Experimental Study Of The Direct Expansion Solar-assisted Heat Pump With Finned-tube Evaporator

How to reduce building energy consumption is one of the issues that are widely concerned.Direct expansion solar-assisted heat pump(DX-SAHP)has been proven to be an effective energy-saving application.Due to simple structure,good economy and high thermal performance,DX-SAHP attracts a lot of attention of people.Because the traditional DX-SAHP with plate type evaporator occupies a large space and has low thermal performance under low solar irradiation,we design and build a new DX-SAHP with finned-tube evaporator.In the enthalpy difference lab with a solar simulator,the effects of solar irradiation,ambient temperature,relative humidity,and wind speed on the space heating performance of the finned-tube type system are experimentally investigated.The effects of ambient temperature,relative humidity,and solar irradiation on the thermal performance of the system and economic efficiency are compared and analyzed between the finned-tube type system and the plate type system.The conclusions are as follows:1.We have studied experimentally on the thermal performance of the finned-tube type DX-SAHP when the ambient temperature is 7.0℃ and the solar irradiation changes from 0W/m2 to 400W/m2.It is found that the thermal performance of the finned-tube type system is improved with the increase of solar irradiation.Compared with finned-tube type DX-SAHP,the COPs of plate type DX-SAHP are low,but its improvement of performance with solar irradiation is much great.The COP of finned-tube type DX-SAHP increases from 2.56 to 2.58,and the COP of the plate type DX-SAHP increases from 2.07 to 2.36 respectively at the ambient temperatures of 15.0℃ with the solar irradiation ranging from 0W/m2 to 500W/m2.2.The thermal performance of the finned-tube DX-SAHP is studied experimentally with the solar irradiation 300W/m2 and the ambient temperatures 5.0℃,10.0℃,and 15.0℃ respectively.The results indicate that with the increase of ambient temperature,the overall performance of the finned-tube type DX-SAHP has been improved and the COPs are 2.22,2.42,and 2.58 respectively.Compared with finned-tube type DX-SAHP,the thermal performance of the plate type has also been improved,but the amplitude of enhancement is small.When the ambient temperature increases from 5.0℃ to 15.0℃,the COP of plate type DX-SAHP rises by 6.6%while the value of the finned-tube type increases by 16.2%.3.Frost forms on surfaces of both types of DX-SAHP when the ambient temperature is 5.0℃ and the relative humidity is 70%and 90%.Moreover,the higher relative humidity,the more severe of frosting.Frosting enhances the overall performance of the plate type,while the performance of finned-tube type significantly declines due to the heat transfer deterioration caused by the frosting.4.Wind speed has great influence on the thermal performance of finned-tube type DX-SAHP.When the wind speed increases from 0 to 1.38m/s,the thermal performance of the system is greatly improved and the COP increases from 1.71 to 2.37;when the wind speed continues to increase,the system performance remains almost unchanged due to the limitation of convective heat transfer coefficient.