49
TEMPMASTER
FORM TPM3-EG1 (518)
VENTILATION CONTROL SEQUENCES
Minimum Outside Air (OA) Damper Position (VAV Units)
With VAV units, there are two minimum OA damper positions: one when the unit is at full
speed and the second when the unit is at approximately half speed. These two points al-
low the control to linearly reset the position of the OA damper in response to fan speed.
When the unit goes into the occupied mode of operation, the unit controller shall moni-
tor the speed of the supply fan and open the OA damper to a calculated minimum posi-
tion based on the fan speed. This minimum position shall vary as the speed of the fan
changes. The damper shall remain at this calculated position as long as the unit is in the
occupied mode and the economizer is not suitable for cooling.
Air Measurement Stations
When the unit is equipped with an air measurement station, the unit controller shall control
the OA damper to a measured flow rate through the air measurement station.
When the unit goes into the occupied mode of operation, the unit controller shall control
the OA damper to maintain the minimum airflow setpoint through the air measurement
station. The unit controller shall control the OA damper to this flow rate as long as the unit
is in the occupied mode and the economizer is not suitable for cooling.
Demand Ventilation
If optional carbon dioxide (CO
2
) sensors are connected to the unit, the unit controller can
reset the minimum OA damper position(s) or minimum flow rate based on demand.
The unit controller shall monitor the CO
2
level within the building. If the CO
2
level rises
above the CO
2
setpoint, the controller will temporarily increase the minimum OA damper
position or minimum OA flow rate to increase ventilation. If the CO
2
level drops below the
CO
2
setpoint, the controller will decrease the minimum OA damper position or minimum
OA flow rate to decrease ventilation. Demand ventilation shall remain active as long as the
unit is in the occupied mode of operation.
EXHAUST CONTROL SEQUENCES
Barometric
The optional barometric exhaust system consists of a lightweight barometric relief damper
installed on the end of the unit in the RA section. As more outside air is introduced into
the controlled zone due to economizer and ventilation control sequences, the pressure
inside the building rises. As building static pressure increases to overcome any exhaust
duct static pressure, air will be allowed to escape through the barometric relief damper.
Because this type of exhaust is not powered, the amount of air exhausted will be limited
to the static pressure that will need to be overcome.