Commissioning commercial buildings: HVAC
Ideally, all nonresidential buildings would be commissioned, and the team would start at the onset of the project. Because that’s not always the case, commissioning authorities and experts offer advice HVAC systems in various stages of commissioning, recommissioning, or retro-commissioning.
Mark A. Gelfo, PE, LEED Fellow, GGP, CxA, EMP, Principal/Vice President, TLC Engineering for Architecture, Jacksonville, Fla.
James I. Givens, CxA, EMP, Division Manager, Field Services, RMF Engineering Inc., Baltimore
Jim Huber, CEM, CDSM, CMVP, LEED AP, NEBB CP, President, Complete Commissioning, Annapolis, Md.
Brian Lindstrom, PE, DCEP, National Director of Commissioning, Burns & McDonnell, Kansas City, Mo.
Paul Meyer, PE, CBCP, LEED AP, CEM, GBE, Senior Vice President, WSP, New York City
CSE: What unique HVAC requirements do commissioning projects have that you wouldn’t encounter in other engineering disciplines?
Meyer: The apparent responsibility the CxA has for delivering working systems with no control over the subcontractors and construction managers. The deficiencies go unanswered and the owner wonders why the CxA didn’t make someone fix it while we have absolutely no managerial control.
Huber: The level of expertise of the installing contractors can vary much more with the HVAC than many of the other disciplines.
CSE: What changes in fans, variable frequency drives (VFDs), and other related equipment have you experienced?
Givens: We have seen an increase in recent years in the application of fan-array techniques—employing the use of multiple smaller fans, often accompanied by multiple VFDs, to deliver air quantities traditionally served by a single, large fan. While design selections and manufacturers have adopted this trend in the interest of increased efficiency and claimed reductions in maintenance costs, it has added levels of complexity to system controls and operating sequences that previously did not exist. Commissioning providers must be able to readily recognize such changes to shepherd the application of this technology through various facility types.
Lindstrom: VFDs are now being used to submeter the energy use of fans and pumps. They are also increasingly being controlled via a single data-communication cable tied directly to the BAS in lieu of separate input/output wires and relays for each control point.
Huber: The use of fan walls has become much more prevalent, as has the speed of many direct-drive fans. It is not uncommon for us to see fans operate at 80 Hz to 90 Hz these days—especially on some of our specialized projects.
CSE: What indoor air quality (IAQ) or indoor environmental quality (IEQ) challenges have you recently overcome? Describe the project, and how you solved the problem.
Meyer: Existing-building commissioning revealed pneumatically controlled variable air volume (VAV) boxes had broken thermostats, their air lines were leaking, the outside air dampers were not functioning, the fan VFDs were in hand mode and not automatic, and the static-pressure sensors were out of calibration. After documenting each issue, we went back to the owner and described the cause and effect of each deficiency as well as explaining the situation with the indoor air quality in the building based on the lack of functionality of the system. Once we stressed the issues with the client and explained the ramifications of their actions, the client stepped up to the plate and made an effort to rectify each deficiency. As this repair process started, not only did the building comfort and environment get better, but the client’s monthly energy and operating costs decreased.
Huber: The most common IAQ issues we come across are usually related to improper building pressurization. In some cases, this is an architectural issue; in many other cases, it is a simple matter or correcting the building operation and HVAC balance. Too many building operators and service contractors see outside air as a necessary “evil,” instead of realizing that the air is going to enter the building one way or another—the question is whether it will be filtered and conditioned before it enters the building.
Lindstrom: During integrated systems testing of a mega-scale, multistory, federal facility that was designed with specialized ventilation to accommodate response to an Anthrax attack, we observed excessive infiltration issues during normal operating scenarios. A high degree of uncontrolled dust and humidity was being introduced into the building and exterior doors were not opening properly. Troubleshooting involved reverifying functional tests and sensor calibration of the outdoor air and building-space pressure controls. After trial and error, we determined that, although all the systems were working as intended and verified to be properly calibrated, the outdoor ambient pressure sensor was located close enough to an exhaust fan that it provided an incorrect reference to the actual outdoor pressure. Once the sensor was relocated the issue was resolved.
CSE: Have you commissioned more alternative HVAC systems recently? This may include displacement ventilation, underfloor air distribution, variable refrigerant flow (VRF) systems, chilled beams, etc.
Meyer: We have commissioned many of these systems; displacement ventilation, underfloor air distribution, VRF systems, chilled beams. These systems are becoming more of the norm.
Huber: We’ve done all of the above, especially VRF.
Lindstrom: Yes, underfloor air distribution, VRF, and chilled beam.
CSE: Describe a challenging building envelope project you recently commissioned.
Meyer: One of our recent enclosure commissioning projects offered a great deal of challenges with the variety of vertical façade systems, the interface conditions, design choices made for the cavity walls that had an unconventional sheathing, and insulation selection that created challenges with water-tightness detailing. This, combined with the limited number of enclosure visits the owner had scheduled for the overall project, created issues that we managed by picking key time frames on the schedule to field-review as many enclosure systems being installed at one time. The field reviews were coupled with functional performance testing of air- and water-infiltration resistance to maximize the value brought to the project. Our field reports were also set up to better facilitate the issues log and speed up the process of resolution by the contractor. As part of our reporting, we met with the waterproofing trades to discuss the challenges and proposed resolutions so we could provide the owner with better guidance on proposed solutions.
Givens: Though not a building envelope-focused commissioning project, we recently provided MEP-commissioning services within a laboratory facility and, as a result, highlighted the need for existing building envelope deficiencies to be addressed. While commissioning various biosafety-level laboratories and associated research support spaces, zone-pressurization tolerances were initially unable to be achieved and maintained. This adversely affected the functional testing process, which precluded the accreditation of the laboratory facility, and ultimately the acceptance and use of the laboratories (so as not to jeopardize the safety of the researchers). Through our commissioning testing efforts, as well as supplementary architectural investigations and recommendations, the need for a building-envelope-remediation project was identified to facilitate the functionality of the laboratory spaces and realize the design intent of the facility.
Huber: Building envelopes are not too challenging on new construction as long as you perform the site inspections early and often. On retro-commissioning projects, the enclosure can be more difficult to commission because you don’t have the same level of access. We recently had a restaurant project where the enclosure was 30 yr old and the interior finishes were very expensive. The owner first tried to correct the enclosure from the outside by sealing the precast, but ultimately the finishes needed to be removed at considerable expense. Once the enclosure and walls were corrected, the heating requirements for the requirement were reduced by 60%.