Comparative analysis of latent thermal energy storage tanks for micro-CHP systems

The efficiency of micro-combined heat and power (micro-CHP) systems can be increased by decoupling the production of electricity and heat by means of thermal energy storage (TES) systems where heat that is not needed during the production period can be stored for later use. The aim of this article is to evaluate the use of different TES units when coupled to micro-CHP systems. An experimental study was carried out to evaluate the thermal behavior of different TES units for coupling with a micro-CHP system. A cylindrical TES tank was used to compare the performance of two phase change materials (PCMs) with different melting temperature and encapsulation method, while using a water-filled unit as a reference scenario. The first concept consists of cylindrical PCM tubes while the second uses small spherical PCM capsules, both commercially available products. The analysis involves three different tests: constant inlet temperature, constant power, and partial capacity loading. The results are evaluated on the basis of a comparison between inlet and outlet temperatures, charging time and thermal energy stored by the TES units. The PCM tubes are characterized by a higher capacity when a low thermal power is applied while the PCM capsules are able to store more energy at higher power. The operating temperatures in partial loading tests indicate that the incorporation of PCM storage units in a smart grid environment may be beneficial from a thermal systems point of view.