Centigrade’s Testing & Training Facility

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Welcome to AIRAH WA’s Site Visit

Upcoming AIRAH WA Events

AIRAH WA Members’ Annual Lunch Tuesday, October 16Aloft Hotel, RivervaleLimited places remain

AIRAH WA Site Visit Tuesday, November 13iFLY TBC

AIRAH WA President ShoutNorthbridge Brewing CoTuesday, November 27

AIRAH WA Members’ Golf Day Thursday, March 21, 2019Maylands Peninsula Golf Course

www.airah.org.au

Presenting:

Michael Anthony, M. AIRAH; Tony Anderson, M.AIRAH;

David Lee, M. AIRAH; Michael Snook, Affil.AIRAH;

David Hammond, Stud.AIRAH; Nathan Johnsen, Affil.AIRAH; Thomas Fellows, Stud.AIRAH

and Scott Hobbs

Effective Airside Commissioning

Michael Snook Affil. AIRAHDavid Hammond Stud. AIRAH

What is Commissioning?

• “The advancement of an installation from the state of static completion to full working order to specified requirements. It includes setting to work of an installation, and regulation of all the system flowrates.” CIBSE Commissioning Code A:1996 (2006)

Why is Effective HVAC Commissioning Important?

Courtesy HVAC HESS, 2013

Key Considerations Prior to Commissioning Air Systems

• Type of facility HVAC system is serving• Allowable tolerances / permissible deviations from design

requirements• Access to equipment• Site cleanliness • Commissioning timeframe• Schedule clashes

Common Issues Faced at Precommissioning

• Site not ready (Builder, Installation, No power)• Volume control dampers not open• Fans not bump tested / fan rotation backwards• Implementation of a commissioning management plan allows

the roles and responsibilities of each stakeholder to be clearly defined.

Hierarchy of Airside Commissioning

Primary Data

• A full system pitot traverse gives the most accurate representation of system performance

• Pitot traverse relies on an average measurement of velocity pressure at a section of duct with a laminar flow characteristic

• Where duct velocities are below 3.5m/s, a hotwire anemometer is the preferable choice₁

Pitot Tube Operating Principle

Pitot Tube Operating Principle

Courtesy BSRIA BG 49/2015

Test Point Locations

Courtesy BSRIA BG 49/2015

Courtesy BSRIA BG 49/2015

Courtesy BSRIA BG 49/2015

Methods to Ensure Accurate Traverse Measurements

• Favour pitot tube over hotwire anemometer where there is a risk of air swirl

• Correctly measure internal duct dimensions• Space test points methodically• Log-Tchebycheff Method of Traverse vs Equal Duct Method

Secondary / Tertiary Data

• Supports primary data (Traverse)• External static pressure (Fan Curve)• Static profile of air system (E.G Coil ∆𝑃𝑃)• Fan running current• Air Balance• Tying several data types together ensures a true

representation of system performance has been shown.

Fan Curves

Proportional Air Balancing

• “The process of bringing the fluid flow rates throughout a distribution system into balance with one another, in their correct proportions and within tolerances specified by the designer” BSRIA BG 49-2015

Setting Fan Volume

• Following pre commissioning, fan is set to 110% of design for proportional balancing as a rule of thumb

• Use of affinity laws / static pressures handy in setting flowrate at this stage

Initial Scan

• Knowing air volume from main traverse, each terminal is measured

• The difference between traverse reading and sum of outlet readings is recorded.

• An “index” is identified, and a proportional balance is undertaken to bring all outlets to within a specified tolerance of design.

System Index

• The air outlet with the highest pressure loss at the design air volume.

• Important to consider whether the index makes sense in relation to the rest of the system.

• Important to physically check the duct and cushion head interface before proceeding with air balance

Is this an index?

Correction Factors

• A correction factor adjusts the measured readings at the terminals to reflect the true system volume.

• Correction factors account for:• Air leakage rate• Back pressure Induction within Balometer• Takes into account free area of register when using vane or

deflection anemometers• Correction factors between 0.8 and 1.2 are generally

considered acceptable (BSRIA BG 49-2015)

Factor Caused By Hood Backpressure

Courtesy Shaun Matthews Use of Correction Factors When Commissioning Air Systems, 2016

Factor Caused By Hood Backpressureand Cushion Head Leakage

Courtesy Shaun Matthews Use of Correction Factors When Commissioning Air Systems, 2016

Correction Factors

• Not an arbitrary figure to cover up lack of volume or poor air balance

• Technicians need to understand why there is a deviation between measured volume at diffusion and at duct traverse.

• Common cause of falsified commissioning data and substandard airside commissioning.

• Must be verified when finalising system.

Case 1: Typical Cleanroom AHU Supply Air

Case 1: Typical Cleanroom AHU Supply Air

True volume measured at laminar traverse point

Case 1: Typical Cleanroom AHU Supply Air

Factor Ties ATBS to DTS

Corrected balometer volume equals duct traverse volume

Likely causes of factor

• Factor is typical for a HEPA terminal outlet, generally caused by instrument (+ / - 3%)

• User factor• Minimal leakage on ductwork upstream of HEPA terminals due

to high static pressure on supply air ductwork

Case 2: Typical AHU with Swirl Diffusion

Case 2: Typical AHU with Swirl Diffusion

True supply air volume measured at laminar traverse point

Case 2: Typical AHU withSwirl Diffusion

Volume corrected to traverse

Likely Causes of Factor

• Swirl diffusion pattern inducting air within balometer• Backpressure exerted by balometer causing restriction• High backpressure of swirl diffuser causing minor leakage

within cushion head- diffuser interface• Instrument factor (+ / - 2%)• User factor

Case 3: Hood Factor Used (No Traverse)

What if a hood factor of “1.0” was used

Volume readon balometernot corrected to a traverse

What if a factor of “1.0” was used

• Established 1879L/s on balometer• AHU would have to be sped up 8% to achieve this.• If a traverse was taken, AHU would likely be supplying 8%

more air than what was measured.

What does this mean?

• Swirl diffusion induction and back pressure within balometercausing 8% differentiation between true traverse volume and volume read on balometer.

• By compensating for a false reading, a power increase of 25% will be experienced as fan motor speed is increased 8%.

Why is this important?

• Key aim for any building design is to minimise energy consumption over an asset’s lifecycle

• In facilities where maintaining specific pressure gradients is important, major issues can arise where true air volumes have not been established via a pitot traverse

• Control oscillation can occur as system is incorrectly commissioned

• Higher maintenance costs• Cost of retrocommissioning vs energy savings

References

-Alnor HVAC Assessment Handbook, 2007, USA-BSRIA BG49-2015, 2015, UK-CIBSE Commissioning Code A:1996. Chartered Institute of Building Services Engineers, (2006), UK-CIBSE Commissioning Code M. Chartered Institute of Building Services Engineers, (2003), UK-AIRAH Technical Handbook. Australian Institute of Refrigeration, Air Conditioning and Heating, 2013, Australia-Matthews. S (2016) The Use of Correction Factors When Commissioning Air Systems. Commissioning Specialists Association, West Sussex, UK-Heating, Ventilation and Air Conditioning High Efficiency Systems Strategy, 2013-P.L Lagus, P.W Butler, K.M Fleming (2006) A Comparison of Tchebycheff, Equal Area and Tracer Gas Air Flow Rate Measurements-NSW Office of Environment and Heritage (2015) HVAC Optimisation Guide, Sydney, Australia

Thank you for attending, please stay for refreshments.

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