The number of times I’ve spoken to customers who have had other reps speak to them about glazing and u-value and not explain actually what this means is frightening.
One lady was told that u-value are of no use to anyone and as long as it’s double glazed it’s fine… Another line is leav your window open for 5 minutes and you’ve wasted the energy you’ve saved throughout the hole day!
And the strangest thing of all which I’m sure all Double glazing guys find really wierd is on new builds we are now fitting energy rated windows to save the planet and then drilling through the frames to fit trickle vents in them for ventilation purposes…
Any way back to my point, I’ve e-mailed a very intelligent chap to try to explain a U-Value in easy speak and the replay is as follows:
“There’s not much to explain. There is a reciprocal relationship between “R” & “U” and value. Both are used in UK and USA wherever appropriate.
R = Resistance (in sq m per deg C / W)U = 1/R (in W / sq m per deg C)U value is used to express and calculate the heat lost through structural elements. So, say a piece 4mm glass has a U value of 5.8 and an area of 1.2 m x 0.9 m, with an internal temp of 21 deg C and an external temp of 1.
The heat lost through that glass will be 1.2 x 0.9 x 5.8 x 20 = 125.28 Watts / hr. (So a 150 W light bulb would offset the heat loss).
With a series of heat loss calculations like this one, you can ultimately determine radiator and boiler sizes. I promise they do it in exactly the same way in the US !
(The same piece of 4mm glass would have an R value of approx 0.1724)
Yours sincerely,
So I think I got it if say for instance we are quoting a 1.5 U-value unit and the Internal temperature is 21 degrees and the outside temperature is 3 degrees with the same size glass then the calculation would be as follows:
Glass Width x Glass Heisght x U-Value x Temperature difference from Inside to outside temparature = Heat Loss
OR
1.2m x 0.9m x 1.5 x 18 = 29.16 Watts / hr
So now you know if you want to really bore someone stupid on your Designers appointment you could work out there heat loss through every window in the house and even work out their expected energy saving per year, and what a close that would be four hours later!!! Of course you’d have to take two thermometers with you!
A little bit of knowledge is dangerous, but hey think of it this way if after changing the clients windows they can save over 150 Watts per hour/ per window what a difference that woul dmake to their heating bill at the end of the year.
Energy Rated Windows here we come!!!
One of the foreseeable problems with energy rating for windows is how easy will it be for manufacturers to over exaggerate the efficiency of their units? There’s many products out there where features and performance is grossly over exaggerated for no other reason than to mislead the customer. Can consumers rest assured that this will not happen with regards to energy ratings?
I think that whenevr figures are involved companies will always massage them somewhat to suit there own requirements. The new energy rated units are undoubtedly more energy efficient than old double glazed units but what the people who test the energy ratings of the windows do is bizzare.
They take an intermediate outerframe which in 75% of installations is not used to give the entire window the energy rating, if you then specify a 70mm profile instead of the 60mm profile they can’t give you the energy rating sticker. However If I fit a 60mm outerframe with a 20mm add on all around it they will still give me the energy rating on the window?????? And as anyone can guess the 70mm will undoubtedly be more energy efficient than the 60mm with the add ons. I know which I’d rather have and that is a 70mm outerframe with “A” rated glazing.
So in alot of ways I agree with what you say overated in a cetain way but it defiantely is a great improvement on what used to be fitted as norma1 “K” or Low E glass or whatever you want to call it.