Research And Application Of Air-Water Hybrid Solar Heating System

Due to the specially advantage in solar energy ultilization and environment protection, solar heating attacts many researchs in the world. In recent years, many demonstrate buildings relate to solar heating were finished, which accumulate great experience in both theoretical and experimental. This paper made some research and discussion on a new type of solar heating system.A new type of air-water hybrid solar collector has been designed, which can use both air and water as the circulate media. This new solar collector can effectively prevent problems like frost crack, leakage and boiloff during the heating season, and reduce the heat exchange system cost during the non-heating season. Cost of the collector is cheap and suitable for practical application. Three prototype collectors are made by different manufacturers in different areas of China. Test results show that efficiency of the collector increase with the increasement of flow rate, ambient temperature and radiation intensity, and it was estimated to be above 50% in most of the time.A practical demonstrate solar air heating system has been established. Design, simulation and optimization have also been done. The system uses air to collect thermal energy and heating the building in the day time, surplus energy was stored in the pebble bed for using at night. Five different working modes were designed based on different working conditions: 1) heat storage mode, 2) heating by solar collector, 3) heating by storage bed, 4) heating at night and 5) heating by an auxiliary source. Annual solar fraction was predicted to be 53.0% by using TRNSYS. The system contains 473.2 m2 solar collector and 3458 m2 heating area.Construction experience is summarized to provide experience for constructe such kind of solar heating system. At last, full system test has been carried out in December 2010. Test results show that the insolation temperature of the collector in December is 89.1℃, heat loss from the air duct is about 17% compared to the total energy gain, and heat loss efficiency of the heat storage bed is 33.3%. During the second half of December, the highest value of daily solar fraction is 33.6%, with an average of 19.1%. The simulation result for this stage before is 22.8%. Decrease of this value is because the greater heat loss. The effect of direct heating in the daytime is obvious, because room temperature remains above 18℃in most time during the day. The comparison experiment between different kinds of heating room shows that the average temperature of a non-heating room is about 8℃, while the temperature of a solar heated room is 12℃. The effect of solar heating system is quite obvious.