Archive for July, 2008

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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