Thermal Conductivity of Cementitious Grouts and Impact On Heat Exchanger Length Design for Ground Source Heat Pumps

Allan, M.L.; Kavanaugh, Steve

doi:10.1080/10789669.1999.10391226

Cited by 82 publications

(22 citation statements)

References 3 publications

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“…Selecting appropriate materials and configurations to optimize the borehole thermal resistance can help decrease borehole length. To reduce the borehole thermal resistance of GHEs made with one or more Upipe, advances were made to develop space clips holding pipes separately, thermally enhanced grout Allan and Kavanaugh 1999;Carlson 2000;Borinaga-Treviño et al 2013a, 2013b and thermally enhanced pipe (Raymond et al 2011a(Raymond et al , 2011c. Further work has recently been conducted on coaxial GHEs, where the exchanger consists of two pipes imbricated into each other.…”

Section: Introductionmentioning

confidence: 99%

Designing coaxial ground heat exchangers with a thermally enhanced outer pipe

Raymond

Mercier²,

Nguyen³

2015

Geotherm Energy

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Background: Ground heat exchangers installed in boreholes are an expensive component of a ground-coupled heat pump system, where minimizing the borehole length with appropriate materials and configuration can reduce the overall cost of the system. Methods: Design calculations performed analytically indicate that the coaxial pipe configuration can be more advantageous than the single U-pipe configuration to reduce the total borehole length of a system. Results: A decrease of the borehole thermal resistance and an increase of the thermal mass of water contained in the coaxial exchanger helped to reduce borehole length by up to 23% for a synthetic building load profile dominated by cooling. The decrease of the borehole thermal resistance was achieved with an outer pipe made of thermally enhanced high-density polyethylene, where the thermal conductivity is 0.7 W m -1 K -1 .

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Section: Introductionmentioning

confidence: 99%

Designing coaxial ground heat exchangers with a thermally enhanced outer pipe

Raymond

Mercier²,

Nguyen³

2015

Geotherm Energy

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“…The cement-sand backfilling materials contain 15% cement, 15% water, 65% sand and 5% bentonite by weight. Thermal conductivity of this backfills is estimated to be about 2.4 W m À1 K À1 compared with 0.803-0.868 for neat cement and 0.75-0.80 for conventional high-solids bentonite [10]. U-tube spacers are used to keep the copper tubes apart from each other and close to the borehole wall.…”

Section: Methodsmentioning

confidence: 99%

An experimental study of a direct expansion ground-coupled heat pump system in heating mode

Wang

2009

Int. J. Energy Res.

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SUMMARYIn this paper, an experimental performance evaluation of a direct expansion ground-coupled heat pump (DX-GCHP) system in heating mode is presented. The DX-GCHP uses R134a as the refrigerant, and consists of three single U-tube copper ground heat exchangers (GHEs) placed in three 30 m vertical boreholes. During the on-off operations from December 25, 2007, to February 6, 2008, the heat pump supplied hot water to fan-coil at around 50.41C, and its heating capacity was about 6.43 kW. The energy-based heating coefficient of performance (COP) values of the heat pump and the whole system were found to be on average 3.55 and 3.28 at an evaporating temperature of 3.141C and a condensing temperature of 53.41C, respectively. The second law efficiency on the DX-GCHP unit basis was around 0.36. The exergetic COP values of the heat pump and the whole system were obtained to be 0.599 and 0.553 (the reference state temperature was set equal to the average outdoor temperature of À1.661C during the tests), respectively. The authors also discussed some practical points such as the heat extraction rate from the ground, refrigerant charge and two possible new configurations to simultaneously deal with maldistribution and instability of parallel GHE evaporators. This paper may reveal insights that will aid more efficient design and improvement for potential investigators, designers and operators of such DX-GCHP systems.

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“…Thermally enhanced bentonite has an increased conductivity of 1.46 W/m.K due to addition of quartzite sand (Remund and Lund, 1993). These values refer to the moist state and simcant decreases in conductivity for bentonite grouts occur on drymg (Allan and Kavanaugh, 1998). Although not measured, the thermal conductivity of bentonites is probably restored on re-saturation.…”

Section: Thermal Conductivitymentioning

confidence: 99%

Thermal conductivity and other properties of cementitious grouts

Allan¹

1998

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898 ~JJG 0The thermal conductivity and other properties cementitious grouts have been investigated in order to determine suitability of these materials for grouting vertical boreholes used with geothermal heat pumps. The roles of mix variables such as waterkement ratio, sandcement ratio and superplasticizer dosage were measured. In addition to thermal conductivity, the cementitious grouts were also tested for bleeding, permeability, bond to HDPE pipe, shrinkage, coefficient of thermal expansion, exotherm, durability and environmental impact. This paper summarizes the results for selected grout mixes. Relatively high thermal conductivities were obtained and this leads to reduction in predicted bore length and installation costs. Improvements in shrinkage resistance and bonding were achieved.

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Thermal Conductivity of Cementitious Grouts and Impact On Heat Exchanger Length Design for Ground Source Heat Pumps

Cited by 82 publications

References 3 publications

Designing coaxial ground heat exchangers with a thermally enhanced outer pipe

Designing coaxial ground heat exchangers with a thermally enhanced outer pipe

An experimental study of a direct expansion ground-coupled heat pump system in heating mode

Thermal conductivity and other properties of cementitious grouts

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