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Was the Building Properly Commissioned?

I recently reviewed a guidebook for investigating indoor air quality. The guidebook included many suggestions for investigating indoor quality. The first set of suggestions consisted of a list of items for initial review by investigators in order to develop an analysis plan. The item that caught my eye referred to commissioning. The item posed a question to investigators: “Was the building properly commissioned when it was first constructed, including testing and balancing of the HVAC system?”

As a commissioning consultant for HVAC systems this question made me wonder what activities I performed to verify proper indoor air quality. After some contemplation I realized that all of my activities provide a level of confidence that an HVAC system will not be the cause of indoor air quality problems. After all, it is the HVAC systems that condition (properly or improperly) the air within the entire indoor environment.

Indoor air quality involves factors that are so numerous that it would seem that everything affects indoor air quality. Examples are: building materials, building configuration, building use, office equipment, occupancy load, operations, maintenance, janitorial practices, local climate, local environmental pollution and HVAC systems. The manner by which these factors cause poor indoor air quality can be arcane and insidious. Commissioning usually does not directly address these factors except for HVAC systems. This column does not attempt to discuss the details of why certain aspects of mechanical systems can cause indoor air quality problems. Professional journals contain an abundance of articles that describe causes of indoor air quality problems.

In general, HVAC commissioning verifies that systems are installed and work in accordance with the design documents. If the system design does not include indoor air quality considerations then verification of an “inadequate” system does not achieve preferred results. Thus, commissioning consultants should include indoor quality items as part of the commissioning design review. Indoor air quality criteria should be included in a design intent document and implemented by design drawings and specifications.

Mechanical system design affects basic indoor quality parameters such as space temperatures, space relative humidity and space outdoor air ventilation rates. The design review process normally involves submitting questions to the design team. Do the design documents indicate the expected levels of temperature, relative humidity and outdoor ventilation rates? The expected levels should be within a design intent document. Has the design team performed and documented a systems heating and cooling load analysis? Does the system have modulating outside air dampers, variable speed fans, variable air volume terminal units and exhaust fans? Does the system design provide for adequate outside air to occupied spaces during all system operating configurations? Has the design team analyzed these configurations and documented the results? Is the outside air flow rate control strategy appropriate for the system’s physical configuration? Do the sequences of operation match the system’s components and performance parameters?

Intimately related to the review of the design are testing, adjusting and balancing (TAB) issues. Does the design provide adequate information for the TAB contractor? Are air and water flows specified? Is the specified outside air flow equal (or greater for positive pressure) to the specified exhaust flow for all operational conditions? Are balancing dampers indicated on drawings? Is system instrumentation (temperature, pressure, flow) adequate or does the system configuration allow the TAB contractor to use temporary instrumentation? Do the specifications require the TAB contractor to measure outside air flow under minimum and maximum conditions? Can the outside air flow be measured directly with pitot tube measurements or a flow hood?

After reviewing the system’s performance items the commissioning design review should check for maintenance items. Will the system continue to perform to the level of the design intent? Is there access to mechanical systems and their components? Does the access allow for cleaning and, of course, filter change-out? Do ceiling panels allow access to terminal units and fire/smoke dampers? Are roof access ladders needed? Is there a chemical injection system for cooling towers? Is cooling coil condensation drained appropriately?

Commissioning design review should include possible detrimental systems interactions due to physical locations. Are exhaust fans’ discharges located away from outdoor air intakes? Are combustion gases exhausted near outdoor air intakes? Can moisture drift from cooling towers enter the building?

Once the design is finalized and the project proceeds into the construction phase the commissioning consultant can perform site observations to confirm that various design features are being properly constructed. Of particular importance, the construction phase is the best time to check for adequate duct cleanliness. Once installed, facilities personnel may never have an opportunity to review internal surfaces of ducts for possible sources of air quality problems.

At the end of the construction phase, the commissioning consultant tests the HVAC systems to verify the systems operate in accordance with the design documents.

With respect to mechanical systems, assuring IAQ amounts to a good design and verifying the design goals are achieved. A methodical commissioning process eliminates any questions about the HVAC system design, construction and performance. IAQ problems may still occur due to the numerous possible causes of poor IAQ. However, confidence that the mechanical systems are not the culprit of IAQ problems allows IAQ investigators to focus on other potential problem sources. This can save much effort since trouble shooting HVAC systems within an occupied building can be inconvenient, time consuming and expensive.

 

Commissioning: Getting It Right

Engineered Systems, July, 1999

by
Rebecca Ellis, PE, LEED AP, CCP, CxA
President
Questions & Solutions Engineering
1079 Falls Curve
Chaska, MN  55318
rteesmag@QSEng.com