Phase change materials effect on the thermal radius and energy storage capacity of energy piles: Experimental and numerical study

Abstract

Geothermal energy is a renewable energy source whose use has been increased dramatically. It is primarily harvested by employing ground source heat pump (GSHP) technology due to its high coefficient of performance (COP) and low greenhouse gas emissions. This study aims to present a potential solution to the challenges preventing a higher adoption rate for ground source heat pump technology using building foundation piles as a ground heat exchanger (GHE) and implementing phase change materials (PCM) containers into the concrete shell. The study was conducted experimentally using two lab-scaled foundation piles (with and without PCM), with 3 layers of insulation. CFD numerical model was developed and validated against the experimental data. The modified model, by replacing the three insulations layers with a sand layer, was used to study the effect of different operating conditions on the heat storage capacity. Results revealed that implementing the PCM containers increased the energy storage from 16.4 to 48.2 kJ/kg (in the case of PCM 2), while the temperature distribution was always lower during the charging, due to the smaller thermal radius of the piles. By increasing the flow rate from the laminar regions to the turbulent regions, the storage capacity was increased by 10%. the study recommended using a turbulent flow inside the GHE and selecting the PCM melting temperature according to the time at which the peak load occurs.

Keywords

• Energy piles
• Phase change materials
• Thermal radius
• Ground source heat pump
• Borehole
• Melting temperature