Schedules and Design and Sizing Simulations

It is important to differentiate between the heating and cooling sizing calculations which are accessed from the Heating design and Cooling design screens and the HVAC autosizing simulations that are automatically carried out before EnergyPlus simulations when using the Compact or Detailed HVAC options and items of HVAC equipment are to be autosized.

Heating and Cooling Design Calculation

Schedules are not used for Heating design calculations which are based on a steady state analysis that does not account for timing. In cases where for example a maximum mechanical ventilation rate is defined and modified by a schedule for simulation purposes, for the steady-state Heating design calculations the same maximum mechanical ventilation rate is used continuously.


Cooling design calculations are of course dynamic and so schedules are required for these. It is possible to select the day type to be used for Cooling design calculations on the Calculation options dialog. By default the Compact schedule day type is SummerDesignDay for Cooling design calculations. For cooling sizing calculations carried out before Compact and Detailed HVAC simulations the SummerDesignDay day type is always used.

HVAC Autosizing Simulations

EnergyPlus provides WinterDesignDay and SummerDesignDay day types in Compact schedules to cover the behaviour of schedules during autosizing simulations. When setting up schedules that will be used in Compact or Detailed HVAC simulations it is important to consider whether the schedule will be active or inactive during the heating and cooling sizing simulations used for autosizing equipment. In particular internal gains must be excluded from heating sizing simulations to avoid undersizing the heating equipment.


More specific advise on this can be found in the 7/12 schedules and Compact schedules sections.


More general advise on HVAC autosizing can be found in the Autosizing HVAC Components section.