Experimental and numerical study of a duct/heat exchanger unit for building ventilation

A mechanical building ventilation unit is presented that unites two functions: fluid transport and heat recovery. Aluminum fins in the supply air duct and in the adjacent extract air duct increase the heat flow from fluid to fluid. This unit is intended to be used mainly for residential ventilation and was investigated by means of experiments and simulations. Airflow rates, temperatures, air humidities and pressure differences were measured on a prototype device in an experimental set-up. Additionally, using a computer program for two-dimensional heat conduction analysis and a simple analytical model, the efficiency of heat recovery was calculated and compared with measurements. Afterwards, the influence of variations of the heat exchanger geometry on thermal efficiency was investigated by means of simulations. It was shown that using this concept it is possible to realize a ventilation unit with high-efficiency heat exchange, e.g. temperature efficiency of 0.7 at a duct length of 6 m.