Commissioning electrical and power systems

Essential/standby power equipment and system components are some of the most critical electrical systems to be commissioned in nonresidential buildings.

06/22/2014


Learning objectives

  • Know the codes and standards that govern commissioning of emergency power supply systems.

  • Understand the emergency power system classifications.

  • Know the documentation required throughout the commissioning process.


This article has been peer-reviewed.Commissioning is the bridge from the design phase through construction and into occupancy. Its purpose is to ensure that building mechanical and electrical systems operate as intended per the owner’s project requirements (OPR). As defined by ASHRAE Guideline 0-2013, the commissioning process is the owner’s “quality-oriented process for achieving, verifying, and documenting that the performance of buildings, systems, and assemblies meets defined objectives and criteria.” In electrical commissioning, the goal is primarily to confirm reliability. This is in contrast to LEED commissioning as defined by the U.S. Green Building Council (USGBC), which has been driven by, and has focused on, energy conservation.

One of the most critical electrical systems to be commissioned in nonresidential buildings is essential/standby power equipment and system components. Given their importance, the NFPA provides specific requirements in NFPA 70: National Electrical Code (NEC), 2013; NFPA 99: Health Care Facilities Code, 2013; and NFPA 110: Standard for Emergency and Standby Power Systems, 2013. (These editions of the associated codes and standards are referenced throughout this article unless otherwise noted).

With these requirements in mind, a standard commissioning process can be developed as outlined by ASHRAE Guideline 0-2013. This allows an owner to define activities and deliverables, such as design reviews, submittal reviews, prefunctional checklists, and functional performance test documents. These tools, along with site observations and owner training, give the owner a level of confidence that all components of the emergency power supply system (EPSS) operate as intended. NFPA 110 provides the defining requirements for these systems and holds the design engineer, installing contractor, and owner accountable for achieving a higher standard of product. At the end of construction, the enforcing agency, the authority having jurisdiction (AHJ), becomes the judge for verifying that the system is acceptable. From a commissioning perspective, the goal for an EPSS—and any electrical and power system—is to ensure that the owner receives an electrical system that meets the OPR for NFPA and passes acceptance by the AHJ.

Figure 1: “Level” classifies the operating status of an EPSS. Level 1, where equipment failure could result in loss of life, is the operating status for a hospital. Courtesy: Jerry ButtsWhat the code requires

One of the biggest coordination issues—comprehension of the code and the application for the EPSS—usually occurs in the design phase of a project. Despite the best intentions, field acceptance testing usually does not go as planned the first time. The EPSS, like many systems, evolves through programming and design via value engineering and cost estimating. The NEC outlines “the provisions [that] apply to the electrical safety of the installation, operation, and maintenance of emergency systems…to supply, distribute, and control electricity for illumination, power, or both, to required facilities when the normal electrical supply or system is interrupted.”

NFPA 99, NFPA 101, and NFPA 110 then form the baseline of the minimum requirements. The commissioning design review is a good time to look for references in the project specifications to these code standards and additional testing that would be recommended to meet the OPR. One classic example is properly defining the class, level, and type of the EPSS (see Figure 1). These tags are not always clearly defined in the project specifications (see Figure 2). There might be a reference in Part 1 (references and codes) and perhaps Part 2 (product data), but typically it is not as clear as: “The generator and EPS components shall be Class 2 (hr), Type 10 (sec), Level 2 (less critical to human safety).”

Figure 2: “Class” defines how long a generator should operate upon a loss of power before requiring to be refueled. “Type” defines how quickly the generator should start upon a loss of power. Courtesy: Dale PhotographicsIt would be great if the EPSS was defined that way, but through design reviews, a commissioning agent can ask those questions to get that level of detail. Those three tags help explain how a system is intended to be used (see “EPSS classifications”).

With this information, questions regarding fuel tank sizing, alarms, site placement, and routine maintenance can be discussed with the design team through the design reviews to ensure that the OPR is satisfied.

Much of the value of the commissioning process in the design phase is to ensure that the EPSS is properly specified for purchasing by the contractor. Sometimes components that are required to meet the standard Part 3 of the project specification (execution, installation, and testing) are not properly identified in Part 2. For example, many standard specifications require backpressure testing. This is a very valuable test for systems that have an EPSS located in a building that has a lengthy exhaust stack. A common problem is that this test is also specified for exterior installed generators that have a factory installed muffler and exhaust system. The engineer must evaluate the return on investment in requiring this test. Additionally, a testing port in the exhaust discharge close to the manifold must be installed at the factory to allow for the insertion of a water manometer, or gauge to measure inches of water (see Figure 3). Most generators do not include this test port unless it is requested.

Further, many design specifications use standard, but vague, testing language in Part 3 of technical specification sections such as, “Load test shall comply with requirements of NFPA 110.” While this reference is factually accurate, it does not clearly define coordination or specific requirements. This ambiguity places the burden on the installing contractor, who almost always puts the onus on the manufacturer of the emergency generator. NFPA 110, Chapter 7 addresses acceptance testing and load bank requirements for EPS systems. The commissioning agent will seek to eliminate such gaps of coordination in the project specification so that the roles and responsibilities are clearly defined and understood, specifically between trades and other vendors. This provides for more accurate costs, fewer rejected/commented submittals, and something to reference during the testing phase for conflict resolution.


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