How to maximize the ‘daylight’ in daylight saving time
This year, the Energy Policy Act (EPAct) extends daylight saving time (DST) in the United States by four weeks. The idea behind this change is to see if it will reduce energy consumption. The U.S. Department of Energy (DOE) will study the affect of daylight saving on energy consumption and report the results of the study to Congress no later than December 31, 2007. After reviewing the study findings, Congress can revert back to the traditional American DST schedule if warranted.
DST was first implemented by the German government around World War I, then the United Kingdom and other Allied countries followed. The purpose was to better align work hours with daylight hours and therefore reduce the need for electric lighting in offices and factories. DST moves sunrise and sunset forward by one hour during that time of year when there are the most daylight hours (late spring, summer, and early fall). It would shift the hour from early morning to evening, better matching waking time with daylight hours.
Benefits of daylight
Anjali Joseph, PhD, completed a study for The Center for Health Design in August, 2006, titled, “The Impact of Light on Outcomes in Healthcare Settings.” She found that light reduces depression among patients, decreases length of stay in hospitals, improves sleep and circadian rhythm, lessens agitation among dementia patients, eases pain, and improves adjustment to night-shift work among staff. There is also a direct correlation between work environment satisfaction and access to daylight in that environment.
A combination of electric lights and daylight can provide the light necessary for the health and well-being of patients and staff. However, natural light does not cost anything and is in the form most people prefer.
Green Guide for Health Care
The Green Guide for Health Care Version 2.2 offers several suggestions under the Environmental Quality Section Credit 8.1. The intent is stated as providing building occupants with a connection between the outdoors and indoors by providing daylight and views into the building's regularly occupied spaces. The suggested design practices include:
Provide access to daylight in diagnostic and treatment areas.
Provide access to daylight in inpatient units by providing window configurations that allow visual connection to the outdoors for private and semiprivate patients, even when cubicle curtains are closed.
Provide access to daylight for 75% to 90% of regularly occupied staff work spaces and non-inpatient room spaces.
Design strategies to maximize windows include:
Building orientation—Northern exposure usually provides the best light source because the light is mostly glare-free and diffuse. Southern exposures may need overhead shielding from high midday sun angles. West and east windows have a greater risk for direct sun glare.
Shallow floor plates for better light penetration into the space.
Increased building perimeter for more window opportunities.
Courtyards and atria to open up the interior of the building for windows (figure 1).
The floor plan (A) of patient rooms overlooking a two-story atrium (B) at Wuesthoff Medical Center in Melbourne, Florida.
Wall color—Internal walls influence window design and placement. Highly reflective—but not glossy—light-colored walls will spread daylight back from sidewalls. Jewel-toned walls will absorb more light and may require more supplemental lighting sources.
As a rule of thumb, if the walls of a building are more than 25% glass, the building can benefit from solar control glass. The further south and the higher the percentage of glass, the higher the percentage of solar energy that should be blocked. The energy efficiency of spectrally selective glazing means that architects who use it can incorporate more glazing area than was possible in the past within the limitations of codes and standards specifying minimum energy performance.
Spectrally selective glazing is window glass that permits some portions of the solar spectrum to enter a building while blocking others (figure 2). This high-performance glazing admits as much daylight as possible while preventing transmission of as much solar heat as possible. This type of glazing significantly reduces building energy consumption and peak demand by controlling solar heat gains in the summer, preventing loss of interior heat in the winter, and allowing occupants to reduce electric lighting use by making maximum use of daylight.
The lobby with spectrally selective glazing at Holy Cross Hospital's Jim Moran Heart and Vascular Center in Fort Lauderdale, Florida.
Because new spectrally selective glazings can have a virtually clear appearance, they admit more daylight and permit much brighter, more open views to the outside while still providing much of the solar control of the dark, reflective energy-efficient glass of the past. They can also be combined with other absorbing and reflecting glazings to provide a whole range of sun control performance.
The solar heat transmission properties of spectrally selective glazing benefit both buildings in warm climates, where solar heat gain can be a problem, and buildings in colder climates, where solar heat gain in the summer and interior heat loss in the winter are of concern. When spectrally selective glazing is appropriately used, the capacity of the building's cooling system might also be downsized because of reduced peak loads.
Spectrally selective glazings screen out or reflect heat-generating ultraviolet and infrared radiation arriving at a building's exterior surface while permitting most visible light to enter. Spectral selectivity is achieved by a microscopically thin, low-emissivity (low-E) coating on the glass or on a film applied to the glass or suspended within the insulating glass unit.
Basic blue- and green-tinted glass can offer some of the same spectral properties as these special absorbers because impurities in tinted glass absorb portions of the solar spectrum. These can perform as well in a double-pane unit as some glass with a spectrally selective low-E coating. Because some of the heat absorbed by tinted glass continues to be transferred to the building's interior, absorption can be less efficient than reflection.
Spectrally selective glazings can be used in windows, skylights, glass doors, and atria. This technology is most cost effective for facilities that have large cooling loads or are located in the southern United States. In the northern United States, spectrally selective low-E windows can also be cost effective.
What about glare?
Spectrally selective glazings may not provide reduced glare control even if solar gain is reduced. Glare can be effectively managed by using motorized window coverings. Motorizing shades or blinds and adding appropriate sensors and controls can permit better control of both energy use and comfort. Exterior architectural features, such as bris soleils, window eyebrows, and vertical fins can also minimize glare.
Using daylight in place of electric light
An effective daylighting system can provide a balance between natural and artificial light levels within the interior of healthcare facilities (figure 3). A completely integrated daylighting-control system consists of controllable light fixtures (such as dimmable fluorescent fixtures), motorized window covers, photosensors that measure light levels, and a lighting controller that adjusts electric levels and the position of the window covers to maintain the desired light level throughout the day.
Treatment area with daylight and outdoor view at Holy Cross Hospital's Michael and Dianne Bienes Cancer Center in Fort Lauderdale, Florida.
Healthcare facilities can achieve the health benefits and energy savings of daylight through careful design and the use of daylighting systems. The additional hours offered by the DST change will only enhance those benefits. HD
Patricia Rice-Spivey, AIA, LEED AP, is a project manager and Associate with MGE Architects, a Coral Gables, Florida-based firm that provides architecture, master planning, and interior design services for healthcare, educational, and transportation projects. She has more than 11 years of experience on major healthcare and education projects, including renovations, newly constructed buildings, and construction documents.
- Joseph A. The Impact of Light on Outcomes in Healthcare Settings. The Center for Health Design, August 2006. http://www.healthdesign.org/research/reports/light.php.
- Lee ES. Spectrally Selective Glazings. Federal Technology Alert. New Technology Energy Management Program, Federal Energy Management Program. DOE/EE-0173, August 1998. http://www.1.eere.energy.gov/femp/pdfs/FTA_Glazings.pdf.