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A New Spin on Efficient Home Ceiling Fans

by LiveModern Webmaster last modified Jan 04, 2012 02:06 AM
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by Brent Ehrlich last modified Apr 22, 2011

Most ceiling fans come without lights, but energy-efficient light kits can usually be added. There are thousands of residential ceiling fans out there. GreenSpec picks three lines that outperform others on performance and effi... Use ceiling fans for cooling--then turn them off It is 33°F and hailing as I write this post, but spring and summer will eventually arrive here in central Vermont along with surprisingly hot weather. Our GreenSpec team is getting a jump on the cooling season by updating our residential ceiling fan listings (in-depth GreenSpec listings are available to subscribers). When used properly, residential ceiling fans provide cooling by creating a downward wind that speeds up moisture evaporation from the skin, which then cools our bodies--a lot like the way that we are cooled by sweating, or by evaporative air conditioning. Conventional air conditioners are energy hogs, so using a ceiling fan can be a great way to avoid A/C use and reduce that energy consumption. But in an empty room fans are counter-productive--the motors just consume energy and generate additional heat, so they need to be turned off when leaving a room. Not that useful in winter In winter, ceiling fan companies recommend reversing the rotation counterclockwise and setting the fan speed to low to circulate warm air "trapped" at the ceiling, but I couldn't find any data to verify that this actually works or whether it just heats up the ceiling instead. In other words, those diagrams that use arrows to show how ceiling fan use in winter keeps you warm may not actually represent reality. Most people turn fans off in the winter to avoid drafts and a cooling effect. It used to be the blade that mattered Ceiling fan performance used to revolve around the shape of the blade. We highlighted Hampton Bay's Gossamer fan when it came out in 2001, for instance, because its blades had an airfoil shape that boosted airflow by 40% over standard flat blades. But product standards are constantly changing as technology advances, and the ceiling fan industry is no different. When I started looking into ceiling fan performance to update GreenSpec standards and searched the Energy Star-qualified ceiling fan database, I was initially disappointed--and a little surprised--to find that the Gossamer is not on the list. Even Energy Star has over 1,000 certified fans Energy Star-qualified residential ceiling fans undergo standardized testing to determine airflow efficiency based on cubic feet per minute (CFM) airflow per watt of energy consumed. These measurements are taken at low, medium, and high speeds, with low and high scores being a pretty good indicator of overall performance. At low speeds, Energy Star's minimum airflow requirement is 1250 CFM with an efficiency of 155 CFM/watt. At high speed the requirement is 5000 CFM and 75 CFM per watt. That's not a very high bar for Energy Star certification, as demonstrated by the well over 1,000 Energy Star-qualified fans hovering around those numbers. Energy Star claims its fans are "50% more efficient than non-qualified models," so I can't imagine how many more thousands of really inefficient fans there are across the U.S., spinning away with their leaf-shaped wicker blades. We found the best of the best When I saw the numbers for several new lines of fans with low- and high-speed maximum efficiencies of 620/350, 978/248, and 683/243 cfm per watt, respectively, I thought they must be misprints or data anomalies. But those numbers are correct; the top performer is six times more efficient than the low-speed Energy Star standard. One uses an airfoil blade design and is more than twice as efficient at high speed than the low-speed Energy Star standard. It's all about motor efficiency These fans are so efficient because of they all use electronically commutated motors (ECM), also known as DC brushless motors (sometimes just called EC motors). ECMs have electronic commutators (part of the motor that helps control motor speed and torque) rather than mechanical commutators and brushes, and use permanent magnet rotors and built-in inverters. ECMs can be precisely controlled to maximize efficiency as the motor changes speeds, and there are almost no mechanical losses or heat generation that you find in AC motors. They are just far superior motors for low horsepower uses like a ceiling fan. Airfoil blades are still used on energy-efficient fans like this one, but it's the fan's use of an ECM motor that leads to real energy-savings. Does blade shape also play a role in these impressive efficiency numbers? I asked the manufacturer's technical service lead about the airfoil blade. "There are a lot of factors that affect the performance of a fan--the pitch of the blade, rpm, motor size," he said. The shape and pitch of the blade can improve fan performance, but it can also bog a fan down if the motor isn't big enough. "It's really all about motor efficiency, and there is a big efficiency difference between an ECM and traditional AC motor," he said. The numbers appear to confirm this. According to Energy Star, the airfoil blade design is the top performer at high speed, but at low speed the other two models perform as well or better--and both of those companies use straight blades. Differences among the top three There are some other differences, as well. One of our top three comes with an integrated compact-fluorescent (CFL) light fixture. If you want a light in the others you'll have to purchase an additional light kit. The airfoil model has a distinct look that might be an asset or liability depending on your tastes. With the other two you'll have more finish and blade combinations, and since fans are often chosen to blend in with the décor, those options can't be discounted. All but one of these fans have 52–54 inch spans, the exception offering 52- and 60-inch models, and all but one come with hand-held remote controls, which are important for making sure fans get turned off when people leave the room. The use of any ceiling fan can offset the use of more energy-intensive air conditioners, but GreenSpec doesn't list just any fan. Our directory strives to select the top-performing products, so our team has decided to only list ECM-driven residential ceiling fans--at least until new technology supplants it. We have added the three fans discussed here, but, alas, we have had to remove the once-innovative Gossamer from our GreenSpec directory. It's hard to see old listings replaced, but at least its airfoil blade design lives on in one of the new models. The full story on each of these fans is in the members-only area of our GreenSpec directory. New members can get a full month's access to GreenSpec, Environmental Building News, and High Performance Buildings case studies for only $1 -- after that, monthly access is only $19.95, and can be cancelled anytime. Click here to try it for $1 . Brent Ehrlich is the products editor at BuildingGreen, Inc.






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