Saving the planet (was:Thermal conductivity of different types of windows)
The Natural Philosopher
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.
Grunff
> 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
Colin Wilson
Kudos for that !
The Natural Philosopher
2000 revision
South Edition.
Jonathan Tong
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.
Putting all this in a steel/upvc frame might raise the U value to around
1.4-1.5?
J
The Natural Philosopher
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
Tony Bryer
> 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
Ian Stirling
> 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
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 Luggage
[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
Ian Stirling
> Ian Stirling wrote:
>> In uk.d-i-y The Natural Philosopher <a@b.c> 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.
>>> 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.
The Natural Philosopher
> 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 ;-)
Tony Bryer
> 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 are:
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.
The Natural Philosopher
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/uk/averages/19712000/mapped.html
But it only makes insulation even more important.
Ian Stirling
> 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 are:
> 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.
Mark T.B. Carroll
> [ 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
Tony Bryer
> 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).
Mark T.B. Carroll
(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
Ian Stirling
> The Natural Philosopher <a@b.c> 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.
CWatters
"Jonathan Tong" <jonath...@arm.nospamthanks.com> wrote in message
news:eoktdq$r89$1...@cam-news1.cambridge.arm.com...
> 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).
Alex Selby
> ...
> 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
The Natural Philosopher
Not sure about what you mean there..
..but there is a definite case for having better insulation when you
don't need the light.
However, it is not a huge factor either way.
> -- Mark
The Natural Philosopher
We have to have the rail 3" away because the curtains are gathered +-3"
at the top. You can or course use a pelmet although those have gone out
of fashion. They should overlap the window boards..and fall against them.
Of course they are not hermetic seals, but they are trappers of air to a
large extent..they must be or I would not see remarkable differences
between windows with curtains drawn, and not.
The Natural Philosopher
> 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.)
>
Agreed. I found te met office stats.
> You've assumed a cost of DG of £600/m^2, but I've just been quoted for a
> job at £270/m^2.
Fair enough. That was a stab in the dark. I reckon that £500 a window
installed with frames is an average sort of figure. And the average
window is about a square meter or so,
>
> 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.
>
Indeed. I thought I had made that point...that unless you had reason to
replace the windows anyway, it wasn't a runner. If you put very cheap
modern sealing strip round and old wood casement I reckon you rep 70-80%
of the benefits of DG at about 1/0th the cost or less.
If you are installing new windows, apart from a severe attack of
aesthetics, there is no reason NOT to install DG, the opportunity cost
is low enough.
I was really coming at this from the point of someone who might be
(genuinely) concerned about energy, and cost benefit on heating, and
pointing out that received wisdom is largely driven by DG marketing and
lack of hard information.
I.e. my conclusins can be stated two ways
'DG windows are 2-3 times as good as single glazed'
'installing DG windows will save you at best 2% of your energy bill,
(all other things being equal)'
Both are reasonably 'true' statements.
> On the other hand, you've assumed 10p per unit. This should be a lot
> less if you used gas, which reduces the ROI.
Its about 3p .. think we worked that out..thats why in the end I
switched to oil burned at 50% efficiency..except where talking about CFL
lamps.
>
> 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).
>
The cheaper the fuel the LESS the ROI is..so I am not sure how you got
more..
> 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).
>
Yup. I never was actually talking about installing SG from new..you only
do that - as we did - out of an attack of aesthetics. Double glazing
cannot be incorporated into lead lights and applied 'glazing bars' looks
crap. So almost certainly your SG units will be more expensive, cos they
are hand made specials.
> 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.
>
Actually, we have high quality sealed SG here, installed from new, and I
have to say the noise reductions is similar. It seems to be the sealing
that is the key, rather than the DG.
>
> Alex
I am not in general trying to say what you seem to think I am..that we
shouldn't be putting DG or even TG in new builds. Of course we should
bne. The *opportunity* cost is low enough, and the gains significant
enough..to make it worth while.
My real thrust was at those people who have bought a nice solid
(literally) walled Victorian property, find it chilly, and costing a lot
to make snug, and instantly go out and fit DG.
The real point is that after whacking in loft insulation and SEALING it
against draughts in the loft,and putting weatherstrip on the windows and
doors, the very next think is to line the walls.
And possibly the floor.
There are HUGE potential gains to be had here, from not all that much
thickness of insulation. 6" of rockwool or celotex is easy to install
under a suspended floor for example. 2" of celotex on the outside walls
is not going to break the bank. And you could be looking at 70% or more
improvement in energy and bills.
