Experimental Study On Heat And Moisture Transfer In Soil During High Temperature Soil Heat Charging

The utilization of sustainable energy has drawn increasing public attention due toenvironmental pollution and energy crisis caused by consumption of traditional fossil fuel.The ground source heat pump (GSHP) technology which uses the main component of thesustainable energy, the geothermal energy, has developed to maturity. However, the existingresearch on soil temperature and humidity migration’s impact on heat transfer effect of GSHPhas failed to explain the temperature and humidity coupled and mutual effect in the heattransfer of buried tube.Soil is a kind of complex porous medium, which is the main medium of buried tube heattransfer process which including moisture migration and transformation. The study of thetheory of the temperature and humidity migration in soil has been very mature when soiltemperature is constant no matter the soil is saturated or unsaturated. The distribution andvariation of the soil’s temperature impacts the water’s physico-chemical property so does themoisture migration movement, matric potential and the kinetic parameters of soil water,which interact with soil temperature when it’s unsteady. Thus the research on temperature andhumidity coupled and mutual effect is a priority for all among the studies of soil heat andmass transfer.Due to the imbalance of heating and cooling demand, the soil temperature decreasedafter several years’ operation for soil source heat pump system, and consequently the systemperformance and COP decreased. Soil heat charging with solar energy was proposed for solar-soil source heat pump compound system. Many studies have been carried out to investigatethe heat and moisture transfer in soil for soil heat charging, but they failed to provide a cleardescription and explanation of the coupled and mutual effect between heat and moisturetransfer. This paper presented an experimental study on the heat and moisture transfer in soilheat charging. The simplified testing rig was constructed to investigate the coupled andmutual effect of one-dimension horizontal heat and moisture transfer in soil heat charging.The results showed that peak volumetric water content (VWC) produced firstly at the positionnear heat source and moved towards the other cold end of the tested soil pillar, but waslimited in an area near heat source. The time consumption and value for peak VWC increasedwith the increasing heat source temperature at the same initial VWC and increased with theincreasing initial VWC at the same heat source temperature as well. The heat sourcetemperature was a main factor affecting the peak soil temperature and peak VWC, while theinitial VWC had little impact on them. Temperature and humidity migration changesregularly when the soil media is different (loam and sandy), which fully proved that there is astrong correlation between temperature field and humidity field in the migration process ofthe soil temperature and humidity.