Understanding U Values: A Quick Comparison and Concerns Addressed

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SUMMARY

The discussion centers on the confusion surrounding U values for windows, specifically the notation used by a manufacturer that presents U values in W/(m²/°C) instead of the more standard W/(m²·K). Participants clarify that the temperature unit's representation can lead to misinterpretation, suggesting that the notation is likely incorrect and should be reformulated for clarity. The consensus is that the correct interpretation should align with the standard unit of W/(m²·K) to avoid confusion in thermal calculations.

PREREQUISITES
  • Understanding of thermal conductivity and U values
  • Familiarity with units of measurement in physics, particularly in heat transfer
  • Knowledge of the relationship between Celsius and Kelvin
  • Basic principles of heat flow and thermal resistance
NEXT STEPS
  • Research the standard units for U values in thermal performance, specifically W/(m²·K)
  • Learn about the implications of incorrect unit notation in engineering calculations
  • Study the conversion between Celsius and Kelvin in thermal contexts
  • Explore best practices for presenting measurement units in technical documentation
USEFUL FOR

Engineers, architects, and construction professionals involved in building performance analysis, as well as anyone working with thermal insulation and energy efficiency standards.

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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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.
 
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) ?
 

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