Arthur Miller, CMS, RCT
HVACR Training Consultant
www.kam-associates.com
info@kam-associates.com
OUTLINE
1. Air Flow Terminology
2. Classification of Duct Systems
3. Duct Design Methods
4. Fans
5. Ducts
6. Air Flow & Issues with Design of Ducts
7. Filters
8. Conclusion(s) & Solution(s)
A
’PRACTICAL
APPROACH’
ALONG WITH SOME THEORY
3 ¼ x 12 wall stack
Who is Liable?
A. The contractor – from design
to installation to service
B. The filter manufacturer
C. The building owner
D. Nobody
AIR FLOW
TERMINOLOGY
CFM
• Volume or Quantity of air
3
• measured in Ft /min
FPM
• Velocity of the air
• measured in Ft/min
STATIC
• Resistance to the air flow
• measured in inches of water
column (“w.c.)
Classification of Duct Systems
1. Low Pressure System - up to 2” w.c.
2. Medium Pressure System - up to 6” w.c.
3. High Pressure System - up to 10” w.c.
Duct Design Methods
1. Velocity Method
2. Static Regain Method
3. Equal Friction Method
Velocity Method
1. Select velocity for main and branch
ducts.
2. Determine duct sizes.
3. Determine frictional pressure drops.
4. Select a fan.
Static Regain Method
1. Select velocity for main ducts.
2. Velocities are selected so the static
pressure at each take-off offsets the
pressure loss of the preceding section
of ductwork.
3. Select a fan.
Equal Friction Method
1. Selection of friction loss.
2. Volume of air is known.
3. Duct is sized based on 1 and 2 above.
4. Select a fan or fan is selected.
FANS
The
‘HEART’
of the air
delivery system
Relationship between
STATIC and CFM
in respect to a
FAN
Are they
A. a direct relationship
B. an indirect relationship
C. neither
CFM
STATIC
STATIC
CFM
two configurations
of fans
1. AXIAL
2. CENTRIFUGAL
First, the
Axial Fans
Definition?
What makes an axial fan
an axial fan?
ANSWER
Discharge Air Flow
PARALLEL
to shaft of motor/fan
(NO change in direction)
TYPES
1. tubeaxial
2. vaneaxial
3. propeller
TUBEAXIAL
1.
operates at pressures up to 16” wc
2.
wheel turns faster than propeller fan
3.
efficiency up to 65%
VANEAXIAL
1.
operates at pressures up to 20” wc
2.
uses guide vanes to improve efficiency
and pressure
3.
most energy efficient fan
PROPELLER
1.
operates at low speeds
2.
handles large volumes of air at
low pressure and at free delivery
3.
efficiency is usually less than 50%
Performance
of
PROPELLOR
Fans
PROPELLOR FAN
What is the LOADING component
on a PROPELLOR fan?
A. CFM
B. FPM
C. STATIC
STATIC
This ‘LOAD’ is then imposed on
the motor.
respond?
How will the motor
STATIC
AMPS
STATIC
AMPS
APPLICATION(S)
(1) The
condenser
conditioner
is
on
very
What will happen to the:
fan delivery in cfm?
fan motor amp. draw?
an
air
dirty.
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
(2) What about a filter on an ice
machine condenser? What
happen to the:
fan delivery in cfm?
fan motor amp. draw?
will
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
(3) Consider a window fan. Is
ductwork connected to the fan?
1. YES
2. NO
(3) Consider a window fan. Is
ductwork connected to the fan?
1. YES
2. NO
Now, the
Centrifugal Fan
Definition?
What makes a centrifugal fan
a centrifugal fan?
ANSWER
Discharge Air Flow
PERPENDICULAR
to shaft of motor/fan
Types of Centrifugal Wheels
1. Backward Inclined (BI)
2. Air Foil Wheels (AF)
3. Forward Curve Wheels (FC)
4. Radial Blade Wheel
Backward Inclined (BI)
Backward Inclined (BI)
1.
used with high pressure systems
2.
high flow
3.
high efficiency
4.
noisy
Air Foil Wheels (AF)
Air Foil Wheels (AF)
1.
used with high pressure systems
2.
high flow
3.
highest efficiency
4.
noisy
Forward Curve Wheels (FC)
Forward Curve Wheels (FC)
1.
used with medium pressure systems
2.
high flow
3.
best for moving large volumes against
low static
4.
quiet
Radial Blade Wheel
Radial Blade Wheel
1.
used with high pressure systems
2.
medium flow
3.
best for moving air against high static
and contaminated airstreams
Performance
of
CENTRIFUGAL
Fans
CENTRIFUGAL FAN
What is the LOADING component
on a CENTRIFUGAL fan?
A. CFM
B. FPM
C. STATIC
CFM
This ‘LOAD’ is then imposed on
the motor.
respond?
