NatVent. Overcoming technical barriers to low-energy natural ventilation in office type buildings in moderate and cold climates

Transcription

1 NatVent Overcoming technical barriers to low-energy natural ventilation in office type buildings in moderate and cold climates EC CONTRACT: JOR3-CT95-22 (DGXII) Barriers to Natural Ventilation Design of Office Buildings National Report: The Netherlands TNO W.F. de Gids TNO Building and Construction Research July 1998 Research part funded by THE EUROPEAN COMMISSION in the framework of the Non Nuclear Energy Programme

2 Contents Introduction...2 Method...4 Questionnaire on general view...5 Questionnaire on specific building project...6 Results...7 The interviewee...7 General view...7 Knowledge on ventilation...8 Experience...9 Project fee...1 Design...1 Performance in practice...11 Controllability...12 Figure 8. The interviewees perception of the costs for natural and mechanical ventilation in cellular and open plan offices. The scale ranks from 1: Inexpensive to 5: Expensive...13 Source to natural ventilation knowledge...13 Expected future use of natural ventilation...14 Restricting requirements in codes...14 Desirable new design tools...15 Desirable new components...15 Specific building project...16 The buildings...16 Design...16 Critical parameters...16 Influence...18 Summary and conclusions...19 Conclusions...19 Recommendations...2 Annex: Requirements in codes related to (natural) ventilation

3 Introduction The objective of the study described in this report is to identify barriers restricting the implementation of natural or simple fan assisted ventilation systems in the design of new office type buildings and in the refurbishment of such existing buildings. The perceived barriers are identified in an in-depth study with structured interviews based on questionnaires among leading designers and decision makers. The interviews have focused on general knowledge, viewpoints, experience and perceived problems with natural ventilation in office type buildings and on the decisions actually taken in specific building projects. Mechanical ventilation systems are often installed in office buildings where good natural ventilation would have been sufficient to obtain comfortable indoor climate and good air quality. It is important to identify the barriers seen by designers and decision makers which restrict the implementation of natural ventilation systems and lead to the decision to install mechanical ventilation plants in office buildings where it is not strictly necessary. Knowing the barriers is the first step in providing solutions to overcome them. To our knowledge it is the first time a study of this type has been performed in the Netherlands. The identification of perceived barriers to natural ventilation design of office buildings is the first phase (work package) of the NatVent project being carried out under the JOULE programme. The two other work packages in the NatVent project are: - Performance of naturally ventilated buildings. The aim is to evaluate the performance of twenty existing buildings designed specifically for natural ventilation. - 'Smart' technology systems and components. The aim is to develop systems, components and solutions to the barriers and shortcomings identified in the first two work packages. This work package includes: - Air supply components suitable for high pollution and noise loads - Constant (natural) air flow inlets - Advanced natural ventilation systems with heat recovery - 'Smart' components and 'intelligent' controls for night cooling - Integration of smart systems for year-round performance The NatVent project is performed by nine organisations in seven central and north European countries. The project is headed by Building Research Establishment, BRE (UK). The other partners are: Centre Scientifique et Technique de la Construction, CSTC (B) Danish Building Research Institute, SBI (DK) TNO Building and Construction Research (NL) AB Jacobsen & Widmark, J&W (S) Technical University, Delft (NL) Willan Building Group (UK) Norwegian Building Research Institute, NBI (N) Sulzer Infra Laboratory (CH) This report is an output from the NatVent project which is part funded by the European Commision DGXII within the JOULE programme and under contract: JOR3-CT The Dutch work in the project is also part funded by the Dutch Ministry of Housing, Regional Development and the Environment (VROM) and the Dutch Organisation for promotion of research on Energy and Environment (NOVEM). 2

4 This report describes the results of the Dutch interviews. Similar reports giving the results of the interviews in the other countries are also produced. In addition the main results of the interviews will be published in a common final international report. The final report will summarise the results from the interviews in each country and compare them to identify common problems with the implementation of natural ventilation systems and to gain experience from countries that have solved some of the problems. The final report will also give recommendations on how to overcome the identified barriers. The NatVent project team would like to thank all the interviewees: designers and decision makers for the knowledge and experience they have brought to the project and for the time they have spend. 3

