This paper described two new control strategies for controlling air economizers when mechanical cooling is required. Because the strategies calculate the coil load for the existing conditions and determine the outdoor air fraction that minimizes this load, they can be applied in any climate. Simulations were used to compare the new strategies with traditional differential dry-bulb tempera- ture control, differential enthalpy control, and the case where no economizer is used. Results of the simulations revealed the follow- ing key findings:
1. With ideal sensors and a perfect model of the coil, optimization- based control yields the lowest annual coil load in all 15 cities considered and, with the exception of the warm–dry climate, also yields the lowest peak coil load of the four economizer strategies considered.