Energy Efficiency

Dear Pablo,

I recently heard a radio ad by a freight train company, claiming that it moves 1 ton of goods 422 miles on 1 gallon of fuel. Can this be true? And how does it compare to my car’s fuel economy?

The freight company is CSX and its exact claim is, “Trains can move a ton of freight more than 423 miles on a single gallon of fuel.” While this number sounds astounding, and the freight company cites it to show off its “environmental stewardship,” the metric used is quite different than the “miles per gallon” we use with passenger cars. (more…)

Dear Pablo,

My parents are from the typewriter generation and insist on printing every document before they read it. Their argument is that reading it on the computer uses more energy than printing it out and turning the computer off. Is this true?

It certainly depends on the document and how you print it. A one-line e-mail would not make sense to print, where a 100-page reference document that is printed double-sided may make more sense to print. But let’s try to back that up with some numbers. (more…)

Dear Pablo,

I was excited to hear that Chevy plans to debut an electric car in 2010. But then a discussion with a friend got me thinking: If the electricity used to charge up an electric car is created by burning fossil fuels, is it better to stick with a gas-powered car with good fuel economy?

It’s true that most electric cars get their electricity from the grid, which, in many states, is made up mostly of electricity from coal-fired power plants. In areas where the power comes mostly from hydro, wind or solar, your electric car would be virtually emissions-free. (Any electric-car owner can achieve this by installing a solar carport at home.) (more…)

Dear Pablo,

It’s too damn hot to sleep at night! To cool our bedroom on these summer nights, my husband and I can run either three fans or one air conditioner. Which is better for the environment?

Let me first answer the question and then I will discuss some alternatives. Based on additional information from the reader, I learned that each fan uses 50 watts of 120 volt electricity (150 total), while the air conditioner uses 530 watts of 120 volt electricity. Already we can see that the three fans use 28 percent as much energy. If the three fans are truly comparable in the level of comfort they provide, by all means, use the fans! (more…)

Dear Pablo,

Since gas prices have topped $4 a gallon, tips on saving gas have been the flavor-of-the-day in the media. But does driving slower really save gas? If it takes me longer to get there, isn’t my car burning more gas?

The short answer is that slowing down does increase the fuel economy of your vehicle. The reason lies in aerodynamics. What you need to know is this: As speed doubles, the force (aerodynamic drag) on your vehicle increases fourfold. For example, a house built to withstand 200 mph wind has to be four times stronger than a house built to withstand 100 mph wind. The formula for aerodynamic drag on your vehicle takes into account how aerodynamic it is, what the area of its cross section is, what the density of the air is, and what your vehicle’s speed is. Since you can’t influence the density of the air, and you can’t change your vehicle’s aerodynamics, that leaves only speed. And slower speed equals less drag. (more…)

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