The total cooling load of the entire facility is only 2700 kW, however the autosized design coil load is 8600 kW, the nominal capacity of the chiller and tower are 8600 and 8100 kW respectively. There is no sharp changes in design day schedule. Yet, how does this oversizing occur ?
When referring to outputs from EnergyPlus, it is important to specify the exact report name and column heading. In this case, "total cooling load of the entire facility" is probably the "Zone Sensible Cooling" loads from the "HVAC Sizing Summary" table output. The coil design load will include the zone sensible load plus outdoor air load, fan heat, and latent loads. The coil sizing relative to zone load can also be impacted by inconsistent inputs for supply air temperatures in the Sizing:Zone and Sizing:System objects. For more details, see answer in the (nearly duplicate) question here.
Comments
There are a variety of sizing factors used throughout E+ that could lead to this. Hard to tell here with no information.
As I understand the oversizing of the coil leads to the oversizing of the chiller and tower. So, the coil is the issue. Can this oversizing be caused by some wrong oversizing of coil inlet/outlet temperatures ?