Once that is done, boiler efficiency is not so important, and there is
always a moot point as to how much MORE energy the new boiler takes to make.
Attention to electrical stuff is fairly trivial in terms of planet
saving. Far better gains can be had by switching off huge amounts of
public lighting between say 2 am and 6 a.m. However CFL bulbs are cheap
enough to pay for themselves in a few months..I use them because they
don't blow up every five minutes.
Likewise teenagers who spend 10-15 minutes in the shower are not saving
water or energy vis a vis a bath, either.
Jonathan Tong
The Natural Philosopher wrote:
> My real thrust was at those people who have bought a nice solid
> (literally) walled Victorian property, find it chilly, and costing a lot
> to make snug, and instantly go out and fit DG.
<snip!>
I'll concur with the gist of this message. In our case, our (modern)
house already had insulation in the cavity (and I'm not going round
adding an inside skin of more insulation and plasterboard). I'd already
topped up the loft insulation to about 12-14". It's a solid concrete
floor. The *last* thing to do was the DG.
That was done primarily to improve comfort levels (less condensation,
less draughts coming off the cold SG pane, more even temperatures) and
the SG windows needed maintenance....
J
meow...@care2.com
> Alex Selby wrote:
> > The Natural Philosopher wrote:
> If you are installing new windows, apart from a severe attack of
> aesthetics, there is no reason NOT to install DG, the opportunity cost
> is low enough.
>
> I was really coming at this from the point of someone who might be
> (genuinely) concerned about energy, and cost benefit on heating, and
> pointing out that received wisdom is largely driven by DG marketing and
> lack of hard information.
> Yup. I never was actually talking about installing SG from new..you only
> do that - as we did - out of an attack of aesthetics. Double glazing
> cannot be incorporated into lead lights and applied 'glazing bars' looks
> crap. So almost certainly your SG units will be more expensive, cos they
> are hand made specials.
I think there is some confusion here btween dg and upvc. The listed
problems apply to upvc, but no such issues apply to dg. Leaded windows
can be dg no problem, and oak dg does not have the butt ugly factor of
upvc.
NT
Frank Lee Speke-King
The Natural Philosopher wrote:
>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.
Over our patio door/window we have net curtains and double-lined thick
curtains. To prevent condensation due to the 'reverse chimney effect'
we also use a sammy snake across the bottom of the curtains, when
drawn for the evening.
One cold night last winter, <0degC outside, I placed our weather
station's outside thermometer betweem the window and the net curtain,
and sat back to watch.
Eventually, the inside thermometer was reading 22degC, but the one
behind the curtains wasn't far off 0degC, about 2 IIRC.
Those curtains were - and are - doing a fine job.
--
Frank
Alex Selby
...
>> 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).
>>
Typo in the above: it should say .03 not .3. The answer is still 2.4%.
>
> The cheaper the fuel the LESS the ROI is..so I am not sure how you got
> more..
Because there are three error factors increasing the ROI from the 1% you
originally calculated and only one (the fuel cost) reducing it. (i) temp
diff, (ii) cost of DG, (iii) you said 8% of the heat loss is through the
window when you should have said 14% = 5*2.5/(3.5*25). The net effect
of all these corrections makes it a 2.4% ROI as a minimum case.
>
>> 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).
>>
>
> Yup. I never was actually talking about installing SG from new..you only
> do that - as we did - out of an attack of aesthetics. Double glazing
> cannot be incorporated into lead lights and applied 'glazing bars' looks
> crap. So almost certainly your SG units will be more expensive, cos they
> are hand made specials.
In that case the benefit of DG could be even more than 16% of course.
>
>
>> 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.
>>
>
> Actually, we have high quality sealed SG here, installed from new, and I
> have to say the noise reductions is similar. It seems to be the sealing
> that is the key, rather than the DG.
Fair enough. If you are comparing with high quality SG which you already
have and are not costing then of course the benefits of DG will be smaller.
>
>>
>> Alex
>
> I am not in general trying to say what you seem to think I am..that we
> shouldn't be putting DG or even TG in new builds. Of course we should
> bne. The *opportunity* cost is low enough, and the gains significant
> enough..to make it worth while.
But you said "it's very hard to see why double glazing is so insisted
on". I was just trying to explain why I think it makes a lot of sense in
many cases.
>
> My real thrust was at those people who have bought a nice solid
> (literally) walled Victorian property, find it chilly, and costing a lot
> to make snug, and instantly go out and fit DG.
