Groundwater Heat Pump (GWHP) system modeling and Thermal Affected Zone (TAZ) prediction reliability: Influence of temporal variations in flow discharge and injection temperature

• When designing GWHP plants it is essential to evaluate thermal effects around the injection wells.
• Numerical modeling enables identification of potential temperature anomalies.
• Flow rates and injection temperatures follow building energy requirements. Reliable simulation results may be obtained using hourly, daily, or monthly data.
• Seasonal averages are not suitable for reliable TAZ simulation.

A fundamental aspect in Groundwater Heat Pump (GWHP) plant design is the correct evaluation of the Thermal Affected Zone (TAZ) that develops around the injection well, which is important to avoid interference with existing groundwater applications and underground infrastructure. Numerical methods facilitate the identification of temperature anomalies, and software tools such as the FEFLOW program used in this study assist in these determinations. The actual flow rate and injection temperature are highly time-variable and follow changes in building energy requirements. In order to accurately predict the TAZ, it is necessary to consider this time variability. We calculated the TAZ using hourly discharge flow and temperature data, then recalculated the TAZ using average daily, monthly, and seasonal energetic equivalents. The four simulation results were compared with groundwater temperature data measured using a downgradient piezometer in order to assess the reliability of the simulations. The quality of the simulation was satisfactory when hourly, daily, or monthly flow rate and injection temperature data were used, whereas the seasonal averages were not suitable for reliably assessing TAZ development.