The World's 2.75B Buildings | Hacker News Reader

The World's 2.75B Buildings

tech.marksblogg.com

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> The United Nations (UN) believes there are 4B buildings on Earth. This week, a dataset called "GlobalBuildingAtlas" (GBA) was published by researchers at the Technical University of Munich (TUM) that attempts to estimate this number at being closer to 2.75B.

If we painted the roofs on all of them white, by how much would the temperature of the planet drop?

Probably not as much as if we “painted” them black with solar panels and used the resulting electricity to displace fossil fuel burning.

A good percentage of Pakistan did this recently and removed 35% of demand off of their grid https://www.ted.com/talks/jenny_chase_solar_energy_is_even_c...

I would love to have an air conditioning / cooling solution that is directly linked to solar panels with no batteries involved. Like the sun shines, we get electricity, we do the work. My main goal for this thought experiment is to come up with uses of solar electricity that is resilient to the unpredictable and unreliable energy generation from solar. Thoughts?

Though experiment? This is already a thing in the off grid community. In practice you need at least small battery to smooth out the power, but it doesn't take much home automation to kick on the mini split when the panels/inverters have power to spare.

> I would love to have an air conditioning / cooling solution that is directly linked to solar panels with no batteries involved.

I think that would be very viable with fridges, that represent a large share of electricity consumption among the poorest. Before electricity, people powered fridges by constantly buying ice blocks. They were just isolated boxes where food was stored together with the blocks. Perhaps it's just necessary to go back at the roots, and make fridges that take energy from solar panels and generate a lot of ice by day, and uses it to keep cold at night, with no need for batteries.

I love this idea but I don't know enough about the specifics. Isn't it really bad(TM) for the pump or compressor or something I don't know about for the input power to be variable like this? Like there might be an errant cloud somewhere.

The whole point of my thought exercise is to see if we can somehow make the cost go down. My understanding is that the panel can easily last twenty five years but the battery you'd be lucky to go beyond eight?

Edit: good news / bad news

Bad news: this is not an original thought

Good news: smarter people than me are already working on this. See solar Variable Frequency Drive (VFD). Basically, my thought is a pump is a pump. if you can build a pump to pump water to irrigate poppy fields, you can use the same pump to drive refrigerant in a refrigerator/ freezer / heat pump.

> I love this idea but I don't know enough about the specifics. Isn't it really bad(TM) for the pump or compressor or something I don't know about for the input power to be variable like this?

No, modern refrigerators and other white box appliances with variable speed motors use electrically commutated (aka EC or brushless) motors that allow for motor speed control. Larger three-phase induction motors can have their speed controlled by a variable frequency drive (VFD).

> Basically, my thought is a pump is a pump. if you can build a pump to pump water to irrigate poppy fields, you can use the same pump to drive refrigerant in a refrigerator/ freezer / heat pump.

You’re close, but it’s more ‘a motor with enough power can drive any pump (or fan)’ than ‘a pump is a pump is a pump’, as there are many different kinds of pumps for various working fluids (water, glycol, oil, refrigerant, etc)

Regarding the fully solar powered A/C, you can smooth out power generation and consumption using capacitors (aka batteries)

Supposedly water heaters are an amazingly good target for variable power. Water heating takes 18% of home energy use[0] and is already a well insulated storage device. Just heat it up as you are able with the day's sun.

If you are looking for a cooling solution, you could go the other way and make water chillers through a dedicated water tank. You would tie the HVAC to pipe air through a heat exchanger. Seems like all of that is well established engineering.

[0] DOE link on water heating https://www.energy.gov/energysaver/water-heating

I'm now wondering if painting a roof white is better than covering the same roof with solar panels and using that to drive air conditioning (in the house). My intuition is that painting it white must be vastly more environmentally friendly, although it probably doesn't reduce the temperature very much compared to aircon.

It's worth factoring in that solar panels also provide solar insulation to the roof by effectively shading it, ie the sun shines on the panels and there is an air gap between the panels and your roof.

In cooler climates, you are now taking a hit on heating costs. That now blocked Winter sun would have provided some amount of free warmth.

If it's that cold, you probably have a fair amount of roof insulation anyway that's preventing heat absorbed by your roof from being conducted to the conditioned space.

Sure, but the physics still cuts both ways. Either sun hitting the roof causes measurable heating or it does not. The temperature gradient must flow.

Sun heating in Winter = awesome. Sun heating in Summer != awesome.

I am not arguing the strength of the effect, only that you must account for all seasons.

Does the house already have AC or not? And are you talking about indoor temperature or outdoor temperature? Also many places are cold. Running AC would make it worse.

