I just read an article in November’s ASHRAE Journal on outdoor air economizers1. It was excellent. It was also above the heads of most non-engineers. In this blog post, I want to describe the basics of economizers, their impact on indoor air quality, and briefly touch on their operation and control.
Introducing outdoor air ventilation into an office, school or home is a good thing. The down side, people quickly point out, is the cost of conditioning that outdoor air. As I write this, the temperature in Chicago is 9° F (-13° C). Introducing 9° air gets expensive because of the energy required to heat it. At extreme temperatures, most buildings will opt for only bringing in the code-required minimum ventilation. What about on more mild days?
Buildings2 have the opportunity to introduce more fresh air when outdoor conditions are favorable. On warmer winter days, outdoor air can be used in excess of code minimums to provide cooling.3 On a pleasant 55° day, the scenario may be such that the building brings in 100% outdoor air, recirculating no air. Those are conditions where energy engineers and IAQ consultants sing Kumbaya together. Energy engineers love the free cooling, IAQ consultants love all the extra ventilation.
- “Economizer High Limit Controls and Why Enthalpy Economizers Don’t Work” by Steven Taylor and C. Hwakong Cheng [↩]
- Sorry most homes… you’re not bringing in outdoor air mechanically and can’t benefit from economizers. [↩]
- I know it sounds strange, but buildings are typically cooling the core in the winter. Lights, people, computers, elevators etc. give off a lot of heat [↩]