Near-optimal transition between temperature setpoints for peak load reduction in small buildings

This paper addresses the problem of the transition between two constant temperature setpoints in small buildings. The proposed method consists of finding a trajectory resulting in significant reduction in the peak thermal load during the transition period. This trajectory should reach and maintain the new setpoint without a subsequent "load rebound". An optimal transition path, which serves as a benchmark, is obtained through an optimization algorithm. A trajectory that can be adjusted with a single "curvature" parameter is then proposed. The value of the curvature parameter yielding the smallest peak is found numerically and a "near-optimal curve" is thus achieved. The properties of this curve are investigated. For the particular case examined, the near-optimal curve yields a peak load about 8% smaller than that corresponding to a linear ramp. A general expression for the curvature parameter of the near-optimal curve is obtained by performing parametric runs. The general formulation is then given as a function of two parameters: (a) the building time constant: (b) and the user-required transition time. The proposed method, suitable for a programmable thermostat, allows achieving considerable peak reductions in an inexpensive and practical manner, without requiring an optimization for each particular case. (C) 2014 Crown Copyright and Elsevier B.V. All rights reserved.