Evaluation of a soil heat exchanger-storage system for a greenhouse. Part i: system performance

The soil within agreen house represents an important thermal mass that can be utilized for heating or cooling. By providing asuitable heat exchange surface, soil can become arelatively low cost storage material that could help to reduce the consumption ofheating energy.Asoil heat exchanger-stor age system was installed in a commercial-type greenhouse. A heat exchanger-storage system, made of 26 non-perforated, corrugated plastic drainage pipes, 102 mm indiameter, was buried inthesoil. Two rows of 13 pipes, 12m long, were buried at 450mmand 750 mm depths, respectively. The pipes were parallel to the longitudinal axis of the greenhouse and were spaced 450 mm apart. A 0.75 kW blower circulated hot air collected in the greenhouse through the pipes at a flowrate of0.91 m/s. The heat stored was recovered both by convec tion at the soil surface and by forced circulation through the exchanger pipes. Aminimum temperature differential of2°C between theairand the soil appears suitable forefficient operation. Results indicate thatan average coefficient ofperformance (COP) of4.6 was obtained during the test period.