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07/24/2012

Time to Harvest

When implemented correctly, daylight harvesting and automated shading strategies can provide impressive energy savings, all while boosting comfort and productivity.

By Brent Protzman, Ph.D

 
  • /Portals/3/images/magazine/2012/0812/I_0812_Web_EDNtbk_1.jpg

    Both retrofit and centralized control systems can automatically adjust lighting levels and shades in response to daylight conditions. View larger

  • /Portals/3/images/magazine/2012/0812/I_0812_Web_EDNtbk_2.jpg

    Both retrofit and centralized control systems can automatically adjust lighting levels and shades in response to daylight conditions. View larger

What is so critical about sustainable building design? Commercial buildings consume nearly 40 percent of total energy consumption, and within that envelope, lighting electricity accounts for 38 percent of consumption, while air conditioning accounts for 23 percent1. Clearly, lighting and air conditioning constitute two of the prime candidates for energy reduction.

Driven by growing energy demands and the significant impacts that lighting and air conditioning have on energy consumption, lighting and shade control are fast emerging as important pathways to responsible energy use.

Daylighting design can have a tremendous impact on lighting and air conditioning use. However, optimal daylighting design is much more than creating window openings to allow daylight into a building. The energy balance alone often creates conflict between reduced electric lighting and the need to cool the building to compensate for the additional solar heat.

More importantly, when we talk about truly sustainable design we need to go beyond energy savings to include the human elements of the workplace, including glare, views and distractions. The complexity and constantly changing nature of daylight requires dynamic solutions to simultaneously optimize these factors.

Strategies such as daylight harvesting and automatic shade control contribute to energy savings by reducing the amount of electric light required when daylight is present, while minimizing solar heat gain. These strategies also work to improve occupant comfort, reduce glare and maximize views without continual user maintenance, thereby achieving an optimal balance between energy, functionality and comfort.

environmental factors
Building location, orientation and layout all affect the way daylight impacts a space. Appropriate daylight design incorporates information about both the quantity and the quality of daylight for a given location. Some of the key design considerations include global location, climate type, typical cloud cover (average number of cloudy, partly cloudy and sunny days) and landscape (number and type of obstructions such as surrounding buildings, vegetation, terrain and so on).

Virtually every building will have to mitigate glare as even cloudy geographies have the occasional clear or partly cloudy day (although Seattle might argue otherwise). However, geographical settings typically determine additional daylight control strategies. In hot climates, the focus is direct solar control through light and heat reduction, and the utilization of light redirection devices (such as Venetian blinds or light shelves) to increase light penetration into the building. In temperate climates that experience large swings in temperature, seasonal daylight control is used to block the direct sun in the summer while allowing sunlight penetration during the winter months to reduce heating needs.

In the Northern Hemisphere, the north façade of a building (or the south façade in the Southern Hemisphere) requires minimal shading and large windows to maximize exposure to diffuse skylight, while the south façade can control most direct sun with fixed shading systems. A building with an east/west orientation will have the greatest reliance on dynamic solar control due to direct solar penetration in the morning and afternoon.

automatic light control strategies
Regardless of a property’s unique environment, each building has opportunities to implement effective light control to save energy and enhance the working environment. Automatic light control strategies, such as daylighting, occupancy sensing and automatic shading help take the guesswork out of efficient lighting, while still providing personal control to accommodate individual preferences.

A daylighting control system works best when combined with a full-building lighting control system which incorporates daylight harvesting, automated shading, occupancy sensing, light level tuning (reducing the maximum light output for spaces that are overlit) and personal dimming controls. By combining these strategies, buildings have been able to reduce lighting usage by 60 percent or more2. It is also true that lighting energy reduction via light level tuning, daylighting and occupancy sensing can reduce HVAC use; an additional 15 percent HVAC energy reduction is possible if automated shading is used3.

Automated daylight harvesting can be achieved using a simple, retrofit control or a central, processor-based control system. Both systems use a permanent light sensor to provide feedback to the lighting system about the quantity of daylight in the space. The purpose of the sensor is to tell the lighting system how much supplemental electric light is required. A setpoint is identified, and this setpoint indicates the required light level that the control system maintains by adjusting electric light output in response to changes in available daylight.

Dimming is the recommended method of daylight harvesting. Dimming provides the least disruption, as studies show that gradual dimming of electric lighting by 15 or 20 percent is virtually undetectable to occupants in a space4, 5 and saves lighting electricity proportionate to the dimming percentage. A dimming daylighting control system can maintain ideal light levels with no action required by the occupant of the space.

More sophisticated daylight strategies will typically include localized, manual override controls for individual users that enable task-oriented lighting adjustments, ensuring optimal light levels and maintaining employee performance. Combined with occupancy sensors to ensure that lighting is not left on when a space is vacant, daylight harvesting delivers savings that can meet or exceed building codes and energy-reduction goals.

automated shade controls
To achieve total light management, that same processor-based lighting control system can integrate with automated, silent, low-voltage shading systems that communicate with the lighting controls.

Shade automation is important to achieve the full energy savings and occupant comfort potential in a building. Manual shades are typically operated only to reduce discomfort. Automated shades are adjusted first for glare mitigation through an understanding of sun position and automated response, blocking direct sunlight on the task surface; they can be adjusted further through local manual override. These systems can also integrate window-based daylight sensors to open shades when they detect cloud cover or environmental shadows, providing the same protection from discomfort while maximizing views and energy savings from electric lighting and air conditioning.

In the end, no matter where your building is, how it is oriented or how much daylight enters the space, a comprehensive light control system that includes both daylight harvesting and automated shading strategies will contribute to significant energy savings, a more comfortable environment and a more sustainable building.

 

Brent Protzman is an energy applications leader with Lutron, a global provider of light control solutions. He is also the author of several published articles on human factors in lighting and lighting energy. Protzman is lighting certified (LC) and has a Ph.D in Architectural Engineering from the University of Nebraska.

 

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REFERENCES

1 According to the Energy Information Administration, 2003 Commercial Buildings Energy Consumption Survey, released September 2008. Online. Retrieved from ftp://ftp.eia.doe.gov/consumption/overview.pdf

2 Glenn Hughes, director of construction for The New York Times Company building in New York City reports 70 percent lighting energy savings using Lutron systems. Jeff Choma, manager of mechanical and electrical systems at Georgian College in Ontario, Canada reports 70 percent lighting energy savings using Lutron light control systems. Lighting energy savings exceeding 60 percent is frequently reported by customers using Lutron solutions as part of an overall energy-savings design program.

3 Lutron-commissioned study by Herrick Laboratories. Purdue University. 2011

4 Newsham GR & Mancini S. 2006. The potential for demand-responsive lighting in non-daylit offices. National Research Council Canada

5 Newsham GR & Birt B. 2010. Demand-responsive lighting: a field study. National Research Council Canada

 

 

 
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