5 Method The perceived barriers to natural ventilation design of office buildings are identified in an in-depth study with structured interviews among leading designers and decision makers: architects, consultant engineers, contractors, developers, owners and the governmental decision maker responsible for regulations and standards. Interviews with ordinary users of office buildings are not included in this study, because they are not the ones making the decisions in the design phase. The users perception of the indoor climate is part of Work Package 2: Performance of naturally ventilated buildings, where physical parameters e.g. ventilation rates, room temperatures and indoor air quality are also measured and compared with the users responses. The interviews consist of two parts: - General view on natural ventilation in office buildings. This part focus on general knowledge, viewpoints, experience and perceived problems with natural ventilation systems in office type buildings. - Specific building project. This part focus on the decisions actually made during the design or refurbishment of an office type building. Both parts of the interview were in general performed with all interviewees. The only general exception is the interview with the governmental decision maker, where only the general view on natural ventilation in office buildings is relevant. The interviews were performed among: 5 Architects 3 Consultant engineers Contractors 1 Developers 2 Owners 1 Governmental decision maker (responsible for regulations and standards) The persons interviewed are selected with the intention to identify a variety in opinions and viewpoints on natural ventilation in office buildings. Due to circumstances we were unfortunately not able to interview contractors. Due to the fact that a limited number of persons per profession (in some cases only 1) are interviewed, one must be careful with drawing conclusion on profession level The interviews were based on questionnaires. There were two questionnaires to be filled in during an interview. The first questionnaire covers: General view on natural ventilation in office buildings and the second questionnaire covers: Specific building project. The questionnaires are designed to facilitate the performance of statistics on the viewpoint of the interviewee. The questionnaires are not too tight and there are ample space for additional comments, remarks and viewpoints not included in the questions. The questionnaires were completed by the interviewee and the interviewer together and the interviewer also if necessary guided the interviewee in understanding the questions. If a question couldn t be answered by the interviewee or is irrelevant to the interviewee it was indicated in the questionnaire. 4

6 Questionnaire on general view The questionnaire concerns general view on natural ventilation in office buildings. The questionnaire comprises 14 subjects: 1. Interviewee Identification of the interviewee 2. Organisation Description of the organisation: type, disciplines, number of employees and building types. 3. Knowledge Knowledge on mechanical ventilation, heat recovery, mechanical cooling, ordinary natural ventilation and special design natural ventilation in offices including special ventilation windows, advanced vents, internal ventilation openings, roof openings etc. The questions were answered by indicating the knowledge on a specific 5 point scale ranking from None to Thorough. 4. Experience Ventilation experience in the organisation focusing on the extension of new and refurbished office buildings designed or owned by the interviewees organisation. Also questions to identify the percentage of buildings with: mechanical ventilation, ordinary natural ventilation and special design natural ventilation in the offices. 5. Project fee Type of project fee received by architects and consultant engineers for the design of office buildings. Questions were asked to identify the percentage of projects with fee paid as: fixed fee, percentage of construction cost, per hour rate or other type of payment for design. 6. Natural ventilation in cellular offices 8. Natural ventilation in open plan offices 7. Mechanical ventilation in cellular offices 9. Mechanical ventilation in open plan offices General views on perceived advantages or problems with either natural or mechanical ventilation in cellular and open plan offices. The questions asked under subjects 6, 7, 8 and 9 are identical and only the ventilation system and the office type differs. The questions concern: design, availability of products, performance in practice, controllability and costs and were answered by checking the same 5 points scale as used in subject Your source of natural ventilation knowledge Possible sources are: standards, guidelines, building studies, experience, own design and other. 11. Expected future use of natural ventilation in office buildings Expected future use of natural ventilation in office buildings designed or owned by the organisation. The question were answered by checking a specific 5 points scale ranking from Decreasing over Unchanged to Increasing. The interviewees were also asked why they have this expectation. 12. Requirements restricting the use of natural ventilation in offices Perceived restriction in the use of natural ventilation in offices from requirements in building codes, norms, standards, working condition codes etc. The question were answered by checking a 5 points scale ranking from None to Comprehensive and by indicating which code, norm or standard that includes the restrictions. 13. Desirable new design tools for natural ventilation Possible new sources and design tools could be source books, guide lines, examples, simple or advanced computer programmes etc. 14. Desirable new components for natural ventilation Possible new components could be air inlets, control systems etc. 5

7 Questionnaire on specific building project The questionnaire concerns one specific building project. The building could be either newly constructed or newly refurbished and could be with either natural or mechanical ventilation. The building were selected by the interviewee to be typical. The questionnaire comprises 5 subjects: 1. Interviewee Identification of the interviewee 2. Building Identification of the building and indication of key figures including building name, address, building type, year of construction, year of refurbishment (if any), site (urban, sub-urban, industrial or rural), m 2 -floor area, number of storeys, building depth from facade to facade and storey height. 3. The design Description of the actual design of the ventilation system and the building design parameters with influence on the ventilation demand and the ventilation system design. The design were described by checking a row of boxes for each room type in the building: offices, meeting rooms, canteen, corridors, stairways, entrance hall, atria, lavatories and others. The design specification includes: Ventilation system: Mechanical cooling: External openings: Internal horizontal flow openings: Internal vertical flow openings: Solar shading: Ceilings: Floor and walls: Mechanical ventilation, mechanical exhaust, natural ventilation, heat recovery, night time ventilation In ventilation system, cooled ceilings Ordinary windows, special ventilation windows, ordinary vents, advanced vents, stack ducts, ventilation chimneys, roof openings, ducted air supply Doors, ventilation openings, open connection Ventilation openings, open connection Internal, between panes, external, protective glazing High ceiling, false ceiling, exposed heavy structure Exposed heavy floor, internal walls, external walls 4. Background for the design Indication of critical parameters in the ventilation system design and in the relevant parts of the building design. The critical parameters were prioritised for each of the room types on a 5 point specific scale ranking from 1. low to 5. high. The critical parameters includes: Winter conditions: Summer conditions: Controllability: Noise: Pollution and odours: Safety: Costs: Room temperatures, indoor air quality, draught Room temperatures, solar loads, internal heat, draught Individual control Internal noise, external noise Internal air and external air pollution or odours Fire regulations, security Construction, operating and maintenance costs 5. Biggest influence on chosen design Indication of biggest influence on the chosen design. The influence could be from: architect, consultant engineer, contractor, owner, developer, investor, user, the actual building site, requirements in codes, norms, standards or from other. The influence were prioritised on the same 5 point specific scale as used in subject 4 above. 6