How will the motor
CFM
AMPS
CFM
AMPS
MOVIE
TIME
APPLICATION(S)
How
would
following
you
answer
questions
CENTRIFUGAL fans?
the
regarding
(1) An addition has been added to a
building and the duct system has
been added onto include this
addition. What will be the:
A. fan delivery in cfm?
B. fan motor amp. draw?
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
(2) As
the
air
filter
gets
contaminated, what will be the:
A. fan delivery in cfm?
B. fan motor amp. draw?
more
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
(3) You remove a supply air panel on
a ‘hot’ day just to cool you off.
What will be the:
A. fan delivery in cfm?
B. fan motor amp. draw?
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan delivery in cfm
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
Fan motor amp. draw
Increases
Decreases
Remains the same
‘CENTRIFUGAL’
FAN
PERFORMANCE
Fan Performance
depends on
(1) CFM
(2) Outlet Velocity
(3) Static Pressure
(4) RPM
(5) Brake Horsepower
Determining Fan CFMs
(1) Using a Fan Curve
(2) Using a Fan Chart
(3) Using a Fan Law
(4) Using Instruments
(1) Using a Fan Curve
Relationship between
STATIC and CFM
in respect to a fan
CFM
STATIC
STATIC
CFM
Relationship between
STATIC and CFM
in respect to the duct system
CFM
STATIC
CFM
STATIC
5 HP
3 HP
1 HP
Original
Operating
Point
New
Operating
Point
(2) Using a Fan Chart
PSC Motor
ECM Motor
And now,
the new kid on the block.
Dec Star
Movie
Using a Fan Law
1. six fan laws
2. HVACR is affected by one of
them
The physics of air flow dynamics
dictates the following:
• CFM – varies as the fan speed
• Static – varies as the SQUARE of the speed
• HP – varies as the CUBE of the speed
APPLICATION
If we increase the cfm ’ s by 20%,
what will be required of the motor
speed(rpm)?
+ 20%
If we increase the cfm’s by 20%,
what will happen to the static in
the system?
+ 40%
If we increase the cfm’s by 20%,
what
will
happen
to
the
horsepower
required
from
the
motor?
+ 80%
Using Instruments
1. Anemometer
2. Velometer
3. Manometer with Pitot Tube
4. Balometer
So why all the fuss about
fans?
Because they must deliver a
volume of air that satisfies
two requirements:
a. Equipment Efficiency
b. Customer Satisfaction
AIR
FLOW
So how much
CFM
can you ‘shovel’ into
a duct?
That takes us to the
DUCT
CALCULATOR
‘Rule of Thumb’
Design Static Pressures
.10 (.08) for SUPPLY AIR duct
.08 (.06) for RETURN AIR duct
.08 (.06) for HEAT PUMP SUPPLY duct
.06 (.04) for HEAT PUMP RETURN duct
Furnace Fan
External Static Pressure
.5” w.c. for the furnace fan, then
subtract any external components:
ACCA Manual D
Component Static Pressure
1. Air conditioner coil = .25”w.c.
2. Filters = .10”w.c.
3. Electric heaters = .10”w.c. to .20”w.c.
4. Humidifiers = .10”w.c.
5. Supply Outlets = .03”w.c.
6. Return Inlets = .03”w.c.
7. Dampers = .03”w.c.
Example #1
• Furnace fan =
.50”w.c.
• less AC coil =
- .25”w.c.
• less air filter =
- .10”w.c.
• less supply registers = - .03”w.c.
• less return grilles =
- .03”w.c.
• less dampers =
- .03”w.c.
• left for duct system =
.06”w.c.
Example #2
• Furnace fan =
.50”w.c.
• less AC coil =
- .00”w.c.
• less air filter =
- .10”w.c.
• less supply registers = - .03”w.c.
• less return grilles =
- .03”w.c.
• less dampers =
- .03”w.c.
• left for duct system =
.31”w.c.
Designing the
Duct System
 Length of duct - measured
 Fittings - Equivalent Length tables
 Velocity Factor - Equivalent Length tables
Supply and Return Plenums
Take-off fittings
Velocity Factor EL Values
Fitting
0
1
2
3
4
5 or
more
35
45
55
65
70
80
20
30
35
40
45
50
65
75
85
95
100
110
Velocity Factor EL Values
Fitting
0
1
2
3
4
5 or
more
35
45
55
65
70
80
20
30
35
40
45
50
65
75
85
95
100
110
CONCLUSION
The equivalent length(EL) of the
duct system has a direct
relationship to the
STATIC
FILTERS
Filters
in relation to the
SYSTEM
STUDY
• ASHRAE
• Published October 2012
• by
John
Proctor,
Member ASHRAE
P.E.
• California Energy Commission
field research
• Two year old homes
• Most common replacement filter
used is a 1 in. pleated filter
• Air Conditioning Contractors of
America’s Manual D
• assumes pressure drop through
a filter to be approx. 0.10 in. w.c.
Field installations showed PD far
in excess of 0.10 in. w.c.
Static pressures for 34 split AC/furnaces
Static pressures for 34 split AC/furnaces
Metric
Filter PD
Mean:
in. w.c.
