What is an “Economizer”?

Curious C: Hey, do you know what is “Economizer”?

Designer: An “Economizer” is essentially an added ventilation damper to a packaged rooftop unit (typically 3–25 tons). An economizer cycle uses cool outdoor air as the supply air to condition the indoors.

Curious C: Show me on the sketch.

Designer: An economizer cycle is often activated when the outdoor air is about 60 degrees Fahrenheit. When the outdoor air temperature is cooler than the preset temperature, then the controller will open the outdoor damper and let it mix with the supply air.

Curious C: How does it help with “indoor air quality”?

Designer: Because economizer controls and filters the outdoor air. It can be considered as a mechanical substitute for an open window. Therefore it improves indoor air quality.

Curious C: mm..

Designer: Economizers are typically installed in large-building central air supply systems. Buildings with high internal loads need cooling even during the colder seasons. An economizer cycle can save a significant amount of energy for commercial buildings with high internal loads and heat gain.

Curious C: What is “Internal load”?

Designer: “Internal loads” means the building energy is driven by high heat gain from occupants, lighting, or equipment. Those buildings are often offices, hospitals, retail stores, or laboratories.

Curious C: mm… Economizer is more complicated than I thought.

Designer: True. Economizer is not easy to understand. International Energy Conservation Code even has an entire section dedicated to properly utilizing “Economizer.” (Like that table, for example.)

Curious C: Thanks! I am still curious, but I will ask you next time.