Heat extraction by deep coaxial borehole heat exchanger for clean space heating near Beijing, China: Field test, model comparison and operation pattern evaluation

Wang Huajun, Xu Yishuo, Sun Yukun and Zhao Sumin

Renewable Energy, 2022, vol. 199, issue C, 803-815

Abstract: Deep coaxial borehole heat exchangers (CBHEs) are being widely used in clean space heating of buildings in winter. Here we report a new field test on a 1800m deep CBHE in the southern Daxing uplift, Beijing, a representative geological region in North China. Under the economic flow rate of 20–25 m3/h, the steady heat extraction power is 237.24–256.54 kW. Further, numerical modelling and simulation calculations are performed to compare the applicability of the Eskilson-Claesson model and Al-Khoury model for different operation patterns and then analyze the operation performance of deep CBHE during the whole heating season. For typical flow rates, compared with the continuous pattern, the intermittent pattern can increase the heat extraction power per unit depth by 25.4–31.0% and reduce the thermal influence radius by 1.46–1.89 m due to a better ground temperature recovery around the borehole. In addition, a new contribution factor (CF) is introduced to evaluate the temperature contribution of different ground layers during the heat extraction, which can reveal the influences of flow conditions, geothermal gradient, thermal properties, and even groundwater flow. The present results support that deep CBHEs have more obvious advantages for space heating of buildings with intermittent heating requirements.

Keywords: Deep coaxial borehole heat exchanger; Heat extraction; Intermittent operation; Thermal influence radius; Long term performance (search for similar items in EconPapers)
Date: 2022
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Citations: View citations in EconPapers (3)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:renene:v:199:y:2022:i:c:p:803-815

DOI: 10.1016/j.renene.2022.09.017

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