| The facility agriculture is a new 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. Therefore, the development of facilities agriculture in China is very rapid in recent years. However, the energy must be consumed in order to create a suitable environment for plant. The most common conditioning device use coal, electricity, oil and other non renewable energy. Not only making the environment pollution but also increase 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 important. This paper summarized the domestic and international solar energy and heat pump technology, combined the solar and air source heat pump together, launched a comprehensive study on system design and selection, system modeling, optimization calculation, temperature experiment and the effect analysis etc,. The main work is as follows:1. According to the climatic conditions and the plant’s need, the thermal equilibrium in the 50m2 Chinese solar greenhouse was analyzed. The heating load was 122.15W/m2 (under the insulation condition). The solar combined with air-source heat pump system has been designed, including:solar collector systems, air source heat pump system, temperature control system and other supporting systems.2. The mathematical model of solar collector system and air source heat pump system is established. The simulation software is written in Visual Basic language. The results show that the air source heat pump system can be improved by reducing the temperature of cooling water and increasing the input frequency of the compressor. In outdoor moust cold conditions, the solar combined with air source heat pump system can satisfied the need of greenhouse heating with 6169.3W average heating capacity, the COP(Coefficient of Performance) 2.91. Based on the simulation optimization, the corresponding control strategies are formulated in three modes:the solar heating, air source heat pump heating, solar energy and air source heat pump heating.3. An experimental platform is built with the experimental system in Xi’an City. Through greenhouse comparison experiment, the results showed that:The solar combined with air source heat pump system has stable and obvious heating effort at night,which not only improve the air temperature and soil temperature, but also reduce the humidity in the greenhouse. From the perspective of the thermal economy,the new system’s COP under different weather conditions is between 2.09 to 10.9, which is better compared with the use of other coal,gas and other energy. The COP of the system is higher than heat pump separate operation mode. So the Solar combined with air source heat pump system is the preferred way of heating in greenhouse. The air temperature and soil temperature could be maintain higher by using floor heating and fan coil fans the terminal heating mode.4. The seeding and tomato cultivation experiment has been done in the greenhouse with the solar combined with air-source heat pump system. In seedling production, compared to the greenhouse without heating,tomato seedling root number and root surface area were increased by 9.8% and 39.5% in greenhouse experiments, and the tomato listed earlier 10 days in early spring growth. Thanks to reduced the disease index of tomato gray mould, early spring tomato yield rate of up to 23.3%; at the same time,compared to the greenhouse without condintion, the tomato red element, vitamin C and soluble sugar content were significantly increased and the sugar acid ratio increased by36.2%,the quality and taste of tomato was improve. Through the economic analysis of the combined solar energy air source of greenhouse temperature control system of the energy cost is coal-fired hot water heating energy cost of 30.7% and CO2 emissions is 44.6% of coal-fired heating system, cost saving effect is remarkable and outstanding environmental benefits, in facility agriculture has great potential for application. |
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