Windows and "Eco Glass"

Can you tell which is which of these pictures?

Exhibit 1

Exhibit 2

One of them is a set of radiator fins designed to take heat away from
electrical devices. The other is part of a window frame, designed to... keep heat in? I've certainly always thought the job of windows is to keep it
warm inside when it's cold outside, and I suppose to keep it cool
inside when it's hot outside. Could you tell which picture was which?
Pretty tricky, eh!

It has been said that aluminium window frames destroyed Japanese
architecture. Apparently when aluminium was discovered, people made
jewellery out of it. It must have seemed like a great option to wood,
when it came to be used in windows. It must have been very cheap. But
when it comes to heat conduction, aluminium conducts about 1500 times
more than wood. Obviously, you can get away with using less aluminium,
but the surface area is likely to be similar, and heat conduction
depends a lot on the surface area.

Japan currently has ratings for window performance, based on their
heat conductivity. There is a star system, going from one star to four
stars. Four stars is the highest rating! This sounds really good,
until you look at what the stars are and are not measuring.
Read more about it here, and hear the annoying jingle! but no actually
meaningful numbers.

First of all, one star means more than 4 W/m2K. That means that at least 4
Watts of heat will flow through each square metre, for every degree of
temperature difference. One star just means that there is glass. A
single pane.

From 4 to 2.7 W/m2K gets 2 stars. This generally means double glazing.
2.7 to 2.33 W/m2K gets 3 stars. To get two stars, you need low-e
glass. This means low emissivity. I don't completely understand this,
but I think it's the opposite of reflectivity, so they could call it
"highly reflective" glass, and people would be able to understand
easily, but in their wisdom they don't. They add a thin film of metal
onto one of the sheets, so more heat is reflected back into the house,
or indeed reflected out of the house, if it's summer.

Less than 2.33 W/m2K gets 4 stars, the highest possible level.
Two-star glass is double glazed, with a 6 mm gap between. In the
example I've got, 4-star glass has a vacuum between the pains.

This is called Eco glass, where once again we have that feel-good
green feeling, but we're not sure whether it's the green trees
swishing in the breeze, or some green notes floating into our wallets,
or not floating out. In fact I think the motivation maybe neither and
the concern to keep the economy of the domestic window industry going.

In the grand scheme of glass thermal efficiency, 2.33 is far from the
highest possible level. I'm not sure how they arrived at the numbers
4, 2.7 and 2.33, but I imagine a few aging window makers got together
over a few beers and discussed the best windows they could remember
making. Anyway, let's say the next logical place for a mythical
5-star window would be around 2. To get to this performance of glass,
you need to start making a bigger gap between the panes. If the gap is
too big, the air in the gap starts circulating, so the convection
starts transferring more heat. The optimum thickness is something like
16 mm, but 12 mm with one low e pain will get under 2 W/m2K. Of
course once you start getting such a huge gap as that, the frame might
start to get bigger than the standard sizes of window frames.

Oh yes. What about window frames? Won't it make a huge difference what
the frame is made of? If you have an aluminium frame, the aluminium
will be conducting heat to its heart's content with something like 60
W/m2K, and condensation will be flowing like the Niagara falls. Since
April 2011, the window rating includes the frame, so it will make a
difference whether it's made of a thin sheet of aluminium, or wood
with a sandwich layer of insulation. The numbers have changed so the
whole window and frame assembly gets two stars if it's less than 4.65
W/m2K, three stars for 3.49 W/m2K and four stars for less than 2.33.
Until you get to the magical figure of 2.33, it seems they are
expecting the frame to conduct more than the glass. This contrasts
intriguingly with European manufacturers who consider that the frame
will conduct less than the glass until you get to triple panes.

It's great that they're taking account of the frames, even if they are
giving them more leeway than they give to the transparent bits that
are pretty much limited to glass. But they still haven't taken account
of how airtight the whole thing is. The window can have as many stars
as you like, but it won't help as much if cold air is blowing in. And
that's not even mentioning thermal bridges. I think we may have to
talk about those another time.

Stars	Eco Glass(old)	Eco Glass Windows (new!)	Notes
****	<2.33	<2.33	Double glazed, 6mm gap between pains, low e
***	<2.7	<3.49	Double glazed
**	<4	<4.65</td>	Double glazed. Wait a minute, why are they allowing the frame to let more heat through than the glass?(1)
*	>4	>4.65	Credit where it's due, one star for not being a hole in the wall!

Note 1. They probably have shares in aluminium manufacturing.

Getting back to the glass, if you start using noble gases instead of
air, there are two advantages. First, the noble gase, usual Argon, Krypton
or Xenon, has single-atom molecules, while air is mostly made up of
double-atom nitrogen and oxygen, so the noble gases hold a lot less
heat. Because they hold less heat, they transfer less heat. Also they
are more viscous, so they don't start moving around until the gap gets
close to 20mm, and a thicker gap means a warmer house. The noble gases
are also inert, colourless and odourless, so they don't go off. Argon
is the cheapest and conducts one third less heat than air. Krypton is
more expensive but conducts half of Argon, so it is only used for high
performance, or extra-thin multi-paned windows. These gases will get
the glass down to 1.5 W/m2K, which should surely be worth 6 stars, and
we haven't even looked at triple glazing yet.

