Use of phase change materials (PCM) for the improvement of energy storage in solar water heating systems

Abstract

In this paper the use of Phase Change Materials (PCM) in solar storage tanks is considered in an attempt to improve the solar system operation without changing the production line of solar water heater manufacturers. Hot water storage tank is one of the main components of any solar water heating system. It is important to increase the storage capacity and to keep the stratification in these systems, as this affects the effectiveness of the solar system operation. In general, PCMs present high latent heat of evaporation and they offer more storage capacity than water. The experimental investigations of the operation of the storage tank were carried out both during heating up and draw off. In all experiments carried at different initial storage temperatures, number of PCM canisters (1-3) and drawoff rates (1, 3 and 6 l/min), the tanks with PCM show superior performance than the same tank operating in similar conditions without PCM. For the 50 l tank used, two PCM canisters showed the best performance and a draw off profile up to 3 l/min. The flow of 6 l/min seems to be excessive for small storage volume as the high flow rate does not allow the PCM to give its heat to the flowing water. Another experiment performed is the intermitted withdrawal of water from the storage tank so as to simulate the actual use. The results were also positive. Therefore, from this work it is concluded that the use of PCM gives improved storage capacity of the system and improved system behavior during draw-off.