8 Results The main results of the interviews are described in this chapter. The interviewee The five architects interviewed represents some of the leading Dutch architect offices. They have between 15 and 18 persons employed. They annually design 2,5 up to 2, m 2 floor area in new office buildings and 5, up to 15, m 2 in refurbishment of office buildings. Most of them, besides offices, also designs other types of buildings e. g. schools, institutions, houses and laboratories. The three consultant engineers interviewed are representative for Dutch consultant engineer offices. They have between 5 and 12 persons employed. They annually design 2, up to 5, m 2 floor area in new office buildings and 2, up to 5, m 2 in refurbishment of office buildings. Besides offices, most of them design houses. The developer interviewed is one of the largest developer and building organisation within the Netherlands. They have about 27 persons employed. They annually built about 1 buildings. Their market is 3% non domestic and 7% domestic. Both owners interviewed work at the same state enterprise. This enterprise also performs engineering activities. This enterprise has about 9 persons employed. Each year their building stock increase with about 5 new buildings, while in general also about 5 buildings are refurbished per year. The governmental decision maker is from the Dutch Ministry of Housing, Regional Development and the Environment (VROM). He is responsible for formulating requirements and guidelines within the Netherlands concerning (amongst other things) ventilation. General view Concerning the application (applicability) of natural ventilation several views and opinions are mentioned by the interviewees. Two architects state that the customers (users, principle) nowadays prefer mechanical ventilation. Furthermore two architects state that the regulations hinder (or do not foresee in) the use of natural ventilation. Within the group of consultant engineers, one consultant engineer states that the customers (users, principle) prefer natural ventilation. An other states the opposite (preference for mechanical ventilation). The opinion of the third consultant engineer is that natural ventilation must always be used in combination with mechanical ventilation for the winter period. The developer also states that customers prefer mechanical ventilation. He says that he has never build an office with natural ventilation. Natural ventilation should only be applicable in industrial situations. Despite of the above mentioned in general it may be stated that the interviewees have a positive attitude concerning the use of natural ventilation in office buildings. This is subscribed by the fact that about 75% of the interviewees foresees an increase in the use of natural ventilation. As main reasons therefor is given the positive impact on energy consumption and environment. 7

9 In the figures in this section of the report the average value for each profession group is given, while all represents the average of all profession groups together. If none of the interviewees in a profession group has answered a question, the result is omitted for that profession group and question. It is notes that contractors are not interviewed. Furthermore is noted (as already earlier stated) that only a few persons are interviewed within each profession group. Sometimes (developer and governmental decision maker) only one person is interviewed. One must therefor be careful in considering the results as representative for a profession group. Knowledge on ventilation Figure 1 shows the interviewees perception of own knowledge on the five topics: mechanical ventilation, heat recovery, mechanical cooling, ordinary natural ventilation and special designed natural. A specific 5 point scale ranking from 1: None to 5: Thorough is used to indicate the level of knowledge. The interviewee have indicated their level of knowledge on the five topics based on the knowledge necessary to perform their normal task in the design or decision process and relative to their profession. It is therefore not possible to compare the level of knowledge between the professions based on the results. The results can merely be used to compare the relative knowledge on the five subjects with each group (with a certain profession). Figure 1 shows no clear tendencies concerning the interviewees perception of own knowledge. The variation of the (supposed) knowledge on the different subjects is in general low within each profession group. Only the results from the consultant engineers seem to indicate less knowledge of ordinary natural ventilation than mechanical ventilation. However, in contradiction with this, the knowledge of special natural ventilation is supposed to be as high as the knowledge of mechanical ventilation. A clear tendency that for instance knowledge of natural ventilation is less, can therefore not be derived from these results. The architects report in general that make their own design only in cases of small and not complex projects. In other cases they let the design be performed by an advisor. The developer states that he makes no own design of technical installation. The interviewed developer and Governmental decision maker both could not make an distinction between their knowledge on the 5 topics. None Thorough Mech. vent. Heat recovery Mech. cooling Ord. nat. vent. Spec. nat. vent. Architects Cons. eng. Developer Owners G. decision All Figure 1. The interviewees perception of own knowledge. The scale ranks from 1: None to 5: Thorough. 8

