| Ground source heat pump(GSHP)technology has been widely used because of its high energy efficiency.However,there are only few cases of GSHP system applications in large-scale commercial buildings due to the reason of limited ground area for borehole drilling.According to this background,this dissertation mainly proposes three cooling/heating system schemes: chiller and central heating system,GSHP combined with chillers and central heating system,,and ground source heat pump system.The simulation models of these three systems have been established in the platform of TRNSYS.The operating performance including the inlet/outlet water temperature of heat pump/chiller,the average underground temperature and the operating cost have been analyzed according to the dynamic simulation results.First of all,the building annual hourly cooling/heating loads are calculated by means of the professional software of DeST according to the design parameters of the real commercial building in Jinan.The ground heat exchangers(GHEs)for the two schemes with GSHP system have been designed using the professional GHE design/simulation program G-star.Then the dynamic simulation model of the three systems have been developed in the platform of TRNSYS based on the designed parameters.According to the on-site thermal response test,,the average thermal conductivity of the underground is 1.872 W/m · ?,the average specific heat capacity of the ground is 1920 kJ/m3·?,and the initial average temperature of the ground is 16.9?.The two GSHP systems are simulated for the operation of 20 years.The simulation results show that for the pure GSHP system,the underground average temperature of the borehole region reaches 18.48 ? and 37.52? respectively after one year's operation and 20 years' operation,while the ground temperature of the hybrid GSHP system is 17.02 ?and 18.23 ? espectively after one year's operation and 20 years' operation.It can be seen that the ground temperature of the pure GSHP system is much higher than the maximum value of the inlet fluid temperature to the heat pump,which means a serious thermal imbalance underground.For a long term operation,the system can not satisfy the requirements of the building cooling load.Next,the initial cost and operation cost of the three systems have been analyzed.The results show that the initial cost of the hybrid scheme is lower compared to the pure GSHP system,only 288 yuan/?,and its operation cost is 21.5 yuan/? which is the lowest among the three systems.In a conclusion,the hybrid GSHP with chiller and central heating system shows a high performance and low operating cost compared the other two systems.Finally,TRNOPT is used to optimize the selected hybrid system to find the optimal control strategy.The simulation results are given as follows:(1)The chiller and cooling tower will start to provide cooling when the source fluid outlet temperature of the heat pump is higher than 33 ? in summer;(2)The plate heat exchanger of the central heating system will start to provide heating when the source fluid outlet temperature of heat pump is lower than 4 ? in winter.Under the aforementioned optimal control strategy,the GSHP provide 42% of the total cooling load and the other is provided by the chiller in summer;it provides 83.5% of the total heating load and the central heating net provides the left.In this optimal control strategy,the comprehensive cost(include initial investment and operating costs for twenty years)of the hybrid system is 717 yuan/ ? and has a comprehensive cost saving of 150,000 yuan compared to the initial control strategy.The simulation results show that: the hybrid GSHP system coupled with the chiller and the central heating system can reduce the initial cost,have a better thermal balance of underground and a lower operating cost compared the pure GSHP system and the conventional heating/cooling system.Compared with conventional chiller system,the payback period of hybrid system is only 1.34 years,which shows that the system has a good economy saving. |
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