Why is my heating system undersized?
Posted by Andy Tindale on 22-Feb-22 11:40 AM
One common cause of under sized heating systems is incorrectly defined schedules. Schedules used to define the operation of equipment, lighting etc should normally be switched off for heating design. A correct form for a schedule used for controlling internal gains, equipment, lighting etc is:

Schedule: Office_Lighting,
Through: 31 Dec,
For: Weekdays SummerDesignDay,
Until: 06:00,      0,
Until: 18:00,      1,
Until: 24:00,      0,
For: Weekends,
Until: 24:00,      0,
For: Holidays WinterDesignDay, AllOtherDays,
Until: 24:00,      0;

Note that for the WinterDesignDay the schedule is switched off.

If the schedule had been switched on for the winter design day, the size of heating system system would be calculated based on the existence of the heating effect of the internal gains. This would lead to the heating system to being undersized.

Updated 22.02.2022