U.S. EPA Heat Island Reduction Program
The Writing's on the Wall: Recent Cool Wall Research and Measures
Webcast Questions and Answers
February 22, 2018
Questions in bold were asked during the webcast
Can you explain how the reduction in canyon temperatures is greater with cool walls than
cool roofs when the graph showed greater effects with roofs? Is it due to greater area of
walls? If so, won't that vary significantly, depending on average building height?
George Ban-Weiss (University of Southern California): First off, there may have been a
misinterpretation. If you look at the daily average temperature reductions for cool walls
versus cool roofs, it was actually cool roofs that led to somewhat larger reductions, although
they are - they are quite similar. The fact that walls were similar to roofs has to do with the
fact that if we're talking about canyon air temperature reductions, the wall itself is actually in
the canyon. You get more direct temperature reductions from walls than you do for roofs.
The roofs are, of course, at the top of the canyon. You can have a cool roof that reduces the
temperature of the air above the roof. Then, that cooling effect needs to be mixed down into
the canyons. So, that is part of the answer. The other part has to do with what was stated in
the question, the fact that wall area is larger than roof area.
And would it depend on the height of the building? Yes, it definitely would. One thing that is
mentioned in the write-up quite extensively on this project is that, you can't really do a one-
size-fits-all study. It's the comparison of cool walls and cool roofs and - not only the
comparison - the absolute temperature reductions that you would expect from cool walls or
cool roofs depends on the city under investigation, the morphology of the urban area, the
building heights, the street widths and then, also, just the overall baseline climate. It wouldn't
be fair to extrapolate the results shown here to other cities necessarily. I think you'd need to
investigate other cities separately for that comparison.
Why is the temperature outdoor going down when the amount of radiated heat increases?
Doesn't more reflectance from walls just get absorbed by the surrounding environment -
other buildings, pavement et cetera - and add to the urban heat?
George Ban-Weiss: Those are related questions. To answer the first one, what we are looking
at is that slide that said that the amount of radiati on leaving the canyon for cool walls is about
40 percent that of roof. We are looking at sunlight that is reflected off of walls or roofs.
When it's reflected from walls or roofs - let's use roof as the simpler example. When
sunlight is reflected by the roof, then it stays as what we call a shortwave radiation. It stays as
basically sunlight and the majority of that reflected sunlight actually makes it back to space
out of the atmosphere entirely.
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If you are talking about walls, then, yes, a fraction of the sunlight that gets reflected by walls
does get absorbed within the canopy by pavements and by other walls. We did account for
that in our calculations, but it's not all of the reflected solar radiation. That's roughly half of
it. If you think about sunlight that's incoming to a wall, you get about half of the reflected
sunlight that gets absorbed by other surfaces in the canopy and then about half that makes it
out of the canopy and back to space.
I think what the first question was missing is that we're not talking about thermal radiation
here. We're not talking about increasing the amount of thermal radiation that's being emitted
by surfaces. We're talking about sunlight that's being reflected from surfaces, not thermal
radiation that's being emitted from surfaces.
Hopefully, that answers both questions. That figure was sunlight being reflected, not thermal
radiation. Yes, a portion of it does get absorbed - a portion of the radiation reflected by walls
does get absorbed by other surfaces in the canopy, but it's only about half of it. The net effect
is that you still get a cooling in the canopy even with that addition of sunlight being absorbed
by pavements and walls, because the net is that you're actually increasing reflected radiation.
That absorption of sunlight by other surfaces can somewhat attenuate the effects, but it
doesn't reverse it.
Do you see any one metric being used to set requirements for codes?
Haley Gilbert (Lawrence Berkeley National Laboratory): When we talk about metrics for
walls and codes, we highly suggest using solar reflectance as a metric to define what would
be the wall requirement. I think that's getting at the root of that question. In ASHRAE 90.1,
we have a different metric, but we are working with them to change that metric to solar
reflectance and thermal emittance. Those are the surface properties of the product, and those
two properties would help to define its coolness. Those are the two measures that we would
be looking to include when it comes to building codes and standards, incentive programs, as
well as anything that needs to specify a cool wall product.
How can people get involved in the code-making process?
Haley Gilbert: In the code-making process or getting cool walls into codes? I'll take both. If
they would like to be engaged with us as we pursue to increase adoption of cool walls in
codes, they can reach out me, Haley Gilbert. My email is on that first slide, that's
hegilbert@,lbl.aov. If you have interest in cool walls and want to learn more, please reach out
to me as well. Getting involved in building codes, Howard probably has some better insight
into that one.
