Thermal performance analysis of slinky-coil ground-air heat exchanger system with sand-bentonite as backfilling material

The ground-air heat exchanger (GAHE) is the promising passive technique for building heating/cooling, but due to its high installation cost (mainly pipe cost and excavation cost), it could not become popular. The required length of pipe can be reduced by using thermally enhanced backfilling material (BFM), while, the length of the trench can be reduced by using slinky-coil pipe layout. In the present study, an experimental laboratory setup of GAHE system has been developed with a slinky-coil pipe layout and sand-bentonite as BFM. For this, a flexible PVC pipe of 75 mm diameter and 30 m length, has been arranged in slinky-coil pattern and installed horizontally in a soil box of 10.2 m length. For the study, variation in soil temperature (23 degrees C-27 degrees C), inlet air temperature (38 degrees C-46 degrees C), air flow velocity (5 m/s-20 m/s) and soil conditions (dry and wet), have been considered. Study reveals that a drop-in air temperature as high as 18.7 degrees C at 30 m pipe length (trench length of 10.2 m) can be achieved with soil at a temperature of 27 degrees C and inlet air temperature of 46 degrees C. The study also revealed that the pipe length could be reduced by 20% with wet sand-bentonite as compared to dry sand-bentonite. (C) 2019 Elsevier B.V. All rights reserved.