Optimization of centrifugal fan position in a particular VRF outdoor unit for European market

Abstract

Variable refrigerant flow systems (VRF), in which refrigerant flows directly through long connecting pipes into different indoor units, are nowadays having more and more market share in central air-conditioning industry. A special flat structure of air-cooled VRF outdoor unit is expected in European market due to local architecture characteristics. Centrifugal fans with forward-curved blades are suitable under this situation. However, the layout concerning the fan position is of key importance for the heat exchange performance. Four layouts with different fan position arrangement in a VRF outdoor unit supposed to reach nominal cooling capacity of 22kW were initially designed and optimized by Ansys. Air volume rate and uniformity through the fin and tube heat exchanger (FTHE) were investigated with velocity contours. When FTHE was set perpendicularly forming a triangle compact space with neighboring cabinet shells, simulations showed a better layout in which the two fans were put side by side but with one near front and the other near rear shell in the bigger empty space. Further adjustment in position details was also carried out via more simulation on selected planes and finally, air volume measurement and nominal capacity measurement were made, matched with four ducted indoor air-conditioning units, showing good performance.