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By Paul Liesman
Energy Efficiency Article Use Policy
The shorthand definition of commissioning as practiced by the Navy to ensure that ships and submarines, and the equipment and systems that operate them, perform according to the design intent is simple: Take it out and run it until it breaks.
From these roots, commissioning has evolved into a formalized and complex process for buildings, as equipment, systems and operating procedures have grown more complex. Ideally performed before owner acceptance, commissioning provides documented confirmation that building systems perform in compliance with the criteria to satisfy the owner’s operational needs as stated in the project documents.
A comprehensive commissioning program identifies and corrects costly performance deficiencies. It’s not a stretch to imagine the lifetime cost of 10 percent duct leakage versus 5 percent or less — which will result in additional operating expenses of $15,000 a year for an average facility with 12 air-handling units operating at 200,000 cfm. Similarly, it is not hard to envision an HVAC system failing to perform to specification. With complete installation costing approximately $4,000 per ton, a 10-percent performance reduction on a 250-ton system translates into $100,000 in wasted capital and an average $6,000 a year in excess energy costs because of extended run times.
In a study of the effect of commissioning on the performance of two buildings of different sizes, the Oregon Department of Energy found direct energy savings of 5 to 10 percent. In a 22,000-square-foot office building, annual energy savings of $7,600 ($0.35 per square foot) were achieved. In a 110,000-square-foot building, annual energy savings of $12,276 ($0.12 per square foot) were achieved following commissioning.
Similarly, a Lawrence Berkeley National Laboratory study on commissioning found that “… commissioning is one of the most cost-effective means of improving energy efficiency in commercial buildings.” In fact, the authors concluded that commissioning potentially can save as much as $18 billion a year in commercial buildings.
In addition to energy savings, the Berkeley study projected a median savings of $1.24 per square foot (in a range of $0.23 to $6.95) in “non-energy impacts,” that is, items identified in the commissioning process that do not affect energy consumption – such as reduced change orders and increased equipment life.
Add to these benefits the “intangible” savings associated with avoiding complaints, system downtime and displaced tenants. Taken together, the savings associated with non-energy impacts and intangibles far outweigh direct energy savings. In fact, in new construction, the savings from non-energy impacts will usually pay for the commissioning fee, or more.
Moreover, the deficiencies found and corrected during the commissioning process make the facility significantly more functional upon delivery to the owner.
A good example of a non-energy impact comes from a recent project, where a commissioning team found a violation of the plumbing section of the project specification. Dissimilar metals were incorrectly used and would have resulted in accelerated corrosion of the chilled water piping. Correcting this problem will save the owner more than the fee for commissioning.
Commissioning has the greatest impact when the commissioning consultant is involved during at the design phase of project. Design-phase comments and planning along with construction-phase corrections avoid delayed facility opening and business interruption. These corrections also generate front-end savings. This is the value of hiring a commissioning engineer at the design development phase rather than waiting until the late stages of construction. A commissioning agent involved in the project early enough can make meaningful contributions to the design as well as the construction of the project.
The commissioning engineer contributes to the design process by:
During the design phase, the commissioning engineer will comment on the ability of the systems, as designed, to be tested and offer suggestions to make the systems more testable. The agent will clarify the basis of design with respect to the performance goals that need to be verified and may suggest minor design changes to mechanical rooms to improve layout, serviceability and maintainability. By gaining a thorough understanding of the design, the consultant will be able to develop more relevant and accurate test scripts to be performed in the construction phase. This will reduce the amount of time required for commissioning, concentrate the commissioning effort on critical systems and reduce the total amount of time spent commissioning the facility.
A commissioning agent who is not brought in until late-stage construction, will have to thoroughly review the design documents to make any meaningful contributions. The incremental cost of bringing the commissioning engineer on board at the design phase is relatively modest, and the owner will reap the benefits of early participation.
For example, in a recent design review of an atrium, the commissioning engineer found that the designer had not considered the effects of frost formation on the glass in winter and had failed to account adequately for cleaning procedures. Addressing these problems at the design phase avoided costs of $250,000 associated with reworking the design of the HVAC system to supply air over the surface of the glass to prevent frost and to bring in power and water to clean the exterior of the glass.
