Estimation of Daily Degree-hours

Abstract

Degree-hours have many applications in fields such as agriculture, architecture, and power generation. Since daily mean temperatures are more readily available than hourly temperatures, the difference between mean daily degree-hours computed from daily mean temperatures and those computed from hourly data is examined. Mean daily degree-hours were modeled assuming normal probability distributions for temperatures and homogeneous variances of hourly temperatures throughout a day. The validity of the assumptions, which is dependent upon time of year and location, as well as the effect of the assumptions on four models of daily degree-hours are discussed. Two of the models require mean hourly temperatures and two require the readily available daily mean temperatures as input. Comparisons among models and observed data show that estimates made from mean hourly temperatures are better than those made from daily mean temperatures. The difference is sizable during the transition months between warm and cool seasons. An aid to computing the difference is presented.