CLOSED-LOOP GEOTHERMAL SYSTEMS: PARAMETRIC STUDY INCLUDING INTERMITTENT OPERATION

Abstract

Closed-loop geothermal wells are gaining traction as a sustainable option for heating due to their (i) low environmental impact, (ii) small land footprint, and (iii) high-capacity factors. Their thermal performance is strongly influenced by parameters such as properties of the sub-surface rock structures, temperature gradient with depth, diameter and depth of the well, pipe insulation, soil surface temperature and the required operational strategies, which include the mass flow rate in the well, the water inlet temperature, the targeted process temperatures (well outlet) and possible intermittent loading conditions that are common in heating applications. This study presents a parametric analysis of the effect of the key control parameters including intermittent operation for a closed-loop co-axial geothermal well, i.e. water flowing through an annular pipe and returning via an insulated central pipe. The main aim is to evaluate their impact on heat extraction performance over a 30-year operational period. Changes in key parameters are investigated to determine the effect on both thermal and temperature outputs. These include (i) Load duration (6-month cycle), (ii) flow rate (1-10 kg/s), (iii) inlet fluid temperature (10-50°C), (iv) ground thermal conductivity (1-5 W/mK), and (vi) well depth (1-5 km).