IEA SHC Task 32: Advanced Heat Storage Concepts
The here described project is a scientific project for the Task 32 "Advanced Storage Concepts for Solar and Low Energy Buildings" in the framework of the Implementing Agreement for Solar Heating and Cooling of the International Energy Agency.
In the project short-term storage units based on Phase Change Materials (PCM) for the purpose of reducing the start/stop-emissions of boilers and for increasing the solar fraction of solar combisystems were developed and tested. This was done using the reference conditions of Task 32 and the involved companies.
Different materials, that can be used as PCM, have been characterised and chosen for the further work within the project. The materials were integrated into storage tanks using different approaches. Detailed measurements were carried out with these experimental tanks in order to determine the power that can be achieved during charging and discharging as well as the storage capacity compared to sensible heat storage with water.
In order to determine the emissions and the efficiency of boilers in start/stop operation measurements were carried out with a gas and a pellet boiler. The obtained data was used to define emission factors for the continuous operation, related on the used fuel energy, and the additional emissions of CO and HC that are caused in each start/stop cycle for both boilers.
The annual number of start/stop-cycles under different conditions concerning the hydraulic integration of the boiler into the heating system, was determined by means of dynamic simulations of the whole system consisting of the building, the heating system and the boiler. Based on these results and the measured emission factors the total emissions were calculated resulting from the continuous and the start/stop-operation. The results show that the emissions caused by the start/stop operation are much higher than the emissions of the continuous operation, if the boiler is integrated into the heating system without an energy storage. By using a small storage tank the number of cycles and thus the emissions can be reduced strongly. The use of PCM allows a further reduction of cycles compared to water tanks with the same volume. A small PCM-storage unit, that was developed within the project and that allows high charging and discharging powers, makes the instantaneous preparation of domestic hot water possible, using the storage tank as the heat source.
A first investigation of the effect of an integration of PCM materials into the storage tank of a solar combisystem for space heating and domestic hot water preparation was performed within the project. For that purpose simulations of a combisystem were carried out using the reference conditions of Task 32 and different configurations concerning the collector area and the storage volume. The results show an improvement compared to water tanks, which however is lower than expected. Especially with small tanks the improvement of the solar fraction due to the higher storage capacity should be higher. In the framework of Task 32 further investigations will be carried to improve these results.
Ao. Univ.-Prof. Dipl.-Ing. Dr.techn. Wolfgang Streicher
Institut für Wärmetechnik, TU Graz
Polymer Competence Center Leoben GmbH (PCCL) (Werkvertragspartner)