Experiment on heating effect in greenhouse by solar combined with air-source heat pump

Abstract: The facility agriculture is a kind of agricultural technology system, which is under controlled environment. With the weak of the natural environment in different degrees, the facility agriculture has important practical significance to change the mode of agriculture, realize the increase of farmers' income and realization for agricultural modernization in China. The development of facilities agriculture in China has been developed very rapid in recent years. However, the energy must be consumed in order to create a suitable environment for plants. The most common conditioning device use coal, electricity, oil and other non renewable energy. Not only making the environment pollution but also increasing the cost of greenhouse. According to statistics, the energy consumption accounts for about 20%-40% of the total operating costs in northwest region of China. Therefore, the design of a new energy-saving greenhouse temperature control system for the development of facilities agriculture in northwest China is quite important. After summarized the solar energy storage technology, water source heat pump technology, this paper combined the solar storage technology and air source heat pump technology, and designed the solar combined with air source heat pump for the greenhouse conditioning system. This system fully embodies the concept of active day lighting and active heat storage. This work improves a solar combined with air-source heat pump system for greenhouse heating experiment in Xi'an. Through experiments of the solar combined with air-source heat pump system, improved environmental factors such as greenhouse temperature, humidity and soil temperature can be compared, also the applied effect of solar combined with air-source heat pump system used in greenhouse in winter can be analyzed. Through the establishment of solar greenhouse air source heat pump heating system efficiency analysis model of three kinds of operation condition on the theoretical analysis of the performance. Compared to the reference greenhouse, the average temperature of the testing greenhouse on sunny and overcast was over approx 2℃. The minimum temperature and average temperature of the testing greenhouse on cloudy was 10.67 and 14.26℃, witch is 1.36 and 1.28℃ higher than the reference greenhouse. The minimum temperature and average temperature of the testing greenhouse in the snow was 8.71℃ and 9.25℃, witch is 3.59℃ and 3.86℃ higher than the reference greenhouse. The results show that this system not only significantly improves the air temperature and soil temperature in greenhouse, but also effectively reduces the humidity in greenhouse. Under the air-source heat pump operating condition, coefficient of performance of the system in experimental weather is between 2.09-2.45. Under solar combined with air-source heat pump operating condition, the system coefficient of performance is between 3.45-5.56. In sunny days, the time of solar storage heating is longer, the time of heat pump supplementary heating are shorter and coefficient of performance of the system is higher, as compared with those in other days. The floor heating combined with fan coil units is used as the heating ways in greenhouse, which can not only maintain higher indoor temperature and soil temperature, but also reduce indoor relative humidity. This work lay the foundation of the previous research for realization the active light and heat storage in Chinese solar greenhouse in the event of simplify the greenhouse structure and reduce the cost of construction.