Let's give seven stars for glass under 1 W/m2K, even though we got an
extra star for an improvement of a little over 10% from 2.7 to 2.33.
If we were following the same progression, there would be so many
stars on the glass by now, you wouldn't be able to see through the
window! It's a good thing that 2.33 is the highest level! To get our
hypothetical seven stars, you need three layers of glass, two of them
should be low-e so they are reflecting back the reflected heat too,
and you need argon filling them.

Southwall Technologies are talking about U values under 0.5 W/m2K. They seem to be from the US, where the units are imperial--British thermal units per square foot degree farehneit--and different to metric by a factor
of six. It can be confusing as the units are usually missing when U
values are quoted.

The answer, by the way: Exhibit 1 is a set of radiator fins for cooling electrical devices. Exhibit 2 is an aluminium window frame.

Stereo view from the North

People talk about 3-D a lot, but actually it's just stereo vision. This is too, if you're eyes were ten or twenty metres apart, with bouts of amnesia.

All around view from the south

I thought this may give an all round view of the progress. Not sure though.

Electricity is on...

A letter came back from Chubu Denki, the local electricity supplier,
saying they had received our application for a contract. The contract
will be for them to buy electricity generated by our solar panels for
the next ten years. And I'm hoping, as the date of the application was
30th March, 2011, that we'll be getting 48 yen for each kilo Watt hour
that we produce, and not the post April 2011 amount of 42 yen. This
will make a big difference over the ten years, especially if we are
selling most of the daytime electricity, and using the night-time off
peak stuff that they will charge us 9 yen for.

I'm not 100% sure that it does mean that as the letter back from them
did not mention any prices and said that these, and other details of
the contract, would come later.

Gaps and crack...

Apparently the gaps in the XPS are because it shrinks. They went to considerable effort to put them all in the right place, and came back to find gaps had appeared, like this:






They added foam insulation on the inside,

so when they took off the frame, it looked like this:


Then later they filled in the gaps in from the outside, although some gaps still remain,


now underground.


As for the crack, apparently it's just the surface layer of the concrete, added to make an even surface to put the wooden frame on, and not structural.

.

Crazy ideas... PV/T ... heat pumps

At the end of the day, in the final design, the roof is simply a
photovoltaic solar array, but many ideas preceded this. If you look at
efficiency, electric solar panels are not terrible good at converting
the sun's bounty into usable means, changing less than one fifth of
solar energy into electricity. Thermal panels--turning sunlight into
heat, either directly using water or using a coolant--are much more
efficient, getting up to half of the sun's energy into hot water.

PV/T

There are also panels that produce both heat and electricity. Solar
panels become less efficient as they get hotter, dropping up to one
percent per degree centigrade they get hotter, so running a coolant
through the panels can make them produce more electricity, as well as
producing heat, so rather than splitting heat and electricity, hybrid
photovoltaic thermal (PV/T) panels give you both. One problem seems
to be that if the temperature is high enough to generate hot water,
electric power will reduce 10-20%.

We looked at some panels from a Turkish company called Solimpeks,
although the cost was very high. Japanese-made panels are all
registered and qualify for government subsidies for installation and
purchasing electricity, but these are not registered and do not
qualify. A Japanese manufacturer did produce some PV/T panels a few
years ago, but they did not take off. In fact Japan falls well short
of its potential in solar thermal systems.

Hot air

When roof-top photovoltaic panels are installed, they usually have an
air channel running behind them, which is important for cooling.
Another idea was taking heat off the air flowing behind the panels
using an atmospheric heat pump. To make the heat pump more effective,
this should be done at the top of the roof, taking heat off the air
coming out. However, if the air was cooled on the way into the channel
under the panels, it would reduce the temperature on the panels and
increase their efficiency. An advantage of this system would be that
the heat pumps could be used from grid electricity on cold days with
no sunlight (if it snows all day, for example), so no backup heating
system is necessary.

Heat pumps are becoming popular in Japan for generating hot water (the
system is know as Eco cute, "cute" sounding like "kyuto", the Japanese
for "boiler"). Usually, they switch on at night to use off-peak grid
power. At night time, especially in winter, the air is at its coldest,
so it is the least efficient time for running the heat pumps, although
is the cheapest time for using electricity so the "eco" may be more to do with economy than ecology. Heat pumps have an average
COP (Coefficient of Performance) of around 3, so you need to spend 1kW of electricity to generate
3kW of heat. As the temperature drops, the COP drops until the heat
pump is doing no better than an electric heat element--the kind you
get in an electric kettle--at which point the system can switch over
to an electric heat element.

