a little bit of technical

Remember “to blind [someone] with science”, means to deliberately confuse someone by giving the impression of highly complex knowledge.

This week I will explain a couple of basics that will give confidence and authority in the area of energy efficiency:

What is a U-Value?

U –values are used to describe the thermal transmittance of building materials.

 in simple terms this means that a U-value measures the transfer of heat (thermal transmittance) through a material.

The lower the U-value, the lower the transfer of heat.

For example: a single glazed window will have a typical U-value of 5.6, while double glazed window will have a U-value of 2.8 (ignore the W/m2K…you don’t need to know!!) or if you really do, it is Watts per meter squared Kelvin

Therefore a low U-value means less heat loss – simple!

What is an R-value (λ)?

The R-value, denoted by the “λ symbol, describes the thermal resistance of a material, and is used as a guide to determine its performance of an insulator.

The higher the R-value (λ), the greater the insulating effect.

For example Cellulose Fibre insulation with an R-value (λ) of 6.4 would have better insulating properties than Glass Wool insulation with an R-value (λ) of 4.0  

Therefore a high R-value (λ) means less heat loss – simple!

Finally to calculate either one to the other, use the following formulae:

R (λ) = 1/U            and      U = 1/R

Or for those who want the complicated version:

R (λ) = DT/Q˙A     and      U = 1/R(λ) = Q˙A/DT            

Finally, if you feel that this information has been useful, please feel free to share it with your friends and suggest that they join me every week for more guidance on energy efficiency measures and renewable technologies.


About Pat Murphy

True to me; Mother, Wife, Friend, Environmentalist; Living comfortably; Being warm; Knowing what's enough; Chair of WFQA (Irish wood fuel quality assurance scheme)
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