A simple model for free cooling calculations.

We present a simple model to calculate the energy loss by free cooling at night. The time dependence of the exhaust air and wall surface temperatures is predicted by a simplified dynamic model that couples air flow, heat transfer, and wall temperature. For given ventilation rate the model predicts that the total heat extracted from the building during the night can be maximized by increasing the heat exchanging surface area and the thermal effusivity, of the wall materials. The influence of ventilation rate on the heat removed by freecooling at night is discussed. The model is tested in field measurements where the air flow is known from the stack effect.