Designing for Daylighting

According to benchmarked studies of university science buildings, lighting of university science buildings may contribute up to 11% of total energy loads and is a significant factor in occupant well-being. Effective natural daylighting is a sustainable design strategy for improving occupant health and reducing a building’s first and operational costs for electric lighting and building cooling.

  • Optimizing the natural daylight entering a building typically accounts for three fundamental design variables:
  • Latitude and longitude of the building site,
  • Building’s solar orientation on its site, and
  • Climate Zone.

To effectively daylight a building, these variables will inform the ratio of glazing relative to wall and roof areas, the distribution of glazing in the building envelope, and the distribution of external sun-shading devices and selection of glass coatings and internal shades. Strategies for providing access to daylight and views while mitigating glare will vary depending on the orientation of a building façade or roof.

Providing effective daylighting requires attention to five measurable metrics that inform the potential performance of an envelope design:

  1. Illuminance: The measure of the amount of light received on a surface, expressed in lux. This measurement can reveal how extensively daylight can penetrate a room.
  2. Luminance: The measure of the amount of light reflected or emitted from a surface. This measurement helps evaluate visual comfort and glare.
  3. Daylight Factor (DF): This is the ratio of indoor illuminance at a specific point to the outdoor illuminance under overcast sky (even light) conditions, expressed as a percentage. Generally, a percentage between 2-5% is ideal.
  4. Daylight Autonomy (sDA): This metric indicates the percentage of time during the day that a space meets a specific illuminance level using only natural light.
  5. Useful Daylight Illuminance (UDI): This measures the percentage of time that daylight levels fall within a range for performing a given task in a daylit room. This metric can predict the value of daylight dimming systems for artificial lighting in each space.

The Cuyahoga Community College STEM Center in Parma, OH is located in Climate Zone 5 and is oriented on a true east-west axis with an even distribution of heating and cooling degree days annually, including both long days with high-altitude summer sun and short days with low-altitude winter sun. The building is occupied year-round, and its site is surrounded by deciduous trees and grass, with excellent access to appealing outdoor views. In this context, shading and glare-reduction strategies to optimize natural daylight and view access vary notably at each of the building’s three exterior facades.

In the case of the STEM Center, every classroom, teaching lab, and the office suite are located near the exterior façade, or, in the case of three teaching spaces, they are adjacent to the skylit Student Commons.

On the south façade, which receives the most solar exposure, optimally-spaced, horizontal terracotta shading baguettes reduce shoulder-season glare and heat gain throughout the year.

A perforated metal roof canopy shades the perimeter of the upper facades of the building and is designed to accept building-integrated photovoltaic panels (BIPVs) that can generate 125,380 kWh/year in the future.

The STEM east façade receives low-raking sun exposure in the morning, which if untreated would subject the interior to excessive glare in every season and excessive heat gain in the summer. While internal shades can reduce morning glare, they block outdoor views and cannot mitigate cooling loads from solar gain that has already passed through the glazing units. Consequently, an innovative daylight control system is employed that retains view access while eliminating glare. “Microlouvre” screens (which are essentially miniature external Venetian blinds) are mounted to the exterior mullions of the curtain wall glazing to screen the window openings.

At the north façade, with its reduced window-wall ratio, daylight harvesting is balanced with energy loss reduction. North-facing vertical fins project from window mullions to bounce eastern morning sun into the classrooms.

The Student Commons is the primary gathering and collaboration space in the building. One hundred feet of photovoltaic PV-integrated skylights provide the Commons and adjacent teaching and study spaces with all-season daylighting. Because these skylights harvest eastern, southern, and western light throughout the day, glare mitigation is essential. Solar exposure simulations identified the need for a 60% opaque glazing pattern to eliminate excessive glare while still providing effective daylighting. In lieu of an opaque frit pattern, PVs were integrated into the skylight glazing to provide the necessary shading, while also generating 125,380 kWh annually, which is sufficient to power 15% of all electric lighting in the building.