10 Experience The interviewees relative experience with mechanical ventilation, ordinary natural ventilation and special designed natural ventilation in new offices is shown in figure 2. Figure 3 shows the interviewees relative experience with mechanical and natural ventilation in refurbished offices. The relative experience is the per cent of mechanical or natural ventilated offices designed, constructed or owned, measured by the floor area or alternatively by the number of office buildings. Figure 2 and 3 clearly show that the experience with ordinary natural ventilation and special designed natural ventilation is very low in relation to the experience with mechanical ventilation. It was one of the architects experience that the use of natural ventilation in low buildings was limited because of psychological reasons (burglary, incorrect functioning because lack of stack effect,..?) One of the consultant engineers stated that you should use natural ventilation always in combination with mechanical ventilation. The natural system can be used during the summer and the mechanical for the winter (better control, less draught,..). The developer stated to have no experience with natural ventilation. According to his believe (findings) natural ventilation is only applicable in industrial halls. 1 8 Per cent 6 4 Mech. vent. Ord. nat. vent. Spec. nat. vent. 2 Architects Cons. eng. Developer Owners All Figure 2. The interviewees relative experience with mechanical and natural ventilation in new offices. The scale is the per cent of mechanical or natural ventilated new offices designed or owned. 1 8 Per cent 6 4 Mech. vent. Ord. nat. vent. Spec. nat. vent. 2 Architects Cons. eng. Developer Owners All Figure 3. The interviewees relative experience with mechanical and natural ventilation in refurbished offices. The scale is the per cent of mechanical or natural ventilated refurbished offices designed or owned. 9

11 Project fee The type of fee received by the interviewed architects, consultant engineers and developer for the design (construction) of office buildings is shown in figure 4. The possible fee types are: Fixed fee, percentage of construction costs and per hour rate. 1 8 Per cent 6 4 Fixed fee Per cent of const. costs Per hour rate 2 Architects Cons. eng. Developers Figure 4. Type of fee received by the interviewed architects and consultant engineers for the design of office buildings. Most of the interviewed architects are paid a percentage of the predicted construction costs. Two architects mentioned that payment per hour (rate) is sometimes used for small projects. The consultant engineers are paid a fixed rate or a percentage of the predicted construction costs. Only a small percentage is paid per hour (rate). The developer only works with a fixed fee. Design The interviewees perception of the design of natural and mechanical ventilation in cellular and open plan offices regarding ease of design, availability of design guidelines and advises, availability of products, flexibility to building use and user satisfaction are shown in figure 5. A specific 5 point scale ranking from 1: Poor to 5: Excellent is used to indicate the interviewees perception of the design. From figure 5 can be derived that, except concerning the item user satisfaction, natural ventilation gets a lower ranking than mechanical. It is noted however that the very low ranking concerning natural ventilation in open plan offices is not correct. This is a result to the fact that the architects have not filled in the questions for open plan offices, because they do not design such building offices. In case the different professions are considered separately on the items ease of design, availability of design guidelines and advises and availability of products, it is shown that: especially the consultant engineers give a lower ranking to natural than mechanical ventilation. The consultant engineers are mostly involved in the actual design of the ventilation system. Their low ranking on these items clearly indicates that the design of natural systems is more difficult; the architects give a slightly lower ranking to natural than mechanical ventilation. Perhaps this relates to the fact that: - a natural system (e.g. ventilation grids in facades) have a greater link with (impact on) the work of the architects than mechanical systems; - in case of mechanical systems the architects make more use of advisors (consultant engineers). Occurring problems are passed on to the advisor. Some of the interviewees emphasise that the ease of design very much depends upon the difficulty degree of the building layout. One of the architects states that the design of natural systems needs a long preparation 1

