Valuable goods.

Formula for emotions
Having an energy efficient home is most of all a matter of senses: warm, comfy, safe and healthy. A good house should meet all your expectations and protects all your valuable goods.

The bad thing about emotions is that they are pretty hard to measure. They are just so individual and hardly comparable. Honestly there is no such formula for measuring the emotional expectations for a healthy home. But there are good scales that help to compare the energy performance of all components of your house.

The performance of windows is measured by the loss of energy they admit. In other words the calculation is all about the quality of insulation. Throughout the world there are different formulas that lead to different values. 
The most important one - and mostly used in Europe - is the U-value, which is the overall heat transfer coefficient. This value measures the rate of heat transfer through a building element (e.g. a window) over a given area under standardized conditions. The lower the U-value the better the insulation.

The U-value of a window is the result of a calculation of different values that work together as a system: Uf (frame), Ug (glass) and ψ (glass edge factor).  The R-value - most common in the English speaking world - is just the reciprocal of the U-value (i.e. R = 1/U).

After all calculations it is again a question of finding the right mixture of ingredients to get the best solution for every single project. And doing this the right way has a lot to do with emotional skills as well.