WattMaster WM-WCC3-TGD-01B - Manual (Page 791)

Operator Interface
VAV/Zone Controller Technical Guide
23
Sequence of Operations
In all cases, before the series box fan can be activated, the air damper
is driven fully closed and held that way for 30 seconds to make sure
the series box fan hasn’t inadvertently started to spin backwards. Once
the series box fan starts, it waits an additional 10 seconds to allow the
fan to spin up before it starts to open the damper and introduce airfl ow
from the HVAC unit fan.
NOTE: If Check for Main Fan Status is selected, the series fan
will activate any time the HVAC unit fan is operating.
Box Fan Relay & Reheat Relay Staging Unoccupied Mode
Relays
Stage On
At
Series
Fan
Parallel
Fan
Heat
Stage 1
Heat
Stage 2
Heat
Stage 3
+0.5 F
Above
Box Heat
Setpoint
See
Note 1
See
Note 2
At Box
Heat
Setpoint
X
-1.0 F
Below
Box Heat
Setpoint
X
-2.0 F
Below
Box Heat
Setpoint
X
Relays
Stage Off
At
Series
Fan
Parallel
Fan
Heat
Stage 1
Heat
Stage 2
Heat
Stage 3
+1.0 F
Above
Box Heat
Setpoint
See
Note 1
See
Note 2
+1.0 F
Above
Box Heat
Setpoint
X
At Box
Heat
Setpoint
X
-1.0 F
Below
Box Heat
Setpoint
X
Notes: 1) If Check for Main Fan Status is selected, the se-
ries fan will activate any time the HVAC unit fan is operating.
2) If the VAV/Zone Controller has been confi gured as a Parallel Fan
Powered terminal unit, the Parallel fan will run continuously when the
VAV/Zone Controller is in the Space Heating mode no matter whether
Check for Main Fan Status has been selected or not.
Table 4: Relay Staging - Unoccupied Mode
Parallel Flow Fan Terminals
If the VAV/Zone Controller has been confi gured as a Parallel Fan Pow-
ered terminal unit, the Parallel fan will run continuously when the VAV/
Zone Controller is in the Space Heating mode no matter whether Check
for Main Fan Status has been selected or not.
If Check for Main Fan Status is selected, the damper will remain in the
closed position until the HVAC unit controller is broadcasting that the
HVAC unit fan is operating, regardless of whether it is calling for heat
or not. Once the broadcast is received, the damper will then move to
its Night/Reheat minimum position until the space temperature begins
to fall below 0.5ºF above the unoccupied heating setpoint. If Check for
Main Fan Status has not been selected, the damper will be held in the
fully closed position until the space temperature begins to fall below
0.5 ºF above the unoccupied heating setpoint. When in Supply Air
Heating mode, the damper will modulate to maintain the Unoccupied
Heating setpoint.
NOTE: For the VAV/Zone Controller to go into Supply Air Heat-
ing mode, the HVAC unit fan must be operating and the
Supply Air temperature must be the deadband amount
above the Space temperature.
Damper Control
The damper position is calculated by the mode and demand from the
space sensor. Included in this calculation is an Integral function. This
prevents the damper/airfl ow from stagnating at a position somewhere
above the setpoint because the supply air temperature or duct pressure
isn’t quite enough to satisfy the space at the currently calculated pro-
portional position. The Integral causes the calculation to keep adding
a small amount of the proportional error back into the damper/airfl ow
position each time a new position is calculated. The amount the Integral
adds back in is user adjustable. This value is presented as a number
between 0.0 and 100.0. That means that if the integral is less than 10.0,
you are adding a percentage from 0 to 100% of the error back into the
calculation. If you increase the Integral above 10, you are adding more
than 100% back in.
With just proportional control, a 1ºF error would cause a 50% increase
in damper/airfl ow if the Integral is not included. (1°F is half of the 2ºF
Proportional Window.)
If you had set the Integral to 10, the calculation would add 2% to the
current damper/airfl ow calculation each time. The calculation occurs
once every 10 seconds, so it would take a little over 4 minutes to reach
the programmed 100% maximum.
Example:
1. 50% Remaining / 2% Integral = 25 Moves to get to a 100%
Maximum.
2. 25 Moves times 10 seconds = 250 seconds or a little over 4
minutes to reach the 100% maximum damper/airfl ow posi-
tion.