Seasonal Storage

Seasonal TES by sorption storage seems to be particularly interesting, because there are no heat losses during the storage period. The stored thermal energy will only be discharged, when the adsorption process will be started. This is only valid, if the sensible heat of the adsorbent is

neglected. About 10 — 15 % of the heat input will be lost by the cooling down of the adsorbent material.

However seasonal storage by sorption systems is strongly influenced by the changes in the ambient temperature between summer and winter. A substantial decrease in the thermal coefficient of performance COPth will be shown in the following example [1]: The charging of the sorption storage will take place in summer time at an ambient temperature of 30 °C (TAC). Discharging will be in winter at -20 °C (TAD). These circumstances lead to a substantial decrease of the ideal ratio of thermal energy output Qout (discharging) and solar input Qin (charging).

In this example the charging and discharging temperature of the storage is 100 °C. In a number of applications the charging temperature is higher than the discharging temperature, which leads to a further decresas in COPth.

If you have a solar application and a Zeolite storage, where you need a charging temperature of at least 160 °C and you are delivering heat to a low temperature heating system running at 40 °C, your thermodynamical maximum COPth can only be 54%.