Commissioning best practices for building performance
There are several commissioning (Cx) certification groups, each expressing various procedures, and most of them generally comply with ASHRAE Guideline 0, The Commissioning Process. One organization, the National Environmental Balancing Bureau (NEBB), has taken a closer look at its procedures to see what can be changed or modified to provide better results for Cx that is being requested by building owners. NEBB has branded this new process “Technical Commissioning,” and it was developed by adopting the best Cx practices from several national Cx providers who have demonstrated a high level of customer satisfaction.
Best practice for HVAC systems requires promoting the following Cx activities as the most important to building performance. Other commissioned systems such as electrical, lighting, fire alarm, fire protection, security, plumbing, and building envelope benefit from the Technical Commissioning best practice process in similar ways depending upon the owner’s desires.
1. Owner’s project requirements (OPR): The OPR is very important to the project’s success; the more an owner tells the design and construction team what he wants, the better equipped they will be to deliver it. Best practice for Cx projects is to have the commissioning authority (CxA) provide a template that simplifies the task of generating an effective.
2. Design review. What a Cx-focused design review is and what it is supposed to accomplish are often misunderstood. First, it is not a peer review of the design but rather a design review of the basic design for functionality, maintainability, and best industry practice. Typical issues to look for are:
- Outside airflow for proper building pressurization (most designers do not allow sufficient outside air to overcome air barrier leakage)
- System effect issues with duct and pipe layout
- Duct and pipe design for lowest practical operating pressure (lowest pressure means best energy efficiency and lowest noise)
- Drawing details for reduced pressure taps, condensate drain traps, maintenance access, and balance test points
- Verification of system diversity for each system
- Verification of exhaust fans’ capacity to overcome duct leakage (fans are sometimes undersized due to the effect of duct leakage requiring more capacity)
- General air diffusion layout for maximum performance (return grilles at exterior walls and windows)
- General coordination between disciplines: electrical, structural, and architectural
- Equipment access and air clearances.
3. Inspection testing scripts. Instead of spending time creating contractor completed checklists that provide little value to either the contractor or to the project, best practice would be for the CxA to complete the inspections and check sheets himself or add them to the test and balance (TAB) as a part of his report. These scripts outline the basic test design and the data to be recorded to prove performance. Once testing is complete, the test script, its data, and data trends become the record of the test performance.
4. Sequences of operations workshops. One of the biggest problems with HVAC control systems is a lack of understanding between the control contractor, the engineer, and the building operator as to the details of the sequences of operations. Best practice is to put all parties in the same room and go through each sequence in detail, making sure that all parties agree upon the sequence and setpoints to be used. The “KISS” principle also applies to control sequences and, if possible, it is always best to use standard sequences that are preprogrammed by the control manufacturer. It is important to complete this review prior to implementing the control programming and certainly before field testing the control systems.
5. Cx coordination meetings. A regular meeting with all the contractors is important for the CxA to keep on top of all project activities. Best practice suggests that these meetings start at about 50% rough-in and increase from monthly to twice monthly and then to weekly at the final testing stage. The frequency of Cx meetings will vary depending upon the complexity of the systems being commissioned.
6. Expert site inspections. The Cx team member performing the site inspection must be an expert in construction, prefunctional testing, and functional testing of the systems; otherwise, he will miss important installation features that may affect functional performance. If the first-party validation method of process Cx is used, the HVAC contractor will normally miss system effect issues or low pressure fitting requirements. Best practice requires using expert CxA and inspectors.
7. Control installation testing. Best practice requires that the CxA and control contractor perform a complete Cx point-to-point and sensor calibration test of all control system components. As with Murphy’s Law, the one point not checked will be the one that is problematic. Functional testing cannot be performed with a control system that has incorrect polarity, uncalibrated sensors, or incorrectly connected points. Best practice requires a separate point-to-point test by the CxA.
8. TAB verification. Most Cx standards require a certain percentage of readings to be repeated to verify accuracy of a TAB report. Best practice calls for a CxA who is highly familiar with TAB to review the balance process with the TAB contractor, review his issue log, and retest several important readings, such as box calibration flow settings, outside airflows, and AHU mixed-air chamber pressure setup. The CxA should spend enough time with the TAB contractor to feel confident that the contractor has done his job correctly.
9. Functional performance testing. Functional testing and integrated system testing separate the professional CxA from the “wanna-be” CxA. The CxA must design the functional tests to put the system through all phases of operation, including emergency operation. Best practice dictates that the CxA be on-site and supervise the contractor in the execution of the functional tests. This allows the CxA to determine if test designs are adequate for the system being tested and to see issues firsthand. This process requires additional time, but successful functional testing is critical to building performance.
10. System troubleshooting and issue log. It is surprising something as simple as an issue log can complicate getting a CxA’s questions answered. Contractors often respond to issues by saying they will fix that later, or it’s not their problem, or that’s the way it was designed—these are, of course, not the correct answers. Best practice requires the CxA to actively manage the issue log and solutions by directing issues to the correct team member, such as the engineer, contractor, or owner. Often a question must be asked more than once, explaining why the previous answer will not solve the owner’s problem. If an issue resolution is not obvious, the CxA will assist the design and construction teams in discovering the underlying problem and its solution.
11. Operations assistance. Assisting the building operations and maintenance (O&M) staff in taking over control of the technical systems is not normally a part of the Cx scope, but it should be. Best practice would allow the CxA to transfer all knowledge he has gained during the construction of the technical systems to the O&M team. This process should happen over the first two or three months of operation and involves the CxA to meeting with, answering questions of, coaching, and training the O&M staff weekly for the first month, twice per month the second month, and once at the end of the third month. The level of effort for operations assistance varies depending upon the complexity of the systems.
12. Final performance verification. As with O&M assistance, performance verification is not normally a part of the Cx scope, but it should be. The purpose of Cx a building is to improve its performance, but if we do not measure and track its performance, we will never know what level of performance was achieved. Best practice dictates that the CxA track and report the performance of the building for the first year of operation. For this to be effective, the project must be designed, constructed, and commissioned with performance verification in mind. This does not mean you have to build a simulation model to predict future performance of the building; it means the CxA should make sure he has the required measurement points and measures actual performance over time. One guide for these measurements is the ASHRAE SP-132 Performance Metrics Protocols – Best Practices Guide.
Jim Bochat, president of Commissioning Concepts, has been involved in the Arizona engineering and construction industry for more than 40 years. His experience includes mechanical design, mechanical construction, controls, test and balance, commissioning, and retro-commissioning. He is also a past president of NEBB, former Commissioning Committee Chair, ASHRAE PMP BP Committee Chair, and continues to teach the NEBB Commissioning Certification Seminars.