Getting three kW of heat for every kW of electricity may sound good,
but when you consider where the electricity is coming from, both in
terms of the original fossil fuel, and the distance it travels, one kW
of electricity actually takes almost three kW of fossil fuel to make
(the figure the Passive House Institute uses is 2.7) so it's not much
better than using fossil fuels directly. If you're using the
electricity from a solar panel to drive a heat pump, it will be less
efficient than a solar thermal panel.

A fairly popular solar heating system in Japan is known as OM solar
http://www.omsolar.net/en/index.html, which takes heat through the
roof, collects it at the top and then pumps it down for under-floor
heating in the winter, or passes it through a heat-converter to heat
water in the Summer. This system needs a backup heat source, which is
used as the primary water heater in the winter.

If solar panels were placed at the top of an OM solar roof (as they
show on their website), optimisation of the two systems would be
working against each other: the heat system wanting the panels as hot
as possible, and the power system wanting them as cool as possible. OM
solar would work much better with solar panels on the lower part of
the roof.

Foundation details

Here are some shots of details of the foundation. Gaps in the XPS seem to have been filled. I think it's very important to get into the corners. The different layers of XPS were in different places, so any gaps will have been covered. I'm a bit worried about a crack in the foundation, right in the middle of the house though.

Out of the fire and into the frying pan - but what about standing in the sun?

There seems to be a bit of a panic at the moment about radiation,
nobody's calling for more coal-fired nuclear power stations and
everyone is wondering what to do. Renewable energy seems like a great
idea, but what can we do to support it?

It's a bit obvious but buying solar panels is one option. Especially
in Japan, photovoltaics (panels that produce electricity) already have
a payback of less than ten years, with national and local government
subsidies and contracts with electric companies to buy electricity off
you at a premium rate for 10 years, so if you've got spare cash it
makes more sense than putting it in a bank. Especially a Japanese bank
where interest rates are a fraction of a percent. As well as directly
producing electricity, increased demand will mean higher production of
panels, which will mean more efficient and cheaper panels, so they
will be more affordable for more people.

Japan subsidised solar panels for around ten years from 1994, during
which time prices fell to well under a half. Grants began at 900,000
yen per kW of generation, more than you would pay now, but a little
under half the cost at the time. Installations increased from 539 in
1994 and peaked at 72,825 in 2005 when the grant had dropped to 20,000
yen/kW and was to fall to nothing. The number of installations started
falling after the government grants stopped, but picked up again in
2008 when grants were re-introduced.

For each kilo watt (kW) of panel, you get very roughly 100 kilo watt
hours (kWh) of electricity per month. If the orientation of the panel
veers from due south you get less, although it drops less than you'd
think. Even at 90 degrees it's worth installing, although east-facing
roofs are better than west-facing as they heat up less and efficiency
drops as panel temperature rises. Vertically, a bit over 30 degrees
from the horizontal is optimum, but again a few degrees doesn't make a
huge difference. If you have obstacles to the south, you'll get less
sun, but most radiation is around noon, and even at midwinter the sun
is 45 degrees above the horizon, so unless you're in a deep valley, a
forest or north of a skyscraper you should get most of it.

Each kW of panel costs around 600,000 yen. The price on the
electricity bill is around 24 yen per kWh. (That's 200 months - 17
years payback.) Until the end of March 2011, the national government
was offering a grant of 70,000 yen per kW installed, and you could get
a 10-year contract with the electric company to pay you 48 yen per
kWh. If you can use cheap off-peak electricity and sell all your
daytime electricity, that's a pay back of 90 months - 7.5 years. From
April 1st, the government grant went down to 60,000, and the electric
companies will pay 42 yen. Not as good, but still a pay back of 100
months - 8.7 years.

Wind power is a bit more tricky for individuals as you need a good
site, on the top of a hill, or offshore. You can't really just stick
one on your roof; if it was going to produce significant power it
would probably tear the roof off. There are some people in the UK who
have been building wind farms and helping others to:
http://www.baywind.co.uk/ are part of http://www.energy4all.co.uk/
supporting community wind farms. Nobody ever heard of a community run
nuclear power station!

Comparing wind and solar, I suspect wind is more compatible with the
Westinghouse model for power generation--big plants and long
distances--and solar more to the Edison small scale model. Edison's
idea lost out to Westinghouse in the battle of the currents at the end
of the nineteenth century, along with several animals that Edison
electrocuted in a pyrrhic attempt to show how dangerous AC was. In the
worst irony, there are still US states that can use the electric
chairs his employees invented, for killing people. It looks like the
electric chair is on its way out, and also I'm optimistic that we're
going to see a move from the big scale model to the small scale model,
and smart grids with micro-generation, electrical storage and
intelligent devices, but that's probably more to do with my politics
than the technical and economic factors that are usually in control!

I think there is increasing momentum to move away from fossil fuels,
but just looking at CO2, nuclear seems like a good option, even to
some environmentalists (at least oustide Germany). In the 1990s
Britain had the NFFO (non-fossil fuel obligation) but this was set up
and almost exclusively used for funding nuclear power. I think going
from fossil fuels to nuclear is going from the fire into the frying
pan, rather than the frying pan into the fire, but it still seems a
bit hot!