THERMAL PERFORMANCE STUDY OF OPEN LOOP GROUND SOURCE HEAT PUMP SYSTEM

Abstract

With rise in energy prices and concern for the environment, conventional energy sources based on oil, coal and natural gas are no longer the easy choice. Cooling and heating applications in buildings consume the greater part of energy. Hence there is a requirement for finding unconventional form of energy resource which is more environmentally friendly, easily available and economically feasible. Geothermal heat pump systems are the most environmental friendly and effective method for cooling and heating buildings, and thus they have the largest potential to cut down greenhouse gas emissions. Ground source heat pump (GSHP) is used as a common term for a variety of systems that use the earth soil, ground, ground water and surface water as heat source and sink. For the efficient working of a GSHP system all its system components must be efficient. Design of open loop system is very complex due to its dependencies on various factors such as temperature of water extracted and rejected into the borewells, depth of well extraction and rejections, effectiveness of heat exchanger interacting heat between the circulating water supplied to the condenser/evaporator and the extracted ground water, flow rate of ground water etc. In this work an attempt is made to provide design methodology for open loop ground source heat pump system to study its thermal performance. For this purpose a systematic design procedure is established. The performance of the system is analyzed considering the effects of ground water temperature and its flow rate, effectiveness of plate heat exchanger, ambient temperature, depth of wells, etc. on coefficient of performance (COP). Exergy analysis is also carried out on all devices for cooling and heating applications. Lastly the optimization of influencing parameters on performance of system is performed by employing Taguchi and Utility concept techniques. Performance study and optimization of control parameters indicate that effectiveness of plate heat exchanger and ground water temperature have the major contributions toward the performance of the system. Using the Taguchi optimisation analysis, the optimized set of parameters for cooling application is A1 B1 C3 D2 E2 F1 and that for heating application is A3 B1 C3 D2 E2 F1 with COP values of 4.58569 and 4.69687 for cooling and heating modes respectively. On implementation of utility concept, the optimized set of parameters for the system is A1 B1 C3 D2 E2 F1, with COP values of 4.58569 and 3.82663 for cooling and heating modes respectively