AN ACTIVE HEAT STORAGE-RELEASE SYSTEM USING CIRCULATING WATER TO SUPPLEMENT HEAT IN A CHINESE SOLAR GREENHOUSE

In north China, Chinese Solar Greenhouses (CSG) with north heat storage wall has been widely used for energy conservation during cold winter. The solar energy is absorbed by north wall during daytime and converted into heat to be stored which could be released into CSG during cold nighttime. However, due to the low specific heat capacity and thermal conductivity of north wall, the heat stored is generally insufficient to maintain the inside air temperature at a suitable level for crop growth during cold nighttime. Therefore, an active heat storage-release (AHS) system using circulating water was developed to supplement heat in CSG. The AHS system consists of heat absorption-release unit with double-layer black plastic films fixed on north wall and water tank for heat storage. During the sunny daytime, the solar energy reaching the north wall is absorbed by water which is flowing through the films and the heat is then stored in the water tank. During the nighttime, the heat is released into the CSG by circulating the warm water from the water tank. The equipment test results showed that 68.4% of the solar energy to the north wall was absorbed by water and 65% of the stored heat was used for heating at nighttime. The average inside air temperature was increased by approximately 4.8°C, and the heat released from the AHS was 3.99 MJ/m2 of wall at night. Therefore, the AHS was demonstrated to be effective to increase the nighttime air temperature in the CSG and thus is a potential means for energy conservation in CSG.