Thursday, November 29, 2007

embodied energy math

We looked at the embodied energy of one building. But what about a group of buildings, say, the number of wrecking permits reviewed by a North Shore HPC in 2006. Last year this HPC reviewed 85 permits. Taken together, these account for 204,920 s.f. of single family demo. That's equal to a whopping 143,444,000,000 BTUs of embodied energy. We go back to our favorite energy converter, converted our BTUs to gallons of gas, and the results are in. Envelope please...

1,148,614 gallons of gas. And at $3 a gallon the embodied energy is--or rather, in this case, was--worth $3,445,842.

Now lets get creative. Say we used our 1,148,614 gallons to fill up. We'll use the NHTSA's CAFE standards, a combined 22.2 for passenger cars and light trucks (that includes SUVs under 8,500 pounds).* 1,148,614 gallons multiplied by 22.2 miles per gallon gives us 25,499,230.8 miles. For a single vehicle, that's about 1,024 trips around the earth's equator. Whew.

Then we checked out the EPA's Personal Emissions Calculator. If we drove those 25,499,230.8 miles in a year in a vehicle with 22.2 mpg, we'd create 23,669,142 pounds of carbon dioxide. Well, we can't possibly drive 25+ million miles in a single year. The same EPA site tells us 12,100 pounds is average per vehicle per year. So divide 23,669,142 of carbon dioxide by the 12,100 pound average and... yes, it's like putting 1,956 cars on the road. That's a year's worth of demo in one town folks.

So why is embodied energy important? The greenest building does the math.

* and these are "standards," mind you, not actual on the road fuel economy numbers!

1 comment:

David said...

Slate has got to be classed as the 'greenest' roof material - as long as it is not transported I suppose? Keep up the good work.Slate is green!!