NatVent

Overcoming technical barriers to low-energynatural ventilation in office type buildings

in moderate and cold climates

EC CONTRACT: JOR3-CT95-0022 (DGXII)

Barriers toNatural Ventilation Design

of Office BuildingsNational Report:The Netherlands

TNO

W.F. de GidsTNO Building and Construction Research

July 1998

Research part funded byTHE EUROPEAN COMMISSION

in the framework of theNon Nuclear Energy Programme

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Contents

Introduction ........................................................................................................................................................2Method ...............................................................................................................................................................4

Questionnaire on general view.......................................................................................................................5Questionnaire on specific building project ....................................................................................................6

Results ................................................................................................................................................................7The interviewee..............................................................................................................................................7General view ..................................................................................................................................................7

Knowledge on ventilation ..........................................................................................................................8Experience..................................................................................................................................................9Project fee.................................................................................................................................................10Design.......................................................................................................................................................10Performance in practice............................................................................................................................11Controllability ..........................................................................................................................................12Figure 8. The interviewees perception of the costs for natural and mechanical ventilation in cellular andopen plan offices. The scale ranks from 1: Inexpensive to 5: Expensive.................................................13Source to natural ventilation knowledge..................................................................................................13Expected future use of natural ventilation ...............................................................................................14Restricting requirements in codes ............................................................................................................14Desirable new design tools.......................................................................................................................15Desirable new components.......................................................................................................................15

Specific building project ..............................................................................................................................16The buildings............................................................................................................................................16Design.......................................................................................................................................................16Critical parameters ...................................................................................................................................16Influence...................................................................................................................................................18

Summary and conclusions................................................................................................................................19Conclusions ..................................................................................................................................................19Recommendations ........................................................................................................................................20

Annex: Requirements in codes related to (natural) ventilation .......................................................................21

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Introduction

The objective of the study described in this report is to identify barriers restricting the implementation ofnatural or simple fan assisted ventilation systems in the design of new office type buildings and in therefurbishment of such existing buildings. The perceived barriers are identified in an in-depth study withstructured interviews based on questionnaires among leading designers and decision makers. The interviewshave focused on general knowledge, viewpoints, experience and perceived problems with natural ventilationin 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 wouldhave been sufficient to obtain comfortable indoor climate and good air quality. It is important to identify thebarriers seen by designers and decision makers which restrict the implementation of natural ventilationsystems and lead to the decision to install mechanical ventilation plants in office buildings where it is notstrictly necessary. Knowing the barriers is the first step in providing solutions to overcome them. To ourknowledge 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 workpackages 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 CommisionDGXII within the JOULE programme 1994-1998 and under contract: JOR3-CT95-0022. The Dutch work inthe 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).

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This report describes the results of the Dutch interviews. Similar reports giving the results of theinterviews in the other countries are also produced.

In addition the main results of the interviews will be published in a common final international report. Thefinal report will summarise the results from the interviews in each country and compare them to identifycommon problems with the implementation of natural ventilation systems and to gain experience fromcountries that have solved some of the problems. The final report will also give recommendations on how toovercome the identified barriers.

The NatVent project team would like to thank all the interviewees: designers and decision makers forthe knowledge and experience they have brought to the project and for the time they have spend.

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Method

The perceived barriers to natural ventilation design of office buildings are identified in an in-depth study withstructured interviews among leading designers and decision makers: architects, consultant engineers,contractors, developers, owners and the governmental decision maker responsible for regulations andstandards.

Interviews with ordinary users of office buildings are not included in this study, because they are not theones making the decisions in the design phase. The users perception of the indoor climate is part of WorkPackage 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 isthe interview with the governmental decision maker, where only the general view on natural ventilation inoffice buildings is relevant.

