A simple design method for mixed-mode ventilation systems in Australian car parks.

Above-ground multi-level car parks in large shopping centres are highly amenable to hybrid ventilation applications, particularly those centres with retail shops at the lower levels and car parks at the higher levels. The higher level car parks allow the benefit of higher wind velocity and better dissipation of car exhaust emissions than at ground level; at the same time, larger perimeter wall opening area can be used without affecting the aesthetic feature of the building. For a typical single-level car park with 600 parking spaces, the mechanical ventilation rate could be about 100 m3/s or more if it is fully enclosed. Thus, for larger shopping centres with multi-level car parks, the energy consumption for mechanical ventilation could be very high. Hybrid ventilation in car parks where natural ventilation is the primary ventilation source can result in large savings in operating costs. A design method for hybrid ventilation systems is proposed in this paper, where a multi-zone ventilation model (MIX2.0) and a pollutant dilution model are used to estimate the ventilation requirement of large car parks. Preliminary results have shown that the design method is in agreement with measured carbon monoxide (CO) concentration levels in the completed car parks for maximum allowable CO exposure target in the Australian Standard.