Automated Functional Testing of HVAC Secondary Systems

1
Automated Functional Testing of HVAC Secondary
Systems

• Peng Xu
• Lawrence Berkeley National Laboratory

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What is functional testing?

• Active testing
• Override controller
• Passive monitoring
• Routine system operation
• Advantages/disadvantages
• Time
• Operating range

3
Why automate?

• Most HVAC systems have operational problems
• Skilled experts are expensive and scarce
• Multiple systems can be tested in parallel
• Procedures and reporting are formalized

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Objectives of functional test

• Extremes of operating range
• Component maximum capacity
• Leakage (can we turn it off?)
• Controllability
• Non-linearity
• Hysteresis
• Mismatch/maladjustment of actuator and final
  control element

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How to design a test - I

• Start with an open-loop test
• Test of mechanical equipment
• Follow with a closed-loop test
• Test of the controlled system
• Examples of control problems
• Oscillation
• Sluggish response
• Offset

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How to design a test - II

• Where to implement
• Embedded in the EMCS
• Standalone tool connected to EMCS
• Communication protocol
• Controller overide
• Data trending

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Procedures to design a test

• Ability to detect all problems
• Finish in a short time frame
• Choose a proper sequence
• Implement during routine operation
• Data analysis
• Steady state tests
• Step tests
• Steady state detector
• Model

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Field trials

• Office buildings
• Mixing box actuator
• Heating coil control valve actuator
• Fan and distribution system
• Test procedures
• Blind test (assume we know nothing about the
  system)
• Open loop step test

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mixing box -I
return air
exhaust air
damper
Te
Tr
damper
Actuator mismatch/hysteresis
To
Tm
damper
supply air
outside air
Drifted sensor
Stuck/leaking damper Incorrect minimum
pos Excessive non-linearity
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mixing box -II
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mixing box -II
12
mixing box -III
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mixing box -III

• Faults
• Bad mixed temp sensor
• Huge hysteresis
• Leakage

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Heating coil - I

• Possible faults
• Stuck/leaking valve
• Drifted sensor
• Undersize(blocked)/oversize coil
• Coil fouling
• Poor linearity
• Improper installation of actuator and valve

15
Heating coil -II
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Heating coil -III

• Faults
• Hysteresis
• Drifted sensor/leakage

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VAV fan system - I
pStat

0
Resistance
Zone
Supply Fan

• Possible faults
• complete failure
• sensor offset
• surge
• stuck at certain speed
• incorrect rotating direction or wrong fan
  installed
• variable speed drive malfunction
• poor tuning

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Supply fan

• Faults
• Fan failure

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Summary

• Functional tests should be economical and
  targeted at potential faults
• Only simply tests can be done in real application
• These functional tests can be automated
• It is worthy having automated functional tests
  embedded in EMCS system
• It is necessary to test over the full range of
  the operation to detect all problems

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Heating coil -I