Hi all,

Anyone know where I can get k values for different types of windows?
Specifically, I'd like to compa

- single pane leaded windows (real leaded, with the lead all the way
through, not stuck on) in a steel frame

and

- 18mm double glased sealed units in an oak frame


TIA


--
Grunff

Grunff wrote:
Hi all,

Anyone know where I can get k values for different types of windows?
Specifically, I'd like to compa

- single pane leaded windows (real leaded, with the lead all the way
through, not stuck on) in a steel frame

and

- 18mm double glased sealed units in an oak frame

The second will win.



As to the leading - it's largely irrelevant.
Glass has a K of 1, so a 6mm pane has a U value of 1*.006= .006.
The air sitting next to the inside of this utterly swamps this in
insulation.

Ian Stirling wrote:

The second will win.



You don't say...


As to the leading - it's largely irrelevant.
Glass has a K of 1, so a 6mm pane has a U value of 1*.006= .006.
The air sitting next to the inside of this utterly swamps this in
insulation.

I dunno - lead has a K of ~35. Steel has a K of ~46. If we take one
opening pane, which is 49cm wide by 90 cm high:

Total area: 4410 cm^2
Glass: 3563 cm^2
Steel: 540 cm^2
Lead: 307 cm^2

That means the glass only makes up 81% of the window area, with the rest
of the area being made up of materials that are over an order of
magnitude more conductive.


--
Grunff

Grunff wrote:
Hi all,

Anyone know where I can get k values for different types of windows?
Specifically, I'd like to compa

- single pane leaded windows (real leaded, with the lead all the way
through, not stuck on) in a steel frame

and

- 18mm double glased sealed units in an oak frame


TIA


I have this somewhere..I have SG leaded..but I haven;t time to look it up.

Its in the building regulations tho..handy guide..

IIRC the SG U value is around 5-7 and the DG is around 1-3 depending

A good insulated wall is less than 0.3...

If you are considering installing new leaded lights, like wot I did you
WILL need to get the whole building energy calculated to convince the
BCO that it is within spec, and this WILL mean extra insulation elsewhere.

If its an upgrade to an existing building, you may also need to convince
him/her that enough extra insulation is applied elsewhere at the same
time to bring the modifications to at least no worse than what was there
before, and preferably a lot better.

The Natural Philosopher wrote:

IIRC the SG U value is around 5-7 and the DG is around 1-3 depending

A good insulated wall is less than 0.3...

Ok, thanks.


If you are considering installing new leaded lights, like wot I did you
WILL need to get the whole building energy calculated to convince the
BCO that it is within spec, and this WILL mean extra insulation elsewhere.

If its an upgrade to an existing building, you may also need to convince
him/her that enough extra insulation is applied elsewhere at the same
time to bring the modifications to at least no worse than what was there
before, and preferably a lot better.

I'm not, I'm just curious about the relative heat loss in different
rooms of our house, and the choices the architect made. It seems to me
that the leaded windows lose several hundred Watts more than the double
glased ones, and I wanted to see if this is really the case.


--
Grunff

Grunff wrote:
Ian Stirling wrote:

The second will win.



You don't say...


As to the leading - it's largely irrelevant.
Glass has a K of 1, so a 6mm pane has a U value of 1*.006= .006.
The air sitting next to the inside of this utterly swamps this in
insulation.

I dunno - lead has a K of ~35. Steel has a K of ~46. If we take one
opening pane, which is 49cm wide by 90 cm high:

Total area: 4410 cm^2
Glass: 3563 cm^2
Steel: 540 cm^2
Lead: 307 cm^2

That means the glass only makes up 81% of the window area, with the rest
of the area being made up of materials that are over an order of
magnitude more conductive.

You can't quite get there from here - as a very significant factor at
this level of conductance is the air next to the window/frame.
Also - the much wider section of the metal, and the fact that it's not
(usually) solid means that it's less conductive.

Ian Stirling wrote:

You can't quite get there from here - as a very significant factor at
this level of conductance is the air next to the window/frame.
Also - the much wider section of the metal, and the fact that it's not
(usually) solid means that it's less conductive.

Yes, for single glazing it's the air boundary layers that dominate.

1/U = Rsi + Rso + sigma(t/k)

Where
Rsi is the resistance of the inside air layer
Rso is ditto for outside
sigma(t/k) is the sum of the thickness/conductivity ratios of
the intervening layers

For horizontal heat flow Rsi = 0.12 m^2K/W, Rso = 0.06 m^2K/W. The sum
of these is 0.18 m^2K/W.

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given earlier
in the thread) t/k is 0.004 m^2K/W so contributes negligibly to the sum.
The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~ 200
W/mK) only increases U to about 5.5 W/m^2K.

--
Andy

Grunff wrote:
The Natural Philosopher wrote:

IIRC the SG U value is around 5-7 and the DG is around 1-3 depending

A good insulated wall is less than 0.3...

Ok, thanks.


If you are considering installing new leaded lights, like wot I did
you WILL need to get the whole building energy calculated to convince
the BCO that it is within spec, and this WILL mean extra insulation
elsewhere.

If its an upgrade to an existing building, you may also need to
convince him/her that enough extra insulation is applied elsewhere at
the same time to bring the modifications to at least no worse than
what was there before, and preferably a lot better.

