An analytical study is conducted to optimize the injection-port geometries of a vapor injection asymmetric scroll compressor operating under various climatic conditions. A numerical model was developed to predict the performance of the vapor injection asymmetric scroll compressor in the heating mode according to various operating parameters, and this numerical model was validated using data measured in a vapor injection heat pump. The effects of the location and number of injection ports on the performance of the asymmetric scroll compressor were analyzed using the numerical model. Both the optimal injection-port angle and required injection-port area increased as the outdoor temperature decreased in order to increase the injection mass flow rate. The optimized injection port designs were then proposed for the asymmetric scroll compressor in order to achieve the maximum SCOP (seasonal coefficient of performance) under various climatic conditions, improving the SCOP by 2%-6% relative to the baseline injection compressor. (C) 2017 Elsevier Ltd. All rights reserved.