U-Value and thermal performance

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The energy performance of Aluminium windows and doors is a critical factor which determines the decision-making of customers, as this value greatly impacts their energy bills. 

The U-Value is the level of heat loss escaped from a glass substance or surface. In our case that is Doors, Windows, Roof Lanterns etc.

This heat loss, or thermal performance, is expressed with the type W/m2 . K., where Watts is the amount of energy conducted per square metre (the area of the substance, i.e. window), multiplied by the temperature difference on either side of the substance (window), which is measured in Kelvin–same structure as Celsius.

In short:

  • the lower the U-value, the better the thermal performance in terms of insulation.
  • the higher the U-value of windows, the higher the energy conductivity through them. 

Simple U-value calculation

A typical ‘C’ rate window measures 1.2m x 1.2m. That makes 1.44 m2, and its U-value is 1.6W/m2.K. 

This further means that this window conducts 1.6 W of energy per m2 for every degree (K) difference in temperature from one side to the other. 

Example: if it is 20 ºC inside the room and -1ºC outside, there is a 21ºC temperature difference. 

The energy equation then is: 

1.6 (U-value of window) x 1.44 m2 (area of window) x 21 (difference in temperature) = (1.6 x 1.44) x 21 = 48W of potential energy loss.

Now, if an ‘A’ rate window comes with an U-value of 1.4W/m2.K, the new equation works out like this:

(1.4 x 1.44) x 21 = 42W of potential energy loss.

If we now increase the dimensions again, and the window comes with an U-value of 2.0W/m2.K (typical old windows with hard coat sealed units), this goes = (2.0 x 1.44) x 21 = 60.48W of potential energy loss.

At C&A Window Systems Ltd we supply high-quality and highly-thermal Aluminium solutions for our customers and pride ourselves in the energy efficiency of them.

To find out more about our range of products, please visit our website or call us now on 01787 477 976.