Latent thermal energy storage for heating and cooling of buildings

Abstract

When renewable energy sources are used for heating or cooling of buildings there is usually a time lag between energy production and energy demand. The utilization factor of e.g. solar thermal systems can be improved by using thermal energy storage units as they provide longer or shifted runtimes. For the same reason thermal energy storage can improve effectiveness of energy converters like heat pumps. In present paper the subject matter of HEART project within the EU Research and innovation program Horizon 2020 is presented. HEART stands for holistic energy and architectural retrofit toolkit where the aim of this project is to improve energy efficiency with a holistic and multi-technological integrated and interconnected system for retrofit of residential buildings. The focus in present paper will be the research of thermal energy storage in phase change materials. Measurements of sensible thermal energy storage with integrated cylindrical nodules filled with phase change materials were carried out in order to perform experimental validation of numerical model of latent thermal energy storage in TRNSYS simulation tool. Maximal relative error of 4.3 % and maximal absolute error of 1.2 K between measurements and numerical simulations represents that numerical model is validated. After validation of numerical model the comparison between sensible and latent thermal energy storage were performed in TRNSYS simulation tool. Results of analysis shows that at 40% of phase change material filling at temperature difference of 5 K latent thermal energy storage unit can store up to 5 times more thermal energy than sensible one because of its higher energy density that can be stored during phase change. Time of supplying thermal energy demand is in case of latent thermal energy storage unit 3.5 times longer than in case of sensible one. Latent thermal energy storage has high potential in applications where small temperature differences in storing of thermal energy take place especially if temperature level of supplying thermal energy in the system needs to be low which is the case in presented HEART project.