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B. USE OF TABLES AND CHARTS

B. USE OF TABLES AND CHARTS

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PRESSURE

LOSS

OF

SYSTEM

COMPONENTS

Figure 9-1 SYSTEM PRESSURE LOSS CHECK LIST
Project

Fan System
Duct System Pressure Loss From Duct Sizing Form
*Allowance for Offsets, Etc., Required in Field
**Building Pressure Allowance (Supply Only)
TOTAL SYSTEM LOSS PRESSURE

All Duct Accessories & Equipment Pressure Losses Must Be Included in

the Calculations entered in the SMACNA Duct Sizing Form.
[] Air Monitor Devices
[] Air Terminal Devices

[] Air Washers
[] Air Washer, Sprayed Coil
[] Boxes, Constant Volume

Mixing

Coils,
[]

[]

[] Boxes, Dual Duct Mixing
[] Boxes, Induction Mixing
[] Boxes, Variable Volume
Cooling (Wet
Surface)
Coils, Heating (Dry Surface)
Dampers, Backdraft
[]

[]

[]

[]

[]

[] Dampers, Fire

[]

[] Dampers, Opposed Blade
[]

Volume

[]

[] Dampers, Single Blade
[]

Volume
[] Dampers, Smoke
[] Diffusers

[]

[]

[]Temperature

[] Duct Heaters, Direct Fired
[] Duct Heaters, Electric
[]

Extractors
Filters
Flexible Duct
Grilles
Heat Exchangers, Air-to-Air
Heat Exchangers, Direct
Fired
[] Heat Exchangers, Water-toAir
[] Humidifiers
Louvers
Obstructions
Orifices
Registers
Screens
Sound Traps
Static Plates
Surface Correction Factor
System Effect Factors
& Altitude
Correction Factor
Turning Vanes

[]
[]
[]
[]
[]

Eliminators
Energy Recovery
Equipment

[]

[]

**Some allowance must be made for offsets, etc., required in the field to avoid conflicts with plumbing,
piping, electric, sprinklers, etc. A reasonable estimate should be made to provide a pressure loss for
anticipated additional fittings; however, this allowance should not be over estimated. Over estimation
will provide an oversized fan selection which will waste energy during operation of the system.
**Building pressure allowance for supply systems should be determined from building requirements
considering acceptable building infiltration. Normally, 0.05 to 0.1 in. w.g. (12 to 25 Pa) static
pressure allowance for building pressurization should be adequate. The designer should determine
the proper building pressurization value based upon individual system requirements. Consideration
should include elevator shaft ventilation requirements, tightness of building construction, stack effect,
etc.

9.2

CHAPTER 9

Table 9-1 FILTER PRESSURE LOSS DATA

Static Pressure Loss
Recommended
Clean Design Dirty
1. Viscous Impingement, Flat Panel Filters
A. Replaceable Media 8-12% Efficiency
B. High Velocity Cleanable 8-12% Efficiency
C. Disposable 8-12% Efficiency

.18
.13
.08

.35
.30
.20

.50
.50
.30

2. Electrostatic Filters 80-90% Efficiency

.24

.24

.24

.20
.75

.45
.75

.55
.75

.30
.55
.30
.40
.40
.15
.25
.15
.135
.20

.45
.65
.65
.70
.60
.37
.42
.42
.41
.40

.60
.75
1.0
1.0
.80
.60
.60
.70
.70
.60

.45

.62

.80

.65
.35
.50
.70
.35
.60
.75
.15
.35
.35
.55
1.00
1.00

.82
.52
.65
.85
.55
.70
.87
.57
.67
.67
.77
1.50
2.00

1.00
.70
.80
1.0
.75
.80
1.00
1.00
1.00
1.00
1.00
2.00
2.00 +

.35
.15

.35
.15

.35
.15

3. Moving Curtain, Viscous Impingement Filters
A. Renewable Media 10-15% Efficiency
B. Self Cleaning Panels 10-15% Efficiency
4. Dry Media Filters
A. Cartridge 30-35% Efficiency 9" Deep
B. Cartridge 30-35% Efficiency 15" Deep
C. Cartridge 35-40% Efficiency 9" Deep
D. Cartridge 35-40% Efficiency 15" Deep
E. Cartridge 40% Efficiency 19" Deep
F. Cartridge 30% Efficiency 9" Deep
G. Cartridge 30% Efficiency 15" Deep
H. Cartridge 30-36% Efficiency 2" Deep
I. Cartridge 30-36% Efficiency 4" Deep
J. Cartridge 55% Efficiency 21" Deep
K. Cartridge 55% Efficiency 29" Deep

L. Cartridge 55% Efficiency 36" Deep
M. Cartridge 85% Efficiency 21" Deep
N. Cartridge 85% Efficiency 29" Deep
O. Cartridge 85% Efficiency 36" Deep
P. Cartridge 95% Efficiency 21" Deep
Q. Cartridge 95% Efficiency 29" Deep
R. Cartridge 95% Efficiency 36" Deep
S. High Efficiency 60% Efficiency 6" Deep
T. High Efficiency 60% Efficiency 12" Deep
U. High Efficiency 90% Efficiency 6" Deep
V. High Efficiency 90% Efficiency 12" Deep
W. High Efficiency 95% DOP
X. High Efficiency 99.97% DOP
5. Carbon Filters
A. Full Flow
B. ByPass

9.3

PRESSURE

LOSS

OF

SYSTEM

COMPONENTS

pressure drop of at least 0.25 in.w.g. (63 Pa) in the
mixed air plenum for an "air blender" to prevent stratification and coil freezing in northern climates.
Fire dampers and other special type dampers, such
as relief dampers, must comply with code requirements or certain job conditions. Therefore, the designer must add the pressure losses of these required items to the system totals. (Figures 9-3 and
9-4.)

