SERVICING
36
S-202 DUCT STATIC PRESSURES AND/OR STATIC
PRESSURE DROP ACROSS COILS
This minimum and maximum allowable duct static pressure
-
tion.
Tables are also provided for each coil, listing quantity of air
(CFM) versus static pressure drop across the coil.
air that can cause icing of the coil. Too much air can cause
evaporator coil causing condensate leakage. Too much air
can also cause motor overloading and in many cases this
constitutes a poorly designed system.
S-203 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, (Positive
Pressure).
3. Add the two (2) readings together for total absolute val-
ue of external static pressure (for example, -0.30"wc
+0.20"wc = 0.50"wc total static pressure).
TOTAL EXTERNAL STATIC
NOTE: Both readings may be taken simultaneously and
read directly on the manometer if so desired.
4. Consult proper table for quantity of air.
If external static pressure is being measured on a furnace to
"A" coil and the furnace.
TOTAL EXTERNAL STATIC
S-204 COIL STATIC PRESSURE DROP
1. Using a draft gauge (inclined manometer), connect the
positive probe underneath the coil and the negative
probe above the coil.
2. A direct reading can be taken of the static pressure drop
across the coil.
3. Consult proper table for quantity of air.
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