Heating system of biogas digester by solar energy assisted air-source heat pump and influencing factors

A heating system of biogas digester by solar energy assisted air-source heat pump has been proposed. The heating system was supplied by hot water from plate solar air collector coupled with air-source heat pump. The system uses flat-plate solar air collector coupled air-source heat pump for heating the digester. For a 20 m3 biogas digester which is for small and medium-sized pigsty, the critical parameters of the heating system of biogas digester by solar energy assisted air-source heat pump were theoretically calculated and selection of the equipment was analyzed. The experiment has been established. It turned out that under the environmental temperature from 22°C to 27°C, it takes 85 min for the temperature of water in tank rising from 25°C to 50°C. The average coefficient of performance (COP) of heating system was about 3.4, the maximum is 4.5. So the effect of energy saving is significant and the system has a good promotional value. In addition, the system was affected by characteristics of air-source heat pump and flat-plate solar air collector, therefore, the further study is needed.