>
> The real point is that after whacking in loft insulation and SEALING it
> against draughts in the loft,and putting weatherstrip on the windows and
> doors, the very next think is to line the walls.
>
> And possibly the floor.
Yes yes, I am completely sold on all that. You are preaching to the
converted. I was just talking about DG and I wanted to fix the calculation.
>
> There are HUGE potential gains to be had here, from not all that much
> thickness of insulation. 6" of rockwool or celotex is easy to install
> under a suspended floor for example. 2" of celotex on the outside walls
> is not going to break the bank. And you could be looking at 70% or more
> improvement in energy and bills.
>
> Once that is done, boiler efficiency is not so important, and there is
> always a moot point as to how much MORE energy the new boiler takes to
> make.
>
> Attention to electrical stuff is fairly trivial in terms of planet
> saving. Far better gains can be had by switching off huge amounts of
> public lighting between say 2 am and 6 a.m. However CFL bulbs are cheap
> enough to pay for themselves in a few months..I use them because they
> don't blow up every five minutes.
>
> Likewise teenagers who spend 10-15 minutes in the shower are not saving
> water or energy vis a vis a bath, either.
>
Alex
The Natural Philosopher
draughty, They need replacing and DG is the way yo go.
The Natural Philosopher
They cannot. Not true lead lights anyway. The frit sealing in DG panels
is about three times as wide as the lead glazing. and a 15mm wide panle
looks silly anyway in a leaded light. The only recourse is to apply fake
glazing bars, and they either look really odd from inside, or outside,
or if applied both sized, at an angle.
and oak dg does not have the butt ugly factor of
> upvc.
Oak with DG is lovely, if the style suits..but as I say, if you want
real leads, DG is out.
>
>
> NT
>
The Natural Philosopher
Was that SG? if so and you had say -2 outside, that would put the
curtains at about 4:1 better than the SG..say around 1 or 1.2 U value.
About twice as good as DG.
Frank Lee Speke-King
The Natural Philosopher wrote:
>Frank Lee Speke-King wrote:
>
>> One cold night last winter, <0degC outside, I placed our weather
>> station's outside thermometer betweem the window and the net curtain,
>> and sat back to watch.
>>
>> Eventually, the inside thermometer was reading 22degC, but the one
>> behind the curtains wasn't far off 0degC, about 2 IIRC.
>>
>> Those curtains were - and are - doing a fine job.
>
>Was that SG? if so and you had say -2 outside, that would put the
>curtains at about 4:1 better than the SG..say around 1 or 1.2 U value.
>
>About twice as good as DG.
Aluminium patio door and window frame, about 8'w x 6'h, 1" air gap
between the DG panels.
--
Frank
meow...@care2.com
> meow...@care2.com wrote:
> > I think there is some confusion here btween dg and upvc. The listed
> > problems apply to upvc, but no such issues apply to dg. Leaded windows
> > can be dg no problem,
> They cannot. Not true lead lights anyway. The frit sealing in DG panels
> is about three times as wide as the lead glazing.
all that tells us is the design of dg you have in mind can't be done.
> and a 15mm wide panle
> looks silly anyway in a leaded light.
The ones I saw were much deeper than that and looked fine. They were
hardly noticeable.
> The only recourse is to apply fake
> glazing bars, and they either look really odd from inside, or outside,
> or if applied both sized, at an angle.
those are like serving up a wimpy in place of beef steak au poivre.
> and oak dg does not have the butt ugly factor of
> > upvc.
> Oak with DG is lovely, if the style suits..but as I say, if you want
> real leads, DG is out.
I've seen it done twice. There is no technical reason not to create
real leaded dg, but obviously the design is different to the popular
sealed panels, since leaded glass is not an airtight glazing surface.
DG does not inherently mean sealed, unsealed dg has been around for a
long time.
The thermal characteristics are not as good as the usual dg, since the
lead is so conductive and not airtight.
NT
Alex Selby
> The Natural Philosopher wrote:
>> My real thrust was at those people who have bought a nice solid
>> (literally) walled Victorian property, find it chilly, and costing a
>> lot to make snug, and instantly go out and fit DG.
>>
>> The real point is that after whacking in loft insulation and SEALING
>> it against draughts in the loft,and putting weatherstrip on the
>> windows and doors, the very next think is to line the walls.
>>
>> And possibly the floor.
>
> Yes yes, I am completely sold on all that. You are preaching to the
> converted. I was just talking about DG and I wanted to fix the calculation.
Sorry I meant to say that more graciously. I think you do us a service
by illuminating these issues.
