This request came from my friend Graham Hill at Treehugger:
I am wondering if we are not quite looking at the right metrics when it comes to buildings being green. And i’d be interested in your thoughts. and ideas about who would really know a lot about the lifecycle/energy considerations of buildings.
Here’s what I think we should be looking at from a carbon perspective: I think we want a measurement of CO2 Emitted per person hour. Here’s how you might figure it out:
(Total Building CO2) = (CO2 of Embodied energy of materials used) + (CO2 of Energy used in construction) + (CO2 of Energy used throughout building’s life) + (CO2 of Energy used to disassemble bldg at end of life) - (CO2 of Embodied Energy of materials reclaimed at end of building’s life)
(Total Building Person Hours) = (Number Building “Users” (density)) x (Hours Used Per Person)
Figure these out and then you can get
_________ CO2 (watts/joules?)/person hour.
That number should give you the relevant metric that we should look at…the overall eco-effectiveness of the building. How much bang we get for the total CO2 emitted.
I think then we’d notice that a normal building that is used closer to a 24 hr cycle and/or by more people could be just as green or more than a less occupied green building. We need to be focused on more than just low energy and green materials… we need to be thinking about density, about length of building life and about how to move towards 24 hour architecture.
Imagine how some mega-green hardly used vacation homes might fare when looked at this way…
I think this is a very reasonable way to look at buildings. Far more effective than the complicated LEED standard. This would motivate better shared use of infrastructure which is key. Certainly would make the “green vacation home” understood as a better prospect for time-share.
The challenge as usual is that to get a meaningful number you need to predict up front how long the building will last for – or in this case how many person hours do you expect to get from this building before it falls over. If you choose 50 years up front, and then it lasts for 200, you were estimating 4 times too high. Similarly if you estimate 200 and it lasts 50 because of bad roofing design or something, you get a number 4 times too low. This with no doubt emphasizes the need to design for longevity. For very long lived buildings the dominant energy use becomes the energy used throughout the building’s life, so if you are designing for real longevity you are also forced to make sure the day to day energy use (or CO2 output) is as low as possible.
The one thing that is missing is something that accounts for location. It could be a perfectly green building in the middle of nowhere that requires lots of carbon to be burnt in driving to and from it, and that would quickly erase any “green-ness” of the architecture. So the equation would look more like:
(Total Building CO2) = (CO2 of Embodied energy of materials used) + (CO2 of Energy used in construction) + (CO2 due to people travelling to and from the building) + (CO2 of Energy used throughout building’s life) + (CO2 of Energy used to disassemble bldg at end of life) - (CO2 of Embodied Energy of materials reclaimed at end of building’s life)