White reflects heat better than darker colors and greenery provides shade and evaporative cooling. Not sure how much it helps with my A/C consumption in AZ where it will be 110 today.

I've contemplated switching to white kaftan this summer.

(Doesn't go over big at shul though.)

Carry a staff and it'll be fine.

"A 2014 study estimated that the average temperature in California would decrease by almost 3° Fahrenheit if all houses had cool roofs."

The results of any one study can present questions for further consideration but rarely anything to draw conclusions from. If you take a more careful look at that study, as I did, you'll note that 1) the California region considered and the data points evaluated appear to all be in the sparsely populated Central Valley that has extreme hot and dry temperatures for 6 months of the year, and 2) the "data" came from modelling, not empirical measurements. The regions containing most of California's population have mild and comfortable summers, certainly much more so than places in the Midwest and South that have oppressively hot and humid conditions and long air conditioning seasons. In such places with more extreme summer conditions, the effect of lighter colors and "cool" roofs would be much more consequential.

The effect of urban concrete and density is well known and long known to make such inhabited areas warmer in the summertime than less inhabited areas. Same with lighter colors - look at what the standard shadings were used centuries ago and even to this day in hot weather, even Third World, regions.

And in the East, humidity isn't improved by white colors. But, yes, you should have a light colored house in warm areas. And shade trees help. But none of that is going to make it comfortable without a/c when you have significant humidity.

But, the reality is that heating is generally more energy intensive than a/c and a/c is more easily reduced by solar.

A/C is a heat pump so the statement that heat pump technology helps is incorrect and illogical. Now heat pumps can represent a more efficient way to heat a space but the article is about air conditioning.

"And in the East, humidity isn't improved by white colors."

No, but heat absorption and temperatures indoors and (if the study's findings are valid) outdoor temperatures and comfort would be equally affected. My point was to suggest that in places where summer conditions are more uncomfortable, one would think the effect could be more significant. And yes I know, for a given mass of air, relative humidity increases when its temperature decreases.

"But, the reality is that heating is generally more energy intensive than a/c"

I'm not sure what "energy intensive" means but in my area, X BTUs of heating from natural gas is less expensive than X BTUs of cooling produced by AC "heat pump" means.

What Elmer Said

I'd bet the person who penned that article was sitting in a nicely air conditioned office building, maybe even a historically-heralded black skyscraper by Mies van der Rohe.

we went with a metal roof in blinding reflective white for the least solar heat gain possible. (it's also pretty hidden) but I could easily see this helping.

We have 2 nearly identically constructed buildings - the shop, which is a little furthe along in the air SEALING, has fewer windows and 3 large insulated garage doors is currently maxing out temp wise at 82 degrees after 20 days or so of mid 90 degree temps. We've keep the humidity at bay with a small portable dehumidifier and that's it. It's quite pleasant inside.

The house - with many more windows - even with the southerly ones fully shaded by a structure - is running at 88.X degrees. Saame dehumifier running- but less comfortable (and it's 4800 sq ft vs 3600 for the shop) . The west facing windows are killing us in the house, as is the fact that we've not compelted 100% of the sealing we've done at the shop.

Will try to compare that soon - as we embark on the sealing portion at least.

But the shop is super comfy and I could possibly live there without AC if we could keep the humidity at the 35% or so level that it is now.

We'd have to change our perspetive on what "looks right" in roofing. A lot of learned behavior in using asphalt shingles.

Back when van der Rohe was active, energy costs and efficiency weren't of the importance they are today. I think you'll find even up-scale residences built during his era often had little or no insulation (especially notable from today's perspectives) no matter if located in places with seasonal weather extremes. I'm not sure if air tightness for interior comfort was a concept anyone ever thought about in the first half of the 20th century and hardly much more later until more recent decades.

I don't want to get into a debate about this. This has been a well known thing for a long time and I linked one of a hundred studies I could have linked. Every developed nation funds this study routinely. In fact, since I was a student in college this has been cited as evidence against global warming. Meteorological stations are less rural than they were 100 years ago and the increase in temperatures has some correlation to the increase in populations around meteorological stations.

There are two brand new inventions that have helped shed some light on different radiative properties of popular materials in cities (1) a brand new thing called a thermometer and (2) this new science called math. We also have the luxury of being able to test the calculations by seeing if they match up to reality. I am not interested in the debate, I lost interest in college... however, I do want to clarify that this is not a fringe article.

ETA: I am removing notifications, because again... this is not my thing.

"Here's my question: It says white paint ............... can make things cooler. Seriously? White paint can make your house cooler? Can anyone comment on this?"

Basic high school physics. "Black body absorption"

Black bodies (roofs) absorb radiation (heat), white bodies reflect it.

"I don't want to get into a debate about this."

