Most office buildings are designed based upon only the outdoor air quantities needed for suitable indoor air quality. However, a constant minimum volume of ventilation air is needed for VAV units depending upon occupant requirements. That is why interior zones are frequently conditioned with an independent system with variable air volume for low or no-load conditions. The building's air filtration needs, pollution sources, service cost and air resistance effect on energy costs should all be considered in system selection.
Economizer cycles can use outdoor air to cool the spaces; dry bulb or enthalpy control should be considered to optimize this practice for energy cost reduction. Zones should also be defined so that the economizer cycle does not increase heating requirements. This is achieved by considering separate air distribution systems for the interior and each major exterior zone.
Ventilation must also be provided for the elevator machine rooms, electrical and communications closets, as well as electrical and mechanical equipment rooms. While these are not mechanically cooled, some spot cooling may be needed. Mechanical rooms must be thermally and acoustically isolated from the occupied office areas.