Keeping HVAC systems running at optimal efficiency can save operating dollars.
Keeping HVAC systems running at optimal efficiency can save operating dollars.
By Susan McClendon, CCS
Keeping HVAC systems running at optimal efficiency can save operating dollars. The fact that commissioning can help make HVAC systems run correctly in the first place or restore them to proper operation is recognized by both the United States Green Building Council's LEED® Green Building Rating Systems and the Green Building Initiative's Green Globes Rating System.
Both organizations give credits or points for commissioning activities. LEED-NC includes basic commissioning as a prerequisite and LEED-EB (2008) includes a prerequisite covering some basic commissioning activities.
If you are an architect, you may be wondering why you need to know about commissioning. After all, isn't it the mechanical engineer's responsibility? Unfortunately, the architect is likely to get involved with commissioning issues whether he/she likes it or not, simply because the architect is usually the primary project liaison to the owner. Commissioning is not typically included in the new construction scope, so many owners question why they should spend more money to "fix" the system the contractor is being paid to build. In theory, if the contractor installs the equipment, piping, ductwork, and wiring in accordance with the contract documents, the system should perform as designed. But HVAC contractors are not usually informed of how the system should operate unless the system is to be provided under a design-build contract. In practice, supposedly completed systems commonly do not operate effectively due to incorrect adjustment, improper installation, or other contractor errors. Typical contract closeout activities, such as system start-up and demonstration, do not provide sufficient evidence that the system is operating properly, much less optimally.
Why Commissioning of HVAC
Commissioning: A systematic process ... that results in the delivery of a building whose HVAC systems perform as intended
Retrocommissioning: Commissioning of an existing system that was never commissioned
Recommissioning: Subsequent repeat commissioning of a system that was once commissioned
Continuous Commissioning: Institutionalizing commissioning activities into operating and maintenance processes so that no separate recommissioning processes are required
On projects involving existing HVAC systems, commissioning is generally considered a good value, even if no modifications are being made, because all but the simplest HVAC systems get "out of tune" over the years. But retrocommissioning is "invisible" work just like commissioning of new systems—owners question whether they are simply paying someone to find out that the system is already in good working order. On the other hand, if energy conservation measures are being considered, the results of retrocommissioning may help evaluate alternative options and, at the very least, establish a reliable baseline for evaluating results.
Quality Assurance Activities
An escalating series of quality assurance activities is commonly used to detect problems that often occur in HVAC systems. The first three activities are: 1) checking shop drawing submittals, 2) demonstration, and 3) training owner personnel. For most large projects, 4) HVAC testing, adjusting, and balancing (TAB) is usually done by a specialty contractor. Unfortunately, none of these, even in combination, can detect all of the potential problems—hence the rise of 5) commissioning as a separate activity.
All of these activities add cost to the construction project, with 1) (shop drawing checking) costing the least and 5) (commissioning) costing the most. Because commissioning includes a demonstration activity, requiring demonstration as a separate activity is probably unnecessary except if it is used to force the contractor to be ready for commissioning. TAB can be done without commissioning (and often is), but TAB is an essential part of commissioning. Training as part of the construction contract is usually optional, but training is often an integral part of commissioning.
Checking shop drawing submittals is an obvious way to forestall errors. Although not likely to purchase equipment larger than that specified, the contractor might offer an apparently equivalent alternative that is unacceptable.
In performing a formal demonstration, the installing contractor shows designated owner personnel that the system works and briefly explains how it operates. Demonstration does not constitute operational training but instead shows, for instance, that equipment turns on at the switch, that thermostats work, and that warm air comes out the registers. The "demonstrator" is usually a member of the HVAC contractor's technical staff. Demonstration that is a requirement of the contract documents should be accomplished prior to Substantial Completion so that any deficiencies are also corrected prior to that time.
Training owner personnel is not usually considered a formal quality assurance activity but it sometimes functions as one. Training on operation and maintenance usually takes 1 to 2 hours to 1 to 2 days, depending on the system or equipment, and is usually performed on-site using the systems already running. Obviously, if parts of the system do not function well enough to accomplish this training, the contractor is obliged to correct the work. If the training sessions are to be considered a quality assurance activity, they should be accomplished prior to Substantial Completion so that deficiencies can be corrected prior to that time. If training is required, demonstration is usually the first step—these two functions are usually separated so the training can be performed without stopping for repairs or adjustments. Training can also be part of the commissioning process.
