Economizer (Airside/Waterside Economizer)

An economizer is a cooling-system mode that uses outside air or water conditions directly, bypassing energy-intensive mechanical chillers whenever ambient temperature and humidity allow. Airside economizers pull in filtered outdoor air to cool the data hall directly; waterside economizers instead route the facility's chilled-water loop through outdoor cooling towers or dry coolers so the compressor-based chiller plant can throttle down or shut off. Economizer hours are climate-dependent — data centers in temperate or cold climates such as the Nordics or the US Pacific Northwest can run on economizer mode for 70-90% of the year, while hot, humid sites near the equator get very few usable hours — which is a major reason PUE varies so much by location. Economizer use is the single largest lever most operators have for cutting the cooling share of PUE without new hardware, and is standard practice in modern hyperscale and colocation designs alongside free cooling and adiabatic assist.