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Green Roofs – Green Revolution

Green Roofs – Green Revolution


LISA VAN PAY: These days, most of us pay attention to
how we live. We recycle, we try to use less water and electricity,
we walk or bike or drive more efficient cars. But a lot of us never really think about where we
live or work or go to school. I mean, a building is a building, right?
Not necessarily. Let’s say you grow a bunch of plants on top of your
building and they use sunlight and water and carbon dioxide just like they’re supposed to.
Suddenly you’ve decreased your energy bill, reduced air and water pollution, and made things a
little greener. Places all over the world have tried it,
so why aren’t there more green roofs? Well, is it worth the extra work? It makes sense that plants on a roof would keep the
building cooler, even if they only provide a little shade.
But what’s really going on? Where is the heat energy going?
How does a green roof change the way a building transfers heat? JALENA SREBRIC: So that simple question led us onto a
ten-year chase. LISA VAN PAY: Jelena Srebric is an architectural
engineer at Penn State University, who studies energy flow in and around buildings.
She and her students built their own green roof. But with their model, they can control the weather to
test what really happens when sun, rain, wind and plants all work together on the roof of a building.
But experiments don’t always go as planned. JELENA SREBRIC: Our first facility was so poorly
designed that it caught accidentally on fire, and we had to remove it. But it was a great
learning experience. LISA VAN PAY: Just because you’re a talented engineer,
doesn’t mean you have a green thumb. JELENA SREBRIC: Plants do die. They get sick,
they need maintenance. LISA VAN PAY: So they went to an expert. LISA VAN PAY: Rob Berghage is a horticulturalist.
He knows all about plants. LISA VAN PAY: So Jelena mentioned that they actually
killed a lot of different plants when they were trying to figure out what would grow
really well on a roof. Can you explain to us a little bit about how you
helped them choose the right plants for a roof setting? ROB BERGHAGE: Okay, so the plants we pick are adapted
to growing in a harsh environment. What we’re really trying to achieve is something that
is more or less in balance. LISA VAN PAY: So you said fifty percent of the water
that would normally have run off is actually taken up by the plants and put back into the atmosphere?
How do plants do that? ROB BERGHAGE: It’s called evapotransporation, and it’s
a normal process that all plants go through. They take water up and they release it into the
atmosphere. LISA VAN PAY: Evapotransporation is one reason a green
roof keeps a building cooler in the summer. Instead of being absorbed by the building, heat from
the sun is transferred to water in the plants and soil, and released to the atmosphere.
Okay, so we’ve got a lab. The plants are alive and well.
What’s next? TYLER MEEK: One of the major questions we wanted to
answer was what is the best way to analyze our data, or collect the data for the first place. LISA VAN PAY: So you wanted to recreate some of the
conditions that might be outdoors, in the lab, and then try to measure the different variables? TYLER MEEK: Right. Well, for a part of the experiment
we needed numbers on how many leaves were actually in this entire sample. So that was fun.
We had to measure each and every leaf that was in that probably 2.5-inch by 2.5-inch square.
It was around 4,000 leaves? (Lisa: That big?) Yeah, probably, yeah. (Lisa: 4,000 leaves.)
Yeah, so I got my counting skills on that day. LISA VAN PAY: So you take a small space and then use
math to calculate about how many leaves are in a much larger area. Beats counting to a million, I guess. TYLER MEEK: It’s a lot easier to start on a small
scale than it is to just go gung-ho at a big project. So if we understand a small scale, the plan is to move
it to the bigger scale and just adjust what we’re finding. We’re taking measurements.
Some sensors take them every second, some take them every minute. But we’re always monitoring that. LISA VAN PAY: So they take that data, everything they
know about that small space, and identify all the factors that affect energy flow.
With all these numbers, they can start to figure out how the energy moves within the system. Then another
lab member, Paulo Tabares Velasco‚ uses math to take what they learned from the lab, and turn it into a
computer model to explain what happened in their experiment, and predict what will happen in the real
world. So Paulo, we saw a lot of the different
instrumentation you had in the lab and the measurements you were taking. How did you take, then,
the numbers and all the data you got there, and make it into a model you might be able to use to predict
what was happening outside? PAULO TABARES VELASCO: That’s something very
interesting. First we do a statistical analysis of the data. We take average of the data‚ and then we put it
in to our model to make sure that our model is predicting the right type of phenomenon. In other
words, we compare what our model says, with the actual data. LISA VAN PAY: So you have to start simple and then
make it more complex as you understand the simple parts more? (Paulo: Yes, that’s correct.) Everybody knows it’s cooler in the shade. But how do you
prove it? What’s different between a green room and a regular room? It might not matter to a lot of
people. All they know is that their buildings are cooler, and they’re saving money. But NSF funds people
who want to know more. Engineers like Jelena and Tyler and Paulo, who build
models and invent ways to test their ideas. Ideas that future architects and designers can use to
make buildings that will change our world for the better. And sometimes the best
place to start is at the top.

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