A direct evaporative air handler for providing supply air to humidify and cool an enclosed space such as a data center. The air handler includes an evaporative cooler and a return air port that is positioned upstream of the evaporative cooler to allow recirculated air from the enclosed space to pass through the evaporative cooler. The air handler includes an additional return air port that is positioned downstream of the evaporative cooler to allow recirculated air from the enclosed space to bypass the evaporative cooler. The air handler includes an outdoor air port that is positioned upstream of the evaporative cooler to allow outdoor air to pass through the evaporative cooler and further includes an outdoor air bypass port that allows outdoor air to enter the air handler without passing through the evaporative cooler. The temperature and humidity of the supply air can be controlled under various ambient conditions by controlling the amount of air that enters the air handler through each port.