Lysak O. Energy-efficient space heating with a combined static-dynamic storage heater with magnesite bricks

The dissertation is devoted to solving the actual scientific and technical problem regarding the utilization of excess electricity. The use of such systems in the complex of production-supply-consumption of electricity has the advantage that otherwise that energy would not be utilized, but dissipated into the environment. The analysis of the known data of theoretical and practical studies of different types of storage heaters made it possible to conclude the need to develop and study the operation of a combined static-dynamic storage heater, which combines the advantages of both natural and forced air movement through air channels. In order to design sizes and power output of the devices, an analysis of the heat storage materials was performed and the specific amount of heat transfer from the storage heater was determined. The magnesite brick was chosen as the material with the highest density of heat storage and lower price than other materials like magnetite and feolite. Based on the size of heat storage material, the ratio of the fraction of controlled and uncontrolled heat output is determined, depending on the size of the device and the temperature of its surface. The value of controlled heat output is determined for two modes of operation: forced air movement and natural air movement. Dependencies were obtained to determine the heat transfer coefficient and the pressure flow rates, depending on the shape of the used bricks and the channels inside of them, the size of the air channel, the temperature of the heat storage material and the air flow rate. The heat transfer coefficient for the external surface is 8.1…10.6 W/(m2·K) which is obtained for the surface temperature of 303,15…333,15 К. The heat transfer coefficient for air channels during the natural air movement mode is 6,5…9,2 W/(m2·K) which is obtained for the surface temperature of 423,15…623,15 К. The heat transfer coefficient for air channels during the forced air movement mode is 28,6…40 W/(m2·K) which data is obtained for the surface temperature of 323,15…423,15 К and air inlet volume of 0,00417...0,00694 m3/s. Experimental studies were conducted to confirm and clarify the dependencies obtained. Industrial studies have also been conducted to determine possible energy savings depending on the mode of operation of the appliance. The air temperature gradient was studied. For the purpose of industrial introduction of technology, a series of devices was developed and the method of their selection was developed. The analysis of the technical and economic indicators shows that the payback period of the offered devices in comparison with standard direct heating electric heating units is less than two years. The results were implemented at LLC “Stolychnyi pekarnyi dim” (Kyiv, Ukraine). The usage of the proposed device helped to decrease the operational cost up to 75 %. It was also shown if there is an application of day charge, the cost for the heating unit can be decreased up to 20 %.