Effects of auxiliary heat sources on energy efficiency of active solar heating systems

According to the solar fraction and the energy efficiency of auxiliary heating equipments, analyses the effects of different auxiliary heat sources on the energy efficiency of active solar heating systems by converting energy consumption to primary energy, and believes that the active solar heating system must satisfy certain conditions for achieving energy saving effect. The results indicate that the auxiliary heat source and the solar fraction have a great impact on the energy efficiency of solar heating systems. Compared to the gas-fired boiler heating alone, the solar heating system assisted by electric heating is energy efficient only when the solar fraction is greater than 65.4%, which is very difficult to achieve for many real systems. The primary energy consumption of the solar heating system assisted by heat pump is lower in general instances (when the average COP of heat pump is 2.5, the solar fraction should be greater than 7%). When heat pumps with average COP above 3.0 or gas-fired boilers are used as auxiliary heat sources, the solar heating system is energy efficient, and the higher the solar fraction is, the more obvious the energy saving effect is.