Alex
The Natural Philosopher
I don't do gracious meself anyway, so no problems ;)
> Alex
The Natural Philosopher
CWatters
"The Natural Philosopher" <a@b.c> wrote in message
news:116911281...@demeter.uk.clara.net...
> The real point is that after whacking in loft insulation and SEALING it
> against draughts in the loft...
You probably know but others might not...
It's very important to NOT to just wack some insulation between the rafters
or you risk a condensation problem and potential long term problems for the
roof structure. Lofts are generally designed to be ventilated spaces to
allow any moisture from the house to be removed.
If you want to put insulation between the rafters and seal the loft to
create a semi-warm storage space then you should consider going the whole
hog as you would for a loft conversion.....
Add batterns to the sides of the rafters to stop the insulation coming in
contact with the underside of the tiles/sarking and provide a 50mm
ventilation space. Install sufficient insulation between and below the
rafters (perhaps 150-200mm thick in total), then a correctly installed
vapour barrier to keep moisture away from the cold tiles/rafters. Add small
vents from the inside of the loft to the outside to allow any moisture in
the loft to get out. The next step would be to line with plasterboard but
that would probably make it a loft conversion in the eyes of building
control.
The alternative is to put insulation between the ceiling joists and retain
it as a cold roof. Seal gaps between the house and loft to keep moisture out
of the loft. Leave the gaps under the eaves open to ventilate the loft.
Insulate the loft hatch.
Colin
Roland Perry
Thu, 18 Jan 2007, The Natural Philosopher <a@b.c> remarked:
>Double glazing cannot be incorporated into lead lights and applied
>'glazing bars' looks crap. So almost certainly your SG units will be
>more expensive, cos they are hand made specials.
What you can do (and I have some DG patio doors, and about a third of
the other windows in my house like this) is make a double glazing unit
that has a traditional sheet of lead lights in between. This has the
added advantage that they are easier to clean, and it looks good too!
--
Roland Perry
Frank Lee Speke-King
The Natural Philosopher wrote:
AFAICR it was something like -5 degC.
--
Frank
Andy Hall
<no....@thanks.invalid> said:
Fairly normal for Speke
I went to the airport there once. I think it involves John Lennon
these days for some reason - goodness knows why. There were tyre
marks on the top of the car factory (Ford I think it was) from the
aircraft. It made Ringway look sophisticated.
The Natural Philosopher
That is actually a very good idea..like a triple glazed unit eh?
Roland Perry
Sun, 21 Jan 2007, The Natural Philosopher <a@b.c> remarked:
>> What you can do (and I have some DG patio doors, and about a third
>>of the other windows in my house like this) is make a double glazing
>>unit that has a traditional sheet of lead lights in between. This has
>>the added advantage that they are easier to clean, and it looks good too!
>
> That is actually a very good idea..like a triple glazed unit eh?
I suppose it has some of the characteristics of triple glazing, but
there's quite a small airgap between the inner or outer panes, and the
encapsulated leaded lights. What I don't know is whether that increases
or decreases the insulation factor.
Your recent posting regarding the relative irrelevance of DG as an
insulating device makes me feel happier about them than I was, so thanks
for that!
--
Roland Perry
Duncan Wood
wrote:
Almost certainly increases it, less convection & two more surfaces ought
to outweigh the conductivity.
The Natural Philosopher
DG isn't so much irrelevant, as completely over-emphasised.
I am wholly in favour of it in new builds or upgrades, except where its
appearance simply won't cut the mustard.
Its the insistence that taking out perfectly good SG and replacing it
should be the *first* thing a homeowner does that gets my goat..whereas
damn thick curtains will achieve far more if the SG is draughtproof.
AND the total underemphasis on cavity wall insulation or dry lining
outer walls, and doing something about suspended wooden floors. Which
are, after the loft, and draughts, the dominant heat loss paths in older
houses.
Myl old hosuse had a convereted single rendred celcon block garage that
was converted by adding in 2" studs with rockwool and plasterboarding it
out. It wass one of the cosiest rooms in that house.
CWatters
"The Natural Philosopher" <a@b.c> wrote in message
> I am wholly in favour of it in new builds or upgrades, except where its
> appearance simply won't cut the mustard.
DG is almost compulsory for new builds to meet the regs. I believe the regs
specify U values for walls and windows that imply DG but I think they also
specify an overall U Value as an alternative method that might allow SG. Got
a feeling that SG windows might have to be small as a percentage of the
area..
The Natural Philosopher
proposed build here. SG windows. They aren't large, but they aren;t
small either.
