Feasibility of Groundwater Source Heat Pumps for Space Heating and Cooling in Mason County and the American Bottoms Area, Illinois

While air temperatures in Illinois vary greatly, shallow groundwater temperatures are nearly constant. Groundwater source geothermal heat pump systems can exploit this temperature difference for energy-efficient space heating, space cooling, and refrigeration. Such systems may contribute to energy efficiency gains and sustainable economic development. This project characterized two areas for geothermal heating and cooling potential. Mason County in central Illinois is mostly rural. The American Bottoms area of Madison and St. Clair Counties in southwestern Illinois is largely urban. Both areas are underlain by a thick sand and gravel aquifer. Although there are numerous water supply wells in both areas, groundwater is readily available for groundwater source heat pump systems. The heating and cooling requirements for a single-family house were estimated using two independent models that use weather data as input. Weather data, including monthly high and low temperatures and heating and cooling degree days, were compiled for both study areas. The groundwater pumping rates for these heating and cooling requirements were then calculated. The performance of a heat pump is expressed as the coefficient of performance (COP), the ratio of heating or cooling rate to the electrical energy input. For groundwater heat pumps, the heating COP value is 3.0 to 4.0. For cooling, COP ranges from 3.5 to 6.7. Calculations were performed using these ranges of COP. The groundwater in both study areas has fairly high hardness and iron concentrations and is close to saturation with calcium and iron carbonates. Using the groundwater for cooling will probably induce the precipitation of moderate amounts of one or both of these minerals. Periodic cleaning of heat exchanger surfaces, other system piping, and possibly well screens will be needed to remove these deposits.