Optimization of an Evacuated Tube Assisted Ground Source Heat Pump System With Slinky‐Coil Ground Heat Exchanger Using Taguchi Method

ABSTRACT

The study proposes a methodology to optimize an evacuated‐tube collector (ETC) coupled solar‐assisted ground source heat pump (SAGSHP) system integrated with a horizontal slinky‐coil ground heat exchanger (GHE) to exploit shallow geothermal energy in North East India. The system is optimized for both heating and cooling, using Taguchi L ₂₇ array and utility‐based multi‐objective framework, applying local heating/cooling degree‐day weighting to select one parameter set that minimizes collector area and GHE length while improving collector efficiency and system COP. The model couples ETC/GHE internal convection and geothermal physics, accounting for adjacent slinky loop thermal interaction and depth‐dependent ground‐temperature profile. Parameters such as ETC absorptivity, ETC/GHE pipe diameters, GHE flow rate, parameters influencing GHE geometry and depth were systematically varied and assessed by signal‐to‐noise ratios and ANOVA. Taguchi optimum parameter levels indicate ETC area of 1.76 m ² at 55.4% efficiency, GHE lengths of 56.4 m (heating), 91.6 m (cooling), COPs of 4.17 (heating) and 3.46 (cooling). ANOVA shows absorptivity drives ETC metrics: 48% (area) and 56% (efficiency). GHE mass‐flow governs subsurface design and performance: 36% (heating length), 50% (cooling length), 26% (heating COP), 49% (cooling COP), while GHE geometry contributes 7%–25% and depth 13%. Utility reflects the site's subtropical climate, selecting cooling‐aligned settings, giving 1.76 m ² ETC area at 55.4% efficiency, GHE lengths 89.7 m (heating) and 91.6 m (cooling), COPs 3.99 (heating) and 3.46 (cooling) for energy efficiency.