Rao Martand Singh

Field and Laboratory Investigation of a Heat Exchanger Pile

Incorporation of heat exchangers into pile foundations is a relatively novel sustainable technology for the intermittent storage of energy in soils. Energy can be utilised in this way for space heating and cooling of buildings by means of suitable systems integrated into buildings. This paper relates to an ongoing study on the impact of coupled thermo-mechanical loads on heat exchanger pile foundations. This study evaluates the performance of a laboratory scale energy pile under different vertical stress levels, temperature gradients and heat transfer modes and presents the full-scale in situ energy pile setup equipped with ground loops for heating/cooling and multi-level Osterberg cells for static load testing.

Determining Soil Thermal Conductivity Through Numerical Simulation of a Heating Test on a Heat Exchanger Pile

Heat exchanger pile foundations have a great potential of providing space heating and cooling to built structures. This technology is a variant of vertical borehole heat exchangers. A heat exchanger pile has heat absorber pipes firmly attached to its reinforcement cage. Heat carrier fluid circulates inside the pipes to transfer heat energy between the piles and the surrounding ground. Borehole heat exchangers technology is well established but the heat exchanger pile technology is relatively new and requires further investigation of its heat transfer process. The heat transfer process that affects the thermal performance of a heat exchanger pile system is highly dependent on the thermal conductivity of the surrounding ground. This paper presents a numerical prediction of a thermal conductivity ground profile based on a field heating test conducted on a heat exchanger pile. The thermal conductivity determined from the numerical simulation was compared with the ones evaluated from field and laboratory experiments. It was found that the thermal conductivity quantified numerically was in close agreement with the laboratory test results, whereas it differed from the field experimental value.

Non-isothermal moisture movement in unsaturated kaolin: An experimental and theoretical investigation

Non isothermal moisture movement in unsaturated kaolin is investigated in a series of experiments. Vapour transfer is then empirically quantified, and its theoretical representation considered. A thermo-hydraulic cell is used to apply thermal and hydraulic gradients to confined specimens in a number of thermal gradient, thermal-hydraulic gradient, and isothermal-hydraulic tests. Transient measurements of the thermal regime are made, and end of test measurement of moisture content, porosity, and chemical composition from a number of identical tests run for different durations allow pseudo transient variations of these parameters to be established. In each of the tests, where a thermal gradient is applied, the accumulation of chloride ions in the hottest regions indicates a cyclic movement of vapour and liquid moisture. Estimated vapour fluxes are determined by consideration of overall moisture and conservative ion movements in the sealed thermal gradient tests. These vapour fluxes are then compared to those predicted by an established vapour flow theory, and a modification to this theory is proposed based on a variable enhancement factor.

An Overview of Ocean Thermal and Geothermal Energy Conversion Technologies and Systems

The Earth and the oceans have a natural temperature gradient between the surface and given depths. The natural temperature gradient is used to operate renewable energy systems, such as power generation and space heating/cooling, which operate on similar thermodynamic concepts. For a given purpose, different technologies are used to extract heat from the two resources. Even though the concepts of the two systems are the same, their energy extracting performance is different. An overview of the similarities between the usages of the two thermal resources is presented in this paper. The energy balances at the surface of the Earth and the oceans, system performances, availabilities and economics are also presented.

Study of thermal properties of a basaltic clay

A clear understanding of heat transfer through soil is important in the design of a thermal-active ground structure such as a geothermal energy pile. Thermal conductivity is an important material parameter for the design of such ground structures. In the work described in this paper, the thermal conductivity and volumetric heat capacity of a basaltic clay was investigated through laboratory studies using a thermal needle probe. The experimental results were analysed to examine the effects of dry density and moisture content on the thermal conductivity and volumetric heat capacity of the soil. Finally it was found that the thermal conductivity and volumetric heat capacity increased with higher moisture contents and dry densities.

Inlet and Outlet Pipe Heat Interaction in a Contiguous Flight Auger (CFA) Pile

The use of energy loop(s), fitted into the structural foundation elements dualizes the role of the pile in meeting the structural performance and the thermal comfort demand of the overlying structure. Heat carrier fluid (HCF) is circulated through the loops, to extract or reject heat energy into the ground, during the space heating or cooling operation. However, this results in thermal interaction between the inlet and outlet leg of the loop especially in contiguous flight auger (CFA) piles where the loops are bunched together to a central steel bar. This paper presents a numerical study to investigate the heat flow characteristics between the inlet and outlet loops installed in a CFA pile. It was found that the central steel bar, used in a CFA pile, contributes towards higher thermal interaction. Similarly, it was found that the use of plastic bar of adequate strength, to substitute the use of steel bar, has both economic advantage and positive significance on the performance of the CFA pile.