HVAC trials:
Commissioning ensures that all components in a new system will work together as designed

By Clifton W. Greim, P.E., Harriman Associates, and David D'Angelo, Bowdoin College

Heating, ventilating, and air conditioning (HVAC) systems in new and renovated buildings have become increasingly complex, with hundreds of components that are connected and interrelated and often controlled by a central computer.

And like the chain with a broken link, if one part doesn't operate as it should, the effectiveness of the whole system is compromised.

Commissioning is a methodical, thorough process that puts all parts of an HVAC system through a trial run, giving owners assurance before move-in that everything works as designed.

It results in energy savings and fewer complaints from building users, and it often uncovers mistakes and omissions that could result in serious safety and maintenance problems if not corrected — from duct smoke detectors that don't respond as they should, to fan motors that wear out too soon.

Why it's needed
--different from pre-occupancy testing
--different from testing and balancing
--starting in design phase

What is checked
--verify proper operation
--proper sequencing

Problems uncovered
Assessing responsibility

Benefits outweigh costs
--safety issues
--indoor air quality
--easier problem resolution


Why it's needed
HVAC systems in the past were relatively simple. With few components and manual controls, starting up a new system often meant a simple equipment start-up by a contractor. That's not enough for today's systems. While they're more efficient and offer greater comfort and better air quality, they're also complicated. The sheer number and interrelationship of components mean more opportunities for problems in both installation and operation.

And the typical bidding process offers more. Designers often have certain products in mind when they conceptualize a system, but rarely specify proprietary components because of competitive bidding. The system that is created may consist of entirely different products, effecting subtle changes in operation that can't always be predicted. In addition, different subcontractors typically procure and install different components, even though the components must work together.

Commissioning tests the whole system. It not only makes sure that each piece of equipment and each control operates properly, but also determines whether they operate in the right sequence with other components.

Different from pre-occupancy inspections Commissioning differs from pre-occupancy inspections in thoroughness, detail, and focus. A pre-occupancy inspection is essentially a visual check of the building, with the owner, designer, and contractor walking through, noting problems that must be corrected before move-in. Are any parts missing? Are equipment and controls where they should be? Are there any broken parts? The emphasis is often on meeting code requirements in time for move-in day.

Commissioning goes further and puts the HVAC system through detailed operational tests. An independent agent, working for the owner, verifies that all components are working as designed, at top efficiency, and meeting manufacturer's specifications. The agent documents any problems, suggests who is responsible for correcting them, and then re-verifies to make certain that the corrections have been made.

While a pre-occupancy inspection might note that a missing thermostat should be installed, commissioning would make certain it was calibrated, that it functioned properly, sending commands to numerous other components in the right sequence, and that those components responded as they should.
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Different from testing and balancing Commissioning is also different from testing and balancing procedures, which measure air and water flow in HVAC systems. While balancing ensures that air and water are being distributed in the right amounts to various spaces, as designated on drawings, it does not check the operation of each component.
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Start in design phase The commissioning process is often a service provided after a project is completed, but before move-in, but it should begin during the design phase. The commissioning agent then becomes a part of the team from the beginning, working with architects, engineers, and contractors. This allows for a more integral process, with peer review throughout the design phase. The expertise of the commissioning agent is available early on, when better solutions can be effected economically.
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What is checked
In commissioning, the HVAC system is put through a four-season "shakedown." Every part in the system is physically checked to make certain that it operates as indicated on drawings and in the sequence that is specified. If a project is completed in the summer, an owner doesn't have to wonder whether the heating system will perform properly when it's needed. Commissioning will have made certain that it will.
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Verifying proper operation The specific tests performed depend on the project and the systems that were designed, but a key element is verifying proper operation among components and the controls that signal them to respond. For example, variable-air-volume boxes in ducts are checked to determine if they respond as they should to a command from a thermostat that calls for heat or cooling and whether air flow for minimum and maximum settings is correct.

Reheat coils in ducts are tested to see if they stage on and off as required. And speed drives on supply- and exhaust-air fans are checked to determine if they adjust to varying air flows. To check the smoke sensors in ducts, commissioning agents sometimes use smoke canisters to determine whether dampers in the ducts close as they should to keep the smoke from being further dispersed and whether alarms are signaling.

The commissioning agent also ensures that enough outside air is being mixed with indoor air to freshen required spaces to meet building codes.
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Proper sequencing Among other components put to the test are air-handling units, condensing units, classroom unit ventilators, pumps, boilers, chillers, automatic valves, system alarms, heating coils, sawdust collectors in wood shops, laboratory hoods, ventilation systems in gymnasiums and auditoriums, and the computerized energy management system. They are all checked to be certain they operate in the correct sequence and are using fuel and electricity efficiently.
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Problems uncovered
The results of each test are thoroughly documented in a report., and an ongoing punch list is generated. The larger and more complex the system, the more probable that many deficiencies will be found, as was the case in a large project involving research labs, in which some 400 problem areas were spotted.

In a smaller project, deficiencies are generally fewer, but it would be unusual for none to be found, despite the best intentions of contractor and subcontractor, who are often hurrying to meet deadlines. The systems and the interrelationships among components are just too complex.
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Assessing responsibility
When problems are found, the commissioning agent describes them specifically and suggests who is responsible for correcting them, usually the general contractor and subcontractors, and, occasionally, the designer. The agent then re-commissions the system or component after corrections are made to verify that the problem has been truly resolved.

Sometimes the correction is easily made, as simple as connecting a loose wire. But for some issues, the fix can be complicated, requiring designer, owner, contractors, and commissioning agent to work out a resolution together.
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Benefits outweigh costs
The cost of commissioning is usually from 1 percent to 2.5 percent of the cost of the HVAC system, but owners find that cost is outweighed by both tangible and intangible benefits. The types of problems found and corrected range from minor to substantial.
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Safety issues Without commissioning, even some major problems could have gone undetected until an emergency. For example, in two recent school commissioning projects, more than half of the smoke detectors in ducts were found to be deficient and 60 percent were not calibrated as they should have been. Without commissioning, it would have been difficult, if not impossible, to determine if the detectors were not functioning properly unless a fire occurred.

Similar safety issues are confronted if fume hoods and pressurization systems in laboratories do not function properly. Both provide protection to building occupants from hazardous materials used or generated in experiments.

In one project, the pressurization control system which keeps contaminants from leaving the lab did not work as designed because controls were not properly calibrated. Discovering the problem would have been difficult and more costly to resolve without commissioning, which tested the pressure control system under many possible conditions.
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Energy efficiency Many problems found affect energy consumption — thermostats not operating correctly, exterior air dampers that don't close properly, finned-tube radiation elements providing heat when they should not be, fans operating too long or running faster than they need to, or even running backwards. In addition, HVAC systems as installed rarely offer optimum performance without fine-tuning.With commissioning, however, energy savings can be significant, and equipment will last longer and perform better when calibrated as designed.
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Indoor air quality And because the system has been fine-tuned and is running optimally, good indoor air quality is maintained. Owners and facilities managers report that their phones ring less often when the HVAC system has been commissioned. Move-in is easier and complaints from building users are virtually eliminated.
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Easier problem resolution Also, because commissioning assesses responsibility for correcting problems before move-in and well before the end of the warranty period, owners and managers are less directly involved. The commissioning agent can shoulder the task of dealing with the general contractor and subcontractors to make certain that problems have been resolved.

Whether the benefits can be quantified through cost savings or are apparent only because they eliminate headaches for owners and facilities managers, commissioning keeps the links in today's complicated HVAC systems solid.