OAC CALIBRATION Ð Once the probe and tubing are in- stalled, input the set point to match the probe readings. Be- fore adjusting the OAVP probe, ensure that the supply-air fan is providing the maximum design air¯ow and that the outside-air dampers are adjusted for the design outdoor air¯ow intake.

To calibrate the PIC processor to match the probe loca- tion, use a precision manometer to measure the velocity pres- sure in the outdoor air duct at design conditions. Use the HSIO (local interface device) or Building Supervisor to in- put the value as the OAVP set point.

Note that the probe does not measure true velocity pres- sure; when positioned as recommended, the probe measures a velocity pressure 1.563 times that of the velocity pressure in the duct. This multiplier (magni®cation) factor varies with the probe's location, and can even be negative if the probe is located at an elbow or turn. All OAVP values displayed on the HSIO incorporate the multiplier factor to show the true duct velocity pressure.

If a precision manometer is not available, read the veloc- ity pressure value at the HSIO when the system is running at maximum design air¯ow and input that value as the set point. During normal operation, the velocity pressure is held constant as the supply fan modulates.

USING OAVP VALUES TO DETERMINE DUCT AIR- FLOW Ð It is possible to determine the air¯ow (cfm) in the outside air duct based on the readings obtained by the OAVP probe. See the following procedure.

Use the HSIO and status function ( ) to display the outside air velocity pressure (Pv) at the transducer.

Find the average velocity (V) in the duct, in fpm:

4005 =--Pv = V

Obtain the cross-sectional area of the duct in sq ft. (A). To determine the air¯ow (F) in the duct, in cfm:

V x A = F

If the air¯ow obtained by the preceding method is differ- ent from the design air¯ow or a measurement obtained with a balancer, the OAVP probe is not sensing the average duct velocity and/or the probe's multiplier factor is effectively not 1.563. To match the design or measured air¯ow to the air- ¯ow determined with the preceding formulas, relocate the probe as recommended or use the HSIO and service

function (

) to change the probe multiplier

factor.

 

FIELD-SUPPLIED OR HIGH-VELOCITY PRESSURE TRANSDUCERS Ð The default pressure transducer in- stalled at the factory (P/N HK05ZG004) has a range of 0.00 to 0.05 in. wg, which matches an air velocity range of ap- proximately 225 to 680 fpm. The maximum velocity for op- timum OAC operation and response, however, is 620 fpm. If the average duct air velocity is greater than 620 fpm, use one of the alternate transducers shown in Table 7.

For a ®eld-supplied pressure transducer, use the service

function ( ) to con®gure the OAC control with the transducer's speci®cations:

OALV = Transducer minimum output voltage OAHV = Transducer maximum output voltage OALR = Transducer low pressure

(range minimum output) value OAHR = Transducer high pressure

(range maximum output) value

Table 7 Ð OAC Pressure Transducers

 

 

 

INDICATED VELOCITY

 

TRUE VELOCITY PRESSURE

 

VELOCITY IN DUCT

 

 

 

PRESSURE AT

 

 

CARRIER

MODUS PART

RANGE

 

IN DUCT (in. wg)

 

 

 

(fpm)

TRANSDUCER (in. wg)

 

 

 

 

PART NO.

NO.

(in. wg)

 

 

 

 

 

 

 

 

 

 

Optimum

 

Theoretical

 

Optimum

 

Theoretical

 

Optimum

 

Theoretical

 

 

 

 

 

 

 

 

 

 

 

Range

 

Range

 

Range

 

Range

 

 

Range

 

Range

HK05ZG004

T40-005C-04-013

0.00 Ð 0.05

0.013 Ð 0.037

 

0.005 Ð 0.045

0.008 Ð 0.024

0.003 Ð 0.029

360

Ð

620

225 Ð

680

HK05ZG005

T40-001C-04-012

0.00 Ð 0.10

0.025 Ð 0.075

 

0.010 Ð 0.090

0.016 Ð 0.048

0.006 Ð 0.057

505

Ð

875

320 Ð

960

HK05ZG006

T40-003C-04-015

0.00 Ð 0.30

0.075 Ð 0.225

 

0.030 Ð 0.270

0.048 Ð 0.144

0.019 Ð 0.173

875

Ð 1520

555 Ð 1665

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

51

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Carrier 39L specifications OAC Pressure Transducers

39L specifications

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