System Airflow Measurement; Measuring Airflow; Alternate Method - Trane RAUJ-C20 Installation, Operation And Maintenance Manual

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W W A A R R N N I I N N G G
L L i i v v e e E E l l e e c c t t r r i i c c a a l l C C o o m m p p o o n n e e n n t t s s ! !
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t t h h e e s s e e t t a a s s k k s s . .
4. Turn the 115 volt control circuit switch 1S2 to the
"On" position.
5. Turn the main power disconnect switch or circuit
protector switch for the unit to the "On" position.
W W A A R R N N I I N N G G
R R o o t t a a t t i i n n g g C C o o m m p p o o n n e e n n t t s s ! !
F F a a i i l l u u r r e e t t o o d d i i s s c c o o n n n n e e c c t t p p o o w w e e r r b b e e f f o o r r e e s s e e r r v v i i c c i i n n g g c c o o u u l l d d
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i i n n j j u u r r y y . .
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d d i i s s c c o o n n n n e e c c t t s s b b e e f f o o r r e e s s e e r r v v i i c c i i n n g g . . F F o o l l l l o o w w p p r r o o p p e e r r
l l o o c c k k o o u u t t / / t t a a g g o o u u t t p p r r o o c c e e d d u u r r e e s s t t o o e e n n s s u u r r e e t t h h e e p p o o w w e e r r
c c a a n n n n o o t t b b e e i i n n a a d d v v e e r r t t e e n n t t l l y y e e n n e e r r g g i i z z e e d d . .
6. Turn the field provided disconnect switch for the
supply fan to the "On" position and "bump" the
field supplied control circuit switch "On", (i.e., "On"
then immediately "Off").
7. If the fan does not start in applications where the
fan control circuit is energized via terminal 7TB5-1
in the RAUJ 115V control circuit, the field power
wiring to the RAUJ unit could be improperly
phased. Phase protection module (1U3) located in
the RAUJ control box interrupts control circuit
power when improperly phased field power is
detected.
8. While the fan is coasting down, check the rotation.
If the fan is rotating backwards, turn the field
provided disconnect switch for the air handler to
the "Off" position and interchange any two of the
main power wires at the fan motor starter or
contactor.
9. After all adjustments have been made, restart the
supply fan and proceed through the following
procedures.

System Airflow Measurement

Much of the systems performance and reliability is
closely associated with, and dependent upon having
the proper airflow supplied both to the space that is
being conditioned and across the evaporator coil.
106

Measuring Airflow

With the supply fan rotating in the proper direction,
measure the amperage at the supply fan contactor. If
the amperage exceeds the motor nameplate value, the
static pressure is less than design and the airflow is too
high. If the amperage is below the motor nameplate
value, static pressure could be too high and CFM could
be too low. To determine the actual CFM (± 5%);
1. Measure the actual fan RPM
2. Calculate the Theoretical BHP:
BHP = Actual Motor Amps X Motor HP)/
Motor Nameplate Amps
3. Plot this data onto the appropriate Fan Performance
Curve or Performance Table that shipped with the
Air Handling equipment. Where the two points
intersect, read the CFM line.
Use this data to assist in calculating a new fan drive if
the CFM is not at design specifications.

Alternate Method

An alternate method with less accuracy is to measure
the static pressure drop across the evaporator coil. This
can be accomplished by the following steps.
1. Drill a small hole through the unit casing on each
side of the coil.
N N O O T T I I C C E E
C C o o i i l l D D a a m m a a g g e e ! !
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d d a a m m a a g g e e . .
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d d a a m m a a g g i i n n g g c c o o i i l l . .
2. Measure the difference between the pressures at
both locations.
3. Plot this value onto the appropriate component
pressure drop curve that shipped with the Air
Handling equipment. Use the data to assist in
calculating a new fan drive if the CFM is not at
design specifications.
4. Plug the holes after the proper CFM has been
established.
After all adjustments have been made, proceed
through the following procedures.
SS-SVX11K-EN