How Do Color Differences Affect Wall Surface Temperatures?

In summary, the conversation discusses the calculation of temperature differences between a white and brown wall surface, taking into account the reflection and absorption indices. It is suggested to measure the spectral reflectance and emissivity of the paints, and account for surface roughness in more accurate computations. The focus is on determining the surface temperature of the walls at the same outside air temperature. However, there is a lack of specific information provided to accurately solve the problem.
  • #1
john_scott
Hello,

I would like to calculate the difference between a white surface wall surface and the same kind of wall but with brown outer surface. I would like to know the reflection and absorption indices and then calculate the surface temperature of the wall in the two solutions at the same temperature as the outside air temperature. How could I proceed?

Thank you in advance.
 
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  • #2
Your question is so vague, my answer would be: "measure it". You need to know, at a minimum, the spectral reflectance of the two paints (I assume these are painted walls, if not then YMMV). More accurate computations require knowing the full BRDF of each surface, which allows accounting for surface roughness as well.
 
  • #3
Many thanks for the prompt reply, I cannot measure it, I'm still designing it!
Your question is so vague, my answer would be: "measure it".
I cannot measure it, I'm still designing it!

You need to know, at a minimum, the spectral reflectance of the two paints (I assume these are painted walls, if not then YMMV).
The emissivity is around 0,3 for the white paint and 0,6 for the brown one.
More accurate computations require knowing the full BRDF of each surface, which allows accounting for surface roughness as well.
My focus is to calculate the surface temperature of the wall in the two solutions at the same temperature as the outside air temperature, How Could I achieve my focus?
 
  • #4
john_scott said:
Many thanks for the prompt reply, I cannot measure it, I'm still designing it!
I cannot measure it, I'm still designing it!

The emissivity is around 0,3 for the white paint and 0,6 for the brown one.

My focus is to calculate the surface temperature of the wall in the two solutions at the same temperature as the outside air temperature, How Could I achieve my focus?

You don't have enough information- or you didn't provide enough information. If this is a zero-order estimation- the emissivities are spectrally independent, thermal loading is from direct sunlight only, there's no heat transfer through the wall (in either direction), there's only radiative heat loss from the wall, then you can determine the equilibrium temperature via energy balance (solar constant = 1 kW/m^2).

Also, this thread wouldn't be an 'advanced' level discussion. Possibly 'intermediate'.
 
  • #5
Andy Resnick said:
You don't have enough information- or you didn't provide enough information. If this is a zero-order estimation- the emissivities are spectrally independent, thermal loading is from direct sunlight only, there's no heat transfer through the wall (in either direction), there's only radiative heat loss from the wall, then you can determine the equilibrium temperature via energy balance (solar constant = 1 kW/m^2).
I'm not agree with you, if I suppose the outside air temperature around 35°C, the inside one at 26°C, you have heat transfer into the wall, I think most of them is radiative heat
 
  • #6
john_scott said:
I'm not agree with you, if I suppose the outside air temperature around 35°C, the inside one at 26°C, you have heat transfer into the wall, I think most of them is radiative heat

Given the (continuing) complete lack of a description of the problem you are trying to solve, feel free to suppose anything you like.
 
  • #7
Andy Resnick said:
Given the (continuing) complete lack of a description of the problem you are trying to solve, feel free to suppose anything you like.
Could you explain to me how I can progress on my aim please? If same value missing, we might suppose it. I'm just saying that I have two same wall but different color surface, if the air temperature outside is 35°C, how many degrees will be the "white wall" and the "brown" wall.
 
  • #8
I think if you Google "ashrae heat gain calculations " you'll find a lot of information.
 

1. What is reflection?

Reflection is the process in which a light ray bounces off a surface and changes direction. This can happen when the surface is smooth and polished, like a mirror, or rough and uneven, like a wall. The angle at which the light ray hits the surface is equal to the angle at which it reflects off.

2. How does reflection affect the color of an object?

The color of an object is determined by the wavelengths of light that it reflects. When white light hits an object, some wavelengths are absorbed while others are reflected. The wavelengths that are reflected determine the color that we see. For example, a red object absorbs all wavelengths except for red, which is reflected back to our eyes.

3. What is absorption?

Absorption is the process in which light is taken in and converted into another form of energy, such as heat. When light hits an object, some of the energy is absorbed by the object's molecules, causing them to vibrate and produce heat. The remaining energy is either reflected or transmitted through the object.

4. How does the color of an object affect its absorption and reflection?

The color of an object is determined by the wavelengths of light that it absorbs and reflects. Objects that appear white reflect all wavelengths of light, while objects that appear black absorb all wavelengths. Other colors absorb and reflect specific wavelengths, resulting in the color that we see.

5. How do reflection and absorption impact the Earth's climate?

Reflection and absorption play a crucial role in the Earth's climate. The Earth's atmosphere reflects some of the sun's radiation back into space, while some is absorbed by the surface and converted into heat. This heat is then re-radiated into the atmosphere, which helps to regulate the Earth's temperature. However, human activities such as burning fossil fuels can increase the amount of greenhouse gases in the atmosphere, which can lead to more absorption and retention of heat, causing global warming.

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