Technical and economic performance study on winter heating system of air source heat pump assisted solar evacuated tube water heater

Abstract

Winter heating with clean energy is very important for coal substitution in rural areas of China. In Northwestern China, winter weather is usually below zero and winter heating lasts at least 5 months, which is a big expense for rural residents. It is well known that solar energy, air source heat pump and other energy-saving technologies could effectively cut down the expenditure. However, it is difficult to consider the economics and stability of winter heating with free solar energy alone, and the cost of winter heating with heat pump alone is too high for locals to afford. Therefore, the concept of air source heat pump assisted solar energy was proposed and a solar evacuated tube water heater -air source heat pump system was built in Lvhua Village, Lanzhou City. Experiment and simulation studies were carried out to discover the technical and economic performances when the system operates in three modes, namely, heating by solar water heater, air source heat pump and solar water heat pump (heat pump used hot water from solar collector as heat). Simulation results were verified and highly consistent with experimental results on December 20th, 2021. The results show that in whole heating season, air source heat pump assisted solar energy system greatly improves technical and economic performance in comparison with heating by solar water heater and air source heat pump. The average daily collector efficiency in the heating season is 45.5 %, and the average daily effective solar heat collection is 43.6 kWh. During the heating season, the effective solar heat collection is 6587.1 kWh, the electricity consumption is 5229.7 kWh, the heat supply is 16392.2 kWh, the solar fraction is about 40.2 %, the energy efficiency ratio is 3.1, the average COP of solar water heat pump is 3.5, and the average COP of air source heat pump is 3.0. The primary energy saving rate of the system is 66.4 %, the dynamic investment pay-back period is 6.5 years, and the CO2 emission reduction is 10960.7 kg. The results demonstrate the feasibility of the winter heating system of air source heat pump assisted solar evacuated tube water heater, which provides a new way for the heating of rural single buildings in cold areas.