The interviews were performed among:

5 Architects3 Consultant engineers0 Contractors1 Developers2 Owners1 Governmental decision maker (responsible for regulations and standards)

The persons interviewed are selected with the intention to identify a variety in opinions and viewpoints onnatural ventilation in office buildings. Due to circumstances we were unfortunately not able to interviewcontractors. Due to the fact that a limited number of persons per profession (in some cases only 1) areinterviewed, 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 aninterview. The first questionnaire covers: General view on natural ventilation in office buildings and thesecond questionnaire covers: Specific building project.

The questionnaires are designed to facilitate the performance of statistics on the viewpoint of theinterviewee. The questionnaires are not too tight and there are ample space for additional comments, remarksand viewpoints not included in the questions.

The questionnaires were completed by the interviewee and the interviewer together and the intervieweralso if necessary guided the interviewee in understanding the questions. If a question couldn’t be answered bythe interviewee or is irrelevant to the interviewee it was indicated in the questionnaire.

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Questionnaire on general view

The questionnaire concerns general view on natural ventilation in office buildings. The questionnairecomprises 14 subjects:

1. IntervieweeIdentification of the interviewee

2. OrganisationDescription of the organisation: type, disciplines, number of employees and building types.

3. KnowledgeKnowledge on mechanical ventilation, heat recovery, mechanical cooling, ordinary natural ventilation andspecial design natural ventilation in offices including special ventilation windows, advanced vents, internalventilation openings, roof openings etc. The questions were answered by indicating the knowledge on aspecific 5 point scale ranking from ‘None’ to ‘Thorough’.

4. ExperienceVentilation experience in the organisation focusing on the extension of new and refurbished office buildingsdesigned or owned by the interviewees organisation. Also questions to identify the percentage of buildingswith: mechanical ventilation, ordinary natural ventilation and special design natural ventilation in the offices.

5. Project feeType 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 ofconstruction cost, per hour rate or other type of payment for design.

6. Natural ventilation in cellular offices 8. Natural ventilation in open plan offices7. Mechanical ventilation in cellular offices 9. Mechanical ventilation in open plan officesGeneral views on perceived advantages or problems with either natural or mechanical ventilation in cellularand open plan offices. The questions asked under subjects 6, 7, 8 and 9 are identical and only the ventilationsystem and the office type differs. The questions concern: design, availability of products, performance inpractice, controllability and costs and were answered by checking the same 5 points scale as used in subject 3.

10. Your source of natural ventilation knowledgePossible sources are: standards, guidelines, building studies, experience, own design and other.

11. Expected future use of natural ventilation in office buildingsExpected future use of natural ventilation in office buildings designed or owned by the organisation. Thequestion 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 officesPerceived 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 rankingfrom ‘None’ to ‘Comprehensive’ and by indicating which code, norm or standard that includes therestrictions.

13. Desirable new design tools for natural ventilationPossible new sources and design tools could be source books, guide lines, examples, simple or advancedcomputer programmes etc.

14. Desirable new components for natural ventilationPossible new components could be air inlets, control systems etc.

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Questionnaire on specific building project

The questionnaire concerns one specific building project. The building could be either newly constructed ornewly refurbished and could be with either natural or mechanical ventilation. The building were selected bythe interviewee to be typical. The questionnaire comprises 5 subjects:

1. IntervieweeIdentification of the interviewee

2. BuildingIdentification 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), m2-floor area,number of storeys, building depth from facade to facade and storey height.

3. The designDescription of the actual design of the ventilation system and the building design parameters with influenceon the ventilation demand and the ventilation system design. The design were described by checking a row ofboxes 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 ventilation, mechanical exhaust, natural ventilation, heatrecovery, night time ventilation

Mechanical cooling: In ventilation system, cooled ceilingsExternal openings: Ordinary windows, special ventilation windows, ordinary vents,

advanced vents, stack ducts, ventilation chimneys, roof openings,ducted air supply

Internal horizontal flow openings: Doors, ventilation openings, open connectionInternal vertical flow openings: Ventilation openings, open connectionSolar shading: Internal, between panes, external, protective glazingCeilings: High ceiling, false ceiling, exposed heavy structureFloor and walls: Exposed heavy floor, internal walls, external walls

