Airflow Made Easy

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Airflow Made Easy

• Technical Training
• Introducing airflow measurement into your program
• And duct leakage too!

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AIRFLOW MADE EASY?
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• We learn something every day, and lots of times
  it's that what we learned the day before was
  wrong.  - Bill Vaughan

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Why are we here?
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How did we get there?
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How do we fix it?
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Quit teaching appliance repair Start teaching
systems and systems commissioning!
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Add Ductwork
Teach Airflow!
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Multiple Duct Designs
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Energy Star on Air Flow
70 of systems have improper airflow
Essential for comfort 70 of systems tested
are operating at less than 350 cfm/ton (ideal is
400 cfm/ton) Annual savings of 8 possible
Technician verifies system is flowing at
400cfm/ton (or cfm specified by manufacturer)
during full-speed testing Systems incapable of
350 cfm/ton or greater must be corrected by
improving ducts or would not qualify
Considering an ENERGY STAR CAC/ASHP
Specification for 2006
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Failure to communicate
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Measuring airflow is easy. Measuring airflow
accurately can be very difficult The trend to
improve efficiency by installing 13 seer
equipment is in turn requiring accurate airflow
measurement. An airflow measurement that is not
repeatable, accurate, and representative of mass
flow will result in calculations of system
operation that are not representative of the
systems efficiency, capacity or latent sensible
split and resulting humidity removal. Without
proper airflow the equipment efficiency and
operation are compromised resulting in
unsatisfactory equipment operation. Without
proper airflow, what is the point?
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AIR-MEASURING INSTRUMENTS and other techniques
FOR DUCT SYSTEMS
In field practice these become
Estimating

• Temperature Rise Method
• Pitot Tube (as normally used)
• Thermal Anemometer
• Wilson Flow Grid (true flow grid)
• Pressure drops across coils filters and heat
  exchangers
• (Provided there is a known CFM)

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It all comes down to one thing.
Making measurements

• In any work that involves
• Engineering
• Design verification
• Installation
• Service
• Factory support
• The goal is to deliver
• the designed efficiency and capacity
• the performance that the customer purchased (13
  SEER / 92AFUE)
• the reliability promised (manufacturer dealer)

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Accurate Instruments are Important!

• 1 F Wetbulb Temperature difference results in
  0.25 ton cooling difference
• 62.5 CFM .25 ton cooling
• Problems inherent with inaccurate instrumentation
  lead to misdiagnoses.
• Technician after technician or student after
  student should get the same measured results.
• Technicians should be able to make equipment
  operate in the field as well as it did in the
  lab!!! (You need lab accurate instruments to do
  it!!!)

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Back to the Basics
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How equipment is really sized!

• Quantity of BTUs required is dependant upon three
  things!
• Weight (mass flow)
• Specific Heat
• Temperature difference

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Sizing of heating equipment

• Q Weight x Specific Heat x ?T
• Where
• Q Heat quantity in BTUs
• Weight Mass flow per hour
• Specific heat the quantity of heat required to
  raise 1 of the substance 1F
• ?T the change in temperature required

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Air has mass and takes up space!!

• We are not conditioning CFMs of air but rather
  pounds of it!
• Standard air weighs .075 lb/ft3
• The reciprocal of the density of the specific
  volume 13.33 ft3/lb

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How much mass flow is required?

• 400 CFM/Ton x .075 30 lb/min/ton
• 1 ton 30 lb/min (1800 lbs/hr)
• 1.5 ton 45 lb/min (2700 lbs/hr)
• 2.5 ton 75 lb/min (4500 lbs/hr)
• 5 ton 150 lb/min (9000 lbs/hr)

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Specific Heat is THE BTU's Needed to raise 1
POUND 1 DEGREE
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Air has an average specific heat of .24
Btu/lb/ºFfrom (-58 ºF to 104 ºF)
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Airflow Constants

• Where do the airflow constants 1.08 for sensible
  heat and 4.5 for total heat come from anyway?

