Analysis of Benefits of Heating Method for Multi-span Greenhouse

In recent years, multi-span greenhouses have made considerable progress in our country. In the production and operation of multi-span greenhouses, heating in winter is the first requirement for ensuring the normal production of greenhouses. There are many types of greenhouse heating equipment, which are mostly coal-fired hot water boilers, followed by coal-fired hot-blast stoves. Different heating methods have different heating effects and different economic returns. The following is a comparative analysis of the heating effects and economic benefits of these two types of heating equipment. First, the coal-fired hot water boiler coal-fired hot water boiler heat transfer medium is hot water, the use of boiler heating, hot water pipeline layout more dense, greenhouse temperature distribution more uniform, the smaller the greenhouse temperature fluctuations. Because the specific heat capacity of water is larger, the greenhouse is less affected by interference, so that the greenhouse temperature fluctuation is relatively small. However, the one-time investment for coal-fired hot water boilers is relatively large. The investment in boilers, boiler rooms and trenches and other facilities and equipment is more than RMB 30 per square meter on average, the round-wing fins are invested RMB 40 per square meter, and the comprehensive investment is RMB 70. / Square meters or more. According to the analysis of the heat loss of a 3 hectare modern glass greenhouse in Shanghai by relevant experts from the Shanghai Jiao Tong University Refrigeration and Cryogenics Research Institute: the annual coal consumption of greenhouses is 1,668 tons, and the converted system operation unit coal consumption is 55.6 kg/sq. The meter costs 15.57 yuan per square meter, and the average annual heating cost is 1,038.25 yuan per 667 square meters. If the boiler capacity is less than 0.35 MW, the coal consumption per unit area of ​​the greenhouse will reach 66.4 kg/m2 and the cost will be 18.59 yuan/m2. That is, it will be higher. According to another survey, the heating cost of large-scale multi-span greenhouses in the Beijing-Tianjin region is 18,000 yuan - 26,000 yuan / 667 square meters (depending on the burning of coal or burning oil). It is difficult to lose money with such high operating costs. Second, the coal-fired hot blast furnace coal-fired hot stove heating is the use of a unique heat transfer method, the heated pure hot air directly into the greenhouse, compared with the hot water boiler, there is no heat capacity loss of the thermal medium at startup, The heat supply of the hot blast stove includes all the heat dissipation of the furnace body for the heating of the greenhouse; and the hot water boiler heats the heat sink by heating the coal and the hot water, and the heat sink reheats the three times of the indoor air heat exchange. The heat is lost in the process of transmission, and the effective thermal efficiency is less than 50%. In the process of starting the hot blast furnace, it is not necessary to first heat the medium. Therefore, it has the characteristics of rapid heating, and the required temperature can be achieved within half an hour of operation. The above advantages of the hot blast stove make its thermal efficiency reach 72%. In addition, the exported hot air has the function of dehumidification and defogging, which is extremely advantageous for controlling plant diseases. Due to the direct heating, the indoor temperature uniformity is slightly worse than that of the hot water boiler. The hot blast furnace is placed in the greenhouse and there is more dust around the furnace. The greenhouse heating and coal-fired hot blast stove designed and manufactured by the Ministry of Agriculture Planning and Design Institute has a total investment of 25 yuan per square meter, which is only 35.71% of the investment in hot water boilers. After practice in a large number of multi-span greenhouses in North China, the average annual coal consumption per unit area is 49.7 kg/m2, the cost is 11.43 yuan/m2, and the average annual heating cost per 667 square meters is 7624. 48 yuan is 42.36% of Beijing-Tianjin area greenhouse heating coal-fired hot water boiler. The coal-fired hot blast stove has the advantages of rapid temperature rise, dehumidification and defogging, and no fear of freezing of the water transmission pipeline after the fire is closed, and saves a large number of heat-dissipation fins to occupy land and the like, and is suitable for the national conditions, and can be used as the main heating device of the multi-span greenhouse.

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