Effective enthalpy of organic phase change material applied in a thermal energy storage cooperating with a district heating system

As part of modernizing the office building of the district heating operator in Ostro & lstrok;& eogon;ka, Poland, a new hybrid substation was built. The system is designed to both heat and cool the office building and is powered by the district heating network. It incorporates an adsorption chiller, three phase change material storages, a photovoltaic system and a smart management system. This paper focuses on the design and experimental determination of the exact characteristics of the phase change material storage, which is intended to support the chiller on the power supply side. The PCM used is RT62HC, with a peak phase change temperature of 63 degrees C and narrow phase transition characteristics. The design, presented briefly, highlights the experimental setup, the characterization of the phase-change material, and the thermal-hydraulic properties of the finned-tube heat exchanger. The laboratory tests included both the charging and discharging processes of the storage. During the tests, a ramp-type thermal forcing was used at rates of 0.5 K/h, 1 K/h, 2 K/h, and 3 K/h. Based on the tests, the dynamic characteristics of the storage were determined in the form of an effective enthalpy function. The results of this analysis were also used to determine the storage density of the system, which was found to be 49 kWh/m3 in the temperature range of 57 degrees C-67 degrees C. In this temperature range, the PCM storage has up to 4.5 times greater thermal capacity than a storage with water.