Environmental and Economic Impact of the Antifreeze Agents in Geothermal Heat Exchangers

Nicola Bartolini, Alessandro Casasso, Carlo Bianco and Rajandrea Sethi
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Nicola Bartolini: Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino, 10129 Torino, Italy
Alessandro Casasso: Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino, 10129 Torino, Italy
Carlo Bianco: Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino, 10129 Torino, Italy
Rajandrea Sethi: Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino, 10129 Torino, Italy

Energies, 2020, vol. 13, issue 21, 1-18

Abstract: Borehole heat exchangers (BHEs) generally employ water-antifreeze solutions to allow working fluid temperatures to fall below 0 °C. However, some local regulations have forbidden antifreeze additives (even non-toxic ones) to avoid groundwater pollution in case of pipe leakage. This paper presents a techno-economic and environmental analysis of four different fluids: propylene glycol at 25% and 33% weight concentrations, calcium chloride at 20% weight concentration (CaCl 2 20%), and pure water. Thermal loads from 36 case studies in six different climate zones are used to perform BHE sizing and compare the abovementioned fluids from the economic, operational, and environmental points of view. The economic analysis and the carbon footprint assessment are performed on a life cycle of 25 years considering the installation (BHE drilling, fluid) and operation (heat pump and ground-side circulation pump energy demand, fluid replacement) of the simulated GSHPs. Results highlight that using pure water as a heat carrier fluid is convenient for cooling-dominated buildings but, for heating-dominated buildings, this choice leads to a noticeable increase of the BHE needed length which is not compensated by the lower operational costs. On the other hand, avoiding the use of antifreeze additives generally leads to a reduction of the lifetime carbon footprint, with a few exceptions in very cold climates. CaCl 2 20% proves to be a good choice in most cases, both from the economic and the environmental points of view, as it allows a strong reduction of the installed BHE length in cold climates with a low additional cost and carbon footprint.

Keywords: borehole heat exchanger; ground source heat pump; heat carrier fluid; propylene glycol; calcium chloride; carbon footprint (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (9)

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