled in Norway. At the same time we se a tendency from choosing exhaust ventilation systems to more balanced ventilation systems. This tendency is strained by stricter energy provisions in the Norwegian building code. It is therefore important to find good solutions to avoid a new generation of problem apartments according to mechanical balanced ventilation. As a solution, centralised systems are introduced as an alternative for decentralised systems, but also these solutions have their disadvantages. Based on results from collection of experience from the building industry in Norway, this paper looks into the challenges mentioned above on balanced ventilation systems used in apartment buildings. KEYWORDS Balanced ventilation, Apartment buildings INTRODUCTION Traditionally dwellings, semi detached houses and row houses have been the most common accommodation in Norway. The building sector has experience an increasing activity in building of apartment buildings the last years, se table 1. The activity has been highest in urban areas, but also village have experienced increased activity for this type of buildings. Actually the number of new apartments has now exceeded the number of new single family houses. The trend is that not only young people demand apartments, but also elderly people who have lived most of their life in a single family house wants easier living with less responsibility and maintenance as in an apartment. Table 1. Completed buildings. Apartments according to building type (Source: Statistics Norway) Year Total number Apartments in apartment buildings Because of this increased activity, there have been a lot of questions on how to solve ventilation of apartment buildings. Typical overall approaches have been the choice between

2 balanced ventilation and exhaust ventilation, central systems or decentralize systems. The interest for balanced systems has increased. As a result of the Directive of the Energy Performance of Buildings (EPBD), the focus on energy saving have been sharpened in the in the building codes in Norway from January There will be a period of change over, but from August 2009 balanced ventilation is the only real alternative for new buildings according to the demand on energy saving. Today's experience on balanced ventilation is often related to dwellings. Differences between apartment buildings and dwellings in respect to user behaviour, internal heat load, heat transmission loss etc. are not taken into account. These differences might result in other problems and recommend solutions. There has also been lack of available information about the topic. SINTEF Building and Infrastructure has therefore focused on ventilation of apartment buildings in a series of projects over the last years. The main goal have been to unveil problem areas, increased knowledge and give guidance to the building industry. This paper describes the collection of experience from the building industry. METHODS This paper is an extract of experience based on results from the project Oikos Nomos. This study was focused on ventilation of apartment buildings in urban environment. Based on a preliminary literature study an interview guide was developed. Trends, type of solutions preferred and problem areas was asked about. Respondents from leading producers, building contractors, consultants and professional and industrial bodies were chosen. Most of the respondents are located in the eastern part of Norway. In total 26 persons were interviewed on telephone or in meetings. The interviews were done in winter 2003 (Mysen, Thunshelle 2004). RESULTS Trends Exhaust ventilation is still the dominating solution in apartments in the Oslo area, but some large projects are choosing balanced ventilation. The division between exhaust systems and balanced systems is estimated to 80/20 and 70/30 from the producers. The interest for balanced ventilation is increasing. Arguments for choosing balanced ventilation is energy saving, pollution in outdoor environment, and better control with ventilation rates and draft. Prize is often the argument for choosing exhaust ventilation. From a user perspective, decentralized systems are recommended by the producers. The reason is the users wish for control of own situation. Entrepreneurs prefer central systems as this is quicker to install, and experience tells that users not always understand how to maintain the system. The total cost, installation included, is for balanced systems 2-3 times the prize for an exhaust system. For systems with less than 3-5 apartments, the producer recommends decentralized system because of prize. Problem areas Noise from the ventilation unit Noise generated in the system, for instance through air terminal devices. Smell of cooking in inlet air

