Originally published in Interiors & Sources

06/06/2013

6 Economizer Must-Dos

A maintenance checklist for air-side units

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How often do you inspect your economizer?

It can be easy to put this equipment on the deferred maintenance list because it’s not always obvious if something is malfunctioning. But simply inspecting and testing the unit once or twice a year can save money and energy.

Check these six potential trouble spots to make sure your economizer is still working as hard as it can for your facility.

1) Check the Dampers
The dampers are a common source of economizer problems and can sometimes get stuck, leading the rest of your HVAC system to consume more energy trying to compensate. Your economizer maintenance should absolutely include a comprehensive visual inspection of all things damper-related to make sure the components are in working order.

“Maintenance on the dampers would consist of checking the operation of the actuator, which opens and closes the damper. Check the dampers’ adjustments to make sure they fully open and close,” recommends Wayne Drooks, senior associate and mechanical group leader for Integrated Design Group. “Also check for broken linkages between the actuators and the damper blades themselves – sometimes they fail. The blades can get jammed, either through debris that’s been pulled in or corrosion in certain environments.”

The seals at the ends of the blades should also be checked regularly because they wear out over time, Drooks adds.

“If you put off maintenance and the dampers don’t operate properly, you’ll lose the efficiency on your economizer and won’t realize the savings you should have,” Drooks says. “You’re basically throwing money out of the window.”

2) Calibrate Sensors
Your economizer’s sensors determine when the dampers should open or close and by how much, so it’s important to make sure they’re functioning correctly. A two-way radio and a coworker are needed to test the sensors, explains Dave Moser, senior engineer for PECI.

“One person is actually at the sensor with a handheld instrument to measure the value at the sensor, and the other person reads the value at the control system at the same time. If there’s a big difference, the sensor might need to be either calibrated or replaced,” Moser explains. “Some facilities can tolerate larger differences in the values, but mission critical and high-tech facilities have tighter tolerances for their sensors.”

Also pay attention to the physical location of the sensors, Drooks recommends. This can affect their accuracy.

“Not only do they need to be recalibrated, but proper location of the sensors is important,” Drooks says. “Sometimes they’re just not put in the right place or the outside air temperature sensor might be in the sun, a shaded location, or an exhaust outlet from the building where it wouldn’t read the right temperature.”

3) Test Controls and Sequences
Next, ensure that the control sequence is working properly and adjust the setpoints to achieve the most efficient operation. It helps to have a second person help out with this task as well, Drooks explains.

“If the control system is commanding the dampers to open or close, your system at the workstation may be telling you they’re open or closed, but you don’t actually know until someone goes and watches it,” Drooks explains. “Also, look at what’s going on in your building when you adjust the operating setpoints. Can you raise that return air temperature a little bit and get more hours of cooling?”

Why Economizers Fail and Increase Energy Use

  • Jammed or frozen outdoor air damper
  • Broken or disconnected linkage
  • Nonfunctioning actuator or disconnected wire
  • Malfunctioning outdoor air or return air temperature sensor
  • Malfunctioning controller
  • Faulty control settings
  • Installed or wired incorrectly
This strategy is most valuable in data centers, Drooks says. The type of space served by the economizer will tell you how far you can expand the allowable temperature range.

“In an office space, the return air would be around 80 degrees F. because you’re trying to keep the space at 70,” Drooks explains. “In a computer room or data center, you could have the return air temperature run up to 90 to 95 degrees F., where it’s at least giving you some partial cooling. You can increase the number of hours per year that the economizer operates, and ultimately you’re saving money by expanding your acceptable conditions.”

This part of the inspection should also include a brief check to make sure no one has overridden the damper controls, Drooks adds.

“One big thing that happens in a lot of buildings is that the operators disable the outside air dampers closed because it’s cheaper to run the units on full air recirculation than outside air,” he says. “That only requires a simple inspection.”


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