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CalculationsUsing the Standard Air Formulas

• CFM

Btuh Output
Sensible Heat Formula
1.08 x ?T
Or
BTUH Output 4.5 x CFM x ?h
Total Heat Formula
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The Sensible Heat Formula

• BTUH SPECIFIC HEAT x SPECIFIC DENSITY x
• 60 MIN/HR x CFM X ?T
• Or
• .24 x 0.075 x 60 x CFM x ?T
• 1.08 x CFM x ?T

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Total Heat FormulaHeating or Cooling

• BTU/HR specific density x 60 min/hr x ?H
• .075 x 60 x CFM x ?H
• 4.5 x CFM x ?H

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Standard Air (.075 /CF)

• 68 degrees F
• 0 Rh
• 14.7 PSIA

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Dont forget the most basic thing!

• The air is never standard!!!
• The constants 1.08 4.5 are derived from
  standard air density at .075 pounds/cf
• If we want accurate calculations, we must correct
  for air density!!!

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Specific Volume
As air is heated or humidified, its specific
volume increases and its density decreases
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Why correction is needed.

• Air always has humidity
• Is outside of standard air temperature
• Is measured at elevations above or below sea
  level
• What we are doing with the measurement has
  changed!

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Density makes a difference!

• Density /- 10
• Inaccuracy of airflow measurement /- 5
• This does not account for error in the
  measurement process, only the calculation!!!

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Results if mass was not considered

• BTUH 4.5 x CFM x ?h
• Enthalpy 6.666 btu/lb
• 55,854 BTUH 4.6 ton 93 rated capacity
• 56,604 BTUH 4.7 ton
• 57,384 BTUH 4.8 ton
• 58,764 BTUH 4.9 ton 98 rated capacity
• Error of 2910 BTUH

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Why density really matters

• If the air density is low, more CFM is required
  to keep the mass flow rate the same!!!

If air density is not considered, many systems
will have very low airflow.
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What we know

• Airflow must be set accurately
• Must use good technique
• Figuring air density can be a pain in the mass
• Service techs are limited
• On time
• By tools
• By skills

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Choices

• Avoid air density and never solve the mystery of
  airflow
• Teach density corrections and hope they are
  corrected for in the field
• Teach them to use tools that measure without the
  need for density correction

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Anemometer Instruments for measuring wind speed
are known commonly as anemometers (from the
Greek anemos wind) or wind meters.
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The beauty of the fan
The volume of air will not be effected in a given
system because a fan will move the same amount of
air regardless of the air density. In other
words, if a fan will move 3,000 cfm at 70F it
will also move 3,000 cfm at 250F
GREENHECK FANS
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If fans move a constant CFM independent of air
density..They can measure airflow independent
of air density also!!!
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Vane Anemometers inherently have

• High accuracy
• Excellent repeatability
• Excellent measurement repeatability using
  different measurement devices and techniques
• Have excellent repeatability even from user to
  user

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Measure Air Velocity and CFMMini Vane

• Airflow in under 3 minutes
• Full duct traverse assures accuracy (timed or
  point)
• Large(small probe) is not affected by stray eddy
  currents
• Ultra low mass rotating vane
• Precision jewel bearings for low breakaway torque
• the thrust of a fruit fly
• Excellent durability and chemical and kid
  resistance.
• No air density correction required.

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Use any place you would use a pitot tube (and
some places you wouldnt)

• Measure directly in the air stream
• Probe has no measurable effect on the airflow in
  ducts 6 and over
• Measure in smooth straight sections of duct when
  ever possible
• Make multiple measurements and allow the meter to
  average them
• When measuring in round ducts over 10 in
  diameter, measure in an X directions to get the
  most accurate airflows

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Where to Make Measurements

• Look for
• Straight sections of duct 2-3 duct diameters away
  from turns and fittings.

Ideal location on a traditionally ducted system
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MEASURING AIR VELOCITY FOR BALANCING

• Air balancing is accomplished by measuring the
  velocity of the air leaving each register
• Face velocity should be 400-600 FPM
• Air velocities over 700 FPM are noisy
• If the duct system is designed properly, equal
  velocity balancing of the system will assure
  proper air delivery to the space.
• If a minivane 416 is used to measure air
  quantity in the duct the K-factor can be
  calculated and CFM measured at the registers with
  the 417.

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The Large Vane Advantage

• True velocity measurement
• No air density correction required
• Simple one hand operation
• Easy to carry and operate
• Required for proper commissioning of residential
  systems
• Low battery consumption
• Averages true flow over a sample area, not just
  responding to local stray eddies.

