Research On The Performance And Optimization Of A Novel Energy-efficient Heat Pump System Using Liquid Desiccant

A novel heat pump system is proposed for hot-summer and cold-winter zone,which operates as heat-tower based non-frosting heat pump in winter and as a hybrid refrigerant system consisting of a conventional water chiller and a liquid desiccant evaporative cooling subsystem in summer,achieving higher efficiency than conventional chillers.The condensation heat is recovered for liquid desiccant regeneration,which would make the application of the restriction of free regernation sources as well as reduce waste heat exhaustion to the atmosphere.The system cooling performance and optimization strategies have been studied thoroughly based on the thermodynamic analysis and experimental stud.The detailed content and results are shown in the following.Firstly,experimental study was carried out with the experimental system,which was built based on the preliminary thermodynamics analysis.However,the match between the liquid desiccant cycle and the refrigeration cycle has not been considered in the preliminary analysis,which leads to unreasonable design values of several parameters.As a result,the sub-cooling degrees achieved in the experiment were ranging from 13-15?in most conditions in summer of Nanjing.A detailed mathematical model of the system was established and models of major components was validated by experiment results,including dehumidifier,regenerator,evaporative cooler and so on.Secondly,the validatied model is used to compare the performance of the system with that of conventional chillers under variable outdoor conditions.The results showed that the proposed system has higher cooling efficiency and more stable system pefoamnce than contional ones especially under hot and humid zones.The effects of key parameters,including solution to refrigerant flow ratio and portion of condensation heat utilization on the cooling performance of the proposed system operating in summer.Besides,the key parameters should be considered in designing the heat exchange area of the solution-cooled condenser was also analyzed.The results show that the COP and ECOP of the prosed system are higher than conventional systems by increasing 13.4%and 10.3%respectively under the typical summer condition of Nanjing.The recommended range of flow ratio is from1.2 to 6 and that for condensation heat recovery portion is from 16%to 40%.It has to mention that the most unfavorable conditions for designing the area of the heat exchanger of the solution-cooled condenser,where the solution-cooled condenser demands the largest heat exchange surface area,is hot and relative colder condition.Thirdly,the energy-saving potial during the cooling season of typical cities in hot-summer and cold-winter zone,including Nanjing,Shanghai,Changsha,was analyzed for prividing guidance for application.When the solution-to-refrigerant mass flow ratio FR is 6,the average improvent of cooligng capacity and electric coefficient of performance?ECOP?is about 11.6%and 4.6%for each city,respectively.In order to prove that the proposed system is worth promotion in heating tower heat pumps,a case stuty was carryed out.When the FR is between 4 to 6,the system could achieve more than 13%cooling capactiy than conventional chillers.At the same time,30%to 40%of the condensation was recovered and 35%percent of the packing towers of the system would be aboundant for other use duiring summer.Finally,the performance improvent of the hybrid cooling cycle with sub-cooling subcycles comapred to vapor compression cycle was investigated.For ideal cycles with isentropic expansion process,subcooling subcycls narrows the gap of the cooling efficiency of the cycle with different working fluids.For practical cycles with insulted throttling process,th subcooling cycles reduces the thermaldynamic loss during the throttligng process as well as increase cooling capacity of the hybride cycles.When the coefficient of performance of the subcooling cycle is 0.5,the subcooling degrees and coefficient of perfomance achieved by the hybrid subcooling system are more than 7°C and more than5%when using refrigerant NH₃,R22 or R152a,respectivel.However,the subcooling benefits are not significant when the hybrid system use R1234ZE,R600a or R1234YF as the refrigerant.