Study On Performance Simulation Of CO₂Heat Pump Water Heater

Carbon dioxide refrigerant is environmental protection, and the heat pump water heater (Referred:carbon dioxide heat pump) can gain high temperature hot water,, however many problems to be solved, such as reducing throttling loss, reducing requirements and so on, applying expander to recover expansion work. By establishing the performance simulation models of the carbon dioxide heat pump and key components, analyzed the carbon dioxide heat pump performance and irreversible loss affected by carbon dioxide physical properties, environment, and the key components, proposed the design criteria of heat pump cycle and the key components. The main contents are as follows:First, studying and comparing the carbon dioxide heat pump cycle, calculating the performance and exergy of carbon dioxide trans-critical, two-stage compressed, expander contained heat pump cycle. For the purpose of improving performance of carbon dioxide heat pump, studying and comparing carbon dioxide trans-critical, two-staged compressed, expander contained, and throttle contained, regenerator contained cycle, getting the maximum efficiency cycle is expander contained cycle, calculating the exergy of this cycle. According to the conclusion of simulation and calculation, put forward a design program:improving efficiency of compressors and expander, reducing exergy loss, improving overall performance of the circulatory system for the purpose of improving the coefficient of system performance.Second, analyze the expansion process and irreversible loss of the expander. Studying the expansion process phased, the expansion work derived differently in different stages, and expansion work influenced by condition of the exit and entrance of the expander. The study to the Rolling piston expander’s irreversible loss show that the irreversible loss influenced not only by stage of the carbon dioxide but also influenced by the structure of the expander itself, for the purpose of reducing irreversible loss of expander, putting forward design principles of the expander:designing a reasonable interval, keeping the total loss of expander low, then improving expander efficiency. Third, analyze the heat transfer performance of the gas cooler. Establishing a micro-element model to the tube gas cooler, setting the exit stage per micro-element model as the entrance stage of the next one, ensured a correct result to the fluid dynamics. Study show that the heat transfer performance of the gas cooler is influenced by stage of carbon dioxide, cooling water stage and structure synchronous. The design principles of the gas cooler are as follows:using small diameter, long tube heat transfer tubes, improving heat transfer coefficient for the purpose improving the heat transfer performance of gas cooler.This article studied and compared the system cycle, simulated the key components for the purpose of improving carbon dioxide heat pump’s performance. The research conclusion can provide theoretical guidance for design of carbon heat pump.