4. Background for the designIndication of critical parameters in the ventilation system design and in the relevant parts of the buildingdesign. The critical parameters were prioritised for each of the room types on a 5 point specific scale rankingfrom ‘1. low’ to ‘5. high’. The critical parameters includes:

Winter conditions: Room temperatures, indoor air quality, draughtSummer conditions: Room temperatures, solar loads, internal heat, draughtControllability: Individual controlNoise: Internal noise, external noisePollution and odours: Internal air and external air pollution or odoursSafety: Fire regulations, securityCosts: Construction, operating and maintenance costs

5. Biggest influence on chosen designIndication of biggest influence on the chosen design. The influence could be from: architect, consultantengineer, 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 4above.

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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 between15 and 180 persons employed. They annually design 2,500 up to 20,000 m2 floor area in new office buildingsand 5,000 up to 15,000 m2 in refurbishment of office buildings. Most of them, besides offices, also designsother types of buildings e. g. schools, institutions, houses and laboratories.

The three consultant engineers interviewed are representative for Dutch consultant engineer offices. Theyhave between 5 and 12 persons employed. They annually design 2,000 up to 50,000 m2 floor area in newoffice buildings and 2,000 up to 50,000 m2 in refurbishment of office buildings. Besides offices, most of themdesign houses.

The developer interviewed is one of the largest developer and building organisation within theNetherlands. They have about 2700 persons employed. They annually built about 10 buildings. Their marketis 30% non domestic and 70% domestic.

Both owners interviewed work at the same state enterprise. This enterprise also performs engineeringactivities. This enterprise has about 900 persons employed. Each year their building stock increase with about5 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 theEnvironment (VROM). He is responsible for formulating requirements and guidelines within the Netherlandsconcerning (amongst other things) ventilation.

General view

Concerning the application (applicability) of natural ventilation several views and opinions are mentionedby 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 naturalventilation.

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). Theopinion of the third consultant engineer is that natural ventilation must always be used in combination withmechanical ventilation for the winter period.

The developer also states that customers prefer mechanical ventilation. He says that he has never build anoffice 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 attitudeconcerning the use of natural ventilation in office buildings. This is subscribed by the fact that about 75% ofthe interviewees foresees an increase in the use of natural ventilation. As main reasons therefor is given thepositive impact on energy consumption and environment.

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In the figures in this section of the report the average value for each profession group is given, while allrepresents the average of all profession groups together. If none of the interviewees in a profession group hasanswered a question, the result is omitted for that profession group and question. It is notes that contractorsare not interviewed. Furthermore is noted (as already earlier stated) that only a few persons are interviewedwithin each profession group. Sometimes (developer and governmental decision maker) only one person isinterviewed. One must therefor be careful in considering the results as representative for a profession group.

Knowledge on ventilationFigure 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 5point 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 knowledgenecessary to perform their normal task in the design or decision process and relative to their profession. It istherefore not possible to compare the level of knowledge between the professions based on the results. Theresults can merely be used to compare the relative knowledge on the five subjects with each group (with acertain profession).

Figure 1 shows no clear tendencies concerning the interviewees perception of own knowledge. Thevariation of the (supposed) knowledge on the different subjects is in general low within each professiongroup. Only the results from the consultant engineers seem to indicate less knowledge of ordinary naturalventilation than mechanical ventilation. However, in contradiction with this, the knowledge of special naturalventilation is supposed to be as high as the knowledge of mechanical ventilation. A clear tendency that forinstance 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 complexprojects. 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 andGovernmental decision maker both could not make an distinction between their knowledge on the 5 topics.

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Architects Cons. eng. Developer Owners G. decision All

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Mech. vent.

Heat recovery

Mech. cooling

Ord. nat. vent.

Spec. nat. vent.

Figure 1. The interviewees perception of own knowledge. The scale ranks from 1: None to 5: Thorough.

