What Is An Economizer In HVAC?

An economizer is a component of a building’s cooling system that uses cool outdoor air to cool the building instead of operating the AC compressor. This is an add-on feature to the HVAC air handler that ultimately draws in outdoor air and mixes it with indoor return air.

HVAC Economizer Function

A controller in the economizer is used to measure the temperature and humidity of the outside air. When the temperature is favorable, the control switches the AC compressor off and cools the building using the outdoor air. The economizer cools the building while utilizing far less energy when compared to AC.

Economizers generally operate at night when the outdoor air cools down. The air is cooler than the indoor air in a process referred to as “free cooling”. Economizers will mix enough outdoor air into the indoor air to meet the thermostat setpoint without ever using the compressor.

Fresh outdoor air that economizers reel in while saving energy at night can count as ventilation. Therefore, the ventilation system can run for fewer hours and avoid operating during the peak electrical load times.

Economizers For Ventilation

Lots of buildings use economizers as their ventilation system. These components don’t normally have heat recovery or energy recovery function, so this type of ventilation system can have energy penalties compared to a heat recovery ventilator.

When buildings use an economizer for ventilation purposes, its dampers are open only a small amount while the HVAC system is heating, cooling, or solely operating the fan. The fan-only alternative is there when you desire ventilation but not cooling or heating.

To run efficiently, the economizer will require very sophisticated control tracking the amount of ventilation air delivered during the ventilation and free cooling mode.

Do Economizers Malfunction?

Unfortunately, economizers can waste a lot of energy if their dampers become stuck while open. Many economizers feature installation flaws causing them to under or over ventilate a building. There are a lot of energy savings available just from fixing these components and installing smarter controls.