HVAC testing, adjusting, and balancing (TAB) is a well-established discipline with many experienced practitioners and four U.S. organizations that provide guidelines for TAB: American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), Associated Air Balance Council (AABC), National Environmental Balancing Bureau (NEBB), and the Sheet Metal and Air Conditioning Contractors' National Association (SMACNA). TAB involves measuring air and water flows, adjusting dampers and valves, and setting sensors; the more complex the system, the more room for error. The TAB contractor works from the contract documents, which must include a Sequence of Operation description for each system and subsystem involved.
Commissioning is a more detailed examination and testing of the installed equipment and systems, usually performed by an independent commissioning authority (sometimes referred to as a commissioning agent). Comprehensive commissioning involves the commissioning authority during the design phase as well as during construction. The most common form of commissioning is limited to construction phase (referred in the LEED rating systems as "Basic Commissioning"). Construction commissioning includes more detailed demonstration, formal detailed testing of all modes of operation, documenting that all the information asked for has been provided, and ensuring that systems that are supposed to interact do so correctly (integration).
The commissioning authority is given the design professional's "Basis of Design" document (BOD) against which to check the installation. (In contrast, TAB contractors are not usually given such a document so must deduce the design criteria from the installed system.) The BOD is detailed documentation of the functional requirements of the project, descriptions of the systems, components, and methods chosen to meet the design intent, and assumptions underlying the design intent. Development of the BOD by the HVAC design engineer is not usually part of basic engineering services. Commissioning also requires more work of the contractors—the commissioning authority defines the commissioning requirements and observes and documents them but the contractor fills out pretest checklists and performs the detailed tests—making it necessary to include those commissioning requirements in the contract documents.
Commissioning an existing building is usually more complicated than the new construction commissioning process. First, the system may or may not be operating as designed. This is probably the case if it hasn't been recommissioned recently or was never commissioned. The operators may have changed the operation because they did not understand how it should operate. Equipment may be non-functional or operating poorly or improperly. Inoperable exhaust ventilation, for example, is not immediately noticeable. Second, there may be no BOD documentation, particularly for older buildings—even today such documentation is not commonplace. Third, there may be no operation and maintenance manuals (O&M) or that data may be skimpy or out of date. Fourth, expert knowledge about how the system should operate may have been lost over the years through changes in on-site personnel or maintenance contractors.
Considering these four complications, commissioning an existing building could bring immediate benefits, if only to return the HVAC system to proper operating condition. Some authorities suggest from 5 to 20 percent energy savings depending on the extent of the problems. Commissioning would be the first step if any of the major equipment is nearing the point of replacement; the type and size of new equipment should be based on the after-commissioning condition rather than the before-commissioning condition. Determination of the energy usage "baseline" for considering energy conservation measures is more accurate after commissioning—making evaluation of everything from replacement of HVAC equipment to added envelope insulation more reliable.
If commissioning is to be undertaken on an existing building or portion of a building, the BOD documentation must be either retrieved from the original designer or prepared using available data. An HVAC engineer will probably need to be hired to deduce the design assumptions, analyze the system, and prepare drawings and descriptions for use by the commissioning authority and O&M staff. The engineer can also recommend additional investigation that would help determine current operating parameters—TAB work would determine current air and water flows, for example—before the commissioning authority begins to design the commissioning plan.
For new construction, the commissioning plan should list all the functional performance tests necessary, with performance values to be achieved, for each piece of equipment and each subsystem. For existing systems, the plan may not list the performance values; instead, the functional performance tests can be used to discover existing values that are subsequently analyzed by the design engineer to determine whether improvements are necessary or desirable. If the TAB work has not been done beforehand, it needs to be accomplished during the commissioning or planned to be done based on the results of the testing and design analysis.
