A Simplified Method for Determining Optimal Cooling Control Strategies for Thermal Storage in Building Mass

Abstract

Previous simulations and experiments have shown that significant operating savings can be realized when cooling commercial buildings if the building structure is used for thermal storage. Research has also shown that the control strategy must be tailored to the application to achieve these savings while maintaining occupant comfort. Developing cooling control strategies which utilize the thermal mass of a building is a formidable optimization problem. By examining optimal cooling results covering a wide range of buildings, cooling plants, weather, utility rates, and internal gains, this study has reduced the dimensionality of the optimal control problem. Two simplified approaches were developed which each employ two control variables while the building is unoccupied, in conjunction with a set of rules for the occupied period. These rules were expressed in terms of occupant comfort. The simplified strategy achieved 95% and 97%, respectively, of the optimal savings relative to conventional control. Using hourly time-steps, the daily optimization problem was reduced from 24 to 2 variables. In addition to reducing the computational requirements required to study optimal control and develop building specific control strategies, these simplifications could be used in the development of an on-line controller.