The Dedicated Outdoor Air System (DOAS) AHU is a central dedicated outdoor unit that typically delivers outdoor air to multiple air loops. The amount of delivered outdoor air is based on a sum of outdoor air flow rate demands from the downstream AHU outdoor air nodes.
Central DOAS systems can also pre-treat outdoor air before distributing it the connected AHUs, with given precool and preheat air conditions. This is achieved by adding components such as heating and cooling coils and humidifiers to the DOAS AHU in the same way as for standard AHUs.
One restriction with DOAS AHUs is that the fan type must be of the 4-System model type.
The DOAS AHU dialog currently has 2 fields, only one of which is user-definable. These are described below.
Note: When including coils in a DOAS AHU, the recommended approach is to use the "blow-through" configuration where the fan is placed upstream of the coils (see above), rather than the "draw-through" configuration. This is because in EnergyPlus v23.1 used in DesignBuilder v2025.1, DOAS loop draw-through fans do not account for fan energy consumption. See issue EnergyPlus issue 10042.
This is a unique, system-defined, non-editable name assigned to the AHU.
This schedule contains information on the availability of the DOAS AHU for operation. A schedule value greater than 0 (1 is usually used) indicates that the unit can be on during the hour. A value less than or equal to 0 (usually 0 is used) denotes that the unit must be off.
When this unit is unavailable (schedule values of 0) then any equipment contained within this AHU will also be switched off.
To allow a DOAS AHU to be connected to standard AHUs, it is necessary to enable the DOAS connections in the standard AHUs.