Experimental Study On Summer Operation Of Closed Cooling Tower-ground Source Heat Pump Air Conditioning System

In order to eliminate the problem of unbalanced cooling and heating load in the application of soil source heat pump technology in cold winter and hot summer regions,improve the system performance of long-term operation of air conditioners,and find out the best operating strategy for such areas to provide research ideas.The existing ground source heat pump air-conditioning system experimental platform was transformed,and an auxiliary heat sink device-closed cooling tower was added.The closed cooling tower was coupled in parallel with the buried pipe loop.The installation on the cooling loop of the system can be controlled by the PLC system:?1?Flow control device-intelligent driver;?2?Wet bulb temperature measurement device-outside air wet bulb temperature transmitter.Taking the soil temperature change characteristics and system operation stability as reference values,the cooling water temperature at the outlet of the heat pump unit,the cooling tower operating time value,and the flow value were used as dependent variables to make the system operate in the optimal mode.Seven different operating strategies are designed:?1?The cooling tower and GCHP are turned on at the same time during the day and the cooling tower is turned off at 22:00 at night;?2?GCHP is turned on at the same time,and the heat pump unit and the cooling tower are turned off at 22:00 at night;?3?Change the cooling water flow rate operation at different times;?4?Change the cooling water flow according to the cooling water temperature operation at the outlet of the heat pump unit;?5?The cooling tower is turned on at night when the cooling water temperature at the outlet of the heat pump unit exceeds 29?;?6?The cooling tower is turned on at night when the cooling water temperature at the outlet of the heat pump unit exceeds 32?;?7?The cooling tower is turned on at night when the cooling water temperature at the outlet of the heat pump unit exceeds 35?.The experimental results show that the operation strategy of turning on the cooling tower is the best when the cooling water temperature at the outlet of the heat pump unit exceeds 29? at night,the system runs for 4 days.Compared with the ground source heat pump alone operation strategy,the cooling performance is the best,with a COP_unit decrease of 24.0%and a COP_system decrease of 8.0%.The soil temperature recovery rate was the highest.At the buried depths of 30m,45m and 60m,the soil temperature recovery rates were 67.1%,66.9%,and 67.0%.As soil depth increases,the temperature recovery rate decreases.The simulation results of TRNSYS software show that the cooling tower is turned on is the best when the cooling water temperature at the outlet of the heat pump unit exceeds 29? at night.The cooling operation period of the system from June 30 to September 30.Compared with the ground-source heat pump running alone,the refrigeration performance is the best,with COP_system drop of 0.4%.The soil temperature recovery rate was the highest,reaching 54.8%.Based on the soil's constant temperature,the soil temperature rise rate has been reduced by 3.8% compared to the operation of the soil source heat pump alone.Through comparative analysis of experiments and simulation results,in summer hot and cold winter regions,long-term operation of closed cooling tower-soil source heat pump air-conditioning system in summer,opening the cooling tower operation mode based on the cooling water temperature of the heat pump unit at night can effectively improve the"thermal Stacking"problem,improve the operating efficiency of the system,improve the system economics of the entire operating cycle.Use cooling towers to operate when the outlet cooling water temperature exceeds 29? at night,the maximum soil temperature recovery rate can reach 67.1%,and the system cooling performance coefficient is 2.5.Operation strategy of opening the cooling tower when the outlet cooling water temperature exceeds 32?and the outlet cooling water temperature exceeds 35?,the soil temperature recovery rate is 60.6% and 57.6%.