Autosizing Heating and Cooling Equipment

The Heating Capacity and Cooling Capacity Model Data is found on the HVAC tab at zone level.  


If the Plant sizing building model option is set to 4-Autosize when not set these heating and cooling capacities can be automatically calculated by the software.


Note: if you change heating or cooling capacities by hand you should be aware that the data will be overwritten if Model Options change.

To keep the heating and cooling capacities fixed, change the Plant sizing model option to 2-Manual. You may choose to use this option if you are already satisfied with the autosized capacities and wish to keep them as they are regardless of future changes to the model.

Detailed HVAC Autosizing

Winter and summer design day simulations are automatically carried out as required for autosizing heating and cooling equipment prior to a Detailed HVAC simulation. There are some considerations you should be aware of regarding autosizing.


  1. Internal gains should normally be excluded from Winter design day calculations.
  2. You therefore shouldn't use the same schedule for equipment, occupancy and HVAC operation because equipment and occupancy should be off for heating autosizing and HVAC should be on.
  3. Typical workday gives the easiest route to defining autosizing operation - the appropriate Winter Design Day schedule data settings are used.
  4. Summer design day schedules are normally the same as the general ones so are easier to deal with.
  5. If you are using Compact schedules then you should ensure that a specific line of WinterDesignDay data is included for all schedule periods.
  6. If you are using 7/12 Schedules then there are 2 options: End-use defaults and Profiles.
  7. You can include intermittent operation by using a time-varying Heating demand or HVAC schedule. This would normally provide heating equipment sizes with higher capacity than a steady-state calculation where the heating is on all day.