3 Noise transmittance between apartments through ventilation system. Marginal capacity for kitchen hoods Problems with adjustment between kitchen and ventilation unit when placed above kitchen hoods. Overheating DISCUSSION Differences between single family houses and apartments There is an increasing interest in balanced ventilation in apartment buildings in Norway, and as pointed out in the introduction, this will probably be the leading solution in the future. However, it is important to have in mind that experience with balanced systems is mostly from use in single family houses. When looking into the problem areas, it is important not to transfer the experience directly from single family houses, but have in mind the differences to an apartment building. Apartments generally have less square meters per occupant than in a single family hose. This results in higher specific internal loads. Apartments also have limited possibilities for ventilation through windows because of traffic noise, pollutants in outdoor air, or the apartment might have windows only on one facade. The occupants in an apartment may have other user behaviors as the apartments have higher turnover, higher percentage of rental and many users are less prepared for being responsible for maintenance of a ventilation system. Apartment buildings often have higher thermal mass that a single family house as the first mentioned often use concrete in walls and floors, while family houses in Norway often in a wooden building. An apartment building also have more problems with installing shading systems as that require a consensus between many apartment owners. Centralized or decentralized systems The last decade decentralized systems have been chosen in most apartment buildings. This solution gives the resident full control of own indoor climate situation without interruptions from the neighbors. Individual systems also give control of fire precautions as each kitchen hood is connected to a separate ductwork. However, separate systems demand increased space for shafts for ductwork and have higher risk for noise problems from ventilation unit. Old centralized systems are often connected with regulation problems, noise and odor from neighbor apartments and have therefore not been a preferred solution. However, new systems seem to have been working on these problems, and the feedback from the first new apartment buildings using these systems seems to be positive. This still need more documentation, both on measurements and user satisfaction. Centralized systems seem to be preferred by entrepreneurs as it is quicker to install, control and maintain. In buildings with apartments for rent, the owners express the beauty of not having to enter the very apartment to control and maintaine the system. This solution secures a good and regularly supervision of the system. All ventilation systems need a minimum of maintenance, for instance regularly changing of filters, to be able to contribute to a good indoor climate. A survey among singe family house owners indicates that 75% of them change filters at least once a year. Similar survey have not

4 been performed among apartment owners, but in one of the largest apartment building projects just finished in Oslo, less than 15% has a service or filter contract with the producers or the entrepreneur. This indicates that maintenance of balanced ventilations systems could be a bigger problem in apartments than in single family houses. Noise Noise from ventilation unit can be experience as troublesome even if the requirements in the building code are met. (32dB(A) max /30dB(A) eq ). Most problems are related to decentralized systems in small apartments. Then there are few options for placing the ventilation unit, which often results in short distance between the unit and the bedroom. This might result in turned of system during nighttime. Placing of ventilation unit above the kitchen hood can also result in a noise problem, especially with an integrated kitchen and living room solution. Measures could be to develop ventilation units with reduced noise, either by lowering the noise effect level, use of noise reduction material or reduce vibration energy. Placing of ventilation unit away from the bedroom and good noise reduction in walls would be other effective measures. Noise transmitting from one apartment to another through ventilation system could be a problem with central system connecting several apartments. This is especially a problem for apartments at the same floor. New generation central systems often solve this problem with a silencer while connecting the ductwork from each apartment to the system. Overheating In several new apartment buildings where balanced ventilation has been chosen, there have been complaints about overheating. The users have registered that the inlet air has had a higher temperature then the outdoor air. According to entrepreneurs contacted in this study, this has never been a problem with exhaust ventilation. This indicates a new problem with use of balanced ventilation. Compared to single family houses, apartments have higher thermal mass, higher internal loads, and reduced possibilities for ventilation through windows. To avoid heat accumulation, it is therefore highly important that the inlet air have a minimum of increased temperature compared to outdoor temperature. Measurements in one of the apartment building projects in Oslo using balanced ventilation showed average indoor temperature of 4,8 C higher than outdoor temperature on during a 24 hour hot summer period. This was caused by 1,5 C increased temperature in the inlet shaft, and 3,3 C increased temperature in the ventilation unit even if the heat exchanger was turned off. Another problem is that most ventilation units don t have the possibility for restricted heat exchange controlled according to a fixed temperature. In practice this results in control of inlet temperature only on cold days. There is a need to go thoroughly into the problem of overheating of apartment buildings in further studies and research activities. Balanced ventilation is supposed to contribute to better indoor climate, and a thermal dissatisfaction like this is not acceptable. Possible solutions that probably will help the situation are air inlet placed on a façade facing north, good insulation of ductwork, minimum of increased temperature in ventilation unit and temperature regulated contribution from heat exchanger. Apartments with windows on two facades will in some areas also be a solution for increased ventilation through windows.

