| The temperature,relative humidity,air flow rate,use of heating devices and the design of heating methods in the greenhouse are all key factors affecting the growth and development of plants in the greenhouse.However,the "greenhouse effect" can lead to an excessive increase in air temperature inside the greenhouse,which affects the normal growth and development of plants,so it is necessary to do a good job of ventilation.In addition,in order to provide the temperature required for the normal growth and development of plants in greenhouses,greenhouses are usually heated during the cold night and winter,but the phenomenon of inadequate heating devices is common in existing greenhouses,and the heat is often provided at the cost of coal burning,which also causes serious environmental pollution and primary energy consumption.Therefore,this paper proposes a solar air collector-air source heat pump system for greenhouses,which combines solar energy technology and heat pump technology to provide sufficient heat to achieve efficient heating of greenhouses on continuous cloudy days and in winter,while heat and moisture recovery of wet air in greenhouses can be achieved according to the characteristics of heat exchangers,and the system aims to provide all-weather suitable environment for plant growth in greenhouses.In this paper,the operational performance of the system under different typical working conditions is experimentally studied with the greenhouse in Lanzhou,Gansu Province as the test target,and the energy saving,environmental protection and economic benefits of the system during the heating season are evaluated.The main research contents and conclusions of this paper are as follows.(1)The construction work of the system is carried out,and the relevant testing scheme and control strategy are given.Firstly,the temperature and humidity distribution in the greenhouse is studied experimentally,and the results show that: when the solar radiation is strong during the daytime,the closer the measurement point in the greenhouse is to the shed film,the higher the measured temperature is,and the humidity at the same measurement point shows an opposite trend to the temperature.(2)The heat collection efficiency of the collector is 56.2 % under sunny conditions and23.6 % under snowy conditions during the heating season.The stronger the solar radiation,the higher the collector efficiency and the better the collector performance.(3)Based on the test data of system operation under different typical working conditions in the heating season,the heating performance of the system can be analyzed and studied:the heating capacity of the system under sunny,cloudy and cloudy working conditions are100.2 kW·h,112.3 kW·h and 157.8 kW·h respectively,and the power consumption is 30.1kW·h,36.1 kW·h and 53.6 kW·h respectively,and the COP of the air source heat pump was3.4,3.2,and 3.0,respectively,and the COP of the solar heat pump was 4.0,3.5,and 3.1,respectively,and the system energy efficiency ratio was 3.3,3.1,and 2.9,respectively.(4)After adding the heat and moisture recovery mode to the system,two different modes of heat and moisture recovery operation are investigated.One is the heat exchanger-fan mode and the other is the combined heat and moisture recovery heat pump mode.In the combined heat and moisture recovery heat pump mode,the temperature difference between air and water is the largest,so the heat exchange with the hot air in the greenhouse is also the largest,and the heat collection of the combined heat and moisture recovery heat pump mode is 66.7%higher than that of the heat exchanger-fan mode.(5)For the experimental data of system operation under different typical working conditions in the non-heating season,the analysis and research can be obtained: the COP of water-side heat pump under sunny,cloudy and cloudy working conditions are 4.2,4.2 and 0,respectively,and the COP of solar heat pump are 4.4,4.2 and 4.0,respectively.the waterside heat collection under heat and moisture recovery mode are 9.6 kW·h,8.9 kW·h,respectively,and the average air outlet temperature The average air outlet temperature was reduced by 5.6℃ and 5.3℃,which effectively prevented all heat and humidity from being dissipated during the ventilation process of the greenhouse.(6)In terms of energy saving analysis,the cumulative heat supply of the system for the whole heating season is 16938.3 kW·h,which can save 3713.02 kg of standard coal if traditional energy coal is used;in terms of environmental protection analysis,the emission reduction of carbon dioxide during the operation of the system is 9884.06 kg,the emission reduction of sulfur dioxide is 74.26 kg,the emission reduction of nitrogen oxides is 74.26 kg,and the emission reduction of soot is 37.13 kg.In terms of economic analysis,the initial investment of solar air collector-air source heat pump system for greenhouse is high,but the operating cost is low,and the dynamic payback period is 6.6 years.This paper designs and establishes a solar air collector-air source heat pump system for greenhouse,which combines solar energy technology and heat pump technology to form a new technology of solar heat pump heating,realizing efficient heating of greenhouse,and at the same time can realize heat and humidity recovery of wet air in greenhouse,providing allweather suitable environment for plant growth in greenhouse. |
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