Live in Cities
Or in other words, suburbs are not green, dude:
- Some 3.5 million commuters drive 3 hours a day.
- The rate CO2 emission from a lawnmower is 11 times that of a car.
- Large apartment/condo buildings are more efficiently heated and cooled.
- The per capita carbon footprint of Manhattan, where car ownership is low, is 30% less than the rest of the country.
A/C is OK
... compared to heating, that is. The heating of US homes releases 8 times more CO2 annually than cooling them. Why? The main reason is that the difference between 70 degrees and 100 degrees is much less the difference between 70 degrees and 0 degrees. A little leg-work and we have the following evidence to support the idea that 'there is more cold temperature than hot':
- The average continental temperature in the US is 52 degrees.
- In New York City, the average temperature runs from 32 degrees in January to 77 degrees in July.
- In Houston, the average temperature runs from 52 degrees in January to 84 degrees in July.
This all sounds very reasonable. But the thermodynamicist in you to balk upon reaching the following parenthetical statement in the article:
(that is, it takes less energy to cool a given space by 1 degree than to heat it by the same amount)Huh!!???!! I believe it can be shown that that is a violation of the second law of thermodynamics.
While this information is interesting, I don't know how practical it is. After all, we are not often faced with the choice, "hmmm, should I use A/C or heat today". It is not like choosing which CD to play on your stereo system. I will admit that there is some choice in whether you live in a suburb or urban area, but not so much if you consider all of the constraints on families. I suppose then that the most practical use for this information is for public planners.
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6 comments:
Two points I noted.
1. The statement that lawn mowers emit 11 times the CO2 of a car! Well how was that measured? By the mile traveled? Time of operation? I buy about 3 gallons of gas for a whole summer and we fill the Prius about every 2 weeks, so that's a lot more fuel and a lot more CO2. Since CO2 is a simple result of the number of molecules of gas burned, more gas = more CO2. So I don't think our lawn mower emits more CO2 than our car. It probably emits more toxic pollutants per gallon burned, but that wasn't what was stated.
2. The heating-cooling issue is not so simple as you make it. Most heating is done by burning fossil fuel, so CO2 produced is directly related to how much you burn. IF you burn a ccf (hundred cubic feet - and yes that is a roman prefix=C !) of natural gas, you emit 12.1 lbs of CO2, and until we find a way to sequester the CO2 it will be the same everywhere natural gas is burned.
Most cooling (though not all) is done by running an electric compressor that transfers BTUs from inside the house to outside the house by raising the temperature of the refrigerant higher than outside temps so the heat will flow as it likes to do, from high to low. An AC unit with an EER of 12 can move 12 BTUs outdoors for every watt it uses. To move 100,000 Btu/hr would take 8333 watt-hrs or 8.333 kWh. In CT each kWh we use emits 0.99 lbs of CO2, so moving those 100,000 BTu/hr emits about 8.25 lbs of CO2. But your state would be different because their mix of electric generation sources is different than ours. As renewable portfolios of our utilities have a higher % renewable, CO2 emitted would go down.
So it looks like you do emit less CO2 when cooling than when heating. That 100,000 BTu/ hour is about 8 tons and most houses are about half that at 50,000 Btu/hr even though the temp difference in-to-out is only about 20 degrees, but with a lot of humidity, and that takes work too. It turns out that a well built house will also need about 50,000 BTu/hr when it is 70 degF colder outside than inside (and humdity is not a factor). So yes it looks like a typical house will emit about 50% more CO2 when heating than if cooling (other heating fuels will be different, more CO2 than for natural gas). So run your AC this winter and reduce your carbon footprint. Or just wear a parka all the time and you won't need to heat or cool.
I think you are right. It does seem a little dubious to assert that lawnmowers are a major source of CO2 since it does not take much gas to run a lawnmower all summer.
I looked up the article's source and I quote from the EPA, "11 times the air pollution of a new car for each hour of operation".
A look back at the Wired article, shows that they did indeed write "pollutants" but only after claiming that lawnmowers are "even worse" than automobiles in their carbon footprint.
Their lawnmower argument violates their own principle which I describe as 'ruthless green'. Or in other words, who cares about air pollution and a few extra sniffly noses when the planet's survival is at stake.
Mr. Anonymous,
Your second point needs translation into English from btu-speak.
Have they factored in what the average American can do to prevent global warming by putting a sweater on?
Oh yeah, about lawnmowers: two-stroke engines are inherently less efficient than four-stroke. But I believe you can get a four-stroke lawnmower. Or (crazy, I know) you could get an old-fashioned hand mower!
No I did not see anything about wearing sweaters ala Jimmy Carter, but isn't that implied by the notion that heating is very carbon intensive? Of course a sweater only gets you so far. You might set the heat to 65 instead of 70.
As I said, getting a four-stroke mower is not going to reduce your carbon footprint very much (unless you are currently commuting to work on your mower).
I am still waiting on a lay-person's explanation of why 1 degree of cooling is more efficient than 1 degree of heating. I will also accept the use of a Rankine cycle in the explanation ;)
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