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Central Return on AHU
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Quantifying System Performance
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Why does equipment fail???

• Our test instruments and techniques do not
  measure up
• We cant get factory accurate results.
• We cannot trust our tools
• Tech after tech should get the same measurements
  and results.
• How often do you think that happens?

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Why do we keep missing the mark???

• Bad experience
• Bad experience
• Bad experience
• Tech after tech should get the same measurements
  and results.

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Insanity Doing the same thing over and over,
each each time expecting a different result.
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REMEMBERThere are no theories in HVAC/R!

• Air conditioning is made of scientific facts
• Repeatable
• Universal
• Well proven
• Understandable
• Provable
• And you can do it!
• Measurements are made to prove facts!

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The Standards are changing!
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What do we need to do?

• Design properly
• Install properly
• Performance test
• Commission the system

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Airside Performance Testing

• Quantify Duct leakage
• Measure and set airflow at the appliance
• Proportional balance the system
• Verify correct charge (A/C Heat pump)
• Verify correct fuel input (gas or oil)
• Verify temperature rise (center of the range)

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Stop teaching Appliance Commissioning and start
teaching System Commissioning

• Too often technicians repair the appliance
  instead of the system.
• Symptoms at the appliance often indicate problems
  elsewhere in the system.
• It is imperative we teach system commissioning
  and not just appliance start-up.
• Airflow and refrigerant charge are two of the
  most common misunderstood and improperly adjusted
  parameters in our industry
• How are you addressing the problem?

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Teach System Design

• Measurements on their own mean nothing without
  knowledge of the design operation
• ARI Design conditions
• Fan Performance
• Whats your design temperature?

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System Design

• Components must be matched and rated.
• Matched condenser and evaporator
• Correct air handler
• Proper type of metering device
• Correctly sized and insulated line set
• Duct systems must be properly designed and sealed
  and insulated when required.
• Duct leakage causes reductions in capacity,
  efficiency, and comfort.
• Proper sealing can yield energy savings on
  average of 17

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System Performance

• Performance cannot be assumed!!!
• Performance varies with load conditions
• Equipment performance does not assure delivered
  performance
• Systems are field installed and require a field
  commissioning procedure
• Efficiency and performance go hand in hand

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Performance testing

• Think clean
• Filter, blower coils
• Verify appliance operation
• Cooling/Heating capacity
• Verify system operation
• BTUH Delivery to the space

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Step 1 Eliminate the Problems!Think clean
Look for the Obvious

• And hopefully you are only finding problems like
  this and not leaving them!

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Its time to replace the Crapmanship with
Craftsmanship
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Common enemies of airflow

• Improper duct design and construction (undersized
  return grills, chases, ducts undersized
  supply duct system, kinked flex duct or excess
  flex length)
• Restrictive filters
• Closed dampers, blocked supply grills
• Clogged or dirty filters, coils, blowers
• Improper blower speed setting

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Filtration or strangulation?
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Look for dumb and obvious stuffObstructed
returns (furniture, boxes)Squashed supply
grills, covered w/ rugs
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Once upon a remodelOOPS!
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DOUBLE OOPS!
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Whats lurking behind that grill? Obstruction
AND Indoor Air Quality issues
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Coils that have not been cleaned in years (if
ever)
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Take a closer look.
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CLOSER!
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BREATHE THIS
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Clean Those Coils!
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After Before
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Distribution problems can defeat even the best
machinery!

• Check for duct leaks, disconnects, insulation,
  damage
• Under-sized or restricted returns
• Restrictive, high-static filters (electrostatic
  or some pleated types, permanent filters)

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Restrictive electrostatic filterYou may need to
prove resistance to homeowner in order to change

• Without filter 60.0 pa, or 0.24 w.g.
• With filter 120.0 pa or 0.48 w.g.

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Free area to match pressure drop caused by
filter
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Restricted return chase
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Undersized filter grills, return chases and ducts

• The REAL rules of thumb (Manual D condensed)
• Filter grills 1.0 to 1.5 sq. ft./ton
• Return ducts and chases 85 to 100 sq. in./ton

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The Kinked Hose Syndrome
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No airflow?

• Gee, your ducts must be getting tired!
• Have a seat and take a load off!

