Duct Static Pressures And/Or Static Pressure Drop Across Coils; Air Handler External Static - Daikin DX17VSS B Series Service Instructions Manual

SERVICING
S-202 DUCT STATIC PRESSURES AND/OR STATIC
PRESSURE DROP ACROSS COILS
this minimum and maximum allowable duct static pressure
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 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 abso-
lute value of external static pressure (for example,
-0.30"wc + 0.20"wc = 0.50"wc total static pressure).
NOTE: Both readings may be taken simultaneously and
read directly on the manometer if so desired.
4. Consult proper table for quantity of air.
30
Supply Sta�c
Blower
(inside)
Inclined
Manometer or
Magnehelic gauge
Return Sta�c
TOTAL EXTERNAL STATIC
Supply Duct
Air
flow
Return Duct