In temperate climates, many buildings need heating in winter and cooling in summer. A significant amount of energy can be saved by storing excess heat during the warmer months, and using it to warm up a building in winter. Similarly, storing the wintertime thermal energy reduces the need for air conditioning during the summer.
PhD student Emma Lepinay and professor Andy Woods have developed a model for interseasonal thermal energy storage. The system uses two aquifers in the subsurface, which contain hot and cold water. During the colder season, hot water is extracted from the hot aquifer and pumped to the surface. The water is used to warm up a building and its temperature decreases. The water, now cold, is then pumped back underground to recharge the cold reservoir. In the summer months, the process is reversed, and cold water is extracted from the cold aquifer and used to condition the temperature in the building. As a result, the water becomes warmer and is pumped back into the hot reservoir.
Emma’s model describes how the temperature of the water in both reservoirs changes over seasonal cycles. The system is thermally very efficient: after just 2-3 cycles, over 90% of the thermal energy injected into the hot reservoir is recovered in the extracted fluid. Hence, using the double well system can lead to significant energy saving over time.
This article has now been published by Renewable Energy, and is available here.