Design and analysis of ejector as an expansion device in a split-type air conditioner

Abstract

Split-type air-conditioners are widely used in residential and commercial buildings. The air-conditioning system consumes more than 50% of the total energy in buildings. An improvement on the performance of the system will generate a significant impact on energy savings. This study introduces a novel cycle using an ejector as expansion device in an air-conditioner to improve the performance. This cycle is named as a modified ejector cycle (MEC). R22 is widely used as refrigerant in split-type air- conditioners, however due to its global warming impact, researchers recommended R290 as a substitute. Thermodynamic modeling was developed to determine the motive nozzle and mixing chamber diameters of the ejector based on the cooling capacity of the air- conditioner. In the modeling, the conservation equations of mass, momentum and energy were applied. The result shows that the COP improvements of MEC using R290 were higher than that of R22 for all ambient temperatures. The COP improvement using R290 are 34.52, 39.53 and 47.58% at the ambient temperatures of 30, 35 and 40oC, respectively. Experiments were carried out on a split-type air-conditioner using a capillary tube (standard cycle) and MEC with three motive nozzle diameters, i.e. 0.9, 1.0, and 1.1 mm. The measurements were carried out at the steady-state condition and repeated five times with 2 minutes interval. Experimental results show that the highest COP improvement of MEC was achieved with a motive nozzle diameter of 1.0 mm that is 30.67%. The results also show that the COP improvements of MEC using R22 are 24.69, 26.06 and 32.12%, whereas using R290 were 27.68, 31.53 and 33.61%, at the ambient temperatures of 30, 35 and 40oC, respectively. This indicates that replacing the R22 with R290 can further enhance the COP improvement of the MEC. Comparison between numerical and experimental results showed poor agreement due to large difference in the entrainment ratio of the ejector.