Cool Me Down

[Christopher A. Steele]

Sometimes it gets so hot around here it's difficult to sleep at night (to the point I sometimes have to get up two or three times to cool off in the shower just to get comfortable for a few minutes).

I'm curious: given 'x' ambient temperature in my bedroom at night (and 'y' relative humidity, I suppose) and closed bedroom windows and doors, how do I calculate the amount of heat (heat load??) that has to be 'removed' from my body so that I can sleep comfortably (e.g., without sweating, without having to rely on the shower, or having so much heat removed I die )?

I don't have an AC -- I'm just trying to figure out how all this works.

Is there a formula?

Christopher A. Steele Son of Col. M.J. Steele, USASA/AGC, Fts: Devens, Rucker, Lawton, OATerm, + [e-mail]

[PaPaPeng]

You will get more math than you want to know. The frugal way may be to get a cheap oscillating table fan and perhaps put a block of ice infront of it. Else rig up some form of water spray to blow into the fan's airstream. I don't know how the spray part will come out in humid air but its an easy and cheap experiment to try out.

[Anthony Matonak]

You are describing an evaporative cooler with the water spray. They only really work in very dry environments and even then they max out at some 20 deg F drop in temperature, usually much less.

My suggestion is to get an AC. Small window units are available for around $100 new (sometimes less). They won't cool more than one room and they do require electricity but it's the only thing that really works well and reliably. If you just needed to sleep then you would only need to run it at night. A ceiling fan will also help as they can drop the perceived temp another 3 or 4 degrees F.

If you really want to get extreme then you can build yourself a box with lots of insulation, a little ventilation through a heat exchanger, and a small heat pump, air conditioner or large blocks of ice. It would be a bit like an oversize coffin with a mattress inside.

The other cheap option is to sleep outside in a hammock. Preferably strung between two trees high up so as to catch any passing breeze.

Anthony

[nickspam]

Where does the OP live? Evaporation works in any climate with an RH less than 100%. An indirect system might cool air without adding humidity.

I noticed $53 for 5000 Btu/h at a local WalMart.

Or more, naked right under a ceiling fan, or shivering under a wet sheet.

If the box were small, you wouldn't need much insulation or an air-air heat exchanger.

I saw something like this at a colonial museum. The loved one rested in a coffin with his face and shoulders exposed to the room, but the rest of his body was under a copper ice tray built into the lid. The top of the lid looked conventional, black, over the ice tray.

You might build a larger version of this, say 4'x8'x4' tall, with 1" double-foil foamboard sides and a layer of water instead of ice on top, over a layer of polyethylene film over welded-wire fencing. The water could cool the box as it evaporates, while 15 cfm of dryer air from the room flowed under the water layer and then into the box. For additional cooling, we might evaporate more water into the air in the box.

With a quilt on top, this might also help with frugal heating in wintertime, as in old Swedish bedchambers or Thomas Jefferson's limited-volume sleeping compartments at Monticello. With two people inside, the bedchamber air might be 30+500xR7/160ft^2 = 52 F in a 30 F room, comfy, under another quilt.

Nick

[Rod Speed]

Not very comfortable at the higher humiditys tho.

In some ways the higher temps are preferable as long as they arent too high.

But arent readily buyable so arent that practical unless you are handy.

Yeah, generally not a bad idea if the main problem is sleeping.

I was always told as a kid that thats got some health downsides.

Likely thats just an urban myth tho.

No thanks.

All rather pointless with small air conditioners so cheap now unless you are desperately poor and cant afford the electricity for it.

Or just use an electric blanket and not even have much power cost.

[nicksanspam]

ASHRAE says 88.2 F and w = 0.012 is comfy...

Only a few commercial products, but some people enjoy tinkering...

You might stay 80 F in a 4'x8'x4' R7 bedchamber in a 100 F room with

253+(100-80)(15+96ft^2/R7) = 827 Btu/h, 81 watts with a COP of 3...

