Performance law of a new composite seasonal underground thermal storage system

doi:10.19799/j.cnki.2095-4239.2021.0334

Abstract

Abstract:

Renewable energy is characterized by intermittency and instability because of weather, region, and season, resulting in a mismatch between supply and demand. Seasonal thermal storage is an effective technology to solve the abovementioned problems. However, the traditional seasonal underground thermal storage has the disadvantages of single storage modes and severe heat loss. In this study, the underground hot water energy storage (HWES) and borehole thermal energy storage (BTES) modes were combined to establish a composite seasonal thermal storage system, and a numerical model was developed and confirmed by comparing with experiments. On this basis, the effects of parameters, such as store/release flow rate, scale matching, number of boreholes, and soil thermal conductivity, on the temperature, thermal energy store/release capacity and power, and heat loss of the composite system were analyzed. The performance law of the composite thermal storage system was examined to maximize efficiency. The results show that with an increase in the store/release mass flow rate, the system efficiency gradually increases. The system efficiency increases with an increase α value of scale matching. However, an increase in the volume ratio of the water tank causes more heat loss. Therefore, scale matching should be comprehensively considered not only to achieve higher system efficiency and obtain larger heat store/release power but also to minimize investment cost and reduce heat loss. Increasing the number of buried pipes increases the thermal energy store/release capacity and improves the system efficiency; however, it increases the investment cost. An increase in the space between the borehole rings increases the soil volume, thus reducing the storage temperature, which is not conducive to energy release and decreases the system efficiency. With an increase in the soil thermal conductivity, heat transfer in the soil, energy store power of boreholes, and peak temperature of energy storage increase. However, heat loss becomes faster, and the energy release power decreases, thereby decreasing the system efficiency.

Key words: underground thermal storage, seasonal thermal storage, composite thermal storage, borehole thermal energy storage (BTES), hot water energy storage (HWES), TRNSYS

CLC Number:

TK 52

Dehou XU, Xuezhi ZHOU, Yujie XU, Zhitao ZUO, Haisheng CHEN. Performance law of a new composite seasonal underground thermal storage system[J]. Energy Storage Science and Technology, 2021, 10(5): 1768-1776.

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参数	取值
土壤热导率/(W·m^-1·K^-1)	1.0
土壤密度/(kg·m^-3)	1500
土壤比热容/(J·kg ^-1·K ^-1)	2200
水热导率/(W·m^-1·K^-1)	0.6
水密度/(kg·m^-3)	1000
水比热容/(J·kg ^-1·K ^-1)	4200
储热体上表面换热系数/(kJ·h ^-1·m^-2·K ^-1)	3.0
线热源系数/(kJ·h ^-1·m ^-1·K ^-1)	9.0
环境空气温度/℃	15.0
储热体初始温度/℃	15.0
储热体侧和底边界温度/℃	15.0

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