272312-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 60,000 BTUH (17.58 kW) furnace with a bottom return
opening and operating on high-speed blower, it is found that total sys-
tem static is 0.58” w.c. To determine the system airflow, complete the
following steps:
Obtain the airflow values at 0.50 w.c. (125 Pa) & 0.60 w.c. (150 Pa)
ESP.
Airflow @ 0.50”: 1250 CFM (35.4 m
3
/min)
Airflow @ 0.60”: 1180 CFM (33.4 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.
1180 - 1250 = -70 CFM (-12 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 (-70) = -56
Subtract airflow reduction value to airflow @ 0.50 w.c. (125 Pa) to
obtain actual airflow @ 0.58 in. w.c. (144 Pa) ESP.
1250 - 56 = 1194
TABLE 15:
Filter Performance - Pressure Drop Inches W.C. and (kPa)
Airflow Range
Minimum
Opening Size
Filter Type
Disposable
Washable Fiber
Pleated
CFM
m
3
/min
in
2
cm
2
In W.C.
kPA
In W.C.
kPA
In W.C.
kPA
0 - 750
0 - 21.4
230
1484
0.01
0.00249
0.01
0.00249
0.15
0.03736
751 - 1000
21.25 - 28.32
330
2129
0.05
0.01245
0.05
0.01245
0.20
0.04982
1001 - 1250
28.33 - 35.40
330
2129
0.10
0.02491
0.10
0.02491
0.20
0.04982
1251 - 1500
35.41 - 42.48
330
2129
0.10
0.02491
0.10
0.02491
0.25
0.06227
1501 - 1750
42.49 - 49.55
380
2452
0.15
0.03736
0.14
0.03487
0.30
0.07473
1751 - 2000
49.56 - 56.63
380
2542
0.19
0.04733
0.18
0.04484
0.30
0.07473
2001 & Above
56.64 - Above
463
2987
0.19
0.04733
0.18
0.04484
0.30
0.07473
TABLE 16:
Field Installed Accessories - Non Electrical
MODEL NO.
DESCRIPTION
USED WITH
1NP0347
PROPANE (LP) CONVERSION KIT
ALL MODELS
1PS0313
HIGH ALTITUDE PRESSURE SWITCH KIT
(Does Not Include Orifices)
40, 57, 80, 100
MBH
1PS0314
120
MBH
1SR0302
SIDE RETURN FILTER KIT 1” FILTER
ALL MODELS
1SR0200
SIDE RETURN FILTER KIT 1-4” FILTER
ALL MODELS
1BR0114
BOTTOM RETURN FILTER KIT 1” FILTER
14-1/2” CABINETS
1BR0214
BOTTOM RETURN FILTER KIT 1-4” FILTER
14-1/2” CABINETS
1BR0117
BOTTOM RETURN FILTER KIT 1” FILTER
17-1/2” CABINETS
1BR0217
BOTTOM RETURN FILTER KIT 1-4” FILTER
17-1/2” CABINETS
1BR0121
BOTTOM RETURN FILTER KIT 1” FILTER
21” CABINETS
1BR0221
BOTTOM RETURN FILTER KIT 1-4” FILTER
21” CABINETS
1BR0124
BOTTOM RETURN FILTER KIT 1” FILTER
24-1/2” CABINETS
1BR0224
BOTTOM RETURN FILTER KIT 1-4” FILTER
24-1/2” CABINETS
1HF0801
INTERNAL FILTER KIT WITH 1” FIBER FILTER
ALL MODELS