I'm not, I'm just curious about the relative heat loss in different
rooms of our house, and the choices the architect made. It seems to me
that the leaded windows lose several hundred Watts more than the double
glased ones, and I wanted to see if this is really the case.



Oh yes, definitely.

But sick a lined and interlined curtain over them, and they are actually
much better than a triple glazed unit without curtains.

Ok, found the book

This is U values not K. Watts per sq meter per degree K.

DG windows range from 2.2 to 4.2..depending on gap, filling and frame.

SG windows are in the range 4.7-5.8 depending on frame.

Note a good wood frame SG is almost as good as a crap DG metal frame...

solid doors are about 3.

9" solid brick wall about 3.5

4.5" single brick wall 7.

10mm expanded polystyrene or rock wool or 6mm Celotex 3.5

...yes folks, thats how little will HALVE the heat loss through a 9"
solid brick wall. and if its a single 4.5" brick wall..just 5mm of
polystyrene will halve it, too..

15mm plasterboard has a U value of about 10.

15mm of wood paneling is about a U value of 10 too.

Its very instructive to see how a brick wall without cavity, a window
and a door are all very similar..this is typical Victorian style
construction, and how little 15mm of wood flooring will help with an
underfloor vented cavity, or 15mm of plasterboard ceiling will help with
a vented roof cavity..Brr!.

Its also very instructive to see how little insulation is needed to make
a substantial difference to this sort of property.

Now building regs are trying to get U values down below 0.3
overall..about TEN TIMES better than a Victorian 'as built' standard.


You can instantly see that uninsulated plasterboard ceilings to a
vented roof are by far and away the worst losers of heat. Which
vindicates the emphasis on loft insulation.

Its also easy to see why Britain, with loads of suspended wooden floors
has a penchant for fitted carpets with thick underlay..

Its very hard to see why double glazing is so insisted on.

Its very easy to see just how bad solid brick walls are as well..and
remember a cavity wall with exterior air bricks is not far off a 4.5"
single brick wall, in a moderate breeze..you don't need a lot of
insulation to radically improve these sorts of wall..dry lining with
just 1/4" of Celotex will halve the heat loss through a solid brick
wall. Add in 15mm of plasterboard and U value is down to 1.5 from 3.5.
For a total loss in room dimensions of less than an inch all round the
exterior walls. No brainer innit?

Now lets consider a room - say its 12x8 ft. and 8ft high, with two
external walls. So external area is 96+64=186 sq ft..and lets consider
it has a suspended floor and be generous with carpeting and put that as
U value of 3.5 same as the walls.. so another 96 sq ft takes us to 270
sq ft.

Thats a total area of 25 sq meters. Lets assume an average annual
internal temp of 19C and 14C average annual external..so 5C drop..so the
watts required is 5x3.5x25= 437.5 watts. And a peak requirement at -6C
external of 5 times that..2187 watts.

Consider how we might improve all this.

Let's say we have two windows totalling 2.5 sq meters. At a U value of
5..so thats just 8% of the total heatloss from the room. A GOOD DG unit
should more than halve that..netting us a 4% gain, or ariound 17.5 watts
average, and annualized around 155KWh..say at 10p per unit..£15 a year
gain.For probably about £1500 outlay. So a 1% ROI.

Now let's dry line the room with 2" celotex on the external walls..thats
50mm. Thats a U value of 0.4, so with 15mm plasterboard at 10, and our
wall at 3.5, neglecting cold bridging by studs we can achieve an overall
wall U value of 0.35. 186sq ft (17.2799654 sq meters) less 2.5 sq
meters of windows nets us 15.2..and the saving in heat will be an
average of 240 W average. Or 2097KWh over the whole year.

Thats for 5 sheets of celotex and 5 sheets of plasterboard..and some
studwork..say 400 quid in all? and a hundred quids worth of skim and
paint..well anyway its WELL under £1000, and at 10p a KWh, it will save
£200 per annum. An ROI of around at LEAST 20%.

Similar gains may be expected from doing the same to the floor.

In short even if my figures for energy costs are high, based on
electricity, the gains to be had from drylining are about 20 times as
cost effective as double glazing.

If we add in an insulated floor as well..then our gains are about 234
watts out of the 437..such that all that is left is the window
really..about 63W average...and our walls are now losing just 40 watts
average.

In short we have come from 437.5 watts down to 103W..75% of the heating
bill has gone. Adding SG might net us a further 40W or so, but so would
a decent set of nice lined curtains.


My points are these.

1/. Loft wall and floor insulation represents ROI of up to 30% or more..

2/. Loft wall and floor insulation on an uninsulated property represents
up to 70% energy reduction. More if you do it to full building control
specs. With a typical figure of less than 10% of wall area and only a
factor of two improvement, double glazing represents at best a 5% energy
saving on an otherwise uninsulated or just loft insulated house, and
probably less than 1% ROI. It is in fact a total waste of money and will
never pay for itself..unless you had to replace the windows anyway.

3/. Fitting a new boiler is easy enough..going from a 50% efficient
boiler to an 80% efficient one is a net energy improvement of 37.5% in
bills..the ROI will be easy to calculate from your annualised fuel bills.

