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May 2, 2018 - Lighting
By Scott Blue
Throughout time, humans have used energy from the sun for everything from illumination to power generation. Now, technology is increasingly focusing on getting the most of our closest star through a variety of techniques in building design and construction.
Daylight harvesting, or daylighting for short, is the strategy of paying special attention to the positioning and shape of windows, atriums, skylights, and glass doors to maximize the benefits of sunlight. Other daylighting tactics include utilization of various kinds of window glass, translucent walls, reflectors, and remote distribution using mirrors or light tubes. To get the most out of this approach, omputational simulations are used to determine positioning and usage of these elements to evaluate daylighting performance.
Motorized window treatment systems can be part of the solution for maximizing daylight harvesting. These systems power the operation of shades, blinds and screens to provide greater control over sunlight levels in interior spaces.
America is a cooped up country. According to a January article in the New York Times this year, we spend up to 90 percent of our lives indoors. This is where we work, play, learn, and reside, and mounting evidence is that we are paying a physiological price for the confinement.
A study of 21,000 elementary school children found that students in naturally lit classrooms scored over 20 percent higher on tests than those in artificially lit rooms. Numerous other research links sunlight with productivity and morale.
Letting more sunlight into interior spaces brings natural lighting and warmth, meaning that facilities need to use less the means for generating both. A 2006 article in Building Operating Management pointed out that the energy from sunlight through glass provides 5,000 foot-candles on a sunny day. Most people need only 35 foot-candles to read. As for warmth, that sunlight can heat 15 to 30 gallons of water to a temperature hot enough for a shower, and certainly can help do part of the job of the HVAC system.
From the standpoint of building operation, the sun becomes a partner for energy savings and sustainability. Good daylighting design can save up to 75 percent of the energy used to electrically light a room.
Not just the sun gives off heat. While this notion is not intuitive, turning down the electrical lights can save a building 10 to 20 percent in cooling energy, or what the Daylighting Collaborative calls “cool daylighting.” Harvesting the maximum amount of sunlight also makes rooms more comfortable, while being properly illuminated, without having the HVAC system work harder or relying on artificial light to achieve both.
Recognizing the impact of sunlight on sustainability, daylighting standards are being developed. California’s Title 24, IECC 2012, and ASHRAE 90-1 already have daylighting guidelines. In 2009 LEED initiated daylighting standards, which were intended to connect building occupants with the outdoors. LEED v4 has the goal of encouraging analysis of both the quality and quantity of the light, as well balancing the use of glazing to ensure more light and less cooling load.
Motorized window treatment systems play a role in managing the daylighting process due to the number of factors associated with sunlight. Throughout the day and the year as the sun travels along the sky, the angle of the sunlight constantly changes. During that trip, objects outside the building such as trees and other structures can temporarily block the amount of sunlight coming through the window.
For daylight harvesting, photosensor-actuated controls track and interpret changes in sunlight intensity. That information enables the artificial lighting system to make decisions as to which lights are turned on in the room based on sunlight levels.
Based on amount of sunlight that enters the room and on what areas the sunbeams illuminate, the system can have all, some, or none of the lights turned on to save energy, yet ensure occupants have sufficient light. Motorized window treatment sensors also can be used in conjunction with occupancy sensors that turn lights on and off.
Motorized window treatment systems take daylight harvesting to another level. Depending upon previous positioning of the shades and blinds before the sun rises, they may need adjustment based on the amount of sunlight pouring into the room. The motorized window treatment system can respond to dedicated photosensors or to the photosensors tied into the artificial lighting system. Depending upon the position of the sun, level of cloudiness, and other factors, the shades and blinds can raise and lower and open and close based on system parameters.
Controlling the entry of sunlight using motorized window treatment systems is particularly useful for facilities with tall windows or skylights, where shades and blinds would be inaccessible for manual operation. There are facilities that have installed floor-to-ceiling windows, and these places have found they needed movable partitions to block the sun from beating down on employees, tenants and customers. For those applications as well as all motorized window treatment systems, remote control systems are available to override system operation when the glare gets to be too intense. There are a variety of wireless remote control designs, including portable, wall-mounted, and those that are touchless and respond to a wave of the hand.
Daylight harvesting is a balancing act; reducing heat from artificial lighting can lead to rising temperatures. The solar heat gain can substitute for the warmth generated by the HVAC system, which is a significant benefit on the very sunny days that take place in winter.
The motorized window treatment system can ensure that the shades and blinds are fully open to exploit the sun’s benefits and reduce heating system use for greater energy sustainability. But there are times when the solar heat gain can be excessively warm and ultimately uncomfortable.
As with controlling glare, the motorized window treatment system positions shades and blinds by either working automatically with the HVAC system, or through remote controls. The amount of glare and warmth tolerated by room occupants is, as always, based on personal preference, and the remote controls enable users to adjust shades and blinds positioning to their liking. Adjustments can be made with little to no disruption to workflow.
Facilities are just starting to use daylight harvesting to control sunlight levels. Right now controlling the amount of sunlight entering an interior space using motorized window treatment systems is less prevalent, though very promising in terms of increasing the sustainability of using passive sunlight over artificial means of generating light and heat.
As application grows, so does innovation. The motorized window treatment system itself can use two-thirds less energy by being powered by DC rather than AC drives. Therefore, use of motorized window treatment systems will grow as facility managers learn where and how to deploy these systems and become more aware of the possible savings.
Scott Blue (email@example.com) is vice president, operations, Nice Group USA, part of Nice S.p.A., offering integrated automation solutions to control gates, garage doors, parking systems, wireless alarm systems, solar screens, awnings, blinds, and shutters for residential, commercial and industrial buildings.