Heat exchanging characteristics of underground heat storage system in greenhouses

A new underground heat storage system for greenhouses which overcomes the structural drawbacks of the heat exchanging system with buried pipes was designed in order to make full use of underground saving heat and increase soil temperature and environmental temperature at night. Some parameters, including air temperature, air humidity at the inlet and outlet, and air flow velocity of flow at the outlet of heat exchanging pipes, were measured during heat saving and heat releasing in this experiment. The results indicated that air temperature and enthalpy at the inlet are distinctly different from that of outlet during heat saving and heat releasing and the differences reduce with the running time. Both the heat saved in the daytime and the heat released at night are greater than the electric energy consumption of the system, and the proper heat saving time is not more than 4.5 h.