Table of Contents
Advertisement
Pulse Width Modulation (PWM)
Pulse Width Modulation (PWM)
modulates 2 stages 0 to 100% with a 3-
minute time base. The first stage (J9) of
PWM modulates 0 to 100% to supply 0
to 50% of the reheat need. The second
stage (J10) modulates 0 to 100% to
supply 51% to 100% of the reheat need.
Hot Water Heat Maximum Override
(Maximum Heat Required)
A UCM with hot water outputs can be
commanded to override the water valve
position to maximum position. For
units with 1 - 3 stages hot water will
turn on all of its water outputs (possible
fan is not affected). For units with
proportional hot water the hot water
valve will be driven open, and if no fan
is present, output 3 (J11) will energize.
The hot water override can be com-
manded via communications and can
be used to assist in water balancing.
See Chapter 7 for Water Balancing
Procedure.
Auto Changeover
Auto changeover is based on zone
temperature and the supply air tem-
perature as communicated or mea-
sured by the auxiliary temperature
sensor.
1. When the supply air temperature is 10
degrees above the zone temperature
the control action will be Heat.
2.When the supply air temperature is
below or equal to the zone temperature
the control action will be Cool.
3.If the supply air temperature is between
the zone temperature and the zone
o
temperature +10
F (zone temperature <
supply air temperature < zone
o
temperature + 10
F), the control action
remains the same and the UCM
controls to the minimum flow set point.
Flow Overrides
During flow overrides of drive to
minimum or maximum the flow is
controlled to the appropriate set point.
With UCM 3.3 and prior during flow
overrides of open or closed, the valve is
continuously driven in that direction
forever. UCM 3.3 and prior rely on the
limit switches to protect the drive train.
UCM 4.0 drives for the stroke time, then
stops.
VAV-SVX01B-EN
UCM Programming
and Operation
Enforce Minimum Flow Set Points
The UCM can be told not to enforce the
minimum flow set point (energy saver)
via communications. This allows the
control algorithm to choose any value
from 0 to the maximum flow set point.
The primary use of this is VariTrac
systems, but it is available for any
configuration.
Calculated Cool Ventilation Ratio (Z
Factor)
As a measurement of zone ventilation,
a "Z" factor is computed and available
over communications (only if using the
COM 4 protocol). The UCM does not
use this value for any control purposes.
It is computed as follows:
Z = (Ventilation Target)/Sensed Flow
Where the ventilation target is
dependent on occupancy and ranges
from 0 to 100.
Z will be set to zero if the active
minimum flow set point is 0.
Z will be set to zero if the sensed flow
(or valve position) is 0.
If position control is being used the
sensed flow is replaced with the valve
position.
The Z factor may then be used by BAS
equipment to satisfy ASHRAE 62-89
and calculate the outside air flow set
point.
IAQ Set Point Modification
Ventilation rate change for IAQ pur-
poses is accomplished by setting the
active minimum flow set point to the
edited cooling minimum flow set point
* IAQ multiplier when no heat is being
supplied to the zone. When heat is
being supplied (heat mode or reheat
active) the active minimum flow set
point is the greater of heating minimum
flow and cooling minimum flow * IAQ
multiplier. The result of cooling mini-
mum flow * IAQ multiplier is limited to
the maximum flow set point. Reheat
continues to stage on/off based upon
the heating minimum flow set point.
The IAQ multiplier range is from 0.0 to
10.0 in tenths.
Wireless Compatibility
Up to five wireless sensors may be
assigned to a UCM. Four sensors may
be classed as "averaging"; one sensor
can be classed as "backup" . The
hardwired sensor is optional and can
be classified as:
" Averaging" (A peer with the averaging
wireless sensors)
"Primary Backup" (Supersedes any
backup wireless sensor)
"Secondary Backup" (Used only if the
wireless backup sensor is not
functional)
"Not Present" (UCM 4.0 only, UCM 3.3
and prior treated this selection the
same as Secondary Backup)
The backup sensors are optional.
Backup sensors for temperature and
set point inputs only affect the UCM if
all averaging sensors are failed. Backup
button functions are always used. Any
combination of backup strategies is
permitted.
Although the hardwired sensor is
optional in a wireless system, having
one provides valid set point and zone
temperature values for the UCM to use
during the time between a reset (power
cycle or via communication) and the
reception of the next wireless data
update. During this time, if there is no
hardwired sensor the zone temperature
o
used by the UCM is 0
F and the global
and hardwired set point and zone
temperature will be indicated as failed.
In a wireless system with a hardwired
sensor enabled and configured as
averaging, primary backup or
secondary backup after a reset the
UCM will use the hardwired sensor
values until the wireless sensor values
are received.
Button pushes from any sensor
assigned to a UCM will be accepted
and used without regards to source,
(i.e., any assigned sensor can cause
any button function). The priority of
button pushes is: 1. Override to
maximum flow, 2. Override to
unoccupied, 3. Timed override, and 4.
Cancel. Any sensor that is generating a
local override will not be used to
calculate the local thumbwheel setting.
The UCM must receive an update from
a wireless sensor at least every 24
minutes for that sensor to continue to
affect the zone control. Sensors that do
17
Advertisement
Table of Contents
