Thermal short circuit on groundwater heat pump

Abstract

This paper presents a study of the feasibility of providing heating and cooling by means of an open-loop groundwater heat pump system for a restored commercial building in Rovigo, located in the Po River Plain (Italy). Results obtained from the modelling confirm the potential hydrogeological capacity of the site to provide the necessary amount of groundwater and associated energy with limited environmental impact. Injection of warmer (or cooler) water into the aquifer creates a thermal plume whose dimensions and geometry depend at first on the properties of the subsurface formations and particularly on working system conditions and by the cooling and heating loads. This study shows the risk of the thermal breakthrough between well doublets and suggests that there are several possible heating/cooling daily timetables that reduce the risk of thermal feedback between extraction and injection wells. These timetables may prevent the GWHP system from becoming uneconomical and energetically inefficient. Thermal breakthrough is common in groundwater heat exchange systems, particularly in historical town districts where the distance between wells is necessarily close due to buildings proximity and the possibility of other group plant in the neighbourhood. Most probably due to modelling difficulties, it is unusual to take into account this type of thermal contamination during an ordinary analysis of the interaction between and consequences of groundwater heat pump and aquifer systems. An approach using complex open loop modelling allows the analysis of a case of thermal feedback in order to obtain the best planning and use of the geoexchange plant