Experimental and mathematical analysis of three ground-coupled heat exchangers.

摘要

Experimental performance data are presented for the well, pebble-bed, and surface-tank configurations of ground-coupling. Results are analyzed in terms of hourly, daily, and seasonal operating characteristics. Compared to a conventional air-source heat pump, the ground-coupled system has a higher coefficient of performance (COP) and is better able to maintain capacity during ambient extremes. Data based on two years (four seasons) of experimental tests are presented. Results are presented in terms of source and sink temperatures, energy fluxes, and the coefficient of performance. The well heat pump system has a seasonal heating COP of 3.5 and cooling COP of 2.8 (EER of 8.8). For the pebble-bed system, the heating and cooling COP are found to be 3.0 and 2.6 (EER of 8.2) respectively. The surface-tank system has a heating COP of 2.6 and a cooling COP of 2.4 (EER of 7.5). Additional comparison is made through sensitivity factors. The effectiveness and the number of transfer units for the ground coupled heat exchangers are also calculated.;In addition to the experimental results, a general, demand driven, numerical model for thermal analysis of the ground loop heat exchangers (TAGLEX) is developed for residential heat pump systems. The model is built from component modules. There are open loop modules for the pebble-bed and surface-tank, and closed loop modules for a vertical well and horizontal pipes. The transient two-dimensional heat conduction equation, which is used to calculate the temperature fields surrounding the ground-coupled heat exchanger, is solved for many slices along the length of the beat exchanger by an explicit finite difference formulation. The predicted seasonal coefficients of performance for heating and cooling are compared with experimental results of three systems. The predictions are found to be in good agreement with the experimental results.;A complete parametric study is done on a two-ton, water-to-air heat pump system using the pebble-bed method of ground coupling. The results identify the optimum surface area, geometry of bed, water flow rate, maximum load capacity, and conductivity of the soil for a given size heat pump.;The performance of a one-ton, water-to-air system is examined with a prescribed heating and cooling load demand. A significant improvement is observed in the cooling COP compared to a continuous run. The required cooling and heating demand load is increased by 250 percent to simulate the.capabilities of the ground-coupled heat exchanger for cold climates. A 12 percent drop is noticed in the heating COP and a 17 percent decrease in the cooling COP.