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This allows air to be drawn into the building at

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This allows air to be drawn into the building at lower thanoccupant comfort temperatures thus allowing the buildingto cool significantly prior to the next day’s expected elevatedtemperatures. More technical information on reverse flowin stacks is published by Li (2002).2.7Commissioning,operation andmaintenance2.7.1Testing and commissioning2.7.1.1IntroductionAll ventilation systems and associated ductwork systemsshould be tested and commissioned, and those of significantsize (e.g. with a fan capacity above 1 m3·s–1) should also beleak tested. The needs of on-site regulation should beplanned and provided for in the design stage, otherwisebalancing the system within acceptable limits may not bepossible. The designer must accept the implications of thecommissioning procedures to which the air distributionsystem will be subjected. Inadequate commissioning willgenerated suction region so that ventilation can be drivenby both wind and stack-driving forces. Make-up air isprovided by trickle ventilators. The essential requirementis for the air in the chimney to be warmer than the ambientair. In dwellings, stacks are placed in ‘wet’ rooms and ‘dry’air is drawn from the living and bedrooms.Standard passive stack ventilation (PSV) systems have asimple inlet grille to the duct. Humidity-sensitive vents areavailable that can provide increased flows when humidity ishigh. Acoustic treatment may be required to reduce ingressof external noise. Fire dampers are required where ductspass through a fire-separating floor.For guidance on sizes and available products, manufacturerswill be able to advise on the maximum and minimum ductsizes to handle the required airflow through the stack orchimney. Manufactures can calculate driving forces andselect suitable equipment to achieve the desired results andprove this system will be able to cope with the requiredspecification.It is possible to enhance the stack pressures by means ofabsorbing solar gain (the so-called ‘solar chimney’)introduced via glazed elements. Location of the solar stackon the sunny side of the building in order to capture thesolar radiation will generally result in cooler air beingdrawn in from the opposite shaded side. Solar performancerequires careful thermal analysis because it relies on a rapidrate of heat transfer from the solar heated components tothe raising ventilation airstream.Care should be taken to ensure that there is a net heat gaininto the chimney during cooler weather, i.e. the solar gainmust be greater than the conduction loss. In cold weather,the conduction heat loss will result in low surfacetemperature for the glass that may be sufficient to generatedown-draughts inhibiting the reverse of the general upwardflow through the chimney. The wind-driving pressures canbe enhanced by careful design of the roof profile and/or thechimney outlet configuration.

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