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ExperienceThe 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 relativeexperience with mechanical and natural ventilation in refurbished offices. The relative experience is the percent of mechanical or natural ventilated offices designed, constructed or owned, measured by the floor area oralternatively by the number of office buildings.

Figure 2 and 3 clearly show that the experience with ordinary natural ventilation and special designednatural 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 limitedbecause of psychological reasons (burglary, incorrect functioning because lack of stack effect, ..?) One of theconsultant engineers stated that you should use natural ventilation always in combination with mechanicalventilation. The natural system can be used during the summer and the mechanical for the winter (bettercontrol, less draught,..). The developer stated to have no experience with natural ventilation. According to hisbelieve (findings) natural ventilation is only applicable in industrial halls.

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Architects Cons. eng. Developer Owners All

Pe

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nt Mech. vent.

Ord. nat. vent.

Spec. nat. vent.

Figure 2. The interviewees relative experience with mechanical and natural ventilation in new offices. The scale is theper cent of mechanical or natural ventilated new offices designed or owned.

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Architects Cons. eng. Developer Owners All

Pe

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Ord. nat. vent.

Spec. nat. vent.

Figure 3. The interviewees relative experience with mechanical and natural ventilation in refurbished offices. The scaleis the per cent of mechanical or natural ventilated refurbished offices designed or owned.

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Project feeThe 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 ofconstruction costs and per hour rate.

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Architects Cons. eng. Developers

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Per cent of const. costs

Per hour rate

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 architectsmentioned 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 asmall percentage is paid per hour (rate).

The developer only works with a fixed fee.

DesignThe 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 alower ranking than mechanical. It is noted however that the very low ranking concerning natural ventilation inopen plan offices is not correct. This is a result to the fact that the architects have not filled in the questionsfor 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 ofdesign 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 degreeof the building layout. One of the architects states that the design of natural systems needs a long preparation

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in advance, while one of the consultant engineers states that special designed natural ventilation requiresinvestigation.

Two architects and two consultant engineers mentioned that the guidelines are more applicable tomechanical than natural ventilation.

One of the architect mentioned that the user satisfaction depends on the information (education) given tothe users. By good information on how to use the natural system, a high user satisfaction is possible. Althoughnot explicitly mentioned in the interviews, it is our believe that the user satisfaction is higher by naturalventilation because of the fact that users can influence their surrounding (e.g. by opening of windows).

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Ease of design Guidelines Products Flexibility User satisfac.

Po

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Natur., Cellular

Natur., Open plan

Mech., Cellular

Mech., Open plan

Figure 5. The interviewees perception of the design of natural and mechanical ventilation in cellular and open planoffices. The scale ranks from 1: Poor to 5: Excellent.

Performance in practiceThe 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 odoursand pollutants, ability to prevent ingress of odours and pollutants, insulation against external noise, generationor 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 thanof natural ventilation systems regard cooling effectiveness, draught minimisation, ability to remove odoursand 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 mechanicalsystems due to the possibilities for active cooling and use of filters. By one of the owners this is explicitlymentioned. 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. Theranking is low despite of the fact that a lot of interviewees state that a good control of a natural system ispossible (which decreases the possibility for draught).

By one of the architect is mentioned that mechanical systems are noisy.

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Cooling eff. Draught Rem. odour Ingr. odour Ext. noise Int. noise

P

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Natur., Open plan

Mech., Cellular

Mech., Open plan

Figure 6. The interviewees perception of the performance in practice of natural and mechanical ventilation in cellularand open plan offices. The scale ranks from 1: Poor to 5: Excellent.

ControllabilityThe interviewees perception of the controllability of natural and mechanical ventilation in cellular and

open plan offices regarding central controllability, local controllability (per office) and individualcontrollability (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 alow central controllability of natural ventilation systems. One of the consultant engineers states that centralclosing and opening of ventilation provisions in case of natural ventilation is a necessity (central closing afterworking hours).

