Cascade thermochemical storage with internal condensation heat recovery for better energy and exergy efficiencies

Thermochemical heat storage processes generally involve significant condensation heat rejection to the environment during charging. This heat rejection is about two thirds of the charging heat of salt hydrates, which are a promising class of materials for heat storage in the low temperature range, i.e. for space heating and domestic hot water production. We showed that internal condensation heat recovery through a new concept of a cascade thermochemical heat storage process leads to an improvement of the energy and exergy efficiencies of the process. To illustrate the potential of this new concept, we compare a classical thermochemical based heat storage with one involving internal condensation heat recovery. In order to have an unbiased comparison basis, the two processes have similar boundary temperature conditions. The energy and exergy efficiencies of the process with internal heat recovery is as much as 1.8 times that of the classical thermochemical heat storage process. The process with heat recovery requires only 55% of the energy input at high temperature during charging of the classical process, for the same discharging heat output.