The Process: Daylighting design can be structured into a linear sequence of phases and steps. However as shown above, the evolution of a design, the refinement of its parts, and their integration with the whole building is best understood as an iterative process.
Somewhere at the beginning of the design process, the first question invariably asked by the client of the daylighting consultant is 'What is it that you do anyway?' The query stems not from doubt that the daylighting specialist imparts a vital contribution to the final product, but more from a desire to understand how these services mesh with the typical process of project design and construction. The intent of this article is to flush out a logical, albeit idealized, sequence of daylighting tasks within the phased process of architectural services.
Successfully daylighted buildings don't just happen. They result from the integrative effort of a multidisciplinary team: the owner, architect, mechanical engineer, structural engineer, curtain wall consultant, daylighting consultant, lighting designer, and sustainable design consultant, among others.
Planning for daylight begins with site selection, the orientation of the building on that site, and the shaping of building form. It continues with the optimization of fenestration, interior finishes, electric lighting, and control systems; and concludes with on-site calibration and commissioning of control systems, end-user training, and third-party evaluation. The goal is a daytime illuminance distribution that meets predefined programmatic requirements, such as occupancy period, space function, and target illuminances, for the greatest time period, through the sole use of light flux from the sun, sky, and ground. To achieve this, a diverse array of building components must coalesce: apertures, glazing, shading devices, interior partitions, surface finishes, electric lighting, HVAC system, and controls.
The Parts: A daylighting system consists of an extensive network of integrated building parts, as shown in the diagram above. Each possesses a unique set of parameters that affect the other parts and the overall performance of the building as a single entity.
INVESTING IN PERFORMANCE
The daylighting process is 'front-loaded,' requiring in-depth knowledge of the site and a substantial investment of thought and effort early in the design process. This translates into an initial increase in design and engineering fees, but does not necessarily mean higher construction or equipment costs. Informed decision-making on how the parts come together can raise the performance level of the 'whole,' without having to rely on expensive materials or complex daylighting devices. For example, control of the fenestration area, location, and glazing light-to-solar heat gain ratio can improve the distribution of daylight into the interior of a space, so that it has minimal impact on a building's cooling load. The result: a downsized HVAC system that costs less to purchase, operate, and house. Conversely, if the climate favors a passive solar heating strategy, the careful selection of glazing may be used to maximize a building's solar heat gain when needed, and reduce building heating load. Similar optimizing efforts involving alternative components can lead to other amenities: the elimination of perimeter heating systems, higher ceiling heights that allow increased views, and an overall space that more efficiently guides daylight flux into its interior. Add to this reduced building energy use and lifetime costs, along with the recent flood of statistical studies documenting how daylighting increases productivity, learning, and sales, and it is no wonder these environments are now becoming coveted by owners, occupants, and developers.
The Players: Successful daylighting designs result from a multidisciplinary team with the architect playing a central role. Information may be exchanged around the outer circle of players, but it must channel through the architect and inform the building process to become part of the building.
Daylighting design is an iterative process where intermediate analysis leads to a successive refinement of the design concept. With this in mind, the following table summarizes a logical sequence of daylighting-related tasks that can be incorporated within the phased process of typical architectural design and construction services:
- Establish all criteria guiding daylighting and electric lighting design, such as sustainability guides, rating systems, energy/ construction codes, energy mandates, and comparative base-building models.
- Assist in selection of site and development of initial building massing, fenestration, and orientation.
- Assess daylight available from sun, sky, and surround for site latitude, obstructions, and predominant sky condition.
- Establish space-by-space programmatic requirements. Include the occupancy period/function/task/area; target illuminance; target daylight factor; and lighting power limits.
- Establish target daylighting autonomy factors that quantify how much electric lighting energy may be saved using available daylight. This step combines the previous steps of the Programming Phase to set a benchmark for the Schematic Design Phase evaluation of daylighting strategies.
Schematic Design Phase
- Assist in space planning based on programmatic requirements and building envelope, orientation, and apertures.
- Develop general daylighting and shading concepts and strategies for each room that meet target illuminance requirements while minimizing heating and cooling loads.
- Analyze selected daylighting options using available physical scale models or simple evaluation methods and graphical techniques. Tools may include sun angle calculator, dot charts, no-sky plot, nomograms, or spreadsheet calculations for daylight factor and effective aperture.
