Daylight Harvesting

One of the intriguing and interesting ways to build sustainably is to use the practice of daylight harvesting or “daylighting” to light a building. As long as there have been windows, daylight has been used to light buildings, but in the era of (relatively inexpensive) electricity, good design practices went out the window, so to speak, and little attention was paid to this aspect of building design. Window placement was then determined based on what the designer was trying to do with the building’s façade, and in many cases, particularly in the 1980’s, it was fashionable to design buildings (particularly schools) without windows as it was considered to be “too distracting” to have windows. LEED has a credit for daylighting – IEQ credit 8.1.
Knowing what we know about human health, hormone production, circadian rhythms, and the various colors and intensities of daylight at different times of the year, one can assume that daylighting is important in human health, therefore in student learning.
Studies show some interesting benefits associated with the use of daylighting. Studies show students in daylit schools experience 3.2 to 3.8 fewer absent days. Studies also show students achieving higher test scores. Fewer dental caries and increased student growth are another correlation between daylighting and student health. In addition, students in daylit schools show better attention spans and better work habits. Schools also report teachers having fewer sick days when teaching in daylit schools. These are a few of the more well-known studies available on this high-performance building strategy.
Daylit buildings also offer substantial cost savings by reducing energy use. Since electrical lighting heats buildings, when lights are turned off cooling loads go down. Since commercial buildings use more cooling, on average, in the course of a year than heating (due in part to lighting, computer and human heat generation), turning off the lights realizes an immediate benefit for both lighting and mechanical systems. A second benefit is that of reduced electrical lighting, which will decrease utility bills. A third benefit of daylighting occurs when the use of HVAC is reduced; then HVAC noise is reduced. (Noise is a big issue in schools and is associated with difficulty in student learning.)
There is no one single successful strategy in the use of daylighting to achieve LEED credit 8.1. Windows should be strategically placed to provide light but not glare. Light should be bounced into areas further away from windows by the use of light shelves and/or reflective surfaces. Other methods are to use clerestory windows or skylights (skylights should be used with caution in areas prone to severe hailstorms). The use of sunshades will reduce glare while providing natural daylight. Interior lighting controls need to be used in order to maximize daylight harvesting. Use building modeling (LEED prerequisite) to determine an overall strategy for successful daylight harvesting. The use of daylight harvesting will create significant cost savings for the building owner and improved outcomes for students.

Student outcomes: http://www.nrel.gov/docs/fy00osti/28049.pdf
Pacific Gas and Electric Company (research conducted by the Heschong Mahone Group, Fair Oaks, CA), Daylighting in Schools: An Investigation into the Relationship Between Daylighting and Human and Performance, 1999.

Energy usage: http://www.lightnowblog.com/2009/01/study-captures-daylightings-hvac-and-lighting-energy-savings-impacts/

Daylight harvesting strategies: http://www.inive.org/members_area/medias/pdf/Inive%5CIBPSA%5CBS05_0501_508.pdf