VAV Box Calibration – Trust But Verify
Quality, Consequences and the Construction Industrial Complex (part 93) – All IMHO:
Does a VAV box require calibration and verification in the field?
Short Answer Always, YES!
“Trust, but verify” is a Russian proverb, used by President Ronald Reagan in the context of nuclear disarmament. Wise words IMHO.
Why?
VAV boxes arrive “factory set” not calibrated. In my experience, VAV box manufactures do not “calibrate”. If they did, it would be on a sampling basis in “laboratory, ideal conditions”. In real life, each VAV box is a unique installation and subjected to multiple variables that affect its performance.
A VAV system and individual box comprise many third party, proprietary components, it is not “plug and play”. VAV boxes are not tested prior to Commissioning. This is an issue because;
- Design assumptions are based on a fully operational and efficient VAV system;
- Energy model assumptions and consumption estimates assume a fully operational and efficient VAV system;
- Every project I have worked on in the last 36 years has required VAV boxes to be calibrated in situ because when tested, many did not meet specified requirements.
Long Answer
Lets start with clarity around definitions:
System: A set of connected components consisting of plant, distribution ducting, piping and terminal units plus arrangements to power and control operation. e.g. a VAV system.
Component: Part or element of a larger whole e.g a VAV box.
Factory setting: Setting of device (VAV box controller), within factory, “laboratory” setting, to deliver specified parameters. Part of manufacturing process.
Calibration: Comparison of measured values delivered by a device under test in situ against specified requirements with a calibration standard of known accuracy.
Test: Procedure to establish performance, quality or reliability.
Validation: Verifying accuracy and efficacy.
Verification: Process by which specific documents, components, equipment, systems, and interfaces among systems are confirmed to comply with specified requirements.
Performance Testing: Testing of a system to determine if specified performance criteria are met i.e means of verification.
Commissioning: Advancement of a system from a state of static completion to full dynamic operation in accordance with specified requirements.
Who “owns” the VAV system during construction?
Everybody and nobody is the the real world answer. Getting a VAV system installed and commissioned requires several parties. So, who does what?
VAV Box supplier:
- Manufactures
- Inputs (factory setting) specified VMax and VMin parameters
Installer:
- Installs VAV Box (the component with its own components) within the VAV System
TAB & Controls Technician:
- Test, calibrate (adjust) and verify in situ, each VAV Box VMax and VMin specified flow rates
Commissioning Authority:
- Tests and / or witnesses VAV system as a whole to validate performance in accordance with specified requirements
ASHRAE, LEED, GSAS, ESTIDAMA, NEBB, ACG Commissioning essentially requires a “trust but verify” process. So why is this a debate? Because VAV box and controls system salesmen tell contractors and MEP design engineers that their equipment is “factory calibrated”. I have yet to see evidence of this on site.
If a contractor or controls technician tells me one more time (you know who you are), that VAV boxes do not need field verification and adjustments because they come factory calibrated, I think I will weep!
A PDF file with the diagram below can be downloaded at https://bldwhisperer.com/downloads.html
Twitter: @BLDWhisperer
Related posts & links:
#36 – How many people does it take to commission one VAV Box? – This is not a joke! ( https://www.linkedin.com/pulse/how-many-people-does-take-commission-one-vav-box-joke-muggleton?trk=mp-reader-card )
#71 – VAV Box – Sensitive, Install as Follows ( https://www.linkedin.com/pulse/vav-box-sensitive-install-follows-adam-muggleton?trk=mp-reader-card )
#37 – Project Managers beware! This is why VAV systems are not “start up and walk away” ( https://www.linkedin.com/pulse/project-managers-beware-why-vav-systems-start-up-walk-adam-muggleton?trk=mp-reader-card )
#64 – Respect the VAV System Static Pressure Sensor! ( https://www.linkedin.com/pulse/respect-vav-system-static-pressure-sensor-adam-muggleton?trk=mp-reader-card )
