Research And Accomplishment Of Cooling Tower Hybrid GSHP System’s Automatic Control Strategy

Energy saving, especially the energy saving in the air condition system, has become a compulsory work which should be promoted in the construction industry. Nowadays, GSHP air conditioning system has been widely used with its good advantage of environmental protection and energy saving. While in the actual use of the system, the heat exhausted in the summer is usually larger than the one in the winter, which will cause the heat stack and increase the temperature of the soil, and the heat transfer will also deviate the from stability. The solution of this phenomenon is critical because the increase of the soil temperature will affect the unit COP significantly.Cooling tower hybrid GSHP system is combinedGSHP system with cooling tower. It can improve theperformance of the GSHP system operation、reduce the number of the buried pipe、 reduce the area covered, balance the heating release and absorption, solve the problem of heat accumulation and make full use of the superiority of the GSHP system.Cooling tower hybrid GSHP system which combine GSHP system with cooling tower system, can effectively improve the performance of the GSHP system, reduce area of buried pipe, balance the full-year heat release and absorption, solve the problem of heat accumulation of soil. The superior performance of GSHP system are fully exerted in this system.Due to the complexity of cooling tower composite GSHP system, large artificial control error will emerge during the operation, the advantages of energy saving of this system can not be fully exerted. In order to solve the this problem, this paper introduced a new control strategy of the cooling tower and buried pipe system, and a set of control system was designed, which can effectively achieved. The cooling tower composite GSHP system was analyzed by control strategy. Foreign scholars have done great simulation in cooling tower composite GSHP system, and three control strategies have been concluded:Cooling tower open time control, heat pump heat source side in (out) into the highest temperature of fluid control, ground heat exchanger (out) of water temperature and the outdoor air wet-bulb temperature control. On the basis of the previous researches, in order to make full use of favorable conditions of the outdoor air, this paper puts forward the following strategy:the cooling tower runs alone at the beginning and the end of the cooling season; when in the middle of the cooling season, cooling tower and ground operates jointly through controlling the difference of the ground heat exchangers inner(outer) water temperature and outdoor air wet bulb temperature.Then, the mathematical model of cooling tower was analyzed. The enthalpy balance equation of cooling tower is firstly established according to Merkel, we drew an analogy between it with the ε-NTU calculationformula method of the sensible heat exchanger, calculated the cooling toweroutlet temperature accuracy results by iteration and we found that it can not meet the demand of automatic control system.so we select the outdoor air wet bulb temperature as control parameter, which directly influences the cooling tower outlet water temperature.Secondly, our team established a GSHP experimental platform on the basis of above and designed a set of feasible automatic control strategy according to the platform. The net control strategy has three levels which is sensor and actuator field as element level. PLC controller and single circuit control as control level and LABVIEW software as manage level The control strategy can make whole design and debug of the whole control system hardware and data exchange among different levels.Furthermore, we invented a convenient and high visual GSHP automatic control software according to the control strategy and experimental platform. This software can real-time monitor the soil temperature field and system operation condition, can set and adjust the system operation parameter, can provide alert when air conditioning system temperature overrun and system error happen, and can real-time display, store and print the system data.Eventually the article testes on-site and analyses the hardware cooperation and software control of the cooling tower hybrid GSHP autonomous system until the system is stable and the data is regular. According to the change of the tubes buried under the ground and the outdoor wet bulb temperature, the system can accommodate the ways of operation of the cooling tower and the tubes buried under the ground.By controlling the operating parameters, cooling tower can run with the buried pipe cooperatively, which can reduce the temperature of cooling water, cut down the heat accumulation, and improve the performance of the unit.