The commissioning authority should prepare a detailed report after completion of commissioning. In new construction, the report should show that all equipment and systems have been adjusted or corrected to achieve the design intent. If that is not possible due to something beyond the contractor's control or contract scope, the report should include recommended solutions. For existing systems, the report should describe elements of the system that are not operating optimally, again recommending solutions. The owner will then decide which improvements are most cost-effective and affordable. For existing systems, the design engineer, the TAB contractor, and the commissioning authority can conveniently be the same entity without creating any conflict of interest, as long as the improvements are contracted to another entity, such as an HVAC subcontractor. This is similar to the practice in new construction where the TAB contractor is commonly contracted directly to the owner to avoid the conflict of interest that might arise out of the HVAC contractor testing his or her own work.
The commissioning authority can also be contracted to prepare a Recommissioning Plan. This applies to both new and existing systems. The Recommissioning Plan is like the original commissioning plan but is adjusted to reflect new knowledge discovered in the process and all modified or replaced equipment and controls. Some authorities recommend "continuous commissioning," which involves building commissioning practices into normal operations and maintenance. In addition, formal recommissioning is made standard for each equipment replacement and system modification or extension. By having a written plan, good O&M practice is hard to overlook.
Existing HVAC System Survey
If an existing system lacks documentation, in whole or in part, more documentation must be prepared before the commissioning plan can be designed. In the worst case—no data available—the only alternative is to study and document the physical systems. This data collection is often the most expensive part of the commissioning process. The owner may decide to do the physical survey and basic documentation using existing staff or others hired for the purpose. An engineer capable of analyzing the system is not necessary at this point, though further investigation may be needed once analysis has begun.
Diagrams and drawings that may need to be developed are mechanical room layouts, piping and duct diagrams, dimensions of equipment, piping, and ducts, and locations of valves, dampers, meters, gauges, thermostats, and other sensors. A photographic survey may reduce repeat trips. It may be necessary to inspect:
Above-ceiling spaces, equipment closets, meter rooms
Cooling towers on the roof or in remote outdoors locations
Terminal units in occupied rooms, such as fan coils in cabinets and in walls
Information about each piece of equipment conveys its capacity and operating and electrical characteristics; identifying the manufacturer and model number may make it possible to get O&M manuals from the manufacturer. Equipment nameplates can be photographed as well as thermostats and other exposed sensors. If such energy conservation measures as replacement of major outdated equipment have already been decided, consider whether the commissioning is to be performed before or after replacement and whether documentation of existing equipment is necessary.
Documenting the sequence of operation may require interviewing the operating staff. Management staff may have information about procedures, service contracts, and maintenance programs in place. To effectively determine sequences of operation, identify all control devices, including switches, motors, pumps, solenoids, computers, and digital control units. This includes manual as well as automatic controls. Copy all existing drawings, specifications, and O&M manuals unless they are obsolete. It may be necessary to search management office files, maintenance offices, storerooms, work rooms, and off-site storage.
Other examples of potentially useful existing documentation:
Utility bills, if they cover all seasons and show quantity as well as cost
O&M manuals produced by original contractors, though they could now be missing pages and could be of uncertain validity
Current service contracts, with scope of work
Capital Improvements Plan, with expected maintenance lifetimes of major equipment and projected replacement value
User manuals for computerized temperature control system software
Drawings of the original system; even blueprints, decades old, are useful, especially when they have been marked by hand to show changes
Diagrams and instruction sheets made by the operators. These may be found taped to walls or equipment as well as in O&M manuals
Procurement of Commissioning
The architect, as the primary design professional, may get involved with the procurement of the commissioning authority's contract, which is usually separate from the construction contract. If so, there are guides for Request for Proposal (RFP) documents in several of the references noted. Even if the HVAC design engineer is responsible for the technical content of such a document, the contractual terms should be coordinated with the contract documents for construction—usually the architect's responsibility.
Susan McClendon (firstname.lastname@example.org), a registered architect and Certified Construction Specifier, is executive vice president of Building Systems Design Inc., Atlanta. She is project manager for BSD SpecLink®, which now includes CSI-DBIA's PerSpective®. She manages the ongoing data development and updating of BSD SpecLink, which includes detailed specifications for general commissioning requirements, Commissioning Authority responsibilities, commissioning of HVAC, and testing, adjusting, and balancing of HVAC.