12 in advance, while one of the consultant engineers states that special designed natural ventilation requires investigation. Two architects and two consultant engineers mentioned that the guidelines are more applicable to mechanical than natural ventilation. One of the architect mentioned that the user satisfaction depends on the information (education) given to the users. By good information on how to use the natural system, a high user satisfaction is possible. Although not explicitly mentioned in the interviews, it is our believe that the user satisfaction is higher by natural ventilation because of the fact that users can influence their surrounding (e.g. by opening of windows). Poor Excellent Natur., Cellular Natur., Open plan Mech., Cellular Mech., Open plan Ease of design Guidelines Products Flexibility User satisfac. Figure 5. The interviewees perception of the design of natural and mechanical ventilation in cellular and open plan offices. The scale ranks from 1: Poor to 5: Excellent. Performance in practice The interviewees perception of the performance in practice of natural and mechanical ventilation in cellular and open plan offices regarding cooling effectiveness, draught minimisation, ability to remove odours and pollutants, ability to prevent ingress of odours and pollutants, insulation against external noise, generation or transmission of internal noise are shown in figure 6. A specific 5 point scale ranking from 1: Poor to 5: Excellent is used to indicate the interviewees perception of the performance in practice. In general the interviewees expect a better performance in practice of mechanical ventilation systems than of natural ventilation systems regard cooling effectiveness, draught minimisation, ability to remove odours and pollutants, ability to prevent ingress of odours and pollutants and insulation against external noise. Regarding generation or transmission of internal noise they expect the same performance in practice. The ranking on cooling effectiveness, removal of odours and ingress of odours is higher for mechanical systems due to the possibilities for active cooling and use of filters. By one of the owners this is explicitly mentioned. He states that in case of natural ventilation the internal load is critical. The low ranking concerning draught relates to the intake of fresh (cold) outside air via the facade. The ranking is low despite of the fact that a lot of interviewees state that a good control of a natural system is possible (which decreases the possibility for draught). By one of the architect is mentioned that mechanical systems are noisy. 11

13 345 Poor Excellent Natur., Cellular Natur., Open plan Mech., Cellular Mech., Open plan Cooling eff. Draught Rem. odour Ingr. odour Ext. noise Int. noise Figure 6. The interviewees perception of the performance in practice of natural and mechanical ventilation in cellular and open plan offices. The scale ranks from 1: Poor to 5: Excellent. Controllability The interviewees perception of the controllability of natural and mechanical ventilation in cellular and open plan offices regarding central controllability, local controllability (per office) and individual controllability (per person) are shown in figure 7. A specific 5 point scale ranking from 1: Poor to 5: Excellent is used to indicate the interviewees perception of the controllability. In general the interviewees expect a high central controllability of mechanical ventilation systems and a low central controllability of natural ventilation systems. One of the consultant engineers states that central closing and opening of ventilation provisions in case of natural ventilation is a necessity (central closing after working hours). The expected local controllability varies little for natural and mechanical ventilated cellular offices. For open plan offices, especially the natural ventilation is indicated as a system with low local controllability. Concerning local controllability two of the architects clearly state that a good control is possible with natural ventilation. It is emphasised that in case of mechanical ventilation a good controllability will depend on the actual system. Poor Excellent Natur., Cellular Natur., Open plan Mech., Cellular Mech., Open plan Central Local Individual Figure 7. The interviewees perception of the controllability of natural and mechanical ventilation in cellular and open plan offices. The scale ranks from 1: Poor to 5: Excellent. 345 Costs The interviewees perception of the costs for natural and mechanical ventilation in cellular and open plan offices regard installation costs, running costs and maintenance costs are shown in figure 8. A specific 5 point scale ranking from 1: Inexpensive to 5: Expensive is used to indicate the interviewees perception of the costs. 12

14 All interviewees expect both higher installation costs, higher running costs and higher maintenance costs for mechanical ventilation in offices than for natural ventilation in offices. One of the consultant engineers and one of the owners however stated that a negative effect on the energy costs in case of natural ventilation is the fact that heat recovery is normally not used in combination with natural ventilation.. Inexpensive Expensive Natur., Cellular Natur., Open plan Mech., Cellular Mech., Open plan Installation Running Maintenance Figure 8. The interviewees perception of the costs for natural and mechanical ventilation in cellular and open plan offices. The scale ranks from 1: Inexpensive to 5: Expensive Source to natural ventilation knowledge The interviewees sources to natural ventilation knowledge regarding standards, guidelines, building studies, experience, own design and others are shown in figure 9. The scale is the per cent of interviewees using a source type. Considering all interviewees together, standards, guidelines and experience get about the same percentage. Considering only the groups that are mostly occupied on system-design (architect and consultant engineers), standards and guidelines get a clearly lower percentage than experience. Standards and guidelines are within these group less seen as a good source to natural ventilation knowledge. As already earlier mentioned, a lot of interviewees considered the guidelines less applicable for natural ventilation. The mentioned sources to natural ventilation knowledge are: - het bouwbesluit (Dutch governmental building regulations); - NEN 187 (Dutch ventilation standard); - AIVC; - guidelines RGD 1 Per cent Standards Guidelines Build. studies Experience Own design Other Architects Cons. eng. Developers Owners G. decision All Figure 9. The interviewees source to natural ventilation knowledge. The scale is the per cent of interviewees using a source type. 13

