Experimental analysis and mathematical modeling of a direct expansion ground coupled heat pump system

In this dissertation, we investigate a direct expansion heat pump system that is uniquely coupled to the earth through a heat transfer concentrator (GLHXC Ground Loop Heat Exchanger Concentrator). In effect the system reduces several of the thermal resistances associated with the heat flow paths in other types of ground-coupled heat pump systems. A description of the system and its instrumentation with a presentation of performance results for winter and summer operation are included. The results are compared to experimental data obtained from four other types of earth coupled configurations (horizontal pipe, pebble bed, surface tank, and a closed-loop vertical well) and an air-source heat pump tested at a research laboratory (AERL).; This dissertation also contains a description of the mathematical model developed for the purpose of simulating the performance of the GLHXC system. The AERL system simulation model is a FORTRAN computer program which predicts the transient performance of a heat pump in which either the condensor or the evaporator is a ground loop heat exchanger concentrator. The performance of the conventional indoor components of the system (i.e., compressor, condenser or evaporator, and expansion valve) are simulated with a heat pump program developed at Oak Ridge National Laboratory (ORNL). The outdoor component (condensor or evaporator) of the system in the ORNL heat pump model is replaced by the ground loop model in order to predict overall system performance in either the heating or cooling mode. Thermal analysis involves the transient conduction in the earth, heat transfer in the ground loop, and component performance. The steady state ORNL program had to be modified to accommodate the transient behavior. Numerical results from the simulation of a particular GLHXC system are compared with experimentally measured performance data in order to validate the model for both heating and cooling mode operations. Parametric sensitivity studies are also presented to determine the influence of bed size and configuration on the performance of the ground coupled heat pump. In general, it is shown that bed length is the most important parameter. The performance of the system is shown to be most sensitive to bed length during cooling mode operation.; The computer simulation model developed has utility as a design tool for ground-coupled heat exchanger configuration used in this investigation and may easily be modified to investigate the performance of other types of ground-coupled arrangements.