I am looking through DOE reference building IDFs. Using the Notepad++ comparison tool, I am finding differences between reference building HVAC equipment characteristics (e.g. DX coil Rated COP or Package Fan Efficiency). I know that simulations preform a sizing run first and then the actual simulation, so I am wondering why these parameters may differ? I am comparing the same building types but for different climate zones, so it may be solely weather based. However, I am wondering if there could be another rationale. Why would these parameters differ before the sizing run occurs?