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.