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Title: Thermal conductivity of cementitious grouts for geothermal heat pumps. Progress report FY 1997

Abstract

Grout is used to seal the annulus between the borehole and heat exchanger loops in vertical geothermal (ground coupled, ground source, GeoExchange) heat pump systems. The grout provides a heat transfer medium between the heat exchanger and surrounding formation, controls groundwater movement and prevents contamination of water supply. Enhanced heat pump coefficient of performance (COP) and reduced up-front loop installation costs can be achieved through optimization of the grout thermal conductivity. The objective of the work reported was to characterize thermal conductivity and other pertinent properties of conventional and filled cementitious grouts. Cost analysis and calculations of the reduction in heat exchanger length that could be achieved with such grouts were performed by the University of Alabama. Two strategies to enhance the thermal conductivity of cementitious grouts were used simultaneously. The first of these was to incorporate high thermal conductivity filler in the grout formulations. Based on previous tests (Allan and Kavanaugh, in preparation), silica sand was selected as a suitable filler. The second strategy was to reduce the water content of the grout mix. By lowering the water/cement ratio, the porosity of the hardened grout is decreased. This results in higher thermal conductivity. Lowering the water/cement ratio also improvesmore » such properties as permeability, strength, and durability. The addition of a liquid superplasticizer (high range water reducer) to the grout mixes enabled reduction of water/cement ratio while retaining pumpability. Superplasticizers are commonly used in the concrete and grouting industry to improve rheological properties.« less

Authors:
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Assistant Secretary for Energy Efficiency and Renewable Energy, Washington, DC (United States)
OSTI Identifier:
573177
Report Number(s):
BNL-65129
ON: DE98002826; TRN: AHC29807%%33
DOE Contract Number:  
AC02-76CH00016
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Nov 1997
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 15 GEOTHERMAL ENERGY; GROUND SOURCE HEAT PUMPS; SEALING MATERIALS; THERMAL CONDUCTIVITY; PROGRESS REPORT; HEAT TRANSFER FLUIDS; COEFFICIENT OF PERFORMANCE; ECONOMICS; FILLERS; POROSITY; MECHANICAL PROPERTIES; PLASTICIZERS; CEMENTS; FLY ASH; SLAGS; LEACHING; EXPERIMENTAL DATA; Geothermal Legacy

Citation Formats

Allan, M L. Thermal conductivity of cementitious grouts for geothermal heat pumps. Progress report FY 1997. United States: N. p., 1997. Web. doi:10.2172/573177.
Allan, M L. Thermal conductivity of cementitious grouts for geothermal heat pumps. Progress report FY 1997. United States. https://doi.org/10.2172/573177
Allan, M L. 1997. "Thermal conductivity of cementitious grouts for geothermal heat pumps. Progress report FY 1997". United States. https://doi.org/10.2172/573177. https://www.osti.gov/servlets/purl/573177.
@article{osti_573177,
title = {Thermal conductivity of cementitious grouts for geothermal heat pumps. Progress report FY 1997},
author = {Allan, M L},
abstractNote = {Grout is used to seal the annulus between the borehole and heat exchanger loops in vertical geothermal (ground coupled, ground source, GeoExchange) heat pump systems. The grout provides a heat transfer medium between the heat exchanger and surrounding formation, controls groundwater movement and prevents contamination of water supply. Enhanced heat pump coefficient of performance (COP) and reduced up-front loop installation costs can be achieved through optimization of the grout thermal conductivity. The objective of the work reported was to characterize thermal conductivity and other pertinent properties of conventional and filled cementitious grouts. Cost analysis and calculations of the reduction in heat exchanger length that could be achieved with such grouts were performed by the University of Alabama. Two strategies to enhance the thermal conductivity of cementitious grouts were used simultaneously. The first of these was to incorporate high thermal conductivity filler in the grout formulations. Based on previous tests (Allan and Kavanaugh, in preparation), silica sand was selected as a suitable filler. The second strategy was to reduce the water content of the grout mix. By lowering the water/cement ratio, the porosity of the hardened grout is decreased. This results in higher thermal conductivity. Lowering the water/cement ratio also improves such properties as permeability, strength, and durability. The addition of a liquid superplasticizer (high range water reducer) to the grout mixes enabled reduction of water/cement ratio while retaining pumpability. Superplasticizers are commonly used in the concrete and grouting industry to improve rheological properties.},
doi = {10.2172/573177},
url = {https://www.osti.gov/biblio/573177}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1997},
month = {11}
}