HIGH-TEMPERATURE HEAT PUMP INTEGRATION INTO DISTRICT HEATING SYSTEM

The replacement of fossil fuel-fired boilers for high-temperature water and steam production is very important to increase the efficiency of the energy supply system. High-temperature heat pumps are considered to be a good technology to produce heat, as well as efficiently recover low-grade waste heat from various processes, thus reducing energy consumption and CO2 emissions. Flexible integration of a high-temperature heat pump into heating systems has been recognized as an important step towards a 100% renewable energy system by converting electrical energy into heat. This paper compiled up-to-date scientific articles on the types of high-temperature heat pumps, options of usage, and advantages. High-temperature heat pumps' cycles, such as single-stage cycle, single-stage cycle with internal heat exchanger, two-stage cycle, two-stage cycle with internal heat exchanger, and two-stage cycle with intermediate internal heat exchanger, were viewed, the most appropriate cycles for different temperature increase values were defined. Also, attention was paid to refrigerants, their types, usage limitations, and appropriate choices. The possibility of using high-temperature heat pumps in Latvian district heating systems was evaluated - reduction of the return temperature of the heating system and increase of the supply temperature in order to ensure the system's operation under the low-temperature graph, thus improving the overall system efficiency.