Cristina Bianqui

The incorporation of phase change materials (PCM) into thermal energy storage systems is a promising strategy to enhance the performance of solar systems for domestic hot water production. In this work, the behaviour of a hybrid accumulator containing water and encapsulated PCM is studied using an analytical model that incorporates data obtained from experimental tests. For this purpose, a series of experimental melting and solidification tests are performed at different temperatures on a single cylindrical encapsulation filled with RT54HC paraffin. The PCM temperature is measured and then fitted, obtaining a heat transfer parameter that characterizes the PCM behaviour during the processes. The heat rate stored and released by the PCM in each test is calculated and an encapsulation heat transfer chart as a function of the water and PCM temperatures is created. This chart is then incorporated into a one-dimensional, non-steady analytical model of a hybrid accumulator. The model is applied to a representative case under realistic operating conditions. The outlet water temperature and the volume extracted at a temperature above a suitable temperature for residential use of 40 ºC are assessed. The results show that continuous discharge or discharge with short no-discharge periods leads to limited recovery of the heat stored in the PCM. In contrast, when sufficiently long no-discharge periods are introduced, the accumulator performance improves significantly, allowing up to 22.8% more water to be delivered at temperatures above 40 °C. The proposed experimental-based analytical approach provides a simple methodology to analyse the PCM-based thermal storage systems response.