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Selecting Fenestration Systems

Selecting Fenestration Systems Without Neglecting the Visual Environment

From eSociety, June 2018

As part of Science and Technology for the Built Environment’s building simulation special edition, “An Integrated Method and Web Tool to Assess Visual Environment in Spaces with Window Shades” explores models and decision strategies of a web-based tool that will extend the industry’s knowledge on selecting fenestration systems properties without neglecting the visual environment, said one of the authors, Athanasios Tzempelikos, Ph.D., Member ASHRAE.

The paper’s other authors are Iason Konstantzos and Michael Kim, Student Member ASHRAE. All three authors are associated with Purdue University’s Center for High Performance Buildings and the Lyle School of Civil Engineering.

Tzempelikos explains the significance of the research and how it will affect the built industry. STBE is ASHRAE’s archived research journal.

1. What is the significance of this research?

Modern office buildings have large glass façades, which have a significant impact on the visual environment of occupants. This research presents a methodology for assessing the visual environment performance in spaces with roller shades, based on three major aspects: visual comfort, lighting energy use and view (connection) to the outdoors. The developed web-based tool and user-friendly interface provide a convenient way to evaluate the visual environment and select shading properties, either during the design phase, or for existing building (retrofit) applications. Carefully selected layouts and proper shading optical properties can lead to higher space usability, lower lighting energy use and higher connection to the outdoors.

2. Why is it important to explore this topic now?

Window shades are widely used in offices to control daylight and solar gains, along with glare and privacy. Although the impact of shading on energy use has been studied, the impact of shading on visual comfort and view preferences of occupants has not been adequately addressed. This study provides a way to consider all three main aspects of the visual environment through a useful tool, which will lead to human-centered building design and future design guidelines with respect to fenestration systems.

3. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?

The effect of shading optical properties on energy, visual comfort and outside view is complex and multi-dimensional. Selecting a high shade openness does not equal better outside view; selecting a darker shade color does not equal better visual comfort or less energy use; etc. In addition, subjective factors are always present. The combination of shade and glazing properties and seating layout play an important role in determining the final impact on visual environment (and resulting occupant satisfaction). The developed tool can guide engineers and provides a decision strategy for selecting shade properties based on different priorities: maximizing outside view, maximizing energy performance, or a balanced approach with fixed or flexible criteria to avoid compromises, always ensuring occupant comfort.  

4. Were there any surprises or unforeseen challenges for you when preparing this research?

This research is a synthesis of the most recent metrics (visual comfort autonomy, lighting energy use, and view clarity) for assessing the visual environment performance of spaces with window shades. This was achieved in the form of an integrated framework/interactive web-based tool. Transferring all this knowledge, complex models and their interactions into a single tool with an embedded decision strategy was a real challenge. Nevertheless, the proposed guidelines and outcomes of the tool can lead to better building design methods with humans in the center of attention.

5. How can this research further the industry's knowledge on this topic?

The models and decision strategies of the web-based tool, which includes a database of different design configurations (climate, envelope configuration, orientation, glazing size and properties, comfort restrictions, occupant view directions, etc.) will extend the industry’s knowledge on selecting fenestration systems properties without neglecting the visual environment. More specifically, shade properties can now be selected based on the variation of quantified visual performance metrics. Moreover, the tool can compare design alternatives and provides useful information about the comfort, energy and view performance of spaces will roller shades, without the need of high expertise or complex simulations.

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