4/. Let's say our 437W room has two 100W lamps, used an average of 4
hours a day..291.2 KWh per year..and we replace then with two 17W
CFLs..costing a fiver each. So we come down to just 49Kwh per annum. AND
we have to make good the heat no longer added to the room..well anyway
the net saving IS about £24 on electricity...not bad returns for a
tenner..but mitigated by the fact that we have to add the heat back with
the boiler..in terms of saving the planet we don't really save that much
after all..as our boiler is not a great deal better than the electricity
generating plant. Still, it's something.

5/. Here's another interesting calculation. Let's say our house is a 4
bed detached one comprising 8 rooms on two storeys as calculated. so
it's total heating is 8x437 watts. Annualised that is 30MWh. About £3000
to heat then with electricity (and as anyone who has used storage
heaters, in a house like that, thats not far off true). Now you get
about 10KWh per liter of heating oil (and similar for a cu meter of gas
actually) so at say a 50% boiler efficiency, that's around 5Kwh per
liter..which equates to 6000 liters of oil to heat that house. Again
those of us who have heated houses like that know thats not unrealistic.



That's 1320 gallons..enough to take a nice tidy 45mpg diesel car 60,000
miles...let's say you insulate your house and knock that down by
70%..you can afford to run a car for 42,000 miles a year and still be
using less oil.

Makes you wonder sometimes why car fuel is 90p a liter and heating oil
is 30p a liter.

That actually puts a new 80% efficient boiler into perspective. Say it
costs a grand. But puts out 8.5Kw/liter. You save 1500 liters a year.
or around £450. On an uninsulated house.

On your 1800 liters a year insulated house, you will save just 450
lites, or £150. Not that great a saving..15% ROI.

6/. Wearing a £50 pullover that you replace every year, and knocking
your stat down by one degree, to 18C..saves you 20% of your annual fuel
bill. If its at £1800 a year (30p/l and 6000 liters) and you are a
family of 4, that's £360 a year off your fuel bill for a cost of £200 of
woollies. :-)

Of course, once you insulate the house and are running at a mere £540 a
year heating bill, the savings of £108 are not worth the cost of buying
(and washing) the pullovers..;-)

7/. One annual trip of 2000 miles by plane (at about 70mpg per
passenger)is peanuts compared with the 12,000 miles you do to commute to
your job at 45mpgh, or less in congestion..

8/. Lets say you do 60 miles a day, 200 days a year ..a nice 12,000
mile commute. And you elect to stay at home and work 3 days a week from
home. That takes you to 3000 miles a year commute. The direct savings on
fuel at 45mpg are 200 liters. About £180 a year..but with motoring costs
in total running at around £.20 a mile your real savings are nearer
£1800..and since you pay out of taxed income, that's about £3600 off
your gross salary..and £4000 of what you cost your employer..before the
cost of office space., heating and lighting, and kit is taken into
account. Probably another £1800 or so. So he could afford to pay you
another £2200 a year to work from home, and you would be directly £1800
better off..so the equivalent to a £4k pay rise to you, and a gain of
about 6 hours a week....240 hours a year on a 200 day working year..or
about 6 weeks extra holiday in gain of leisure hours, to you.

Why ARE we commuting then? No real answer.


9/. What does a hot bath cost? well mine is 1.3 long x .5 wide x .3deep
195 liters. But I take up a lot of that so lets say 100l for a really
good soak. I like my bath to be as hot as I can stand..lets say 45C and
we will assume the average incoming water temp is around 14C ..so 39 c
rise and 100liters is 3900 calories or 16.4 Mjoules. That's getting on
for a liter of fuel with a 50% efficient boiler. Gosh. Almost 30p.

Could cost as much as 100 quid a year to have a real soak every day.

10/. Do showers save money and the planet?
Well that depends on how good they are. we know that a mingy electric
shower soaks up 10KW..so on a 6 minute shower thats 1KWh..3.6MJ. Most
decent showers will do at least twice that..a typical combi today might
do 30KW..so a 6 minute shower would be 10.8MJ. In short unless you
simply use showers for a quick brush up and are in and out quickly, they
don't save you any money or water really at all over a medium bath.

11/. Does an electric kettle half full save the planet? Let's say your
kettle is a liter. 2 pints or thereabouts. And the water in it is at
room temp..say 20C because you left it there from the last cup of
coffee. And you make 10 cups of coffee or tea a day. That's 800
kilocalories of heat a day. 3.36MJ. At a 50% fuel to electric conversion
ratio that's almost a 1/6th of a liter. 5p!! almost £15 a year on coffee
boiling!!! so lets say we save half of that directly..30 liters of fuel
a year..In fact we don't, because a lot of the time we are heating our
houses and the kettle is part of that..the net gain is probably less.
say 15 liters of fuel a year. about a fiver. Or to put it another way
thats about 3.3 gallons of fuel a year, or 150 miles of road fuel usage.

Taking two days off work saves nearly that. or going to the supermarket
at a 5 mile round trip one time less a week saves more.


Why did I taker the time to write all this?

Well..in cam.misc someone complained their gas bill was too high, and in
UK.D-i-y, someone wanted to know how much better double glazing was than
single glazing..and I really thought.."we get bombarded with green crap,
told to buy CFL's take showers not baths, half fill kettles, buy new
boilers, fit double glazing and not fly"

And yet the reality is that the massive dominant and overriding two
things we do that chew up oil and cost us a bloody fortune, are heat
uninsulated houses, and drive to work every day. And the supermarket
every other day and the kids to school half the year..

