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Spotlight on Systems Research
Four universities strive to improve the way lighting systems, solar-harvesting technologies, and HVAC work
(archrecord.construction.com - June 2005)

By Ted Smalley Bowen

... and poses no environmental problems throughout its lifecycle.

For designers and builders, the cell’s benefits would include lower transportation costs and easier handling and installation, according to Kippelen. Layered on substrates as thin as a few microns, the cells would conform easily to most roof and wall shapes.

Organic semiconductors, however, are sensitive to moisture and oxygen, and a highly flexible plastic substrate will be needed to provide a sufficient barrier, he added. But while durability is a question mark—they’re unlikely to match the 20-to-30-year life span of silicon-based PV cells—the light weight and low cost of the cells would make frequent replacement feasible. “If you just have to peel them off and put new ones on, it could make sense to change the cells as often as every two years, especially if you can make them by the mile, printing roll to roll,” Kippelin said.

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The researchers’ cell has a power conversion efficiency of 3.6 percent, slightly better than the 3.5 percent achieved by most existing organic cells.They expect to raise that to 5 percent soon, said Kippelen, who added that 10 percent efficiency can be achieved within the next few years. Typical silicon PV cells are about 10 to 15 percent efficient, with some high-end cells achieving closer to 30 percent efficiency. Kippelen stressed that a lot of research stands between this early work on organic cells and their widespread use. “Organic materials for semiconducting have only been around for about 10 years,” he said. “The science of these materials is not as advanced as for silicon. It’s difficult to predict what the upper efficiencies are going to be.”

Small versions of the Georgia Tech researchers’ cell—on the order of a square centimeter—could provide power to distributed building sensors or radio frequency identification (RFID) tags within a couple of years. Larger solar panels or rolls of sheeting might be 5 to 10 years away, according to Keppelen.

Environmentally, making organic PV cells poses no significant problems compared to some of the more advanced thin-film solar cells that use harsh chemicals containing cadmium, copper, and arsenic, said Keppelen. “During the manufacture of these cells, people are exposed to nasty chemicals and the process generates toxic waste,” he said. “The materials we’re using are carbon-based and fairly harmless. Photovoltaic technology should be environmentally friendly,” he said.

Up to half the electricity used in commercial buildings is consumed by lighting, but control schemes that match lighting use to actual demand can significantly cut that figure. A wireless lighting control system under development at the University of California at Berkeley puts sensors and switches where the action is, on the theory that letting users, building managers, and even utility companies control the lights makes for greater efficiency.

The Berkeley researchers have assembled a prototype system of programmable wireless switches, each of which can control many individual light fixtures. The scheme uses wireless sensors developed at Berkeley that together form a “mesh network” of distributed switches. The fixtures controlled by such a network can be operated manually or automatically, in response to conditions in the immediate surroundings, predetermined schedules, or triggers like signals from utility companies. The scheme doesn’t rely on a single existing control protocol, such as the Digital Addressable Lighting Interface (DALI) or Building Automation Control network (BACnet), but is intended to be compatible with existing and new lighting equipment, according to the researchers.

	This diagram shows the design of a flexible solar cell containing a layer of “quantum dots” that harvest sunlight, pioneered by the University of Toronto.

In spring 2004, a test of the Berkeley system in which users were given control of the lighting in their workspaces yielded a 40 percent drop in lighting energy use. The pilot installation was a small office with eight workstations and eight fixtures controlled by a pair of switches. “Our starting point is providing local control to occupants,” said Charlie Huizenga, a Berkeley research specialist and lecturer.

The test results highlight the inefficiencies of inflexible central control schemes for lighting, especially for open-plan offices. “One person near a window kept his light off because his space was nicely daylit. Another person kept the lights off when using her computer, but turned them on when reading and doing other paper-based tasks. Another person worked half-time, and was able to turn the light on and off as he came and went,” Huizenga said. A similar but larger-scale test program, involving roughly 40 controlled lights, is slated for this summer.

Because it doesn’t require rewiring, the low-cost wireless system developed for this study makes it more feasible to retrofit existing buildings with the technology. And the mesh network also makes it easier to provide precise lighting control in new buildings, says Huizenga. Drawing on sensor research conducted at Berkeley, the control scheme taps a variety of power sources. Where relay devices are part of light fixtures, they can draw regular A/C power, but remote switches and motion sensors can run on batteries. Huizenga said, “We are looking at powering them using solar cells, or scavenged vibrational energy.” Other researchers have developed push-button switches powered by piezoelectric elements (typically crystals that produce a voltage when they’re under compression or tension, or that cause compression or expansion when a voltage is applied).

