Analysis Of Energy Saving Potential And Optimal Design Of Two-stage Compression Dual-temperature Air Conditioning System

Conventional air conditioning system has the disadvantages of high energy consumption and poor comfort due to the phenomenon of heat and moisture coupling.The combined air conditioning system composed of multiple components is a good alternative,and the dehumidification methods of the system mainly include solution dehumidification,solid desiccant dehumidification and cooling dehumidification.However,due to the problems of high equipment cost,complicated structure and needed reheat source for desiccant regeneration,the air conditioning system with solution or solid desiccant dehumidification has not been widely applied in residential buildings.Fortunately,the multi-evaporator system has the excellent capability of heat and humidity independent processing without the above-mentioned problems.Therefore,this paper studies a two-stage compression dual-temperature air conditioning system.It's comprised of two indoor heat exchangers,one outdoor heat exchanger,two compressors and two throttles.In cooling conditions,one of the indoor heat exchangers with a relatively higher evaporating pressure undertakes most sensible heat load in the room,and the other with a lower evaporating pressure has the main role for undertaking the latent heat load and partial sensible heat load of the room by handling fresh air.Mathematical modeling method,which is economical,time-saving and practical,is employed here to investigate the energy-saving performance of the system,and the following work has been carried out.(1)The model was validated based on experimental data published in literature;(2)The influences of the ratio(RA)of low temperature evaporator and indoor heat exchangers on the coefficient of performance(COP)were analyzed;(3)The COP and energy saving rate of the system were calculated under different climate;(4)With the goal of minimum life cycle cost(LCC),genetic algorithms were used to search for the optimal values of tube lengths of the three heat exchangers.Results indicate that the COP increases first and then decreases as RA increases from 0.25 to 0.5,and the COP reaches the maximum when the RA is equal to 0.35.In cooling conditions,as the outdoor air temperature or the relative humidity increases,the COP of the system gradually decreases,while the energy saving rate increases as the outdoor air temperature decreases or the relative humidity increases,and energy saving rate ranges from 12.6% to 30.97%.After optimization,the initial investment of the system increased by 815.52 yuan,but the operating cost decreased by 1107.07 yuan,and LCC decreased by 291.55 yuan.