Understanding U Values: A Quick Comparison and Concerns Addressed

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In summary, The conversation discusses the different units used for U values in windows and how one manufacturer's units are causing confusion due to their notation. The correct interpretation of the units is either "W/(sq meters)/(degrees C)" or "W/[(sq meters)(degrees C)]".
  • #1
Kavy
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Hello,

My first post! Thank you for any replies!

When looking at U values for windows (= 1/R) they are 99% of the time in the units

W/(K*sq meters)

A certain manufacture has their units in

W/(sq meters)/(degree C)

Now, the degree C to Kelvin should have no effect on my calculations (because the Heat flow formula subtracts temp), but the fact that the temperature unit is being divided twice (or just multiplied) instead of just being divided causes me some worry.

Has anyone seen this before, can you convert from the bottom units to the top? Do you think its just a mistake?

The bottom units have unusually small U values compared to the normal.

Thank you!
 
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  • #2
What does "W/(sq meters)/(degrees C)" mean? That's just bad notation. It could mean either "W/[(sq meters)/(degrees C)]" which would be better written "[W(degrees C)]/(sq meters)", which seems to be they way you are interpreting it, or "[W/(sq meters)]/(degrees C)" which would be better written "W/[(sq meters)(degrees C)]" and is probably what was intended.
 
  • #3
HallsofIvy said:
What does "W/(sq meters)/(degrees C)" mean? That's just bad notation. It could mean either "W/[(sq meters)/(degrees C)]" which would be better written "[W(degrees C)]/(sq meters)", which seems to be they way you are interpreting it, or "[W/(sq meters)]/(degrees C)" which would be better written "W/[(sq meters)(degrees C)]" and is probably what was intended.

Thank you for your reply!

Sorry, that's how I typed it, here is how they have it

(W/m²/C)

But you think they mean

(W/m²*C) ?
 

What is a U value?

A U value, also known as thermal transmittance, is a measure of how well a material can conduct heat. It is typically used to determine the energy efficiency of a building or product.

How is the U value calculated?

The U value is calculated by dividing the heat transfer rate through a material by the temperature difference across that material. It is typically expressed in units of watts per square meter kelvin (W/m²K).

What is a good U value?

A lower U value indicates a better insulating material, as it means less heat is able to pass through it. The specific value considered "good" can vary depending on the location and climate, but generally a U value of 0.15 W/m²K or lower is considered to be energy efficient.

What factors can affect the U value?

The U value can be affected by the type of material, its thickness, and the presence of any additional layers or insulation. Other factors such as air leakage, moisture, and temperature can also impact the U value.

Why is the U value important for energy efficiency?

The U value is important because it helps to determine how much heat is able to transfer through a material, which in turn affects the amount of energy needed to heat or cool a building or product. A lower U value can result in lower energy costs and a more comfortable living or working environment.

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