An economizer is a control strategy that uses outdoor air to help cool the building when outdoor conditions are favorable, reducing the energy needed from mechanical cooling. It achieves this by opening dampers to bring in outside air to mix with return air, so the chill of the outdoor air can offset some of the cooling load instead of relying entirely on the refrigerant-and-fan cycle. Outdoor air during cooling is beneficial when the outside air is cooler (and not excessively humid) than the indoor air, and when ventilation requirements allow bringing in that air without compromising comfort or IAQ. In that case, using outside air lowers the indoor cooling load and saves energy. If outside conditions are hot or humid, the economizer should close or limit outside air to avoid making cooling worse. Humidification, refrigerant-only cooling, or automatic thermostat setpoint control are not what an economizer does, which is why those options don’t fit.