Assessment of Heat Recovery and Recovery Efficiency of a Seasonal Thermal Energy Storage System in a Moist Porous Medium

Thermal energy storage has received a great interest by researchers and industrials as part of designing new systems able to store and deliver thermal energy efficiently for long periods, especially in regions characterized by important solar energy potential.The aim of this preliminary work is to simulate the performance of a novel seasonal heat storage system dedicated to store heat in the ground during hot period then to recover it during cold period.The system investigated herein is a ground heat exchanger buried at only 8 m below the underground while other technologies go deeper than 100 m.Several case studies have been simulated according to different types of hot fluid carrier and moisture content of the porous medium.Comsol Multiphysics was used to model heat exchange between a fluid carrier flowing through a GHX, and a partially saturated porous medium composed essentially of gravel and located at about 0.5 m underground.Performance of the system was evaluated for a one-year period in order to get a good estimation of long-term heat storage and recovery.The results showed that the use of gasoline as a fluid carrier will yield higher temperature levels than the other fluids particularly during cold season; however, the use of water allowed for the storage and recovery of bigger heat energy than gasoline or glycol do.However, moisture content of the porous medium did not influence the whole process.System heat recovery has been enhanced by the use of two ducts to extract more heat from the underground.This approach led to a remarkable increase in temperature levels, as well as heat energy and recovery efficiency which went up from 41% when using only 1 duct to 71%.