The rest is completely irrelevant as long as we don't insulate the walls
ceilings and floors, and continue to use the car on a daily basis to do
an average of around 50 miles a day.

The Natural Philosopher wrote:
Ok, found the book

snip great post

Thanks v much for the detailed info, and the work-through. What book is
the data from? Sounds like a very handy book to have on the shelf.


--
Grunff

Andy Wade wrote:

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given earlier
in the thread) t/k is 0.004 m^2K/W so contributes negligibly to the sum.
The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~ 200
W/mK) only increases U to about 5.5 W/m^2K.


Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?


--
Grunff

big snip

Kudos for that !

Grunff wrote:
The Natural Philosopher wrote:
Ok, found the book

snip great post

Thanks v much for the detailed info, and the work-through. What book is
the data from? Sounds like a very handy book to have on the shelf.


"Building Regulations Explained"
2000 revision
South Edition.

Grunff wrote:
Andy Wade wrote:

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given
earlier in the thread) t/k is 0.004 m^2K/W so contributes negligibly
to the sum. The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~
200 W/mK) only increases U to about 5.5 W/m^2K.


Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?


The fact that celotex traps a far far larger 'boundary' layer - about
100mm in fact ;-)

And what GRUNFF is missing, is that in a 30mph gale, the boundary layer
gets stripped away on copper, and glass, both.

It also gets pretty bad with rockwool in the loft.

Its not often mentioned, but I did get significantly better insulation
when I boarded over mine..noticeable in strong winds..

Likewise my suspended (and insulated) concrete floor is significantly
colder when the wind blows..the underfloor space is a good insulator
when its calm.

The Natural Philosopher wrote:


This is U values not K. Watts per sq meter per degree K.

DG windows range from 2.2 to 4.2..depending on gap, filling and frame.

Hmmm, I hope not... I understood that current building regs requires
windows with U values of less than 2.0 to be installed. Our DG is
apparently approx U=1.2 using Pilkington Optitherm (soft-coated glass),
argon filled and a super-spacer-bar-thingy. The units are called
Pilkington Insulights.

http://tinyurl.com/2rkpv7

Putting all this in a steel/upvc frame might raise the U value to around
1.4-1.5?

J

Jonathan Tong wrote:


The Natural Philosopher wrote:


This is U values not K. Watts per sq meter per degree K.

DG windows range from 2.2 to 4.2..depending on gap, filling and frame.

Hmmm, I hope not... I understood that current building regs requires
windows with U values of less than 2.0 to be installed. Our DG is
apparently approx U=1.2 using Pilkington Optitherm (soft-coated glass),
argon filled and a super-spacer-bar-thingy. The units are called
Pilkington Insulights.

http://tinyurl.com/2rkpv7

Putting all this in a steel/upvc frame might raise the U value to around
1.4-1.5?

I can only go by what the building regulations data says. Mine is 2000 data.

they give 2.2 for a double glazed argon filled 12mm gapped window in a
wood or UPVC frame..

I am sure the GLAZING is better, but the frame area represents a
significant cold bridge.

However the point of that post was to demonstrate that really it makes
sod all difference to the overall house heatloss.

If you trap 6" of air behind a set of thick curtains, that's not far off
the same insulation as 6" of rockwool. Far better than any window itself
can achieve.

I didn't go into air changes either. Now its hard to translate the
regulations into actual airflow of ventilation but e.g. a fan of 15l/s
minimum is what is required for otherwise unventilated bathrooms etc.

If we take that as a minimum ventilation requiremennt, that is .015 cu
meters or .019 kg of air per second, with a specific heat of around 1000
joules per kg per deg ..which is 15 joules per second, per degree C or
75Watts for a 5C internal to external temperature difference.


In the case of our room, insulated down to a U value of less than .75
overall, 25 square meters of external surfaces.. the lossse are 93watts.

Adding in ventilation of 15l/s NEARLY DOUBLES THE HEATLOSS.

Or to put it another way, in a perfectly insulated room of that size and
shape that loses no heat except by ventilation, the ventilation alone
will increase the U value to 0.6 all by itself.

So whether you go for a calculated U value of 0.7, or the recommended
0.3 or less becomes completely irrelevant as long as you have the actual
ventilation that the regulations insist on.

The conclusion is that much beyond a U value of less than 1, unless you
also either break the ventilation requirements or arrange in addition
some heat exchanging on the ventilation, you are wasting your time largely.

I can foresee in the future that some form of twin coaxial tubes will be
used to allow hot air to rise out of rooms, heating up incoming air as
it does so...









J

In article ,
Grunff wrote:

I'm not, I'm just curious about the relative heat loss in
different rooms of our house, and the choices the architect
made. It seems to me that the leaded windows lose several
hundred Watts more than the double glased ones, and I wanted to
see if this is really the case.

Don't forget to factor-in the Hereford&Worcester
planning dept into the architect's decisions.
Are the leaded windows the ones visible from any
direction to which the public has access?

--
Tony Williams.

Tony Williams wrote:

Don't forget to factor-in the Hereford&Worcester
planning dept into the architect's decisions.

