WattMaster WM-WCC3-TGD-01B - Manual (Page 324)

WCC III Technical Guide 4-14
4. SCUSCR.EXE SCREENS
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 proportional 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 1 ºF error would cause a 50%
increase in damper/airfl ow if the Integral is not included. (1 °F is
half of the 2 ºF 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 position.
Of course, different space temperature errors and different Integral
values cause this calculation to operate slower or faster. It is up to
the user to determine the optimum setting that provides the tightest
temperature control without causing the damper to continue to
hunt or modulate, causing premature wear of the actuator gears
and motor.
On pressure dependent terminal units, the damper position is
maintained to within ± 3% of the calculated position. No attempt
is made to position the damper exactly on the calculated position.
This reduces wear and tear on the actuator gears and motors, and
the amount of airfl ow involved is not affected by that small amount
of damper error.
On pressure independent terminal units, the airfl ow is maintained
to within roughly 3% of the terminal unit size constant but no
tighter than 16 CFM on the smallest terminal units. The actual
control window is based on the formula:
Window = Terminal unit size X Square Root (1 / 750), where
Terminal unit size refers to the total rated CFM of the terminal
unit.
This sliding window allows the control to be much tighter on the
smaller terminal units than can be achieved on the larger terminal
units as far as CFM readings. On a large terminal unit, 25 CFM
may not be noticeable, but on a small terminal unit, 25 CFM may
be more than the minimum airfl ow setting for the space.
If the pressure sensor is disconnected or fails on a pressure
independent terminal unit, the damper position goes to 100% open
and the VAV/Zone controller generates a General TUC Alarm to
alert the user that a failure has occurred.
On either type of terminal unit, a space sensor failure will force the
damper to position itself to the 45% position and it will not change
until the sensor is repaired or replaced.
Tenant Override Logs
If you require tenant billing for push-button override usage, the
MCD has the ability to track the amount of override time generated
by each space sensor equipped with push-button override.
NOTE: The VAVBOX TUC-2R controller will go into an
override condition for the user programmed amount of time
when this button is pushed even if the unit is already in a
occupied condition.
Storing and retrieving these logs requires a dedicated front end
computer running the WCC III Trendlog front-end software
program. No other method exists for retrieving these logs. That
means that all of your VAV/Zone controllers will be connected
together on the communications loop and the loop will be terminated
at a Satellite device which is connected to another communications
loop that is terminated at an on-site MCD computer. The tenant
logs are kept on the dedicated job site computer’s hard drive. The
only limitation to the number of logs stored is the capacity of the
hard drive on the computer to which it is being logged.
NOTE: There is also a Tenant Override software that can
be programmed that tenants can use to turn on multiple
zones(among other things) at once without having to use the
push button override on the space sensor. See Section 6 of the
WCC III manual for detailed operation of this program.
WARNING: This WCC III - MCD computer must be on 24
hours a day, 7 days a week, running the Backtask.exe software
in order for tenant logging to be tracked. The tenant logs are
kept on the dedicated end user job site computer’s hard drive.
The only limitation to the number of logs stored is the capacity
of the hard drive on the computer they are being logged to.
WCC III VAV BOX III Tenant Override Logs