Principal Component Analysis of Heat Transfer for Ground Heat Exchanger

Abstract

Shallow geothermal resource is used as a heat source/sink for ground source heat pump system (GSHP), which has become one of the most feasible alternative energies for space heating and cooling in residential and commercial buildings. As the fossil energy is drying up day by day and the world environmental pollution is becoming more and more serious, GSHP will be widely used on account of being environmental friendliness and the potential of energy conservation. With the increase of construction area, large scale group ground heat exchangers (GHEs) need to be installed in the soil. The analysis of heat transfer on large scale GHEs, even only a few groups, is a key difficulty. The performance of heat transfer on GHE is strongly affected by the geologic conditions of the soil, the hydrogeology condition, thermophysical parameters of pipe, the configuration of side tube, and so on. Based on the hypothesis of homogeneous isotropic medium for soil, the heat transfer of ground heat exchanger is analysed by means of theoretical analysis and numerical simulation during refrigeration operation in summer. First the temperatures of outlet are obtained, and then the data are analyzed with the help of the principal component analysis of the multivariate statistics. From the results, we can conclude that the thermal conductivity of the soil is the decisive one among the numerous factors influencing heat transfer performance. Secondly, it is affected by the density and specific heat of the soil. What is more, the impact caused by groundwater flow depends on the flow velocity-the larger the flow velocity, the larger the influence of the groundwater.