Little by little, whether by dirt, leak or vibration, misalignment, miscalculation, or misfire, a poorly maintained HVAC system will erode an energy management program as surely as moisture corrodes metal.
These days, building owners and operators are inundated with literature on the subject of energy management. They’re advised to appoint an energy coordinator, perform an energy survey, analyze the results, set goals, devise an energy management plan and – of course – implement it.
They also may be advised to devise a maintenance plan for HVAC and other energy-related systems, though reductions in energy consumption are usually a secondary consideration. More frequently, the primary objective is to prevent equipment failure.
Resulting initiatives run the gamut from reactive to preventive to predictive maintenance. The outcomes are predictably scattershot.
Government and industry interests have begun to take notice, albeit with similarly mixed results. Although the U.S. Department of Energy’s Federal Energy Management Program requires federal operators to implement an energy-oriented operations and maintenance (O&M) plan, it only addresses the issue of HVAC maintenance in general terms, as does the USGBC’s LEED for Existing Buildings: Operations and Maintenance.
The most comprehensive document to date may be ANSI/ASHRAE/ACCA Standard 180-2008, Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems, the first standard to address "inconsistent practices for inspecting and maintaining HVAC systems – practices ranging from rigorous maintenance to run-to-failure policies."
Its title is misleading – the standard also addresses institutional buildings – but the point is clear. "Consistent maintenance ensures energy efficiency remains at design levels," says Robert Baker, owner of Riverview, FL-based BBJ Environmental Solutions and chair of the committee that wrote 180-2008. "When maintenance is neglected, energy costs rise and shelf life drops."
Baker acknowledges that the standard marks a departure for ASHRAE, whose purview typically is limited to design issues. It’s new mantra, "Maintain to Sustain," is not only the result of increasing litigation involving HVAC failures, but recognition that designers should support the maintenance of their systems for environmental reasons.
The standard, which California’s Department of Energy has incorporated into its codes, is particularly useful for developing an energy-oriented inspection and maintenance program. Among other activities, it advises owners to:
- Quantify goals for energy and equipment performance.
- Take inventory of system components, identify performance parameters for each, and devise an inspection and maintenance schedule.
- Calculate the time and manpower required to implement the program.
- Revise inspection and maintenance frequencies as conditions warrant.
- Verify that inspection and maintenance have been performed and that performance objectives have been met.
The standard also contains maintenance schedules for "the 100 items most likely to negatively impact energy efficiency, indoor air quality, and thermal comfort as a result of neglect," says Baker.
The standard recognizes that requirements can vary widely depending on the building, the nature of its occupancy, and the condition of its mechanical equipment. "This isn’t a cutting-edge standard," Baker says. "It sets the bar at the lowest acceptable level for commercial buildings."
Predictive Maintenance and Beyond
Predictive maintenance purports to raise the bar by continuously measuring key performance indicators, allowing operators to identify problems before equipment or energy efficiency is compromised.
The most common energy-oriented predictive methods are vibration analysis and oil analysis, the former to evaluate compressors, the latter chillers. Vibration analysis collects structural vibration data from the compressor and compares it to specifications in order to identify unwanted deviations. Oil analysis identifies particulate contamination and equipment wear.
Less frequently, predictive technologies are employed to identify conditions that result in bearing and motor failures.
The technologies, which deploy both hardware and software, don’t come cheaply. Recent estimates by the U.S. Department of Energy indicate costs for predictive gear may exceed $50,000. Likewise, employee training requires "considerable funding."
Greg Hughel, mechanical engineer with Facility Engineering Associates, a Fairfax, VA-based facility management consultant, says he isn’t convinced predictive maintenance yields better results than the kind of preventive maintenance program outlined in the ASHRAE standard. "Frankly, if an operator finds he isn’t having success with preventive maintenance, I’d question whether he’d fare
better with predictive maintenance."
Nevertheless, studies indicate that predictive maintenance can yield savings 8 to 12 percent greater than programs that don’t. Assuming capital isn’t readily available, operators may wish to contract with a service provider. Increasingly, suppliers provide a full suite of predictive maintenance services, from vibration analysis and eddy current testing to chiller tube and chemical analysis. They also maintain the resulting data on a server.
A relatively new approach known as reliability-centered maintenance (RCM) recognizes that some components are more critical to operations than others and allocates resources accordingly, with inspections and repairs focusing on dominant causes of failure. Ostensibly intended for operations with limited resources, RCM allocates few, if any, resources to non-critical components. Nonetheless, the approach relies extensively on predictive maintenance, making it a potentially costly proposition.
While recognizing the importance of system-critical components, San Francisco-based utility Pacific Gas and Electric (PG&E), author of Energy-Efficient Operations and Management Strategies for Packaged HVAC Systems, urges operators to likewise focus on components with the greatest energy-savings potential, notably condenser coils, evaporator coils and controls.
Hughel cites many of the same items, noting they tend to fall prey to predictable problems.
With evaporator coils, the primary culprit is dirt, which hampers air flow and heat transfer. Good filtration minimizes the problem, and coils should be inspected once a year to ensure filters are performing as intended. Filters should be replaced on a quarterly basis, says Hughel.
Dirt also is the enemy of condenser coils, and a very persistent one, since the coils are continually exposed to unfiltered outdoor air. Although they require more frequent cleaning – up to twice a year – energy savings can be dramatic, given that a dirty coil can cut cooling capacity by 7 percent and increase power consumption by 10 percent – a net efficiency reduction of 16 percent, according to PG&E.
Continual exposure to dirty air likewise sullies dampers, including their pivot points and sensors. Once stuck, dampers deprive buildings of free cooling when closed, or subject cooling coils to excess hot air when open. Consequently, cleaning and lubrication are critical. "Impaired dampers and sensors can be particularly costly," says Bill Holloway, an instructor at PG&E’s Energy Training Center in Stockton, CA. "We’ve seen dampers stuck wide open in the winter and wide shut in the summer."
"In older systems, controls should be inspected on a quarterly basis," Hughel says. "Annual or semi-annual inspections usually are adequate for new systems.
"Think of maintenance as a seasonal activity – heaters in the fall, chillers and cooling towers in the spring," Hughel advises. "Motors and bearings should be lubricated seasonally. Belts should be checked for tension and alignment."
In House or Outsource?
PG&E indicates that in-house maintenance is cost efficient for facilities with 200,000 square feet or more. This size is typically sufficient to keep two employees fully occupied, assuming that they are trained and equipped to perform an array of tasks, from scheduled maintenance and record keeping to troubleshooting and repairs.
"So much depends on the experience of the facilities management staff," says Holloway. "I wouldn’t advise assigning major maintenance tasks to someone who isn’t well versed in HVAC."
As they pare overhead and focus on their core businesses, more and more building owners are opting for contract services. As PG&E notes, contracts assume numerous forms, usually some combination of a fixed fee for routine inspection and maintenance, and time- and material-based fees for additional services.
Some services are surprisingly inexpensive. According to PG&E, a basic maintenance contract for a 10-ton rooftop unit costs about $150 per year if the unit is 3 to 6 years old, in reasonable condition, and easy to access.
Nevertheless, the costs associated with executing a maintenance program inevitably add up. "Garnering support to perform these tasks before something fails is a very steep climb indeed," says Holloway.
As always, buy-in for effective maintenance must first be sold to management.
John Gregerson is a contributing editor writing from Chicago.