Closed sorption heat storage based on aqueous sodium hydroxide

Application limitations for solar heating are overcome by greatly improving heat storage. Adequate heat storage is achieved by: reducing time dependent thermal losses, reducing storage volume, and allowing easy adjustment of storage geometries. To this purpose much theoretical and practical work has been done at Empa, including a laboratory scale proof of concept of a closed sorption heat storage. This work has provided valuable insight into the potential as well as the challenges and limitations of this technology for the application as heat storage. The closed sorption heat 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 significant benefit in this is undoubtedly the time independent energy losses. Losses are encountered in the conversion processes during charging as well as discharging but not during storage time. For this reason there is great potential in the application of the closed sorption heat storage as a long term solar heat storage. In the scope of the EU funded project COMTES a prototype system based on the working pair sodium hydroxide and water is under construction. The system is dimensioned to cover space heating as well as domestic hot water in a single family house built to passive energy standards and stationed in Zurich. The two major challenges in the system design are: keeping the system volume favorable and keeping the parasitic electric energy consumption at a minimum. (C) 2014 The Authors. Published by Elsevier Ltd.