IEEE Spectrum - North American - March 2015 - 28
nUMbeRS Don't Lie_bY VAcLAV SMiL
The Visionary energy
soluTion: Triple WindoWs
The lusT for unTesTed Technological fixes is The
curse of energy policy. Take your pick: self-driving solar-powered
cars, inherently safe nuclear minireactors, or genetically enhanced photosynthesis. * Why not start with what is proven?
Why not simply reduce the demand for energy, beginning with residential
and commercial buildings? * In the United States that sector accounts for
about 40 percent of total primary energy consumption (transportation is
a distant second at 28 percent). Even now heating and air-conditioning account for half of residential consumption, which is why the single best thing
we could do for the energy budget is to keep the heat in (or out) with better
insulation. * The most rewarding place to do that is in windows, where the
energy loss is the highest. That is to say, it has the highest thermal transmittance, measured in watts passing through a square meter of material, divided
by the difference in temperature in kelvins on either side. A single pane has a
heat transfer coefficient of 5.7 to 6 watts per square meter per kelvin; a double
pane separated by 6 millimeters has a coefficient of 3.3. Applying coatings
to minimize the passage of ultraviolet and infrared radiation lowers it to between 1.8 and 2.2, and filling the space between the panes with argon chops
it to 1.1. Do that with triple-glazed windows and you drop to between 0.6 and
0.7. Substitute krypton for argon and you can get it down to 0.5. * That's a
reduction of up to 90 percent. In the world of energy savings there are no
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other opportunities of that magnitude
applicable on a scale of billions of units.
Bonus point: It would actually work.
And there is also a comfort factor: With
the outdoor temperature at -18 °C and the
indoor temperature at 21 °C, the internal
surface temperature of a single-pane window is just around 1 °C, an older doublepane window will register 11 °C, and the
best triple-glazed window 18 °C. At that
temperature, you can sit right next to it.
And triple windows have the added advantage of keeping out noise and reducing condensation. They are common in
Sweden and Norway, but even in Canada
windows must meet the standard that is
equivalent to just a double-glazed window
with one low-emissivity coating.
Cold-weather countries have had a
long time to learn about insulation. Not
so in the warmer places, which need
it now that air-conditioning is becoming widespread. Most notably, in rural
China and rural India, single panes are
still the norm. Of course, the temperature differential for hot-weather cooling is not as large as in higher latitudes
for heating. For instance, at my home,
in Manitoba, Canada, the average lows
in January are -25 °C, enough to make a
difference of 40 °C even when the thermostat is turned down for the night. On
the other hand, air-conditioning in many
hot and humid regions runs for much
longer periods than does heating in
Canada or Sweden.
Physics is indisputable, but economics
rules. Although triple-glazed windows
may cost just 15 percent more than double
panes, their payback times are obviously
longer, and it is commonly claimed that
the step from double to triple design is
not justified. That may be so if you ignore
comfort, condensation, noise, and above
all, the fact that triple panes will keep reducing energy use for decades to come.
