HVAC Trials

Heating, ventilating and air-conditioning (HVAC) systems in new and renovated buildings have become increasingly complex. Hundreds of components are interrelated and often controlled by a central computer. And, like a chain with a broken link, if one part does not work correctly, it compromises the effectiveness of the whole system.

To make sure your HVAC chain has no weak links, consider testing it thoroughly with a process known as commissioning.

Commissioning puts all parts of an HVAC system through a trial run. It gives you assurance before occupying a building that everything is working. It saves energy, reduces complaints from building users, and often uncovers potentially dangerous mistakes and omissions-from duct smoke detectors that do not respond as they should, to fan motors that wear out too soon.

Going further Commissioning not only makes sure that each piece of equipment and each control operates properly, but also determines whether they operate in the right sequence with other components.

Compared with pre-occupancy inspections, commissioning is more thorough, detailed and focused. A pre-occupancy inspection is essentially a visual check of the building. The owner, designer and contractor walk through and note problems that must be corrected. Are any parts missing? Are equipment and controls where they should be? Are there any broken parts? The emphasis often is on meeting code requirements in time for occupancy.

Commissioning goes further. It puts the HVAC system through detailed operational tests. An independent agent, working for the owner, verifies that all components are working as designed and meeting manufacturer's specifications. The agent documents any problems, suggests who should correct them, and subsequently re-verifies to make certain that the corrections have been made. A pre-occupancy inspection might note that a missing thermostat should be installed, but in commissioning, the agent would make certain it was calibrated, that it was sending commands to the numerous other components in the right sequence, and that those components responded as they should.

Commissioning also is different from testing and balancing procedures, which measure air and water flow in HVAC systems. Balancing ensures that air and water are being distributed in the right amounts to various spaces, but it does not check the operation of each component.

Commissioning often is provided after a project is completed and before move-in, but it should begin during the design phase. That allows the commissioning agent to be a part of the team from the beginning.

Making a difference In commissioning, the HVAC system is put through a four-season "shakedown." Every part in the system is checked physically to make certain that it operates as indicated on drawings and in the sequence that is specified. If a project is completed in the summer, an owner does not have to wonder whether the heating system will perform properly when it is needed.

The specific tests performed depend on the project, but a key element is verifying proper operation among components and the controls that signal them to respond. For example, variable-air-volume boxes in ducts are checked to determine if they respond correctly to a command from a thermostat that calls for heat or cooling, and whether air flow for minimum and maximum settings is correct. Reheat coils in ducts are tested to see if they stage on and off as required. And, speed drives on supply- and exhaust-air fans are checked to determine if they adjust to varying air flows.

To check the smoke sensors in ducts, commissioning agents sometimes use smoke canisters to determine whether dampers in the ducts close to keep the smoke from being further dispersed, and whether alarms are signaling. The commissioning agent also ensures that outside air is being mixed properly with indoor air to freshen required spaces sufficiently and meet building codes.

Other components tested include air-handling units, condensing units, classroom unit ventilators, pumps, boilers, chillers, automatic valves, system alarms, heating coils, sawdust collectors in wood shops, laboratory hoods, ventilation systems in gyms and auditoriums, and computerized energy-management systems.

Problems uncovered The agent thoroughly documents the results of each test and generates an ongoing punch list. The larger and more complex the system, the more probable that the tests will uncover deficiencies.

In a smaller project, deficiencies are generally fewer, but it would be unusual to find none despite the best intentions of contractor and subcontractor. The systems and the interrelationships among components are just too complex.

When problems are found, the commissioning agent describes them specifically and suggests who should correct them. Once the flaws are corrected, the agent re-commissions the system or component to verify that the problem has been resolved. Sometimes the correction is as simple as connecting a loose wire, but the fix can be complicated.

Benefits outweigh costs The cost of commissioning is usually from 1 percent to 2.5 percent of the cost of the HVAC system, but owners often find that the benefits outweigh the costs. Without commissioning, major problems may go undetected. For example, in two recent school commissioning projects, more than half of the smoke detectors in ducts were deficient, and 60 percent were not calibrated correctly. Without commissioning, it would have been difficult to determine if the detectors were not functioning properly unless a fire occurred.

Many problems uncovered in commissioning affect energy consumption: thermostats do not operate correctly, exterior air dampers do not close properly, finned-tube radiation elements provide heat when they should not be, fans operate too long or run faster than they need to, or even run backwards.

With commissioning, energy savings can be significant, and equipment will last longer and perform better when calibrated as designed. And because the system has been fine-tuned and is running optimally, the building maintains good indoor air quality.

Bowdoin College, a 1,500-student liberal-arts school in Brunswick, Maine, is in the midst of a major building program, and commissioning HVAC systems has become an integral part of the process. While not every project is deemed large or complex enough to warrant commissioning, a line item for commissioning is part of the planning spreadsheet, and the benefits are always evaluated.

Deciding whether to commission is based on a review of the size and complexity of the basic building systems, as well as the need for specialty systems. For instance, exhaust hood systems in laboratories deal with hazardous materials and have an impact on other building systems. Bowdoin believes that there are too many opportunities for problems in such a system and that commissioning is to the college's advantage.

On some projects, Bowdoin involves a commissioning agent during the design phase, rather than waiting until construction is complete. This brings a second set of eyes to the project at a point when problems can be resolved economically and with the least impact to the project or its users. Experience has shown that adding a commissioning agent to the project team can help identify issues that have the potential to save a good portion of the commissioning fee.

Discovering and correcting problems prior to building occupancy is one of the major benefits for the college's facilities management department. Doing it right the first time means customer satisfaction, on-time and on-budget projects, and it enables department personnel to focus on future projects, rather than ones that are supposed to be completed. While the department has not put a figure on the actual energy dollar savings that commissioning brings, the process has assured the college that the equipment supplied is running at peak efficiency-and that saves money.

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