The reduction of heating and cooling CO2 emissions with the ATES triplet

Low temperature Aquifer Thermal Energy Storage (ATES) is increasingly used for space heating and cooling. Though these systems emit 3-4 times less CO₂ compared to gas heating, they still require a substantial amount of electricity, mostly because of the heat pump (~60%). Storing higher temperatures (HT) to be used for direct heating can be a solution to circumvent the use of a heat pump, however the return temperature after heating is not usually cold enough to use directly for cooling. The first HT ATES systems that are implemented have either no cooling, or alternative means for cooling. With better insulated buildings, that require both heating and cooling, as well as an increased pressure on the electricity grid, an autarkic system is needed that can supply both heating and cooling. The ATES Triplet system aims to do just that.

Similar to and HT ATES system, the ATES Triplet stores hot water at supply temperature needed for space heating in a hot well. Unlike the HT-ATES system, it also aims to store water at the supply temperature for cooling in a cold well. This heat and cold can be harvested by solar collectors and dry coolers (or other green heat/cold sources locally available). After the water extracted from the wells is used to heat/cool the building, the solar collectors and dry coolers can be used to store water at the right temperatures. However, the availability of these sources can be insufficient to reach the required temperatures. A third well is added that functions as a buffer. Water used for heating or cooling can be stored here until there is enough heating/cooling capacity available from the solar collectors and dry coolers to upgrade the water to the required temperature, and store in the hot or cold well. Furthermore, the solar collectors and dry coolers can also be used for direct space heating and cooling, making the entire system and autarkic heating and cooling system.

Initial simulations show a substantial reduction to operational CO₂ emissions compared to conventional heating systems. Though a higher initial investment is required, systems also show an increased economic performance over conventional ATES systems and gas heating. Further research will investigate the effect of subsurface conditions, system layout and other operational conditions on the economic and environmental performance of the system.