5 Smell of cooking in the inlet air Placing of air inlet and exhaust might on the roof might cause problems. This is most likely because of exhaust air entering the air inlet at a moment of unlucky wind situation. This could especially be the problem with decentralized systems where a lot of air inlets and exhausts are placed on the roof. The problem can be solved with sufficient space between air inlet and exhaust. Air inlet in the façade and exhaust placed on the roof is normally a good solution. Use of carbon filter at the air inlet is also a possibility. In central systems exhaust air from kitchen hoods might be connected to the general ductwork. Then use of an efficient filter in the kitchen hood is essential. Regular cleaning of filters, kitchen hood and duct would be necessary and rotating heat exchanger is not recommended. Kitchen hoods There are often complaints about the capacity for the kitchen hoods, even if the requirements in the building code guidance are fulfilled (108m 3 /h). This is partly caused by not optimal shape of the kitchen hood seen from a fluid mechanic perspective. Design is an important issue for the user when refurbishments are done. By experience m 3 /h is necessary to avoid complaints when using today solutions. The new and upcoming kitchen hoods indicate 500m 3 /h or more. This will probably pick up vapor and odors from cocking effectively, but can easily cause new problems like noise, negative pressure in the apartment and draft problems. Here more documentation and research is needed. Also better guidance on fire precaution and guidance on good solutions are needed. Ventilation unit placed above kitchen hood This is an unfavorable solution in many ways. At least in Norway the turnover of kitchen refurbishment is increasing. When placing the ventilation unit above the kitchen hood the possibilities for changes are limited, both of layout, changing between electric or gas stove or different kitchen hoods. Additionally noise and capacity are known problems as earlier mentioned. It is therefore recommended to avoid this kind of solution. Need for further research This study points out problem areas with balanced ventilation. There are many reason to establish projects for further research to solve these challenges and be able to give valuable feedback to the different actors involved. Among actual topics can be mentioned documentation of centralized systems, over heating, kitchen hoods, fire precautions and maintenance. The need for more guidance and recommended solutions to the building industry is clear to achieve well being for the dweller and good indoor environments in apartments. ACKNOWLEDGEMENT Thanks to "Foreningen for Dansk-Norsk Samarbejde" for contributing to SINTEF Building and Infrastructures participation at this conference The results in this study are part of the project Oikos Nomos, partly financed by the Norwegian Research Council and The Norwegian State Housing Bank.

6 REFERENCES Thunshelle Kari Balanced ventilation in apartment buildings Literature study (in Norwegian). Norwegian Building Research Institute. Project report Oikos Nomos. Thunshelle, Kari et. al Evaluation of alternatives to balanced ventilation in urban apartments (in Norwegian). Norwegian Building Research Institute. Project report Oikos Nomos. Mysen Mads, Thunshelle Kari Balanced ventilation in apartment buildings Collection of experience (in Norwegian). Norwegian Building Research Institute. Project report Oikos Nomos. Schild Peter G., Thunshelle Kari Development of the future energy efficient low pressure drop ventilation of dwellings with demand control (in Norwegian). Norwegian Building Research Institute. Project report Oikos Nomos. Schild Peter G., Grini Catherine Design guidance for ventilation of apartment buildings (in Norwegian). SINTEF Building and Infrastructure. Project report. SINTEF Building and Infrastructure Building Research Design Guides Design of balanced ventilation in apartment buildings. Statistics Norway. Building- and floorage statistics Table 14: Completed buildings. Apartments according to building type