Energy and Buildings, Vol.155, 151-165, 2017
Estimation of the daylight amount and the energy demand for lighting for the early design stages: Definition of a set of mathematical models
A set of logistic mathematical models to estimate the daylight amount and the energy demand for lighting of a room is presented. The models were built upon a database of results obtained for a sample room through Daysim simulations: features such as site, orientation, external obstructing angle, window size, glazing visible transmittance and room depth were parametrically changed, resulting in 102 cases. For each case, the target workplane illuminance and the lighting power density were also changed, producing a final database of 408 cases. Two groups of models were built, for two different external obstructions: a building ahead and an overhang used as shading system. Each group contains a set of models for different daylighting metrics (daylight autonomy, continuous daylight autonomy and spatial daylight autonomy) and for the energy demand for lighting, considering a manual on/off switch or automated daylight responsive lighting control. The estimates that were obtained using the models showed, compared to the corresponding simulations results, a coefficient of variation CV lower than 16% for all the models, with one exception, having a CV up to 30%. The aim of the study was to elaborate models that could be used to incorporate daylighting strategies since the earliest stages of the building design process. Using the models, it is possible to predict the annual daylight amount in a room and the corresponding energy consumption of the lighting systems starting from some given room features (for instance the room depth or the window area) or, the other way around, estimate the suitable values of room features (glazing area, visible transmittance or room depth) to guarantee a target value of energy demand for lighting or of a daylighting metric. (C) 2017 Elsevier B.V. All rights reserved.
Keywords:Mathematical models;Energy demand for lighting;Light controls;Daylighting metrics;Daylight autonomy;Spatial daylight autonomy;Building ahead;Overhang