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Cooling of commercial buildings contributes significantly to the peak demand placed on an electrical utility grid. Time-of-use electricity rates encourage shifting of electrical loads to off-peak periods at night and weekends. Buildings can respond to these pricing signals by shifting cooling-related thermal loads either by precooling the building''s massive structure or by using active thermal energy storage systems such as ice storage. While these two thermal batteries have been engaged separately in the past, this paper investigates the merits of harnessing both storage media concurrently in the context of optimal control. The objective function is the total utility bill including the cost of heating and a time-of-use electricity rate without demand charges. The evaluation of the combined optimal control assumes perfect weather prediction and plant modeling, which justifies the application of a consecutive time block optimization that optimizes 24 hour horizons sequentially. The analysis shows that the combined utilization leads to cost savings that is significantly greater than either storage but less than the sum of the individual savings. The findings reveal that the cooling-related on-peak electrical demand of commercial buildings can be drastically reduced and justify the development of a predictive optimal controller that accounts for uncertainty in predicted variables and modeling mismatch in real time. [Copyright &y& Elsevier]

This numerical study evaluates and compares four different flexibility and storage options in building energy systems (batteries, fuel switch, water tanks, and thermal building mass) in terms of potential improvements in load scheduling and energy efficiency. Using a generic modern office building with concrete core conditioning as an example, two different supply concepts (one based on a heat pump, one based on a CHP unit) are considered. A novel hybrid control concept is applied which is designed to be compatible with state-of-the-art controllers implemented in the field. The results show that batteries are the most technically attractive options in terms of grid support, efficiency and ease of implementation. Fuel switch is comparably straightforward to implement, but provides significant benefits only for the considered CHP system. Water tanks with a capacity of about two full operation hours offer nearly the same flexibility as much larger tanks, but negatively influence the efficiency of heat pump systems. The thermal building mass can be used effectively and efficiently for thermal storage, particularly in the heating season, but this is technically challenging to realize. It is shown that current electricity prices do not offer sufficient variations to stimulate grid-supportive operation. [ABSTRACT FROM AUTHOR]

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 for a design day 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 set-point depression), depending on the utility rate structure, occupancy and on-peak period duration and onset, internal gains, building mass, occupancy period temperature set-point 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 may be developed in the future. [ABSTRACT FROM AUTHOR]