SCXF-SVX01T-EN
67
with a GBAS and is used to reduce electrical consumption
at peak load times. Demand limiting can be set at either
50% or 100%. When demand limiting is needed,
mechanical cooling and heating (with field-provided 2-
stage electric heat only) operation are either partially
(50%), or completely disabled (100%) to save energy. The
demand limit definition is user definable at the HI panel.
Demand limit binary input accepts a field supplied switch or
contact closure. When the need for demand limiting has
been discontinued, the unit’s cooling/heating functions will
again become fully enabled.
GBAS Communication (Analog Inputs)
The GBAS accepts external setpoints in the form of analog
inputs for cooling, heating, supply air pressure. Refer to the
unit wiring diagram for GBAS input wiring and the various
desired setpoints with the corresponding DC voltage
inputs.
Any of the setpoint or output control parameters can be
assigned to each of the four analog inputs on the GBAS
module. Also, any combination of the setpoint and/or
output control parameters can be assigned to the analog
inputs through the HI. To assign the setpoints, apply an
external 0-5 Vdc signal to one of the following:
• Directly to the signal input terminals
• To the 5 Vdc source at the GBAS module with a 3-wire
potentiometer.
Note: There is a regulated 5 Vdc output on the GBAS
module that can be used with a potentiometer as a
voltage divider. The recommended potentiometer
value is 1000-100,000 ohms.
The setpoints are linear between the values shown in Table
36, p. 67. Reference Table 37, p. 68 for corresponding
input voltage setpoints. Following are formulas to calculate
input voltage or setpoint. SP = setpoint, IPV = input
voltage.
• If the setpoint range is 50-90°F:
– IPV = (SP - 50) (0.1) + 0.5
– SP = [(IPV - 0.5)/0.1] + 50
• If the setpoint range is 40-90°F:
– IPV = (SP - 40)(0.8) + 0.5
– SP = [(IPV - 0.5)/0.08] + 40
• If the setpoint range is 40-180°F:
– IPV = (SP - 40)(0.029) + 0.5
– SP = [(IPV - 0.5)/0.029] + 40
• If the static pressure range is 0.03-0.3 iwc:
– IPV = (SP - 0.03)(14.8) + 0.5
– SP = [(IPV - 0.5)/14.8] + 0.03
• If the static pressure range is 0.0-5.0 iwc:
– IPV = (SP)(0.8) + 0.5
– SP = [IPV/(0.8 + 0.5)]
GBAS Demand Limit Relay (Binary Input)
The GBAS allows the unit to utilize the demand limit
function by using a normally open (N.O.) switch to limit the
electrical power usage during peak periods. Demand limit
can initiate by a toggle switch closure, a time clock, or an
ICS control output. These contacts must be rated for 12 ma
@ 24 Vdc minimum.
When the GBAS module receives a binary input signal
indicating demand limiting is required, a command initiates
to either partially (50%) or fully (100%) inhibit compressor
and heater operation. This can be set at the HI using the
setup menu, under the “demand limit definition cooling” and
“demand limit definition heating” screens. A toggle switch,
time clock, or building automation system control output
can initiate demand limiting.
If the cooling demand limit is set to 50%, half of the cooling
capacity will disable when the demand limit binary input
closes. The heating demand limit definition can only be set
at 100%, unless the unit has field-provided two-stage
electric heat. In that case, if the heating demand limit is set
to 50%, half or one stage of heating disables when the
demand limit binary input closes. If the demand limit
definition is set to 100%, then all cooling and/or heating will
disable when the demand limit input closes.
GBAS Diagnostics (Binary Outputs)
The GBAS can signal up to five alarm diagnostics, which
are fully mappable through the setup menu on the HI.
These diagnostics, along with the alarm output on the
RTM, allow up to six fully mappable alarm outputs.
Each binary output has a NO and NC contact with a rating
of two amps at 24 Vac. The five binary outputs are factory
preset as shown on the unit wiring diagram (on the unit
control panel door). However, these outputs can be field
defined in a variety of configurations, assigning single or
multiple diagnostics to any output.
For a complete listing of possible diagnostics, see the Self-
Contained Programming Guide, PKG-SVP01. For terminal
strip locations, refer to the unit wiring diagram for the
GBAS.
Table 36. GBAS analog input setpoints
Control Parameter
Signal Range Vdc Setpoint Range °F
Occupied zone cooling setpoint (CV units only)
0.5 to 4.5 50 to 90°F
Unoccupied zone cooling setpoint (CV and VAV)
0.5 to 4.5 50 to 90°F
Occupied zone heating setpoint (CV units only)
0.5 to 4.5 50 to 90°F
Controls
To Next Page
Loading...