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How Many People Does It Take To Commission One VAV Box? – This Is Not A Joke!

How many people does it take to commission one VAV Box? – This is not a joke!

​Quality, Consequences and the Construction Industrial Complex (part 36) – All IMHO:

A construction project manger, a MEP building services engineer and a Commissioning engineer walk into a bar…….”Why is the Commissioning taking so long? When can I put back the ceiling access tiles?” Asks the project manager. “Not sure, should be soon, all the VAV boxes come factory calibrated” answers the MEP engineer. The Commissioning engineer looks deep into his beer glass and dies a little on the inside……..

VAV is an established technology, even an outdated technology, yet is still a miss understood solution for heating and cooling buildings. A VAV system is a complex, multi third party component system that is absolutely not, plug and play. VAV systems are rarely designed, installed or commissioned correctly. Lets not talk about VAV’s alleged efficiencies and persistence of performance as a heating and cooling system here. However, after 35 years of working on VAV systems, I am still astonished to find many construction professionals do not understand their complexity and how to set them to work then commission them.

Project managers should note, scheduling and managing the risk of commissioning large VAV systems will be a factor in the successful completion of a project. How projects complete is the  80% factor in how clients remember and rate performance of their project managers. 

So how many people does it take to commission a single VAV box? For each VAV box the installation and commissioning tasks are: 

Installation and pre-commissioning tasks

  1. Install the VAV box and the whole system including the entire ductwork distribution network, all AHU’s, power, VFD’s, controls plus other system interfaces 
  2. Quality control checks, ductwork pressure testing, controls programming plus uploading of controls “code” and system start up 

Dynamic commissioning tasks for each individual VAV box

  1. Controls point to point testing
  2. Set and calibrate in situ, the VAV box maximum design flow rate (V Max cooling)
  3. Proportionally balance the secondary side terminal diffusers
  4. Set the diffuser air patterns
  5. Set and calibrate in situ, the VAV box minimum design flow rate (V Min heating)
  6. Test, tune and validate all controls sequences (V max, V min, morning boast etc.)

Despite what the sales man tells you, VAV boxes come “factory set” but still have to be calibrated and commissioned in situ. This is proven every day on job sites by the commissioning teams that have to adjust and set the VMax and Vmin on VAV boxes. So how many and who are the players required to commission a single VAV box?

  1. The main contractor / GC – to coordinate the specialist sub-contractors, provide access etc.
  2. The Commissioning engineer / technician / authority – please don’t call him or her an “agent”! Agents are sales reps in my mind not commissioning professionals. 
  3. The mechanical contractor – typically the installation is their responsibility
  4. The TA&B specialist – to measure and calibrate the VAV boxes plus balance the terminal diffusers
  5. The controls specialist – probably the most important player

It is important to note that the above applies to each and every VAV box. If a project has 800 VAV boxes then the above has to be done 800 times! 

VAV systems are a good example of why process commissioning is not sufficient by its self to ensure systems and building performance (this will be subject of a posting on another day). To deal with complex systems the commissioning authority must be technical not just process or no value is added IMHO. It takes an independent technical commissioning authority to validate VAV systems commissioning. 

So what can be done to mitigate risk and ensure fully commissioned VAV systems?

  1. Hire a commissioning professional early to do a design commissionability review. Any problems found pre-installation can be fixed for little or no costs.
  2. Agree the controls sequences as early as possible and bench test any complicated sequences. 
  3. Identify access issues as early as possible.
  4. Prioritize the installation of the VAV systems and their commissioning in the project schedule.
  5. Ensure the TA&B and controls firms have sufficient resources for the project. This is one of the most frequent issues during dynamic commissioning. 

Next, I will post about commissioning the whole system once each individual VAV boxes have been set up.

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