Study On Soil Seasonal Thermal Response Of SGCHPSS In Northwest China

Solar energy is rich in most of heating area in the Northwest China, cooling load ofthe building is small, heating load of building is relatively large, solar andground-source coupled heat pump system is appropriate for the application. On the onehand, solar energy storage could vastly improve the problem of soil thermal imbalance,On the other hand, ground-source heat pump overcome the weakness of instability andintermittent of solar energy. According to SGCHPSS, three-dimensional unsteady heattransfer model of soil heat storage and heat release is set up. Analyze change rule of soiltemperature field over annual and several years operating process by studying soilthermal response, and then with the analysis of soil heat balance, the best proportion ofborehole heat accumulated storage and heat accumulated release in the Northwest China,maximum cooling and heating load ratio for the building suitable for application of thesystem in different solar resource areas of the Northwest China can be concluded.First, analyze property of soil thermal response over annual and several yearsoperating process by transient numerical simulation，and study property of soil thermalresponse in different heat storage and heat flux, and select representative temperature ofsoil temperature field in order to evaluate overall recovery of soil temperature field.Then, analyze affecting factors of soil heat balance, expression of cooling and heatingload ratio for the building and proportion of borehole heat accumulated storage and heataccumulated release is concluded. Based on building thermotechnical design divisionand solar heat energy division, nine typical cities of the Northwest China are selected,which is Xi’an, Yulin, Yan’an, Hami, Urumqi, Lanzhou, Jiuquan, Xining, Yinchuan.Based on different cooling and heating load ratio for the building and different solar energy guarantee rate of typical cities, according to the soil temperature resuming-rate,proportion of borehole heat accumulated storage and heat accumulated release whilesatisfying the need of soil heat balance is concluded. And based on soil heat balance,maximum cooling and heating load ratio for the building suitable for application of thesystem in different solar resource areas of the Northwest China can be concluded. Getthe following conclusion:(1) Soil temperature fluctuate most rapidly in former ten days of per season. Soiltemperature difference at radial direction is always very small in the process of systemrunning10years. With the increase of system running time, difference of soiltemperature increase gradually at depth direction, rate of temperature rise is not big.(2) Soil temperature of20m depth can represent approximately the whole soiltemperature field for50m depth borehole of soil heat exchanger heat pump system.(3) The borehole’s heat flux proportion of summer and winter depend on coolingand heating load ratio for the building, COP and EER of ground-source heat pump andsolar energy guarantee rate through soil heat balance analysis.(4) The proportion of borehole heat accumulated storage and heat accumulatedrelease determine the recovery level of the temperature field of soil, and soil can meetthe demand of soil heat balance for the whole year while it is0.88.(5) Based on soil heat balance, maximum cooling and heating load ratio for thebuilding suitable for application of the system in different solar resource areas of theNorthwest China can be concluded. According to fitness of system, order of fivenorthwestern provinces from most to least is Qinghai, Xinjiang, Gansu, Ningxia,Shaanxi.The innovation of this paper is on the following aspects: given formula of soiltemperature resuming-rate combined with coupled system, selected temperature canrepresent the whole soil temperature field by transient numerical simulation, set uprelational equation among main factors of influence soil heat balance and get the bestproportion of borehole heat accumulated storage and heat accumulated release.