There are certain materials that aren't just white but also specifically radiate heavily in IR bands that the atmosphere is particularly transparent to and so can actually stay sub-ambient temperature while in sunlight. See, for example, https://onlinelibrary.wiley.com/doi/full/10.1002/eom2.12284

But adding conventional AC is never going to cool down the world.

AC doesn't make it cool it merely transfers the heat to the outside in an energy efficient manor. The emerging tech is special coatings that convert heat to an infrared frequency that easily escapes the Earth's atmosphere.

Most manors aren’t very energy efficient. Take Downton Abbey for example.

Thank you!

man·ner /ˈmanər/ noun 1. a way in which a thing is done or happens.

Given the era it is about, Iy could be considered energy-efficient, as the carbon footprint of individuals and households was much lower a century ago.

There was a good study on this a few years ago that ran the numbers on this and landed on white paint for residential homes as the best option, for a few reasons, if I remember correctly:

- Installation, maintenance and transmission costs are lower when solar is aggregated on farms - Solar offsets air conditioning, but that moves the heat outside. White roofs reduce the need for AC, which helps significantly with urban heat scenarios

A quick search yields a UCL study, which supports the lower claim: https://phys.org/news/2024-07-roofs-white-city.html

I would guess not that much - certainly fractions of a degree - because the proportion of the planet's surface is still relatively low, and as much as 60% of that reflected light would be scattered and absorbed by the atmosphere.

It'd have a much bigger impact if all those roofs had solar panels, and the resulting electricity was used to replace carbon-emitting energy sources.

Paris and other climate accords have much ado about fractions of a degree, leading me to believe that that's highly consequential.

I think we should do more albedo engineering. like white roads and car roofs.

White roads could potentially be blinding, but yeah something lighter than what we do currently could be very worthwhile. It'd have much higher nighttime visibility too.

> White roads could potentially be blinding

Hell I was just walking down the street a minute ago and thinking the same! It's October ffs! (It IS October right?)

I'm thinking about light colored roads that seem to be made of concrete. See them here and there. Seemed to be more of them when I was a kid.

Wonder if that would make a substantial difference? Much brighter than asphalt but not bright enough to bother drivers.

I was thinking you could potentially engineer them to reflect IR light, but I feel like dust and dirt would probably quickly eat into the effectiveness. The question is whether it'd really make a difference on a global scale at all.

There are materials that do what you're looking for surprisingly effectively, staying many degrees sub-ambient even in direct sunlight. (See https://onlinelibrary.wiley.com/doi/full/10.1002/eom2.12284 for example). But a roadway is a really difficult use case for a surface coating. With something like 50% of the surface area of many American cities being road or parking, there's a lot of potential room for effectively mitigating the urban heat island effect, but I think roofs are a better target. They don't have cars sitting on top of them blocking sightlines nearly as often.

Back-of-the-envelope - Road area. World road length ≈ 60–70 million km. Using an average paved width of ~8–10 m ⇒ area ≈ (0.9–1.3)×10¹² m². Earth’s surface is 5.1×10¹⁴ m², so roads cover ~0.09–0.13% of the planet.

- Albedo change. Dark asphalt is ~0.05–0.10. “White” coatings can push toward ~0.4–0.6 (fresh), but weathering quickly dulls them. So a plausible Δalbedo for roads is +0.2 to +0.5.

- Global albedo change. Δα_global ≈ (road fraction) × (Δalbedo_road) ≈ (0.001)×(0.2–0.5) ≈ +0.0002 to +0.0005.

- Radiative forcing. Globally averaged incoming sunlight ≈ S₀/4 ≈ 340 W m⁻². Forcing from an albedo change is ΔF ≈ −Δα_global × 340 ≈ −0.07 to −0.17 W m⁻².

- Temperature response. Using a standard sensitivity ~0.8 °C per W m⁻² (≈3 °C per CO₂ doubling): ΔT ≈ −0.05 to −0.14 °C at equilibrium.

Teslas will start crashing like there’s no tomorrow.

So nothing much will change?

Painting roofs (or even all man-made surfaces) white wouldn't do much globally at all, but it might reduce the urban heat island effect. But probably (speculating a bit here) not quite so much as creating more green spaces (or green roofs, for that matter).

there is a cool project that explores this topic: https://coolcolors.lbl.gov/

AI is responsible for 60% of all internet traffic this morning, OP is the other 40%.

But on a serious note this is an interesting project highlighting the sheer volume of power usage across the world. .. I'm also curious given the data and power usage, if AI assisted heatmap is actually more accurate than one developed by downloading a single dataset of high resolution satellite imagery at night, performing algorithmic analysis to draw heatmap based on light output or !maybe even simple image processing downsampling the image and shifting white-blue to red?

70% of daytime RGB sat imagery is covered by clouds. I'm not sure how easy it would be to spot if clouds were covering a city's lights at night.

