A review of grout materials in geothermal energy applications

Montaser Mahmoud,Sumsun Naher,Mohammad Ali Abdelkareem,Abdul-Ghani Olabi,Tabbi Wilberforce,Keith Pullen,Mohamad Ramadan

doi:10.1016/j.ijft.2021.100070

Abstract

Ground heat exchangers are surrounded by grout material, making it one of the most important components in geothermal energy applications since it significantly affects the system's thermal performance. The current study reviews the different types of grout materials and compares their thermophysical properties. The most critical parameter is the grout's thermal conductivity in which it always presents a proportional relation with the system's efficiency. Numerous factors are involved in this review to ascertain theier impact on the grouts’ performance such as flowability, shrinkage, moisture content, freezing, heat capacity, strength, permeability, solubility and thermal imbalance. The different grouts compared are bentonite, cement, sand, graphite, controlled low-strength material, dolomite, and phase change materials. The literature shows that phase change materials are the best choices of grouting since they can provide high storage capacity, stability and temperature uniformity. The major problem of such materials is their low thermal conductivity. Thus, it is recommended to use composite phase change materials to enhance their thermal conductivity and increase the storage/retrieval rate.

Highlights

The development of systems incorporating renewable energy sources (RESs) is a growing field of research nowadays, targeting the reduction in pollution which results from the burning of fossil fuels [1]
Ground-coupled heat exchangers have helped in improving heating, ventilating, and air conditioning (HVAC) systems such that the ground source heat pump (GSHP) and earthair heat exchanger (EAHE) have been frequently used as airsource heat pump alternatives
The high capital cost of geothermal energy (GE) system’s installation makes it essential to study the different components of the BHE

Summary

Introduction

The development of systems incorporating renewable energy sources (RESs) is a growing field of research nowadays, targeting the reduction in pollution which results from the burning of fossil fuels [1]. This encourages to use horizontal and shallow GHEs instead of vertical and deep systems Another factor that helps to reduce the volume of installation is the low soil thermal interference radius which can decrease the required space between the GHE’s pipes. The risk of using a high degree of saturation needs to be considered as an important factor since it has a significant effect on the grout’s freezing which may cause critical damage to the GHE’s pipes and grout material. This may occur due to ice formation followed by volume expansion. The results showed that the grout materials having low permeability and high porosity may be fractured when applying the freezing test

Findings

Discussion

Conclusion