Hello! Does someone know how to compare the four different Window Energy Ratings (UK, Denmark, Finland, Sweden) used in EU? I would like to know, for example, what does an 'A' in UK means Sweden, etc. Thank you!

It might help to put in a link to an example of what you are refering to, as I have not studied the EU ratings and don't even know where to look. In general most ratings are based on some form of energy transfer testing. The window is installed into a test "room", or perhaps more appropriately put between two test rooms. Then the energy(temperature) levels in the rooms are varied as well as the pressure and very carefull measurements are taken to establish the energy and air transfered thru the window opening. In some tests pressurized water is introduced to simulate wind driven rain. It is a very involved process but it basically results in 4 or 5 specific numbers. 1. heat transfer thru center of glass. 2. Heat transfer thru frame. 3. Overall heat transfer(derived from 1 and 2) 4. Air leakage@ X pressure and 5. Water infiltration @ X velocity. The heat transfer numbers are usually expressed as a "u" factor or BTU per SQ/FT per degreeF of temperature difference. Or in Europe more likely Watt per SQ/M per degreeC of temp difference. Airflow in CFM or cubic meters per minute.

Now the issue is who and specifically how these tests are accomplished and to what standard. IF the test standards are different you are comparing apples to oranges and will probably never get a clear answer to your question. Since they have equated the efficiency numbers into a letter scale, there might be other factors included like a judgment of overall quality? It might be better to get back to the raw U factor and infiltration numbers and make your own determinations.

Thank you for your answer.

I have actually just found a power point presentation where there is a comparison between different EU countries. You can see it here (slide n°9) : https://www.ift-rosenheim.de/documents/10180/873076/ff2014_Energy_labelling_systems_Norbert_Sack_ift.pdf/eb11f352-035f-4c17-ba1b-c6145fc5e771

But the problem is that it doesn't match with the other informations I have gathered.
(See from p.32 : https://www.google.be/url?sa=t&rct=j&q=&esrc=s&source=web&cd=23&cad=rja&uact=8&ved=0CCkQFjACOBRqFQoTCI2Tx-X6oscCFWWa2wodqhgB8w&url=http%3A%2F%2Fwww.buildup.eu%2Fsystem%2Ffiles%2Fcontent%2FTask_2_report.pdf&ei=Yu3KVY3aFOW07gaqsYSYDw&usg=AFQjCNFgk7DLNHpdDOg5bmFy9QvVW6XkIQ&bvm=bv.99804247,d.bGQ )

Well that first link looks like an overview or evaluation for suggested improvements. It summarizes with basically what I said above. There needs to be a common reference/standard...

The second link appears to be a little more detailed as to how the information is derived and represented on the label. It would be good to know when these two documents were created as some of the info in one or the other may be out of date which could explain the differences you are seeing.

The letter score reference back to energy transfer though, but of course different countries evaluated that information differently so the labels may not be all that valuable to you as some do and do not include solar gain. Many are taylored to specific climate zones found in that particular country. ANd some appear to rate in annual average energy consumption/savings.

Where are you located at? Are you in europe or just looking at european windows? At least on this side of the pond we have the NFRC rating system that many manufacturers are participating in. But if you have looked at NFRC data you will note it is all rated in U factor, solar heat gain, and air infiltration so yu can compare apples to apples. They are also very specific in how the windows are tested so the different windows can be compared to others more accurately so it is a little easier. There may even be some EU windows in the NFRC system as they want to be in that system to more easilly sell to the US market.

At any rate, windows can be a tough decision, which is how I came to take a run at answering your question. Since it is such a large percentage of my build budgett, I spent a little bit of time learning about window energy transfer to help me understand the numbers I was being presented with to help me make a decision. It apears that the european system attempts to take some of that education requirement out of an informed window decision(they dummed it down for the general public). but unless you are in those climate zones specified, I don't know how usefull that info will be... There are also other factors to consider such as design, construction, frame material and even overall customer satisfaction(probably equally dependent on manufacturer and installer). A tough bet with a huge pricetag riding on it

U factor is really not all that difficult to understand. It also allows you to pretty easilly and accurately calculate your heat loss for YOUR environmental conditions when considered along with the rest of your envelope makeup. As an example: 70F inside 30F outside = 40F difference. 10 SQ/FT of window at a .19U is .19BTU per SQ/FT (.19X10 = 1.9BTU) per degreeF (1.9X40=76) per hour. So 76BTU/HR lost out of a 10SQ/FT window.

U factor is the inverse of the common insulation R value. IE: a lower U factor = a higher R value. To invert a number you divide it into one. 1 divided by .19 = an R value of 5.2 for the .19 overall U factor window assembly I just used as an example.

The same can be done with the wall for heat loss calculations since R is the inverse of U. Say your wall is R30. 1 divided by 30 = a U factor for the wall of .033 BTU heat loss thru the wall and is applied the same way to say 100SQ/FT of wall and same temps as above .033 BTU per SQ/FT(.033X100=3.3 BTU) per degreeF(3.3X40=132)per hour so 132 BTU lost thru 100Sq/FT of wall over that same hour when it is 30F outside.

Solar heat gain coefficien(SHGC) is a little more complex as it relates to the ammount of sun you get actually shining thru that window, but it works in a similar fashion once you know the ammount of sun comming thru the ammount of windows that have sun exposure. You may want more or less of this depending on where you are located and your heating or cooling needs, and the glass package coatings can be taylored to allow more or less of this. Window location and eave overhang can be taylored to help control this energy transfer also.

Air infiltration is air infiltration, less is usually better.

Oops, double tap...

Ok thank you!

I'm actually in Europe

I want to make an analyse comparison of the different WER (Window Energy Ratings) used in Europe. Thing that I can't do as in the tables I have found, some are rated in annual average energy consumption/savings and others depending on the U-value. (like you said "comparing apples to oranges")

The aim is that a regular person can just look at it and understanding depending on his geographical zone or country, what the label of another country represents in his.

By the way, the first document I have sent you dates from 2014 and the second from May 2009.

Ok, I understand. Because the countries applied the similar format differently, I can see the difficulty in completing your analisis/comparison.

In My Opinion, education is always the best way. If you want this to be a tool to help people apply what they are seeing on different countries WER labels, you should probably educate them on what U factor means, and how the U factor is applied to windows and climate. They all appear to have some U factor rateing. This takes the way they applied the U factor to derive annual energy consumption or savings on the WER out of the picture, and makes apples look a little bit more like apples When I was doing my window search, that knowledge was very important in my ability to evaluate windows I was interested in. Unfortunately as that more recent article reccomended, even this information can be in doubt as there appears to be no real european standard for testing and deriving that U factor... The same happens in the US as getting thru the National Fenstration Registration Council(NFRC) testing is no doubt a complex and expensive proposition. So some don't do that and publish a U factor based on some other form of testing(or estimate?). Probably the most trustworthy EU manufacturers are the ones who fully describe under what standard and method they test their windows to get their published U factor.

Good luck with yor project.

Yes, you right. Now that I look again, they all depend on the U-value!

I'll continue with my research!

Thanks for the help!