Research On Performance Of Self-coupling Heat Pump Air Conditioning System In Hot Summer And Cold Winter Regions

Ground source heat pump is an energy-saving technology that efficiently utilizes shallow geothermal energy.It has been widely used in the field of building air conditioning.Driven by the concept of energy conservation and environmental protection,its technology is developing rapidly.For regions with hot summer and cold winter,the cooling load in summer is greater than the heat load in winter,and the air conditioner runs for a long time in summer.The impact of the heat accumulation problem caused by the operation of the ground source heat pump will gradually increase,and the temperature in the buried pipe area will increase year by year,resulting in the outlet temperature of the buried pipe fluid at the beginning of each cooling cycle being higher than that of the previous cycle,which causes the EER of the system to decrease year by year during summer operation.The heating time is less than the cooling time in summer,so the performance coefficient of the system will decrease year by year.Solving the problem of heat accumulation is a key point of ground source heat pump technology.This paper proposes an air-ground source self-coupling heat pump system.The system can flexibly switch between the air source heat pump mode and the ground source heat pump mode.The system shares one compressor,and the mode switching is realized by switching two four-way reversing valves and three electronic expansion valves.A small office building in Changsha was selected as the analysis object,the dynamic load of the building was calculated by using De ST,and a simulation model of the coupling system was built in TRNSYS.The parameters of the typical meteorological year derived from De ST and the typical meteorological year invoked in TRNSYS are compared and analyzed.It is found that the latter has a 10-month monthly average temperature and the median of the dry bulb temperature are greater than the former.For the purpose of system simulation uniformity and accuracy,the meteorological parameters provided by De ST are adopted and imported into the system simulation model together with the load.In winter,the ground source heat pump mode is completely operated in a small flow rate.In summer,a ratio is determined as the first cut-off point according to the ratio of the hourly cooling load to the maximum cooling load.When the hourly cooling load ratio is greater than the first cut-off point,the system is completely operated in the ground source heat pump mode with a large flow rate.When the hourly cooling load ratio is less than the first cut-off point,the ground source heat pump mode and the air source heat pump mode are switched to operate,and an outdoor air dry bulb temperature is determined as the second cut-off point through analysis.When the hourly cooling load ratio is smaller than the first cut-off point,and the outdoor dry-bulb temperature is greater than the second cut-off point,the system operates in the ground source heat pump mode with a small flow rate;when the hourly cooling load ratio is smaller than the first cut-off point,and the outdoor dry-bulb temperature is lower than the second cut-off point,the system operates in air source heat pump mode.Three modes with better soil heat balance were identified as the objects of detailed analysis.Mode 1-the first cut-off point is 0.6,the second cut-off point is 28.6°C;Mode2-the first cut-off point is 0.6,the second cut-off point is 29.6°C;Mode 3-the first cut-off point is 0.5,the second cut-off point is 30.7°C.The research results showed that the annual variation of soil temperature was the largest when operating in mode 2,and the temperature dropped by 0.35°C in the first year,and the soil temperature dropped by 0.84℃after ten years of operation.The maximum summer EER values of mode 1,mode 2,and mode 3 air source heat pump are 4.22,4.28,4.05,the minimum values are 3.40,3.47,3.43,and the average values are 3.85,3.83,3.77;Mode 1 has the largest total energy consumption during the 10-year operation period,followed by Mode 3,and Mode 2 is the smallest.Considering economy and soil heat balance,mode 2 is the best operation mode.