Long-term performance investigation of a GSHP with actual size energy pile with PCM

Abstract

• Long term Performance investigation of ground source heat pump system. • Energy pile coupled with phase change materials under an actual building load. • Optimization of Phase change materials’ location inside the energy pile concrete shell. • Effect of utilizing multiple PCM melting temperature inside a single energy pile. The use of geothermal energy has increased significantly (90 time) since 1995. Among these increases, Ground Source Heat Pumps (GSHP) has contributed by 40 times in an effort to reduce the burning of fossil fuels and contribute to the reduction of green house gas emissions. The space requirements and high initial cost of borehole fields hinder the widespread use of GSHPs. The use of foundation piles, used as a ground heat exchanger, has been proposed to overcome these limitations. Research has shown that foundation piles have a lower depth and smaller spacing compared to boreholes. Phase Change Materials (PCMs) have been proposed as a potential solution to increase the storage capacity and decrease the thermal radius of energy piles. In the current study, a 3-D finite element model was developed to study the effects of PCMs on the performance of energy piles against a real building load for a complete year, while integrating an actual heat pump (HP) performance curve into the numerical model. The effects of the PCM location and melting range were also investigated. The study revealed a 5.2% enhancement in the Coefficient of Performance (COP) during the melting of the PCM, and a negative effect of up to 1.8% during the completely solid-state. Locating the PCM cylinders inside of the concrete shell led to better performance compared to when the PCM cylinders were located outside of the concrete shell. The best locations were found to be between the center of he pile and the U-loop. The PCM melting range of (4–6)°C was better than the melting range of (1–3)°C for the current study load. Lastly, the use of multiple PCM melting temperatures for a given design was investigated. The results revealed that the use of multiple PCM melting temperatures led to a performance enhancement of up to 26%.