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935SB: Installation, Start-up, Operating and Service Maintenance Instructions
Table 10 – Filter Media Pressure Drop (Clean) Versus Airflow - in. w.c. (Pa) (Continued)
20 x 25 Filter
Factory-Accessory
(508 x 635 mm)
Washable
CFM
(L/s)
(1-in. / 2.5 cm)
800
(378)
0.04
1000
(472)
0.05
1200
(566)
0.06
1400
(661)
0.07
1600
(755)
0.08
1800
(850)
0.08
2000
(944)
0.09
2200
(1038)
0.09
If the filter size that you are looking for is not contained in
versus Face Velocity for a variety of filter media types.
The following equations relate Face Velocity (FPM), Filter Area and Airflow (CFM):
Filter Face Velocity = Airflow / Filter Area
Minimum Filter Area = Rated System Airflow / Maximum Filter Face Velocity
Factory-Accessory
Face Velocity
FPM
(m/s)
200
(1)
0.04
300
(1.5)
0.05
400
(2)
0.07
500
(2.5)
0.08
600
(3)
0.09
700
(3.6)
0.10
*. Representative estimates from filter manufacturer data sheets.
See manufacturers' specifications for pressure drop versus airflow data for specific filter media.
AIR DUCTS
!
Many states, provinces and localities are considering or have
implemented standards and/or restrictions on duct sizing practices,
ductwork leakage, and/or ductwork thermal, airflow and electrical
efficiencies. CONSULT LOCAL CODE OFFICIALS for ductwork
design and performance requirements in your area.
General Requirements
The duct system should be designed and sized according to accepted
national standards such as those published by: Air Conditioning
Contractors Association (ACCA Manual D), Sheet Metal and Air
Conditioning
Contractors
National Association
American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE) or consult The Air Systems Design Guidelines
reference tables available from your local distributor. The duct system
should be sized to handle the required system design CFM at the design
external static pressure. The furnace airflow rates are provided
- CFM (with Filter). When a furnace is installed so that the supply ducts
carry air circulated by the furnace to areas outside the space containing
the furnace, the return air shall also be handled by duct(s) sealed to the
furnace casing and terminating outside the space containing the furnace.
Secure ductwork with proper fasteners for type of ductwork used. Seal
supply- and return-duct connections to furnace with code approved tape
or duct sealer.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
Factory-Accessory
Media*
(4-in. / 10 cm)
(11)
0.05
(12)
(13)
0.07
(18)
(15)
0.09
(22)
(17)
0.12
(31)
(19)
0.15
(38)
(21)
0.18
(47)
(23)
0.22
(56)
(24)
0.26
(66)
Table
Table 11 – Filter Media Pressure Drop (Clean) Versus Face Velocity- in. w.c. (Pa)
Washable
(1-in. / 2.5 cm)
(1-in. / 2.5 cm)
(10)
0.05
(14)
0.09
(17)
0.13
(21)
0.18
(23)
0.23
(26)
0.29
NOTICE
(SMACNA)
Representative After-Market Filter Media*
Fiberglass*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.06
(16)
0.09
0.08
(21)
0.13
0.11
(27)
0.16
0.13
(33)
0.20
0.16
(40)
0.24
0.18
(47)
0.29
0.21
(54)
-
0.25
(62)
-
10,
Table 11
for a comparison of Pressure Drop (initial/clean resistance to airflow)
Representative After-Market Filter Media
*
Fiberglass
(2-in. / 5 cm)
(13)
0.08
(20)
(22)
0.13
(34)
(32)
0.20
(50)
(44)
0.27
(69)
-
-
-
-
Cabinet air leakage is less than 2% at 1.0 in. w.c. Cabinet air leakage is
less than 1.4% at 0.5 in. w.c. when tested in accordance with ASHRAE
Standard 193.
NOTE: Flexible connections should be used between ductwork and
furnace to prevent transmission of vibration.
Ductwork passing through unconditioned space should be insulated to
enhance system performance. When air conditioning is used, a vapor
barrier is recommended.
Maintain a 1-in. (25 mm) clearance from combustible materials to
supply air ductwork for a distance of 36-in. (914 mm) horizontally from
the furnace. See NFPA 90B or local code for further requirements.
or
Return Duct Sizing
Refer to the Filter Selection and Duct Sizing section for information on
the proper selection of filter sizes and the associated ductwork and duct
transitions. Improperly designed filtering systems and return ductwork
Table 20
are the most common causes of airflow and/or noise complaints in
HVAC systems.
Ductwork Acoustical Treatment
NOTE: Metal duct systems that do not have a 90 degree elbow and 10
ft. (3 M) of main duct to the first branch take-off may require internal
acoustical lining. As an alternative, fibrous ductwork may be used if
constructed and installed in accordance with the latest edition of
SMACNA construction standard on fibrous glass ducts. Both acoustical
lining and fibrous ductwork shall comply with NFPA 90B as tested by
UL Standard 181 for Class 1 Rigid air ducts.
NOTE: For horizontal applications, the top most flange may be bent
past 90_ to allow the evaporator coil to hang on the flange temporarily
while the remaining attachment and sealing of the coil are performed.
22
Pleated*
(1-in. / 2.5 cm)
(24)
0.22
(55)
(32)
0.29
(72)
(41)
-
-
(51)
-
-
(61)
-
-
(73)
-
-
-
-
-
-
-
-
*
Pleated
(1-in. / 2.5 cm)
0.18
(47)
0.30
(75)
-
-
-
-
-
-
-
-
-
-
NOTICE
!
(2-in. / 5 cm)
0.15
(37)
0.20
(49)
0.25
(63)
0.31
(79)
-
-
-
-
-
-
-
-
*
(2-in. / 5 cm)
0.12
(31)
0.21
(52)
0.31
(78)
-
-
-
-
-
-
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