The ASHRAE 55-2004 comfort spec says a person in summer clothing is equally comfy at 77 F and 50% RH without a fan and 82 F and 50% RH with a 200 fpm fan.

Direct evap cooling works in the ASHRAE comfort zone while To < 136-4500wo, where To is the outdoor temp and wo is the outdoor humidity ratio. NREL says Phoenix is 93.5 F on an average July day, with 81.0 and 105.9 daily min and max and a record high of 118 and an average wo = 0.0105 humidity ratio. Direct evap cooling would only work until the outdoor temp hit 89 F, but indirect cooling with a good air-air heat exchanger could work until the wet bulb temp hit 89 F, at a 179 F dry bulb temp :-)

If it's 120 F with a 76.5 F WBT, keeping the bedchamber 88.2 F with w = 0.012 and a C cfm chamber airflow requires that 1000x60C0.075(0.012-0.015) = 6.75C

• (82.2-76.5)C = 253 + 96ft^2/R7, so C = 55 cfm. The internal chamber water consumption would be 60x55x0.075(0.012-0.0105) = 0.374 gpm or 0.045 gph. With Pw = 0.1367 and Pa = 0.5663 and 374 = 100A(Pw-Pa), we need A = 4.67 ft^2 of internal evaporation surface, eg a shallow pool on another layer of poly film under the wet bulb canopy, with a solenoid valve in series with an 88.2 F cooling thermostat and a 56% dehumidistat in series with the fan.

This IS a frugal newsgroup. Some people live off the grid or like to save energy to avoid oil wars. Others really are desperately poor, especially in hot parts of the world. You can meet some of them at the SR4 conference from 9/27-10/05/2004 in Boulder, CO,

Including the cost of the Iraq war? :-)

Nick

[Rod Speed]

Pity it says that higher humiditys aint.

So your original at the top is a complete dud.

Pity there is bugger all buyable at anything like that $100.

Pity there is bugger all buyable at anything like that $100.

$100 for summer sleeping is quite frugal and a hell of a lot less than anything you can buy to do what you wave around there.

He doesnt.

Just another of your pathetic little drug crazed fantasys.

There problem. Even you should have noticed that hardly any of those ever show up in here.

Pass. Their dud economys are their problem.

Its cost me f*ck all. And a few pathetic loons using contraptions like that aint gunna stop wars like that anyway.

[nicksanspam]

Just reality, based on surveying 21,000 people.

You appear to be ignorant, my good man. The ASHRAE comfort zone is a box in the temp/hum plane with 4 corners defining "slight discomfort" (Y = +/-0.5)... 88.2 and 0.012 is the upper right corner... 77 F and 50% RH is in the center, with Y = 0 ("comfy.")

You are incorrect, my good man. The foamboard costs $33. Add 7 $2 2x4 studs, $3 worth of fencing and $2 worth of poly film. About $36, after subtracting the cost of the usual posts and mosquito netting, with manual controls. Or less, with some local value engineering.

Scrounge the solenoid from an old washer, add a $5 used muffin fan, a $10 line voltage thermostat and Herbach and Rademan's ([phone]

fine $4.95 Navy surplus humidistat, item number TM89HVC5203, with a 20-80% range, a 3-6% differential, and a 7.5A 125V switch that can be wired to open or close on humidity rise. A motorized damper would be a nice alternative to the fan. Also cheap, but a bit harder to contrive.

Would you have any evidence for this article of faith? :-)

Would your grammar exceed your compassion?

Nick

[wmbjk]

The Rod Speed FAQ

Wayne

[Rod Speed]

A reality that is nothing like your original.

You are a pathetic excuse for a bullshit artist, you terminal f****it.

STILL nothing like that crap of yours right at the top which is a complete dud.

We'll see, you pathethic excuse for a bullshit artist.

Thats no commercial product, you pathetic excuse for a bullshit artist.

