Exhaust-air heat pump technology has proven to be the most efficient way of recovering heat from a ventilation system. In Sweden this technology is now playing an important role in the heating market, particularly in new singly-family homes. However, larger exhaust-air heat pump systems are also being installed here, the largest unit, with a heat output of 3.4 MW, serves 2,500 flats. This article describes some of the projects that have contributed to the development of exhaust-air heat pumps in Sweden.
Direct capture efficiency of a local exhaust system is defined by introducing an imaginary control box surrounding the contaminant source and the exhaust opening. The imaginary box makes it possible to distinguish between contaminants directly captured and those that escape. Two methods for estimation of direct capture efficiency are given: (I) a numerical method based on the time-averaged Navier-Stokes equations for turbulent flows; and (2) a field method based on a representative background concentration.
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