How Do Color Differences Affect Wall Surface Temperatures?

[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.

 

[Andy Resnick]

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.

 

[john_scott]

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?

 

[Andy Resnick]

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'.

 

[john_scott]

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

 

[Andy Resnick]

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.

 

[john_scott]

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.

 

[sandy stone]

I think if you Google "ashrae heat gain calculations " you'll find a lot of information.