Air System Balancing

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Air System Balancing

• MET 150

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What is TAB?

• Testing to document existing conditions
• Adjusting to match contract requirements
• Balancing to provide acceptable space conditions
  in accordance with the system design requirements

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Who Does It?

• Certified Balancing Technician
• AABC Associated Air Balance Council requires
  TAB contractors to be independent cannot be a
  contractor who also performs installation work,
  on this job or any other.
• NEBB National Environmental Balancing Bureau
  installing contractors who have personnel trained
  to perform test and balance functions
• TABB Testing, Adjusting and Balancing Bureau, a
  subsidiary of the National Energy Management
  Institute provides training and certification
  to contractors and independent test and balance
  companies

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Qualifications

• Vary by certifying organization but, in general
• Training in proper methods of measurement, use of
  testing equipment, and system balance procedures
• Lead engineer or technician qualified to evaluate
  test data, determine necessary system adjustments

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Preliminary Work

• Equipment data
• Fan curves for all fans
• Performance data for all installed equipment
  take special notice of equipment changes from
  original specifications
• Motor nameplate data, motor starters, overload
  protection and drive information

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Preliminary Work

• Equipment data
• Air distribution devices effective areas,
  pressure drops, required pressure behind
• Temperature control diagrams
• Manufacturers catalogs for equipment
• OM instructions for all equipment

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Schematic Layout

• Indicate dampers, regulating devices, terminal
  units, outlets and inlets
• Sizes and CFMs for main ducts, outlets and
  inlets, and fresh air and return air quantities
• Convert cfm to fpm (velocities easier to work
  with)

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Prepare Schematics
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Pre-balance Checks

• Fans
• Bearings lubricated
• Fan wheels clear of housing, correct rotation
• Foreign objects removed
• Motors fastened securely, drives aligned, drive
  set screws and keyways tight
• Belt tensions correct, belt guards in place
• Check motor and fan rotation
• Check blower motor amperage and voltage

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Pre-balance Checks

• Fans
• Vibration isolators or bases have correct springs
  in correct location, springs not collapsed
• Equipment leveled
• NO CLOSED OR UNCONNECTED DAMPERS ANYWHERE IN
  SYSTEM
• Filters properly installed (either temporary for
  TAB work or permanent)

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Pre-balance Checks

• Other equipment
• Check coils for proper installation, insure coils
  are clean and free of obstructions
• Check and set all automatic control dampers as
  required
• Confirm that crankcase heaters on refrigeration
  systems have been operating for at least 24 hours

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Pre-balance Checks

• Duct System
• Intake, return and exhaust dampers in proper
  position and operable
• All system volume dampers, fire dampers and smoke
  dampers installed and fully open
• Air terminals and terminal units installed,
  terminal dampers fully open

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Pre-balance Checks

• Duct System
• Confirm openings in walls and plenums for proper
  air passage
• Inspect duct system for proper construction,
  including turning vanes installed where indicated
  and joints sealed as specified
• Confirm required architectural features
  (ceilings, doors, etc.) in place as required

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General Balancing Procedure

• Check airflow for all fans should be within /-
  10 before starting system balance.
• If too low, investigate system to determine there
  are no blockages, excessive system effects, etc.
  
• If too high, reduce airflow to specifications /-
  10.

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General Balancing Procedure

• Main supply ducts
• Adjust volume dampers serving each branch to the
  approximate airflow required (note that changing
  one will change another may have to adjust
  multiple times)
• Once mains and branches balanced, proceed to air
  terminals and balance each successively may
  have to repeat multiple times

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Terminal Balancing

• Check farthest outlet of each branch.
• If below design fpm, leave damper fully open and
  go on to next outlet upstream.
• If outlet velocity at farthest device above
  design specifications, throttle down and proceed
  to next outlet upstream.
• Proceed upstream until all outlets have been
  adjusted.

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Terminal Balancing

• Repeat procedure three times through system until
  all outlets are close to required fpm.
• If terminal dampers are generating noise,
  readjust branch air volume and recheck outlets.
  Adjust as required. May need to go through
  entire system again.

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General Balancing Procedure

• Exhaust and return systems
• Adjust return and exhaust fan volumes within /-
  10 of specifications
• Adjust each main and branch as before
• Adjust terminal devices
• Verify overall system balance

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Mixed Air Section

• Check all dampers for free travel
• Set outside air damper for minimum outside air
  verify with airflows or by temperature
• MB IB FA (OB-IB)
• MB MA drybulb
• IB indoor drybulb
• OB outdoor drybulb
• FA fresh air

Outside Air
Mixed Air
M
Exhaust Air
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Mixed Air Section

• If economizer used, check outside air/return air
  for 25, 50, 75 and 100 outside air will need
  to work with temperature control contractor to
  perform these checks
• Check for leakage when OA dampers are 100 closed
  (such as for morning warm-up of off-hours
  operation)

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Coil Section

• Verify control valve operation over entire range
  of travel
• Check heating coil performance using energy
  balance equations
• Check cooling coil performance using
  psychrometric equations

H E A T
C O O L
Supply Air
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Heating Coil Performance

• Air side Q 1.08 x CFM x Dtair
• Water side Q 500 x GPM x Dtwater
• Example 30 gpm of 200oF water circulates through
  a coil, heating 4000 CFM from 50oF to 120oF.
  What is the leaving water temperature?
• 1.08 x CFM x Dtair 500 x GPM x Dtwater
• 1.08(4000)(70oF) 500(30) Dtwater
• Dtwater 20.2oF twater 200 20.2
  179.8oF

H E A T
Supply Air
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Cooling Coil Performance

• Air side Q 4.5 x CFM x Dhair
• Water side Q 500 x GPM x Dtwater
• Example 30 gpm of 40oF water circulates through
  a coil, cooling 4000 CFM from 85oF/40 to
  55o/90. What is the leaving water temperature?
• 4.5 x CFM x Dhair 500 x GPM x Dtwater
• 4.5(4000)(31.8-22.2) 500(30) Dtwater
• Dtwater 11.5oF twater 40 11.5
  51.5oF

C O O L
Supply Air
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Cooling Coil Performance
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Coil Performance

• What if performance doesnt match?
• One of the parameters is not as expected
• Usually, you can easily measure everything but
  the gpm, so calculate the gpm being delivered and
  compare to that specified to verify performance

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Humidifier

• Verify equipment operates upon a call for
  humidification
• Check air off humidifier for desired
  temperature/humidity condition
• Check humidifier performance using psychrometric
  equations

Supply Air
Steam Grid or Pan-type
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Smoke Dampers

• Verify that damper is properly connected
• Check damper operation on signal that smoke is
  present
• Fire inspector may want to see damper operate in
  presence of real smoke

M