The CT-DH-4P is designed to be used with CO2 equipment, dehumidifiers, and exhaust fans. While it is similar to the CT-DH-3 it has the added feature of offering independent outlets for temperature and humidity control. It is ideally suited for use with dehumidifiers. Temperature raise will activate the right hand outlets and deactivate the CO2 outlet. Humidity rise will activate the dehumidifying outlet. Internal sensors will allow a 7 temperature comfort zone and a 7% humidity (differential) between the time the equipment goes Off and comes back On again. Plug the controller into a power surge protector to protect your valuable equipment, and then plug the surge protector into a 110 wall outlet. Set the temperature and humidity to the desired settings. The CO2 outlet is normally in the On position and is able to activate CO2 equipment as needed, but is defeated when exhaust function is active. The photosensor will defeat CO2 enrichment during darkness hours.