Numerical Simulations on the Application of a Closed-Loop Lake Water Heat Pump System in the Lake Soyang, Korea

A lake is one of the geothermal energy sources to meet increasing demands for renewable energy use. In this study, a series of numerical modeling was performed to evaluate the applicability of a close-loop lake water heat pump (LWHP) system in Lake Soyang, Korea. A non-isothermal pipe flow model was used to simulate the flow and heat transfer processes occurring in the LWHP system with the main pipe and several helical tubes for heat exchange. Based on the temperature data measured in the Lake Soyang for 4 years, the installation depth and the number of helical tubes were determined sequentially, and the sensitivities of additional installation and operation factors on the system performance were analyzed. Assuming a mild current in the lake, the installation and operation conditions for the efficient operation of the system were suggested as follows: The installation of 16 helical tubes at 50 m deep, the circulation rates of heat-carrier fluid of 189.3 L/min, the inner diameter of tubes of 32 mm, and the wall thickness and thermal conductivity of 2.9 mm and 0.4 W/mK, respectively. Considering many lakes and reservoirs in Korea, the closed-loop LWHP system would be a viable renewable energy application.