15 Expected future use of natural ventilation The interviewees expectations on the future use of natural ventilation in offices are shown in figure 1. The expectation is indicated on a specific 5 points scale ranking from 1: Significant decreasing over 3: Unchanged to 5: Significant increasing. Both owners expect definitely an increase of the use of natural ventilation. Furthermore all 3 consultant engineers and 3 architects also believe in an increase of the use of natural ventilation. Typical reasons mentioned by the interviewees for expecting increasing use of natural ventilation in offices are: - energy savings; - positive impact on environment; - less sick building problems; - higher users satisfaction; - preference for natural systems; - less costs for installation and maintenance. One of the architects thinks that the use of natural ventilation will be unchanged and one believes in a decreasing use. The developer and the governmental decision maker both believe that the use of natural ventilation will not change. Typical reasons mentioned by the interviewees for expecting decreasing use of natural ventilation in offices are: - requirements in building codes; - preference for mechanical systems; - need for comfort. Decrease Unchange Increase Architects Cons. eng. Developers Owners G. decision All Figure 1. The interviewees expectations on the future use of natural ventilation in offices. The scale used ranks from 1: Significant decreasing over 3: Unchanged to 5: Significant increasing. Typical reasons for expecting unchanged use of natural ventilation in offices are: Restricting requirements in codes By the Dutch interviewees and interviewers on this question not only restrictions in the requirements in codes are considered but restrictions more in general are considered. The interviewees perception of items restricting the use of natural ventilation in offices are shown in figure 11. A concentrate of Dutch regulations, codes, norms and standards related to natural ventilation or simple fan assisted ventilation systems in offices is given in annex III: Requirements in codes related to natural ventilation. 14

16 Restrictions to the use of natural ventilation in offices mentioned by the interviewees in relation to requirements are: - insufficient attention to natural ventilation in requirements; - combination of natural and mechanical ventilation does not fit the Energy Performance Standard (EPN); - ventilation requirements too high for piston flow; - interpretation of outside air is not clear. Other restrictions to the use of natural ventilation in offices mentioned by the interviewees are: - mechanical system are wanted (have the preference); - inadequate temperature control in the summer; - little experience and knowledge on natural ventilation; - outdoor quality not suited for the use of natural ventilation (noise, pollution). None Comprehensive Architects Cons. eng. Developers Owners G. decision All Figure 11. The interviewees perception of requirements in building regulations, codes, norms and standards restricting the use of natural ventilation in offices. The scale ranks from 1: None to 5: Comprehensive. Desirable new design tools A lot of the interviewees expressed the need for setting up or improving guidelines for natural ventilation. Especially by the owners ( who in this case also have an engineering background) the need for simple guidelines was emphasised. The need for design tools was also mentioned by a lot of the interviewees. This varied from simple tools up to advanced computer programs. The owners mentioned the need for simple tools and rules of thumb for the pre-design phase. One of the consultant engineers mentioned the need for a tool to derive wind pressure coefficients in the building environment. The governmental decision maker expressed the need to couple CAD-systems on physical models. By one architect was mentioned that the requirements in building codes should be based more upon common sense, thus giving the designer more freedom. By two architects, one consultant engineer and the developer the need for example projects, showing possibilities to use natural ventilation, was expressed. Desirable new components In general the need is expressed for developing or improving components for the control of natural ventilation. The need for self-regulating ventilation grids are mentioned by a lot of the interviewees. The owners (who in this case also have an engineering background) express the need for application and implementation of (already developed) constant flow inlets. Concerning air-inlets also by a lot of the interviewees the need is expressed for provisions that limit the risk on draught. By the governmental decision makes is mentioned the need for component in natural system to filter the outside air. 15

17 Specific building project Only the governmental decision maker did not fill in the questionnaire on a specific building project, because of the fact that due to his profession he has no direct link to a specific building project.. The results in the figures in this section of the report are the average of all the buildings included in the interviews The buildings From the 11 buildings, 1 buildings are office buildings and 1 building concerns a school. Two of the office buildings also include laboratories. One of the buildings is a complex with offices, houses and stores. The buildings date from this year up to about 7 years ago. All buildings are build in an urban area. The storeys of the buildings vary from 3 up to 2. The floor area s vary from 4. up to 32. m 2. Design For typical ventilation systems in office buildings is referred to annex IV. About 35% of the buildings has a natural ventilation system in the offices and about 35% of the buildings a mechanical ventilation system in the offices (mechanical supply with or without mechanical exhaust in the offices). The remaining 3% of the buildings has a combination of natural and mechanical system in the offices. For 1 building this means that a part of the offices is naturally ventilated and a part mechanically. For the other 2 buildings however an actual combination of the systems is used. For one of these buildings is namely clearly stated that the mechanical system is used during the winter and the natural system during the summer. Mechanical exhaust of the lavatories is available in almost all the buildings. In about 7% of the buildings with mechanical system, heat recovery is used. In 3 buildings active cooling is used. This concerns buildings with a mechanical system and in one case a building with a combination of mechanical and natural system. In 2 buildings cooling ceilings are used. In 3 of the 4 buildings with natural system, night time ventilation is used. In 2 of the 4 buildings with mechanical system, night time ventilation is used. Furthermore is in all 3 buildings with a combination of mechanical and natural system night time ventilation used. This seems to indicate that in several natural systems a automatic closing provisions of ventilation in- and outlets is available. Most of the natural ventilated offices (including those in combination with mechanical ventilation) have ordinary windows and vents. In 1 building special vents are used and in 2 building special ventilation windows. The application of atria s is rather high. In 7 of the 11 buildings atria s is used. For solar shading mostly protective glazing is used (4 of the 11 building). In 3 buildings external shading and in 1 building internal shading is used. In the remaining 3 buildings combinations are used. In only 3 of the buildings false ceilings are used. In most buildings the building mass is exposed to room temperatures thus providing means for heat accumulation and heat delivery. Critical parameters The interviewees perception of the critical parameters for the design of the ventilation systems in the offices are shown in figure 12a en 12b. Each interviewee were allowed to point out maximum 5 critical parameters and were ask to prioritise them from 1: Low to 5: High. Three of the architects and 1 consultant engineer have done so and their results are given in figure 12a. The other interviewees have however given a ranking to all parameters. Their results are given in figure 12b. In both groups the internal heat load is seen as an important critical parameter. Furthermore the summer temperature (figure 12a) and the solar loads (figure 12b) are seen as critical parameters. All these items relate 16

