system the system includes sensors for generating signals dependent upon the temperature and humidity of the outdoor air return air and discharge air a damper position controller for generating a damper position signal dependent upon these outputs and a control means for receiving said damper position signal for adjusting the position of the outdoor air damper at a position requiring the lowest total energy input into the system for establishing a desired set of conditions application_number US 53730174 A description in fig1 is shown a typical air conditioning system wherein outdoor air is drawn into the building through outdoor air damper 10 and is mixed with return air drawn through return air damper 12 from return air duct 11 the mixture of outdoor air and return air is then drawn through a filter 13 if the climate is one in which the cooling coil 14 is subject to freezing i e in northern climates a pre heat coil 15 is used to insure that the air passed to the cooling coil is above freezing in southern climates where there is little chance of freezing conditions there is little need for a pre heat coil and it can be eliminated from the system since a pre heat coil requires a certain amount of energy for its operation a system without a pre heat coil can function more efficiently and economically than a system having a pre heat coil the air is then cooled by cooling coil 14 and.