Abstract
Aquifer thermal energy storage (ATES) is a technology with worldwide potential to provide sustainable space heating and cooling using groundwater stored at different temperatures. In areas with high ambient groundwater flow velocity (>25 m/y) thermal energy losses by displacement of groundwater may be prevented by application of multiple doublets. In such configurations two or more warm and two or more cold wells are aligned in the direction of the ambient groundwater flow. By controlling the infiltration and extraction rates of the upstream and downstream wells, the advection by ambient groundwater flow can be compensated by storing thermal energy through the upstream well, while re-extracting it from the downstream well.This study uses analytical and numerical tools and a case study to analyze the relevant processes, and provides guidelines for well placement and an operation strategy for ATES wells in aquifers with considerable groundwater flow. The size of the thermal radius relative to ambient groundwater flow velocity is an important metric. With multiple wells to counteract groundwater flow, this ratio affects the pumping scheme of these wells. The optimal distance between them is around 0.4 times the distance traveled by the groundwater in one year. A larger distance negatively affects the efficiency during the first years of operation.
Highlights
Many governments and companies set targets to reduce greenhouse gas (GHG) emissions (EU, 2010; UN, 2015; SER, 2013; Ministry-ofEconomic-affairs, 2016)
In winter a building is heated by means of a heat pump that extracts heat from warm groundwater that was stored in the previous summer
The groundwater is moved when the Aquifer thermal energy storage (ATES) system is inactive, which suggests that the ratio between storage and pumping time determines the required distance between the wells
Summary
Many governments and companies set targets to reduce greenhouse gas (GHG) emissions (EU, 2010; UN, 2015; SER, 2013; Ministry-ofEconomic-affairs, 2016). To meet these goals, the heating and cooling demand in the built environment is important because it consumes about 40% of the total fossil energy worldwide (Jong, 2016; EIA, 2009; RHC, 2013). While delivering its heat to the building, the heat pump simultaneously cools this groundwater, which is re-injected into the subsurface with a second well, the “cold” well. The flow is reversed, and cold water is extracted and used to directly cool the building (generally bypassing the heat pump). The groundwater is warmed up in the heat exchanger and immediately injected into the other well, the “warm” well
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