System Optimization And Economic Analysis Of A Hybrid Power Gas Engine Heat Pump

The adjustment of energy structure and the laying of National Urban Pipelines provide convenience for the development of natural gas in new period.The hybrid gas heat pump（HGHP）has wide application prospects due to its better partial load characteristics,higher efficiency,lower emissions,and effectively balancing the demand of gas and electricity.However,most of the prior researches on HGHP were limited to basic system construction and performance analysis,and the quantitative optimization design and comprehensive evaluation analysis of the system have not yet been fully covered.A coaxial parallel hybrid power gas heat pump（HPGHP）with LiFePO₄ battery pack as a dual power source is selected for research in this article.The instantaneous optimization strategy based on the optimal torque curve of the gas engine is proposted and the exergy analysis method is applied to optimize the system and study the comprehensive performance of the system.The major contributions of current research may be summarized as follows:After a brief introduction of composition and operation principle of HPGHP,models of main components are constructed by combining experimental models with theoretical models.Taking the differences between load distribution under heating and cooling conditions,based on the optimal torque curve of the gas engine,the transmission ratios of the drive system are optimized with the thermal efficiency of the gas engine regarded as the optimization goal.The instantaneous control strategy based on the optimal torque curve of gas engine combined with the state of charge parameter of the battery is adopted,after that,the boundary conditions of mode switching are determined,and the performance parameters such as gas consumption and battery aging（SOH）are recorded in real time by means of the Matlab/Simulink platform.The results show that after a whole simulation period,SOC increased from 55%to 59.85%,and SOH decreased from 100%to 99.942%.Under the low load,medium load and high load,the thermal efficiency of gas engine presents a similar trend.With the increase of compressor speed,the thermal efficiency of gas engine first rises to a maximum and then decreases.The engine basically runs within the range of the prescribed optimal torque curve with the thermal efficiency at around 0.27.Compared with the results of Wang et al^[1],the average thermal efficiency increased by 1.16%,4.87%and 3.05%,respectively.As for the most unfavorable part of the waste heat recovery system,the flue gas heat exchanger,the exergy analysis method is applied with the annual net income of the unit flue gas heat recovery as the objective function,the area of the flue gas heat exchanger is optimized.The research indicates that with the increase of NTU,the annual net income will increase to the maximum and then decrease.When the NTU value is approximately 0.7,the annual net income of per unit waste heat recovery reaches a maximum of approximately RMB 1.77/GJ.At this time,the heat exchanger area is about 2.0 m².Finally,the calculation method of system operating cost including gas consumption and battery aging is constructed,and the economic comparison of HPGHP system and GHP system is carried out.Then,an energy utilization rate PER is selected as a measure parameter to evaluate the comprehensive performance of the system.Generally speaking,compared with traditional GHP system,HPGHP system still has significant economic advantages in terms of operation cost.What’s more,the average PER value of the HPGHP system is about 14.06%higher than that of GHP.The system optimization design and comprehensive performance analysis of a coaxial parallel gas heat pump are carried out by modeling simulation and experimental verification.The results show that the operating performance has been greatly improved especially under low load and high load condition,and the poor partial load characteristic of the GHP system is solved effectively.It provides theoretical basis and technical support for further research and optimization of the system.