Perspectives of using the Quaternary groundwaters in the low-temperature geothermal systems in Poland

•Temperature of 82 % Quaternary groundwater is between 9.0–12.0 °C.•Groundwater hardness is the biggest hurdle in heat pumps correct operation.•Only 1.5 % of Quaternary groundwater can't be used in heat pumps.•Quaternary water quality is not a factor when using it as a lower heat source. Low-temperature geothermal energy obtained from a shallow rock mass or groundwater, with a temperature below 20 °C, is used in heat pump installations. The possibilities of using the groundwater of the Quaternary aquifers in Poland as a lower heat source for heat pumps - are presented. The analysis of physical and chemical parameters of water, based on groundwater monitoring carried out by the Polish Geological Institute - National Research Institute (PIG-PIB), is the basis for the discussion. The water temperature measured at the surface, using 596 monitoring points, ranged from 7.20 °C to 19.60 °C. The analysis of 12 chemical parameters in water, to determine the correct operation of the pumps (including corrosivity and scaling), indicates that the most common problem is the hardness of these waters. Therefore, scale deposition in installations may be a more common problem than corrosion. Exceedances of limit values of parameters, preventing the use of heat pumps, have been found in only 1.5 % of the waters examined. Water may contribute to both copper and steel corrosion; however, the number of measurement points indicating the former possibility is definitely higher. Therefore, in many cases, the use of pre-exchangers may be needed when designing the installations.