HVAC: The Energy-Maintenance Connection
By Chuck Dale-Derks, P.E. - November 2006 - HVAC
In institutional and commercial facilities these days, financial considerations can greatly affect day-to-day maintenance and engineering activity, but the dynamic can work the other way, too. For managers looking to contribute to the financial health of an organization, the name of the game is cutting energy use, a strategy that also can lead to lower operating costs.
A closer look at the strategies, tactics and decisions affecting the maintenance of HVAC systems can reveal numerous opportunities for managers to deliver both of these benefits, and more, to their organizations.
Pinpointing Energy Use
Tracking energy-use trends is an essential process, but comparing use from year to year can be tricky because managers must adjust a large portion of energy use to the actual weather profile or degree-day. Baseline energy use does not follow the outdoor weather condition and is not always easy to separate from the variable of weather.
For these reasons, managers need to review and use every available resource regularly to determine its applicability to a particular facility or organization.
Some managers today still seem to make decisions based on the old adage, “If it’s not broke, don’t fix it.” But a growing number have tapped into more modern concepts and practices related to maintenance, including reliability-centered maintenance, facility condition assessments, and predictive and preventive maintenance.
In seeking to identify the right tools to attain peak performance for HVAC systems, managers are finding that the rules of the energy game have changed. For example, electric utilities in the Midwest are advertising a coming rate hike, while natural gas prices are expected to decline this winter. In addition to energy rate structures and changes, many hospitals, school districts, and universities regularly change the size and location of operations within their facilities.
In an effort to match the most effective and efficient HVAC equipment to these changing conditions, managers often tamper with such variables as airflow, air temperature, pump speed, fan speed, evaporator temperature and condenser-water temperature. Finding the right combination can be a daunting task.
From Large to Small
The best strategy for achieving this goal is to start with largest factors and work down to the small ones. In schools or office buildings, the biggest factor is the schedule.
The largest component of energy use in most parts of the county is conditioning the ventilation air, and the easiest way to reduce the associated cost is to reduce the ventilation rate. There is no need to ventilate a building for 600 students when the students are not present or when only 30 teachers are present.
Managers can cut the ventilation operating costs by closely scrutinizing the operating schedules. Control systems will reduce ventilation rates during unoccupied periods by allowing variable air volume boxes to modulate fully closed in lieu of their minimum occupied setting or switch constant-volume heat pumps from fan “on” to modulating “on” only when needed. Technicians also should closely review last year’s schedule to see if it is adequate for this year’s operations.
Another energy-saving measure is to maintain enough ventilation air to keep the building pressurized, while at the same time reviewing exhaust fans and the areas they serve. Some fans might operate manually and therefore can’t be controlled by the building automation system. Some might serve chemical-storage areas that should not be turned off for safety reasons. Most fans, however, can be turned off during an occupied period with no negative effect on operations or occupants.
Lighting controls also offer energy-savings opportunities. For example, do all lights need to be on for workers to empty trash containers and sweep floors? Consider adding automated controls where they make sense. Even if a facility operates 24/7, some areas or even entire systems do not need to operate around the clock.
Reviewing the cycles of operation and automated control-loop tuning also can yield energy savings. Are chillers or refrigerant compressors cycling on and off as quickly as the time delays will allow? Are boilers cycling on and off and wasting valuable heat as they operate through a purge cycle?
By trending system operations and reviewing these trends closely, managers can identify energy waste, or at least the major contributors to energy use. When reviewing a trend, managers should consider the sample rate of the trend. A sample rate of once per hour might not reveal equipment that cycles on six times per hour.
One control representative has developed a system of providing three trends for a number of points — one with a sample rate every hour, one every 10 minutes, and the third every minute — to capture a special event or conditions as they were immediately before a failure. In an alarm condition, the trend might be stopped or the data copied for later review.
Reviewing these trends for seasonal changes or errors in control-loop tuning also can help managers identify components or operations that require adjustment. Control-loop tuning requires reviewing conditions that often are not part of the control loop itself.
Finally, the energy-use points to consider beyond the control system and schedule become more specific to equipment. Watching temperatures where energy exchanges occur — such as chillers, boilers, cooling towers, and heat exchangers — is important to detect and monitor slowly degrading operating conditions.
Filters also can significantly affect operating performance and operating costs. These operations and components must become part of regular maintenance plan and must be considered for continuous improvement.
The stakes can be high for managers and their departments when it comes performing their duties up to expectations. Shareholders of a major oil company, for example, recently filed a lawsuit charging breach of duty against its executives for not ensuring the proper maintenance and repair processes of equipment.
As the business environment becomes more litigious, managers in all types of facilities can expect to see major overhauls in legislation and, in some cases, new requirements and responsibilities added to their job description.
A thorough, ongoing review of maintenance and operation procedures for HVAC systems, with a special emphasis on detecting energy waste, is an important step in meeting the expectations of facilities executives and other interested parties.
Chuck Dale-Derks is a principal at McClure Engineering Associates in St. Louis. The majority of his work involves the design of education projects with tight budgets and short schedules.
Standard Update: HVAC Maintenance
Managers soon might have a new standard to guide them in implementing and upgrading HVAC maintenance programs.
— Chuck Dale-Derks
Spotlight: ENERGY STAR®
ENERGY STAR® is a joint program of the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy designed to help individuals and businesses save money and protect the environment through energy-efficiency. The EPA provides an energy-performance rating system that businesses already have used for more than 26,000 buildings across the country.