Improvement of Thermal Properties in Grouting Materials of Heat Exchange Wells in Ground-Coupled Heat Pump Systems

• Published in: Shigen to sozai Vol. 119; no. 6,7; pp. 403 - 409
• Main Authors: FUJII, Hikari, ISHIKAMI, Takashi, OHSHIMA, Kazuo
• Format: Journal Article
• Language: Japanese
• Published: The Mining and Materials Processing Institute of Japan 01.06.2003
• Subjects: 3D Model; Bentonite; Ground-coupled Heat Pump; Silica Sand; Thermal Conductivity
• ISSN: 0916-1740; 1880-6244
• DOI: 10.2473/shigentosozai.119.403

In Ground-Coupled Heat Pump (GCHP) systems, the thermal conductivity enhancement of grouting materials in heat exchange wells increases the heat exchange rate between formations and boreholes and hence greatly contributes the improvement of feasibility of the systems. In this paper, series of laboratory measurements were conducted to develop highly thermal conductive cement mortars to be used as grouting materials. Silica sand was mixed with cement paste for increasing the thermal conductivity, while bentonite was added to the mixture of cement and silica sand for establishing a uniform distribution of silica sand in the grouting materials. In the measurements, the relationship between the thermal conductivities of mortar samples with different recipes on silica sand / cement ratio, cement specific gravity, and bentonite mixture ratio were investigated under water-saturated conditions. After thermal conductivity measurements, permeability measurements were conducted to confirm the impermeable nature of the mortar samples. Viscosities of mortar pastes were also measured to confirm the easiness of grouting operation in well completions. The experiments showed (i) addition of silica sand greatly improves the thermal conductivity of grouting materials, (ii) addition of bentonite of 1.5 to 2.0 % (wt% to cement) maximizes the effect of silica sand, (iii) the permeability grouting materials proposed in this work was low enough to avoid any cross flow between aquifers.