In order to avoid high utility demand charges from cooling during the summer and to level a building’s electrical demand-profile, precooling of the building’s massive structure can be applied to shift cooling-related thermal loads in response to utility pricing signals. Several previous simulation and experimental studies have shown that proper precooling can attain considerable reduction of operating cost in buildings. This paper systematically evaluates the merits of the passive building thermal capacitance to minimize energy cost using optimal control. The evaluation is conducted by means of a sensitivity analysis utilizing a dynamic building energy simulation program coupled to a popular technical computing environment. The optimal controller predicts the required extent of precooling (zone temperature setpoint depression) depending on utility rate structure, occupancy and on-peak period duration and onset, internal gains, building mass, occupancy period temperature setpoint range, and weather as characterized by diurnal temperature and relative humidity swings. In addition to quantifying the building response, energy consumption, and utility cost, this paper extracts the dominant features of the optimal precooling strategies for each of the investigated cases so that guidelines for near-optimal building thermal mass savings can be developed in the future. These will offer guidance to HVAC system operators and practitioners on how to adapt existing or design new building thermal mass control strategies in order to save operating cost or energy.

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