Regulation of the output temperature in a novel water heating system using solid graphite as sensible heat thermal energy storage medium: Effects of water tank

Abstract

The quality of output temperature is one of the key parameters for the reliability of water heating system. In this work a simulation work was done to regulate the output temperature in a novel water heating system using solid graphite as thermal energy storage medium. The effects of water tank on the quality of output temperature was considered. Two different strategies were thus considered: (i) single tank system, and (ii) double-tank system. And two different working conditions were analyzed: (i) standard design condition, and (ii) demand change conditions. The results showed that the application of water tanks can reduce the standard deviation of output temperature by 68.49% and 68.81% under the standard design condition, respectively. And the improvement is highly related to the capacity of hot water tank. For the demand change condition, the regulation strategy was carried out based on the criterion of heat power equilibrium. The results showed that the single tank system will deteriorate the reliability of water heating for demand change condition, though it can reduce the oscillation of the output temperature. For the double-tank system, a two-step adjustment method was applied. The results showed that the average output temperature can be quite close to the target value when demand ratio changes to 0.8 and 0.9. And the standard deviation of temperature has also reduced by 24.19% and 63.06%, respectively.