Design Development Phase
- Develop working daylighting and solar shading strategies for different parts of the building as the design evolves. Implement shading strategies to block, filter, or redirect sunlight. Fine-tune fenestration strategies to maximize available daylight, provide views, and control heat and glare.
- Coordinate the lighting zones of the daylighting plan with the electric lighting plan. Research and select control logic and control systems for dimming/switching electric lighting in response to available daylight.
- Develop advanced daylight devices such as double façades, skylights, light shelves, light pipes, heliostats, and apertures with sunlight-redirecting/rejecting glazing.
- Use advanced tools and techniques such as computer modeling to: simulate daylighting characteristics for specific times and sky conditions; determine boundaries of daylight zones and optimize photosensor placement; and calculate daylight autonomy factors.
- Use energy analysis software to evaluate the thermal impact of all daylight-related system components on the building. Refine decisions to optimize performance.
Construction Document Phase
- Provide glazing specifications for daylighting-related glass, describing the visual characteristics of the glazing system. Coordinate glazing types with drawings.
- Review, make recommendations, and contribute to all drawing and specifications related to the daylighting systems, such as windows, interior roller shades, light shelves, skylights, exterior shading devices, interior materials, and paint finishes.
Commissioning and Post-Occupancy
- Assist in the commissioning and calibration of lighting controls.
- Provide a user manual that documents the operating features of the daylight system, as well as the maintenance requirements for sustained performance.
- Explain operation and maintenance requirements of the daylighting system to the owner, building manager, and occupants.
High-performance buildings have daylighting strategies that are inseparable from their site and architectural design. The level of performance they achieve is a result of unifying these elements in the earliest phases of the building design. A logical progression of tasks can be tailored to fit into typical architectural design and construction services. The role of the daylighting consultant is to provide these essential services, and thereby, guide the entire project team closer to a well-daylighted building.
Matthew Tanteri is principal of Tanteri + Associates, a consulting practice offering award-winning daylighting design and evaluation services. An adjunct professor in the lighting MFA program at Parsons the New School for Design, he teaches the studio course, 'Natural and Technological Light,' and the lecture series, 'Daylighting and Sustainability.'
Daylight Autonomy: Percentage of occupied time per year when target illuminance can be maintained by daylight alone. May be used to express the percentage of electrical lighting energy saved by a daylighting system.
Daylight Availability: Daylight illuminance from sun and sky at a particular site that impacts a building exterior on a horizontal, vertical, or other light-admitting surface.
Daylight Factor: Interior horizontal daylight illuminance expressed as a percentage of the horizontal daylight illuminance available to an unobstructed site.
Daylight Factor Dot charts: A series of circular formatted charts for overcast and clear sky conditions. Each chart contains a pattern of dots randomly distributed as a function of sky luminance and cosine corrected for the angle of incidence. When overlaid onto a site obstruction diagram and an interior room drawing, allows estimation of light available to a particular interior point as a fraction of the light available to an unobstructed site.
Effective Aperture (EA): Measure of the light-transmitting ability of a glazed window aperture. Product of glazing visible transmittance and the ratio of window-to-wall area.
Lighting Power Density: The maximum lighting power per unit area of a building allowed by code according to the classification of space function.
Light-to-Solar-Gain (LSG): Ratio of visible light transmitted to solar heat gain. A value below one means the glazing transmits more heat than light. A value above one means the glazing transmits more light than heat. Spectrally selective glazing is characterized by having a high LSG value (_1.25).
Luminous Flux: Rate of flow of radiant energy, measured in lumens (lm).
Nomogram: Graphical assessment tool consisting of a three coplanar curves, each graduated for a different variable so that a straight line cutting all three curves intersects the related values of each variable.
No Sky Plot: Plan drawing that shows the extent of daylight penetration by dividing the work plane into two parts: the part from which the sky can be seen directly, and the part from which it can't.
Passive Solar Heating Strategy: Use of the sun's energy for heating a building interior.
Sun Angle Calculator:
Solar shading design tool consisting of a series of sun path charts with a profile angle and incident angle overlay. Used for determining solar position at a specific latitude and time, and the associated profile angle relative to a particular fa?ade orientation. (Originally produced by Libbey-Owens-Ford up until 1974, but now available from the Society of Building Science Educators. Visit www.sbse.org/resources/sac/index.htm
Target Illuminance: Established minimum illuminance based on space function, task, and occupants’ age; measured in lux (lx) or footcandles (fc).