Yes, there is that. I did talk to him about it actually, and the general
reply was something like "it was I was instructed to do".


Are the leaded windows the ones visible from any
direction to which the public has access?

No, that's the odd thing - they are randomly scattered. Some are visible
from the road, some are visible from the courtyard - same with the oak
framed DG windows (which IMHO look a lot nicer anyway).


--
Grunff

On Wed, 17 Jan 2007 11:15:30 +0000 The Natural Philosopher wrote :
I can foresee in the future that some form of twin coaxial tubes will be
used to allow hot air to rise out of rooms, heating up incoming air as
it does so...

It's mechanical ventilation with heat recovery. Once you build highly
airtight housing you need something like this to maintain air quality.

The new (as of last April) imposes compulsory sample air pressure testing
of virtually all new housing as air leakage through badly sealed gaps etc
can seriously undermine the gains made through better insulation.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

In uk.d-i-y The Natural Philosopher wrote:
Jonathan Tong wrote:


The Natural Philosopher wrote:


This is U values not K. Watts per sq meter per degree K.

DG windows range from 2.2 to 4.2..depending on gap, filling and frame.

Hmmm, I hope not... I understood that current building regs requires
windows with U values of less than 2.0 to be installed. Our DG is
apparently approx U=1.2 using Pilkington Optitherm (soft-coated glass),
argon filled and a super-spacer-bar-thingy. The units are called
Pilkington Insulights.

http://tinyurl.com/2rkpv7

Putting all this in a steel/upvc frame might raise the U value to around
1.4-1.5?

I can only go by what the building regulations data says. Mine is 2000 data.

they give 2.2 for a double glazed argon filled 12mm gapped window in a
wood or UPVC frame..

I am sure the GLAZING is better, but the frame area represents a
significant cold bridge.

However the point of that post was to demonstrate that really it makes
sod all difference to the overall house heatloss.

If you trap 6" of air behind a set of thick curtains, that's not far off
the same insulation as 6" of rockwool. Far better than any window itself
can achieve.

This is rubbish.

15cm of rockwool has a U value of .266.

Internal surfaces have a R value of .12, and curtains have two, so
that's .24 thermal resistance. Assuming the curtains have the same
resistance of 5mm of rockwool, that's another .12, and that gets to .36
a 50mm cavity has a thermal resistance of .18, taking it to a total of
..54.
Or a U value of 1.85, or around 2cm of rockwool.



I didn't go into air changes either. Now its hard to translate the
regulations into actual airflow of ventilation but e.g. a fan of 15l/s
minimum is what is required for otherwise unventilated bathrooms etc.

If we take that as a minimum ventilation requiremennt, that is .015 cu
meters or .019 kg of air per second, with a specific heat of around 1000
joules per kg per deg ..which is 15 joules per second, per degree C or
75Watts for a 5C internal to external temperature difference.

Tha'ts assuming you don't have a heat exchanger in there, which is
possible.

The Natural Philosopher wrote:
Grunff wrote:
Andy Wade wrote:

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given
earlier in the thread) t/k is 0.004 m^2K/W so contributes negligibly
to the sum. The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~
200 W/mK) only increases U to about 5.5 W/m^2K.


Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?


The fact that celotex traps a far far larger 'boundary' layer - about
100mm in fact ;-)

And what GRUNFF is missing, is that in a 30mph gale, the boundary layer
gets stripped away on copper, and glass, both.


Only on the outside.
Hopefully, on the inside, the gale doesn't get in.

Grunff wrote:
Hi all,

Anyone know where I can get k values for different types of windows?
Specifically, I'd like to compa

- single pane leaded windows (real leaded, with the lead all the way
through, not stuck on) in a steel frame

and

- 18mm double glased sealed units in an oak frame


On a sort-of-related topic, I'm insulating my house at the moment.
As part of this, while I've got the plasterboard off, it's fairly easy
to add a sheet of kingspan inside the wall, that slides out on concealed
runners over the windowsill, forming a tightly fitting shutter.

In use, it looks like a 3cm or so deep alcove, with trim round it.

Ian Stirling wrote:
The Natural Philosopher wrote:
Grunff wrote:
Andy Wade wrote:

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given
earlier in the thread) t/k is 0.004 m^2K/W so contributes negligibly
to the sum. The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~
200 W/mK) only increases U to about 5.5 W/m^2K.

Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?


The fact that celotex traps a far far larger 'boundary' layer - about
100mm in fact ;-)

And what GRUNFF is missing, is that in a 30mph gale, the boundary layer
gets stripped away on copper, and glass, both.


Only on the outside.
Hopefully, on the inside, the gale doesn't get in.

true, but that doubles the U value right away.

Ian Stirling wrote:
In uk.d-i-y The Natural Philosopher wrote:
Jonathan Tong wrote:

The Natural Philosopher wrote:


This is U values not K. Watts per sq meter per degree K.

DG windows range from 2.2 to 4.2..depending on gap, filling and frame.
Hmmm, I hope not... I understood that current building regs requires
windows with U values of less than 2.0 to be installed. Our DG is
apparently approx U=1.2 using Pilkington Optitherm (soft-coated glass),
argon filled and a super-spacer-bar-thingy. The units are called
Pilkington Insulights.

http://tinyurl.com/2rkpv7

Putting all this in a steel/upvc frame might raise the U value to around
1.4-1.5?