3. Duct System Apparatus
Shop fabricated dampers with frames would have
loss values similar to the volume dampers in Figure
9-2.
Volume dampers are needed to balance even the
most carefully designed system. But excessive use,
particularly of dampers with high pressure losses
where tight shut-off is not essential, can quickly build
up the duct system pressure losses and be a source
of noise.
For outside air and mixed air dampers, use a minimum velocity of 1500 fpm (7.5 m/s). Also include a

Figures 9-5 to 9-11 contain pressure loss data for
commonly used HEATING AND COOLING COILS.
Data needed for determining the free area of LOUVERS is furnished in Tables 9-2 to 9-4, as the "free
area" velocity must be used to obtain louver pressure
losses in Figure 9-13. Tables for other types of entries
and exits can be found in Chapter 14.
The pressure loss data for several sizes and types
of SOUND TRAPS should be used for preliminary
calculations only, with manufacturers data being entered into the final design. (Figures 9-14 to 9-18.)
Pressure loss for a SPRAYED COIL AIR WASHER
can be obtained by combining the loss of an appro-

Table 9-2 LOUVER FREE AREA CHART
2"-45° BLADES

9.4

CHAPTER 9

Table 9-3 LOUVER FREE AREA CHART
4"-450 BLADES

Table 9-4 LOUVER FREE AREA CHART
6"-45°BLADES

9.5

PRESSURE

priate cooling coil (Figures 9-9 to 9-11) with the pressure loss of the 3 bend eliminator (Figure 9-19).
Duct mounted HUMIDIFIERS normally offer minimal
resistance to the duct air flow. Should the humidifier
manifold be installed in a narrow duct where it would
serve as an obstruction, Tables 14-18 G or H (Chapter
14) could be used to calculate the pressure loss, or
the duct could be expanded around the manifold (use
the transition pressure losses).
ENERGY RECOVERY EQUIPMENT is divided into 5
categories: Air-to-air Plate Exchangers, Single Tube
Exchangers (Heat Pipe Banks), Rotary Wheel, Runaround Coil Systems, and Multiple Tower Systems.
Pressure loss data charts (Figures 9-22 to 9-25)
must be used for rough estimates only as testing and
rating methods and procedures have not been standardized within the industry. Heating and/or cooling
coil data can be used for run-around coil systems.
The DRY AIR EVAPORATIVE COOLER pressure loss
data (Figure 9-26) is for the type of unit where the
two air streams are totally separated with no moisture interchange.

DAMPER
C

4. Room Air Terminal Devices

A WORD OF SPECIAL CAUTION CONCERNING
AIR TERMINAL DEVICE SELECTION. Total pressure loss for room air terminals should be used to
compute system total pressure loss. The fan is required to provide sufficient static pressure to overcome the static pressure loss through the air terminal
and to overcome the velocity pressure loss as a result
of delivering air at a given velocity through the air
terminal opening into the room.
Air terminal pressure losses shown in Tables 9-5 to
9-7, are total pressure losses. The values shown
serve to demonstrate comparative total pressure
losses encountered using different types of air terminals. ALL AIR TERMINAL DEVICES INCLUDED
IN EACH DUCT SYSTEM SHOULD BE CHOSEN
WITH SIMILAR TOTAL PRESSURE DROPS (within
0.05 in. wg. or 12 Pa). If air terminals requiring substantially different total pressure loss values are included in the same duct system, balancing will be
difficult, if not impossible.
THE DESIGNER SHOULD SELECT AIR TERMINAL
DEVICES FROM MANUFACTURERS' CATALOGUE
DATA PRIOR TO COMPLETING THE SYSTEM DESIGN. Air terminal device total pressure requirements will vary with the terminal velocity selected
(see Chapter 3).

9.6

LOSS

OF

SYSTEM

COMPONENTS

5. Operating Conditions
The pressure drop data found in the following subsections C (Damper Charts) and D (Duct System
Apparatus Charts) is for standard air (0.075 lb/cu ft,
700F, 29.92 in. Hg at sea level or 1.2041 kg/m3, 20°C,
101.325 kPa at sea level), and needs to be corrected
where necessary to operating conditions by the following equation:
Equation 9-1

Where:
Pa = Actual pressure drop, in. w.g. (Pa)
Ps = Pressure drop from tables, in. w.g. (Pa)
da = Actual air density, lb/cu ft (kg/m3)
ds = Standard air density,

0.075 lb/cu ft (1.2041 kg/m3)

CHARTS

Figure 9-2 VOLUME DAMPERS (BASED UPON
AMCA CERTIFIED VOLUME DAMPERS)

CHAPTER 9

Figure 9-3 BACKDRAFT OR RELIEF DAMPERS

D

FIRE & SMOKE
Figure 9-4
(BASED
ON 2-HOUR
AMCA CERTIFIED
FIRE DAMPERS
DAMPERS)

DUCT SYSTEM
APPARATUS CHARTS

Figure 9-5 HEATING COILS-1 ROW

9.7

PRESSURE

9.8

LOSS

OF

SYSTEM

COMPONENTS

Figure 9-6 HEATING COILS-2 ROW

Figure 9-7 HEATING COILS-3 ROW

Figure 9-8 HEATING COILS-4 ROW

Figure 9-9 COOLING COILS (WET)-4 ROW