Evaluation of hydrogeologic conditions for groundwater heat pumps: analysis with data from national groundwater monitoring stations (original) (raw)
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Differently to the deep, high enthalpy geothermal resources exploitation, the widespread use of low grade, shallow geothermal systems for heating and/or cooling has not come along with a proportional development of conceptual and numerical understanding of the impacts of these systems on groundwater. Environmental agencies' requirements often neglect the particularity of the hydrogeological systems and consequently, adverse situations such as increase of temperature of water may occur in aquifers but also in the heat pump extraction wells themselves. This latter should be of particular concern yet reduces the long-term efficiency of these systems.
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In east Asia, where significant economical growth in this century is expected, intensive installation of geothermal heat pump (GHP) system may be important from both energy security and environmental protection aspects. Detailed underground temperature survey is essential for its promotion. Possibility of geothermal heat-pump application in tropical Asia is studied based on groundwater temperature data. Although generally geothermal heat-pump system may not have thermal merit for space cooling in tropics because subsurface temperature is generally higher than average atmospheric temperature, there may be some places in tropical regions where underground can be used as "cold heat-source". In order to confirm this possibility, groundwater temperature surveys were widely conducted in the Chao-Phraya plain, Thailand and Red-river plain, Vietnam to compare with atmospheric temperature data. As a result, regional variation of subsurface temperature at depths from 20 to 50 m of 3.4 K was observed in the whole Chao-Phraya plain while that of 2.0 K was observed in the Red-river plain. In some cities, subsurface temperature lower than monthly mean maximum atmospheric temperature for 5 K or more over four months was identified. Thus underground may be used as cold heat-source even in parts of tropical regions.
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Geothermal Energy, being a clean and sustainable source of energy, is gaining importance worldwide due to various reasons. Geothermal power can be generated throughout the year on twenty four hour basis as it's not much dependent on ambient temperature and weather conditions. Recently there is an increased interest in exploitation of low enthalpy geothermal resources for other applications such as geothermal space heating and cooling for domestic, industrial and commercial applications. GroundWater Heat Pump systems (GWHPs) extract water from one or more wells, pass it through a heat exchanger or a heat pump, which either extracts heat from, or rejects heat, and discharge water back into the aquifer or nearby surface water. This reinjection disturbs the natural aquifer temperature, producing a local temperature anomalies (cold or heat plume) known as the thermal affected zone (TAZ). Moreover, it is important to know if the TAZ can interfere with downgradient pre-existing plants or subsurface infrastructure or with the plant itself (thermal feedback). It is then important to know, even before constructing a GWHP system, the future TAZ extent around the planned injection point. Due to these risks, the increasing number of GWHP systems enforces the need for new criteria to develop subsurface energy policies that allow planning their spatial distribution. To obtain these sustainability criteria, the results of different dedicated studies are here proposed, in order to optimize the design and operation of GWHP systems.
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Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings by groundwater heat pumps can provide significant energy savings followed by economic and environmental benefits. The paper describes the procedure for selection of optimal low-temperature groundwater heat pump vapor compression cycle based on thermodynamic analysis of applied high temperature heat pump heating system. In comparative energy and exergy analysis observed are six different heating cycles, five of which utilize two-stage refrigerant compression, and one operate as basic one-stage heat pump system with an auxiliary heater. The systems validation is performed accounting strongly for the boundary conditions of the selected location.
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Open-loop groundwater heat pumps (GWHPs) are considered one of the most energy efficient and environmentally friendly airconditioning systems for temperate zones. A fundamental aspect in GWHP plant design is early evaluation of the thermally affected zone (TAZ) that develops around the injection well. This is particularly important to avoid interference with previously existing groundwater uses (wells) and subsurface underground structures. Numerical modelling is useful for delineating temperature anomalies. We carry out numerical simulations and a sensitivity analysis for the subsurface parameters affecting the TAZ. Using the simulation results we obtain a relative hierarchy of significance for the parameters with respect to the final result and then apply this analysis to an actual site. The results of the analysis indicate that the hydrodynamic parameters correlated with groundwater flow such as the hydraulic conductivity and the gradient are highly important, particularly those relating to the advective heat flow component.
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Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings by groundwater heat pumps can provide significant energy savings followed by economic and environmental benefits. The paper describes the procedure for selection of optimal low-temperature groundwater heat pump vapor compression cycle based on thermodynamic analysis of applied high temperature heat pump heating system. In comparative energy and exergy analysis observed are six different heating cycles, five of which utilize two-stage refrigerant compression, and one operate as basic one-stage heat pump system with an auxiliary heater. The systems validation is performed accounting strongly for the boundary conditions of the selected location.