Window coatings for enhanced lighting/heating efficiency
A lighting control system is only one part of an extensive building management system that includes environmental controls such as heating, air conditioning, air circulation, and air quality, as well as building security and safety. Because of the close relationship between lighting and heating, the building control system should consider environmental comfort and illumination needs together to optimize building comfort and energy efficiency.
Letting sunlight in through the windows can help illuminate the building’s interior, but it might also raise the internal temperature. Many modern office buildings implement low-emissivity (low-E) glass coatings, a thin transparent layer laid over the glass to reflect infrared energy, which creates heat. Low-E coatings work like the silver lining on the inside of a thermos. During cooler months, the coating seals the warmer air inside the building, preventing it from escaping to the colder exterior. Conversely, when it’s warmer outdoors, materials such as silver in low-E coatings can keep the cool air inside (see illustration). Double-paned windows have a gap between the two glass layers to create a naturally insulating air pocket, similar to that between the inner and outer shells of the thermos.
The major components of a responsive lighting system include LED light sources, power control devices, and sensors and microcontrollers to provide distributed intelligence required for lighting control and communication with the system’s secondary devices.
Daylight harvesting is one way companies can save energy and reduce ongoing costs in commercial buildings. It uses natural light and heat to illuminate and/or warm a building when possible. For instance, a lighting control system may dim the lights on the east side of a building in the morning as sunlight enters and may slowly bring light levels up throughout the day as the sun makes its way to the west. Potential energy savings depend on how windows are situated relative to the location of the sun and geography. There is more daylight to be harvested in northern California than in Seattle, for instance.
Natural light levels can also be adjusted with tinted or shaded windows to meet the needs of a given workplace scenario. For example, a conference room presentation might not require as much light as employees working at their desks.
Occupancy sensors are key to lighting adjustments. Motion sensors in a particular room or on a specific building floor will automatically request that the lighting control system dim the lights if they sense the area has been unoccupied for a predetermined period. Occupancy sensors may be used in conjunction with a timer function that dims every light in a building after occupants have left for the day, and then increases light levels in the morning when employees typically arrive.
Some lighting and HVAC systems utilize Bluetooth-enabled devices to identify when individuals enter or leave a space. Perhaps an executive on the fourth floor would prefer their office temperature a few degrees higher or lower than the rest of the building. In that case, the internal lighting/heating system can begin making that adjustment when they get out of the elevator or even when they are located pulling into the parking lot in the morning.
Due to variables such as building size, operating hours, and types of LED technologies installed, calculating how much energy a business might save by using lighting control systems equipped for daylight harvesting with sensors and timers can be difficult. However, if the rate of LED penetration continues at its current pace, the DOE projects energy savings nationwide will amount to 4.8 quadrillion BTUs annually by 2035 — approximately half of the total U.S. energy consumption from lighting in 2017.
Window coatings for enhanced lighting/heating efficiency
A lighting control system is only one part of an extensive building management system that includes environmental controls such as heating, air conditioning, air circulation, and air quality, as well as building security and safety. Because of the close relationship between lighting and heating, the building control system should consider environmental comfort and illumination needs together to optimize building comfort and energy efficiency.
Letting sunlight in through the windows can help illuminate the building’s interior, but it might also raise the internal temperature. Many modern office buildings implement low-emissivity (low-E) glass coatings, a thin transparent layer laid over the glass to reflect infrared energy, which creates heat. Low-E coatings work like the silver lining on the inside of a thermos. During cooler months, the coating seals the warmer air inside the building, preventing it from escaping to the colder exterior. Conversely, when it’s warmer outdoors, materials such as silver in low-E coatings can keep the cool air inside (see illustration). Double-paned windows have a gap between the two glass layers to create a naturally insulating air pocket, similar to that between the inner and outer shells of the thermos.
Passive low-E coatings are designed to absorb sunlight and reduce electric heating costs. In contrast, solar control low-E coatings are designed to reflect sunlight and keep the internal temperature (and air conditioning costs) down. Passive Low-E coatings are most effective when applied to the interior surface of windows (number 4 surface), as far away from direct sunlight as possible. In contrast, solar control coatings are best applied on exterior panes (number 1 surface). There are different standards for measuring the effectiveness of low-E coated glass. U-value measures how much heat dissipates through a window, while visible light transmittance is the amount of light the glass lets in. The solar heat gain coefficient measures how much solar radiation a window absorbs, both directly from sunlight and the reflection of that radiation to the interior glass. The lower a window’s solar heat gain coefficient, the less heat it transmits.
There are different standards for measuring the effectiveness of low-E coated glass. U-value measures how much heat dissipates through a window, while visible light transmittance is the amount of light the glass lets in. The solar heat gain coefficient measures how much solar radiation a window absorbs, both directly from sunlight and the reflection of that radiation to the interior glass. The lower a window’s solar heat gain coefficient, the less heat it transmits.
Conclusion
Reducing energy consumption is one of the few areas where public and private sectors seem aligned — businesses and governments are investing more in LED lighting and other energy-efficient technologies. In the commercial sector, the adoption of LED lighting and control systems could reduce the amount of energy consumed by lighting in the U.S. by as much as half in the next 15 years, according to the DOE. Eventually, we may see responsive systems catch up in the residential market as well, as technologies that are scaled to consumer needs and economies.
