CONDITIONING THE GREENHOUSE CLIMATE BY MEANS OF A HEAT PUMP
Taking advantage of the presence of an underground water table, located at a depth of about 3 m below the soil surface, as heat source, a water-water heat pump and two different heat distribution circuits (subsurface soil pipe grid and fan coils) were used to conditioning the inside ambient of two tunnel type plastic cladded greenhouses. The heat distribution systems were able to delivery, in steady state, a heating power of about 70W.m-2(pipe grid) and 140W.m-2(fan coils) of greenhouse floor. For a continuous regime, for the same winter night meteorological boundary conditions and for the same circulation water temperature, different inside night air temperatures were achieved with each system: for the greenhouse with the fan coil system we had a difference of about 11°C between inside and outside air temperature; for the greenhouse with underground pipe grid system that difference was only 2°C but the temperature of the upper 20 cm thick soil layer was about 2.5°C above its normal value in the absence of heating.
Silva, A. and Rosa, R. (1989). CONDITIONING THE GREENHOUSE CLIMATE BY MEANS OF A HEAT PUMP. Acta Hortic. 245, 232-235