That's good because what I was trying to point out politely was that you cited a study that wasn't particularly relevant to a discussion about indoor air conditioning. The data modeled (not measured) in the study you cited is for a very large inland area with very hot summers and a lot of agriculture but little population, compared to other parts of the state. I suspect that similar data "modeling" for the much more temperate and considerably more populated parts of the state would have yielded results the author would have found less significant and less dramatic, and so less interesting to publish.

I grew up in a house with no A/C (yes, I am old). We had an 'attic fan' that pulled air from outside through the house (the design of the house is important). We had mature trees. Yes, it was hot and humid (Houston, TX).. My grandparents house also had no A/C, large overhangs on the roof, covered/shaded front porch, lots of mature trees.

Could I do it again, yes, would I 'like' it - no. Humidity gets to be uncomfortable when we frequently have it almost as high as the temp. But surely with modern materials, better insulation, better roofing, etc. new homes could/should be built to better deal with the heat/humidity/cold.

I am guessing the price/cost would be unpleasant to a lot of buyers, but down the road what kind of price will we be paying for electricity?

Will everyone need solar? Or wind power in their backyard? I worry about how my grandchildren will manage in the future.

I grew up in a house with no A/C (yes, I am old). We had an 'attic fan' that pulled air from outside through the house (the design of the house is important). We had mature trees. Yes, it was hot and humid (Houston, TX).

Yeah I grew up without AC as well, but I wasn't 3 clicks west of the gates of hell then either. (Houston, Tx) --- are you nuts? I can't imagine living anywhere near here without AC.

At the time that I remember we lived in Bollingbrook, IL a suburb of Chicago. My mom came up with the idea of putting box fans in several windows creating a steady flow of cool air at night.

While that worked better than nothing it wasn't what I would call "comfortable" compared to having air conditioning. (humid nights)

In terms of damaging the planet: Older refrigerants eat holes in ozone layer... now newer refrigerants supposedly less risk against ozone layer, but they are around 2000 times worse than carbon dioxide in terms of "global warming" or if you prefer "climate change".

The replacements are coming, higher costs & not much better than the refrigerants they are replacing. Plus they are considered "mildly flammable" - how flammable? mildly. (write an insurance policy for that one.)

This video below describes how we got here... it's only the beginning so keep that in mind.

"Plus they are considered "mildly flammable" - how flammable? mildly. (write an insurance policy for that one.)"

I believe we have had this discussion before. But here is some information.

Flammability

Now accepted as a classification in the International Standard ISO 817:2014, R32’s A2L mildly flammable classification is reserved for flammable gases with a burning velocity of less than 10cm/s. This means that the flame front does not propagate readily in a horizontal direction and effectively means that an A2L refrigerant is not explosive if ignited.

And ignition, tests have shown, is hard to achieve. R32’s flammability limit is between 14% volume (300g/m³) and 29% volume (620g/m³). AREMA points out that a 14% concentration of any foreign gas in air is the accepted oxygen deprivation safety limit and, in addition, is well above the acute toxicity exposure limit for existing refrigerants like R22 (5.9%) and R134a (5%).

As well, in order to ignite, a flammable gas mixture must have a velocity lower than 3 to 4 times its burning velocity. In the case of a heavier than air R32 leaking from a wall-mounted split, the refrigerant will exceed 4 times its burning velocity due to gravity within 40cm. In addition, the new document maintains that measurements and computational fluid dynamic modelling has shown that even a rapid R32 leak of 1kg in one minute will not present a flammable mixture outside of the wall unit due to dilution and the falling velocity of the refrigerant.

Unlike common flammable gases such as propane, R32 cannot be ignited by static electricity and tests are said to have shown that sparks from light switches or contactors in residential appliances do not have sufficient energy to ignite the refrigerant.

“Therefore,” says AREMA/CESA, “the most likely source of ignition in a residential application is an open flame such as a candle, combustion heater or gas cook top.”

Consequently, if an accidental release of R32 refrigerant occurs from a cylinder or piping, the velocity will be too high to ignite near the release point and the concentration will be too low where the velocity becomes low enough.

“So, ignition of R32 is difficult even if it is attempted intentionally,” says the document.

ETA: So lets put this into perspective... its a gas and gasses always introduce problems in somewhat confined spaces. However, it is less flammable than most fabrics and textiles and certainly less flammable than many aerosols used in a home.

I think we should recognize that eventually someone is going to do something stupid and burn their house down with the new refrigerant. However, before you get too worked up let's remember that ignited farts have started structural fires before.

ETA2: Please note that many things will burn when ignited. The trick is how difficult things are to ignite. Wood and fabric both burn well and both wood and fabric are more sensitive to ignition from sparks than R32. So let's just quit here, people can choose to either trust tests by scientific organizations or Youtube videos. By the way, have you seen the videos where the Covid vaccine makes you magnetic?

I would never live in a place where cooling is essential.

