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!

Concept Model of Embodied Energy Investment in Existing Buildings

So here's the first model presented in the ACHP report mentioned below. Quick and easy, it will give you a simple figure to build from. All you need to know to get started is the building type and size in square feet to figure how much energy, in MBTU, is embodied in that building.

Procedure: multiply the s.f. by the energy investment shown below in table 1 to = embodied energy.

TABLE 1 Embodied Energy of Materials and Construction Per Square Foot of Construction

Residential – Single Family......700 MBTU/s.f.
Residential – 2-4 Family.........630
Residential – Garden Apartment...650
Residential – High Rise..........740
Hotel/Motel.....................1130
Dormitories.....................1430
Industrial Buildings.............970
Office Buildings................1640
Warehouses.......................560
Garages/Service Stations.........770
Stores/Restaurants...............940
Religious Buildings.............1260
Educational.....................1390
Hospital Buildings..............1720
Other Nonfarm Buildings.........1450
a. Amusement, Social & Rec......1380
b. Misc Nonresidential Bldg.....1100
c. Laboratories.................2070
d. Libraries, Museums, etc......1740


so an example is always helpful: 3000 s.f Single Family home X 700 MBTU/s.f = 2,100,000 MBTU of embodied energy.

Wow! It's in the millions?! But what's a BTU? It's a British Thermal Unit.* And 1 MBTU is equal to 1,000 BTU. That gives us 2.1 billion BTU, or 2.1 million multiplied by 1000. Is that a lot of energy? You bet it is. But how can we make sense of it?

Here's an idea. Go find yourself an online converter, or look up some tables if you're the do-the-math-myself type of person. We like OnlineConversion.com's energy page. Type in your BTUs (remember, multiply your MBTU from the ACHP equation by 1000) and choose something we all can understand, say, gallons of gas. Our 3000 s.f. home, at 2,100,000,000 BTU of embodied energy, is equivalent to 16,815.54 gallons of gas. Whoa! Now we're getting somewhere... what about another number most of us are familiar with, kilowatts? That 3000 s.f. building represents 615,449.309 kilowatt hours. This DOE report here says the average midwest household used 9206 kWh a year. The math is easy: 615,449.309 divided by 9206 = over 66 years of electricity use!

If all of this sounds like a lot, well, it is. To put it in dollars and cents, going back to our 16,815.54 gallons of gas, at $3/gal, you're sitting on $50,446.62. That's the investment locked inside 3000 s.f. of home. Would you throw $50,000+ in the landfill? If you're the sort, let the May T. Watts Appreciation Society know immediately. We have landscapes to save.

The greenest building respects its embodied energy!


* a single BTU is the amount of heat required to increase the temperature of a pint of water (which weighs exactly 16 ounces) by one degree Fahrenheit. We read that here.

ACHP embodied energy report available on Forum

You're a NTHP Forum member, right? Then get over to their pdf file cabinet and download the Advisory Council on Historic Preservation's Assessing the Energy Conservation Benefits of Historic Preservation: Methods and Examples. This is THE embodied energy resource. The ACHP report provides three models to assess embodied energy: concept, survey, and inventory. These models are based on the amount of information available on a given building, and range from the most general--gross floor area and building type for the concept model--to more specific, including the embodied energy of a range of specific "per unit" building materials (e.g., a brick, a single brick, is worth 14,300 BTUs). There are also demolition and renovation models. Neat stuff.

Watch this space and we'll post some tables to help you get started on concept modeling.

counting bricks

So all your preservation buddies are talking "embodied energy" again (they've been at it since the 70s, but it just wasn't cool for the last 20 years)... and you've been fed nothing but LEED-driven developer drivel and need to get hip. So check it out: Mike Jackson at the 2007 NTHP Conference in St. Paul. Mr. Jackson isn't afraid of blasting the consumer approach to green that many have found success in promoting. We think he has a great point, one that preservation takes to heart: how can you buy your way to green? And as he likes to say, preservation isn't recycling, it's REUSE. No need to repackage, resell, and re-whateverelseitisyou'retryingtodo. It's just smart. Like Mike.

So check out his presentation. Embodied Energy is a fairly intuitive concept, if you stop to think about it. Basically (very basically), it's the idea that the building materials in our existing structures represent a considerable investment in energy. And why waste that investment by tearing down historic buildings. There are some great tools out there to figure our how much energy your old house is worth, and we'll post them later.

We won't even try to hide it: the MTWAS loves Mike Jackson, thinks he's brilliant, and are damn happy he works for the IHPA. The NTHP Conference was great too, so a big hello to everyone we met there. The Trust was nice enough to put up a ton of handouts, so check out more stuff here, including something from another favorite, Carl Elefante.

badges

We got buttons! Thanks to fellow traveler L.S. for the photo.

want one?

so you want to get in the green preservation business...

Our friend K. has an idea for you: start stocking up on free storm windows now, before the snow hits.

OHJ had a great article in their Sept/Oct 2007 issue, "Embracing Energy Efficiency." Their graphic showed a single-pane window coupled with a storm window with a combined u-value of 0.5, better than the double-pane thermal replacement... not to mention $400 cheaper!* Yes, a low-e double-pane window has a lower u-value at 0.35, but the payback is considerable... at 34 years, probably longer than the window itself will last, and very likely longer than your warranty on a new window. So instead of putting one window in the dumpter--the original, replaced sash--you'll be putting a window in the dumpter every 20 years! And paying $550 for the low-e opportunity!

* u-values rate energy efficiency. We found this article from doityourself.com helpful.

The greenest building keeps its windows out of the dumpster!

The Greenest Building...

Let me begin with an apology to Carl Elefante, who's little phrase has set off a storm of preservation activity and reminded us that preservation IS conservation... so without further ado, "The Greenest Building Is... One That Is Already Built."