Experimental Investigation on a Combined Sensible and Latent Heat Storage Unit Integrated with Solar Water Heating System

Renewable energy supplies are steadily gaining increasing importance in all the countries. In particular, solar energy, being non-polluting, clean and inexhaustible, has received wide attention among scientists and engineers. Though there are many advantages, an important factor is that solar energy is time dependent energy source with an intermittent character. Hence some form of thermal energy storage (TES) is necessary for the most effective utilization of this energy source. Most of the TES systems in use rely on the specific heat or sensible heat of the storage material, such as water, oil and rock beds and they are known as sensible heat storage (SHS) systems. The main disadvantage of SHS systems is low heat storage capacity per unit volume of the storage medium. On the other hand, latent heat storage (LHS) concept, which involves storing and recovering heat through the solid-liquid phase change process, has advantages of high heat storage capacity and isothermal behavior during charging (heat storage) and discharging (heat release) processes. Though the LHS systems have desirable characteristics, they are not in commercial use as much as SHS systems because of the poor heat transfer rate during heat storage and recovery process. The main reason is that during phase change, the solid-liquid interface moves away from the convective heat transfer surface (during charging in cool storage process and discharging in hot storage process) due to which the thermal resistance of the growing layer of solidified PCM increases, resulting in poor heat transfer rate. The combined sensible and latent heat storage system eliminates the difficulties experienced in the SHS and LHS systems to a certain extend and posses the advantages of both the systems. The present work deals with the study of combined sensible and latent heat storage system integrated with solar water heating system