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Aaaah! Thats better!
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Slight modifications of the design
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Dead headed ducts
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A little dirt on the blower wheel
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Step 2 Eliminate the Leaks!
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Duct Leakage A calibrated fan is used to
determine how mush air is being lost through
leakage. Typical duct systems loose over 30 of
there capacity to leakage 5 leakage is the
accepted standard
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• Duct Leakage Basics
• All grills are taped off with grill mask
• A duel channel manometer measure the duct
  pressure and airflow across the fan
• Air leakage in CFM is quantified at 25 Pascal's
  (.1 H20)

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Duct pressure testing system is mounted to the
furnace and the entire system from supply to
return can be tested.
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Return leaks can pull pollutants and irritants
such as mold, insulation fibers, pollen and dust
directly in the house.
Leaks in supply ducts cause expensive conditioned
air to be dumped into the attic, crawlspace or
garage instead of the house.
Return duct leaks pull outside air (hot in the
summer, cold in the winter) into the duct system,
forcing the cooling or heating systems to run
longer to keep the house comfortable.
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Visual duct leakage inspection

• You can spot many serious duct leakage problems
  without doing a test
• If you dont go, you dont know!
• Physical damage (crushed, broken, etc.)

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Mashed Disconnected
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Ducts in poor condition
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Never been sealed with ANYTHING!
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Read the signs dirty insulation indicates return
leaks Undersized return duct increases pressure
on leaks.
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Return leaks to attic at top plate of chase
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Gross return chase leakage to crawl
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Insulation

• Not enough
• Damaged
• Missing
• It all need fixed

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Filet of Duct
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Filet of Duct with Orange Sauce
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Peeking Duct
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Leaks in return ductwork draw air into the
building from crawlspaces, garages and attics
bringing with it dust, mold spores, insulation
fibers and other contaminants.
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Leaks in the supply ductwork cause expensive
conditioned air to be dumped directly outside or
in the attic or crawlspace rather than delivered
to the building.creating a negative pressure in
the home!!!
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Leaks in the return ductwork pull unconditioned
air directly into the HVAC system reducing both
efficiency and capacity. If 10 of the return air
for an air conditioning system is pulled from a
hot attic, system efficiency and capacity are
often reduced by as much as 30.
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In humid climates, moist air being drawn into
return leaks can overwhelm the dehumidification
capacity of air conditioning system causing
buildings to feel clammy even when the system is
operating. This can lead to mold problems also.
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Step 3 Set the airflow at the appliance!
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System Airflow

• Airflow must ALWAYS be set at the appliance
  first!
• Airflow is critical to system performance
• Refrigerant charging requires proper airflow
• Set to a nominal 400 CFM/Ton for A/C
• Set to 450 CFM/Ton for heat pumps
• Middle of temperature rise range for furnaces
• Always refer to manufacturers specific
  instructions
• After the airflow has been set at the appliance
  NEVER adjust it to change system characteristics!

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Measure or Estimate

• Estimation Methods
• Initial equipment setup/commissioning
• Accurate and Precise Measurements Methods
• Equipment performance
• System performance
• Duct leakage
• Capacity testing

Accurate and Precise
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Total External Static Pressure

• Airflow in CFM is measured by the manufacturer
• Pressure drop across the heat exchanger or
  evaporator coil is measured.
• If a pressure drop and a CFM are known, a new CFM
  can be calculated at any measured pressure drop.
• Can only be used as a diagnostic tool for airflow
  without manufactures literature.
• The industry standard for TESP in equipment
  design is .5wc, ranges from .3-1.0wc are
  possible

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Pitot Tube (Static and Total Connections)
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Static Pressure Tips Tubes with hose tap
connections and magnetic attachment plates
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ESP External Static Pressure
Measuring external Static Pressure is the same as
measuring pressure drop across a calibrated
resistance. It is only as accurate as the initial
measurement, and is air density dependant
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Pressure Drop Across the Evaporator Coil

• Easy way to estimate airflow
• Record during commissioning
• Density dependant
• Will vary significantly if the coil is wet!!!

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• Large static pressure drops across system
  components like
• Coils
• Filters
• Secondary heat exchangers
• Indicate excess restrictions normally due to
  dirt!

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Step 4 Commission the equipment and verify
capacity!
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System and equipment commissioning should always
be based on measurements!

