Use of Phase-Change Materials in Solar Domestic Hot Water Tanks

摘要

Storage of heat is seen as a major issue for the large-scale and long-term development of solar energy for house heating and cooling in all climates. Most of the storage systems available on the market use water as the storage medium. Enhancing storage performance is necessary in order to increase the performance of most systems. The idea studied here was to add a phase-change material (PCM) module at the top of a hot water storage tank with stratification. The advantages of the stratification still remain in this new system, but the addition of a PCM module would give higher density in the top layer. For this work, an experimental solar pilot plant was constructed to test the PCM behavior in real conditions, which could work continuously with the solar system or could also work with an electrical heater. The PCM module geometry adopted was to use several cylinders at the top of the water tank. Several experiments with two, four, and six PCM modules were carried out in the real installation. A granular PCM-graphite compound of about 90% sodium acetate trihydrate and 10% graphite was chosen as the PCM for the experiments presented here. This paper also describes the modeling of this new technology. A new TRNSYS component based in the already existing TYPE 60 was developed—TYPE 60PCM. This new component was first tuned with experimental results and afterwards validated with further experiments. Concordance between experimental and simulated data was very good. Since the new TRNSYS component was developed to simulate full solar systems, comparison of experimental results from a pilot plant solar system with simulations was performed and confirmed that the TYPE 60PCM is a powerful tool for evaluating the performance of PCM modules in water tanks.