The expected local controllability varies little for natural and mechanical ventilated cellular offices. Foropen 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 withnatural ventilation. It is emphasised that in case of mechanical ventilation a good controllability will dependon the actual system.

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Central Local Individual

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Natur., Cellular

Natur., Open plan

Mech., Cellular

Mech., Open plan

Figure 7. The interviewees perception of the controllability of natural and mechanical ventilation in cellular and openplan offices. The scale ranks from 1: Poor to 5: Excellent.

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CostsThe interviewees perception of the costs for natural and mechanical ventilation in cellular and open planoffices regard installation costs, running costs and maintenance costs are shown in figure 8. A specific 5 pointscale ranking from 1: Inexpensive to 5: Expensive is used to indicate the interviewees perception of the costs.

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All interviewees expect both higher installation costs, higher running costs and higher maintenance costsfor mechanical ventilation in offices than for natural ventilation in offices. One of the consultant engineersand one of the owners however stated that a negative effect on the energy costs in case of natural ventilationis the fact that heat recovery is normally not used in combination with natural ventilation..

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Installation Running Maintenance

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Natur., Cellular

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Mech., Cellular

Mech., Open plan

Figure 8. The interviewees perception of the costs for natural and mechanical ventilation in cellular and open planoffices. The scale ranks from 1: Inexpensive to 5: Expensive

Source to natural ventilation knowledgeThe 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 intervieweesusing 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 withinthese group less seen as a good source to natural ventilation knowledge. As already earlier mentioned, a lot ofinterviewees considered the guidelines less applicable for natural ventilation.

The mentioned sources to natural ventilation knowledge are:

- het bouwbesluit (Dutch governmental building regulations);- NEN 1087 (Dutch ventilation standard);- AIVC;- guidelines RGD

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Standards

Guidelines

Build. studies

Experience

Own design

Other

Figure 9. The interviewees source to natural ventilation knowledge. The scale is the per cent of interviewees using asource type.

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Expected future use of natural ventilationThe interviewees expectations on the future use of natural ventilation in offices are shown in figure 10.

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 consultantengineers 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 inoffices 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 adecreasing use. The developer and the governmental decision maker both believe that the use of naturalventilation will not change.Typical reasons mentioned by the interviewees for expecting decreasing use of natural ventilation in officesare:- requirements in building codes;- preference for mechanical systems;- need for comfort.

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Figure 10. 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 codesBy 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 naturalventilation’.

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Restrictions to the use of natural ventilation in offices mentioned by the interviewees in relation torequirements 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).

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Figure 11. The interviewees perception of requirements in building regulations, codes, norms and standards restrictingthe use of natural ventilation in offices. The scale ranks from 1: None to 5: Comprehensive.

Desirable new design toolsA 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 simpleguidelines was emphasised.

The need for design tools was also mentioned by a lot of the interviewees. This varied from simple toolsup to advanced computer programs. The owners mentioned the need for simple tools and rules of thumb forthe pre-design phase. One of the consultant engineers mentioned the need for a tool to derive wind pressurecoefficients in the building environment. The governmental decision maker expressed the need to coupleCAD-systems on physical models.

By one architect was mentioned that the requirements in building codes should be based more uponcommon sense, thus giving the designer more freedom.

By two architects, one consultant engineer and the developer the need for example projects, showingpossibilities to use natural ventilation, was expressed.

Desirable new componentsIn 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. Theowners (who in this case also have an engineering background) express the need for application andimplementation of (already developed) constant flow inlets. Concerning air-inlets also by a lot of the interviewees the need is expressed for provisions that limit therisk on draught.

By the governmental decision makes is mentioned the need for component in natural system to filter theoutside air.

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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 theinterviews

The buildingsFrom the 11 buildings, 10 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 20. The floorarea’s vary from 4.000 up to 32.000 m2.

