The uncertainty of manual shade control on west-facing facades and its influence on energy performance

Abstract

Due to the stochastic nature of occupant behavior on manual shades, energy prediction based on realistic shade behavior models differs largely from simplified shade assumptions adopted by building energy codes. Three important questions (when is it important to consider shade behavior models, when does shade behavior related energy uncertainty need to be accounted and when can simplified shade assumptions be used instead of behavior models?) remain unanswered. To address these issues, this paper investigates the impact of occupant uncertainty of solar shade control on building energy performance at temporal and spatial scales as well as predicted performance gaps between simplified shade assumptions and shade behavior models. A stochastic model of manual solar shades developed in a previous study based on field measurements was used in this paper. Co-simulation, statistical calculation and uncertainty analysis were conducted. The results show that energy uncertainty should be considered when evaluating the energy performance of a single room at hourly, daily, monthly and total annual scales. In other cases, shade behavior and related energy uncertainty may be ignored. Fully shade open or closed assumptions lead to a significant deviation of predicted energy performance and thus cannot be used for simulating energy performance of manual shades. Simplified shade assumptions (such as half-open in this research), which is capable of representing average shade behavior patterns, can be used to evaluate the annual energy performance of office buildings and to size cooling/heating equipment instead of a shade behavior model. While for commonly used pessimistic assumptions on manual shades (fully open in summer and fully closed in winter), they over-predict maximum cooling/heating rate by at least more than 5% compared to the shade behavior model.