Controlling the disparate parts of such schemes—by integrating motion sensing, daylight sensing, remote switches, and central switches—is a complex and expensive undertaking, which is why so few buildings use advanced lighting-control systems. But Berkeley researchers believe electricity prices will rise in the next several years, creating an incentive to owners and operators to adopt such measures to slash costs. The cost of mesh networks like the one studied here will also likely drop as the technologies are refined. Unlike earlier systems, the devices in Berkeley’s scheme can be installed in a matter of minutes, Huizenga noted. “Maintenance is also an important issue for affordability—the controllers will need to last 15 to 20 years, at least as long as a ballast,” he said. Components like those used in the Berkeley study will be on the market within a year or so, he predicts.

The study’s results are “very encouraging, and say a lot about how much commercial space is overlit in the U.S. and perhaps elsewhere,” said Stephen Conners, director of MIT’s analysis group for regional electricity alternatives. Ideally, he added, a wireless system’s interface will allow lights to be controlled individually or in groups—but does that mean that pranksters could hijack and change your lights, à la television’s The Office? Typical security measures like password-protection systems would eliminate this concern, Conners says.

New study may boost an old energy-saving technique for HVAC By Peter Criscione In many buildings across the U.S., outdoor air is pulled in throughout the day at rates designed to satisfy ventilation requirements for maximum-occupancy conditions, even during times when there are few people in the building (think schools at night or restaurants between lunch and dinner). But a recent study conducted at Purdue University in Indiana has given a shot in the arm to an old strategy for managing energy waste. For more than a decade, waste from HVAC systems that condition spaces with variable occupancy has been addressed through demand-controlled ventilation (DCV), a strategy that links the amount of outside air drawn in for ventilation to the actual occupancy of the building at any given time, via a network of sensors that use airborne carbon dioxide concentration as a proxy for occupancy levels. DCV has been shown to produce annual energy savings of up to $1 per square foot. Up until now, the high expense and frequent maintenance required for DCV equipment limited the application of this strategy. But the technology has improved lately. A decade ago, sensors used in DCV systems ranged in cost from $500 to $800 each; now many newer devices cost $200 or less. In addition, some of them remain accurate for 10 to 15 years, substantially reducing the cost of the yearly calibrations that were required for older sensors. Also, many rooftop air conditioners, frequently used in commercial and institutional buildings, come equipped to accommodate sensor inputs, which reduces the amount of labor needed to implement DCV. DCV uses carbon dioxide monitors and special controls to estimate occupancy and adjust air intake. A study at Purdue concludes that DCV would be financially feasible for several types of buildings. Photography: Courtesy Carrier Corporation The Purdue study, conducted in 2003 and 2004, highlights these recent improvements in DCV technology and points out new opportunities for energy savings. Jim Braun, professor of mechanical engineering at Purdue University, and his colleague Kevin Mercer, modeled four types of buildings—a restaurant, a retail store, a school, and an office—in two cities in California and three cities outside the state (see table, above). The cities were selected to represent a range of climates for the study, and the modeled buildings varied in size from 5,250 square feet for the restaurant to 80,000 square feet for the retail store. The study compared traditionally operated HVAC systems to those using DCV. The restaurants and retail stores showed the most potential for savings with DCV, with savings estimated at around 50 percent of the total energy operating cost for HVAC in some cities. Across all the cities and buildings, payback periods ranged from 0.2 to 6.8 years, although 16 of the 20 modeled scenarios yielded a payback of fewer than two years, and 12 yielded a payback of one year or less (see table). The modeling used more conservative numbers for design occupancy than those set forth in the relevant ASHRAE standard for all but office buildings—so it’s likely that payback periods would be even shorter than what the study predicts. Along with improvements in the DCV hardware itself, new online software tools, available through the Web sites of HVAC manufacturers, make it easier for design teams to determine where DCV can be used. The tools include Carrier’s “Hourly Analysis Program” (www.carrier.com), Honeywell’s “Savings Estimator” (www.honeywell.com), and AirTest’s “CO2 Ventilation Control and Energy Analysis” (www.airtest.com). Each allows users to enter information about a project, such as building type, size, and location. The software takes this information and provides users an analysis of the potential cost-effectiveness of a DCV system—which helps reduce the risk and uncertainty of moving forward with this strategy. “Our hope is that this research will increase the usage of this effective energy-saving strategy,” said Jim Braun. His hopes have already been realized: Two utility companies, in California and Connecticut, are now using the Purdue study to build programs that will help their customers identify opportunities to implement DCV. In the not-too-distant future, all HVAC systems may be smart enough to know when a building’s empty enough to call it quits.