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CI/SfB (57) Uniclass Ss_65_40_33_56 October 2019 NATURAL VENTILATION STRATEGIES FOR COMMERCIAL BUILDINGS ................................

NATURAL VENTILATION STRATEGIES · 2019. 11. 4. · Passive stack ventilation (PSV) is the most effective natural ventilation strategy as it uses a combination of cross ventilation,

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  • CI/SfB (57) Uniclass Ss_65_40_33_56October 2019

    NATURAL VENTILATION STRATEGIESFOR COMMERCIAL BUILDINGS

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    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .NATURAL VENTILATION

    The low-energy strategyLow-energy natural ventilation is anincreasingly important design strategy forcommercial and other non-domesticbuildings.

    In comparison with air conditioning ormechanical ventilation it can bring:● Economic benefits through savings inboth capital equipment and running costs.● Environmental benefits in reducingenergy use and cutting greenhouse gasemissions and CO2 levels.● User benefits in providing controlled,comfortable conditions.

    Intelligent solutionsCurrent technology and design softwarecombined with sophisticated controlsystems mean that natural ventilation canprovide optimum performance as well as thebenefits indicated above.

    Using the latest techniques, intelligentnatural ventilation solutions can be appliedto many buildings that would otherwisehave defaulted to air conditioning.

    Hybrid Plus systems can also be used forpre-warming incoming air in winter periodsby mixing air and in summer months, theycreate airflow in times of low air movement.

    Early consultationThe key to the successful implementation ofa natural ventilation strategy is to considerits application during the preliminary stagesin the design of a building (preferably atoutline proposal stage). Decisions aboutbuilding plan, orientation and other factorswill enable the most effective use to be madeof natural ventilation.

    Clients, developers and building designersshould therefore consult natural ventilationexperts such as Passivent as early as possiblein the design process.

    PASSIVENT

    Passivent servicesDesigning natural ventilation systems to be asefficient as possible requires specialisedexpertise.

    With its in-house research and design team,Passivent can provide a comprehensive designand advisory service tailored to specificprojects, covering both system design andproduct selection from a range ofcomplementary ventilation strategies.

    Passivent expertisePassivent are specialists in delivering naturalventilation solutions, and a leading UKcompany in the field of sustainable andenergy-efficient ventilation for commercialbuildings.

    A pioneer in natural ventilation, Passivent hasbeen at the forefront in developing innovativeproducts and systems to provide optimumperformance in all types of buildings.Combined rooflight/ventilators complementPassivent’s natural ventilation range.

    Passivent design softwareWith so many variables in natural ventilationdesign it is important to understand how theelements interact with each other within thecontext of the building.

    A key part of the NatVent™ research project(see overleaf) has been the production ofsoftware to assess the various forms of naturalventilation in different types of building.

    Following on from this Passivent hasdeveloped its own advanced software‘AirSoft™’ (based on CIBSE AM10) to providean integrated design approach that takesaccount of all facets of the ventilationrequirement. This software is used tocalculate sizes of air inlets and outlets toachieve optimum performance.

    Passivent productsPassivent has developed a range of products(including acoustically treated and hybridplus options) which can be incorporated intonatural ventilation systems for commercialbuildings. More information on these isavailable on request.

    Passivent Products are also embedded withinEDSL’s TAS programme for ease of thermalmodelling.

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    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .THE BACKGROUND

    The NatVentTM projectNatVentTM was an EC/EU-funded projectinvolving nine partners in seven countries,co-ordinated by the UK Building ResearchEstablishment and published during 1999.Passivent, as one of the NatVentTM partners,has taken a leading role in developingpractical solutions for the commercialbuilding sector. Passivent have beenproviding solutions to clients since.

    The NatVentTM group has carried out an in-depth study of natural ventilation and foundthat it is an effective design strategy foroffice buildings in the UK and otherEuropean countries with a moderateclimate.

    BenefitsThe many benefits of naturally ventilatedbuildings identified by the NatVentTM projectinclude:

    Cost efficiency● Naturally ventilated buildings typicallyconsume less than half the energy used inair-conditioned buildings.● Initial capital costs are also lower,typically by 15%.● Operating costs can be 40% less in termsof energy consumption.● Due to simplicity and durability of thecomponents, costs are spread over a longerlifetime.● Maintenance costs are significantly lower.● Less space is required for plant roomsand services distribution.

    Productivity gains● 90% of building occupants prefernaturally ventilated buildings.● Fewer incidents of sick buildingsyndrome are reported.● Occupants are provided with control overtheir immediate environment.

