Study on Appropriate Diameter of Centrifugal Fan Surrounded by Heat Exchanger in Air Conditioner

To meet the demand for energy-saving air conditioners, the pressure drop must be reduced and the air velocity distribution of the heat exchanger made uniform to improve the performance of both the fan and the heat exchange cycle. To investigate the effect of the fan on the pressure drop and the velocity distribution, we changed the fan diameter and fixed the shape of the heat exchanger. First, we investigated the fan by comparing the total pressure efficiency when the fan was mounted in an indoor unit and unmounted as a standalone fan. We found that the mounted fan performed worse than the standalone fan. The difference between these conditions was whether the heat exchanger was around the fan. Next, to determine the appropriate diameter, the performance of the mounted fan was evaluated by measuring its efficiency and the fan power. The diameter with the highest efficiency differed from the diameter with the lowest fan power. Because of this, the fan performance was strongly affected by the heat exchanger and the vortex. When the standard deviation of the air flow distribution in the heat exchanger was evaluated, the diameter with the lowest standard deviation was the same as the diameter with the lowest fan power. Since the standard deviation needs to be reduced to improve the performance of both the fan and the heat exchange cycle, the mounting conditions need to be considered to determine the fan shape. Thus, the flow field around the fan was visualized, and the velocity distributions for the investigated diameters were compared. We found the distance between the fan and the heat exchanger was an important factor determining the performance. A fan with the most appropriate diameter was prototyped to evaluate the fan performance. Results revealed it used 3% less power than a standard-diameter fan.