Development Line B

Liquid Sorption

This storage concept is based on a continuous, but not full cycle, liquid state absorption heat pump. Heat is not directly stored. Instead the potential to regain heat at a desired temperature from a low temperature thermal input is stored. The main benefit is that there are no capacity losses during storage time. The operating principle is as follows: Two chambers are connected as shown in the scheme (the concept of the closed sorption heat pump based heat storage).

Chamber 1 functions as desorber as well as absorber and contains the sorbent, aqueous sodium hydroxide. Chamber 2 is the condenser and evaporator, containing the sorbate, water. The reversible chemical reaction is: NaOH . (m+n)H2O + heat ⇔ NaOH . mH2O + nH2O

In the charging phase of this liquid sorption storage, a diluted mixture of sodium hydroxide (or sodium lye) and water is concentrated by evaporating the water. The concentrated lye is stored without heat losses until heat is needed.

To produce heat, water vapour is recombined with the lye, diluting the concentration and generating heat. In a first stage, low temperature heat for space heating is produced and in a second stage, high temperature heat for hot tap water. The storage depends on the charging and discharging parameters.

A TRNSYS simulation type will be developed and the simulations will be performed to determine the size of the other components like solar collectors, ground heat exchanger and buffer storage. A full scale demonstrator storage is build up and its functionality is under testing.

The concept of the closed sorption heat pump based heat storage.

The hydraulic scheme of the storage.

The absorber / desorber of the storage..

The built up prototype.

The control system and the storage tanks.

Photos © Empa