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Many building control systems offer facility executives the opportunity for free cooling – using the economizer cycle to bring in additional outside air rather than running the chillers. For that strategy to work, of course, the outside air has to be cool enough – typically in the mid 60s or below. When the outside air temperature falls below the low 50s, a facility may not need chillers at all.
The specific temperatures to be used for free cooling vary from building to building. One reason is that the needs of buildings are different, and so are their HVAC system designs. Another important reason has to do with outside humidity levels. Dryer air can be used at higher temperatures than air with more moisture in it.
But not all buildings that could run economizer cycles are getting the benefits of free cooling. It is possible that the controls aren’t correctly programmed. Or that dampers aren’t operating properly. It’s also possible that the temperature or humidity sensors are out of calibration. Those factors are all worth checking if the chiller is operating when the outside temperature is low enough for free cooling.