Carrier 33ZCVAVTRM Specifications download pdf (Page 22)

OPERATION

System Pressure Operation

NORMAL OPERATION — The bypass controller will mod-

ulate its damper to maintain the proper system static pressure

set point. The bypass controller does this by comparing its

pressure sensor input reading to the configured system static

pressure set point and determining the error (sensor reading —

set point). The bypass controller then compares the calculated

error to the configured deadband value. If the error is greater

than

of the deadband value (configured deadband times a

constant of 0.05), then the bypass controller commands the

damper to open or close (depending on the positive or negative

value of the error). If the error is less than

of the deadband

value, the bypass controller holds the damper position. If the

pressure sensor fails, the bypass controller will move the

damper to the configured Pressure Sensor Error Damper

Position. See Fig. 12 for an operation flow chart.

LEAVING AIR TEMPERATURE (LAT) MODE — The by-

pass controller will provide LAT protection by controlling the

system pressure based on its duct temperature. If the duct

temperature goes above the configured heating LAT limit or

below the cooling LAT limit, the bypass controller will

increase the pressure set point by the configured LAT Pressure

Delta value. This will cause the amount of bypassed air going

back to the air source to be reduced. If the LAT Pressure Delta

decision is configured for zero, the LAT protection function

will be disabled. The bypass controller will control to the

normal system pressure set point again at the end of the current

heating or cooling cycle, or when its duct temperature sensor

reads greater than the Cooling LAT limit plus five degrees or

less than the Heating LAT limit minus ten degrees. This

temperature swing would indicate that the air source cycled the

heating or cooling as part of its LAT protection, or because the

system conditions are close to satisfying the mode.

NOTE: Bypass LAT protection is disabled during Bypass

Commissioning mode, or if the duct temperature sensor fails.

Bypass Controller Calibration — The bypass con-

troller allows calibration of the damper and pressure sensor

from the Bypass Commissioning Maintenance screen. Refer to

the System Check-Out section for the step-by-step procedure.

DAMPER CALIBRATION — If the bypass controller is not

operating in stand-alone mode, it will verify the system fan

status with its associated Linkage Controller. If the fan is on,

the bypass will request its Linkage Controller to turn the fan

off.

NOTE: If the bypass controller is in stand-alone mode (not

communicating with a Linkage Coordinator) the user must

ensure the pressure reading is zero before performing

calibration. The bypass controller will not be allowed to enter

calibration mode if the fan is on.

In either case, the bypass will check to ensure the fan is off

by reading its pressure sensor and damper position. If the

pressure reading is less than 10% of the static pressure set point

and the bypass damper position is less than 25% of the

resistance of the feedback potentiometer for greater than

60 seconds, then the bypass controller assumes the fan is off.

When the fan is off, the bypass controller will drive its damper

to the fully closed position. The bypass controller will read the

value of the actuator’s feedback potentiometer until the value

stops changing. This indicates the damper is fully closed. If

the feedback resistance value meets the Damper Closed

Criteria in Table 15, the bypass controller will store the value in

non-volatile memory as the resistance at fully closed. The

bypass controller will then position the damper fully open.

When the feedback resistance value stops changing, the bypass

controller reads the value and if the feedback resistance value

meets the Damper Open Criteria in Table 15, the bypass

controller stores the value as the resistance at fully open. The

bypass controller will use the following formula to determine

damper position:

For damper rotation configured as Open:

Damper Position (% open) = ((Feedback Resistance –

Resistance at Full Closed)/((Resistance at Full Open) –

(Resistance at Full Closed))) * 100.

For damper rotation configured as Closed:

Damper Position (% open) = 100 – ((Feedback Resistance –

Resistance at Full Closed)/((Resistance at Full Open) –

(Resistance at Full Closed))) * 100.

Table 15 — Damper Position Criteria

If an invalid resistance value is read, the bypass controller

will not store or use the value, and will issue a Damper

Calibration Alarm. If the bypass controller loses communica-

tion with its associated Linkage Coordinator, the damper

calibration process will be terminated. When the damper

calibration is completed, the bypass controller will signal the

Linkage Coordinator to return the fan to normal operation.

PRESSURE TRANSDUCER ZERO CALIBRATION —

Pressure transducer calibration will occur under two conditions

if it is not operating in stand-alone mode. The first condition is

when it is forced by the user in the BPCOMMIS maintenance

table to perform this operation. The second condition is when

the system goes in to the unoccupied mode for at least 5 minutes

or 168 hours (7 days) since the last calibration, whichever

comes first. If the bypass controller is not operating in

stand-alone mode, it will verify the system fan status with its

associated Linkage Coordinator. If the fan is on, the bypass

controller will send a high priority request to its Linkage

Coordinatortoturnthefanoff.Ifthefanisalreadyoff,the

bypass controller will send the same priority request to ensure

that the fan stays off during the calibration procedure. If for

some reason the bypass controller loses communication with its

Linkage Coordinator for more the 60 minutes or the procedure

takes longer the 60 minutes, the Linkage Coordinator will return

the fan and system to normal operation and the bypass controller

will terminate the calibration procedure and return to normal

operation.

NOTE: If the bypass is in stand-alone mode (not communicat-

ing with a Linkage Controller), the user must ensure the

pressure reading is zero before performing calibration.

DAMPER

ROTATION

CLOCKWISE

COUNTER

CLOCKWISE

Damper

Open Criteria

The resistance value is

greater than 75% of

the full range

of the potentiometer

The resistance value is

less than 25% of

the full range

of the potentiometer

Damper

Closed Criteria

The resistance value is

less than 25% of

the full range

of the potentiometer

The resistance value is

greater than 75% of

the full range

of the potentiometer

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Carrier 33ZCVAVTRM Specifications Page 22

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