    Environmental gains● Significant reduction in emissions of thegreenhouse gas carbon dioxide (CO2).● Avoids using ozone-depleting substancesas refrigerants.

    CO2 reduction37% of CO2 emissions in the UK derive fromenergy consumption in buildings. Allbuildings, both new and refurbished, mustuse energy more efficiently to reduceenvironmental damage. Energy PerformanceCertificates (EPCs) have been introduced tohelp improve the energy efficiency ofbuildings.

    Building Regulations Approved Document LConservation of fuel and power includesperformance targets for CO2 emissions.

    System designGood design is based on theprinciple that adequateventilation is essential forthe health, safety andcomfort of buildingoccupants, but thatexcessive ventilation leadsto energy waste anddiscomfort. Buildingtightness, good ventilationfor occupants and naturalventilation design shouldbe considered together for asuccessful energy-efficientnatural ventilation scheme,as set out in BuildingRegulations.

    Strategies have to be developed for winterand summer often requiring differentproducts and control logic. Winterventilation to maintain good indoor airquality must be balanced against minimisingheat losses. Summer ventilation must offsetexcessive daytime heat gains and providefresh air distribution.

    Since 1999, Passivent have continuouslydeveloped our solutions, whilst sticking tothe findings of this project.

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    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .NATURAL VENTILATION STRATEGIES

    Single-sided ventilationSingle-sided ventilation, usually throughlarge façade opening devices, is mainlydriven by wind turbulence. Relatively lowventilation rates are achieved except withpenetration depths of less than 21⁄2 times thefloor-to-ceiling height. Penetration depthsare based on typical office low occupantdensities and are not applicable to higheroccupant densities such as teaching spacesand seminar rooms.Hybrid Plus versions of single sidedventilation systems are available to pre-warm incoming air in winter and assist withairflow during the warmer summer months.

    Cross ventilationCross ventilation achieves good air changerates driven by pressure differences acrossthe building. This method uses controllablehigh-capacity inlets/outlets on two opposingbuilding façades, and can achievepenetration depths of up to 5 times the floor-to-ceiling height.

    Mixed-mode ventilationNatural ventilation alone may not be suitablefor some rooms due to their depth, internalheat loads or other factors. In these casessome mechanical assistance can beincorporated e.g. low powered boost fans inoutlets or local comfort cooling devices.

    Background ventilationis necessary to provideadequate indoor air qualitythroughout the year. This can be achieved byvarious types of façademounted controllableventilators often controlled by internal CO2 levels.

    Rapid ventilationis necessary to remove excesstemperature from the spaceand is of prime importanceduring the summer.

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    Passive stack ventilationPassive stack ventilation (PSV) is the mosteffective natural ventilation strategy as it usesa combination of cross ventilation, buoyancyand the suction effect as the wind passes theterminal. It can ventilate to twice the depth ofcross ventilation, up to 10 times the floor-to-ceiling height, as the outlet can be in thecentre of a building. It can be an effectivenight cooling strategy as internal and externaltemperature differences at night are typicallyhigh, so increasing convection. PSV stacks canrange from large central atria to local stacksfeeding to roof-mounted terminals. HybridPlus versions of passive stack ventilationsystems are available to pre-warm incomingair in winter and assist airflow during thewarmer summer months.

    Displacement ventilationDisplacement ventilation uses wind drivenroof-mounted terminals with separatedchambers to channel air down into thebuilding regardless of wind direction. Thecooler, denser air displaces warmer, lighterair upwards, which is drawn out through theleeward chambers of the terminals. Thismethod can be used as part of a nightcooling strategy.

    Night coolingNight cooling uses the lower externaltemperatures at night to reduce thetemperature of the building fabric, by meansof automatic ventilation devices. The cooledthermal mass of the building is used the nextday to reduce internal temperatures. It is best suited to heavy weight structures. A night cooling strategy in a suitablebuilding design can reduce peak internaltemperatures by 2 - 3ºC the following day.Natural night cooling by lowering theambient temperatures can delay the use ofenergy consuming cooling equipment.

    SYSTEM CONTROLAn efficient and effective natural ventilation system should move airthrough the building in a carefully designed manner. The sizing and positioning of inlets, stacks and outlets are critical inachieving the correct ventilation performance.Control of systems is also important to ensure maximum effectivenessand provide the correct level of ventilation at minimum energy cost.

    Control components are available from Passivent that vary from simpleoccupant controlled devices to intuitive systems triggered by sensorswhich detect temperature and CO2, matching ventilation to demand.These can be integrated with an overall building management system(BMS) via our intelligent controls system.

