The ERV function interacts directly with the exhaust control function. Only enable the ERV Interaction on VAV units equipped with exhaust VFDs.
Setpoints and related data
The setpoints and related data include the following items:
- Power exhaust fan type (ExFType) variable frequency fan
- Fan control type (FanCtlType) variable speed
- ERV Enabled (ERV-En)
- ERV Unoccupied Fan Enabled (ERVUnoccFan-En)
- Operational Occupancy (OprOcc)
Outputs
The outputs include the following items:
- 2 to 10 VDC from EX VFD
- 24 VAC from EX-FAN
Operation
The ERV function provides input to the exhaust control sequence by determining if energy recovery is installed and when it is active. The ERD state is determined based on Table 1.
| ERV enabled | ERVUnoccFan-En | OprOcc | State |
|---|---|---|---|
| Disable | * | * | OFF |
| Enable | Enable | * | ON |
| Enable | Disable | Occupied | ON |
| Enable | Disable | Unoccupied | OFF |
| * This state has no effect on the output. | |||
When the ERV state is on, and applied to a VAV unit with exhaust VFDs, the EX VFD output is controlled by tracking the VFD OUTPUT of the supply fan.
When the ERV installed is disabled, the exhaust VFDs are controlled based on building static pressure. See Modulating power exhaust with VFD, for additional information.
When the ERV installed is enabled and ERV unoccupied fan is disabled, the exhaust outputs are turned off in the unoccupied mode.
On any unit without exhaust VFDs, the ERV installed parameter must be set to disabled.