svetz
Works in theory! Practice? That's something else
Used to have a waterbed in a house with no AC. In the winters if was great to crawl into because it was warm, in summer it was great because it was cool. The only bad time was just after filling the waterbed, it was waaaay to cold to sleep on then.
But what about a power outage? Could it be a way to stay cool and sleep comfortably at night despite the sweltering heat?
Credit where it's due... I saw this in another thread today ... it's from month's ago, hard to keep up with all the forum's activities...
I thought the idea ingenious enough to be resurrected and warranted it's own thread. So, the question is does a waterbed actually need cooling and if so how much?
Theory
Practice
But what about a power outage? Could it be a way to stay cool and sleep comfortably at night despite the sweltering heat?
Credit where it's due... I saw this in another thread today ... it's from month's ago, hard to keep up with all the forum's activities...
and has some great posts by fhorst, Sparky, Supervstech, OffGridIdaho, and a number of others.
I thought the idea ingenious enough to be resurrected and warranted it's own thread. So, the question is does a waterbed actually need cooling and if so how much?
Theory
Might not need any cooling
Direct contact with a waterbed (through a thin sheet) has a higher heat transfer rate than with air (just like metal feels hotter/colder than ambient). So while a 77° F air might feel cool, that's because the human body is at 98.6° F. That is air's thermal conductivity takes a 20° difference to get heat to flow quickly. So, the temperature of the waterbed can be higher and it'll still feel cooler. In fact, the ideal waterbed temperature is between 85° and 92° F. So, if your ambient temperature is in that range so will the waterbed be, chances are you don't have to do anything to sleep comfortably. If the waterbed is too cold, you can start there and wait until you feel chilled, then put more blankets under you or sleep elsewhere.
How much cooling would be required?
Possibly none. The bed will try to stay at room temperature, a human body at 98.6F will transfer heat into the bed as long as the bed is cooler.
A human body radiates ~40W/m2 while sleeping, let's say a big guy has a surface area of 2 m2, so 80W. A queen sized Waterbed holds about 196 gallons. At 75°F, that's 1600lbs mass. So, 8 hours of sleeping the bed would absorb 80Wx8h=640Wh or about 2,200 BTUs, with 1600 lbs of water that's enough to raise the waterbed's temperature almost 1.3 degrees. But, the bed has 3x the surface area of a person and is radiating heat, but because the bed's temperature is lower it might not radiate as fast.
What if the waterbed temp is to warm?
If your tap water is cooler, you could just exchange some water to cool the bed's temperature down. Or, using Jeremiah's idea, from the paragraph above you'd need 2,200 BTUs of cooling per person over 8 hours. From Sparky's thread, we know it's about 7 lbs of ice (~112 ice cubes) per degree to cool 1600 lbs of waterbed mass (e.g., cool the bed from 88° to 87°). Without ambient radiation of the waterbed, to eliminate the heat from a single person would take 2200 BTUs over 8 hours, or ~9.5 lbs of ice.
Practice
Do you own a water bed? What's your experience? If folks have solid flooring that can take the weight and nights where it's too hot to sleep... should they look into a waterbed?
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