| The area of facility agriculture in our country ranks forefront in the world.In recent years,as an emerging technology of greenhouse environment regulation,Ground Source Heat Pump(GSHP)is given emphasis and studied by scholars,while most researches focus on warming effect of greenhouse,and they seldom study cooling effect.Embracing the physiological barrier caused to crop in the greenhouse by high temperature in South Jiangsu in summer,the experiment,starting from cooling,analyses the change in humiture,soil temperature,enthalpy difference,accumulation of heat capacity,energy consumption of geotherm exchange system at the superficial layer and thus concludes the cooling effect and practicability of the system in greenhouse of South Jiangsu.The experiment was conducted in a plastic greenhouse in Zhangjiagang,Suzhou from May to July,2016.The greenhouse was running north to south,with the length of 88 m,span of 7 m,and the height of ridge 3 m.The greenhouse was assembled by the steel tube with the film of PEP film.The experiment selected two plastic greenhouses with the same external environmental condition and specification for processing and contrast.It set air inlet at the ridge and air outlet on the west side of greenhouse with 20 cm from the ground.The buried depth of pipe processing heat exchange in the greenhouse was 60 cm,there are 14 groups of pipes with the PVC pipe diameter of 110 mm.The input power of fan was 160 W,the measured air quantity was 0.2 m3/s,and the rotation was 40 r/s.The fan was turned off at6:00 a.m.and turned off at 6:00 p.m..The bottom ventilation was set at 80 cm from east and west side of greenhouse.The greenhouse was ventilated normally from 6:00 to 18:00 every day without using sunshade net.The crop was watermelon.The experiment tested ambient humiture,soil temperature of 60 cm,40 cm and 15 cm,and processing humiture at inlet and outlet of heat exchange pipe of greenhouse every 10 minutes,calculated and analyzed enthalpy difference,accumulation of heat capacity,average heat flux,average density of heat flow,and energy efficiency consumption.The main conclusions are as follows:1.Influence on indoor environment: the result indicated that from May to July in this region,the average temperature reduction in sunny day was 3.4 °C,in cloudy day was 1.46 °Cand in rainy day was 0.8 °C.The change in humidity by contrast was insignificant.It was40 %-90 % in sunny day,60 %-100 % in cloudy day and 80 %-100 % in rainy day.2.Influence on ground temperature: in three continuous sunny days,the ground temperature with the contrast depth of 60 cm was basically at the constant temperature of21.3 °C,and the soil temperature with the processing depth of 60 cm fluctuated at 21.8 °C±0.4 °C;the average daily temperature with the contrast depth of 40 cm was basically at22.7 °C,rising at 0.1 °C/day,and the average daily temperature with the processing depth of40 cm was 23.9 °C,rising at 0.5 °C/day;and the average daily temperature with the contrast depth of 15 cm was basically at 24.8 °C,and the average daily temperature with the processing depth of 15 cm was 25.7 °C,rising at 0.5 °C/day in a wave mode.3.Variation law of enthalpy: three consecutive days,the pipe inlet and outlet enthalpy difference was 0.166-9.56 kJ/kg,in 12:00-15:00 reached a high level,the heat storage efficiency is high,the fan is opened and closed for one hour before the minimum,the daily mean enthalpy difference was 3.37 kJ/kg.4.Thermal capacity analysis: in 10 hours a day for active heat storage,the accumulation of heat capacity was 3.94×105 kJ,the daily electricity consumption was 0.8×105 kJ and the energy efficiency ratio(COP)was 4.21.5.Energy consumption and cost analysis: compared with the investment cost of standard AC with highest energy efficiency standard,its investment cost was only 15.5 % and the energy consumption ratio was 1.4 times of that of AC.Compared with cooling method such as sunshade net and natural ventilation without energy consumption,its cooling effect still fell behind. |
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