Exceedance Degree-Hours: A new method for assessing long-term thermal conditions

Abstract

Several “discomfort indices” have been proposed and codified into building standards, with several needs usually reported for such indices. They should: express the severity of discomfort in time steps while incorporating all environmental and personal factors; be usable with any comfort model (and thus, a variety of interests, for example, traditional thermal comfort, sleep comfort), among other requirements. The existing indices, however, fall short of meeting all these goals, limiting their usefulness in many situations, such as assessing conditions in mixed-mode buildings, especially when used for building performance simulation and design optimization purposes. Here, a new discomfort index called “Exceedance Degree-Hours” is developed, which accounts for all six main environmental and personal factors. By using an equivalent temperature index, “Exceedance Degree-Hours” can capture variations in discomfort severity between different thermal conditions that other indices cannot. In contrast with other indices, “Exceedance Degree-Hours” can be paired with various comfort definitions from literature, and, importantly, it can be used to assess thermal comfort in mixed-mode buildings, providing a single value as a result. Here, the results of the proposed method are compared to those of existing discomfort indices suggested in standards, and the advantages and limitations of the proposed approach are discussed.