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How to Sleep Comfortably on a Hot Night

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Re: How to Sleep Comfortably on a Hot Night

#11

Post by phreanix »

dmoho wrote: post #3
ojbyrne wrote: post #2

Air conditioning is a wonderful thing. And, often, cheaper and more environmentally friendly than the things described here.

Here are most of the suggestions from the link: - Have fan with a pan of ice in front if it pointed towards you - Keep a damp hand towel on your forehead - Put an ice pack under your neck - make a rice sock, put it in the freezer and then inside of your pillow - sleep nude - sleep in a 'spread eagle' position - take a cool shower, wet your face, run your wrists under the cold tap Please correct me if I'm mistaken - H…

Let me get this straight, you're asking how an air conditioner uses less power than a regular fan?

While I can't cite any wattage/amps/etc. figures, an air conditioner runs several things besides a fan motor, most notably its compressor. The more advanced ones also have other electrically driven parts, like a thermostat.

As for real world stats, when I lived in the Philippines, I can say for a fact that running a fan vs an airconditioner makes at least a 60-70% difference in my electric bills.

Re: How to Sleep Comfortably on a Hot Night

#13

Post by bootload »

"... 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 good

That and eat lots of icy poles (don't laugh) and drink water.

Re: How to Sleep Comfortably on a Hot Night

#14

Post by swombat »

Elepsis wrote: post #10
jacquesm wrote: post #6

Earlier 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.

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…

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). If it's not so good, you'll incur a constant "your freezer sucks" tax.

In the case being discussed, we're talking about freezing stuff every day, and letting it thaw in/near your bed during the night. So the cost would definitely be there.

Re: How to Sleep Comfortably on a Hot Night

#15

Post by cromulent »

When I lived in Melbourne and the house was over 30C, I would take a soaking wet towel and use it as a blanket on my bare skin.

It sounds bad and the first minute is a bit creepy (until it warms up to your body temperature) but I would fall into a deep sleep in 10 minutes. It worked for me.

Re: How to Sleep Comfortably on a Hot Night

#16

Post by arithmetic »

Think of the winter that will be here very soon, and the time when you'll have to turn on the heater constantly. A few days of sun (especially in a city like Seattle where sighting the sun is a rare occurrence), is not that hard to deal with. Open out the windows, switch on the fan if you have one, take a cold shower and you'll fall asleep.

Re: How to Sleep Comfortably on a Hot Night

#17

Post by jacquesm »

Elepsis wrote: post #10
jacquesm wrote: post #6

Earlier 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.

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 imbalance, the bigger the imbalance the faster the heat will transfer.

If the stuff in the freezer is light (air) then it will take less energy to keep it cold than if the stuff in the freezer is heavy (ice), because there simply is less leakage from air (a thermal insulator) to the walls than there is from ice (a pretty good thermal conductor).

Thermal conductivity is not very tightly coupled to mass but it usually is a good indicator, in the case of ice vs air it works pretty good.

So, it takes more energy to keep a freezer full of ice at a low temperature than a freezer full of air...

For an encore, which is heavier: A cubic meter of dry air vs a cubic meter of humid air ?

Re: How to Sleep Comfortably on a Hot Night

#19

Post by calambrac »

swombat wrote: post #14
Elepsis wrote: post #10

Earlier 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…

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 experiment?

Re: How to Sleep Comfortably on a Hot Night

#20

Post by calambrac »

jacquesm wrote: post #6
calambrac wrote: post #5

Earlier 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.

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/f can be put right next the sleeper while an a/c has to sit all the way over in the window? Etc, etc.

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