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A novel oscillatory thermal response test for deep U-tube borehole heat exchanger: In situ data.

Number: 0931

Author(s) : SERAGELDIN A. A., KATSUNORI N.

Summary

The current study proposed a novel thermal response test methodology to minimize the testing time, and save labor time and testing cost; it utilizes an oscillatory heat flux called OscTRT. The oscillating heating flux has the shape of a sinusoidal wave with a frequency of 1.74x10-3 Hz, an average value of 14 kW, and an amplitude of ±6 kW. A new TRT machine is customized to control the heating injection pattern frequency and amplitude. Five OTRTs are conducted at sites with various geological and hydrological conditions with an apparent thermal conductivity range of 1.2 ~ 3.1 W/m.K. The sites are located in Sapporo city, Niseko city in Hokkaido prefecture, Miyoshi city in Hiroshima prefecture, Kai city in Yamanashi prefecture, and Tokyo city in Japan. All sites' borehole depths and diameters are 300 m and 250 mm. The fluid temperature and soil undisturbed temperature profiles are measured using optical fiber cables inserted inside the U-tube legs. While, A new analysis method is presented to filter, smooth, and fit the recorded data to find the response temperature amplitude at inlet and outlet to the borehole. The borehole and subsurface thermal response are analyzed to find the amplitude ratio, phase shift angle between inlet and outlet temperature responses, and effective thermal conductivity. The accuracy and validity of the proposed method are examined by comparing the output with the results from the conventional TRTs. Five OscTRTs are carried out for 24 hours, while the normal TRTs are conducted for 60 hours. The results show that the OscTRT shortened the time needed for TRT by 60% with high accuracy. Also, a linear relationship between the amplitude ratio and effective thermal conductivity is derived.

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Pages: 15 p.

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Details

  • Original title: A novel oscillatory thermal response test for deep U-tube borehole heat exchanger: In situ data.
  • Record ID : 30033518
  • Languages: English
  • Subject: Technology
  • Source: 14th IEA Heat Pump Conference 2023, Chicago, Illinois.
  • Publication date: 2023/05

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