Ventilation and energy flow through large vertical openings in buildings

After a short description of the physical phenomena involved, unified expressions are worked out describing net airflow and net heat flow through large vertical openings between stratified zones. These formulae are based on those of Cockroft for bidirectional flow, but are more general in the sense that they apply to situations of unidirectional flow as well. The expressions are compatible with a pressure network description for multi zone modelling of airflow in buildings. The technique has been incorporated in the flows solver of the ESP-r building and plant energy simulation environment. The relative importance of the governing variables (pressure difference, temperature difference and vertical air temperature gradients) is demonstrated by parametric analysis of energy performance in a typical building context and by comparison with experimental data in the literature. It is concluded that vertical air temperature gradients have a major influence on the heat transferred through large openings in buildings and should be included in building energy simulation models. Finally, it is discussed how the air temperature gradient, an input parameter which depends strongly on the heating and cooling mode, could be predicted.