Peak load reduction by preconditioning buildings at night

Cooling loads during the peak period can be reduced if a building is subcooled a few degrees below its normal thermostat set-point during the preceding night. During the day the thermostat must control the warm-up in such a way that the stored energy is released when it brings maximum benefit. This strategy exploits the heat capacity of the building itself; it can be implemented at low cost and without sacrifice of comfort. To evaluate the strategy for a given building and to control the thermostat, one needs to know the thermal behaviour of the building. Building temperature, internal load and solar data are used to determine a small number of thermal parameters which characterize the building. Several thermostat control strategies, distinguished by their knowledge of the building dynamics, are described and simulated, with a data-based dynamic model. Universal graphs for effective storage capacity and storage efficiency are developed. A simple economic analysis shows that subcooling is likely to be cost-effective for many commercial buildings, with current electric rate schedules.