In this study, the infiltration rate from opening doors in a commercial building during business hours was calculated using CFD and compared with the prediction results from Pham & Oliver's Model. At the same time, the cooling and heating energy consumptions due to changes of door opening hours were calculated using DesignBuilder and compared with the calculation results when doors are closed. Results show that infiltration rates calculated by Pham & Oliver's Model shows excellent prediction results compared to the CFD analysis, with error rates of 1.6% in cooling and 7.3% in heating. Energy consumption due to opening doors during business hours were then calculated, with cooling energy consumption increasing by about 1.5 to 1.7 times for 0.16 ACH, about 1.4 to 1.6 times for 1.0 ACH, and about 1.4 to 1.5 times for 2.0 ACH, while heating energy consumption increases by about 46.4 to 102.9 times for 0.16 ACH, 7.9 to 17.4 times for 1.0 ACH for heating, and 3.2 to 7.0 times for 2.0 ACH.