A novel high temperature electrical storage heater using an inorganic salt based composite phase change material

We have studied a high temperature storage heater containing an inorganic salt based composite phase change material (CPCM) for electrical load shift and operation cost reduction. The storage heater consists of CPCM modules with embedded electrical elements for charging at off‐peak hours and flow channels for discharging the stored heat in a controlled manner when needed. The flow channels are for heat transfer fluid (HTF, air in this work) to exchange heat with the CPCM modules and transport the heat to the heating space. A series of experiments are carried out to study the charging and discharging behavior of the storage heater. The effects of the flow channel arrangements between the CPCM modules, and the heating element arrangements inside the heater are studied. A mathematical model is also developed to investigate the performance of the storage heater with a focus on the performance comparison of the storage heater filled with the CPCM and that with the ferric oxide bricks (the conventional sensible heat storage material), and the evaluation of temperature control strategy for the CPCM based storage heater. The results show that a charge of 8 hours of the storage heater during the off‐peak period is sufficient to supply heat for the whole day under the conditions of this work. The flow channel arrangements have significant influences on the storage heater performance in terms of temperature distribution of the CPCM modules and HTF outlet temperature, and the efficiencies of the charging and discharging processes. An interlaced arrangement of CPCM modules in the heater can effectively reduce the temperature swing (eg, between 21.7°C and 22.5°C over a day) and hence improve the room thermal comfort level. The results also show that the CPCM based storage heater gives a superior performance than the ferric oxide based storage heater. Given the storage volume, the power rating, and the amount of stored heat, the mass of the ferric oxide based storage heater is more than 1.6 times that of the CPCM based storage heater. Given the mass and power rating, the heat storage capacity of the CPCM based heater is nearly 68% higher than that of the ferric oxide based storage heater. It is also found that the heat storage performance could be enhanced through a temperature control strategy with the temperature measurement located 15 mm away from the heating elements, for which the heating elements only need two start‐stops over the 8‐hour charging period.