Improved Fourier series approach to modeling hourly energy use in commercial buildings

Modeling hourly energy use in commercial buildings can be useful for (i) retrofit savings analysis, (ii) diagnostic purposes, and (iii) acquiring physical insight into the operating pattern of buildings. Electric and thermal energy uses in commercial buildings, being strongly periodic, are eminently suitable for Fourier series analysis. Earlier studies assumed trigonometric polynomials with the hour of the day as the primary variable and one week as the period. This model, though suitable on the whole, was poor during certain weekday periods and during weekends. The present study presents an improved Fourier series approach to modeling hourly energy use in commercial buildings which yields superior regression fits partly because of the care taken to separate days of the year during which commercial buildings are operated differently and partly because of the rational functional form of the regression model proposed. The validity of this approach is verified with year long data obtained from several monitored buildings. The study also looked at the consistency with which certain frequencies appeared in the diurnal scheduling of buildings and discusses the physical basis of these frequencies.