Editor's Note: Scientific American's George Musser will be chronicling his experiences installing solar panels and taking other steps to save energy in 60-Second Solar. Read his introduction here and see all posts here.
This year, I’ve been spared the annual ritual of lugging the window air conditioners out of the closet. Not only has it been one of the mildest summers on record in the New York area, but our house has a spiffy new cool white roof, so our attic is no longer the hothouse it once was. Reflective window blinds, compact fluorescent and LED bulbs, and an attic fan have also helped to keep the house cool. In past summers, there usually came some days in August where we vowed to upgrade to a whole-house air conditioning system, but so far we’ve just sweated them out.
Ever on the lookout for other ways to save energy, I sought advice from Gordon Wuthrich of Trane, a leading air-conditioner manufacturer. Obviously, a more efficient air conditioner helps. Units are ranked by their seasonal energy efficiency rating (SEER), which is a charming hodgepodge of a number: the cooling output in Imperial units divided by the electricity input in metric units, multiplied by a factor that accounts for the on-off cycling. Doubling the SEER value halves your electric bill.
Unfortunately, the cost is not so linear. High-performance units come with high price tags. They might make sense for a new house, but retrofitting an existing unit can be prohibitively expensive. A couple of online calculators (here and here) can help you determine whether it's worth it. Long payback times are a sad reality of reducing energy use, as I’ve found when my dreams of triple-glazed windows and a new water heater met financial reality.
A more cost-effective step is to make sure that whatever you already have is well-maintained, much as I saved huge wads of cash just by turning down the overpressure setting on my steam heat system. For air conditioners, there are many equally easy steps (see here and here). One that Wuthrich emphasized is to make sure your system is topped-up with refrigerant. A study in Florida found that three-quarters of air conditioners were severely undercharged with refrigerant, which reduced their cooling capacity by 15 percent or more. That can double or triple your electric bill as the a/c struggles in vain to cool the house off. The cost of a service call can pay itself off real fast. Last year Trane came out with a device, Charge Assist, that lets technicians add precisely the right amount of refrigerant. Trane's top-end air conditioners continuously monitor and recalibrate themselves.
Danny Cohen of Sun Microsystems—who, like many other Silicon Valley types, has taken up energy technology as the next big thing—has argued that there is a “long green tail” of savings from monitoring buildings’ energy consumption. Neil Gershenfeld of MIT says his group found they could cut energy consumption by a third by dimming or turning off lamps when there was enough light coming through the windows and shutting down the a/c when someone opened the window or when there was nobody in the room. The good thing about using energy inefficiently is that it’s so easy to do better.
Charge Assist photo courtesy of Trane