| The ground source heat pump system has the advantages of high efficiency energy saving.But the long-term operation will cause the problem of "heat accumulation" in hot summer and cold winter areas and the cooling towers are often used to establish the hybrid ground source heat pump system in the engineering.However,most of the strategies control single parameter.In this paper,the single-parameter control strategy is analyzed and the multi-parameter coupling control strategy is proposed to seek the optimal control strategy and the optimal control working point.This paper selects a residential building in Nanjing as the research object.The main research work of this paper:(1)Use De ST software to simulate the hourly load of the selected buildings throughout the year to construct a parallel hybrid ground source heat pump system.(2)Establish the hybrid ground source heat pump operating strategy simulation platform based on the TRNSYS platform and verify the accuracy of the model.(3)Simulate single parameter control strategy;Simulate the total energy consumption of the whole life cycle of the system with temperature control strategy and temperature difference control strategy,and soil temperature change,soil heat exchange and average COP of heat pump under different control conditions to determine the best control method situation point.(4)Simulate the multiparameter coupling control strategy: Firstly,the temperature-temperature difference coupling control strategy is proposed,and considering the seasonal variation of the load,the cooling period segmented temperature control strategy,the cooling period segmented temperature difference control strategy and the cooling period segmented coupling control strategy are proposed.Finally,the system operating characteristics of each control strategy are simulated separately.(5)Explore the influence of the soil temperature balance point on the operating characteristics of the system throughout the life cycle.Analyze the system life cycle energy consumption and soil heat balance response.The main results of this paper are:(1)The maximum annual heating load is 87 k W and the annual maximum cooling load of air conditioning is 179 k W.The annual cumulative heating load is 69719 k W·h and the cumulative cooling load is 140238 k W·h.The annual cumulative cooling load is 2.01 times than the annual cumulative heating load.(2)The best operating conditions of temperature control: The cooling tower is opened when the fluid temperature at the outlet of the source side of the soil source heat pump is higher than 31.0℃ and the cooling tower is closed when the cooling tower is closed when the temperature is lower than 30.0℃ and the total energy consumption of the system is 783258 k W·h.The best working condition of temperature difference control: When the difference between the inlet fluid temperature at the source side of the soil source heat pump and the outdoor wet bulb temperature is higher than 4.0℃ and the cooling tower is opened.When it is lower than 3.5℃ and the cooling tower is closed and the total energy consumption of the cooling tower system is 782641 k W·h.(3)Adopt the temperature-temperature difference coupling control strategy: When the temperature is kept constant.With the increase of the control temperature difference,the total energy consumption of the heat pump will increase while the energy consumption of the cooling tower water pump and cooling tower fan will decrease.The energy consumption of the whole life cycle of the system will be the first decline and then increase trend.When the heat pump source side outlet temperature is set to 30.0℃ and the source side inlet temperature difference is set to 4.0℃,the total energy consumption of the system is the lowest,which is 768495 k W·h.When keeping the temperature control point constant,the highest average soil temperature in the first year and 10 years of system operation will increase with the increase of the temperature difference set point.When the temperature difference control points are maintained at 3.0°C and 4.0°C,and the temperature control points change between 29.0°C and 31.0°C,the difference in soil temperature rise between the first year and the tenth year is not significant.The larger the temperature difference setting,the less conducive to the soil heat balance.(4)Compared with the single-parameter temperature control strategy in the refrigeration period,the energy consumption is reduced by 11188 k W·h.The highest average soil temperature dropped by 0.26℃ in the first year of system operation,and the highest average soil temperature dropped by 1.21℃ in the tenth year of system operation.Among the various control strategies,the total energy consumption of the system is the smallest when adopt the temperature difference control strategy during the middle of refrigeration period,and the total energy consumption of the single-parameter temperature control strategy system is the highest.Separately operating the cooling tower in the early and late stages of refrigeration,and adopting the temperature-temperature coupling control strategy in the mid-refrigeration period is more conducive to soil heat balance.(5)The higher the soil temperature equilibrium is set,the smaller the soil temperature rise will be after 10 years of operation,and the faster the system reaches thermal equilibrium,but the energy consumption of the whole life cycle of the system will be increased.It is more beneficial to the stability of soil temperature and the thermal balance of the system to adopt the piecewise coupling control strategy during refrigeration period.In this paper,it is found that the multi-parameter coupling control strategy has better soil heat balance and more energy saving than the single-parameter control strategy.The innovation of this paper is that the multi-parameter coupling control strategy is proposed and the influence of the soil temperature equilibrium point on the system operation characteristics is studied,which has a guiding significance for the energy saving operation of the soil source heat pump system. |
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