I can only go by what the building regulations data says. Mine is 2000 data.

they give 2.2 for a double glazed argon filled 12mm gapped window in a
wood or UPVC frame..

I am sure the GLAZING is better, but the frame area represents a
significant cold bridge.

However the point of that post was to demonstrate that really it makes
sod all difference to the overall house heatloss.

If you trap 6" of air behind a set of thick curtains, that's not far off
the same insulation as 6" of rockwool. Far better than any window itself
can achieve.

This is rubbish.

15cm of rockwool has a U value of .266.

Internal surfaces have a R value of .12, and curtains have two,

six. Plus about 3 mm of insulating material. I am talking about REAL
curtains..outer fabric, interlining, lining. Not a bit of chintz slung
up hopefully.

so that's 0.72..

so
that's .24 thermal resistance. Assuming the curtains have the same
resistance of 5mm of rockwool, that's another .12

Which takes us up to 0.84

, and that gets to .36
a 50mm cavity has a thermal resistance of .18, taking it to a total of
.54.

My cavity is 150mm, so that's another 0.54 taking it up to 1.38..

Or a U value of 1.85, or around 2cm of rockwool.

so a U value of 0.72, way better than any DG window.

And that's without adding in the window itself.

add in the SG window at say 5 U value, and it's down to 0.63

Ok its not as good as 150mm of rockwool, but its BETTER than 50mm of
rockwool.

Thick curtains are in every way better than DG, except for condensation.
The windows WILL get ICY.

The Natural Philosopher wrote:
[snip]

Thick curtains are in every way better than DG, except for condensation.
The windows WILL get ICY.

The analysis is ONLY valid if your curtains trap the cold air
efficiently. Unfortunately, the current fashion is for curtains to hang
on a rail 3-4 inches outside the window recess, so the air trapping is
very poor. It's even worse if there is a radiator under the window and
long curtains that hang over it directing the heat towards the window,
not the room.

Great original post, BTW.

TL

In uk.d-i-y The Natural Philosopher wrote:
Ian Stirling wrote:
In uk.d-i-y The Natural Philosopher wrote:
Jonathan Tong wrote:

The Natural Philosopher wrote:


This is U values not K. Watts per sq meter per degree K.

DG windows range from 2.2 to 4.2..depending on gap, filling and frame.
Hmmm, I hope not... I understood that current building regs requires
windows with U values of less than 2.0 to be installed. Our DG is
apparently approx U=1.2 using Pilkington Optitherm (soft-coated glass),
argon filled and a super-spacer-bar-thingy. The units are called
Pilkington Insulights.
snip
If you trap 6" of air behind a set of thick curtains, that's not far off
the same insulation as 6" of rockwool. Far better than any window itself
can achieve.

This is rubbish.

15cm of rockwool has a U value of .266.

Internal surfaces have a R value of .12, and curtains have two,

six. Plus about 3 mm of insulating material. I am talking about REAL
curtains..outer fabric, interlining, lining. Not a bit of chintz slung
up hopefully.

so that's 0.72..



Alas, it's not.
The thermal resistance is not inherent to the surface, it's the still
layer of air next to it.
Two surfaces close together do not have four times the insulating
capacity as simply multiplying the per-surface value for a large cavity
by 4.


so
that's .24 thermal resistance. Assuming the curtains have the same
resistance of 5mm of rockwool, that's another .12

Which takes us up to 0.84

, and that gets to .36
a 50mm cavity has a thermal resistance of .18, taking it to a total of
.54.

My cavity is 150mm, so that's another 0.54 taking it up to 1.38..

You can't simply multiply the thermal resistance of a 50mm cavity by
three to get the value for 150mm, otherwise the middle of a room would
be warmest.

Annoyingly I lost the nice graph I had from somewhere that gave thermal
resistance of a cavity as it scales with size.


Or a U value of 1.85, or around 2cm of rockwool.

so a U value of 0.72, way better than any DG window.

And that's without adding in the window itself.

add in the SG window at say 5 U value, and it's down to 0.63

Ok its not as good as 150mm of rockwool, but its BETTER than 50mm of
rockwool.

Thick curtains are in every way better than DG, except for condensation.
The windows WILL get ICY.

The Luggage wrote:
The Natural Philosopher wrote:
[snip]
Thick curtains are in every way better than DG, except for condensation.
The windows WILL get ICY.

The analysis is ONLY valid if your curtains trap the cold air
efficiently. Unfortunately, the current fashion is for curtains to hang
on a rail 3-4 inches outside the window recess, so the air trapping is
very poor.

That depends a lot on how the curtains themselves are designed.

Ours hang against the window boards and there is almost no real space to
allow a good air circulation, despite the cat that they ARE indeed 3"
from he wall..but the 'ruffle' is deeper than that..and some curtains go
down practically to floor level.

Oh and I don't have ANY radiators except in the bathrooms Its UFH or hot
air convectors.

The difference oon a cold night betweenm a window with a drawin curtain
and one without is astonishing.

It's even worse if there is a radiator under the window and
long curtains that hang over it directing the heat towards the window,
not the room.

That is of course a complete waste of time ;-)

Great original post, BTW.

