TEMPERATURE CONTROL
The FBVI-2U4-4T continuously compares the zone temperature with the active setpoints. Zone
temperature is detected from UI1 or a CBT-Stat.
Heating demand and cooling demand calculations are constantly updated. These calculations are
expressed as 0
…
100% heating needed and 0
…
100% cooling needed.
Default temperature setpoints are 71°F/75°F for the occupied mode heating/cooling and 65°F/85°F for
the unoccupied mode heating/cooling.
HEATING MODE
In the heating mode, stages of heat are energized, and/or valve positions are increased, as the heating
demand increases. The primary supply air Flowrate is set to the current primary air heating flow setpoint.
If the unit includes a fan, see the Fan Control section in Section 3.
In an OCCUPANCY state, on a fall in zone temperature below the occHeatStpt (A124), the heating
demand will rise from 0-100%. If heat is available, the stages of heat will be enabled. The damper will
modulate to maintain the activeAirflow (A250) to the activeFlowSetpoint(A236), and it will reset from
minHeatFlowStpt (A230) to maxHeatFlowStpt (A229), depending on the VAV configuration. On a rise in
zone temperature above the occHeatStpt (A124), the heating demand will fall from 100%-0. If heat is
available, the stages of heat will be disabled.
The occHeatStpt (A124) setpoint can be affected by shed or standby modes. The active heating setpoint
will be reflected by the activeHeatStpt (A188).
If the discharge air temperature is above the highDuctTempLockout setpoint (A34) of 180F (82C ) the
heat will be locked out until it falls below 120F (49C)
Note: While in warmup mode or hot air is present, accessory heat will not be commanded on.
In an UNOCCUPANCY state, on a fall in zone temperature below the unoccHeatStpt (A126), the heating
demand will rise from 0-100%. If heat is available, the stages of heat will be enabled, and the unit will be
in Setback Mode. The damper will modulate to maintain the activeAirflow (A250), and it will reset from
minHeatFlowStpt (A230) to maxHeatFlowStpt (A229), depending on the VAV configuration. On a rise in
zone temperature above the unoccHeatStpt (A126), the heating demand will fall from 100%-0. If heat is
available, the stages of heat will be disabled.
COOLING MODE
In the cooling mode, the primary air Flowrate setpoint is modulated toward maximum as the cooling
demand increases. If the unit includes a fan, see the Fan Control section in Section 3.
In an OCCUPANCY state, on a rise in zone temperature above the occCoolStpt (A123), the cooling
demand will rise from 0-100%. The damper will modulate to maintain the activeAirflow (A250) to the
activeFlowSetpoint(A236), and it will reset from minCoolFlowStpt (A227) to maxCoolFlowStpt (A228). On
a fall in zone temperature below the occCoolStpt (A123), the cooling demand will fall from 100%-0.
The occCoolStpt (A123) setpoint can be affected by shed or standby modes. The active heating setpoint
will be reflected by the activeCoolStpt (A187).
In an UNOCCUPANCY state, on a rise in zone temperature above the unoccCoolStpt (A125), the cooling
demand will rise from 0-100%. The unit will be in Setup Mode. The damper will modulate to maintain the
activeAirflow (A250), and it will reset from minCoolFlowStpt (A227) to maxCoolFlowStpt (A228). On a fall
in zone temperature below the unoccCoolStpt (A125), the cooling demand will fall from 100%-0.
Note: If the user tries to set the cooling setpoint occCoolStpt (A123) lower than the heating setpoint
occHeatStpt (A124), the heating setpoint will be automatically lowered. If the user tries to set the
heating setpoint occHeatStpt (A124) higher than the cooling setpoint occCoolStpt (A123), the heating
setpoint will not change.
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