18 to the occurring indoor temperatures or thermal comfort. In general therefor can be stated that the indoor temperatures (and thermal comfort) are seen as an important critical parameter. From figure 12a furthermore individual control can be seen as a critical parameter. Figure 12b points out security and fire regulations as critical parameters. Figure 12b furthermore indicates indoor air quality, internal pollutants and external pollutants as critical parameters. All these items point out the pursuit for a good indoor air quality. From figure 12b also the construction costs can be indicated as critical Winter temp. Ind. air qual. Draught, wint. Summer temp. Solar loads Int. heat loads Draught, sum. Indiv. control Internal noise External noise Int. pollutions Ext. pollutions Fire regulat. Security Const. costs Oper. costs Maint. costs Other Low High Figure 12a. Critical parameters in the design of the buildings (architects A2, A3, A5 and consultant engineer E3). Low High Winter temp. Ind. air qual. Draught, wint. Summer temp. Solar loads Int. heat loads Draught, sum. Indiv. control Internal noise External noise Int. pollutions Ext. pollutions Fire regulat. Security Const. costs Oper. costs Maint. costs Other Figure 12b. Critical parameters in the design of the buildings (architect A4 and consultant engineers E1, E2 and owners O1, O2). 17

19 Influence The interviewees perception of the persons or conditions having the biggest influence on the chosen design is shown in figure 13. Again each interviewee were allowed to point out a maximum of 5 critical parameters and were ask to prioritise them from 1: Low to 5: High. Figure 13 shows that the architects, the consultant engineers and the owners are the ones with high influence on the chosen design. It is noted however that the architects state that the architects has a high influence, the consultant engineers state that the consultant engineers has a high influence, etc. However architects and consultant engineers also see one an other as persons with a high influence. Low High Architect Cons Engineer Contractor Owner Developer Invester Users Build. site Codes Other Figure 13. Influence on the design of the buildings. 18

20 Summary and conclusions The objective of the study is to identify barriers restricting the implementation of natural or simple fan assisted ventilation systems in the design of new office type buildings and in the refurbishment of existing such buildings. The perceived barriers are identified in an in-depth study with structured interviews based on questionnaires among leading designers and decision makers. The interviews have focused on general knowledge, viewpoints, experience and perceived problems with natural ventilation in office type buildings and on the decisions actually taken in specific building projects. The interviews were performed among: 5 architects, 3 consultant engineers, 1 developer, 2 owners and a governmental decision maker. The persons interviewed are selected with the intention to identify a variety in opinions and viewpoints on natural ventilation in office buildings. Due to the fact that a limited number of persons per profession (in some cases only 1) are interviewed, one must be careful with drawing conclusion on profession level. Due to circumstances we were unfortunately not able to interview contractors Conclusions The interviews points out that the interviewees consider their knowledge on natural ventilation about the same as their knowledge on mechanical ventilation. On the other hand however the interviews point out that the experience of the interviewees with natural ventilation (ordinary or special systems) is much less than with mechanical ventilation. One can therefor wonder whether the interviewees are capable of making a correct judgement on their own knowledge of natural ventilation. It is our opinion that besides experience also the knowledge of the interviewees is less on natural ventilation compared to mechanical ventilation. Furthermore the interviews show that the standards and guidelines are insufficient or too much focused on mechanical systems. In relation with this it is noted that the Dutch regulation standards however form no obstruction for the use of natural ventilation. There is a need for improving guidelines and a desire for new design tools and example projects, which show the possibilities of natural ventilation. The wanted design tools vary from rules of thumb up to advanced computer programs. There is a need for developing or improving the control of natural ventilation systems. The need for selfregulating ventilation grids is mentioned by a lot of the interviewees. It is not clear whether this is a result of bad experience with the available self-regulating grids or unfamiliarity with the existing grids. It is noted that the need for improving the control must relate to automatic control devices, because the interviewees on the other hand state that a good local control of natural ventilation is possible which probably relates to the manual adjustment possibilities of ventilation grids and/or windows. Furthermore there is a need for grids that limit the risk on draught, components to filter the outside air and heat recovery units. In the interviewees perception mechanical ventilation has several advantages compared to natural ventilation regarding cooling effectiveness, draught minimisation, ability to remove odours and pollutants, ability to prevent ingress of odours and pollutants, insulation against external noise and central controllability. Nevertheless the interviewees do not expect a higher user satisfaction in mechanical ventilated offices. In fact they expect the highest user satisfaction in natural ventilated cellular offices. Perhaps this relates to the fact that in case of a natural system the occupants can easily individually control their surrounding by adjusting the windows and/or ventilation grids. In relation to this is noted that the local and individual controllability for natural and mechanical systems is almost ranked similar by the interviewees. All interviewees expect higher installation, higher running and higher maintenance costs for mechanical ventilation in offices than for natural ventilation. One of the consultant engineers has stated however that 19

