08:46
TED2010

Catherine Mohr: The tradeoffs of building green

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In a short, funny, data-packed talk at TED U, Catherine Mohr walks through all the geeky decisions she made when building a green new house -- looking at real energy numbers, not hype. What choices matter most? Not the ones you think.

- Roboticist
Catherine Mohr works on surgical robots and robotic surgical procedures, using robots to make surgery safer -- and to go places where human wrists and eyes simply can't. Full bio

First of all, I'm a geek.
00:16
I'm an organic food-eating,
00:19
carbon footprint-minimizing, robotic surgery geek.
00:21
And I really want to build green,
00:24
but I'm very suspicious
00:27
of all of these well-meaning articles,
00:29
people long on moral authority
00:31
and short on data,
00:33
telling me how to do these kinds of things.
00:35
And so I have to figure this out for myself.
00:37
For example: Is this evil?
00:39
I have dropped a blob of organic yogurt
00:42
from happy self-actualized local cows
00:45
on my counter top,
00:47
and I grab a paper towel and I want to wipe it up.
00:49
But can I use a paper towel? (Laughter)
00:52
The answer to this can be found in embodied energy.
00:55
This is the amount of energy that goes into
00:58
any paper towel or embodied water,
01:00
and every time I use a paper towel,
01:02
I am using this much
01:04
virtual energy and water.
01:06
Wipe it up, throw it away.
01:08
Now, if I compare that to a cotton towel
01:10
that I can use a thousand times,
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I don't have a whole lot of embodied energy
01:15
until I wash that yogurty towel.
01:18
This is now operating energy.
01:20
So if I throw my towel in the washing machine,
01:23
I've now put energy and water
01:25
back into that towel ...
01:27
unless I use a front-loading, high-efficiency washing machine, (Laughter)
01:29
and then it looks a little bit better.
01:31
But what about a recycled paper towel
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that comes in those little half sheets?
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Well, now a paper towel looks better.
01:38
Screw the paper towels. Let's go to a sponge.
01:40
I wipe it up with a sponge, and I put it under the running water,
01:42
and I have a lot less energy and a lot more water.
01:45
Unless you're like me and you leave the handle
01:47
in the position of hot even when you turn it on,
01:49
and then you start to use more energy.
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Or worse, you let it run until it's warm
01:53
to rinse out your towel.
01:55
And now all bets are off.
01:57
(Laughter)
01:59
So what this says is that
02:01
sometimes the things that you least expect --
02:03
the position in which you put the handle --
02:06
have a bigger effect than any of those other things
02:08
that you were trying to optimize.
02:10
Now imagine someone as twisted as me
02:12
trying to build a house.
02:14
(Laughter)
02:16
That's what my husband and I are doing right now.
02:19
And so, we wanted to know, how green could we be?
02:22
And there's a thousand and one articles out there
02:24
telling us how to make all these green trade-offs.
02:26
And they are just as suspect
02:28
in telling us to optimize these little things around the edges
02:30
and missing the elephant in the living room.
02:33
Now, the average house
02:35
has about 300 megawatt hours
02:37
of embodied energy in it;
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this is the energy it takes to make it --
02:42
millions and millions of paper towels.
02:44
We wanted to know how much better we could do.
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And so, like many people,
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we start with a house on a lot,
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and I'm going to show you a typical construction on the top
02:53
and what we're doing on the bottom.
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So first, we demolish it.
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It takes some energy, but if you deconstruct it --
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you take it all apart, you use the bits --
03:02
you can get some of that energy back.
03:04
We then dug a big hole
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to put in a rainwater catchment tank
03:08
to take our yard water independent.
03:10
And then we poured a big foundation
03:12
for passive solar.
03:14
Now, you can reduce the embodied energy
03:16
by about 25 percent
03:18
by using high fly ash concrete.
03:20
We then put in framing.
03:23
And so this is framing -- lumber,
03:25
composite materials --
03:27
and it's kind of hard to get the embodied energy out of that,
03:29
but it can be a sustainable resource
03:32
if you use FSC-certified lumber.
03:34
We then go on to
03:37
the first thing that was very surprising.
03:39
If we put aluminum windows in this house,
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we would double the energy use right there.
03:44
Now, PVC is a little bit better,
03:47
but still not as good as the wood that we chose.
03:49
We then put in plumbing,
03:52
electrical and HVAC,
03:54
and insulate.
03:56
Now, spray foam is an excellent insulator -- it fills in all the cracks --
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but it is pretty high embodied energy,
04:01
and, sprayed-in cellulose or blue jeans
04:04
is a much lower energy alternative to that.
04:07
We also used straw bale
04:09
infill for our library,
04:11
which has zero embodied energy.
04:13
When it comes time to sheetrock,
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if you use EcoRock it's about a quarter
04:17
of the embodied energy of standard sheetrock.
04:19
And then you get to the finishes,
04:22
the subject of all of those "go green" articles,
04:24
and on the scale of a house
04:27
they almost make no difference at all.
04:28
And yet, all the press is focused on that.
04:31
Except for flooring.
04:33
If you put carpeting in your house,
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it's about a tenth of the embodied energy of the entire house,
04:37
unless you use concrete or wood
04:40
for a much lower embodied energy.
04:42
So now we add in the final construction energy, we add it all up,
04:44
and we've built a house for less than half
04:47
of the typical embodied energy for building a house like this.
04:49
But before we pat ourselves
04:52
too much on the back,
04:54
we have poured 151 megawatt hours
04:56
of energy into constructing this house
04:59
when there was a house there before.
05:01
And so the question is:
05:03
How could we make that back?
05:05
And so if I run my new energy-efficient house forward,
05:07
compared with the old, non-energy-efficient house,
05:10
we make it back in about six years.
05:13
Now, I probably would have upgraded the old house
05:16
to be more energy-efficient,
05:18
and in that case,
05:20
it would take me more about 20 years to break even.
05:22
Now, if I hadn't paid attention to embodied energy,
05:26
it would have taken us
05:28
over 50 years to break even
05:30
compared to the upgraded house.
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So what does this mean?
05:34
On the scale of my portion of the house,
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this is equivalent to about
05:39
as much as I drive in a year,
05:41
it's about five times as much
05:43
as if I went entirely vegetarian.
05:45
But my elephant in the living room flies.
05:47
Clearly, I need to walk home from TED.
05:50
But all the calculations
05:53
for embodied energy are on the blog.
05:56
And, remember, it's sometimes the things that you are not expecting
05:58
to be the biggest changes that are.
06:01
Thank you. (Applause)
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About the Speaker:

Catherine Mohr - Roboticist
Catherine Mohr works on surgical robots and robotic surgical procedures, using robots to make surgery safer -- and to go places where human wrists and eyes simply can't.

Why you should listen

Catherine Mohr began her career as an engineer, working for many years with Paul MacCready at AeroVironment to develop alternative-energy vehicles and high-altitude aircraft. Her midcareer break: medical school, where she invented a brilliantly simple device, the LapCap, that makes laproscopic surgeries safer.

Mohr now oversees the development of next-generation surgical robots and robotic procedures, as the director of medical research at Intuitive Surgical Inc., where she's the clinical design leader for the DaVinci Surgical Robotic system. She also works at Stanford's School of Medicine, where she studies simulation-based teaching methods to teach clinical skills to budding doctors. And she's a senior scientific advisor to the GlobalSolver Foundation, an innovative funding and study group that looks at ways to match up scientists and money to help the world's oceans.

More profile about the speaker
Catherine Mohr | Speaker | TED.com