Title:

Field Test of Horizontal Ground Heat Exchangers Installed Using Horizontal Directional Drilling Technology

Authors:

Hikari FUJII, Shunsuke TSUYA, Retsu HARADA, Hiroyuki KOSUKEGAWA

Key Words:

ground source heat pump, ground heat exchanger, directional drilling

Conference:

Stanford Geothermal Workshop

Year:

2019

Session:

Direct Use

Language:

English

Paper Number:

Fujii

File Size:

1282 KB

View File:

Abstract:

In ground source heat pump (GSHP) systems, the drilling cost of Ground Heat Exchangers (GHE) needs to be minimized for the promotion of the systems. Horizontal Directional Drilling (HDD) is a no-dig drilling technology which is often used for the installation infrastructures, i.e., pipes, cables, etc., in the ground. Since the cost of HDD and the surface land requirement are significantly smaller than conventional excavation, the combination of HDD and horizontal GHE is expected to improve the competitiveness of GSHP systems. In this research, field tests are carried out in shallow horizontal GHEs drilled using HDD in Saga, Japan. One of the GHE were completed with 25 mm ID U-tube of 40 m long, while a one-way 50 mm ID pipe was installed in the other GHE of 63 m long. Thermal response tests (TRTs) were performed with a fixed heat load of 40-50 W/m for each GHE to investigate their heat exchange performances. Also, an additonal TRT for the one-way GHE was conducted after inserting an inner pipe (34 mm OD) to check the improvement of heat exchange capacity by increasing the fluid velocity. The TRTs showed that both GHEs had comparable heat exchange capacity with the conventional vertical GHEs though the installation cost is much cheaper. The use of inner pipe in the one-way GHE was found to be quite effective; the heat exchange rate increased by above 25%, indicating the promising performance of the horizontal GHEs by HDD technology.


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