268882-UIM-A-0407
Unitary Products Group
27
APPLYING FILTER PRESSURE DROP TO
DETERMINE SYSTEM AIRFLOW
To determine the approximate airflow of the unit with a filter in place, fol-
low the steps below:
1.
Select the filter type.
2.
Select the number of return air openings or calculate the return
opening size in square inches to determine the proper filter pres-
sure drop.
3.
Determine the External System Static Pressure (ESP) without the
filter.
4.
Select a filter pressure drop from the table based upon the number
of return air openings or return air opening size and add to the
ESP from Step 3 to determine the total system static.
5.
If total system static matches a ESP value in the airflow table (i.e.
0.20 w.c. (50 Pa), 0.60 w.c. (150 Pa), etc,) the system airflow cor-
responds to the intersection of the ESP column and Model/Blower
Speed row.
6.
If the total system static falls between ESP values in the table (i.e.
0.58 w.c. (144 Pa), 0.75 w.c. (187 Pa), etc.), the static pressure
may be rounded to the nearest value in the table determining the
airflow using Step 5 or calculate the airflow by using the following
example.
Example: For a 100,000 BTUH (29.3 kW) furnace operating on high-
speed blower, it is found that total system static is 0.58” w.c. To deter-
mine the system airflow, complete the following steps:
Obtain the airflow values at 0.50 w.c. (0.124 Pa) & 0.60 w.c. (0.149 kPa)
ESP.
Airflow @ 0.50”: 2034 CFM (58 m
3
/min)
Airflow @ 0.60”: 1924 CFM 54 m
3
/min)
Subtract the airflow @ 0.50 w.c. (0.124 kPa) from the airflow @ 0.60
w.c. (0.149 kPa) to obtain airflow difference.
1924 - 2034 = -110 CFM (-4 m
3
/min)
Subtract the total system static from 0.50 w.c. (0.124 kPa) and divide
this difference by the difference in ESP values in the table, 0.60 w.c.
(0.149 kPa) - 0.50 w.c. (0.124 kPa), to obtain a percentage.
(0.58 - 0.50) / (0.60 - 0.50) = 0.8
Multiply percentage by airflow difference to obtain airflow reduction.
(0.8) X (-110) = -88
Subtract airflow reduction value to airflow @ 0.50 w.c. (.0124 kPa) to
obtain actual airflow @ 0.58 inwc (0.148 Pa) ESP.
2034 - 88 = 1946 CFM
TABLE 16:
Field Installed Accessories - Non-Electrical
MODEL NO.
DESCRIPTION
USED WITH
1CT0302
CONCENTRIC INTAKE/VENT 2”
ALL MODELS
1CT0303
CONCENTRIC INTAKE/VENT 3”
ALL MODELS
1PS0901
HIGH ALTITUDE PRESSURE SWITCH KIT
(Does Not Include Orifices)
60/100
1PS0903
80
1NK0301
CONDENSATE NEUTRALIZER KIT
ALL MODELS
1HT0901
SIDEWALL VENT TERMINATION KIT 3"
ALL MODELS
1HT0902
SIDEWALL VENT TERMINATION KIT 2"
ALL MODELS
1CB0317
COMBUSTIBLE FLOOR BASE
These kits are required in downflow application when using G*F*
series coils. These kits are not required with MC/FC series coils,
but please ensure that the coil and furnace are secured and that
there are noair leaks.
17-1/2” CABINET
1CB0321
21” CABINET
1TK0917
COIL TRANSITION KIT
17-1/2” CABINET
1TK0921
21” CABINET
1VK0901
3-WAY TRANSITION KIT
All MODELS
