Experimental study on the thermal characteristics of gravel layer in a solar thermal energy conversion system for house heating

In order to provide heat for a house without power and fossil energy consumption, a solar thermal energy conversion system for house heating was designed and manufactured. The system was mainly composed of a solar collector, gravel layer and a house. The solar collector had 28 vacuum tubes. The diameter and length of each tube were 47 mm and 1500 mm, respectively. The gravel layer with thickness of the 150 mm was put in the house whose length and width were 4 m and 2.7 m, respectively. The particle size of the gravel was ranged within 50～100 mm. Thermal characteristics of the gravel layer in the system heated by hot water natural circulation with solar collector were studied. Temperature of each element was measured. Results showed that it was possible to realize heat natural circulation when temperature difference at inlet and outlet of the system, and that of the gravel layer and cement mortar surface were occurred when delay time of heat transfer in each element was considered. In addition, it was confirmed that horizontal temperature distribution of the gravel layer and cement mortar surface appeared evenly. Heat storage period of the gravel layer was 10 hours and its radiation period was 24 hours. The quantity of heat storage of the gravel was about 49 MJ/day when the difference of daily average temperature of gravel layer and daily average temperature of the outdoors was applied.