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2022 | Book

Overhang Design Methods

Optimal Thermal and Daylighting Performance


About this book

It is estimated that windows in office buildings are responsible for one third of energy used for their heating and cooling. Designing window shading that balances often contradictory goals of preventing excessive heat gains in hot periods, without compromising beneficial heat gains in cold periods or visual comfort in indoor spaces of modern buildings with highly glazed facades, is an interesting multi-objective optimisation problem that represents an active research topic in the field of building energy and daylighting. Window overhangs are the simplest and most traditional shading devices that are easy to install, highly cost-effective, require low or no maintenance and offer unobstructed views outside. This book provides a review of overhang design methods for optimal thermal and daylighting performance. It starts with a historical overview of methods based on solar positions and shading masks. Next it discusses current research methodology, including shading calculation methods, ways of quantifying thermal and daylighting overhang effectiveness and the use of multi-objective optimisation approaches, together with the case studies that employ them. It further covers methods for designing innovative overhang types such as NURBS outlined overhangs and PV integrated dynamic overhangs. The appendix classifies published overhang case studies according to major climate type and latitude of their locations. As such, the book presents a valuable resource for understanding subtle nuances of interaction between solar radiation, shading devices and indoor comfort. The intended target audience are building energy researchers interested in optimisation of window shading devices.​

Table of Contents

Chapter 1. Introduction
Modern façades, in particular those of office buildings, are highly glazed both to provide daylight and exterior views, which influence occupants’ well-being, and to improve the architectural appearance of buildings. Solar radiation through such façades easily causes glare and overheating, so shading is of vital concern for them. Shading devices aim to prevent excessive heat gains from solar radiation in hot periods, without compromising beneficial heat gains in cold periods or visual comfort in adjacent indoor spaces. Balancing these often contradictory goals is an interesting multi-objective optimisation problem that represents a very active research topic in the field of building energy and daylighting. Overhangs are the simplest and most traditional shading devices that have several beneficial traits: easy installation, high cost-effectiveness, low maintenance and unobstructed view outside. Our goal here is to provide an overview of historical development of the methods for designing overhangs. These methods improved hand in hand with the development of methods for obtaining information about thermal and daylighting behaviour of building models, so this book also represents an overview of the development of building performance simulation tools as related to shading calculations.
Sanja Stevanović
Chapter 2. Solar Path Methods
The oldest methods for overhang design were proposed in the second half of the twentieth century and based solely on solar paths. Their aim is to protect glazing from direct solar radiation during overheating periods, usually specified by cut-off dates and cut-off times during these days. In the first two sections, we review Olgyays’ and Mazria’s methods based on superimposing overhang and fins’ shading masks upon charts of solar paths in horizontal and cylindrical projections, respectively. In the third section, we review methods based on backward tracing of solar rays until they intersect a predefined shading support surface.
Sanja Stevanović
Chapter 3. Current Overhang Research Methodology
In this chapter, we review the methodology used in current overhang research. The first section discusses simulation methods and algorithms, both those developed specifically for overhangs and those developed for general shading calculations in simulation engines. The second section is concerned with the ways of quantifying overhang effectiveness in the research literature, from the viewpoints of both thermal and visual performance. Genetic algorithms are the most used optimisation approach in overhang design, as well as in general building energy optimisation. The third section, in addition to describing the work and practical setup of genetic algorithms, reviews the overhang studies employing them.
Sanja Stevanović
Chapter 4. Design Methods for Particular Overhang Types
This chapter deals with overhang studies that do not easily fit the previous two chapters due to their innovative approaches. The first two sections bring the methods motivated by Kaftan’s remark that one should not expect optimal overhang shape to be of simple geometry even for a rectangular window, as solar gains and daylight intensities vary with changing solar angles. Methods in the first section are based on the division of the underlying overhang support surface into a cell array which are then treated individually, while the second section discusses a method that divides the support surface into a one-dimensional array of strips attached to the wall, whose outer edges are modelled by a smooth, continuous NURBS line. The third section presents a method in which the shading design problem is reversed so that instead the window is trimmed to optimally suit a given rectangular overhang. The fourth section discusses the results of a few studies that recommend overhangs as suitable exterior shading devices for building retrofits due to their structural properties. The last section describes methods for constructing and optimising PV integrated overhangs, whose sunny side uses blocked direct solar radiation to generate electricity, and movable overhangs, whose position can be updated from season to season.
Sanja Stevanović
Overhang Design Methods
Sanja Stevanovic
Copyright Year
Springer Nature Singapore
Electronic ISBN
Print ISBN