If there were 2 rooms that were exactly the same except for colour would they have the same temperature?

ayw...@gmail.com

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Jan 23, 2015, 2:34:29 PM1/23/15

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If these 2 rooms had exactly the same furniture in them and both faced the sun exactly the same but one room had all black furniture and flooring and one had all white furniture and flooring would the temperatures be the same in them during the day in full sun? The amount of sunlight hitting them is the same so they should be the same temp, right?

Morris Dovey

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Jan 23, 2015, 6:13:13 PM1/23/15

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One room would have slightly higher air temperature, the other slightly
higher furniture/floor temperature.

You might /feel/ slightly warmer in the room with white furniture and
flooring.

But it might be difficult to distinguish. :-)

--
Morris Dovey
http://www.iedu.com/Solar/

Bob F

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Jan 23, 2015, 7:17:40 PM1/23/15

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Morris Dovey wrote:
> On 1/23/15 1:34 PM, ayw...@gmail.com wrote:
>> If these 2 rooms had exactly the same furniture in them and both
>> faced the sun exactly the same but one room had all black furniture
>> and flooring and one had all white furniture and flooring would the
>> temperatures be the same in them during the day in full sun? The
>> amount of sunlight hitting them is the same so they should be the
>> same temp, right?
>
> One room would have slightly higher air temperature, the other
> slightly higher furniture/floor temperature.
>
> You might /feel/ slightly warmer in the room with white furniture and
> flooring.

I would expect the white room to radiate more of the light energy back out of
the windows before it heats anything, thereby reducing the room temp. Higher
floor/furniture temp will all be transferred to the air. Kind of like a white
car compared to a black car.

Morris Dovey

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Jan 23, 2015, 10:59:52 PM1/23/15

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Windows? Methinks we were both making unstated (unwarranted)
assumptions. My bad.

My real-life "windows" were thermal diodes. :-)

BTW, it does appear possible to construct a closed system such that, at
equilibrium, one object within can be warmer than another. Fascinating
stuff!

--
Morris Dovey
http://www.iedu.com/Solar/Panels

Dan Coby

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Jan 24, 2015, 3:14:48 AM1/24/15

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On 1/23/2015 7:59 PM, Morris Dovey wrote:>
> BTW, it does appear possible to construct a closed system such that, at
> equilibrium, one object within can be warmer than another. Fascinating
> stuff!
>

I will bite. How does one create a closed system in thermal equilibrium
with objects at different temperatures?

Are you calling a system with an outside source (sunlight) coming into
it and heat radiating out, a 'closed' system?

Dan

Morris Dovey

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Jan 24, 2015, 3:58:24 AM1/24/15

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On 1/24/15 2:14 AM, Dan Coby wrote:
> On 1/23/2015 7:59 PM, Morris Dovey wrote:>
> > BTW, it does appear possible to construct a closed system such that, at
> > equilibrium, one object within can be warmer than another. Fascinating
> > stuff!
> >
>
> I will bite. How does one create a closed system in thermal equilibrium
> with objects at different temperatures?

By creating an object that more readily absorbs energy than emits it. I
ran across some interesting projects while researching absorber
geometries, but didn’t bookmark because the material didn’t relate in a
practical way to what I was doing.

> Are you calling a system with an outside source (sunlight) coming into
> it and heat radiating out, a 'closed' system?

Nope. I just thought Bob might find the idea interesting.

Bob F

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Jan 24, 2015, 11:00:03 PM1/24/15

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Interesting maybe, but entropy suggests it's unlikely. Evacuated tube solar
water heaters may sort of meet that description, but they need an outside
radiant energy source. I came into this discussion with only the input I
quoted, so I guess the origional discussion was different than I commented
about.

BobVM

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Mar 9, 2015, 2:54:18 AM3/9/15

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A black surface is absorbing more radiation. A white surface is reflecting
more radiation. If the black furniture is in the sun, it will be warmer.
The white furniture will reflect solar gain. However, most of it will
reflect it to somewhere else in the room. Some sunlight will be reflected
out of the room, so the white furniture room might be slightly cooler. If
it's summer on a sunny day, would you rather sit in a car with all black
interior or a car with all white interior. The car with the black interior
would be noticeably hotter, but much of the inside is black. It depends on
how much black surface there is and if the sun is hitting it. The black
surface may be absorbing over 95% while the white surface might only be
absorbing 20-30% depending on the mix of white. Flooring receives a lot of
sunlight, so if it's black they floor will be noticeably warmer. If it's
white, then it will reflect more. It might go to another surface which
might warm up instead. Over all, if a room was almost all white, a
significant amount will reflect out of the room and it will be cooler. If
you want one spot to be warmer, then color it dark. There will be a
difference though not on a cloudy day or at night, only when significant
solar gain is present. Also if the window area is small, then it won't be
much different. If it's winter or cloudy, it might not be as much.

TomHR

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Mar 22, 2015, 9:44:44 PM3/22/15

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Hi BobVM,

If it's winter or cloudy, it might not be as much.

If the sun isn't shinning and it is cold outside, will the black room cool down faster? If a dark color absorbs heat faster will it also resease it faster?

Morris Dovey

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Mar 23, 2015, 7:33:12 AM3/23/15

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A black surface may appears black because it doesn’t radiate, reflect,
or transmit energy at a frequency your eye can detect.

If you talk about energy flow to/from an object in terms of your own
sensory apparatus, you’ll be missing just about all of it. ;-)

Morris Dovey

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Mar 23, 2015, 7:45:25 AM3/23/15

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On 3/22/15 8:44 PM, TomHR wrote:

An object is “black” if it does not radiate, reflect, or transmit energy
at a frequency/wavelength your eyeball can detect.

You might find some of the presentation at
http://www.iedu.com/Solar/Energy/Absorber interesting. :-)

--
Morris Dovey
http://www.iedu.com/Solar/

Morris Dovey

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Mar 24, 2015, 9:21:46 PM3/24/15

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On 3/22/15 8:44 PM, TomHR wrote:

> Hi BobVM,
>
> If it's winter or cloudy, it might not be as much.
>
> If the sun isn't shinning and it is cold outside, will the black room
> cool down faster?

That’s going to depend on the insulation, no?

> If a dark color absorbs heat faster will it also

> release it faster?

Maybe yes, maybe no. However, the Stefan-Boltzmann law, states that the
total energy emitted by a black body is proportional to the 4th power of
its temperature...

You may want to read up on black/gray body radiation. See
https://en.wikipedia.org/wiki/Black-body_radiation and linked articles
for a good starting point.

You’ll find there’s more to this than you’re probably expecting, and at
first glance it looks intimidating – but the basic concepts are actually
fairly simple (they’re just not particularly intuitive) :-)