THE PERFORMANCE OF A GREENHOUSE HEATED BY AN EARTH AIR HEAT-EXCHANGER

An earth-air heat exchanger consisting of 20 aluminium pipes 15 m long, 0.2 m in diameter and 0.2 mm thick, was installed at a depth of 2 m in a greenhouse of floor area 150 m2. The greenhouse air temperature was adjusted by blowing the greenhouse air through the pipe system whenever the air temperature dropped below 12.degree. C or exceeded 28.degree. C. Recorded from November to May, this resulted in a minimum mean night air temperature of 8.1.degree. C inside the greenhouse with an absolute minimum of 7.degree. C while the outside minimum mean and absolute minimum air temperatures were -0.8.degree. C and -3.0.degree. C, respectively, during the same period. The electrical energy used by the fan of the earth-air exchanger was only 20% of the energy input to the greenhouse from the earth-air heat exchanger.