| With the rapid development of economy and the continuous improvement of living standards,China's energy consumption continues to rise.Excessive consumption of fossil fuels leads to ecological damage,and coal-based energy structure causes urban air pollution,bringing about increasing ecological stress.Energy and environmental issues have become a key issue to be solved urgently attracting widespread concern.Therefore,improving the proportion of renewable energy in the energy structure and exploring more efficient energy utilization method are important guarantee to realize the sustainable development of society.By integrating solar thermal utilization technology and heat pump technology,solar assisted heat pump system(SAHP)can utilize solar energy as the heat source.On one hand,solar energy can effectively improve the heat pump system evaporation temperature,thereby improving the heat pump system performance.On the other hand,the refrigerant in heat pump system works as the coolant in solar collector,removing heat from solar collector to improve the collector efficiency.According to the media in solar collector,solar heat pump system can be categorized as:direct-expansion solar assisted heat pump(DX-SAHP),and indirect-expansion solar assisted heat pump(IX-SAHP).The direct-expansion solar assisted heat pump can operate effectively under high solar irradiation.However,due to the random change of solar radiation and other outdoor environmental conditions,the operation performance of the direct-expansion solar assisted heat pump is not stable.In indirect-expansion solar assisted heat pump system,the buffer storage is introduced to balance the solar irradiation and heating load and achieve stable operation,which also results in the complexity of structure and high initial investment.Concerning about the operating problem existed in DX-SAHP and IX-SAHP,the dual source multi-functional heat pump system and parallel type dual source heat pump system have been proposed and investigated.The main content and results are as below.The dual source heat pump system,which can operate all the year round by utilizing solar energy and air source to realize space cooling,space heating and water heating has been proposed.The experiment setup has been designed and constructed.In the enthalpy difference lab with a solar simulator which can crate stable external conditions,the performance of solar water heating mode and solar space heating mode in different operating strategies is investigated experimentally under different initial and boundary conditions.The results show that the evaporating capacity and condensing capacity in solar water heating mode increase with the initial water temperature,thus leading to the increase of energy consumption and COP of the system.In solar space heating mode,improving the initial water temperature can significantly improve the evaporating capacity and condensing capacity,as well as the energy consumption and COP.When the solar thermal system and multi-functional heat pump system operate simultaneously,the evaporating capacity,condensing capacity and COP increase with the rise of solar irradiation.According to the second law analysis,for both solar water heating mode and solar space heating mode,the exergy efficiency of the system can be improved with inputting solar energy at evaporating side,due to the rise of evaporating capacity and condensing capacity.In solar water heating mode,the exergy efficiency of the system increase with the rise of the water temperature in domestic water tank.In solar space heating mode,as the evaporating temperature decreases and the condensing temperature remains stable during operation,the exergy efficiency of the system increases.The dynamic model of the dual source multi-functional heat pump system has been proposed,and validated with the experimental results.The RMSDs between the simulation data and experimental results are below 5%.On the basis of the dynamic model,the performance of the system in different district under different operation conditions has been evaluated.To make full use of solar energy,minimize the source energy consumption,and meet the heat load,the annual control strategies in heating season and non-heating season has been proposed.With the annual operation strategy,the annual performance of the dual source multi functional heat pump in Hefei,Beijing and Xining has been evaluated by the dynamic model.The system can obtain relatively high COP all the year around in the above three cities.To overcome the operation problems of direct expansion solar assisted heat pump system and air source heat pump,a parallel type dual source heat pump system has proposed in this study.In the system,the PV/T evaporator is connected in parallel with the air source evaporator,so the system can recover energy from the ambient and solar irradiation to produce hot water and electricity.The dynamic model of the parallel type dual source heat pump is proposed to investigate the influence of solar irradiation,ambient temperature and PV packing factor on the performance of the PV/T evaporator and the overall performance of the system.The results show that in the parallel type dual source heat pump system,the PV/T evaporator and air source evaporator can compensate for each other under adverse operating condition.When the condensing temperature increases,the evaporating capacity in PV/T evaporator increases,while evaporating capacity in air source evaporator shows the opposite variation trend,which could reduce the negative effects on the overall performance of the system caused by the increasing condensing temperature.Under low solar irradiation,the evaporating capacity PV/T evaporator decreases,and air source become the main heat source.When solar irradiation increases,the evaporating capacity in PV/T evaporator increases,while the evaporating capacity in air source evaporator decreases,leading to increasing amount of refrigerant flows into the PV/T evaporator.Both thermal and electrical efficiencies of PV/T evaporator decrease with solar irradiation,while the power consumption and COP of the system show the opposite variation trend.When the solar irradiations are 100W/m2,200W/m2 and 300W/m2,the average thermal efficiencies are 49.27%,45.40%and 44.16%respectively,the average electrical efficiencies are 15.54%,15.46%and 15.36%,and the average COP of the system are 2.25,2.45 and 2.66.When the ambient temperature increases,both air source evaporator and PV/T evaporator can recover more heat from the ambient,leading to more refrigerant flows into air source evaporator.With the rise of ambient temperature,the thermal efficiency of the PV/T evaporator increases,while the electrical efficiency of the PV/T evaporator decreases,and both the power consumption and COP of the system increases.When the ambient temperature increases from 10? to 30?,the average thermal efficiency of the PV/T evaporator increases from 49.27%to 78.72%,the average electrical efficiency of the PV/T evaporator decreases from 15.54%to 14.81%,and the average COP of system increases from 2.26 to 3.08.In the parallel type dual source heat pump system,higher packing factor results in the degradation of heat gain and thermal efficiency of PV/T evaporator leading to more refrigerant flowing into the air source evaporator.While the electrical gain and electrical efficiency of PV/T evaporator increase with the rise of packing factor,which results in the rise of COP and energy saving efficiency of PV/T evaporator.When the packing factor of the PV/T evaporator increases from 0 to 1,the average electrical efficiency of the PV/T evaporator increases from 0 to 16.29%,the average thermal efficiency of the PV/T evaporator decreases from 55.88%to 44.64%,the energy saving efficiency of PV/T evaporator increases from 55.88%to 87.51%,and the average COP of the system increases from 2.14 to 2.32.Comparing the performance of dual source heat pump system employing normal solar thermal collector and PV/T collector,the system utilizing PV/T evaporator is more efficient for energy saving and performance improvement. |
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