Study On Layout Of VRF Air-conditioning Outdoor Units Based On CFD Simulation

Due to its unique advantages,the VRF air-conditioning system has developed rapidly in recent years,and has occupied nearly half of the market of central air-conditioning system.Even under the influence of COVID-19 in 2020,the VRF air-conditioning system market also has a good performance.For the air-cooled VRF air-conditioning system,the improper installation of outdoor unit and the bad operating environment lead to the rise of air inlet temperature of outdoor unit,which directly leads to the reduction of operating efficiency and unnecessary energy loss.In the current era of promoting building energy conservation and emission reduction,such waste is not allowed.Therefore,it is of great significance to study the reasonable unit layout.In this paper,the inlet air temperature of outdoor unit is taken as the evaluation index,and the influence of different outdoor environmental factors on the operating conditions of the outdoor unit is analyzed by means of numerical simulation.Suggestions are put forward on the setting of the outdoor unit,and the installation spacing requirements are put forward for different outdoor units arranged centrally.Firstly,the influence of outdoor environment factors on the air inlet temperature of a single unit is analyzed by orthogonal test.The results show that the main influencing factors of inlet air temperature are outdoor environment temperature > wind speed > wind direction,and the air inlet temperature is almost linear with the increase of outdoor temperature.It is found that if the outdoor wind blows from the front to the outdoor unit,the inlet air temperature will decrease when the wind speed increases,which is beneficial to the operation of VRF air-conditioning outdoor unit.The results are verified by using multi-layer outdoor units.The results still show that the outdoor unit layout on the windward side of the building is a better arrangement mode.Centralized layout is another way often used in the layout of VRF outdoor units.When many units are put together,the influence of heat dissipation on the operating condition caused by the change of surrounding thermal environment cannot be estimated.A certain distance should be kept between units to reduce the influence between each other.Based on this,the paper puts forward the requirements for the spacing of different outdoor units.In order to improve the credibility of the results,this study selects eight units with different volume and heat dissipation,changes the unit spacing,and makes a comparative analysis of the air inlet temperature of the units placed in different positions.Then,the inlet air temperature change of outdoor unit at the most unfavorable position is analyzed,and the installation spacing requirements of different types of units are given.In order to predict the installation spacing of other outdoor units which are not included in this study,a multiple nonlinear regression method is used to establish the fitting formula between the inlet air temperature and the unit volume,heat dissipation and spacing.The data with spacing less than 0.3m are eliminated,and the obtained formula has a high fitting degree,which can be used to predict the installation spacing of other types of outdoor units.