Abstract: An air handling unit utilizing a humidifier in conjunction with a heat exchanger to provide a means for free cooling recirculating return air with evaporatively cooled outside air. A first air stream comprising outside air can be circulated through the evaporative humidifier and a first portion of the energy recovery heat exchanger, while a second air stream comprising recirculated inside air can be circulated through a second portion of the heat exchanger. The outside air will be humidified as it circulates through the humidifier, thereby cooling the outside air to its adiabatic saturation temperature. The heat exchanger will cool the recirculating inside air with the evaporatively cooled outside air.