Essentially I had to go thicker on wall and roof insulation, thats all.
simon
and then this:
> 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..
OK, so for a family of four you have to multiply that up, (which you
don't for an equivalent car journey), and 2000 miles is the round-trip
so you "only" get to go 1000 miles away.
To be more realistic, a single holiday to (say) New York for a family of
four equates to an approx. total round trip of 8000 miles per passenger,
so 32,000 miles at 70mpg. So that's the equivalent fuel use of 16,000
miles in a 35mpg car, which is substantially more than I do in a year.
Simon.
The Natural Philosopher
If fuel costs go high enough, time to unmothball the 'queen mary' or
whatever..
whats a liner do..40mph? 3000 miles..? 75 hours..thats three and a bit days.
Nice trip.
Roland Perry
Mon, 22 Jan 2007, The Natural Philosopher <a@b.c> remarked:
>whats a liner do..40mph? 3000 miles..? 75 hours..thats three and a bit days.
The problem is that for many USA destinations there's another thousand
or two miles to go ! And they don't have many trains left running.
--
Roland Perry
The Natural Philosopher
The reality is that international travel and commerce exists the way it
does because of the cheap cost of fuel.
If that gets expensive. travel patterns will alter to suit.
If a return ticket to LA was 6000 quid not 600, a lot of people would
decide that they really didn't need to go there all that often.
The Natural Philosopher
..oh and of course nuclear electric generation and 400mph trains are
ideal for the USA.
With loading times being far faster, coast to coast times would be
similar to a subsonic airliner.
Need to lay some decent track mind you..
Tony Bryer
> The reality is that international travel and commerce exists the
> way it does because of the cheap cost of fuel.
>
> If that gets expensive. travel patterns will alter to suit.
http://business.guardian.co.uk/story/0,,1837748,00.html gives BA's
summer quarter figures, £2.3bn sales, £512m of which went on fuel.
So, simplistically I admit, fuel prices can double and only put 22%
on fares.
> If a return ticket to LA was 6000 quid not 600, a lot of people
> would decide that they really didn't need to go there all that
> often.
If fuel prices went up that much, they wouldn't be able to afford
the cab to the airport!
--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
The Natural Philosopher
There is a lot to be said for raising fuel prices until the alternatives
ARE cost competitive...
simon
> I wonder how much of what you consume is airfreighted in, though.
That should have been pre-pended with <tangent-alert> ;-) I was talking
about holidays, but if you insist...
Actually, I do check the source of origin of what I buy, so that for
example I would opt to choose apples from England or near-Europe in
preference to South Africa or New Zealand for exactly that reason. Even
then I don't get a choice of whether the product is flown in from (say)
France, or uses land- and sea-freight, but at least it hasn't had to
come so far. For electronic goods the consumer only really has the
choice of buying something made in the far east, or not buying it at all.
> If fuel costs go high enough, time to unmothball the 'queen mary' or
> whatever..
Or just buy products that are locally sourced. I don't need to buy
strawberries in January - we eat locally-grown in-season organic vegetables.
simon
The Natural Philosopher
well we grow our own, so there!
Not from any huge Green motivation, it has to be said, but because they
taste better.
>
> simon
>
Linda Fox
wrote:
>If that gets expensive. travel patterns will alter to suit.
>
>If a return ticket to LA was 6000 quid not 600, a lot of people would
>decide that they really didn't need to go there all that often.
It's scary really. When you think how many states depend to a large
extent on tourism, and the tourism seems to depend on being able to
fly, isn't it all going to have a nasty knock-on effect on the economy
of quite a lot of the world?
(We're going boat/rail to Holland this summer, but this is prompted
partly by OH's reluctance to fly since he's still coping with DVT. But
then we like trains anyway)
cheers
Linda ff
The Natural Philosopher
> On Mon, 22 Jan 2007 12:39:27 +0000, The Natural Philosopher <a@b.c>
> wrote:
>
>
>> If that gets expensive. travel patterns will alter to suit.
>>
>> If a return ticket to LA was 6000 quid not 600, a lot of people would
>> decide that they really didn't need to go there all that often.
>
> It's scary really. When you think how many states depend to a large
> extent on tourism, and the tourism seems to depend on being able to
> fly, isn't it all going to have a nasty knock-on effect on the economy
> of quite a lot of the world?
>
Indeed. We will have to go back to being a nation that does productive
work and have real farms growing real crops and probably keeping real
animals on them,and hunting real foxes with real dogs.
Why, Cambridge might even have to become part of a real world, with real
shops, again.