Energy Efficient Windows

Industry Leading Energy Savings, Made in Germany

As home to the Passivhaus standard and high tech manufacturing, Germany is world renowned for its high quality windows with excellent insulation performance. Whereas old windows may be paid for, they unfortunately continue to cost you money every month due to heat loss and higher energy bills. Whether replacement windows or new construction, choosing modern energy efficient windows will save money in the long run and are often even eligible for government subsidies or tax credits in many countries. As building regulations require greater efficiency and energy prices rise, high quality German windows will add value to your home while reducing bills over time.

Heat Loss in Windows Explained

Windows can lose heat in a number of ways, beginning with the area between the frame and masonry or wall. Professional installation is critical to ensure that the outer area of the frame is installed properly and sealed against air infiltration. The best window in the world cannot make up for poor installation and gaps with the masonry.

Next, seals can allow cold air in and warm air out. Opening mechanisms like hung sash windows constantly rub against the seals every time the window is open and closed leading to their rapid deterioration. Many older windows also feature far fewer seals than those today. Finally, the frame and glazing itself can lose heat via conduction. With single glazed windows, conduction is a particularly large source of inefficiency. To summarize, heat loss can be attributed to:

  1. Air leakage between the frame and masonry
  2. Air leakage from worn seals
  3. Conduction via the frame
  4. Conduction via glazing.

What Material are Windows made from?

Energy conduction via the frame is one source of heat loss and thus the choice of frame material plays an important role in the overall energy rating. The exact same triple glazing will perform the same whether in timber, uPVC or aluminium (i.e. have the same Ug-value). However, the frame's efficiency, or Uf-value, will still affect the overall window value (Uw-value). 

Thus, energy efficient windows are most frequently made of uPVC which is both easy to work with and can be engineered with multiple internal chambers. Timber, on the other hand, naturally features good thermal insulation properties. However, it cannot be further improved to overcome its natural limitations. Aluminium, being metal, is naturally conductive and is therefore often only used for external cladding. When used alone, the window must be thermally broken meaning the exterior portion is separated by another material from the interior so that energy cannot move from one side to the other.

How does Energy Efficient Glazing work?

The largest portion of any window is the glass surface. Therefore, it has the greatest potential for both loss and savings. Historically, windows featured only a single pane of glass and energy could easily move from one side to the other. The area near windows was usually cold compared to the other side of the room and the panes themselves were cold to the touch. 

Then came double glazing and today triple glazing. Using multiple panes of glass creates an insulating gap, often filled with an inert gas such as argon. The additional panes and air gaps serve to trap heat inside and prevent energy from moving from the inside to the outside.

Gas fillings such as argon, krypton and xenon are less conductive than air, meaning it is even harder for heat to move through it. 

Double-glazed windows may be sufficient for mild climates but triple-glazed is increasingly the norm.

Finally, sealing the insulated glass units with warm edge spacers is critical to ensure that the gas does not escape and no moisture enters. The spacer is also made of thermally optimised material which helps prevent energy from moving from pane to pane via the spacer. 

Low-E Coatings

In addition to the glass itself, special coatings can be added to influence the amount of infrared radiation (i.e. heat) allowed to pass through the glass. This is known as low-e or low-emissivity.

In colder climates, it is often applied to the interior so that heat is deflected back into the home whereas in warm areas, the opposite is done to minimize internal heat gain. 

How Energy Efficiency is Measured: U-values

The heat transfer coefficient, referred to as the "U-value" or "U-factor", measures  the amount of heat transferred through components of a building. Simply put, that means how much cold or heat moves from the outside to the inside of your home. Just as your home has many parts, each of which perform differently, so too do windows and doors. Both the window frame and glazing have individual values that make up the overall U-value. Like jackets, the difference between an old window and new one is similar to that of a thin windbreaker and a thick down jacket.

U-values are given in W/m²K (Watt per m² Kelvin). The lower the number, the better the insulation. A U-factor of 0.6 W/m²K is one of the best possible today.

The following make up the overall U-value of a window:

  • Uf - heat transmittance coefficient of the frame
  • Ug - heat loss through the glazing
  • ψg - energy loss through the spacer (warm edge)
  • Uw describes the u-factor of the overall window 

R and G-Values

The G-value measures how much solar heat (infrared radiation) is allowed in through a specific part of a building. Therefore, a low value indicates that a window allows a very small percentage of solar heat to enter. This may be desirable in hot climates but not in cooler ones.

High R-values are good. Low U-values are good and a balanced G value is the best for most climates.

The R-value is the measure of thermal resistance. The higher the R-value is, the better that material prevents heat transfer. 

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