Thermal Properties of a Solar Greenhouse with Inhouse Heat Storage and Heat Exchange Water Tanks for Nighttime Heating

Abstract

Environmental measurements were made on a solar greenhouse (Floor area 856m2) with inhouse heat storage and heat exchange water tanks for nighttime heating. The greenhouse was installed with double layer movable thermal screen. The heat exchange fans were operated, in principle, when the inside air temperature was above 22-23°C or below 13°C. The oil heater for auxiliary heating was switched on when the inside air temperature was below 11°C. Thermal properties of the greenhouse were analyzed as follows:1) Average solar energy collection factor, η, was 0.11.2) Average oil reduction factor, r, was 0.93.3) The coefficient of performance of the greenhouse system, C.O.P., was 2.4, on average.C.O.P. of the system was considered to be much improved if the friction loss of spiral air ducts in the heat storage and heat exchange tank (1.2mmAq/m at an air speed of 5m/s) was reduced to that of a normal rigid PVC pipe with a diameter of 90mm (0.4mmAq/m at an air speed of 5m/s).Average solar energy collection factor could probably be improved as high as 0.15 if the setpoint inside air temperature for ventilation was raised from 23-24°C to 27-28°C, while the setpoints for heat exchange fans were remained the same.As for the solar greenhouse, the split-night air temperature control was considered to be essential to improve the oil reduction factor. Much more work will be needed for making clear the effects of that on crop growth, as well as on the thermal properties of the greenhouse.