0.282
- 0.417
0.887
Range:
in. w.c.
0.275 –
0.792
- 0.143 –
- 0.928
0.533 –
1.21
Return PS Total ESP
Static pressures for 34 split AC/furnaces
Metric
Filter PD
Mean:
in. w.c.
0.282
- 0.417
0.887
Range:
in. w.c.
0.275 –
0.792
- 0.143 –
- 0.928
0.533 –
1.21
Return PS Total ESP
Static pressures for 34 split AC/furnaces
Metric
Filter PD
Mean:
in. w.c.
0.282
- 0.417
0.887
Range:
in. w.c.
0.275 –
0.792
- 0.143 –
- 0.928
0.533 –
1.21
Return PS Total ESP
Static pressures for 34 split AC/furnaces
Metric
Filter PD
Mean:
in. w.c.
0.282
- 0.417
0.887
Range:
in. w.c.
0.275 –
0.792
- 0.143 –
- 0.928
0.533 –
1.21
Return PS Total ESP
Research results of PD for 53
ducted systems.
Filter face area required for 0.05”w.c. PD at 400
cfm/ton for one manufacturer’s line of filters
16 x 25 = 400
2
in
Filter face area required for 0.05”w.c. PD at 400
cfm/ton for one manufacturer’s line of filters
• The following two charts are tests
performed by Kevin O’Neill.
• HVAC Service Manager
• Carolina Clg. & Plbg.
• Surfside Beach, SC
Filter Pressure Drop Table
20 in. x 20 in. x 1 in. – clean except as noted
FILTER NAME
PRESSURE DROP (IN. W.C.)
AIRFLOW
Air flow hood and egg crate filter grille
.03 in.
800 cfm
Standard fiber glass filter Brand A
.075 in.
800 cfm
Standard fiber glass filter Brand B
.08 in.
800 cfm
Very dirty Brand A
.15 in.
800 cfm
1 in. thick pleated Brand C - clean
.2 in.
800 cfm
1 in. thick pleated Brand D - clean
.2 in.
800 cfm
Dirty 1 in. thick pleated Brand C @ 1 month
.24 in.
800 cfm
Dirty 1 in. thick pleated Brand C @ 3 months .32 in.
800 cfm
Filter Pressure Drop Table
20 in. x 20 in. x 1 in. – clean except as noted
FILTER NAME
PRESSURE DROP (IN. W.C.)
AIRFLOW
Air flow hood and egg crate filter grille
.03 in.
800 cfm
Standard fiber glass filter Brand A
.075 in.
800 cfm
Standard fiber glass filter Brand B
.08 in.
800 cfm
Very dirty Brand A
.15 in.
800 cfm
1 in. thick pleated Brand C - clean
.2 in.
800 cfm
1 in. thick pleated Brand D - clean
.2 in.
800 cfm
Dirty 1 in. thick pleated Brand C @ 1 month
.24 in.
800 cfm
Dirty 1 in. thick pleated Brand C @ 3 months .32 in.
800 cfm
Filter Pressure Drop Table
20 in. x 20 in. x 1 in. – clean except as noted
FILTER NAME
PRESSURE DROP (IN. W.C.)
AIRFLOW
Electrostatic filter Brand E
.125 in.
800 cfm
Electrostatic filter Brand F
.14 in.
800 cfm
Electrostatic filter Brand G
.29 in.
800 cfm
Electrostatic filter Brand H
.35 in.
800 cfm
Combination electronic, charcoal & fiber .18 in.
glass - clean
800 cfm
Same filter after 1 month of use
.34 in.
800 cfm
Same filter after 3 months of use
.45 in.
800 cfm
Filter Pressure Drop Table
20 in. x 20 in. x 1 in. – clean except as noted
FILTER NAME
PRESSURE DROP (IN. W.C.)
AIRFLOW
Electrostatic filter Brand E
.125 in.
800 cfm
Electrostatic filter Brand F
.14 in.
800 cfm
Electrostatic filter Brand G
.29 in.
800 cfm
Electrostatic filter Brand H
.35 in.
800 cfm
Combination electronic, charcoal & fiber .18 in.
glass - clean
800 cfm
Same filter after 1 month of use
.34 in.
800 cfm
Same filter after 3 months of use
.45 in.
800 cfm
CONCLUSION
every
system
has air flow issues
CONCLUSION
Unfortunately there will always be
those who:
1.
will not keep up with technology.
2.
have always done it this way.
3.
don’t need to know that.
4.
will do it the least expensive way.
SOLUTIONS
All designers of air flow systems
need to check the manufacturer’s
specs.
of
equipment
designing a system.
before
SOLUTIONS
Filters may be a point of interest
for
poor
performance
equipment and comfort.
of
SOLUTIONS
The consumer is getting smarter
about our industry and making
demands on us.
SOLUTIONS
Professionalism
has
to
be
promoted inside and outside the
industry.
SOLUTIONS
Continuing Education