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Title: Borehole thermal resistance: Laboratory and field studies

Abstract

Vertical ground heat exchangers are a common method of linking geothermal heat pump systems to the earth, and they consist of pipe installed into a borehole that is subsequently backfilled with a material that forms the heat transfer link between the pipe and earth. In many states that material must also be a grout to form a barrier against water migration in any direction along the entire borehole length. Until recently, little attention has been given to the thermal properties of commonly used backfill and grouting materials or to the effect of the thermal conductivity of those materials on the thermal performance of the vertical ground heat exchanger. Laboratory studies were performed to determine the effect of grout thermal conductivity, borehole diameter, pipe size, and pipe configuration on the total thermal resistance in the borehole. It was found that borehole thermal resistance decreased with increasing grout thermal resistance decreased with increasing grout thermal conductivity, but increasing grout thermal conductivity above 1.0 Btu/h{center{underscore}dot}ft{center{underscore}dot}{degree}F provided very small additional reduction. The studies resulted in a set of relationships for borehole thermal resistance, depending on the pipe configuration in the borehole, that can be utilized in the calculation of design length of a verticalmore » ground heat exchanger for a prescribed heating and cooling load. A series of independent field tests verified that the assumption of equal spacing between the pipes and the borehole wall conservatively accounted for the thermal conductivity of the backfill or grout material. The effect of increasing grout thermal conductivity from 0.43 to 0.85 Btu/h{center{underscore}dot}ft{center{underscore}dot}{degree}F resulted in overall reductions in thermal resistance between the circulating fluid and the earth by 15.3% to 19.5%.« less

Authors:
Publication Date:
Research Org.:
South Dakota State Univ., Brookings, SD (US)
OSTI Identifier:
20002326
Report Number(s):
CONF-990102-
ISSN 0001-2505; TRN: IM200002%%326
Resource Type:
Conference
Resource Relation:
Conference: ASHRAE Winter Meeting, Chicago, IL (US), 01/23/1999--01/27/1999; Other Information: PBD: 1999; Related Information: In: ASHRAE transactions 1999: Technical and symposium papers. Volume 105, Part 1, 1387 pages.
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; GROUND SOURCE HEAT PUMPS; HEAT EXCHANGERS; BOREHOLES; HEAT TRANSFER; THERMAL CONDUCTIVITY; GROUTING; BACKFILLING; SIZE; PIPES

Citation Formats

Remund, C.P. Borehole thermal resistance: Laboratory and field studies. United States: N. p., 1999. Web.
Remund, C.P. Borehole thermal resistance: Laboratory and field studies. United States.
Remund, C.P. Thu . "Borehole thermal resistance: Laboratory and field studies". United States.
@article{osti_20002326,
title = {Borehole thermal resistance: Laboratory and field studies},
author = {Remund, C.P.},
abstractNote = {Vertical ground heat exchangers are a common method of linking geothermal heat pump systems to the earth, and they consist of pipe installed into a borehole that is subsequently backfilled with a material that forms the heat transfer link between the pipe and earth. In many states that material must also be a grout to form a barrier against water migration in any direction along the entire borehole length. Until recently, little attention has been given to the thermal properties of commonly used backfill and grouting materials or to the effect of the thermal conductivity of those materials on the thermal performance of the vertical ground heat exchanger. Laboratory studies were performed to determine the effect of grout thermal conductivity, borehole diameter, pipe size, and pipe configuration on the total thermal resistance in the borehole. It was found that borehole thermal resistance decreased with increasing grout thermal resistance decreased with increasing grout thermal conductivity, but increasing grout thermal conductivity above 1.0 Btu/h{center{underscore}dot}ft{center{underscore}dot}{degree}F provided very small additional reduction. The studies resulted in a set of relationships for borehole thermal resistance, depending on the pipe configuration in the borehole, that can be utilized in the calculation of design length of a vertical ground heat exchanger for a prescribed heating and cooling load. A series of independent field tests verified that the assumption of equal spacing between the pipes and the borehole wall conservatively accounted for the thermal conductivity of the backfill or grout material. The effect of increasing grout thermal conductivity from 0.43 to 0.85 Btu/h{center{underscore}dot}ft{center{underscore}dot}{degree}F resulted in overall reductions in thermal resistance between the circulating fluid and the earth by 15.3% to 19.5%.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1999},
month = {7}
}

Conference:
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