I've only seen Maxar publish one night time image and that was of Dubai. I suspect smaller buildings in not so well lit areas could end up getting missed out.

SAR imagery would work well for seeing at night and through clouds but I'm not sure what the state of AI building footprint detection is with SAR atm.

Fascinating. So no such satellite data exists. Thanks for the insight, makes the linked write up much more satisfying.

Meta note: don’t see many blog posts as detailed as OP with seemingly mundane details. It assumes almost nothing of the user. So many posts would just say “install this QGIS plugin” with no mention of the pip calls, etc.

Not sure if this comes from search engine optimisation or years of experience consulting to clients that know nothing :)

Anyway, good work Mark. Another of your posts I’ll bookmark.

Is it possible to calculate from that data the total surface area of all roofs? I think there is paint that converts solar energy into radiation that goes straight back into space. I wonder if using that paint on a significant percentage of buildings would matter.

Are you perhaps thinking of radiative cooling, e.g. paint that reflects close to 100% of all light, excluding the spectrum at which room-temperature objects radiate heat, resulting in a net cooling effect?

E.g. [Revolutionary Paint: How to Make Surfaces Stay Cool in the Sun](https://youtu.be/dNs_kNilSjk)

Thanks for the video!

Yes, from chatgpt:

These are so-called “radiative cooling paints.”

Here’s how they work:

They reflect almost all sunlight, so the surface doesn’t heat up.

At the same time, they emit thermal radiation in a specific infrared range (around 8–13 micrometers) that can pass through the Earth’s atmosphere and escape into space.

Such paint can make surfaces cooler than the surrounding air, even in sunlight.

So it doesn’t convert solar energy into another form — it selectively reflects and emits infrared radiation that sends heat directly into space.

The 151M Buildings for the US is a bit of a surprise for me.

I found it interesting the disparity between the number of buildings in India and the rest of the world (3 times the next country). And the close parity in number between China and the US.

From what I've seen in news reports, China has built a lot of tower blocks that are 10s of floors, rather than the 4-5-floor buildings I saw when I worked in and travelled around India.

India has ~4x the population of the US so the ratio of buildings isn't much of a surprise.

Ok a bit off topic but isn't a 1200W PSU overkill for this system? For a 9950X and 1080, 500W seems plenty.

I see it says Corsair so cannot tell what exact model it is but I did relatively similar thing. Reason being if you keep the load under certain wattage the PSU will run in passive cooling mode. My rig will never reach 50% of what Corsair SF750 Platinum can deliver and not mention in normal light load circumstances. It spins up its fans only when the load reaches ~300W or so.

Some people are very anal about any kind of noise coming out of their rigs. I personally undervolt everything to keep the fans at bay/minimum and having extra legroom in PSU department helps a lot

Same. Part of the background info on this is PSUs are usually most efficient at (or just under) 50% load. They are also more efficient at 240 V than 120 V, if you have the circuit. So the real efficiency can end up varying significantly, depending how you use it. The efficiency is not usually much to write home about in terms of your electric bill, but it does help drive the ability for the PSU to cool itself passively.

I'm hoping to use most of this system for the next 10 years. At some point, I want to add some beefy GPUs to it when I get back into 3D again.

I remember reading something interesting, in a good way, but I'm not sure whether it's fully accurate: That the majority of the planet (land, not counting water) is still unpopulated by people.

Can someone verify?

Depends on how you measure it. Do you subdivide all land in 1 cm squares and only count the ones with somebody standing on them as populated? Then almost all land is unpopulated. With 8.2 billion people in the world, each one occupying a 0.5x0.5 meter square, you have 2.05e9 m^2 populated land, out of Earth's total land area ~1.5e14 m^2 [1]. That's less than 0.0014%.

As you increase the size of your subdivisions, the unpopulated fraction goes down. In the limit of all land being in just one subdivision, it's obviously 0.

[1] https://en.wikipedia.org/wiki/Population_density

These type of calculations don't really work for things like skyscrapers, high-rise apartment complexes, or the slum-towns of Asia and South America, and conversely for very sparsely populated regions like the fringes of the Sahara. Antarctica has people too but it doesn't make any sense to count it as "populated".

I think we can just draw an outline around cities, towns, and villages and count that area as populated, no matter how many people are actually in there.

For long stretches of land where there's just a single highway going through and a few gas stations, motels and shacks, totaling maybe <100 people for many miles around, we can count that land as unpopulated.

Isolated islands with indigenous/uncontacted tribes, not sure.. We may have to consider their population growth and see if they're in "equilibrium" with "nature" and so on.

A simple glance at Google Earth shows large parts of Russia as clearly unpopulated/undelevoped, then there's the deserts of China and Africa, and some natural land in the Americas, and finally of course there's Antarctica, until the Elder Things awaken.