DesignFor 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 amechanical ventilation system in the offices (mechanical supply with or without mechanical exhaust in theoffices). The remaining 30% of the buildings has a combination of natural and mechanical system in theoffices. For 1 building this means that a part of the offices is naturally ventilated and a part mechanically. Forthe other 2 buildings however an actual combination of the systems is used. For one of these buildings isnamely clearly stated that the mechanical system is used during the winter and the natural system during thesummer. Mechanical exhaust of the lavatories is available in almost all the buildings.

In about 70% of the buildings with mechanical system, heat recovery is used. In 3 buildings active coolingis used. This concerns buildings with a mechanical system and in one case a building with a combination ofmechanical 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 withmechanical system, night time ventilation is used. Furthermore is in all 3 buildings with a combination ofmechanical and natural system night time ventilation used. This seems to indicate that in several naturalsystems a automatic closing provisions of ventilation in- and outlets is available.

Most of the natural ventilated offices (including those in combination with mechanical ventilation) haveordinary windows and vents. In 1 building special vents are used and in 2 building special ventilationwindows.

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 parametersThe 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 criticalparameters and were ask to prioritise them from 1: Low to 5: High. Three of the architects and 1 consultantengineer have done so and their results are given in figure 12a. The other interviewees have however given aranking 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 summertemperature (figure 12a) and the solar loads (figure 12b) are seen as critical parameters. All these items relate

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to the occurring indoor temperatures or thermal comfort. In general therefor can be stated that the indoortemperatures (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 outsecurity and fire regulations as critical parameters.

Figure 12b furthermore indicates indoor air quality, internal pollutants and external pollutants as criticalparameters. 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.

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Figure 12a. Critical parameters in the design of the buildings (architects A2, A3, A5 and consultant engineer E3).

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Figure 12b. Critical parameters in the design of the buildings (architect A4 and consultant engineers E1, E2 and ownersO1, O2).

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InfluenceThe 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 parametersand 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 highinfluence on the chosen design. It is noted however that the architects state that the architects has a highinfluence, the consultant engineers state that the consultant engineers has a high influence, etc. Howeverarchitects and consultant engineers also see one an other as persons with a high influence.

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Figure 13. Influence on the design of the buildings.

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Summary and conclusions

The objective of the study is to identify barriers restricting the implementation of natural or simple fanassisted ventilation systems in the design of new office type buildings and in the refurbishment of existingsuch buildings. The perceived barriers are identified in an in-depth study with structured interviews based onquestionnaires among leading designers and decision makers. The interviews have focused on generalknowledge, viewpoints, experience and perceived problems with natural ventilation in office type buildingsand on the decisions actually taken in specific building projects.

The interviews were performed among: 5 architects, 3 consultant engineers, 1 developer, 2 owners and agovernmental decision maker. The persons interviewed are selected with the intention to identify a variety inopinions and viewpoints on natural ventilation in office buildings. Due to the fact that a limited number ofpersons per profession (in some cases only 1) are interviewed, one must be careful with drawing conclusionon 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 thesame as their knowledge on mechanical ventilation. On the other hand however the interviews point out thatthe experience of the interviewees with natural ventilation (ordinary or special systems) is much less thanwith mechanical ventilation. One can therefor wonder whether the interviewees are capable of making acorrect judgement on their own knowledge of natural ventilation. It is our opinion that besides experience alsothe 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 onmechanical systems. In relation with this it is noted that the Dutch regulation standards however form noobstruction for the use of natural ventilation. There is a need for improving guidelines and a desire for newdesign tools and example projects, which show the possibilities of natural ventilation. The wanted designtools 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 self-regulating ventilation grids is mentioned by a lot of the interviewees. It is not clear whether this is a result ofbad experience with the available self-regulating grids or unfamiliarity with the existing grids. It is noted thatthe need for improving the control must relate to automatic control devices, because the interviewees on theother hand state that a good local control of natural ventilation is possible which probably relates to themanual adjustment possibilities of ventilation grids and/or windows. Furthermore there is a need for grids thatlimit 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 naturalventilation 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 factthey expect the highest user satisfaction in natural ventilated cellular offices. Perhaps this relates to the factthat in case of a natural system the occupants can easily individually control their surrounding by adjustingthe windows and/or ventilation grids. In relation to this is noted that the local and individual controllabilityfor natural and mechanical systems is almost ranked similar by the interviewees.

