paint outside house walls black for cheap solar heating?

jimmyhackers

10 kW
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just wondering if this is a thing?

with energy prices going up in the uk/world i wondered how cost effective this could be?

you could paint only the sides of your house that face the sunlight to reduce paint usage....or limit it to walls that wont offend your neighbours.

anyone done this or knows what kind of benefit it could have?
 
Because of the insulation inside the walls, the heat on the outside won't have a huge effect on the inside.

There is a popular structure in solar-heated homes called a "Trombe Wall".

Mark the track of the sun in winter, and choose a wall of your home that has good solar gain in winter.

Add lots of glass windows, or sliding glass doors. Just a short distance inside those windows, add a masonry wall to absorb any available heat that it can. It is quite useful to paint the sunny side of the wall black.

People intuitively understand harvesting visible light, but if you set two identical items in the sun, the white item will be cooler, and the black item will be hotter.

They both absorb the same amount of visible light, but the darker item also absorbed the infrared/ultraviolet energy, and converted it to heat.

This is why you can get a sunburn on your skin during a cloudy day. The visible light is partially blocked, but the IR/UV is still pebetrating the clouds.

There is more specific information at "builditsolar.com"
 
yeah i had a look at that site before i posted....

i couldnt see anything about a trombe wall minus the glass bit (so just a black wall :) )

ive seen a few youtube people compare white to black roof tiles etc and that seems to be a 10c difference....

my house already is insulated well, double glazed, solar pv, and solar water heating. atin of black masonry paints about 20 quid.. could probably do a whole side of my house with it. even if it only helps 1 or 2 c......its gotta be a worthwhile improovment.

i could just put a temp sensor in a white box/cup and one in a balck box/cup see what difference i can get
 
Black surfaces adsorb the uv energy better than white etc, ..BUT remember they also radiate the uv back out again.
So you need to be able to remove from the wall, the heat adsorbed before it is reradiated back out.
EDIT..
Oop’s !…for uv read ir !
Thanks AW . :bigthumb:
 
Just curious: Do y'all mean IR, rather than UV?



AFAIUI, as a definite non-expert ;) there is much more total energy from sunlight in IR (and other sub-red wavelengths) than in the UV (and other post-violet wavelengths) down here at the bottom of the atmosphere. (not counting anything within the visible light spectrum itself).

Also, I thought I understood that when higher-energy wavelengths were absorbed by matter, they would generally (except in certain special circumstances) re-radiate that energy in lower-energy wavelengths, such that in the black-absorbing-everything example, the energy not kept within the matter (by moving it's constituents faster, etc) would then be reradiated as IR (felt as heat by us).
 
jimmyhackers said:
just wondering if this is a thing? with energy prices going up in the uk/world i wondered how cost effective this could be? you could paint only the sides of your house that face the sunlight to reduce paint usage....or limit it to walls that wont offend your neighbours. anyone done this or knows what kind of benefit it could have?
Jimmy,

From my experience: I have a Firebird automobile with glass T-tops. The glass "roof panels" are very dark, with a black perforated metal screen embedded. On any warm sunny day, the glass was too hot to touch. At freezing air temperatures, this was okay, but in the summer, even the air conditioning struggled to cool the car inside. Being an RC airplane guy, I decided to coat the T-tops outside with silver (chrome) Mylar film (by Monokote). It is applied to the glass with a clothing iron, wrapped in a towel. It is heat-shrink material, so compound curves are no problem. In strong summer sunlight, with the chrome film applied, the T-tops are cool to the touch inside. I peel and discard the Mylar film each Autumn, get my solar heating back for Winter driving.

So, I have a suggestion. There are lots of options, but some solar mods to the house may be offensive to the neighbors. Certainly the Trombe wall is a nice start, but you can double the sunlight (heat) applied if you lay out "chrome" reflective panels flat on the ground at the base of the window wall. The sun-angle at your location will dictate the best placement (and width) of these reflective panels. At sundown, you would want to roll down full-cover window shades inside your glass, using white or reflective materials. If the window shades travel down in channels on each edge of the glass, and the bottom edge seals by weight, your window shades will prevent a lot of heat from escaping back into the atmosphere. Quite possibly, the neighbors may not shoot you for creating an eyesore, because they can't see the reflective panels.

The Trombe wall inside your house does not support anything, it is just a heat sink. You can paint it a dark color. Dark green is better than black, for solar heating; you have never seen a black tree growing. If you use (cheaper) cinder blocks for the Trombe wall inside the house, you can fill the big voids in the blocks with rock salt, because salt retains heat like mad, even better than solid blocks. Regulate the heat you will capture by adjusting the reflective panels and window shades. A ceiling fan near the Trombe wall can help to distribute the heat inside the house. HTH.
 
i was looking for stats on the easiest option, just paint a wall black.

glass panels and reflectors are a bit to much hassle.

ive scoured the internet a bit more for some numbers and i seen about a 5-10 degrees c difference between a white and a black objects surface tempreture in direct sunlight. not much data from double skin redish brick wall to black masonry paint though :( .

i did think about black radiating more heat....but at the same time its creating more heat from light, also 50% of that radiated heat will be into the walls/at my house.

i remeber a mightycar mods video where they compared an intercooler stock vs painted black...the black one did radiate more heat (cooler exhaust air)....but as soon as air flow was allied the exterior surface of both, their performance were identicle.

with my house being out in the wind im not sure if it will make my house warmer in the sun, colder at night, or both
 
jimmyhackers said:
i was looking for stats on the easiest option, just paint a wall black. glass panels and reflectors are a bit to much hassle.
Jimmy,

Reflective panels can be any size of solid panel, covered with (survivalist) cheap Mylar silver solar blankets. Apply thin glue to the panels with paint rollers.
Hang the panels flat against the wall for cooling in the summer; lay them flat on the ground next to the wall for winter heating.
I got free glass doors (on roller tracks!) from a building they were planning to demolish.
Glass will be a big help there. If you buy it, some sizes will cost less than others, to buy and ship. Ask the suppliers.
 
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