Technical Guide
Operator Interfaces
30
Programming The VAVBOX Controller
Setpoint Screen #4
HC Box Spts IDxxxx
Damper/Airflow Spt
Integral [Ki]..: xxx
The Box Controller normally opens it’s damper based on a Proportional
Error from Setpoint. That means if the zone temperature is 4°F from
setpoint, the damper would be 100% open or it would be modulating to
provide the Maximum CFM on Pressure Independent boxes. If the er-
ror is less than 4°F, the damper may stagnate at that position and never
satisfy the zone. If you add Integral into the damper calculation pro-
cess, this will cause the damper or airflow calculations to continue to
increase as long as the zone temperature is still above the setpoint. That
means it can provide 100% or Maximum CFM before the 4°F error is
achieved, bringing the zone under control faster than it normally would.
Start with a small ( 5 or 10 ) value, if you use this, and monitor the effect
it has. If you enter too large a value, you can create “hunting” situations
that can cause the damper actuator to prematurely wear out.
Description
Minimum
Default
Maximum
Integral
0
0
100
Setpoint Screen #5
HC Box Spts IDxxxx
Damper/Airflow Spt
Maximum..: xxx %
Vent Min.: xxx %
The Box Controller will not allow the damper or airflow calculation to
exceed the Maximum setpoint while it is allowing the damper to modu-
late. During Vent mode when there is no heating or cooling demand, the
damper or airflow will maintain at least the Vent Min amount of airflow
into the zone for ventilation.
Description
Minimum
Default
Maximum
Maximum
0% or
0 CFM
100% or
1000 CFM
100% or
30000 CFM
Vent Min.
0% or
0 CFM
25% or
250 CFM
100% or
30000 CFM
Setpoint Screen #6
HC Box Spts IDxxxx
Damper/Airflow Spt
Cool Min.: xxx %
Heat Min.: xxx %
During Supply Air Cooling Mode if the space being served by this damper
is satisfied and has no cooling demand the damper will close to this
Cool Min setting. This provides a minimum amount of airflow into the
space for ventilation, even if the space does not require additional cool-
ing. During Supply Air Heating Mode if the space being served by this
damper is satisfied and has no heating demand the damper will close to
this Heat Min setting. This provides a minimum amount of airflow into
the space for ventilation, even if the space does not require additional
heating.
Description
Minimum
Default
Maximum
Cool Min
0% or
0 CFM
10% or
100 CFM
100% or
30000 CFM
Heat Min
0% or
0 CFM
10% or
100 CFM
100% or
30000 CFM
Setpoint Screen #7
HC Box Spts IDxxxx
Damper/Airflow Spt
Nt/Rh Min.: xxx %
Fan On Min: xxx %
The Nt/Rh Min (Night or Reheat Minimum Damper Position) has dif-
ferent functions depending on whether the VAVBOX controller is in
the occupied or unoccupied mode and whether the VAVBOX controller
is used on a fan powered or non-fan powered terminal unit.
Occupied Mode
If the VAVBOX controller is used on a non-fan-powered terminal unit
that has reheat, the VAVBOX damper will move to the Nite/Reheat po-
sition whenever a Space Heating demand occurs and the HVAC unit is
in Supply Air Cooling or Vent modes. When the HVAC unit is in Sup-
ply Air Heating mode the VAVBOX damper will modulate as required
to maintain the Space Heating setpoint. This setting has no effect on fan
powered terminal units when they are in the occupied mode.
Unoccupied Mode
When using non-fan powered terminal units, the VAVBOX damper will
position itself in the Nite/Reheat minimum position. In order for fan
powered terminal units to position the damper to the Nite/Reheat mini-
mum position, the check for main fan status must be selected and the
HVAC unit fan must be operating.
The Fan On Min is used for Parallel Fan boxes only. This is the damper
position that will cause the Parallel Fan to start if the damper/airflow
drops below this value. Normally the Parallel Fan only operates when
the Reheat stages are activated. If this is not a Parallel Fan box, the last
line will remain blank. Series Fan boxes are not affected by this setting
as the fan is always on anytime the HVAC unit fan is running.
Description
Minimum
Default
Maximum
Nt/Rh Min
0% or
0 CFM
0% or
0 CFM
100% or
30000 CFM
Fan On Min
0% or
0 CFM
0% or
250 CFM
100% or
30000 CFM
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