Howard Wiig (State of Hawaii): I did outline that in a couple of my slides. I deal with the
International Energy Conservation Code (IECC) because that's our code of choice. As
mentioned, there also is ASHRAE and, then, there are a number of beyond codes out there
also, and you can get involved in those. If you email me, I can detail them for you.
As I said, just sticking to IECC, you need to register with the International Code Council
(ICC) as a lobbyist and then get to the hearings and then go through the selection process that
I outlined. You get to know the efficiency advocates, speak individually with them, ask their

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support for cool wall proposals, do some favors for those who are supporting you, and ideally
talk to people on the "other side," the builders, construction people, suppliers and so forth.
When we are talking about cool walls, are we talking about just paint to make a cool wall
or paint plus insulation?
Ronnen Levinson (Lawrence Berkeley National Laboratory): Cool walls in this case just
refers to the ability of the wall to reflect sunlight. We are not proposing increasing insulation
or making other structural changes to walls, just modifying the nature of its surface.
How does glazing impact the results and benefits of cool walls? You mentioned that other
buildings absorb reflected light. Do the models include the effect that would increase the
heat gain for those buildings?
Ronnen Levinson: We have, in fact, done some building-to-building interactive modeling. It
seems like the crosstalk between buildings is pretty modest. The reason is that if a building is
close to its neighbor, that wall in the central building that's in the sun tends to be shaded by
that neighbor. If the neighbor is far away, then only a small fraction of the sunlight that is
reflected from the wall of the central building reaches the opposing wall of the neighboring
building. It's pretty modest.
One of the thing I would point out that is if making the wall of the central building more
reflective increases the amount of sunlight that strikes the opposing wall of the neighboring
building, that's actually probably a pretty good thing because to the extent that you are
increasing usable daylight that enters the neighboring building, you get to turn off artificial
lights. That turns out to be a big win for energy savings.
You showed the pictures of temperature variation over the exterior surfaces of buildings.
Are there data on the temperature changes inside the building?
Howard Wiig: Not from my standpoint. Our previous speakers are specializing in that. I just
did the very informal test at the Laie Elementary School, which resulted in a five-degree drop
even though the temperature was measured later in the day. There's plenty of data on the
effect - interaction - between exterior temperature and interior. That is subject to a whole lot
of variables, mainly how well insulated the interior wall is. Other people are better disposed
to answer that.
With fully glass fenestration, walls become more and more popular for urban center
construction. What effect does this construction method contribute or reduce to urban heat
island effects versus the use of cool walls?
Ronnen Levinson: The first thing I would point out is that all of the analysis that we
presented today is taking into account the fact that there are windows in buildings. When we
showed certain energy savings, those were energy savings per unit area of wall that you
modified or, in the case of the two-story home that I showed, we included the windows as
part of that analysis.
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If you are interested in mitigating the urban heat island effect and your building's facade is
dominated by windows, there is an interesting technology that one of our project partners
has, which is a certain type of solar control film for windows that specifically is designed to
reflect the invisible near-infrared component of sunlight that strikes the window up and out
of the city. If somebody has a glass-faced building, they might want to look into that sort of
technology. I could provide some contact information if somebody emails me after the
presentation.
Since the results of the cool wall study vary based on the building landscape, how can this
be translated to codes?
Haley Gilbert: That's a good question. It's one that we are working with individual code
entities on. It depends on the code itself - you have specifics that vary depending on building
type, residential versus non-residential, and we also include things like climate zone. You
will find that certain measures are in certain climate zones. They are appropriate for certain
building types. As well, you put in language that can offer paths to compliance.
With cool walls, you often see measures that call for either shading - and that's provided by
an awning or a tree or some sort of shading on a wall - or a cool wall. You often find there
are different paths to compli ance with the same idea of reducing the solar heat gain into the
building. That's probably the approach that we'll take with many of these codes at first. It's
this kind of more open, prescriptive compliance options. Depending on if we're working in
California or on the national code, we will work with that entity to best tweak and alter the
language so it fits the context as needed. No one size fits all, I would say.
Are learning credits or continuing education credits for today's webcast?
