Economizers

If you are responsible for a cooling system that has a capacity of 7.5 tons or more, you probably have an air-side economizer—and chances are it could use some attention.

When the outdoor temperature and humidity are mild, economizers save energy by cooling buildings with outside air rather than using refrigeration equipment to cool recirculated air (Figure 1). A properly operating economizer can cut energy costs by as much as 10 percent of a building’s total energy consumption (up to 20 percent in mild coastal climates), depending mostly on local climate and internal cooling loads.

Figure 1: The components of an economizer
An economizer is collection of dampers, sensors, actuators, and logic devices that work together to decide how much outside air to bring into a building.

So economizers are designed to save energy, and that’s good. The bad news is that probably about half of all newly installed economizers don’t work properly, and their problems increase as they age. To make matters worse, there’s a good chance that malfunctioning economizers waste much more energy than they were intended to save. If an economizer (which is actually a temperamental collection of parts including dampers, sensors, actuators, controls, and linkages) breaks down when its damper is in a fairly wide-open position, peak loads shoot up as cooling or heating systems try to condition the excess air entering the building. A computer simulation of an office building in arid Phoenix, Arizona, shows that a damper permanently stuck in the wide-open position could add as much as 80 percent to that building’s summer peak load—that is, assuming the building had enough cooling capacity to condition the excessive outside air.

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Content last reviewed: 
09/15/2014