FEATURES OF GEOTHERMAL ENERGY USE WITH APPLICATION OF HEAT PUMP UNITS UNDER LOW AIR TEMPERATURE CONDITIONS

The relevance. The use of low-potential energy of water reservoirs with the help of heat pump stations in conditions of low ambient temperatures-air (time period autumn-winter-spring), characteristic for the most part of Russian territory, is related to possible freezing of evaporator pipes of heat pump stations, which leads to a change in its operation mode. The analysis of the basic laws of operation of heat exchange equipment, as well as the assessment of energy efficiency of heat pump stations under conditions of ice formation on the evaporator surfaces, have not been carried out before. The main aim of the research is the experimental study of the main laws of ice formation on the working surfaces of heat pump evaporator pipes, surrounded by water with the temperature corresponding to the conditions of autumn, winter and spring periods for most natural water reservoirs in the Russian Federation, as well as an analysis for the main operating characteristics of the heat pump stations under such conditions. Object of the research is a vapor compressor heat pump, operating under conditions of ice formation on the working surfaces of the evaporator pipes, surrounded by water with thetemperature under 280 K. Methods. Temperature values in characteristic points on the surface of the heat exchanger-evaporator pipe and water were measured by 15 chromel-alumel thermocouples (CA thermocouples) connected via ADC to a computer; these values were registered in experiment real time. Based on the data obtained, the heat pump coefficient of performance was calculated by a defined method. Results. The authors have highlighted the effect of formation of ice with a thickness up to 10 mm on the surface of the evaporator pipes located in water with a temperature below 280 K and the device operation time up to 8000 s. it is established that this layer reduces significantly the intensity of heat transfer to the refrigerant in evaporation zone. The efficiency of the heat pump is reduced to a minimum. According to the experiments, it is concluded that the heat pump operation is possible with partial covering of evaporator pipe with ice. The authors stated the hypothesis on the mechanism of heat transfer processes and phase transformations occurring near the coolant pipes in water with temperatures lower than 286 K. The study results are the base to define the conditions of efficient use of heat pump in the territories with negative air temperatures during the autumn, winter and spring periods.