I am modelling a existing 12 storey office building. For validation purpose, I conditioned only 10th floor with actual cooling load and internal heat gains. I took water cooled chiller for my simulation. The OpenStudio design cooling load of 10th floor is 63 kW. My actual cooling load is 147 kW. I hard sized the chiller capacity as 147 kW, hence the zone set point temperature was met. If I take OpenStudio design cooling load of 63 kW as my chiller capacity, the zone setpoint temperature was not met. I assumed wall and window material properties with reasonable accuracy.

Please clear my doubts.