WattMaster WM-WCC3-TGD-01B - Manual (Page 794)

VAV/Zone Controller Technical Guide
Operator Interface 26
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 VAV/Zone controller will go into an override condi-
tion for the user-programmed amount of time when this
button is pushed even if the unit is already in an 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 communica-
tions 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.
WARNING: This front end computer and the MCD
computer must be on 24 hours a day 7 days a
week running the WCC software in order for
tenant logging to be tracked.
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 Tenant Override software that can be
programmed so that tenants can 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.
Sequence of Operations