| The outdoor heat exchanger is utilized in the conventional air-source heat pump (ASHP) system to extract heat from air or release heat to air, and the heat transfer is not so effective, so the coefficient of performance (COP) of ASHP is lower than that of water cooling chiller when cooling in summer. But the water cooling chiller can not operate normally, and the ASHP system often run under a low heating efficiency, even can not run for frosting on the surface of outdoor heat exchanger in winter, especially when the temperature lower than zero. All these will hinder the popularization of ASHP system greatly. In this paper, a novel frost-free air-source heat pump (FFASHP) system is proposed. The new system operate under the water cooling model in summer, it will take the advantages of water cooling chiller, and this system can extract heat from air to be a ASHP in winter, moreover, the new system can avoid frosting and heat continuously in winter.The FFASHP system is composed of three subsystems:a compression refrigeration subsystem, a solution endothermic subsystem and a solution regeneration subsystem. Compared with ASHP system, solution cycle is added in the FFASHP system, and the key parts of solution system is regenerator, so it is necessary to master the law of heat and mass transfer and performance of regenerator under winter conditions firstly, and the performance of regenerator with liquid desiccant under winter conditions is detailedly studied in this paper.An experimental system was established to test the performance of regenerator under winter conditions, and the effects of inlet air temperature, mass flow rate humidity ratio, and inlet desiccant temperature, mass flow rate, mass fraction on the performance of regenerator were experimentally investigated as LiCl aqueous solution was regenerating solution, and the effects of inlet parameters on evaporation rate and enthalpy effectiveness were analyzed. According to the experiment data, the multiple regression equations of evaporation rate and enthalpy effectiveness of regenerator under winter conditions were obtained.To analyze the law of heat and mass transfer in the regenerator under winter conditions, the heat and mass transfer model of regenerating process was set up, and the discretization model was numerically solved. To simplify and generalize the analysis and computation, the dimensionless heat and mass transfer correlations are obtained based on the experimental data and the correlations can be used to design and optimize the regenerator under winter conditions.The thermodynamic calculation model of FFASHP system was established to analyze the effects of ambient air temperature and relative humidity, inlet solution temperature in solution tower, mass fraction of solution in solution tower, solution-to-refrigerant mass flow rate ratio in evaporator, air-to-solution mass flow rate ratio in solution tower, air-to-solution mass flow rate ratio in regenerator, total heat transfer efficiency of solution tower and total heat transfer efficiency of the regenerator on the performance of FFASHP system. From the results, it can be seen that COP of the FFASHP system is higher than conventional ASHP in winter under the same conditions.The experimental system for testing the performance of FFASHP was established, and the effects of ambient air temperature, condensing temperature, solution flow rate in evaporator, mass fraction of solution, solution flow rate in regenerator, air flow rate in solution tower and air relative humidity on the performance of FFASHP were experimentally studied. Results show that the simulated results are good agree with experimental results, and the FFASHP system proposed in this paper can realize heating, need not to run in defrosting mode and can operate continuously under the easily frosting-temperature range for traditional ASHP system. |
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