Numerical Simulation on the Continuous Operation of Aquifer Thermal Energy Storage System

Abstract

As the demand for energy increases, any work to enhance energy conservation becomes crucial. Thermal energy storage (TES) system applications around the world have been known to provide economical and environmental solutions to the energy problems (Paksoy et al., 2004). TES systems contribute significantly to improving energy efficiency by helping match energy supply and demand. TES also makes it possible to more effectively utilize new renewable energy sources (solar, geothermal, ambient, etc.) and waste heat/cold recovery for space heating and cooling. With a storage medium of various types and sizes, TES systems therefore contribute to enhancing energy efficiency. The storage medium can be located in containers of various types and sizes. Underground thermal energy storage (UTES) is mostly used for large quantities of seasonal heat/cold storage (Nielsen, 2003). There are several concepts as to how the underground can be used for underground thermal energy storage depending on geological, hydrogeological, and other site conditions. The two most promising options are storage in aquifers (aquifer thermal energy storage, ATES) and storage through borehole heat exchangers (borehole thermal energy storage, BTES) (Sannerb, 2001; Andersson, 2007). In borehole thermal energy storage systems, also called “closed” systems, a fluid (water in most cases) is pumped through heat exchangers in the ground. In aquifer thermal energy storage or “open” systems, groundwater is pumped out of the ground and injected into the ground by using wells to carry the thermal energy into and out of an aquifer (Novo et al., 2010). Aquifer thermal energy storage (ATES) system utilizes low-temperature geothermal resource in the aquifer (Sannera, 2001; Rafferty, 2003). Aquifer thermal energy storage, which is similar to the groundwater geothermal system under direct uses, involves storage and provides for both heating and cooling on a seasonal basis. An advantage of open systems is generally higher heat transfer capacity of a well compared to a borehole. This makes ATES usually the cheapest alternative if the subsurface is hydrogeologically and hydrochemically suited for the system. Such aquifers offer a potential and economical way of storing thermal energy for long periods of time. ATES systems have been used successfully around the world for the seasonal storage of heat and cold energy for the purpose of heating and cooling buildings (Probert et al., 1994; Paksoy et al., 2000; Allen et al., 2000; Schmidt, 2003; Paksoy et al., 2004).