Design of outdoor unit heat exchanger for variable refrigerant flow air conditioner to improve energy efficiency
As one of the main components of air conditioner,heat exchangers play an important role in improving energy efficiency.Based on the limitation of performance or manufacturing to Φ 5mm heat exchangers and microchannel heat exchangers used as outdoor unit heat exchangers,a new heat exchanger is proposed to improve the energy efficiency of Variable Refrigerant Flow(VRF)air conditioner.By reducing tube pitch of Φ7 mm copper round tube heat exchangers and thus increasing tubes quantity in each row,the new heat exchanger structure can simultaneously enhance the heat transfer capacity inside the tubes(by increasing the heat transfer area inside the tubes)and the heat transfer capacity outside the tubes(by increasing the maximum air velocity at the narrowest to enhance the air side heat transfer coefficient).Based on simulation and performance testing,a comprehensive analysis and verification were conducted to the new heat exchanger.Compared with the prototype Φ7 mm heat exchanger,simulation shows that at same air flow resistance(13.6 Pa),the air side KA value(which represents heat transfer capacity that equal to the product of heat transfer coefficient K and corresponding heat transfer area A)of the new Φ7 mm heat exchanger is 20.7％higher than that of the prototype Φ7 mm heat exchanger,and the correspond total KA value of the heat exchanger is 12.02％and 9.11％higher,respectively;The performance test results of the VRF air conditioner show that the new heat exchanger has improved energy efficiency by 1.9％,1.8％,and 1.5％in the standard cooling,the standard heating,and low-temperature heating,respectively.
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