A technique to improve the performance of displacement ventilation during cold climate conditions.

Ventilation by displacement is a type of ventilation where the air flow is thermally driven. By this arrangement one obtains two zones in the room - a lower zone with supply air conditions and an upper recirculation zone with extract air conditions. Cold climate causes downdraught from windows and external walls and results in a mixing of air from the upper into the lower zone. To avoid this problem during cold climate a new principle for ventilation by displacement is tested. Excess heat from the upper zone of the room is used for heating cold surfaces. The principle involves creation of a narrow space in front of the exterior wall, separating the cold wall from direct contact with room air. Extract air from the ceiling level is forced down through this space by an extraction fan. This method can advantageously be applied in large buildings where an external wall mainly consists of glass panes. In this case it might be appropriate to utilise the space between the inner couple of glasses for extract air. Tracer gas and temperature measurements were carried out in a test-room. The result shows that the ventilation efficiency improves when using the new principle. The thermal climate also improves due to less down-draught and higher surface temperatures.