> underground car parks tend to get hot too

This is something that has puzzled me every time I park in the underground garage under City Hall in Palo Alto. It is always so hot down there compared to the outside air.

I was about to ask if anyone knows why that is, and then realized I could search for the answer:

https://www.google.com/search?q=why+do+underground+garages+g...

Lots of interesting opinions there, including a previous HN thread.

One discussion I liked showed up when I'm signed into Google but was missing from an incognito search:

https://philip.greenspun.com/blog/2013/07/05/stupid-geophysi...

This reminds me of how the London Underground used to be much cooler, but the trains have raised the temperature of the clay surrounding the tunnels sufficiently that it never cools off:

https://en.wikipedia.org/wiki/London_Underground_cooling

Relevant: https://youtu.be/Y8RfeAmLfn8

There's also all the body heat, and the resistive braking of the trains which is being phased out.

Hello 2013: https://news.ycombinator.com/item?id=5997368

> Cold cellars can be in short supply

If this starts to happen semi-regularly, you can bet my garden will turn into a little hobbit hill/cellar.

That said, I agree that if it happens suddenly to that extend, we would likely be looking at more than 0.1%.

True. Which is why what always puzzles me is that cities like Austin or Phoenix are gaining population. It's so hot there!

"Many apartments don't have a bathtub, only a shower. And if everyone keeps tap water running, the pressure will drop down to trickle."

People don't have trashcans, storage bins, etc?

"And seems you probably never bathed in 35°C water, it's definitely not refreshing."

Where is this 35C water coming from?

Also, if it's a humid heat, there are likely to be natural or artificial bodies of water around. Hopefully the people have been taking care of them and they aren't a cesspool.

Sure, some people may die, but it should be very low.

Edit: why downvote? All the excuses the previous person gave seem petty to me, so I'm wondering how that person came to their conclusion. Especially for where that hot water is coming from.

> WB 35 °C (95 °F) – theoretically equivalent to a heat index of 70 °C (160 °F), though the heat index does not go that high

I’m inclined to say that this is not very survivable, regardless of your precautions, if your air conditioning has died.

I'm not sure you understand wet bulb and heat index. Heat index is largely irrelevant when talking about the precautions mentioned. The actual temperature is no where near 70C, and actual temperatures matter when talking about cooling that does not use ambient air (and evaporative cooling assuming 100% humidity in this case).

A wet bulb of 35C means that there is a thermometer covered with a wet cloth reading that temperature. That could be 35C with 100% humidity, or it could be a higher temperature with a lower humidity.

Can you explain how your air conditioner keeps you cool? Do you think this machine is the only thing that can perform a similar function? It's all about removing excess heat from your body. An air conditioner does this by cooling air and removing humidity. This can be from the cool air on your skin and the ability for your sweat to evaporate. When your sweat can't evaporate you need another way to transfer heat. Water is very efficient for this due to its specific heat (anything at a cooler temperature with sufficient thermal mass can work). Some people can even become hypothermic in 27C water if left in it long enough.

Edit: I guess people just downvote things they don't like or find to be inconvenient.

Re-read the comment you're responding to.

I did... and?

You come off as browbeating him, accusing him of not knowing things, when he said a small thing that was fully accurate if not precise. That's why you're being downvoted.

"I’m inclined to say that this is not very survivable, regardless of your precautions, if your air conditioning has died."

How is that fully accurate? It seems to me that "not very survivable" is not accurate and is an over exaggeration. I don't expect a 50% death rate, even 10% would be extremely generous. It would be like me saying linux desktops are very common.

This is silly/pedantic. He's talking about being in a typical house with a dead A/C, experiencing the equivalent of 70C. Please tell us how you're going to survive that circumstance. Answer: you're not. You're going to change your circumstance, since it's not very survivable. You're going to leave your house and try to find somewhere cooler. His statement is accurate if not precise.

Lol it is not the equivalent of 70C. Please see the other resources people have posted here about understanding wet bulb temperatures. Even a wet bulb of 35C can be tolerated by most for hours - 70C could not.

I would not leave my house. My house has insulation and thermal mass, which would delay the tempature from reaching that level until later. I could use water to cool myself, whether in the bath tub or a trashcan. I could use a fan if there's power (depends on the temperature and humidity to reach that wet bulb). I could use frozen objects (even without power, the freezer will stay cold for at least a day). I also have a generator to power these things if there's a short to medium term outage.

Their statement was not about changing one's circumstance. It was that even with precautions, it's not very survivable. This is neither accurate nor precise. It is very survivable with precautions.

You're describing tactics that will lead to your tenuous survival. If the heat doesn't last too long. And if you don't have anyone else is your house, not a likely circumstance globally considered. Almost like 35C wet is not very survivable. Your claim that 35C wet can be tolerated by most for hours contradicts the article, and your claim that it's more tolerable than 70C dry contradicts the concept of heat index. Anyhow, you're welcome for my charitably stepping in to let you know why you're being downvoted. You're stuck on pedantry and straw manning and pointless unproductive argument. The Hacker News collective had you pegged, and I'll just join the downvote parade and ignore your type in the future. I'm out.

Thanks for making my argument for me anyway ;) you said it better than I probably could.

I feel sorry for you.

Even if my air conditioner was still functional, its output, the attic-based tubing used to push the air around, and the cheaply-built and leaky house to which it all attaches would never be able to keep out the heat.

Also the outside end of the heat pump wouldn't be able to cool off, so it wouldn't be making any cool air inside anyway. The tipping point there seems to be way lower than the numbers above, around 50 C / 120 F.

Huh, that’s a good point. Never considered that.

You’re being unreasonably optimistic. It’s wishful thinking.

How so? What part is unreasonable?

I was specifically questioning things like where is the hot water coming from, people without tubs can't figure out how to save water, etc. Those claims sound overly pessimistic and simplistic to me.

It's not about saving water, it's about immersing yourself in water. You seem to have a different natural disaster in mind.

It is about conservation of water because as the person pointed out, you can't have a bunch of people running water continuously. You can store the water in a trash can or other large container. You can immerse yourself, or parts of yourself, in this water. You can even make a gravity shower to reuse the water since it's used for cooling and not cleaning. Replace the water when it gets too warm. This would greatly reduce the water usage compares to continual showers and provides a suitable substitute the previously mentioned bath tub when one is not available.

In some places people used to pump groundwater out of the ground to use. That water should be at a temperature of around 10-20C. So you could soak your feet in that to cool off.