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    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .SUSTAINABLE BUILDING DESIGN

    Sustainability can be best defined as“improving the quality of life for all withoutdamaging the environment or the ability offuture generations to meet their ownneeds” Vision 21.

    Sustainable buildings will encompass allfacets of design but include naturalventilation, optimum use of daylighting,high thermal mass, solar shading, improvedlevels of insulation, use of renewable/recyclable materials and effective lightingcontrols.

    It is important that all members of thedesign team sign up to the achievement of a common project environmental policy,which acknowledges a commitment tomaximise the environmental potentialwithin reasonable constraints. Guidancedocuments such as BREEAM can lead aproject to produce a successful andsustainable ‘green building’.

    The generic project illustrated opposite demonstrates many of theventilation and daylight considerations required to achieve asustainable building.

    Ground and First Floor Ventilation (illustrations 1 and 2 opposite)

    The inlet path for natural ventilation is via openable high-levelfaçade devices and windows. The high level openings allow fresh airto pass into the ceiling void and then into the space below. This strategy provides cooling of the structure at night duringsummer months as well as tempering incoming air the next day. In winter this eliminates sources of draughts by opening windows, asthe fresh air passing through the ceiling is prewarmed. A degree ofexternal acoustic attenuation is also provided via the ceiling void.The openable windows are used to boost the ventilation rate, whilstproviding additional user control of their own environment.

    The façade and ceiling outlet louvres are insulated, so closure atnight and during the morning warm-up period reduces heat loss,during cooler periods. These motorised louvres are controlledautomatically with manual override facility, to allow user interface.

    The room with higher internal heat gains has been located on thelower floor of the North façade as this experiences the lowest solargains. A boost fan or comfort cooling can be incorporated to providea mixed mode strategy during warmer weather. The roof-mountedterminals provide large fixed openings with Class-A rain rejectionperformance.

    Daylighting and Corridor Ventilation (illustration 3 opposite)

    External southerly solar shading reduces the external solar gains insummer, whilst the building orientation maximises passive heat gainin winter. Tubular rooflights allow natural daylight to enter the rearof the rooms. The reduced window area on the South façade,together with solar control glazing, reduces external heat gains.Daylight control is used with efficient artificial lighting to reduceenergy usage.

    Ventilation of the corridor is achieved using insulated openablefaçade devices at either end. The air is exausted via high levelopenings in the glazed façade. These motorised louvres arecontrolled automatically.

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    Illustrations based on a design produced byStride Treglown Davies

    Illustration 1Ground Floor Ventilation

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    Illustration 2First Floor Ventilation

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    Illustration 3Daylighting and Corridor Ventilation

  • PASSIVENTNorth Frith Oasts, Ashes Lane, Hadlow, Kent TN11 9QU Tel: 01732 850770 Fax: 01732 850949

    Email: [email protected] Web: www.passivent.com

    Passivent maintains a policy of continuous development and reserves theright to amend product specifications without notice.

    A division of Building Product Design Ltd. Company Registration No: 3944123

    FURTHER INFORMATION

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    910038 October 2019 4671

    ServicesPassivent offers a comprehensive design andadvisory service tailored to your specificproject, covering ventilation design andproduct selection. Advanced software basedon CIBSE AM10 is used to calculate sizes ofair inlets and outlets to achieve optimumperformance.

    Names of approved installers can be providedon request.

    Quality assurancePassivent is committed to the continuousimprovement in the quality of its products,service and method of operation. Its products are designed, developed andmanufactured under the ISO 9001 qualitymanagement system, providing anindependently audited assurance that theproducts will fulfil their intended purpose.The company also works to an occupationalhealth and safety (OH&S) managementsystem and has been accredited to theinternational standard ISO 45001.

    EnvironmentPassivent conducts all business processesunder the international ISO 14001 qualitymanagement system, giving an assurancethat all activities are carried out havingminimal impact upon the environment.

    Other productsPassivent sells a range of other ventilationand daylighting products for commercial anddomestic buildings including:

    Natural ventilation systems.

    Aircool® ventilators for windows, curtainwalling and walls.

    Airstract® roof terminals for passive stackand other natural ventilation systems.

    Airscoop® wind-driven ventilation terminals.

    Litevent combined ventilator and rooflight.

    iMEV intelligent mechanical extractventilation system.

    Hybrid Plus2 Aircool® ventilators.

    Hybrid Plus Airstract® ventilators.

    SoundScoop® acoustic transfer ventilationproducts.