Earth-air and earth-water heat exchanger design for ventilation systems in buildings

Earth-air heat exchangers are often used for (pre)heating or (pre)cooling of ventilation air in low energy or passive house standard buildings. Several studies have been published in the passed about the performance of these earth-air heat exchangers [1-8]. Often this is done in relation to the building energy use. Several software codes are available with which the behaviour of the earth-air heat exchanger can be simulated. De Paepe and Janssens published a simplified design methodology for earth-air heat exchangers, based on thermal to hydraulic performance optimisation [7]. Through dynamic simulations and measurements it was shown that the methodology is quite conservative [9-10]. Hollmuller added an earth-air heat exchanger model to TRNSYS [11]. In stead of using earth-air heat exchangers, earth-water heat exchangers are now getting more attention. In this system the ventilation air is indirectly cooled/heated with the water flow in a fin-tube heat exchanger in the inlet of the ventilation channel. The water-glycol mixture transfers heat with the earth by flowing through e.g. a polyethylene tube. In the second part of this paper a design methodology is first derived and then applied to this type of system