WattMaster VAVBOX - Manual (Page 19)

VAVBOX Controller
Technical Guide
19
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/airflow
position.
Of course different space temperature errors and different Integral val-
ues 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 posi-
tion the damper exactly on the calculated position. This reduces wear
and tear on the actuator gears and motors and the amount of airflow
involved is not affected by that small amount of damper error.
On pressure independent terminal units, the airflow 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
airflow setting for the space.
If the pressure sensor is disconnected or fails on a pressure independent
terminal unit, the controller automatically reverts to pressure depen-
dent operation and generates an 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 50% 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, a MiniLink
Polling Device must be installed on each local loop. The MiniLink Poll-
ing Device has the ability to track the amount of override time gener-
ated by each space sensor equipped with push-button override.
Storing and retrieving these logs requires a dedicated computer running
the Prism front-end software program. No other method exists for re-
trieving these logs. That means that all of your units will be connected
together on the communications loop and the loop will be terminated at
a CommLink II device connected to an on-site computer.
Warning: This computer must be on 24 hours a day 7 days a
week running the Prism 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 they are being logged too.
Note: For proper time and date stamping of the tenant log, you
must configure the air handler to broadcast the time so
that the VAVBOX Controllers can read it and use it in
their tenant and trend logs.
Alarm Detection And Reporting
The VAVBOX controller continuously performs self diagnostics dur-
ing normal operations to determine if any operating failures have oc-
curred. These failures can be reported to the user in several ways, de-
pending on the type of system and options installed by the user. If a
System Manager or a Modular Service Tool is connected, the alarms
will be reported on the Status Screens. If the Prism computer front end
software is installed, the alarms will be reported on the main screen of
the program and be logged to disk. If the remote communications op-
tion is installed, all alarms except the Damper Feedback Failure con-
dition can initiate a callout to a pager to alert someone to the alarm
condition. See the computer front end program operations manual for
further information on this topic.
Internal Trend Logging
The VAVBOX controller continuously maintains an Internal Trend Log,
which records a fixed set of values at an interval programmed by the
user. These values can be retrieved only with the graphical front-end
program. In order to utilize these logs, a computer with Prism front end
software installed must be connected to the system.