Alexis St. Juliana (Abt Associates): Unfortunately, the Heat Islands Program is not affiliated
with any organization to offer those types of continuing education credits. If you do need
record that you participated, we can provide that. Contact Victoria Ludwig.
Please send me the language for codes and standards. I want to look at it for inclusion in
National Green Building Standard.
Howard Wiig: Hawaii's amendments to the 2015 IECC are available online:
https://ags.hawaii.gov/wp-content/uploads/2012/09/StateEnergyConservationCode-
20170331.pdf
What about glass walls?
Howard Wiig: Architecture goes through "the latest fashion" just as predictably as women's
clothing after The Paris Fashion Show. Today's fashion is all-glass. They're sprouting up
like mushrooms here in Honolulu - looks like 100% glass facade.
I queried an architect. He said that glazing is now so high-performance that they're
measuring in R-value rather than the solar heat gain coefficient. He's specified R-7.5 glazing
- triple-pane, low-emissivity glass. The building meets the energy code by following the
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Performance Path and offsetting the poor wall performance with high-seasonal energy
efficiency ratio mini-splits (this is a high-end residential high-rise) and I assume a variety of
other beyond-code measures.
What is the effect of a large tree?
Ronnen Levinson Lawrence Berkeley National Laboratory has not quantified the effect of
tree shading, but it could diminish both the annual cooling energy savings and the annual
heating energy penalty of a cool wall by blocking the beam (direct) component of sunlight. If
you're curious, you could draw a tree next to a building in SketchUp and look at its shadow
by hour. See https://help.sketchup.com/pl/article/3000148.
As a paint manufacturer that deals with this already, how can I best get involved with helping
this project going forward and also help with writing codes if possible?
HG: Please send an email to Haley Gilbert, LIEGilbert@lbl.gov. to get involved in our Cool
Wall Stakeholder Working Group. We are working to advance all the efforts described in the
presentation.
In Zone 3C is there a 'heating penalty' that offsets the cool wall benefit? How much?
Ronnen Levinson Yes, in most climates there is both cooling savings and a heating penalty.
The heating, ventilation, and air conditioning (IiVAC) annual energy cost savings shown in
the presentation include changes (warm wall - cool wall) to HVAC energy costs over the
course of the year.
Do cool walls need to have cool pavements/vegetation for max effect?
Ronnen Levinson No.
What is the effect of wall construction- Polyvinyl chloride (PVC) siding, stucco, brick wood?
Ronnen Levinson Variations in thermal resistance or thermal mass might affect energy
savings.
Can someone characterize the potential benefit impacts from surface roughness for cool walls?
Ronnen Levinson Surface roughness can lower albedo, which in turn would reduce cool wall
savings.
Are there any intellectual property issues with implementing cool walls?
Ronnen Levinson No.
Also, in carrying out research on cool walls, can few buildings be selected for the purpose?
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Ronnen Levinson Lawrence Berkeley National Laboratory would like to conduct
demonstration projects.
Why would sea air affect the cooling- shouldn't that be normalized out?
George Ban-Weiss As air moves from west to east in the Los Angeles basin, the cooling
effect from cool walls accumulates. This is why cooling effects can be stronger on the east
side of the basin. This would generally be true in most locations. The downwind part of the
city would be expected to have larger temperature decreases than the upwind part. Our goal
was to quantify the climate effects of hypothetical city-scale cool wall deployment, so this
effect needs to be included, not normalized out.
Is there a tool available per latitude and climate zone to account for square foot energy savings
and greenhouse gas reduction?
Ronnen Levinson Lawrence Berkeley National Laboratory has created the Cool Surface
Savings Explorer, a tool that can report these savings by building type and location. We will
make it public later this spring.
Apart from white color, which other color is recommended for a cool? Are there special paints
manufactured for such purpose?
Ronnen Levinson Many light colors, and some dark colors that incorporate special pigments,
are cool. Lawrence Berkeley National Laboratory is working to develop a product rating
system that will help consumers identify paints with high solar reflectance.
Have winter penalties been evaluated?
Ronnen Levinson Yes. The HVAC annual energy cost savings shown in the presentation
include changes (warm wall - cool wall) to HVAC energy costs over the course of the year
Can you talk about the challenges of trying to require high albedo walls which would affect the
design aesthetic?
Ronnen Levinson Many buildings already have dull-white or off-white walls with albedo
(solar reflectance) > 0.60.
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