Numerical study of horizontal ground heat exchangers for design optimization

•Comparison for thermal performance of horizontal ground heat exchangers.•CFD simulation of three dimensional models was performed for short time analysis.•Positioning of return pipe in vertical orientation is crucial.•Composite pipe coating restricts its performance identical of that in HDPE pipe.

Despite ground source heat pump has been proven as highly efficient, high initial cost discourages homeowners and small-medium enterprises to opt for such systems. Horizontal ground heat exchangers offer relatively low-cost solution that may help promoting these systems usage worldwide. This study examines ways to optimize the designs for horizontal ground heat exchangers by using different layouts and pipe materials. CFD simulation of three dimensional models was performed to achieve this objective. All cases tested are able to yield comparable heat exchange rate for an equal trench length. However, the effective period differs one from the other. Additional initial and overhead costs are worthy as slinky ground heat exchangers prolongs heat transfer process when compared against straight configuration. Pipe materials with superior thermal conductivity also promote longer high efficiency operation. An improvement of 16% is reported when copper pipe is used instead of the conventional HDPE pipes. Effective period can be extended by 14% when ground heat exchangers are installed in vertical orientation. Thermal interference in slinky configuration is prevalent during initial operation. In a long run, the effect is observed to be minimal except in vertical orientation. However, it is avoidable beforehand at design stage.