Feasibility study of an ATES triplet

Abstract

Aquifer Thermal Energy Storages (ATES) are used to store hot or cold water in an aquifer, where the thermal energy of the water can be used at later times. This way, the discrepancy between a heating demand of buildings in winter and a cooling demand in summer can be overcome. In order to provide in heating and cooling demands, a heat pump is currently required to heat or cool a building at effective temperatures. In buildings with ATES doublet systems, the heat pump uses the most energy for space conditioning. An ATES system without a heat pump is proposed in this work by using three wells (triplet), solar heat collectors and a dry cooler. The solar heat collectors are used to inject water at 40°C in the warm storage when there is incoming solar radiation. Similarly, the dry cooler is used to inject water of 5°C in the cold storage when the air temperature is below 4°C. The feasibility of the ATES triplet is mostly affected by the thermal losses of the warm well, which are consequently influenced by: a) the ratio between the area and volume of the warm storage and b) the hydraulic conductivities in the aquifer. Apart from that, the weather conditions also have a great impact on the feasibility of an ATES triplet. The best conditions for the realization of an ATES triplet are buildings with a gross surface area over 40.000m2 in temperate climate conditions on top of fine-sanded aquifers. By looking at a case scenario on the TU Delft campus, the triplet is shown to be feasible in a temperate marine climate like in the Netherlands and shows massive improvements in operational costs and CO2 emissions. Investment costs of the ATES triplet are high compared to the investment costs of an ATES doublet or a conventional, gas-fired boiler system. The high investment costs are due to the high price of solar heat collectors and hence a high equity capital is required for the realization of an ATES triplet.