.: Green Technology : Help, Save Our Planet :.: June 2009

Before the electric light was invented, and for a good while after that too, designing buildings so that daylight could enter interior spaces was a necessity. Yet despite a long history of using daylighting as a design strategy, building owners, architects, engineers and lighting designers are only just beginning to understand how to use it effectively.

But why would a building owner even want to take on the challenge of using daylight to light a building? In a word, money. A good daylighting design can save up to 75 percent of the energy used for electric lighting in a building. The amount of daylight available, the occupancy pattern, and the control strategy can all affect energy savings. In addition, because significant daylight is often available during utility peak demand hours, a good daylighting design can reduce demand charges. Electric lights also generate significant heat in a building and by turning off or dimming the lights when not needed, 10 to 20 percent of the energy used to cool a building can be saved. On top of that, so-called soft savings attributable to increases in productivity and health of the building occupants can add to the hard savings, researchers say.

Roof Glazing for Daylighting
(Skylight)

Using daylight correctly takes a multidisciplinary approach to design and an understanding of the strategies and technologies available to control the sun.

A facility executive’s daylighting goals of holding down first cost and decreasing operating costs often go unmet when the entire building team isn’t brought into the design process from the beginning.

Improper daylighting system will effect the cooling load, heat gain, glare and thermal comfort.

In a typical case, the architect’s design offers plenty of glass for light, but that light brings with it too much heat, forcing the engineer to increase the cooling tonnage when the building is complete. It also becomes difficult to decrease lighting energy costs because when the building is complete, occupants demand blinds to cut down on glare. As a result, the blinds are drawn much of the day, requiring the use of electric lights. An owner who thought daylighting was going to save money finds out that the design not only costs more upfront but costs more to operate as well.

Both the location and interior characteristics of a building are important in daylighting design and should be the first things to consider. Because location varies, as does its effect on the interior design, there can be no cookie-cutter approach to daylighted buildings.

Location has everything to do with access to daylight. An urban building may be shaded during part of the day, which will affect, not rule out, a daylighting strategy.

Multiple stories also have an impact on how deep within the floorplate daylight can travel. There are solutions for multiple-story buildings, such as placing little-used, transitional or unoccupied spaces near the core of building — restrooms, copy rooms or elevators.

Good daylighting design will also affect a building’s interior spatial characteristics. A daylighted building’s interior should have the task areas close to daylight sources — whether that is sidelighting from the windows or top lighting from skylights. The placement of transitional or unoccupied spaces should be moved to the core or other areas with minimal windows.

Although the space is air-conditioned, due to the increased in cooling load, the building management is forced to add more facility to improve the thermal comfort .
(inefficient electricity usage).

The taller and higher the windows, the farther light can reach into the interior. Optimally, the ceiling plane and top of the windows are at the same level. And ceilings higher than 3 meters are important to deeper penetration of light. A rule of thumb, is light penetration is equivalent to 1.2 to 1.5 times the height of the windows, assuming that the ceiling is also that high. In fact, properly designed windows and ceilings could distribute light as far as twice the height of the windows.

That doesn’t necessarily mean a huge expanse of glass. When window-to-wall percentage is less than 35 percent, the usual design includes some combination of solar control glass as view glass at the occupant level with clearer glass as clerestory windows. The clerestory windows become the primary source for distribution of daylight deeper into the space while the view glass offers buffered sidelighting.

To achieve the high perimeter ceiling height for clerestory windows without changing overall floor-to-floor height, ceilings can be sloped, or stepped, away from the windows to allow HVAC ducts to be accommodated in the center of the space.

The biggest challenges in daylighting design are controlling glare and heat. The building owner’s choice of glass for a daylighted building is really a function of geographic location.

Once the design effectively distributes cool daylight around the space, the electric lighting needs to be balanced with available daylight.

Unlike other physical features in a daylighted space, whether it’s structural beams or ductwork that should run perpendicular to the windows, the lighting fixtures should run parallel to the windows. This is so the lights can be zoned — dimmed or turned off in sections according to the intensity and penetration of daylight into
the space during various times of the day.

Save energy with daylighting without compromise the thermal comfort.

To save energy, the electric lighting needs only to augment the daylight. In some case, dimming or turning lights off manually can be an effective method and has worked in a number of buildings where the staff has sufficient introduction into daylighting.

In poor examples of daylighting designs, lighting sensors are poorly located and rarely commissioned. The installation is handed off to contractors who have little understanding about the complexities of a daylighting system. Contractors often merely split the distance between the windows and the farthest wall with little regard as to how daylight is actually distributed.

Good daylighting offers a number of benefits, including energy savings, improved occupant comfort and possibly greater productivity. Creating cool, controlled daylight is a complex design challenge that is only possible with a coordinated group effort by the whole building team.

The energy benefits of a good daylighting system are critical to building owners. To achieve the benefits, building owners have to support a design strategy for their buildings that involves all the design professionals — architects, engineers, designers and contractors — working together from the beginning. That’s the only way to be successful and for the building to be cost-effective.

Energy Efficiency practice in Airport Cafetaria