Instruction manual

OM 751 Page 23 of 32
Indoor Air Fan Operation
The UVC supports a 3-speed IA fan: Low, Medium, and High. The
UVC will calculate the effective fan speed and operation based upon
the unit mode, the occupancy mode, and the values of several network
variables.
AUTO MODE
The UVC is provided with a user selectable auto fan mode feature.
When in auto fan mode, the UVC uses the space temperature PI loop
to automatically adjust the fan speed as needed to maintain space
temperature. This ensures that the UVC will maintain the lowest and
quietest fan speed whenever possible. When in auto fan mode, a
maximum of 6 fan speed changes per hour is allowed (by default), this
prevents frequent automatic fan speed changes from disturbing room
occupants.
OCCUPIED, STANDBY AND BYPASS OPERATION
During occupied, standby and bypass modes the IA fan will, by default,
remain On.
UNOCCUPIED OPERATION
During unoccupied mode the IA fan will typically remain off and will
cycle with calls for heating and cooling.
CYCLE FAN
The UVC is provided with a Fan Cycling Configuration variable which
can be used to force the IA fan to cycle with calls for heating and
cooling during the occupied, standby and bypass occupancy modes.
When the fan is off, the OA damper will be closed, therefore, it is
recommended that this feature only be used when it is acceptable that
normal ventilation is not required.
OFF DELAY
When the IA fan is set to cycle, or during the unoccupied mode, or when
the UVC is placed into off mode, the UVC is configured to continue fan
operation for a time period (30-seconds default) after heating or
cooling is complete.
Outdoor Air Damper Operation
The UVC is configured for an OA damper operated by a floating-point
actuator. The OA damper actuator contains a spring which will ensure
that the OA damper is closed upon loss of power. The floating-point
actuator is driven by the UVC using two binary (Triac) outputs. The
OA damper is typically open to the current minimum position during
the occupied and bypass occupancy modes, and closed during the
unoccupied and standby occupancy modes.
MINIMUM POSITION
The UVC is configured to maintain three OA damper minimum
positions based upon the operation of the IAF. This allows the ability
for each unit to be field configured to provide the amount of fresh air
required to the space at each of the three IA fan speeds.
Table 16. Default OA Damper Minimum Positions
w/o CO
2
w/ CO
2
IAF High Speed 20% 5%
IAF Medium Speed 30% 5%
IAF Low Speed 35% 5%
NOTICE
If the CO
2
Demand Controlled Ventilation (DCV) option is used,
then the UVC will only use the IA fan high speed OA damper
minimum position regardless of fan speed, the DCV function will
adjust the OA damper above this minimum as needed to maintain
CO
2
setpoint.
ECONOMIZER OPERATION
The economizer function is used by the UVC to determine if the OA is
adequate for economizer (primary) cooling. When both the economizer
and mechanical cooling are available, the economizer will be used as
primary cooling and the UVC will add mechanical cooling only if the
economizer is not adequate to meet the current cooling load (i.e. the OA
damper reaches 100% and cooling is still required).
The UVC is configured to support three economizer types:
• Temperature Comparison Economizer (default)
• Temperature Comparison with OA Enthalpy Setpoint
Economizer (optional)
• Temperature Comparison with Enthalpy Comparison
Economizer (optional)
Temperature Comparison Economizer
The UVC uses two configuration variables to determine if the
economizer can be used: Economizer OA Temp Setpoint and
Economizer Temp Differential. See Table 17.
EffectiveOutdoorTemp <
(EconomizerOATempSetpoint –
EconomizerTempDifferential)
Economizer Available OR
EffectiveOutdoorTemp <
(EffectiveSpaceTemp –
EconomizerTempDifferential)
Temperature Comparison with OA Enthalpy Setpoint
Economizer (optional)
The UVC uses three configuration variables to determine if the
economizer can be used: Economizer OA Temp Setpoint, Economizer
Temp Differential and Economizer OA Enthalpy Setpoint. See
Table 18.
EffectiveOutdoorEnthalpy <
EconomizerOAEnthalpySetpoint –
EconomizerEnthalpyDifferential
AND
((EffectiveOutdoorTemp <
Economizer Available (EconomizerOATempSetpoint –
EconomizerTempDifferential)
OR
EffectiveOutdoorTemp <
(EffectiveSpaceTemp –
Economizer TempDifferential))
Temperature Comparison with OA Enthalpy Setpoint economizer
requires an optional OA humidity sensor.
NOTICE
Table 17. Economizer Available Calculation – Temperature Comparison
Table 18. Economizer Available Calculation – OA Enthalpy Setpoint