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OCCUPIED/UNOCCUPIED — The unit control system will
initiate normal occupied mode functions (including Morning
Warm-up, Economizer Minimum Position, and Cooling Cycle)
whenever a contact closure is made that emulates the normal
timeclock contacts. See Fig. 23. (‘‘Occupied/Unoccupied
Switch’’). The contact closure from the BMS must be an iso-
lated contact set, normally open, and suitable for 24 volts AC
pilot duty.
NIGHT SETBACK CONTROL — Night setback control is
used to control the space to a set point level that is typically
lower than during normal occupied periods (Heating Only
mode). Some applications also require a limitation on the max-
imum space temperature during unoccupied periods (Cooling
mode). Both modes are possible by closing the same contacts
used in the Occupied/Unoccupied control, or by installing a
dedicated contact set in parallel with the Occupied/ Unoccu-
pied control contacts, and using the BMS space temperature
sensing system and its logic to determine when to initiate unit
operation.
Once the unit operation has been initiated by the BMS con-
tact closure, the unit operates in its normal occupied mode
manner, initiating morning warm-up if needed (as sensed by re-
turn air temperature to the unit) or cooling (controlling to cur-
rent SASP value). The Night Setback Control contacts will in-
terrupt normal unit operation when the BMS senses that space
temperatures have returned to unoccupied set point levels, and
the unit will shut down normally.
The contact closure from the BMS must be an isolated con-
tact set, normally open, suitable for 24 volts AC pilot duty.
NOTE: If the rooftop unit is equipped with a VFD and night
setback cooling operation is intended, the fan system must be
controlled to permit FULL SUPPLY FAN AIR DELIVERY
during unoccupied cooling operation. This is most conve-
niently attained by replicating the HIR relay function of the
rooftop unit. An HIR control sequence will force all room ter-
minals to their minimum heating CFM position, thus assuring
adequate airflow through the rooftop unit during night setback
cooling operation. During night setback cooling operation, the
return-air temperature (RAT) will be well above normal levels.
The higher RAT means that the air temperature leaving the
evaporator coil will also be well above normal levels. This sit-
uation is interpreted by the unit control system as a demand for
additional cooling stages. The unit control responds to this
demand by bringing on more stages, until typically all stages
are active. If the VFD is not working in-step with the refrigera-
tion system demand, it is possible to produce low suction pres-
sures and local frosting on the evaporator coil during the night
setback cooling operation.
UNIT SUPPLY AIR SET POINT ADJUSTMENT — The
minimum Supply Air Set Point (SASP) temperature is estab-
lished by the setting at Potentiometer P1 on the unit display
board (see Fig. 6). The control point can also be adjusted
upward by emulating the function of the accessory Space Tem-
perature Reset package. The BMS can be used to cause this
reset by adjusting the resistance value in a variable resistance
transducer with a 4 to 20 mA or 2 to 10 vdc signal generated
by the BMS.
This emulation requires the following field-supplied parts:
• Variable resistance transducer (Kele RES-1 or equiva-
lent, range 0 to 1000 ohms)
• Series resistance with potentiometer, suitable for manual
adjustment to 12.5 to 13.0 k-ohms total resistance
Field Connections (see Fig. 30)
— Connect fixed resistance
with manual potentiometer and variable resistance transducer
in series.
Connect wiring to rooftop unit at:
Size 034-044: TB3-12 and TB3-15
Size 054-104: TB4-12 and TB4-15
Configuration
— Configure as follows:
1. Set DIP switch no. 2 to ON.
2. Adjust manual potentiometer to 12.6 to 12.8 k-ohm.
3. Configure transducer for job site input signal from BMS.
4. Adjust Potentiometer (P3) on the rooftop to MAXIMUM
SASP value (typically 65 to 70 F). The maximum P3 SASP
control limit is 70 F.
Operation
— Unit will initiate SASP Reset (adjust configured
SASP upward) when the sum of the resistance (fixed resistance
+ potentiometer + transducer) exceeds 13.1 k-ohm. Once reset
is initiated, full range of reset (P3 setting minus configured
SASP) will be reached with 500-ohm increase in transducer re-
sistance (TR).
During Reset mode operation, Code 21 will appear on unit
display board.
Formula:
MSP = SASP +
MSP: Modified SASP (SASP plus Reset)
TR: Resistance at transducer
R@13.1: TR required to reach 13.1 k-ohm start level
DEMAND LIMIT (1-STAGE OR 2-STAGE) — Both of the
Demand Limit functions on the units rely on external switches
to initiate the reset functions. Contact closures by the BMS can
be used in place of these switches. Contacts must be isolated
and suitable for 115-vac pilot duty operation.
For Single-Step Demand Limit, emulate function of switch
SW with contact closure controlled by the BMS. Set potenti-
ometer P4 manually at the unit control box. Alternatively, po-
tentiometer P4 might also be emulated by a variable resistance
transducer, with the BMS now able to adjust the amount of de-
mand limit.
For 2-Step Demand Limit, install the accessory Demand
Limit Control Module (DLCM) according the instructions on
page 18. Replace switch functions Switch 1 and Switch 2 with
contact closures controlled by the BMS (see Fig. 29).
Follow unit control configuration instructions in the De-
mand Limit section on page 18.
SUPPLY DUCT PRESSURE SET POINT ADJUSTMENT
— Supply duct pressure set point adjustment from a remote
BMS is possible when the unit has been equipped with a fac-
tory-option VFD (variable frequency drive). There are two
methods available:
• Direct 4 to 20 mA signal
• DDC direct to the VFD
Direct 4 to 20 mA Signal
— During normal unit operation,
the factory-installed VFD receives a 4 to 20 mA signal from
the Duct Pressure (DP) transducer which indicates current sup-
ply duct pressure. The VFD then determines the appropriate
fan speed (using its internal PID logic feature) and adjusts its
output to the supply fan motor to suit. It is possible to emulate
this 4 to 20 mA control signal by the BMS, which will transfer
control of the VFD to the BMS.
NOTE: When providing a direct 4 to 20 mA signal to the VFD
from a BMS with DP logic, disable the PID (proportion inte-
grated derivative calculation process) feature of the VFD.
DDC Direct to the VFD
— Several accessory interface
boards are available for the VFDs that permit direct communi-
cation between the VFD and several BMS communication sys-
tems. Contact your Carrier representative for information on
selecting an appropriate accessory interface board and the
name of the local service office (for sale and installation of the
accessory boards).
[
(P3 — SASP)
X
(0.6 F)
X (TR — R@13.3)
]
(3) (100 ohm)