“So, ignition of R32 is difficult even if it is attempted intentionally,” says the document.

Yet, this unit in the video clip below... is likely R410a refrigerant.

FYI: R410a is a blend of two seperate refrigerants. 50% R32 & 50% R125

Good night, and good luck.

This video is wood burning.

Thanks, but air conditioning units aren't made with wood. The video I posted does not show wood burning.

Wood isn't turned on via a mechanical switch with electricity running thru it.

Class dismissed.

does a white roof burn? or is it a cooler burn than a dark roof?

this has certainly taken a turn.

I think it is OK to recognize the science behind something while not rushing out to do it. The problem with many environmental type studies is they lack perspective. If we suddenly converted every house in the world to white roofs the lower troposphere would certainly be cooler. Cities themselves would be cooler and that would itself likely lower AC usage. Some might want to debate the magnitude of the impact, but there is no doubt it would have an impact. In fact, it already does, after significant snows the temperature differential between urban and rural areas decreases.

Having said that, there is a danger when focusing on the benefits of a single action. I don't care what kind of roof you put on a house with a 6,000 ft² footprint, it is going to be worse for the environment than a 1,200 ft² house. Having said that I have two homes and both are quite a bit larger than 1,200 ft².

So yes, a white roof is going to be cooler than a black roof and converting enough things in cities from dark materials to white materials will reduce the temperature in the city. Does that mean you should run out and change your roof? No... however, it does mean if a white roof is right for your house and right for your environment that maybe you should give it a little extra weight the next time you are replacing your roof.

I believe a community's beneficial impact of white or cool (reflective) roofs is decreased energy use during hot weather, not lower temperatures for people walking or driving down the street. Reducing "city temperatures" doesn't strike me as something anyone would much care about in a collective sense. Hit their pocketbooks, different story.

In the US, there are too many people whose lack of common sense and selfish attitudes causes them to eschew conduct for the greater good. And often to ignorantly challenge what to many others is obvious - look at our current health situation for an example.

As with other things, laws can be used to either encourage certain behaviors (tax incentives or credits of various kinds) or to require it (building code changes). Absent that, I wouldn't expect much to change other than on a one here, one there basis.

White reflects heat better than darker colors and greenery provides shade and evaporative cooling. Not sure how much it helps with my A/C consumption in AZ where it will be 110 today.

That's kinda what I thought: Yes, white reflects heat, but is it enough to really matter when you're talking about really hot temperatures.

A 2014 study estimated that the average temperature in California would decrease by almost 3° Fahrenheit if all houses had cool roofs.

What is a "cool roof"? Is it just a white roof?

Same with lighter colors - look at what the standard shadings were used centuries ago

Yeah, I live in a rural area, and all the old-old farmhouses are (or originally were) white with metal roofs. I always thought this was largely because white paint was what was available.

And shade trees help.

Yes, but that's a tangent.

But none of that is going to make it comfortable without a/c when you have significant humidity.

Agree.

My point was to suggest that in places where summer conditions are more uncomfortable, one would think the effect could be more significant.

As I said, I grew up in a rural area -- in the deep South -- and I know old farm houses. They were built to be cooler in that they are designed so that every room has windows on two sides to catch the breeze ... and they have high ceilings ... and they have wide porches and large trees to block the hot summer sun. Those things make a big difference, but I just don't see the paint color as significant.

I'd bet the person who penned that article was sitting in a nicely air conditioned office building, maybe even a historically-heralded black skyscraper by Mies van der Rohe.

Probably right!

Basic high school physics. "Black body absorption" ... Black bodies (roofs) absorb radiation (heat), white bodies reflect it.

But to what effect? A degree or two is what I'm thinking. Science measures change, and I'm not denying that's true -- but we are real people and don't care too much about the difference between 88 degrees and 90 degrees.

I grew up in a house with no A/C (yes, I am old). We had an 'attic fan' that pulled air from outside through the house (the design of the house is important). We had mature trees. Yes, it was hot and humid

Me too! It definitely affected our life in the summer months. We got up early to tend the garden, always had a cold lunch, and spent the hot middle of the day lying on the floor in the wide hallway under the attic fan reading or napping. Then we'd become active again around dinner time.

Could I do it again, yes, would I 'like' it - no.

Agree.

I would never live in a place where cooling is essential.

Pretty much, you're either going to pay for cooling or heating for a large part of the year. I can take the heat, but I can't stand the cold.

Here's a Dept of Energy explanation of what a cool roof is and how they work

DOE Cool Roofs

"But to what effect? A degree or two is what I'm thinking. Science measures change, and I'm not denying that's true -- but we are real people and don't care too much about the difference between 88 degrees and 90 degrees."

The question becomes, how did you determine it was only a degree or two? Science often uses actual measurements or experiments to measure differences which it then models to predict change or impact.

