Temperature Conditions and Thermal Characteristics in the Earth-Air Heat Exchange Greenhouse

It is a well-known fact that the ground temperature is stable all the year round. Paying attention to this fact, a new type greenhouse was devised for the purpose of making use of the difference between the temperature inside of the greenhouse and that in the ground. This newly devised greenhouse is called by the author “an earth-air heat exchange greenhouse”.Fig. 1 shows the structure of an experimental “earth-air heat exchange greenhouse”. Many earthen pipes are laid in the ground at the depth of 64cm, 100cm and 136cm in 10 rows at 36-cm intervals, so that they may serve as the earth-air heat exchangers. With the help of a motor-fan installed on the wall, the air is circulated throughout the inside of the greenhouse and the pipes. The greenhouse room is heated in the night-time, while cooled in the day-time by the circulated air which was heated or cooled by passing through the heat exchange pipes. Since the ground has by a the grater heat capacity than air, excessive heat conveyed by the air can easily be accumulated in the ground in the day-time. In other words, in case of this greenhouse, its heat balance phase is by far expanded, as compared with that in the case of a conventional geenhouse. Therefore, extra-high temperature in a greenhouse is saved as a result of accumulating the excessive heat in the ground during the daytime, and the accumulated heat is available in the night-time.An example of changes in temperatures in winter season is shown in Fig. 2. The temperature under the ground being maintained at about 10°C, the air temperature inside of the greenhouse is kept at about 7°C, even if the outside air temperatue drops to -5°C in the night-time.This closed thermo-control system is especially effective in case of CO2 and other gas control culture in the greenhouse.