TL

The Natural Philosopher wrote:
Ian Stirling wrote:
The Natural Philosopher wrote:
Grunff wrote:
Andy Wade wrote:

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given
earlier in the thread) t/k is 0.004 m^2K/W so contributes negligibly
to the sum. The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~
200 W/mK) only increases U to about 5.5 W/m^2K.

Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?


The fact that celotex traps a far far larger 'boundary' layer - about
100mm in fact ;-)

And what GRUNFF is missing, is that in a 30mph gale, the boundary layer
gets stripped away on copper, and glass, both.


Only on the outside.
Hopefully, on the inside, the gale doesn't get in.

true, but that doubles the U value right away.

No, it doesn't - the outside R value is taken to be much smaller than
the inside one - IIRC around 0.02, or something, compared to compared to
0.18.

The ~5W/m/k figure is pretty much the accepted one for a single pane
of glass.
Of course, double glazing has 3 'windless' surfaces, so that really
helps it.

On 17 Jan 2007 15:54:34 GMT Ian Stirling wrote :
You can't simply multiply the thermal resistance of a 50mm cavity by
three to get the value for 150mm, otherwise the middle of a room
would be warmest.

For a standard double glazed window the U-values in SAP2005 a
6mm gap: 3.1; 12mm gap: 2.8; 16mm or more 2.7

My understanding has always been that beyond this you get next to no
improvement since the extra space allows for convection currents up
the warmer face and down the colder one.

My guess is that the biggest effect of curtains is to kill the heat
loss from radiation.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

In uk.d-i-y Tony Bryer wrote:
On 17 Jan 2007 15:54:34 GMT Ian Stirling wrote :
You can't simply multiply the thermal resistance of a 50mm cavity by
three to get the value for 150mm, otherwise the middle of a room
would be warmest.

For a standard double glazed window the U-values in SAP2005 a
6mm gap: 3.1; 12mm gap: 2.8; 16mm or more 2.7

Taking this apart - neglecting the glass.

6mm 12mm 16mm
R value .32 .357 .370

Delta-R
.037 .013

Total cavity inside thermal resistance. (-.18)


.14 .177 .19


Interestingly, the cavity is a worse insulator in many cases than the
interior face.


My understanding has always been that beyond this you get next to no
improvement since the extra space allows for convection currents up
the warmer face and down the colder one.

My guess is that the biggest effect of curtains is to kill the heat
loss from radiation.

Tony Bryer wrote:
On 17 Jan 2007 15:54:34 GMT Ian Stirling wrote :
You can't simply multiply the thermal resistance of a 50mm cavity by
three to get the value for 150mm, otherwise the middle of a room
would be warmest.

For a standard double glazed window the U-values in SAP2005 a
6mm gap: 3.1; 12mm gap: 2.8; 16mm or more 2.7

My understanding has always been that beyond this you get next to no
improvement since the extra space allows for convection currents up
the warmer face and down the colder one.

My guess is that the biggest effect of curtains is to kill the heat
loss from radiation.

I don't think so.

I have been watching the digital stat this winter..a sunny clear day as
opposed to a dull one nets only about 1-2C rise in the room. And thats
from the solar systems best 'radiator'

I guess the reason why we put on anoraks is to stop our bodies losing
heat by radiation eh?

multi layer things like coats and jackets that trap air in spaces are
known to be better than one thick layer..curtains when lined are simply
an example of the same.

When hanging naturally our curtains are about 1cm thick. I can't begin
to consider that is worse than a 12mm gap between two pieces of glass.

Incidentally, my figure of 14C average annual temperature is
optimistic..here's the reality.

http://www.metoffice.gov.uk/climate/...00/mapped.html

But it only makes insulation even more important.

Ian Stirling wrote:
The Natural Philosopher wrote:
Ian Stirling wrote:
The Natural Philosopher wrote:
Grunff wrote:
Andy Wade wrote:

Taking a 4mm (t = 0.004 m) pane of glass with k = 1 W/mK (given
earlier in the thread) t/k is 0.004 m^2K/W so contributes negligibly
to the sum. The U value is 1/0.184, i.e. about 5.4 W/m^2K

Replacing the glass with a sheet of 16 swg copper (t = 0.0016 m, k ~
200 W/mK) only increases U to about 5.5 W/m^2K.
Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?


The fact that celotex traps a far far larger 'boundary' layer - about
100mm in fact ;-)

And what GRUNFF is missing, is that in a 30mph gale, the boundary layer
gets stripped away on copper, and glass, both.

Only on the outside.
Hopefully, on the inside, the gale doesn't get in.
true, but that doubles the U value right away.

No, it doesn't - the outside R value is taken to be much smaller than
the inside one - IIRC around 0.02, or something, compared to compared to
0.18.

The ~5W/m/k figure is pretty much the accepted one for a single pane
of glass.
Of course, double glazing has 3 'windless' surfaces, so that really
helps it.

and triple layer curtains and a SG window have 7..

The Natural Philosopher writes:

[ plenty of interesting stuff ]

I was wondering, is there any real value to these powdered paint
additives that are sold as imbuing the paint with insulating properties?

FWIW with windows I'm wondering how regular heavy curtains compare to
these honeycomb shades and blinds with the air cells in them that sit
actually in the frame.

