Installation and Maintenance Manual

Startup
80 UV-SVN02C-EN
(configurable using the Tracer TU service tool), and the
cooling capacity is at a minimum, the available heating
capacity is used to raise the discharge air temperature
to the low limit (refer to the following section,
“Discharge Air Tempering (UC400).”).
• Simplified zone control— if discharge air
temperature failure occurs, then simplified zone
controls runs. In the unoccupied mode, the controller
maintains the zone temperature by calculating the
required heating or cooling capacity (0–100%)
according to the measured zone temperature and the
active zone temperature setpoint. The active zone
temperature setpoint is determined by the current
operating modes, which include occupancy and heat/
cool modes.
• Di
scharge air temperature control— is the backup
mode that runs only if there is not valid zone
temperature. In this mode, the active space
temperature setpoint is used as the discharge air
temperature setpoint.
Important: T
his is not a normal operating mode. The
source of the invalid zone temperature
needs to be corrected to restore normal
operation.
Discharge Air Tempering (UC400)
If the UC400 controller is in cooling mode, cascade zone
control initiates a discharge air tempering function when:
• The discharge air temperature falls below the
disc
harge air temperature low limit setpoint
(configurable using the Tracer TU service tool)
• All cooling capacity is at a minimum. The discharge air
tempering function allows the co
ntroller to provide
heating capacity (if available) to raise the discharge air
temperature to the discharge air temperature low limit
setpoint.
• The cold outdoor air is brought in through the outdoor
air dam
per and when the damper is at (high) minimum
position. This causes the discharge air temperature to
fall below the discharge air temperature low limit
setpoint.
Heating or Cooling Mode (UC400)
The heating or cooling mode can be determined in one of
two ways:
• By a communicated signal from a BAS or a peer
co
ntroller
• Automatically, as determined by
the UC400 controller
A communicated heating signal permits the controller to
on
ly heat and a communicated cooling signal permits the
controller to only cool. A communicated auto signal
allows the controller to automatically change from heating
to cooling and vice versa.
In heating or cooling mode, the controller maintains the
zone temperature based on the active heating setpoint and
the active cooling setpoint, respectively. The active
heating and cooling setpoints are determined by the
occupancy mode of the controller.
For 2-pipe and 4-pipe changeover units, normal heat/cool
operation will not begin until the ability to conduct the
desired heating or cooling operation is verified. This is
done using the entering water temperature sampling
function, for which a valid entering water temperature is
required. When neither a hard wired nor a communicated
entering water temperature value is present on
changeover units, the controller operates in only heating
mode and assumes the coil water is hot. The sampling
function is not used.
The entering water temperature sampling function is used
only for changeover applications and for information and
troubleshooting. It does not affect the operation of the
controller. (For more information, refer to the following
section, “Entering Water Temperature Sampling Function
(UC400)”.)
Entering Water Temperature Sampling
Function (UC400)
The entering water temperature sampling function is used
with 2-pipe and 4-pipe changeover units and requires a
valid entering water temperature value. If the entering
water temperature value is less than 5°F (2.8°C) above a
valid zone temperature value for hydronic heating, and
greater than 5°F (2.8°C) below a valid zone temperature
value for hydronic cooling, the sampling function is
enabled. When the sampling function is enabled, the
UC400 controller opens the main hydronic valve to allow
the water temperature to stabilize. After 3 minutes, the
controller again compares the entering water temperature
value to the zone temperature value to determine if the
desired heating or cooling function can be accomplished.
If the entering water temperature value remains out of
range to accomplish the desired heating/cooling function,
the controller closes the main hydronic valve and waits 60
minutes to attempt another sampling. If the entering water
temperature value falls within the required range, it
resumes normal heating/cooling operation and disables
the sampling function.
Fan Operation (UC400)
The UC400 controller supports 1-, 2-, 3-speed fans and
variable-speed fans. The fan always operates
continuously while either heating or cooling during
occupied, occupied standby, and occupied bypass
operation. During unoccupied operation, the fan cycles
between OFF and HIGH, regardless of the fan
configuration. When running in AUTO mode, the fan
operates differently based on the mode and the type of fan.
For 1-, 2-, and 3-speed fans, each time the fan is enabled,
the fan begins operation and runs on high speed for a
period of time (0.5 seconds for fan coils and 3 seconds for
unit ventilators and blower coils) before changing to
another speed. Initially running on high speed provides
UV-SVN02_-EN.book Page 80 Thursday, January 24, 2013 4:48 PM