Apples and oranges.

Apples and oranges again when compared with a cheap room airconditioner or fan.

You can make the fan frrom scrounged components too.

And buy a small room airconditioner second hand too. Or scrounge one of those for next to nothing too.

His location is in the sig of his original post, fool.

Pathetic, really. Even you should be able to do better than that, child.

[nicksanspam]

I'd say hot. So would ASHRAE, (Y = 1.79, with 67% of people dissatisfied, vs Y = 0, with 6% dissatisfied), based on 21,000 people around the world, who'd prefer adding some moisture to reduce the air temp, which might come from a swimming pool :-)

Imagine yourself in a 90 F office, in a dry shirt...

Nick

[TURTLE]

This is Turtle.

Still you living out of a book and do not understand the part %RH plays in the comfort levels. I would have 90ºF and a 10%RH in my home before I would have

60ºF with a 100%RH. Shut the Books up and get out and go see the system that are running and get a Clue as to what is comforteriable or not.

TURTLE

[nicksanspam]

I understand thoroughly, my good man. In this case, I'm afraid you are the one lacking average empirical understanding, and an understanding of the way surveys work.

OK. Everyone's tastes are different. There's nothing wrong with your misunderstanding average human behavior. It's a matter of surveys and preferences, vs absolute science. But you must admit facts. It's hard to deny the average tastes of 21,000 people around the world :-)

Nick

[Robert Morein]

Do those 21,000 people from around the world reflect your tastes?

[~^Johnny^~]

Here is where statistics fail.

which 21,000 people?

Is the target random and unbiased? It is not!

Only paramaters will do. Statistics are, statistically, on a bias. Their results are slanted. They can err on many facets (sides, if you will).

On some days, I can be quite comfortable at 90 deg F and 70% RH, yet on other days, I am sweltering 83 deg F and 60% RH or lower, AT THE SAME ACTIVITY LEVEL! It naturally follows that sometimes I am ectstatic at 40 F and 90 to 95% RH, while other times 50 deg F at 50% RH is too cold for me.

IOW, your mood, health, etc also comes into play. Statistics just don't cut it.

This is why the comfort zones are based partly on parametric data, as opposed to purely statistical data.

I think Nick is right. Your mileage may vary.

-- -john wide-open at throttle dot info

~~~~~~~~ The time to repair the roof is when the sun is shining - JFK ~~~~~~~~

[Robert Morein]

I love nicks answers, I can't imagine what goes thru his mind when he posts a page of figures to reach a point. But the question is valid: Do those 21,000 people from around the world reflect nicks tastes?

[Hagrinas Mivali]

In a properly done study, they most likely would. One would have to look into other factors such as whether there were significant differences based on nation or region or prevalence of air conditioning in those regions compared to where you live. If the study was done properly, then it's reasonable to assume that it will reflect the tastes of a typical person.

But I'm not the OP and I didn't read the study.

[Hagrinas Mivali]

It's not that the statistics fail. It's that they often get misused. But if a competent engineer or scientist can figure out that failure by looking at the data, then it's not that the statistics failed, but they were misapplied, or accurate but irrelevant.

Bill Gates walks into a bar and a patron says to his buddy, "Congratulations. We're all rich." His buddy asks him why, and he responds, "The average person in this bar is now worth over a billion dollars." His statement is true statistically, but irrelevant. In a case like this, the relevant type of average would be the median and not the mean. A statistician could figure that out easily, and it should be obvious to everybody anyway. It's not that the statistics were wrong, but they were used wrong.

[Hagrinas Mivali]

If the study were done properly, they would reflect those 6.5 billion folks on average quite well. What's relevant is whether the average is relevant to your area or to a group of people who are used to air conditioning to the same extent as you, or whose climate is similar to yours, and a bunch of other factors.

[modervador]

Who's gonna taste all 21,001 to find out?

%mod%