SERVICING
22
DUCT STATIC PRESSURES AND/OR STATIC
PRESSURE DROP ACROSS COILS
This minimum and maximum allowable duct static pres-
sure for the indoor sections are found in the specifications
section.
Tables are also provided for each coil, listing quantity of air
(CFM) versus static pressure drop across the coil.
Too great an external static pressure will result in insuffi
-
cient air that can cause icing of the coil. Too much air can
cause poor humidity control and condensate to be pulled off
the indoor coil causing condensate leakage. Too much air
can also cause motor overloading and in many cases this
constitutes a poorly designed system.
AIR HANDLER EXTERNAL STATIC
To determine proper air movement, proceed as follows:
1. Using a draft gauge (inclined manometer), measure
the static pressure of the return duct at the inlet of the
unit, (Negative Pressure).
2. Measure the static pressure of the supply duct, (Pos-
itive Pressure).
3. Add the two (2) readings together.
4. Consult unit nameplate for quantity of air.
Checking Static Pressure Single Piece Air Handler
Measure static pressure of the supply duct at the outlet
of the air handler.
Measure the static pressure of the return duct at the
inlet of the air handler
Single piece air handler evaporator coil is already
considered in airflow calculation
NOTE:
Both readings may be taken simultaneously and
read if so desired.
COIL STATIC PRESSURE DROP
1. Using a draft gauge (inclined manometer), connect
the positive probe underneath the coil and the nega-
tive probe above the coil.
2. A direct reading can be taken of the static pressure
drop across the coil.
3. Consult unit nameplate for quantity of air.
If the total external static pressure and/or static pressure
drop exceeds the maximum or minimum allowable statics,
check for closed dampers, dirty filters, undersized or poorly
laid out duct work.