In another case, the mechanical/electrical/plumbing engineer intended to design a stand-by power plant comprising five separate generators with a dedicated 5,000-gallon fuel oil tank for each generator. As part of the operability and maintainability review, the commissioning agent concluded that use of two larger tanks instead of the five dedicated tanks, with the ability to share fuel oil among the tanks and the generators, would reduce the operating cost of filling the tanks and improve monitoring capability. Correcting this design error reduced capital and operating costs and increased the utility of the stand-by power plant, while saving the costs associated with a significant redesign later in the project.
It is important to understand that the commissioning agent is not there to redo or even verify design calculations; the agent’s role is to verify that the design will meet the owner’s objectives. Moreover, when the commissioning agent is part of the project at the outset, the owner benefits from a commissioning team that fully understands the design intent and the challenges that lie ahead in the construction phase.
In the past, many owners perceived the role of the commissioning agent solely as witness and documenter of functional testing of equipment and systems. However, the commissioning agent makes important contributions from the outset of the construction phase, including:
Commissioning benefits all project stakeholders. Indeed, an unlikely beneficiary is the general contractor and its subcontractors. Although this has greatly improved recently, the general contractor has usually been least familiar and most leery of the commissioning process, and understandably so. On the surface, it can appear that the commissioning process is aimed directly at the general contractor’s efforts. That is another reason to have a commissioning agent involved early on; the agent is then in a position to differentiate design from construction issues and will not rely on the general contractor to understand the project.
The commissioning agent helps the contractor to fulfill its contractual obligations with respect to achieving the design intent. As a result, general contractors find they are done with a project more quickly and the risk of a call back to correct a construction error is reduced because of the rigorous testing performed to commission the facility. This is not to say that contractors deliberately skirt their own construction process, but the mere fact that a facility will be commissioned adds discipline to the entire construction effort.
Teamwork and communication are critical to successful commissioning. In properly specified commissioning projects, one of the contractor’s responsibilities is completion of pre-functional checklists under the supervision of the commissioning agent. Yet without a full understanding of the nature and importance of this step and the associated documentation, the general contractor may not properly complete this task.
It is worthwhile for the commissioning agent to review the purpose of these checklists, which document that equipment installation has been completed and the equipment is in proper condition to be run through its functional tests. Experience has shown that this is among the most difficult phases of a commissioning project, as it is the first real opportunity for the general contractor and the commissioning agent to verify that equipment is installed and functioning properly. It is essential that the commissioning agent work closely with the general contractor so the contractor understands the process; an owner must insist on team work and cooperation.
The construction phase is also the time to detect and correct the numerous minor defects that occur in the installation of equipment and systems, avoiding their cumulative effects — including major operational deficiencies — down the road. During the process of resolving these problems, the commissioning agent will report all deficiencies to the designated project contacts for the designer and contractor. Both the deficiencies and their resolution will become a part of the commissioning record. Finally, retesting will be scheduled, as required, to ensure that the corrected system meets the design intent.
In one case, an air-cooled chiller was tested and found to be out of compliance with contract documents. The commissioning agent identified and documented the following deficiencies and issues:
The commissioning agent required the following corrections to the chiller:
In another case, in a test of variable air volume (VAV) boxes in a laboratory under construction, the commissioning agent found that only about 70 percent of the design air flow was being delivered to an internal lab due to improper operation of a VAV box. It was estimated that the 30 percent reduction in air flow would result in a room temperature of 78 to 80 degrees. As a result, occupants would likely have complained about discomfort, and adjacent areas of the building would have been overcooled to draw heat out of the lab, wasting energy and driving up operating costs. The commissioning agent required corrective action, and the contractor was still on-site to fix the problem quickly.
These are typical of the kinds of issues found on almost every commissioning assignment, issues that will have an impact on system performance. An owner must determine if the resources are available to identify these issues without outside help.
Clearly, an owner benefits when the commissioning process is integrated into a project. Here are a few tips to get the most from an integrated commissioning approach.
Owners who make the investment in this approach reap significant benefits above and beyond direct energy savings. They discover problems early, assure project accountability, and have documented confirmation that building systems and equipment meet the design intent. They have the data they need as a performance baseline for building systems and a point of reference for future renovation and re-commissioning efforts. And they gain the full lifecycle value out of their capital investment in building equipment and systems.
Paul J. Liesman, CFM, is senior vice president of the facilities management division of Syska Hennessy Group in New York.