Proximity effects: air infiltration and ventilation heat loss of a low-rise office block near a tall slab building.

In the mid-1980s, two London architects postulated that deflection of higher speed air from tall slab buildings could increase air infiltration from a neighbouring low-rise block, increasing its associated ventilation heat loss. These issues have been of much concern during the past two decades among designers, developers and local authorities; especially those considering in-fill near tall buildings. This preliminary study looks at the ventilation and space-heating loss of a three-storey low-rise office block located near a taller nine-storey slab building. A multi-zoned prediction program is used to determine the air infjdtration through the envelope of the low building and ventilation through its purpose-provided trickle ventilators. Measurements carried out in the Building Research Establishment's Environmental Wind Tunnel provide the necessary input data on surface wind pressure coefficients. The wind tunnel measurements show that a tall building near to (and in line with) a low building markedly changes the distributions of wind pressures on the latter. Analysis carried out here confiis that this near-proximity does have an impact on ventilation. Compared with an isolated building: (a) ventilation rates are reduced by as much as 35% for winds blowing normal to the front (broad) face, (b) the average ventilation rates expected during the heating season are reduced by about 15% if the buildings are on an open site and by 10% if sheltered. However, adequate ventilation for occupants is met by using the controllable trickle ventilators, and (c) overall space-heating requirements are marginally increased by 3% as a result of higher convective losses offsetting the reduced ventilation losses.