Critical medical and industrial applications sometimes require 100% outdoor air (OA) units. Because of the large quantity of air that needs to be conditioned, these OA units consume a great deal of energy. To save energy, one approach is to lower the air supply temperature. Using cold air supply on mixed air systems decreases the quantity of air handled and, hence, the fan energy required. However, a designer faces a dilemma when trying to apply the same approach to 100% OA systems.