Abstract
The use of shallow geothermal energy systems utilizing groundwater temperature for the air-conditioning of buildings is increasing worldwide. The impact of these systems on groundwater quality has become crucial for environmental regulations and system design. For the long-term operation of geothermal systems, it is important to evaluate their influence on the geochemical properties of groundwater, including precipitation and dissolution of secondary minerals. This research was conducted in a real-scale geothermal system, consisting of a groundwater heat pump (GWHP). Hydrochemical data were obtained from samples collected from an aquifer before heating, during heating, and before cooling operations of the GWHP. The Langelier Saturation Index and Ryznar Stability Index were calculated, and the saturation index was simulated with the PHREEQC program. Evidence from water table variation, temperature change, and 87 Sr/ 86 Sr isotope distribution showed that groundwater flows from a well located on the northwest side of the geothermal well. The saturation index values showed that the pristine groundwater favors carbonate dissolution, however, manganese oxides are more sensitive to temperature than carbonate minerals. In addition, mineral precipitation and dissolution were found to vary with depth and temperature.
Highlights
In the last few decades, extensive CO2 gas emissions have been linked to several aspects of global changes and the scarcity of energy resources by many researchers [1,2,3]
The hydrochemical condition of groundwater and the precipitation of minerals affect the lifespan of groundwater heat pump (GWHP). Considering these issues, this study investigates the effect of GWHP operation on groundwater using hydrochemical monitoring data for one season of heating and cooling operation at a GWHP site
The temperature of re-injected water ranged from 13.9–15.9 ◦ C in the monitored heating season
Summary
In the last few decades, extensive CO2 gas emissions have been linked to several aspects of global changes and the scarcity of energy resources by many researchers [1,2,3]. Environmental problems are becoming evident at local and global scales. Protocol and the Paris Agreement call for the reduction of fossil fuel consumption as well as enforce developments in renewable energy [4,5,6]. Wind, and hydro-energy, shallow geothermal energy is an alternative to fossil fuel that is used for space heating and cooling worldwide [7,8]. With the advantages of flexible system design for various capacity ranges, site availability, long sustainability, environmental friendliness, and simple simplicity of installation, the geothermal heat pump market has experienced dramatic growth since the 1990s [9,10,11,12].
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