Development of a Closed Sorption Heat Storage Prototype

In order to overcome limitations of solar heating, great improvements in seasonal heat storage are required. Adequate heat storage is achieved by: reducing time dependent thermal losses, reducing storage volume, and allowing easy adjustment of storage geometries to enable building retrofitting.To this purpose much theoretical and practical work has been done at Empa, including a laboratory scale proof of concept of an aqueous sodium hydroxide based seasonal thermal storage.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. For this reason there is great potential in the application of the closed sorption heat storage system for long term solar heat storage. Due to the losses encountered during charging/discharging (efficiency of the heat and mass exchanger), the concept is less suitable for short term heat storage. Therefore a hybrid system is proposed, consisting of hot water tanks for short term storage and closed sorption heat storage for seasonal storage.In the scope of the EU funded project COMTES a prototype aqueous sodium hydroxide seasonal thermal storage system 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 located in the region of Zurich.