So rather than guess maybe try this ... https://web.ornl.gov/sci/buildings/tools/cool-roof/

I'm with bry here. Watch the video in the DOE link - it suggests that roof surface temperatures can be decreased by more than 50 degrees. That's a lot and maybe that's an extreme measurement, like comparing a black tar roof with a white one with reflective material with sun directly overhead. No way to know, but the effect of cool roofing material is certainly much more than a few degrees.

DOE Cool Roofs

Thanks for that info. I enjoyed reading it and would absolutely investigate the topic further.

However, I am somewhat doubtful that the difference between a black roof and a cool roof could be 50 degrees. It just doesn't seem realistic; I mean, if I wear a white shirt vs. a black shirt on a hot-hot day -- yes -- the color will make a difference, but not so much as this.

I'm also wary about the comment at the end that such roofs in warm, moist areas can grow mold -- I do live in a warm, moist climate. Definitely a topic for further investigation.

The question becomes, how did you determine it was only a degree or two? Science often uses actual measurements or experiments to measure differences which it then models to predict change or impact.

I guessed. I'm trying to learn something here, and I am looking for a starting point. I'm trying to understand what's realistic. I genuinely don't know whether 2 degrees is realistic, but -- as I said above -- I am skeptical about the 50 degrees in the previous article.

So rather than guess maybe try this ... https://web.ornl.gov/sci/buildings/tools/cool-roof/

I tried to go through this cool roof calculator, but I just don't know these details, so I put in what the calculator says is "average" for my area ... and the net savings for a house the size of mine in my area with average numbers is $68.60/year.

That's interesting, but I was really more interested in the original question about air conditioning /now cool roofs.

After reading the two sites, one thing that seems crystal clear is that black roofs are "the worst" in terms of environmental impact and cost. Yet I think they are the most common. That, in and of itself, is interesting.

We had an off-white roof when we moved into our last house. It was in awful shape, and we had to replace it almost immediately. I was glad of it because it was terribly stained. I wonder if all white roofs do this age they age?

However, I am somewhat doubtful that the difference between a black roof and a cool roof could be 50 degrees. It just doesn't seem realistic; I mean, if I wear a white shirt vs. a black shirt on a hot-hot day -- yes -- the color will make a difference, but not so much as this.

You are forgetting that your body is actually a really good climate control apparatus.

You are forgetting that your body is actually a really good climate control apparatus.

yes, it's your mind that tells you... "Hey, if we're gonna get along here we need air conditioning."

And so the body does what the mind tells it to OR the mind makes the decision and the 'body' comes along for the ride.

@Austin Air Companie - what are you talking about? Are you trying to be funny or witty or something?

The reason a dark shirt laying in the sun is warmer than a dark shirt you have on is not a mystery. Your body cools the shirt you have on.

dark colors absorb light / heat where as light colors reflect.

BUT... if you go onto a light / white colored roof in the heat. It's still hot.

Go onto a dark colored / black roof in the heat. It's still hot.

Hot is hot... you can reflect or absorb it all you want. Comfort is a feeling and you don't magically create a "cool" feeling. That requires work. (Removing heat... for the absence of heat is cool)

Fools: hey we got errands to run!

@Austin Air Companie - what are you talking about? Are you trying to be funny or witty or something?

Guilty, Guilty, Guilty on all counts.

Unsuccessful, unsuccessful, unsuccessful on all counts.

(Not to mention just plain wrong!)

Why is it that when I'm wearing light colored clothing working outdoors in the heat that I still sweat / feel hot?

Cooling apparatus malfunction?

An easy experiment for you to try. (You need to get out more.)

Another one:

White cement versus black asphalt: conduct an experiment to see if you can cook an egg on either substrate in the afternoon sun.

Common sense would tell you?

@just_janni: "The west facing windows are killing us in the house"

Consider applying window film (3m, LLumar, Solargard) to these windows. I have a skylight which used to broil my condo in the summer. After the window film was applied, the condo was much cooler. You can find films that are barely visible; the windows are only slightly tinted gray.

Our previous house came with a huge bay window facing west with only a young maple in the middle of the front yard. By the end of the first summer we installed a 3M film to block heat and UV rays. Previously we closed the full curtains just after noontime. With the film, we didn’t close them till about 5 or 6 for half an hour, when the sun was really streaming. HUGE difference with the 3M film in the comfort level, both light- and heat-wise.

The dining room had a window wall facing due east, but there were tall trees at the back of the yard that mitigated the sun a bit. The heat wasn’t so bad, so we only installed UV film, to protect the furniture.

Insulation beyond currently mandated levels can greatly reduce energy needs in all seasons. You’ll still need a dehumidifier and AC in summer in humid climates. And a fresh air exchange. But it’s one of the best front end choices that you can make. And it carries through the life of the home, regardless of roof color.