Performance Analysis Of Soil Temperature Recovery Under Intermittent Operation Mode Of Ground Source Heat Pump

The intermittent operation of ground source heat pump is an effective way to improve the operation efficiency of heat pump.Soil properties and intermittent operation mode play a major role in the process of temperature recovery under intermittent operation.Actually,soil heat transfer is a process of heat and moisture transfer under the coupling of temperature field and humidity.Under the effect of soil moisture content,the thermal and moisture characteristics of soil will not remain unchanged,thus affecting the heat transfer and temperature recovery of soil.A small test rig was built to study the effect of operation mode and soil moisture status on soil temperature recovery.In the experiments,the water bath provided a constant temperature of water as heat source and stable water flowed through the buried pipe.Each test lasted for 24 hours.The experiments under different operation and stop ratios(1:2,5:7,1:1,2:1)were carried out in soil with 15% initial moisture content.The comparative experiment between the intermittent operation and recovery mode and the continuous operation and recovery mode was carried out.The temperature change of soil with three initial moisture status(15%,25%,infiltration condition)were tested under the 1:1 operation and stop mode and continuous operation mode respectively.The experimental results show that increasing soil moisture content and infiltration condition are beneficial to heat transfer between soil and buried pipes.The recovery efficiency of soil temperature and the phase of efficient temperature rise and efficient temperature recovery time under different operation and stop ratio are obtained.The smaller the operation and stop ratio,the better the performance of soil temperature recovery will be.The results also show that intermittent operation and recovery are conducive for soil to maintain the ability of temperature change,and increasing soil water content and infiltration state are beneficial to soil temperature recovery.The performance of soil temperature recovery under infiltration state is the best.Lower water content of soil near the heat source will lead to worse heat transfer between heat source and soil.A one-dimensional soil column test bench was set up to study the effect of humidification near heat source on soil heat transfer and temperature recovery.Each test lasted for 24 hours and the 1:1 operation and stop mode was adopted in the experiment.For soil with low moisture content,humidification experiments at the initial time of heating and humidification experiments at the initial time of recovering were carried out respectively with 50 ml,100ml and 150 ml amount of water injection.Soil temperature rise and temperature recovery rate increased with the increase of water amount at the initial time of heating.It was found that the soil temperature recovery rate was the highest when the amount of humidification was 50 ml.There is no significant difference in the degree of soil temperature recovery with the increase of the amount of humidification at the initial time of recovering.For the soil with low initial moisture content,a small amount of humidification can enhance soil temperature recovery.Compared with humidification at the initial time of recovering,the performance of soil temperature recovery is stronger in the mode of the humidification at the initial time of heating.