21 there is a negative effect on the energy costs in case of natural ventilation because of the fact that nowadays used heat recovery units are not applicable with natural ventilation. As important critical parameter for the design of natural ventilation systems, the internal heat load, summer temperatures and solar loads are mentioned. These items all relate to the indoor climate (thermal comfort), so in general the indoor climate can be seen as an important critical parameter. Furthermore several items are indicated as being about even critical. This concerns: security, fire regulations, indoor air quality, internal and external pollutants and construction costs. The architects, consultant engineers and owners have the biggest influence on the design of a building. Some important restrictions, that are mentioned to the use of natural ventilation in offices, are: insufficient attention to natural ventilation in requirements, inadequate temperature control in the summer, little experience and knowledge on natural ventilation. Mentioned restrictions or problems concerning regulations (standards, guidelines, etc.) are: combination of natural and mechanical ventilation does not fit with the Energy Performance Standard (EPN), ventilation requirements too high for piston flow, interpretation of outside air is not clear. About 75% of the interviewees expects an increase in the use of natural ventilation in office buildings in the Netherlands in the future. This concerns 3 of the 5 architect, the consultant engineers and owners (who by the way have a engineering background). Typical reasons given for the expected increase in use are: energy savings, positive impact on environment, less sick building problems, higher user satisfaction, preference for natural systems, less costs for maintenance and installation. Typical reasons given for a decrease in use are: requirements in building codes, preference for mechanical system and the need for comfort. Recommendations For an increase of the use of natural ventilation in office buildings, based upon the interviews, can be recommended: a) the setting up or improving of guidelines; b) development of simple and advanced design tools; c) adjusting the requirements in building codes. It is noted that this item is not subscribed by the author because in fact the current Dutch requirements form no restriction for the use of natural ventilation in any way; d) development or improvement of various components for natural ventilation. The knowledge on natural ventilation can be considered to be somewhat little. The guidelines and design tools are needed to fill in this knowledge. An other option is to set up or improve education on the use of natural ventilation. Furthermore the execution of demonstration projects, showing what is possible with natural ventilation, can be considered. For natural ventilation provisions to improved the control, to limit draught, to filter outside air and to make heat recovery possible need to be developed. On these aspects mechanical ventilation is nowadays seen as the better option. 2

22 Annex: Requirements in codes related to (natural) ventilation This annex gives an overview of the requirements in the Dutch Building Regulations, occupational health regulations, standards, codes etc. related to (natural) ventilation systems. The objective is to identify requirements possible restricting the implementation of natural ventilation. In the Netherlands the Building Regulations are principally performance oriented. That means that in the case of ventilation a certain performance in terms of flow rates must be achievable with a ventilation system, regardless the type of ventilation system. The Building Regulations have their roots in the Dutch Building Law. The Regulations specifies the requirements. To check whether or not a certain project fulfils the requirements the Building Regulations refer to standards. These standards give determination methods which are mainly test- or measurement methods but can be also a calculation method in special cases. The check on the requirements of the Building Regulations is carried out by the local Municipalities. Beside the test standards which are referred to in the Building Regulations there may be on certain items also a Dutch Standard. If so this is described below. Relevant documents BD 97: Building Decree. Dutch Building Regulations, 1997 ( in Dutch and English) NEN 187: NEN 2916: HTN: Ventilation of Buildings, Determination methods for new estate, 1997 (in Dutch) Energy performance of non residential buildings, Determination method, 1997 (in Dutch) Guide for the application of standards related to the Building Decree, 1997 (in Dutch) PR: Policy Rules related to the work Environment, 1997 (in Dutch) RGD: Guidelines for Governmental Buildings 1994 (in Dutch) Requirements Topic: Requirements: Document Ventilation BD 97 Requirements 1 dm 3 /s per m 2 floor area of the occupation zone 21