How to Sleep Comfortably on a Hot Night
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If you have computers and electricity, by 10-11pm it will be significantly cooler outside so if you have a deck or roof or backyard, try sleeping there.
Please correct me if I'm mistaken - How does an air conditioner use less energy than a fan turned on for the same amount of time? I did a quick search and most of the hits say that air conditioners use more power. (Here is one of the links that came up: http://www.todaysgreenconstruction.com/2008/07/battle-green-...).
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.
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'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 leakage, too, air obviously exits the freezer much more often than its contents do.
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.
Any ideas on how to be more rigorous about thinking this through or running an experiment?
Then compare that with the energy consumption of an air-con unit.
You can then compare (b)-(a)+(c) vs. (d) or (e).
Ideally, you'd do these experiments in identical conditions (temp., sunlight, wind, humidity, etc.), of course.
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 ?
Humid air is less dense (dry air heavier) because water has a lower molecular weight than the average molecule of dry air.
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.
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?
The freezer, of course, works just like an AC: it moves the heat from inside the freezer to outside the freezer — i.e., to the room its sitting in (some large commercial freezers actually use outdoor parts so then can dump the heat outdoors). Assumably, during the day, the windows are open, so that heat will escape outdoors.
Random note: If you could prevent all heat transfer with the outdoors, the freezer/fan/ice cycle would actually heat the room.
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.
The problems with that design are highlighted in the comments, but it mostly comes from really not having enough surface area.
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.
It really depends. On the really hot days having a window open increases the interior temperature if the previous days have been cooler. On successively hot days leaving the window open decreases the interior temp but only if there is a wind.
I don't know what latitude where you come from since you don't have any identifying information but being smart has nothing to do with understanding how to keep cool. It comes from local knowledge. If you come from the continental Europe or the UK I'd guarantee you'd miss half these hacks due to the heat.
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.