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LCBS CONNECT SOLUTION
21
31-00118EFS—01
Honeywell LCBS offers two basic multispeed control options. They are:
—
Two speed, discrete fan control.
—
Multispeed variable-constant fan control, up to six stages of fan.
Two Speed Discrete Fan Control
In a two-speed discrete fan supply strategy, the fan
SPEEDS
must be able to be operated and controlled in a discrete
manner. Specifically, there are two outputs on the LCBS Connect controller that controls "Fan Low Speed" and "Fan High
Speed." The two-winding, two-speed motor is the simplest of the three options that the LCBS Connect controller can
control. The motor will have two sets of windings. One set of windings is energized for one discrete speed and the other
set is energized for the second speed. If you encounter a motor like this, it is probably already wired to control the two
discrete speeds to existing control system.
NOTES:
1.
Speeds are probably unchangeable in the field as they are "hardwired" by the motor manufacturer.
2.
If you are replacing a control system with the LCBS Connect controller, the HVAC system may "hide" the com-
plexity of control of the two speed fan and actually allow the service contractor to apply a standard staged
heating, staged cooling, fan with two speed logic performed on the line voltage side of the control system. A
typical way a fan is controlled on a 3 - 25 ton constant volume air handling unit is low speed as follows that
DOES NOT require two speed control interface and just a simple R,G,W,Y thermostat. Please refer to this
sequence to understand this point:
Table 4.
WARNING
If the constant volume control system controls a system as shown above,
do NOT use the two fan speed logic
provided by LCBS controller.
Two Speed and Multispeed VFD Application
The LCBS Controller sends a control signal (0-10 VDC) to a VFD that changes frequency and the speed of the supply fan
motor.
NOTES:
1.
Consult with VFD manufacturer to ensure that the supply fan motor in your constant volume air handling unit
is able to be controlled by the VFD. As time goes on, older technology motors in typical 3 - 25 constant volume
air handling units become ever less applied, but care must be taken retrofitting motors.
2.
While changing the speed of a fan motor can yield excellent energy savings, the service contractor must take
care to ensure that reduced air flow is substantial to dissipate heat or cool load across the heat exchanger. If
airflow is dropped to severely, damage to heating or cooling equipment can occur, not to mention reduced
comfort conditions.
OCCUPANCY
CONDITION
LOW VOLTAGE INTERFACE, WHAT THE
EXISTING THERMOSTAT DOES
HOW SYSTEM IS CONTROLLED, LINE
VOLTAGE
UNOCCUPIED
NO CONTROL SYSTEM VOLTAGE, NO CALL FOR
HEATING OR COOLING.
CONTROL SYSTEM FEATURES A TIMING
FUNCTION TO TURN OFF 24 VAC.
TRANSITION
FROM
UNOCCUPIED TO
OCCUPIED
NO CONTROL SYSTEM VOLTAGE, FAN CIRCUIT
(G) ENERGIZED W (CALL FOR HEAT) Y (CALL
FOR COOL).
24 VAC TOGGLES FROM OFF TO ON, Y AND W
CYCLE WITH LOW SPEED FAN WINDING.
OCCUPIED, NO
CALL FOR
COOLING
CONTROL SYSTEM VOLTAGE PRESENT, FAN
CIRCUIT (G) ENERGIZED.
24 VAC ON, PROVIDES VOLTAGE TO
ECONOMIZER AND LOW SPEED FAN WINDING.
OCCUPIED, CALL
FOR COOLING
CONTROL SYSTEM VOLTAGE PRESENT, Y (CALL
FOR COOLING) FAN CIRCUIT ENERGIZED.
24 VAC ON, PROVIDES VOLTAGE TO
ECONOMIZER AND HIGH SPEED FAN WINDING.
OCCUPIED, CALL
FOR HEATING
CONTROL SYSTEM VOLTAGE PRESENT, W
(CALL FOR HEATING) FAN CIRCUIT ENERGIZED.
24 VAC ON, PROVIDES VOLTAGE TO
ECONOMIZER AND HIGH SPEED FAN WINDING.
Содержание LCBS Connect
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