Paul Crovella
Department of Sustainable Construction
Management and Engineering
8/3/10
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How old is your computer?
How old is your car?
How old is your house?
Green – Reduced negative environmental
impact (LEED, Green Globes, CHPS, ICC 700)
 Sustainable – No negative environmental
impact (Living Building Challenge)
 Restorative – Positive environmental impact
(photocatalytic cements)
In terms of alternative energy sources, many
owners are interested in “net” zero energy
buildings (site vs. source).
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Conduction, convection,
and radiation are the
three methods:
How would we make a
good insulation to stop
heat transfer?
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By Conduction? Thermal
conductivity inversely
proportional to density
By Convection? Film
coefficient depends on
rate of fluid flow and type
By Radiation? Emissivity
depends on material
surface characteristics.
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Vacuum Insulated Panels
for attic entries.
Insulation tester….
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Any warm body radiates,
and the radiation that it
emits is either reflected,
absorbed, or transmitted
The cameras offer both
qualitative as well as
quantitative
opportunities.
Their use in forensics is
extensive, development of
standards is ongoing for
use in commissioning
In this case, the frost on the roof is the
result of the roof radiating to deep space
on a clear night.
What does the frost pattern tell us about
the material temperatures?
Energy improvements to building shell
Installed appearance
Loss of seals, infiltration
Note cavities with light fixtures
Infiltration during blower door testing
Early Energy Use in Buildings - 1994
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Juneau, Alaska
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Avalanche on April 16 2008
cuts lines supplying (cheap)
hydropower. Using back up
diesel generators raised
rates by 400% (from 11 to
53 cents per kWh)
31,000 residents cut
electricity use by 30% in
two weeks – stores ran out
of clothespins, etc
One month after price
returned to normal (after
repairs) the electricity use is
only 13% less than previous
level.
Information from
http://www.nytimes.com/2008/05/1
4/us/14juneau.html?_r=2
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What if we could come up with a way to
capture the incoming solar energy and
convert it at a high efficiency to provide
useful work?
Presenting the selective coating…..
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Solar radiation that strikes a surface is either
absorbed, transmitted, or reflected. The
absorption of material is equal to its emittance
(at the same temperature).
Incoming visible light can be absorbed and
converted to IR. To heat water in the winter
the heat in the water must be trapped.
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With a selective absorber, incoming visible light
can be absorbed, converted to heat (IR) and
then re-radiance can be blocked by glass and
convection can be controlled by vacuum
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Integral storage systems –
Flat plate collectors – very
common in warm climates for
DHW or preheat. Works in warm
climates and with diffuse radiation
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Evacuated flat plate collectors – hard to maintain
vacuum in a box
Evacuated tube collectors – Vacuum is like a thermos
bottle, eliminates convection loss. Reflector
concentrates direct irradiation
Works in cold climates and works best with direct
radiation
Single circuit systems –
Used where there is no
danger of frost (or even
night radiation)
 Double circuit systems –
propylene glycol is kept
separate from potable
water by use of a heat
exchanger. Drainback
systems are also
available (no antifreeze)
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Flow
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Pump – Tank can be
located anywhere relative
to the collector.
Thermosiphon – hot
water will rise, so if the
tank is above the
collector, the fluid will
circulate constantly w/o
pump.
Tanks – a solar system
can provide Pre-heat in
a separate tank or in the
main tank
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Tubes cost 50-100 each. 20
tubes will supply most of the
DHW during 9 months of the
year in CNY.
Tubes are made of metal
alloys and glass, but none of
the materials is highly toxic
Efficiency most commonly
referred to is “Solar fraction”
= percent of daily DHW
energy that came from sun.
EVT Collector efficiency
about 80% - good payback
without government help
http://www.sunviewer.net/portals/SUNYESF/
Efficiency = captured power flux/incident
power flux
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Efficiency =( Liters x ΔT (C) x
633/Minutes/Irradiance) x 100