Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The peak coincidence ratio can be expected to be unity because at some point, say during morning pulldown, the unit is going to be operated full on. Whenever full-on operation occurs during times when conditions are more demanding than the rating point, the unit will draw more power than nominal capacity suggests.
Keep in mind that the sizing factor in that model is also being applied in the context of a load averaging window of one hour. That will smooth out the sizing impact of recovering from thermostat setback schedule changes. But once the modeling gets to the final simulation that averaging is not occurring and the actual loads when recovering from setback will usually end up large compared to those during sizing. You might see the 1/1.2 ratio you expect if the system was inadvertently sized so large as to be able to fully recover in one zone timestep. But that is considered poor practice and to be avoided by either using flat thermostat schedules during sizing or a long averaging window.
