Daylight-Based Controls

Controls are the heart of a good daylighting system and the benefits are many. Here are some tips and myths about daylighting.

Daylight-Based Controls
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What isn't there to like about sunshine? We like sunny days over cloudy, rainy, dreary days. It's a proven fact that humans have more energy and feel better about themselves when the sun is out. There is a reason, after all, why the suicide rate is so high in cloudy, rainy Seattle, for instance. There are other reasons to like daylight, especially as it pertains to buildings: sunlight makes for a better scene (key in retail applications), it saves energy and operating costs, and it is said to reduce our impact on the planet.
Studies do show that shoppers linger longer and buy more in naturally lit environments, students do better on tests, and office workers are more productive and absent less. And, of course, energy costs keep skyrocketing. In fact, energy costs are surpassing salaries and benefits as the number one cost to businesses. So, it makes sense for daylighting technology to flourish, right? And to be effective, daylighting needs good controls.
"Controls are the key component for both lighting and daylighting and they have come a long way in just the past couple of years of making the transition from lighting to daylighting more seamless," says Earl Houston, ceo, Ciralight.
The good, no bad and no ugly
Good daylighting is the result of an integrated design process, which includes the building design, installation of the right materials and controls that make the system work. According to the Energy Center of Wisconsin, good daylighting design can include elements such as concepts of lighting power density, illuminance levels, contrast ratios, window-to-wall ratios, ceiling to skylight area percentages, and reduction in glare. Good daylighting principles can vary among geographics, building design and climate. It is a mix of art and science.
But what makes good daylighting? From the controls sense, it is the ability to save energy costs and provide the right amount of light during the day—as noted seamless light. With that, there are four basic types of controls:
Schedule-based.Occupancy-based.Personal control.Daylight-based control/harvesting.
The objective of the daylight-based controls is to turn off lights in areas with abundant daylight or dim the artificial lights as natural light increases, says Eddie Hickerson, staff marketing specialist, lighting controls, Square D. In the end, energy is saved.
"Savings can be 20 percent of 30 percent via occupancy sensors, for instance, so savings can be significant," Hickerson notes. He adds the savings can even reach 80 percent.
"Savings from lighting controls can be determined pretty quickly," Hickerson adds. "Lighting controls should be an area in which contractors and building owners can be more creative and take liberties in looking for opportunities to save."
Houston adds that overall energy savings can range anywhere from 15 percent at the minimum to better than 40 percent. Houston also notes that with his company's SunTracker system, the return on investment often is in the months and, in fact, the ROI in some cases has been too quick for businesses to enjoy rebates and other energy-saving tax incentives.
The benefits of daylighting also extend beyond just lower lighting costs, it also can cut HVAC costs as well. Termed cool daylighting, it takes a holistic approach to the entire building, and aimed at reducing the cooling load of the building. The cooling load primarily is a function of internal heat gain from lights, equipment, people and sunlight. Daylighting reduces the need for electric lighting, which lowers the heat produced by electric lights.
When incorporating high performance glazing and exterior shading recommended for a comprehensive cool daylighting design, it also minimizes heat gain from the sun through the envelope. It is said these overall reduced loads often result in a reduction in the size of the cooling system.
The environmental and monetary benefits are many. For instance Wal Mart has been installing daylighting systems in its stores. For just one store, it is estimated there is a estimated cut of 618,000 pounds of carbon dioxide, 1,800 pounds of nitrogen oxides and 1,100 pounds of sulfur dioxide from being produced at power plants.
Contractor's role
Houston says electrical contractors can play a significant role in the daylighting realm. One role is integrating artificial and daylight systems.
Hickerson concurs. He adds, "A huge opportunity exists for contractors to sell real value-added products to a project."
And those benefits ultimately help the building owner. Hickerson says that for every $1 reduction in operating cost $10 is added to the buildings's value.
"Good contractors work with and do understand what to do in regard to energy efficiency and selling daylighting technology," Houston explains. And, as the concept of daylighting grows, the role of contractors will grow as well. "Daylighting will be run by sensors," he adds. "Photocells, computerization, photovoltaic technology, all of that will require the expertise of the contractor."
Photocell placement is key, correct system configuration and the coordination of controls and systems are all vital to attaining the most effective and cost-savings daylighting system.
"Daylighting systems are highly visible and they are something the building owner and the electrical contractor can show off," Hickerson contends. "People will take notice."
Shining Light on Daylighting Myths
From the Energy Center of Wisconsin, Dayligthting Collaberation comes these myths and facts as they pertain to daylighting:
MYTH: Daylighting costs more.
FACT: Daylighting does not have to increase construction costs if it's done using an integrated design approach. An integrated approach considers the effect of lighting on air conditioning. The electric lights in modern buildings produce a lot of heat, while properly directed natural lighting generates almost no heat at all. The decrease in internally generated heat allows designers to downsize the air conditioning system. The resulting cost reduction helps pay for daylighting improvements.
MYTH: Daylighting is complicated.
FACT: It need not be. The Daylighting Collaborative has developed daylighting designs that work in most commercial and educational buildings. The result is reproducible energy savings and performance, minimal investment of design time and no risk.
MYTH: Daylighting lets in too much heat.
FACT: The light-to-heat ratio for daylighting is far better than even the most efficient electric lights. Properly designed daylighting screens out 99 percent of the sun's heat while providing 50 foot-candles of light, more than enough for most tasks.
MYTH: Daylighting causes glare.
FACT: Glare happens when too much light enters a building, which happens all the time in conventionally lit buildings. A properly daylit building uses carefully placed windows, shading devices and low-transmittance glass—techniques that block direct sunlight and greatly reduce glare.
MYTH: It's better to upgrade lighting and HVAC efficiency.
FACT: It's better to reduce the need for electric lighting and cooling in the first place. Cool daylighting does both. Natural light reduces the amount of installed electric lighting. Less electric lighting means less heat gain, which means less heat to remove with air conditioning, using less energy. What lighting and cooling is left can then be done by the most efficient equipment available. Being efficient is always a good idea, but needing less energy is even better.
MYTH: Daylit buildings need clear glass windows.
FACT: Clear glass windows let in too much light, far more than what's needed for effective lighting. The sun provides 7,000 to 10,000 foot-candles of light, while indoor office spaces need about 50 foot-candles. Too much light causes glare and the "cave effect," where the back of the room appears dark compared to other surfaces. This encourages people to close the blinds and turn on overhead lights to cut down the contrast in the room.
MYTH: Daylighting = skylighting.
FACT: Properly designed skylighting is a good technique in certain situations, such as enclosed hallways. However, in many schools and offices, windows can provide most of the daylighting that's needed. It's the placement and size of the windows that matters for effective daylighting. Clerestory windows—a row of small windows near the top of the wall—bring light in high in the room, producing a natural glow on the ceiling that mimics our experience of the sky.
MYTH: You need sunny, clear days.
FACT: A completely overcast sky provides 5,000 to 6,000 foot-candles of illumination—100 times more than needed. In some ways, overcast skies often provide a better lighting source because the light is more diffuse and even. Daylighting is most challenging in the sunny climates of the south because of the immense amount of illumination from the sky and sun.
author: By John Dyslin, editor - Electrical Contracting Products




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