Research On Economic Control Strategy For Hybrid Ground-Source Heat Pump Systems In Long-term Operation Conditions

With the intensification of energy crisis and environment pollution,ground-source heat pump (GSHP) is booming in engineering application dueto its potential in energy-saving and emission-reduction. However， as forother different geographical and climatic conditions, this kind of potentialwould not come true under improper design or administration. For instance, incooling load dominated areas, the initial investment of GSHP systems onlywith ground-loop heat exchanger as their sole heating and cooling sources ishigher, and efficiencies of the systems are bound to be reduced year by year.Therefore, In Hot Summer and Cold Winter Region such as Hunan Province,hybrid GSHP system with cooling towers as supplemental heat rejecter comesto be the first choice.A commercial building served by a hybrid cooling tower-GSHP systemin Zhuzhou City is taken as the research object in this article. First, thecooling load results which calculated by cooling load coefficient method arecompared to the simulation results by Energyplus to verify the rationality ofthe simulation results, and the annual hourly dynamic air-conditioning load issimulated by Energyplus.Then, the mathematical models of the components of hybrid in parallelGSHP system are elaborated firstly, such as the models of heat pump units,ground-loop heat exchangers, cooling towers，and so on. Secondly, the systemis designed by the ground source heat pump design software—GLD. Thirdly,based on Modular concept, the simulation model of the system is set up inEnergyplus. Finally, the simulation results and the on-site experimental dataare analyzed to verify the accuracy of the simulation model.The long-term outputs of the system operating under different controlstrategies are simulated by Energyplus, then the heat balance of the soil,energy consumption and operating cost of the system are analyzed.Conclusions are obtained as follows: the third control strategy which controlsaccording to the difference between the heat pump exiting fluid temperatureand the ambient air wet-bulb temperature is the optimum scheme of thehybrid GSHP system, because not only the long term heat balance achievesthe best state, but also the total running cost appears the lowest. Ultimately, the initial investment, operating cost, total cost and the lifecycle cost of the hybrid in series system of another building, in which thecooling tower and ground-loop exchanger undertake different ratios ofcooling load are calculated. The analysis results show that improperconfiguration cases will result in the diseconomy of the system.This paper analyzes the long-term economy issue and operation effect ofthe hybrid GSHP system operating in different system types, under differentcontrol strategies. Some suggestions about the application of hybrid GSHPsystems are given. The research results provide some reference for the furtheroptimization and extensive application of hybrid GSHP systems.