Simulation And Analysis To The Thermal Environment Around The Outdoor Units Of VRV Air-conditioner System

In recent tens of years,traditional central air-conditioning system is usually used for buildings that has cooling load in hundreds of thousand Watt.But people turn to VRV (variable refrigerant volume) air-conditioner system for its advantages such as flexible control and energy saving.The outdoor units of VRV air-conditioners are usually air-cooled finned condensers,whose heat dissipation efficiency will decrease with the close placement for limited space,and finally result in the air conditioner's low efficiency and more power consumption.Therefore,it is of great significance to study the heat exchange between condensers and the ambient,and optimize the assembling schemes.The experiment studies include on-site measurement,laboratory experiment with full scale models and reduced scale models.In order to save the test space and minimize the expense,the experiment with reduced scale(1:3) model models are selected by choosing the proper rules of similarity—Gr/Re~2,and the heat source similarity rule derived form energy conservation equation.The good agreement of the both experiment data shows the feasibility of investigating the thermal environment around the outdoor unit by applying a reduced scale model with the dimensionless number,Gr/Re~2.The on-site measurement and laboratory experiment with full scale models give the parameters of thermal environment around the condensers,which are used to supply the boundary conditions and validate the numerical simulation result.In order to simplify the computing process,the finned coils of the condenser are considered as porous medium,so the porous computational fluid dynamics(CFD) model is employed to predict the thermo-fluid status and optimize the placement of units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distribution,and the comparison with the experiment data shows a good agreement.By evaluating the outdoor units' sucked air temperature from CFD analysis for three units(all are ECO-i multi made by SANYO,SPW-CR704DDCH8) in a line,it finds:(1) There are no walls around the condensers,with the separation distance reduction the sucked air temperature increases while heat exchange rate decreases due to air interaction among units,0.2 m can be thought as a critical and proper distance for the small space,which will not decrease the unit's performance badly.(2) Three condensers(separation distance is 0.20m) stand in a line with a vertical wall in parallel with the condenser's main sucking air side;with the distance between the units and wall reducing the sucked air temperature increases,0.8 m can be thought as a minimum distance for the small space,as if it continues reducing,the air inlet temperature will rise more remarkably.(3) Three condensers standing in a line with no wall around,one or two of the three condensers in large fan pressure jumps will not affect others' sucked air flow rates and the whole heat transfer condition obviously.This thesis also adds the optimal schemes for 9 outdoor condensers standing in rows:(1) There are no walls around the condensers;0.8 m can be thought as a critical and proper distance(including transversal and longitudinal distances) for small space,which will not decrease the unit's performance seriously.(2) The outdoor units stand on a roof and the roofing parapet wall around deteriorates the heat transfer condition,which can be improved by elevating the height of the basement under the condensers(the transversal and longitudinal distances among the condensers are 0.8m), and the suitable relative height between the roofing parapet wall and the basement is 0.7m..