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No Efficiency Without Controls
Jeremy Faludi, 23 May 07
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Many people are working on inventions that push the efficiency envelope in lighting, heating, computers, and more. But control technologies may actually be more important--by only using what we need, we can save huge amounts of energy with existing systems, and control technologies help us take only what we need.


You may be good about turning off the lights when you leave a room, but your office-mate might not be. Occupancy sensors eliminate the need for anyone to remember. An excellent paper by researchers at Rensselaer Polytechnic quotes energy savings of up to 43% for office environments, and 60% for some other environments. Established companies such as Johnson Controls and Lithonia have been selling these systems for years, and a new startup called Adura Technologies will now provide lighting control with no wiring, giving users a handheld remote control. They report a "40% reduction in lighting energy use and high user satisfaction" from the test installation. In addition to occupancy sensors, daylight sensors can also turn down or turn off lights when they sense there is plenty of natural sunlight around. These aren't just for indoors, either--some city street lamps use them too.

Occupancy sensors still have a ways to go, though. They are not tremendously accurate, so they usually compensate by not turning off the lights right away, just in case someone is still around. (And still, we've all had the experience where the lights go out on us and we need to wave our arms or stand up in order to set off the sensors again.) The Rensselaer study above showed that the amount of energy the sensors save is directly tied to how soon they shut off the lights, with up to 50-60% savings for five-minute shutoff times in classrooms, restrooms, and conference rooms compared to 40-50% savings for fifteen-minute shutoff times. This 10% energy efficiency gain can probably be achieved much more easily through better sensors than it can through better lighting technologies.


Heating, ventilation, and air conditioning ("HVAC") is another realm where control is crucial. It's also the realm that tends to be the #1 and #2 complaints of building occupants (with "it's too hot" and "it's too cold" vying for the top gripe position). In addition to occupancy sensors, the revolution that has happened over the last decade is giving individual users control over the temperature and ventilation of their own spaces. Companies that do this include Computrols and Argon Air among others; the latter claims "reduction in cost and energy consumption of at least 20%" using their system, and say it "requires 50% less outside air". Extensive research has also been done on it at Berkeley, Carnegie Mellon, and other institutes. A joint study between Carnegie Mellon and Oak Ridge National Lab showed that individual HVAC control not only yielded 20-35% less energy use, but also "lower first costs, significant churn savings [reconfiguration costs], measured thermal comfort and indoor air quality gains".


Energy-saving computers actually save most of their energy through better control of their systems, not through fundamental changes in how the chips or boards are built. Most of the Energy Star and 80-plus certification points are about getting your systems to sleep when not in use, and to minimize vampire power when they are sleeping. Even the low-power CPU's made by Sun, Intel, AMD, and others largely reduce their power usage by powering down parts of themselves when not in use, nanosecond-by-nanosecond.


The reason stick shifts get better mileage than automatic transmissions is that the control algorithms of automatic transmissions are not very good. However, even better is the continuously variable transmission, which can always keep a car's internal combustion engine running near its peak efficiency point no matter what speed the tires are spinning. The Wikipedia article on CVT's claims that "Fuel efficiency advantages as high as 20% over four-speed automatics can be obtained." Car companies around the world have been putting CVT's in cars for thirty years, yet they are still a rare find.

Of course, shipping has been improved by good vehicle-routing algorithms; these have been in use for decades and are now fairly mature, even including biomimetic algorithms based on the swarming of bees and ants. Public transportation can also be improved in similar ways, though less has been done in the sector. The main advantage of still-hypothetical Personal Rapid Transit is the deployment of only the vehicles actually needed by users for only the distance they wish to travel.

In short, all areas which are concerned about efficiency should be concerned about controls. It is an embodiment of one of the core principles of sustainable design (and nature's design), "more intelligence, less stuff". With the explosion of cheap computing and sensors, it should be easy to make sizeable reductions in energy and materials use that do not require better energy technologies or manufacturing technologies, but simply have smarter usage controls.

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Great article, Jer. Efficient controls are vital - to the extent that we need HVAC equipment, electric lighting, etc. But those of us who've been designing low-energy buildings for a long time (egads, am I really that old?) have a guiding principle: Favor Envelope Over Equipment. In other words, designing to employ daylight reduces the need for lamps, ballasts and controls. Insulation, air-sealing, glazing, proper roofing, overhangs and shading, etc., reduce the need for HVAC equipment and controls. Synergies abound: careful daylight design lowers wattage in the building, reducing AC loads. A well-detailed thermal envelope evens out mean radiant temperatures inside, providing superior thermal comfort even with some fluctuations of air temperature and relative humidity.

Generally speaking, the fewer "moving parts" within a building, the better. Of course we'll still rely on equipment, and your points about elegant controls are spot-on. But don't overlook the ability of the building itself to be a well-controlled system. That's really elegant design.

Posted by: David Foley on 23 May 07

Personal Rapid Transit (see wikipedia) also provides non-stop travel from origin to destination, which is much more efficient that stopping and starting.

Posted by: prt on 23 May 07

I think about this kind of thing all time, especially lights and AC. The high school I attend could definitely do better job of this. Excellent article.

Posted by: Will Pierce on 23 May 07

I totally agree, managing 'controls' should at a greater priority than coming up with new technologies to combat global warming. Just take a look at our waste in our landfills - I bet we can reduce it by nearly 40% if we only use what we need. Furthermore, we need to educate the public through public announcement - radio, TV, and web. We need to take advantage of the subminimal messages the advertising companies use to change people's habits to use only the things they need and not be wasteful. As you have noted, companies should come up with innovative controls, however it is the consumers who need to demand these new technologies and change their habits.

Posted by: Mike on 23 May 07

Hey, David, excellent point.

And here's more food for thought on that: By making passive-solar and other self-regulating systems, what you're doing is actually building the controls into the structure. Not all controls have to be electronic. This is another thing that nature does everywhere: stores information in physical structure instead of behavior. The more smarts you have built into the physical matter, the less smarts you need to operate it.

Posted by: Jeremy Faludi on 28 May 07



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