Trade-Off Between Energy Consumption and Utility Cost in the Optimal Control of Active and Passive Building Thermal Storage Inventory

In contrast to building energy conversion equipment, less improvement has been achieved in thermal energy distribution, storage and control systems in terms of energy efficiency and peak load reduction potential. Cooling of commercial buildings contributes significantly to the peak demand placed on an electrical utility grid. Time-of-use electricity rates are designed to 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 (passive storage) or by using active thermal energy storage systems such as ice storage. Recent theoretical and experimental work showed that the simultaneous utilization of active and passive building thermal storage inventory can save significant amounts of utility costs to the building operator, yet in many cases at the expense of increased electrical energy consumption. This article investigates an approach to ensure that a commercial building utilizing both thermal batteries does not incur excessive energy consumption. The model-based predictive building controller is modified to trade off energy cost against energy consumption. This work shows that buildings can be operated in a demand-responsive fashion to substantially reduce utility costs, however, at the expense of increased energy consumption. Placing a greater emphasis on energy consumption led to a reduction in the savings potential. In the limiting case of energy-optimal control, the reference control was replicated, i.e., if only energy consumption is of concern, neither active nor passive building thermal storage should be utilized. On the other hand, cost-optimal control suggests strongly utilizing both thermal storage inventories.