Why, then, do visionaries want to pour
money into arcane conversion technologies that may not even work and, even if
they did, would likely have bad side effects on the environment? What's wrong
with simple insulation? n
illustration by
Harry Campbell
http://SPectRUM.ieee.oRG
Table of Contents for the Digital Edition of IEEE Spectrum - North American - March 2015
Contents
IEEE Spectrum - North American - March 2015 - Cover1
IEEE Spectrum - North American - March 2015 - Cover2
IEEE Spectrum - North American - March 2015 - 1
IEEE Spectrum - North American - March 2015 - 2
IEEE Spectrum - North American - March 2015 - Contents
IEEE Spectrum - North American - March 2015 - 4
IEEE Spectrum - North American - March 2015 - 5
IEEE Spectrum - North American - March 2015 - 6
IEEE Spectrum - North American - March 2015 - 7
IEEE Spectrum - North American - March 2015 - 8
IEEE Spectrum - North American - March 2015 - 9
IEEE Spectrum - North American - March 2015 - 10
IEEE Spectrum - North American - March 2015 - 11
IEEE Spectrum - North American - March 2015 - 12
IEEE Spectrum - North American - March 2015 - 13
IEEE Spectrum - North American - March 2015 - 14
IEEE Spectrum - North American - March 2015 - 15
IEEE Spectrum - North American - March 2015 - 16
IEEE Spectrum - North American - March 2015 - 17
IEEE Spectrum - North American - March 2015 - 18
IEEE Spectrum - North American - March 2015 - 19
IEEE Spectrum - North American - March 2015 - 20
IEEE Spectrum - North American - March 2015 - 21
IEEE Spectrum - North American - March 2015 - 22
IEEE Spectrum - North American - March 2015 - 23
IEEE Spectrum - North American - March 2015 - 24
IEEE Spectrum - North American - March 2015 - 25
IEEE Spectrum - North American - March 2015 - 26
IEEE Spectrum - North American - March 2015 - 27
IEEE Spectrum - North American - March 2015 - 28
IEEE Spectrum - North American - March 2015 - 29
IEEE Spectrum - North American - March 2015 - 30
IEEE Spectrum - North American - March 2015 - 31
IEEE Spectrum - North American - March 2015 - 32
IEEE Spectrum - North American - March 2015 - 33
IEEE Spectrum - North American - March 2015 - 34
IEEE Spectrum - North American - March 2015 - 35
IEEE Spectrum - North American - March 2015 - 36
IEEE Spectrum - North American - March 2015 - 37
IEEE Spectrum - North American - March 2015 - 38
IEEE Spectrum - North American - March 2015 - 39
IEEE Spectrum - North American - March 2015 - 40
IEEE Spectrum - North American - March 2015 - 41
IEEE Spectrum - North American - March 2015 - 42
IEEE Spectrum - North American - March 2015 - 43
IEEE Spectrum - North American - March 2015 - 44
IEEE Spectrum - North American - March 2015 - 45
IEEE Spectrum - North American - March 2015 - 46
IEEE Spectrum - North American - March 2015 - 47
IEEE Spectrum - North American - March 2015 - 48
IEEE Spectrum - North American - March 2015 - 49
IEEE Spectrum - North American - March 2015 - 50
IEEE Spectrum - North American - March 2015 - 51
IEEE Spectrum - North American - March 2015 - 52
IEEE Spectrum - North American - March 2015 - 53
IEEE Spectrum - North American - March 2015 - 54
IEEE Spectrum - North American - March 2015 - 55
IEEE Spectrum - North American - March 2015 - 56
IEEE Spectrum - North American - March 2015 - 57
IEEE Spectrum - North American - March 2015 - 58
IEEE Spectrum - North American - March 2015 - 59
IEEE Spectrum - North American - March 2015 - 60
IEEE Spectrum - North American - March 2015 - 61
IEEE Spectrum - North American - March 2015 - 62
IEEE Spectrum - North American - March 2015 - 63
IEEE Spectrum - North American - March 2015 - 64
IEEE Spectrum - North American - March 2015 - 65
IEEE Spectrum - North American - March 2015 - 66
IEEE Spectrum - North American - March 2015 - 67
IEEE Spectrum - North American - March 2015 - 68
IEEE Spectrum - North American - March 2015 - 69
IEEE Spectrum - North American - March 2015 - 70
IEEE Spectrum - North American - March 2015 - 71
IEEE Spectrum - North American - March 2015 - 72
IEEE Spectrum - North American - March 2015 - 73
IEEE Spectrum - North American - March 2015 - 74
IEEE Spectrum - North American - March 2015 - 75
IEEE Spectrum - North American - March 2015 - 76
IEEE Spectrum - North American - March 2015 - Cover3
IEEE Spectrum - North American - March 2015 - Cover4
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