## Wednesday, November 28, 2007

### 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.

#### 1 comment:

Kevin Dickson said...

Wait a minute.

Usually the problem is whether or not you should rehab the old building or replace it with a new one.

You don't "waste btu's" when you tear down an old building. Those btu's were spent when the building was originally built, and there's nothing you can do to get 'em back. You can only choose not to spend new btu's on a new building.

And btu's are just another form of dollars.

So it's always an economic problem, eg., what's the present value of retrofitting the old building vs. building an entirely new one. This analysis must be done for every building using each case's unique problems and assumptions.

In residential at least, it's fairly easy to build a new "zero energy" replacement house, but fairly hard to retrofit the old house to zero energy. The cost of the new house can be estimated pretty accurately, but trying to estimate the retrofit cost of the old house is risky. Every old building is different.

The embodied energy of the new building is just the down payment on a really good investment.

Therefore, it may be a catchy phrase, but it's very unscientific and specious to generalize: "The Greenest Building is the One Already Built".