All interviewees expect higher installation, higher running and higher maintenance costs for mechanicalventilation in offices than for natural ventilation. One of the consultant engineers has stated however that

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there is a negative effect on the energy costs in case of natural ventilation because of the fact that nowadaysused 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 (thermalcomfort), so in general the indoor climate can be seen as an important critical parameter. Furthermore severalitems 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 abuilding.

Some important restrictions, that are mentioned to the use of natural ventilation in offices, are: insufficientattention to natural ventilation in requirements, inadequate temperature control in the summer, littleexperience 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 theEnergy Performance Standard (EPN), ventilation requirements too high for piston flow, interpretation ofoutside air is not clear.

About 75% of the interviewees expects an increase in the use of natural ventilation in office buildings inthe Netherlands in the future. This concerns 3 of the 5 architect, the consultant engineers and owners (who bythe way have a engineering background). Typical reasons given for the expected increase in use are: energysavings, positive impact on environment, less sick building problems, higher user satisfaction, preference fornatural 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 berecommended: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 requirementsform 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 designtools are needed to fill in this knowledge. An other option is to set up or improve education on the use ofnatural ventilation. Furthermore the execution of demonstration projects, showing what is possible withnatural ventilation, can be considered.

For natural ventilation provisions to improved the control, to limit draught, to filter outside air and to makeheat recovery possible need to be developed. On these aspects mechanical ventilation is nowadays seen as thebetter option.

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Annex: Requirements in codes related to (natural)ventilation

This annex gives an overview of the requirements in the Dutch Building Regulations, occupational healthregulations, standards, codes etc. related to (natural) ventilation systems. The objective is to identifyrequirements possible restricting the implementation of natural ventilation. In the Netherlands the BuildingRegulations are principally performance oriented. That means that in the case of ventilation a certainperformance in terms of flow rates must be achievable with a ventilation system, regardless the type ofventilation system. The Building Regulations have their roots in the Dutch Building Law. The Regulationsspecifies the requirements. To check whether or not a certain project fulfils the requirements the BuildingRegulations refer to standards. These standards give determination methods which are mainly test- ormeasurement methods but can be also a calculation method in special cases. The check on the requirements ofthe Building Regulations is carried out by the local Municipalities. Beside the test standards which arereferred to in the Building Regulations there may be on certain items also a Dutch Standard. If so this isdescribed below.

Relevant documents

BD 97: Building Decree. Dutch Building Regulations, 1997 ( in Dutch and English)

NEN 1087: Ventilation of Buildings, Determination methods for new estate, 1997 (in Dutch)

NEN 2916: Energy performance of non residential buildings, Determination method, 1997 (in Dutch)

HTN: 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:Document

Requirements:

VentilationBD 97Requirements 1 dm3/s per m2 floor area of the occupation zone

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no recirculation

exhaust from wet rooms direct to outside

flow rates must be determined by NEN 1087

PRRequirements 30 m3/h per person

NEN 1087 Test method no combined ventilation ducts

above 13 m building height

WindowsBD 97Requirements smoke removal capacity:

6 dm3/s per m3 net volume of the roomflow rates must be determined by NEN 1087

Roomtemperatures

BD 97Requirements no requirements

RGDRequirements PMV + 0,5/-0,5

100 hours limit on temperature exceeding

DraughtBD 97Requirement < 0,2 m/s

exceeding on maximum on 10 % on the definedmeasurement pointsdraught must be determined by NEN 1087

NoiseBD 97

RequirementsNo specific requirements on ventilation systems

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EnergyBD 97

RequirementsEPC 1,9 determined according to NEN 2916