Seasonal Thermal Store - Temperature Classifications of STES Systems

Temperature Classifications of STES Systems

Seasonal (or "annualized") thermal storage can be divided into three broad categories:

• Low-temperature systems (such as Passive Annual Heat Storage (PAHS) and Annualized geo solar (AGS)) use the soil adjoining the building as a low-temperature seasonal heat store (reaching temperatures similar to average annual air temperature), drawing upon the stored heat for space heating. Such systems can also be seen as an extension to the building design (normally passive solar building design), as the design involves some simple but significant differences when compared to 'traditional' buildings. Rock caverns filled with water have also been proposed.
• Warm-temperature interseasonal heat stores also use soil to store heat, but employ active mechanisms of solar collection in summer to heat thermal banks in advance of the heating season.
• High-temperature seasonal heat stores are essentially an extension of the building's HVAC and water heating systems. Water is normally the storage medium, stored in tanks at temperatures that can approach boiling point. Phase change materials (which are expensive but which require much smaller tanks) and high-tech soil heating systems (remote from the building) are occasionally used instead. For systems installed in individual buildings, additional space is required to accommodate the size of the storage tanks.

Effective insulation or superinsulation of the building structure is desirable to minimize heat-loss from the building, and reduce the amount of heat that needs to be stored for space heating.