The US has only used 25% of its land. Overture published a land use dataset a while back that could go some way to verify how much land on earth is urban, covered in forest, etc.. That might only need a single SQL statement given how they structured their data.

I have some analysis around that topic in the middle of this post: https://tech.marksblogg.com/overture-land-cover.html

I remember the same thing. I don't have any sources, but I've come to understand that a lot of land is on hills/mountains and is therefore an inconvenient/dangerous place to build.

I think the "overcrowded planet" scenario is not very plausible, except if we're talking about resources. There is plenty of land for everyone, especially if we start to construct efficiently.

> There is plenty of land for everyone, especially if we start to construct efficiently.

I was afraid someone will get it the wrong way: I hope it STAYS that way; that the majority of the planet remains unpopulated, but humans learn to make better use of the space we're already occupying.

Does Agriculture land count as "populated" or not? If not, most of the land is empty in most countries (even in Japan). A quick search shows Singapore "built-up" area around a third of its total surface.

The only exception might be the vatican, if you consider it a country.

Kind of crazy to think that there are almost half as many buildings as people and yet me and my wife can't even afford the deposit to buy a single one on a mortgage after 10 years of saving, hustling hard, taught myself to code, got a university degree, worked in the tech sector, near the forefront of all the hot tech tends... Meanwhile, all this time, I'm told I'm privileged. I must be the victim of some kind of massive PsyOp conspiracy.

You can buy a small house in rural America for $25,000

Rural Russia as well. But you will probably have to get your water from a well and poop into a latrine.

In my country (Australia), the cheapest I can get is like $250k USD equivalent... But that's a shack in the middle of the desert in some tiny ghost town. Even in a normal small town, houses are like $350k USD minimum. In capital cities, it's like $500k USD minimum for a tiny apartment... Top salaries for top senior software devs are like $130k USD before tax, taxed at about 40%... So take home pay is like $78k USD net income. Rent is like $22k per year minimum. Impossible to get fixed-rate mortgages; banks only only do variable rate... 20% minimum deposit. This is in a country with a LOT of spare land which is scarcely populated.

Your country exports timber to China and has a lot of empty land.

Who benefits from this situation ?

Queensland exports about 25% of timber production, but changes are now in progress to ensure local housing demands are met, as the current material costs are exobitant:

https://www.dpi.qld.gov.au/business-priorities/forestry/qld-...

Many buildings will be commercial, industrial, military etc. That said one building can house 1000 people.

Chatting with ChatGPT:

Humans are in oversupply currently - for what needs doing.

And as we all know, products in oversupply lose their value.

The algorithms that drive the world are optimised for money and capital, humans are just one product in that structure.

Enjoy the ride.

IMO the real problem is that the monetary system creates asymmetries which create monopolies, which force everyone to participate in 'the economy' through rigid, inefficient, bureaucratic structures. People are literally not allowed to service each other, even through they have the time and capacity to so; simply because they do not have access to a specific currency which they are forced to use... That same currency is not universally scarce though; it's basically handed out to their biggest corporate competitors in large quantities via government contracts and from banks in the form of low interest loans. It creates a kind of fictitious planned economy which becomes increasingly inefficient and bureaucratic by the day; the money is the only quantity which is increasing (and only for some people), almost every other economic metric is decreasing. The real economy is hollowing out.

The financial system has become a giant game of Monopoly, but unlike Monopoly, when all the capital has accumulated with one player, this financial system isn't restarted and the wealth redistributed.

Instead it feels like playing Monopoly, round for round, and all the money goes to the one player with all the hotels and train stations and there is no opportunity for other players to obtain any property or wealth.

If you are lucky enough to be in the circle of that one player with all the wealth, good for you. For the rest of us, it's just rolling the dice and going in circles - round for round.

Yep pretty much. It's just absurd. I wonder if billionaires notice any difference at all going from a net worth of $100 billion to $200 billion. I doubt they feel any difference at all in their lifestyles or happiness levels. Maybe they just get a tiny amount of satisfaction knowing that they're a couple of billions above the next richest person... Well it's basically the same for everyone in this society. The monetary amounts go up but nothing else does.

For most people, it feels like opportunities evaporate and disappear into the void. Nobody gains anything meaningful from the monopolization of opportunities. One regular person's "opportunity of a lifetime" turns into a billionaire's "spam in the inbox".

It's lose-lose but the billionaire may think of this as neutral or "not a problem" from their end. Easily solved by a spam filter, an assistant and a personal security team.

Oh, poor poor jongjong... my sympathies!

Most of those buildings are so poor you probably wouldn’t even consider one outside the top 10% of the world for free assuming you want a first world kind of accommodation. Source: I’ve seen the world.

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