The cooling and heating performances of R410A and R32 multi-heat pumps with a sub-cooler vapor injection (SCVI) were measured and compared with variations in the outdoor temperature, compressor speed, and injection ratio. Optimum injection ratios were determined to obtain maximum cooling and heating performances at a given operating condition. In the cooling mode with the optimum injection ratios, the R410A and R32 multi-heat pumps with vapor injection showed 2.1%-6.3% higher cooling capacity than those without vapor injection. In the heating mode, the R410A and R32 multi-heat pumps with vapor injection showed 7.5%-13.9% higher heating capacity than those without vapor injection, while showing 2.6%-7.0% and 1.1%-4.7% higher COPs, respectively. In addition, the SCVI cycle was more effective for improving the cooling and heating performances under extremely hot and cold weather conditions, respectively. (C) 2016 Elsevier Ltd. All rights reserved.