105564-UIM-A-0205
24
Unitary Products Group
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 120,000 BTUH (38.06 kW) furnace with 2 return open-
ings and operating on high-speed blower, it is found that total system
static is 0.58” w.c. To determine the system airflow, complete the follow-
ing steps:
Obtain the airflow values at 0.50 w.c. (125 Pa) & 0.60 w.c. (150 Pa)
ESP.
Airflow @ 0.50”: 2285 CFM (64.70 m
3
/min)
Airflow @ 0.60”: 2175 CFM (61.59 m
3
/min)
Subtract the airflow @ 0.50 w.c. (125 Pa) from the airflow @ 0.60 w.c.
(150 Pa) to obtain airflow difference.
2175 - 2285 = -110 CFM (3.11 m
3
/min)
Subtract the total system static from 0.50 w.c. (125 Pa) and divide this
difference by the difference in ESP values in the table, 0.60 w.c.
(150 Pa) - 0.50 w.c. (125 Pa), 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. (125 Pa) to
obtain actual airflow @ 0.58 inwc (144 Pa) ESP.
2285 - 88 = 2197
FIELD INSTALLED ACCESSORIES - NON-ELECTRICAL
MODEL NO.
DESCRIPTION
USED WITH
1NP0347
PROPANE (LP) CONVERSION KIT
ALL MODELS EXCEPT 135 MBH
1NP0349
135 MBH ONLY
1CT0302
CONCENTRIC INTAKE/VENT 2”
40, 60, 80, 100 INPUT MBH
1CT0303
CONCENTRIC INTAKE/VENT 3”
120, 135 MBH
1PS0307
HIGH ALTITUDE PRESSURE SWITCH KIT
(Does Not Include Orifices)
80, 100 MBH
1PS0309
60, 120 MBH
1PS0322
40, 135 MBH
1BR0414
EXTERNAL BOTTOM FILTER RACK
14-1/2” CABINETS
1BR0417
17-1/2” CABINETS
1BR0421
21” CABINETS
1BR0424
24-1/2” CABINETS
1NK0301
CONDENSATE NEUTRALIZER KIT
ALL MODELS
1SF0101
EXTERNAL SIDE RETURN FILTER RACK
ALL MODELS
1HT0901
SIDEWALL VENT TERMINATION KIT
ALL MODELS
