Experimental Analysis And Theoretical Modeling Of A Solar/Gas Driven Ammonia-water GAX Heat Pump For Space Heating

In this study,we presented a detailed experimental investigation and theoretical modeling of an air source gas-solar driven absorption heat pump(LSAHP)using Generator Absorber heat eXchanger(GAX).It is presented in depth the design of the system and the equipment for the testing,located at Shanghai Jiao Tong University.The air source absorption heat pump with has nominal heating capacity of 55kW,utilizes ammonia-water as working fluid and is driven by the combination of solar and gas energy sources:a 45m~2 parabolic trough solar collector(PTC)and a direct-fired liquefied petrol gas(LPG)burner.The thermal performance of the solar collector is investigated under chosen on-sun conditions.Experimental results showed that solar thermal efficiency can reach up to 53.55%with direct normal insolation(DNI)of 450W/m~2 and entering thermal oil temperature in of 191~oC.Three operation modes were studied under different driven energy sources:i)LPG-Solar hybrid mode,ii)Solar only mode,and iii)LPG only mode.Mode i and ii were used to provide domestic hot water(55~oC)and mode iii was designed for district heating(45~oC).Under the average ambient temperature of 17.52~oC,20.0~oC,8.77~oC the averaged COPs of three modes are 1.54(mode i),1.63(mode ii)and 1.20(mode iii)respectively.Solar energy contributions reached up to 40.2%in mode i and 55.10%in mode ii.This experimental result proves that the GAX heat pump can considerably reduce the amount fossil fuel dependence if paired with solar PTC.The influence of operation conditions(ambient temperature,inlet hot water temperature and LP gas flow rate)on the heating capacity and system COP were studied under steady state conditions.Results indicated that higher ambient temperature,higher gas flow rate,and lower inlet hot water temperature can enhance the heat pump COP.In particular the increased ambient temperature positively affect the system performance.COP reaches 1.47 with 19~oC ambient temperature and 35~oC inlet hot water temperature.In the ideal case of negligible heat loss due to exhaust gas from the flue,it is calculated that the COP'reach 1.82 with unchanged operational conditions.Parallel to the experimental results,the simulation results are compared with the experimental data.The model is calibrated with sensitivity and quantitative tests under different parameters(high and low pressure,concentration of weak and strong solution and heating capacity of WCA,COND and EVAP)for a range of ambient temperatures.Comparison between the simulation result and the experimental data are investigated on the COP with different parameters(generator temperature,ambient temperature and inlet hot water temperature,total heating capacity).Results indicated that higher ambient temperature,lower inlet hot water temperature and higher generator temperature benefits the heat pump performance.Above all of them,the model results point out that the ambient temperature influence the most the heat pump COP,as suggested by the experimental investigation.From ambient temperatures of 7.8~oC to19.1~oC,the COP rises from 1.58 up to 1.82,which is a relative 13.19%increase.Despite comparison between the total heating capacities are reasonably matched,the match is less close for the COP confrontation.This is due to the fact that the heat capacity required by the generator in the model is calculated with the first law of thermodynamics,without taking into consideration the heat loss by exhaust gas from the flue.Thus COP from the model and COP'from experimental data are compared with a maximum deviation of 0.7%in the case of different ambient temperatures and a maximum deviation of 6.2%in the case of different hot water temperatures.