Two-zones model for predicting passive stack ventilation in multi-storey dwellings.

Proper dimensioning of natural ventilation system for multi-storey buildings is a critical matter, because the air flow rate depends on many parameters as outdoor temperature, wind, distribution of air inlets and envelope air leakage, characteristics of outlets and cowls. The computer code GAILNE BIZONE predicts the ventilation rates in multi-storey dwellings equipped with passive stack ventilation system. Each level is treated as a two-zones configuration, but each zone is linked to the collective ventilation shaft of the building. The model calculates the pressures in every zone of the building and the ducts, using iterative method to balance the mass flows in and out of each zone. One of the both zones represents the kitchen, the other one the rest of the dwelling including the bathroom and the toilets. The kitchen door that links the both zones is represented by an internal transfer opening. The model takes into account the common cowls used to avoid reverse flow, but also the cowls with motorised device. The latter are very useful, especially to achieve the peak flow rate when cooking or when the stack effect is insuficient because of moderate wind and outdoor temperature. In addition, the model makes it possible to treat a gas appliance linked to the exhaust duct of the kitchen. The basic modelling method used is known as the 'ping-pong' method because the two-zones model combines two models which are called in turn. In the first step, the ventilation rates are calculated in a stack of storeys representing a part of dwellings, then for the other part. The both models are called in turn until that, for each dwelling, the exchanged flow rate between the two zones are balanced. Examples of applications conducted with the two-zones model are presented in this paper.