Geotechnical Engineering Lecture

Introduction

The Geotechnical Engineering Lecture by Dr Fleur Loveridge

Thermal Response Testing: Challenges and New Applications

Thermal conductivity of the ground is an important parameter in the design of ground energy systems, which have an increasing role to play in providing renewable heat to the built environment. For larger schemes, the bulk thermal conductivity of the ground surrounding the system is often determined in situ using a thermal response test conducted on a borehole heat exchanger. There is also an increasing trend to apply the test to energy piles. Although the test method is commonly used, its limitations are often not fully understood, leading to an over-simplistic interpretation that may fail to identify key facets of the ground and heat exchanger thermal behaviour. Some of these limitations will be magnified when applied to larger diameter energy piles.
This presentation will explore some of the uncertainties and limitations of thermal response testing with reference to two case studies. First an instrumented thermal response test carried out in a 150m deep borehole in east London will be examined. This test shows how a single unique value of bulk thermal conductivity may not be appropriate in all cases due to ground stratification and the presence of groundwater flow. Secondly the potential pitfalls of applying thermal response testing to energy piles will be explored using data from an instrumented test site in Texas. Here the effect of pile size and construction materials on the required test time will be discussed.
The presentation will then conclude with some practical recommendations about application of the thermal response test to both boreholes and piles and how it may fit within the site investigation process.

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