Development of High Efficiency Fan System for Outdoor Unit of Air-conditioner
3.6 Case Studies: Aerodynamics
Developing high efficiency air-conditioners is currently a pressing demand for environmental conservation and energy saving. Reducing fan power consumption comprises a large percentage of the total energy consumption of an air-conditioner. High efficiency fan systems therefore directly contribute to energy saving of the air-conditioner.
Recently, it is important to considering influence of equipped condition in the development of fan system. We therefore estimated flow rate and fan shaft power considering the condition equipped with the fan systems in the air-conditioner by computational fluid dynamics (CFD). The feature of the estimation is that we can consider an influence of components which are fan, bell mouth, motor and heat exchanger etc. The computational model consists of doom shaped region and region of the outdoor unit. The grids were composed of tetra and prism elements. The prism elements are set on blade surface. Part around propeller was in the rotating frame of reference. The other parts were in the stationary frames. The numbers of elements were approximately from 25 million to 35 million. The numerical simulation code employed an incompressible Reynolds-averaged Navier-Stokes simulation (RANS) commercial solver. It also employed a k-epsilon turbulence model and wall function. Heat exchanger was simulated by porous model. Moreover, we analyze total pressure loss in the outdoor unit by investigating calculated results.
It was confirmed by CFD that the outlet loss of fan was the largest. The inner loss of fan was second and the loss of heat exchanger was third. From this analysis, we could propose the new fan system of 2 fan type, improved long bell mouth, and sigma shaped heat exchanger. We confirmed by CFD that the fan shaft power of the developed outdoor unit decreased by 56% compared to the old outdoor unit. The effect of the improvement of the bell mouth was 22%. That of the increase of number of fan was also 22%. That of the improvement of heat exchanger shape was 12%. Finally, we checked the high efficiency effects experimentally. As a result, we confirmed that the fan shaft power of the developed outdoor unit decreased by 50%.