By Lindsay Audin
HVAC Article Use Policy
What’s wrong with the system, HAL?” asked the astronaut in the film classic, 2001: A Space Odyssey. “I don’t know, Dave,” answered the computer. “But if we put it into operation and let it fail, the cause of the problem should then become obvious.”
Such is the way that many HVAC systems are treated: Let it run until it fails, and then try to figure out the problem. But when business, sales or employee time is lost, the cost is typically many times greater than the small expenses involved in proper maintenance. One facility executive drew this analogy: “If you hear a knocking sound in your car’s engine, do you wait for the engine to fail before having it examined by a qualified mechanic?”
HVAC complaints, mold, odors or high energy bills could be that knocking in the engine that needs attention before a system fails, creating greater inconvenience and higher cost than if earlier attention had been given to the problem.
One difficulty is that problems are not always obvious in their early stages. While water pouring out of a ceiling or an angry call from a sweating executive may draw immediate attention, not all problems occur so suddenly. Mold development, for example, may take an entire season to appear while increased absenteeism due to illness may not become obvious until an end-of-the-year productivity assessment. Some problems exist for years, but only become visible when triggered by an unusual condition, such as a cool but very humid summer.
During discussions with facility executives about ways to stay on top of potential HVAC problems, several requirements stood out:
In many cases, problems that could have been detected before they became costly instead continued, resulting in major damage. Had a few sensors been in place, or a space been “walked” while unoccupied, or maintenance steps been well documented, a small leak caused by a freeze-up could have been avoided before it turned into a small flood.
Tales told by facility executives illustrate problems and steps that could have been taken to avoid them.
While a college was on winter break and parts of the facility, including its cafeteria, were unoccupied, a control valve feeding a heating coil in a rooftop air handling unit failed during a sustained cold snap. The lack of water flow caused the heating coil to freeze and split. The cafeteria was empty, and no low-temperature alarms existed. Baseboard radiation was sufficient to maintain the internal room temperature so none of the cafeteria piping froze, but when the damaged coil thawed, water poured from it into the ducts serving the cafeteria. Because the problem was not found for several days, damage occurred to the space and ductwork.
The root cause of the problem was traced to poor installation or maintenance: The rooftop unit’s coils were insufficiently weatherized to avoid a freeze condition. Although the valve failure was the immediate cause of the problem, the same problem could have resulted from simply shutting down the system for an extended period during the winter.
Had a facility worker been walking the space daily during the winter break, water dripping from the ductwork and diffusers would likely have been seen less than 24 hours after it started. While not an ideal way to minimize damage, ongoing examination is a low-tech way to spot problems before they become unmanageable.
A better way to avoid such a situation would be temperature sensors feeding the building management system and software that issues alarms when out-of-spec room temperatures are detected. The failure of the heating coil caused the discharge temperature into the room to be far below specification, but no alarm was programmed to highlight that fact to the system operator.
Other control and system changes could also be employed to avoid such problems. Pursuing thorough documentation during commissioning should have revealed the lack of weatherization (i.e., injection of antifreeze) into the circulating water flowing through the hot water coil.
In another case, mold developed in a library because of insufficient humidity control during an unusually cool and moist summer. A mechanic had previously noticed a slightly musty odor but ignored it as simply the smell of old books. Several problems contributed to the condition:
The lack of tight humidity control of a library space, where rare books are often stored, was considered a design error that should have been caught prior to installation, but the presence of a new odor should have caused some investigation. The issue had not previously arisen because unusual weather conditions had not yet challenged the system.
In a third case, occupants had complained several times of a lack of cooling during very hot spells, but the problem re-occurred despite actions taken by several different controls mechanics. To respond to the complaints, the variable speed fan (VAV) control system had been shut off, resulting in full fan speed at all times. The systems operator had set the outside air damper to minimum flow year-round, and various other efforts had been made during several past summers. The result was higher energy costs while occupants continued to complain.
When the system was reviewed as part of an overall building recommissioning, it was found that some of the control panel wiring had been overridden inside control panels. No record had been made of this change so the condition was never corrected. Instead, simpler efforts that overrode other systems (e.g., VAV, economizer cycle) were implemented that merely created a new problem: higher energy bills.
Lack of documentation of the prior alterations was endemic at the facility; major improvements were made to work order tracking and logging.
As Ben Franklin said, “A little neglect may breed great mischief.” Small problems may escalate into big ones that cost a company its operating budget — or a facility executive his job. Some who would now do things differently offered the following advice.
Lindsay Audin is president of EnergyWiz, an energy consulting firm based in Croton, N.Y. He is a contributing editor for Building Operating Management.
In a category by itself — as both a source of problems and source of solutions — are the direct digital controls (DDC) that, at many facilities, have replaced pneumatic systems for actuating dampers, valves and other equipment. In many cases, DDC technology has challenged mechanics and even the engineers specifying it, resulting in problems much more technically sophisticated than the people directed to solve them.
An excellent review of the problems related to improper DDC implementation and ways to address them has been assembled by Gregory Churchill of the Oregon Department of Energy. Many Oregon schools with new DDC systems did not realize the expected energy savings often claimed by DDC vendors, and some were experiencing serious operating problems. The 12-page study provides many insights on dealing successfully with this technology.