-- Mark

On Wed, 17 Jan 2007 16:38:06 +0000 The Natural Philosopher wrote :
I don't think so.

I have been watching the digital stat this winter..a sunny clear
day as opposed to a dull one nets only about 1-2C rise in the room.
And thats from the solar systems best 'radiator'

I guess the reason why we put on anoraks is to stop our bodies
losing heat by radiation eh?

multi layer things like coats and jackets that trap air in spaces
are known to be better than one thick layer..curtains when lined
are simply an example of the same.

Yes, but curtains, mine away, are not trapping air behind them to any
extent. You've got gaps at the cill and at rail level a continuous gap
(with most curtain rails anyway).

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

Tony Bryer writes:
(snip)
Yes, but curtains, mine away, are not trapping air behind them to any
extent. You've got gaps at the cill and at rail level a continuous gap
(with most curtain rails anyway).

Mmmm, true. Sometimes when I see insulating/thermal curtain and blind
installation described, it turns out that some come with a magnetic
strip you install to have the edge snugly meet the wall or frame. How
available this is, I don't know: I don't think I've seen it in real
life.

-- Mark

In uk.d-i-y Mark T.B. Carroll wrote:
The Natural Philosopher writes:

[ plenty of interesting stuff ]

I was wondering, is there any real value to these powdered paint
additives that are sold as imbuing the paint with insulating properties?

Certainly - if you put on 10cm thick of it.

FWIW with windows I'm wondering how regular heavy curtains compare to
these honeycomb shades and blinds with the air cells in them that sit
actually in the frame.

"Jonathan Tong" wrote in message
...

Hmmm, I hope not... I understood that current building regs requires
windows with U values of less than 2.0 to be installed.

I can confirm that. We are putting in some metal framed windows that only
take 4-6-4mm panes (eg 6mm spacer). To meet 2.0 we had to use coated glass.

Our DG is
apparently approx U=1.2 using Pilkington Optitherm (soft-coated glass),
argon filled and a super-spacer-bar-thingy. The units are called
Pilkington Insulights.

I believe Krypton is slightly better than Argon. Not too much more expensive
(if you can find someone who already has a cylinder of the stuff).

Grunff wrote:

Thanks for the input Andy. While I understand your logic, something
still feels instinctively wrong - can't the same calculation be done to
show that the difference between copper walls and 100mm celotex walls is
negligible? What am I missing?

The t/k term! For 100 mm of Celotex you have t = 0.1 m and k = 0.019
W/mK, if memory serves. So t/k = 5.26 m^2K/W and adding the boundary
layer resistances make a total resistance of 5.44 m^2K/W or a U-value of
about 0.18 W/m^2K.

The point is that with the single-glazed window the glass contributes
about 2% of the total thermal resistance whereas the Celotex is
providing nearly 97% in your example. Taking up Nat Phil's point, with
the Celotex wall it doesn't make much difference if the outer boundary
layer is blown away in a gale; with the s-g window it does.

It helps to think in terms of R-values rather than U-values. To use an
electrical analogy, we're talking about resistances in series here, so
to think in terms of their conductances would be a bit silly.

--
Andy

Andy Wade wrote:

It helps to think in terms of R-values rather than U-values. To use an
electrical analogy, we're talking about resistances in series here, so
to think in terms of their conductances would be a bit silly.

Ok, I got it now - thanks very much for the explanation.


--
Grunff

The Natural Philosopher wrote:
...
Its very hard to see why double glazing is so insisted on.

...

Let's say we have two windows totalling 2.5 sq meters. At a U value of
5..so thats just 8% of the total heatloss from the room. A GOOD DG unit
should more than halve that..netting us a 4% gain, or ariound 17.5 watts
average, and annualized around 155KWh..say at 10p per unit..£15 a year
gain.For probably about £1500 outlay. So a 1% ROI.


Great post. It's really good to cut through the hype with some
calculations, but I don't totally agree with all of your figures.

In the above case, you've assumed an average temperature difference of
5C, but 10C is nearer the mark. (This improves the benefit of insulation
but doesn't alter the calculation of the benefit of turning your heating
down by a degree.)

You've assumed a cost of DG of £600/m^2, but I've just been quoted for a
job at £270/m^2.

You've assumed that you are replacing a fairly good existing SG unit.
This may be the case, but if you want to understand why DG is insisted
on then what about the case of replacing a drafty SG unit at the end of
its life, or the case of a new building. In these cases you need to
subtract from £270 the cost per m^2 of SG to make a proper comparison.

On the other hand, you've assumed 10p per unit. This should be a lot
less if you used gas, which reduces the ROI.

So the minimum ROI is
10*.3*2.5/1000*365*24/270 = 2.4%
(assumes you're replacing a perfectly good SG unit and heating with gas
at 3p per unit).

To work out the maximum ROI we need to know the cost of SG, which I
don't. Taking it to be £135/m^2 we get
10*.1*2.5/1000*365*24/135 = 16%
(assumes you're building from new or the existing SG unit needs
replacing; assumes heating with electricity).

There are also benefits in terms of quality of heat. If you just replace
heat lost from the windows with central heating then you get
temperature differentials - colder nearer the floor than at head level
etc - which is not as snug as uniform heat (in my opinion).

And there are benefits of DG in terms of extra sound insulation too.


Alex