Thermohydraulic Comparison of Horizontal Geo-Exchange Pipes Versus Traditional Boreholes
Ground Source Heat Pump (GSHP) systems provide efficient, low-emission heating and cooling but remain constrained by the high drilling costs associated with deep vertical boreholes. This study evaluates a shallow, cost-effective alternative: Horizontal Plastic Geo-Exchange Pipes (PGEPs) installed using Horizontal Directional Drilling (HDD), and compares their thermal performance to a conventional vertical U-tube borehole. A thermohydraulic PGEP model was developed and experimentally validated, while the borehole model was benchmarked against a finite line-source analytical solution. A full-year simulation incorporating hourly school building loads and a Toronto-based ground temperature model was conducted for both systems. The horizontal PGEP delivered a maximum capacity of 1.5 tons and an annual average COP of 3.7, outperforming the vertical borehole, which achieved only 1.0 ton under identical constraints. PGEP performance advantages stem from its larger heat-exchange surface area, laminar-flow-enhanced residence time, and installation depth benefiting from seasonal thermal recharge.