Influence of geometry on the thermal performance of water pit seasonal heat storages for solar district heating
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Influence of geometry on the thermal performance of water pit seasonal heat storages for solar district heating
1. Key Laboratory of Solar Thermal Energy and Photovoltaic Systems, Chinese Academy of Sciences, Beijing 100190, China 2. Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China 3. University of Chinese Academy of Sciences, Beijing 100049, China 4. Department of Civil Engineering, Technical University of Denmark, Brovej 118, 2800 Kgs. Lyngby, Denmark 5. Joint Laboratory, Institute of Electrical Engineering, Chinese Academy of Sciences and Guangdong Five Star Solar Energy Co., Ltd., Beijing 100190, China 6. Lanzhou University of Technology, Gansu 730050, China
Abstract
Keywords
The aim of the study is to investigate the influence of geometry on the thermal capacity and stratifications of a water pit heat storage for solar district heating. A TRNSYS component model for a truncated cone water pit was developed based on the coordinate transformation method and validated by experimental results from the water pit heat storage in Huangdicheng in 2018. The thermal performance of 26 water pits with different heights and side wall slopes was calculated for 10 consecutive years. It takes four to six years for the water pit to reach steady-state operation. The operation data from the tenth year was selected to evaluate the thermal performance of each configuration. The results show that because of the thermal insulation on top of the water pit, the height to diameter ratio of a water pit with minimum annual heat loss was always smaller than 1.0. The annual storage efficiency of a water pit increases with side wall slope due to the reduced side wall area. There is an almost linear increase in the thermal stratification number of a water pit with height. With an increase in the height, thermal stratification in water pits with a steeper slope increased more gradually than water pits with a lower slope. The findings in this paper are relevant for the design optimization of water pits as seasonal thermal energy storages.
water pit,
Introduction
Current energy demand in the building sector accounts for approximately 20% of the total energy demand in China (Xu and Wang 2020). This demand has always been met by burning fossil fuels. As such, the building sector plays an important role in the production of pollutant emissions. Solar energy is inexhaustible, clean, and pollution-free, making it an ideal renewable energy for the heating and cooling of buildings (Guo et al. 2018). As is the case with most other renewables, the main drawback of solar energy is its fluctuating nature on a daily, weekly, and seasonal basis. The greatest mismatch is that between the solar heat availability in summer and the high space heating demand E-mail: [email protected]
seasonal heat storage, truncated cone, storage capacity, thermal stratification, coordinate transformation
Article History Received: 16 February 2020 Revised: 11 May 2020 Accepted: 01 June 2020 © Tsinghua University Press and Springe
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