Experimental Research On Greenhouse Heating With Direct-expansion Solar-assisted Heat Pump

In order to solve the problem that produced tremendous crisis of emission greenhouse gas,waste energy and unsustainable by heating greenhouse method of traditional,a heating greenhouse measurement was studied that rhizosphere-air heating with direct-expansion solar-assisted heat pump（DX-SAHP）of tomato in large-span greenhouse.The heating effect,coefficient of performance（COP）and heat-collecting efficiency were tested.The operation mode under different weather conditions was optimized.A set DX-SAHP was designed and installed in the multi-span greenhouse by calculated the load of heating in cold winter.The COP,collect-heating efficiency,the rate of coal saving and greenhouse gas emission was tested.In order to further improvement control level of multi-span greenhouse environment,an airtight active heat storage-release system（AAHS）was designed and installed.The feasibility of overall system,stability and uniformity of fluid as well as the relationship of heat-collection volume flow rate fluid and condition.The results were as followed:1)Under the conditions of consecutive cloudy days and consecutive sunny days,the heat utilization efficiency of the heat releasing system was higher than 97.2%and 92.7%corresponding;Under different weather conditions,the rhizosphere temperature and air temperature in the experiment area were above17.9 and 11.6℃respectively,which were 1.5 and 3.6℃higher than those of the control area;The relative humidity in the experimental area was below 90.8%,which was 3.2%lower than that of the control area;The energy-saving rate of the whole system under different weather conditions was higher than 47.2%,and the COP was above 1.9;Under different weather conditions,the heat collection system could reach the set temperature objective for heating within the set time while keep the COP above 2.3 and the heat-collecting efficiency higher than 149.6%;Additionally,it could realized the greenhouse energy conservation goal by using the operating mode of DX-SAHP,which could be adjusted in accordance with variation in solar radiation intensity and the water temperature in the tank.2)The heating load of the multi-span greenhouse in Beijing is 145.4W/m²,and the DX-SAHP with a power of 16.6W/m² can meet it.The tested of DX-SAHP results showed that the heat-collecting efficiency of DX-SAHP higher than 489.2%,and that had a little lower with time delay of start-collecting.No matter how weather conditions DX-SAHP could achieve set temperature 50℃,and that the sunny days’COP higher than cloudy days’0.6.However,under different weather conditions COP almost same in night,sunny night and cloudy night was 2.5 and 2.4 respectively.DX-SAHP have a positive effect the days and night saving-coal higher than 217.7kg and 119.6kg respectively,reducing emission CO₂ higher than 544.3kg and 298.0kg respectively,reducing emission SO₂ higher than 16.3kg and 9.0kg respectively in different weather conditions.3)A set of AAHS was designed and installed in multi-span greenhouse,which was tested.The results showed that the AAHS was feasibility,the fluid of heat-collectiing stability and uniformity.The range from3.51m³/h to 9.5m³/h of volume flow of fluid with AASH was consist of 36 heat-collector plate,which input power was 0.6kW to 1.0kW corresponding.The range form 0.10m³/h to 0.27m³/h of volume flow of fluid with AASH heat-collector per-plate,which input power was 0.017kW to 0.028kW corresponding.In same heat-collection conditions maximum flow total heat-collecting 574.6MJ higher than minimum186.9MJ and consumption power 28.9MJ higher than 11.9MJ,heat-collecting efficiency 92.7%higher than 30.0%,heat-collecting COP 19.2 lower than 2.3.The heating method combining rhizosphere and air not only was good for heating greenhouse,but good enough utilization heat-energy and improvement heat-collection efficiency.The COP could be improvement by adjusted operation mode of DX-SAHP according to heat-collecting conditions.Meanwhile,there are reducing waste-energy and avoid pollution by the application of combining AASH and DX-SAHP in multi-span.Therefore,the heating measurement of AASH and DX-SAHP combining provided a new way to solution multi-span or others heating in cold winter.