Suggestion of a design method for horizontal spiral coil type ground heat exchangers

The need of geothermal energy is constantly increasing for economical and environmental benefits. Horizontal ground heat exchangers (GHEs) can reduce the installation cost and they can also compromise between increasing in efficiency and costs. There are many kinds of GHEs, and it is known that slinky and spiral coil type GHEs show high thermal performance in the horizontal system. However, there is no adequate guideline to design the spiral coil type GHEs even though there is a design program for the slinky type GHEs. Therefore, this paper presents a design module for the horizontal spiral coil type GHEs. Dried Joomunjin standard sand was filled in a steel box including a horizontal spiral coil type GHE of which the size was 5m x 1m x 1m and thermal response tests (TRTs) were conducted for 30 hours to evaluate heat exchange rates. Based on the experimental results, a modified design module, that includes a scheme to properly evaluate design parameters such as ground thermal resistance and borehole thermal resistance used in the Kavanaugh theory for designing a spiral coil type GHE, was suggested.