Evaluation of Enhanced Heat Exchange Performance of Vertical Ground Heat Exchangers with Water Injection

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  • KOMANIWA Yoshihito
    Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University（. Present: ZENERAL HEATPUMP INDUSTRY Co., Ltd.）
  • FUJII Hikari
    Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University,（. Present: Akita University）
  • MAEHARA Takahiro
    Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University
  • CHOU Naokatsu
    Kyushu Electric Power Co., Inc.

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Other Title
  • 垂直型地中熱交換井への注水が熱交換能力に与える影響に関してのフィールド試験による検討
  • スイチョクガタ チチュウ ネツコウカンイ エ ノ チュウスイ ガ ネツコウカン ノウリョク ニ アタエル エイキョウ ニ カンシテ ノ フィールド シケン ニ ヨル ケントウ

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Abstract

In this study, thermal response tests (TRTs) with water injection into a ground heat exchanger (GHE) were conducted to evaluate how vertical water flow in the well influences the heat exchange performance. The GHE used for TRTs has slotted screen pipes with depths from 41 m to 71 m, and natural groundwater level is 14.5 m. Hydraulic conductivity of the reservoir is 6.35×10&sup-6; m/s. Thermal tracer tests were first carried out for understanding how deep the injected water in the well runs out into fractures. The results of thermal tracer tests showed that the injected water runs out into fractures with depths from 57 m to 64 m. Thus, injected water in the well generates vertical water flow in this well. TRTs were then conducted on 4 different patterns of water injection rate; no injection (TRT-0), 5 l/min (TRT-5), 10 l/min (TRT-10) and 20 l/min (TRT-20). Temperatures of injected water were stable through each TRT. Averaged temperature of injected water in the case of TRT-5, TRT-10 and TRT-20 was 20.9°C as against 15.5°C for temperature of ground. The results of TRTs showed that the averaged temperature of heat medium during the circulation of between 43 to 46 hours in the case of 20 l/min injection is 5°C lower than ones in the case of no injection. Therefore, it can be said that vertical water flow induced by water injection into the GHE can enhance heat exchange performance of the GHE drilled throughpermeable layers.

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