1. temporary storage of high- or low-temperature energy for later use.

2. accumulation of energy in a body or system in the form of sensible heat (temperature rise) or latent heat (change of phase).

quantity of heat that can be retained by a thermal storage system and be available for future use.

container plus all the contents of the container used for storing thermal energy. The transfer fluid and accessories, such as heat exchangers, agitators, circulating pumps, flow-switching devices, valves, and baffles which are integral with the thermal storage container are considered a part of the storage device.

ratio of the integrated discharge capacity to the hypothetical maximum available capacity for a single cycle of operation. Note: Hypothetical maximum available capacity is computed as follows—for sensible storage, multiply the average specific heat of the storage medium by the mass of the medium in storage and the difference between the average storage inlet temperatures during charging and discharging, for a single cycle. For latent storage, multiply the change in specific enthalpy associated with the liquid-solid phase change by the mass of medium in storage that changes phase, for a single cycle.

charging a thermal storage system at a constant rate during a complete cycle.

system wherein the load demand is met by stored thermal energy. See instantaneous capacity.

insulation of very high thermal resistance. Usually refers to that used in cryoengineering.

1. time interval by which the peak thermal response falls behind (lags) the peak thermal excitation in a thermal system.

2. phase difference in hours between the exterior and interior surface temperatures when the exterior surface is subjected to a sine-wave temperature change having a 24-hour period.