Abstract
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.
Highlights
Among several types of geothermal energy applications, a lake-based geothermal cooling, and heating system, called the lake water heat pump (LWHP) system, has more advantages in terms of energy-efficiency, ease of installation, and cost comparing to a ground source cooling and heating system [1]
This study is to demonstrate the potential for the utilization of and to evaluate the applicability of a closed-loop LWHP
Based onProcedure the long-term temperatures measured in Lake Soyang over 4 years, a series of numerical modeling to assess the effects of several andover operation conditions
Summary
Among several types of geothermal energy applications, a lake-based geothermal cooling, and heating system, called the lake water heat pump (LWHP) system, has more advantages in terms of energy-efficiency, ease of installation, and cost comparing to a ground source cooling and heating system [1]. The LWHP system can be operated in ways of the open-loop or the closed-loop for heat exchange with lake water. The open-loop scheme of the LWHP can provide higher efficiency than the closed-loop scheme. It has a burden of legislative permits and costs for lake water extraction and returning and risks of freezing, corrosion, and biofouling, which can obstruct the stable operation of the system [2,3,4,5]. Comparing the open-loop system to the closed-loop LWHP system may have relatively low efficiency and a concern for leakage of a heat-carrier fluid due to accidental pipe failure [7]. The closed-loop system has little effect on the lake water; it can be applied in lakes with low water quality or high sediment content
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