If only Starbucks were open all night...
How to Sleep Comfortably on a Hot Night
21–30 of 34 posts
Re: How to Sleep Comfortably on a Hot Night
#22Better idea... http://lifehacker.com/5335024/how-to-build-a-diy-dorm+legal-...
I highly, highly doubt that would actually work. You would be much better off taking advantage of evaporating water somehow, such as putting a light damp cloth in front of a fan or something else.
The problems with that design are highlighted in the comments, but it mostly comes from really not having enough surface area.
Re: How to Sleep Comfortably on a Hot Night
#23Earlier quoted context omitted.
You had to expend the energy to freeze the water. You probably did that with a freezer, which runs using a compressor just like an air conditioner, except that it has to get a lot colder. I think you're still right that it comes out cheaper, though, because you'd be spending most of the freezer's energy output anyways.
The freezes compressor will run longer if you stuff it with things that are not yet at the temperature of the rest of the stuff in the freezer. This is also why it is a good idea to de-ice your freezer every now and then, keeping all that ice at a low temperature against the leakage through the walls of the freezer costs energy.
The real reason to de-ice is that the ice interferes with the flow of heat between the items you place in the freezer and the cooling coils. It wastes energy, but by making it take longer to cool things down.
Re: How to Sleep Comfortably on a Hot Night
#24Earlier quoted context omitted.
Air has a very low heat capacity. It doesn't take much energy to cool a cubic metre of air quickly (see air con, for example). On the other hand, cooling a cubic metre of water and other watery solids takes a load more energy. In terms of keeping it cool, that probably depends on how good your freezer's insulation is. If it's really good, it probably doesn't take too much energy to keep things cool (air or otherwise)…
No doubt there's still an additional cost, I just don't think it would be high enough to make it more expensive than running an air conditioner, given that you're going to be running the freezer regardless (depending, of course, on how much we're talking about. I'm picturing a window unit vs. a window fan with a baking pan's worth of ice). Any ideas on how to be more rigorous about thinking this through or running an…
You could take a certain quantity of ice, figure out how long it takes to melt under a fan in hot weather, then calculate the energy required to get that quantity of water into ice (heat capacity equations), and you'd have a rough figure for energy spent per unit time.
Then compare that with the energy consumption of an air-con unit.
Re: How to Sleep Comfortably on a Hot Night
#25"... How to Sleep Comfortably on a Hot Night ..." hotest it got here in Melb last year was 46C and multiple days above 43C with extreme fire weather ~ http://www.flickr.com/photos/bootload/sets/72157614397725714... Couple of measures you take: - open windows - multiple 4Ltr freezer blocks work well - stay at the pool till late - sleep on concrete or tiles - use fans - wet towels & buckets of water for feet are pretty…
I think anyone who reads HN who needs to be told to open windows in order to keep cool should maybe hand in their hacker badge.
Re: How to Sleep Comfortably on a Hot Night
#26No clothes + fan. No matter how hot, you'll start needing a sheet to keep the surface of your skin warm. It works for me in an AC-less shack on the equator!
Re: How to Sleep Comfortably on a Hot Night
#27Better idea... http://lifehacker.com/5335024/how-to-build-a-diy-dorm+legal-...
I highly, highly doubt that would actually work. You would be much better off taking advantage of evaporating water somehow, such as putting a light damp cloth in front of a fan or something else. The problems with that design are highlighted in the comments, but it mostly comes from really not having enough surface area.
Care to explain? I am not good at science/physics.
Re: How to Sleep Comfortably on a Hot Night
#28Earlier quoted context omitted.
I'm not so sure this logic makes sense -- in fact I think it might be entirely backwards. I've always been under the impression that though you pay a penalty for freezing things the first time you put them in, thereafter a full refrigerator (and freezer) is actually much more efficient because it's more difficult to keep air cold than it is to keep any variety of items that are more dense. If we're talking about leak…
reduce it to an absurdity: If you imagine a giant freezer filled with ice it will eventually melt. This takes energy, a larger freezer will take more, an empty one will take less than a full one. Counteracting the heat transferred through the freezer walls from the outside in will require an amount of energy proportional to the mass in the freezer and the leakage from the outside. It takes energy to maintain that imb…
Most people will get the last question wrong.
Humid air is less dense (dry air heavier) because water has a lower molecular weight than the average molecule of dry air.
Re: How to Sleep Comfortably on a Hot Night
#29Earlier quoted context omitted.
You had to expend the energy to freeze the water. You probably did that with a freezer, which runs using a compressor just like an air conditioner, except that it has to get a lot colder. I think you're still right that it comes out cheaper, though, because you'd be spending most of the freezer's energy output anyways.
The freezes compressor will run longer if you stuff it with things that are not yet at the temperature of the rest of the stuff in the freezer. This is also why it is a good idea to de-ice your freezer every now and then, keeping all that ice at a low temperature against the leakage through the walls of the freezer costs energy.
Very true. Your comment reminds me of a question I've always had. Does a refrigerator full of stuff take more energy per unit time (after the stuff is all cooled down) than an empty refrigerator? I don't know exactly how to do rough calculations of that sort of thing in my head, but my best guess is that since more food in the frig means less air, the question becomes, is air easier to keep cool than food?
Re: How to Sleep Comfortably on a Hot Night
#30Earlier quoted context omitted.
The freezes compressor will run longer if you stuff it with things that are not yet at the temperature of the rest of the stuff in the freezer. This is also why it is a good idea to de-ice your freezer every now and then, keeping all that ice at a low temperature against the leakage through the walls of the freezer costs energy.
Of course, but is the marginal cost of adding a few trays of ice really more expensive than running an air conditioner? The problem is so under-specified at this point it's kind of silly to pretend we could get a meaningful answer yet. Are we talking about the ice/fan and a/c cooling the room to the same temperature? Or are we just talking about the sleeper's comfort, in which case we should take into account that i/…
Well, that isn't quite a fair comparison, since the ice-fan only cools the small column of air between the fan and your bed, while an air conditioner cools all the air in a room or building. That said, the ice-fan is probably more efficient than a very small air conditioner than performs the same level of cooling (not that such small air conditioners exist), whereas an air conditioner is surely more efficient than the quantity of fans and ice that would be required to cool an entire room or building.
I have another question, since my basic physics knowledge is a bit lacking. Compressed refrigerant system like air conditioners work by expending (electrical) energy to move heat from one system (the inside air) to another system (generally outdoors). With the ice-fan, where does the heat go? This is probably a fallacious way to explain it, but is the energy being removed from the air and used to transfer the state of the H20 from solid to liquid? And if that's the case, if you wanted to cool an entire room rather than a column of blown air, you'd have to have the liquid water end up outside the room, just like the exhaust from an AC system is outside?