Performance assessment of refrigerants for enhanced COP and pipe efficiency in horizontal geothermal cooling systems for Southeast Asia

This study investigates the performance of nine refrigerants, including pure, zeotropic, and natural options, in horizontal geothermal cooling systems. It aims to evaluate the coefficient of performance (COP) and assess the influence of key parameters, such as evaporating temperature, ground temperature, pipe diameter, and soil thermal conductivity, on the required buried pipe length. The analysis reveals that while refrigerant mass flow rate has little effect on COP, it significantly influences pipe length, impacting material cost and installation feasibility. Evaporating temperature varies from −5 °C to 5 °C, with condensing temperatures between 40 °C and 50 °C. Among the selected refrigerants, R407C achieves the highest COP, making it suitable for residential applications with moderate cooling loads. Polyethylene (PE) and high-density polyethylene (HDPE) pipes demonstrate superior thermal performance, durability, and cost efficiency, making them effective materials for underground installation. Soil thermal conductivity is a key factor affecting system performance, with values around 2 W/m·K at depths of 1.5–2 m being most effective under Southeast Asian conditions. These findings offer insights to improve geothermal cooling system design in Southeast Asia, where increasing cooling demands require energy-efficient and cost-effective solutions. The research enhances understanding of refrigerant selection, system configurations, and soil properties in sustainable cooling technologies.