Effect of thermal insulation layer on thermal performance of energy slab

A energy slab is a ground coupled heat exchanger equipped in building slab structures, which has a layout similar to the horizontal ground heat exchanger (GHEX). The horizontal GHEX allows circulation of a working fluid through heat exchange pipes that are buried underground with horizontal arrangements, inducing heat exchange between the fluid and the surrounding ground formation. The energy slab is installed as one component of the floor slab layers to utilize the underground structure as a hybrid energy structure. However, its thermal performance is usually poorer than the conventional vertical GHEXs because the energy slab cannot use the high thermal capacity of deep underground and is significantly affected by air temperature. In this paper, stainless steel (STS) pipes were alternatively considered for the heat exchanger instead of high-density polyethylene (HDPE) pipes to enhance the thermal performance of energy slab. Two types of field-scale energy slabs were constructed in the test bed, which consists of both the STS and HDPE pipe. Then, a series of thermal response tests (TRTs) and thermal performance tests (TPTs) were conducted to evaluate heat exchange efficiency according to the pipe material and the structure of the energy slab. In addition, the energy slabs were compared with other types of GHEXs to evaluate the applicability of energy slabs with respect to relative heat exchange efficiency.