• We are not in the business of estimation where
• An actual measurement is possible
• The parameter can be measured directly without
  calculation or correction
• Factors that compromise the quality of the
  measurement are not considered and accounted for
  like
• Instrument and probe design
• Application
• Qualities of the measured medium

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Accurate Measurement?

• What are you trying to do with it?
• Approximate airflow
• Duct leakage
• Equipment Capacity
• Delivered BTUH

Without a high degree of accuracy the pieces
wont fit!
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We need to use modern technology

• Benchmarking equipment requires lab accurate
  tools
• Field instruments are available with lab accuracy
  
• With new technology, and tools comes new and
  quicker and methods

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Appliance and System Performance
If the airflow is correct. The A/C refrigerant
charge is correct The Gas furnace manifold
pressure correct The heating and cooling
capacities should be correct.. Benchmarking
system performance assures your customer is
getting the designed BTUh!!! If you dont
measure, how can you ever know???
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Calculating Equipment Capacity
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• Dont Panic
• Its as easy as
• 1-2-3

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3 Step testEven a kid can do it!!
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Calculating Equipment Capacity

• Measure
• CFM
• Entering and leaving wet bulb
• Find change in enthalpy (?h)
• Capacity calculation
• BTUh 4.5 x CFM x ?h
• Tons BTUh/12,000
• Adjust the constant if outside of standard
  air!!!

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Step 5 Proportional balance the system!
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Starting with the register with the highest
airflow work room by room to proportional
balance the system Face velocities should
typically be 450 to 750 FPM Return opening
500-600
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Advanced applications

• Calculate real time heating and cooling capacity
• Trend and log date
• Multiple points of measure allow for complex real
  time data acquisition
• USB

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The proof is in the pudding
airflow

• The 435 can be used with the pitot tube (the
  industry standard) to prove accuracy
• 435 is a lab quality but not a reference class
  instrument.
• Air density correction
• Accurate calculation of A/C capacity is proof the
  airflow measurement is accurate and repeatable

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An Arsenal for Airflow
460 510 410-1/2 416 417 435 425
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TACHOMETER optically measures rpm, e.g. of
ventilators and shafts. Static Pressure and RPM
are used with the manufacturers table to
estimate airflow
Companion product Pocket Manometer
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• Pocket Manometer
• Differential pressure manometer for pressure
  measurements in the range 0 to 40 wc. Readings
  can be displayed in Pascal over the whole
  measurement range.
• Set / measure, airflow, air velocity, static
  pressure, draft, room depressurization, fuel
  pressure, check pressure switches
• Air velocity measurement with Pitot tube (Pitot
  tube extra)
• Switchable units hPa, mbar, Pa mmH2O, mmHg,
  inH2O, inHg, psi, m/s, fpm

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• Pocket Manometer
• Measurement of air flow velocity, temperature and
  humidity.
• Walk-around tool, quick and accurate for
  job-estimating
• Air velocity measurement with rotating vane
• Timed average calculation
• Wind chill calculation for outside areas
  (perceived temperature)
• Dew point calculation and wet bulb

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Mini-Vane Anemometer
Accurate volume flow calculation via easy input
of duct area. Excellent for airflow in ducted
system Probe design does not require air density
correction Designed for typical HVAC airflow
measurement range Direct display of CFM
Velocity Multi-point or timed mean calculation
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Large Vane Anemometer
Accurate volume flow calculation via easy input
of register area. Excellent for airflow in flex
ducted systems with single or dual returns Probe
design does not require air density
correction Designed for typical HVAC airflow
measurement range Direct display of CFM,
temperature and velocity Multi-point or timed
mean calculation
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Thermal Anemometer

• Temperature, flow and volume flow measurement
• Not corrected for air density due to humidity or
  pressure
• Multi-point and timed mean calculation
• Hold button to freeze readings

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• MULTI-FUNCTION
• Does it all and more!!!
• Airflow via vane, hot wire, or Pitot
• Velocity, Volume, and Capacity
• Memory and software
• Large probe selection!!

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Tools for Success

• Mini-Vane anemometer for duct airflow
• Large Vane for register velocity and capacity
• Digital Monometer for static pressure measurement
• Multi Function Meter for capacity testing (BTUh
  or cooling tons), airflow measurement with air
  density compensation