U-Value: Calculating Energy Loss for W/M2/K

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In summary, the conversation is discussing the concept of u-values and their relationship to heat loss calculations. The u-value describes the rate of energy transfer in watts per square meter for each degree of temperature difference. It is the inverse of the r-value for insulation. There is no time dependence for heat transfer, as it only depends on the temperature differential. However, the amount of heat flow can vary depending on the timescale being considered.
  • #1
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u values ...W/M2/K

I am getting confused by the definition of the u-value .
I want to do some calculations for heat loss but I do not understand the timescale for the U- value calcs
I understand that a U value describes the energy in watts that is lost per Sq Mtr for each degree (K) diferential , but is that per hour , day ,year ?
I may have missed something obvious but any advice would be gratefully accepted
Kev
 
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  • #2


A watt is a joule per second.
 
  • #3


If the 'U-value' is the concept as the 'R-value' for insulation, then there is no time dependence.

http://en.wikipedia.org/wiki/R-value_(insulation [Broken])

Heat transfer (as a thermodynamic application) has no time dependence. The amount of heat flow depends only on the temperature differential.
 
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  • #4


Thanks for the help
I have sussed now that the figure relates to the rate of energy transfer and that the amount of energy transferred is calculated by the the timescale .
I probably was being thick, but at the time I just couldn't see it .
Kev
 
  • #5


Andy Resnick said:
If the 'U-value' is the concept as the 'R-value' for insulation...
They are inverses of each other.
...then there is no time dependence.

http://en.wikipedia.org/wiki/R-value_(insulation [Broken])

Heat transfer (as a thermodynamic application) has no time dependence. The amount of heat flow depends only on the temperature differential.
What? That's like saying velocity has no time dependence!? Quite obviously, for a given piece of insulation, "the amount of heat flow" in an hour is 60 times larger than "the amount of heat flow" in a minute.
 
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What is U-Value and why is it important?

U-Value, also known as thermal transmittance, is a measure of how much heat is transferred through a material. It is an important factor in determining the energy efficiency of a building, as it helps to calculate the amount of heat loss or gain through walls, windows, and other building materials.

How is U-Value calculated?

U-Value is calculated by dividing the heat transfer coefficient by the thickness of the material. The heat transfer coefficient is determined by the thermal conductivity of the material and the surface heat transfer coefficient.

What is the unit of measurement for U-Value?

U-Value is measured in watts per square meter per degree Kelvin (W/m2/K). This unit represents the amount of heat energy that is transferred through one square meter of material when there is a temperature difference of one degree Kelvin between the two sides.

What is a good U-Value for a building?

A lower U-Value indicates a better insulating material, as it means that less heat is being transferred through the material. The recommended U-Value for building materials varies depending on the climate and location, but generally, a U-Value of 0.2 W/m2/K or lower is considered good for energy efficiency.

How can U-Value be improved?

To improve the U-Value of a building, it is important to use materials with lower thermal conductivity, such as insulation, double or triple glazed windows, and insulated doors. Proper installation and sealing of these materials can also help to reduce heat transfer and improve the U-Value.

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