Heat transfer and soil thermal stability as related to a plate-type heat exchanger in ground-coupled heat pump systems

Ground Source Heat Pump (GSHP) Systems are being promoted as the most efficient heating and cooling systems available today. GSHP systems are also clean energy systems which provide many advantages in meeting various environmental protection requirements. The installation cost, however, has been one of the major factors affecting the widespread adoption and utilization of GSHP systems. Various efforts have been made in the past decade to lower the cost by seeking a better type of ground heat exchanger, or performing more accurate design calculations to save material as well as the installation cost while still meeting the performance requirements. It has been well understood that the performance of a ground heat exchanger depends heavily on the long term thermal performance of the soil which surrounds the heat exchanger. Soils which are thermally unstable under the specified load conditions will degrade the GSHP system performance. Prediction of long term soil thermal performance will ensure better ground heat exchanger design.; This research studies the plate type ground heat exchanger, a new form of GSHP heat exchanger. The plate type ground heat exchanger provides the potential for enhancing heat transfer by having a larger soil contact area, lower thermal contact resistance and a large thermal storage effect. Numerical models were established to study the heat transfer process and the soil thermal stability around the plate heat exchanger. A method was developed to predict soil thermal performance under specified thermal conditions. Tests were performed on a GSHP system equipped with plate type ground heat exchanger. Intensive data analyses were performed to compare the analytical results and experimental results. A parametric model analysis was performed to predict the performance of plate type ground heat exchangers under various design and operating conditions. Certain design criteria and system limitations were established for the design of plate type heat exchangers.