Development of thermal steel sheet piles

The use of thermal bored piles is an established and proven foundation element that can be constructed with closed ground source heat pump (GSHP) systems to provide renewable heating and cooling energy to new buildings. The thermal-hydro-mechanical (THM) interaction for thermal retaining walls has also been studied for Crossrail stations.

To advance the adaptation of this technology to thermal steel sheet piles walls the Grand Piling funded a comparison study and installation trial to demonstrate feasibility. In this study, the application of steel sheet piles for their geothermal potential are investigated by numerical analysis. Comparison with equivalent concrete secant piles is also made.

Low-carbon steel has a thermal conductivity between 40 and 50Wm-1K-1; higher than concrete, which is typically in a range of 1 to 2Wm-1K-1. As a consequence of this higher conductivity, the soil mass can potentially be more efficiently activated via a steel sheet pile wall. To make use of the high thermal conductivity of steel all that is required is to establish a simple loop installation system.

In a concrete secant pile, the thermal U-loop heat exchanger system is fixed to the pile’s reinforcement cage and encased within the cast concrete. Refrigerant fluid (water with additives) is circulated through the loops from the heat pump down the piles where heat is exchanged with the surrounding soil.

Two steel sheet piling heat exchanger configurations have been considered: U-loop and concentric (coaxial) pipe, as shown in figures 1 and 2. For the sheet pile U-loop heat exchanger system, the pipework is held to the side of the sheet pile plate. For the sheet pile concentric pipe heat exchanger system, the pipe is welded to the side of the sheet pile plate to improve the heat conduction. Fluid is circulated through the inner concentric pipe and is returned to the surface through the annulus between the inner and outer pipes; the flow is regulated by a well head on top of the pipe.

In this study, the feasibility of installing thermal steel sheet piles and heat output rate are both investigated. The purpose is to find out whether steel sheet piles can provide a viable alternative for ground energy to traditional concrete secant piles.

This article comes from geplus edit released