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Passive Refrigeration and AC
By scottsAI, Section Remote Living Posted on Thu Sep 07, 2006 at 03:50:55 AM MST
Passive AC seems to be an interest lately

Ancient Egyptians made ICE, yes ICE. Blocks of ice.
Two central arguments about how they did it.

Water evaporation at night.
Black body radiation at night.
Water evaporating works to help cool it, can't take it below ambient temperature.
My bet is black body radiation.
I'm wondering the BTU/hr per square foot it can loose. Totally passive system.
Like to know how practical to use for refrigeration and/or AC.
Looking for a sensor to make it automatic, need to know when the sky is clear. Thinking of using a Harbor Fright tool NON-CONTACT LASER THERMOMETER. $30 on sale often.
Has anybody pointed this at a clear sky? What was the reading? Cloudy sky? Readings?
Have fun,
Scott.

Passive Refrigeration and AC | 14 comments (14 topical)

Re: Passive Refrigeration and AC (3.00 / 0) (#1)
by Countryboy on Wed Sep 06, 2006 at 09:58:16 PM MST

My mechanic brother has a fancy laser thermometer he uses on cars. It has a range of 25 feet.

If you point it at something very far away, it won't give you a reading.

Re: Passive Refrigeration and AC (3.00 / 0) (#2)
by scottsAI on Wed Sep 06, 2006 at 10:46:08 PM MST

That could be a problem. May have to make my own sensor.
Scott.

[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#3)
by scottsAI on Wed Sep 06, 2006 at 10:56:14 PM MST

Physic books say the BTU/hr per sqft = 31.7 BTU/hr per sqft.
Or 100.2 watts/m2.
Under ideal conditions. Not good enough for AC maybe, but fridge just fine.
Great fridge is 500wHr per day, so this would need 1m2 for 5 hr to meet.

AC 24,000 BTU/hr several hours per day. 6 hr per day would need 63 x 63 m for one hour. My back yard is not that large!
Have fun,
Scott.

Re: Passive Refrigeration and AC (3.00 / 0) (#4)
by nothing to lose on Wed Sep 06, 2006 at 10:58:26 PM MST

Are you SERIOUS dude??? Whacha smokin, I want some.

Just joking with you Scott.

"Harbor Fright tool NON-CONTACT LASER THERMOMETER. $30 on sale often."
I think that's the one I got, I love it and it works very well.

"Has anybody pointed this at a clear sky? What was the reading? Cloudy sky? Readings?"

Well the sun was 99,999F before the meter fried, ha ha.

Ok, all jokes aside, probably not funny anyway, but I was in an odd mood ok.

The Non-contact thermometer I have reads by reflection I think basically. So I "THINK" it will not really work pointed into the air. I should try tommorow durring the day.

I will go try now, on a clear night.

Ok, 11:14 PM S. MO. USA, Motorhome body is 63F, tree in yard is 65F, dirt in yard varies 63-65F, Moon is 000F, sorry no clouds tonight a clear sky, outer space -018F.

OK, not sure what 000F for the moon and -018F for just into clear black sky means?? NO joke, I expected no reading for either, so why the -018F?
This does puzzle me, about 65F outside tonight, but still I am sure the moon and space readings were not correct!!

If I remember I will try tommorow durring the day for clouds and clear sky etc..

After the dumb jokes and all, I would like to point out that one of these "NON-CONTACT LASER THERMOMETERS" is a great thing to have.

I really don't know about the sky thing, I don't think it will work, but for most things it does work very well and I have used mine a ton! Well worth the money!
When used to read a good normal wall type thermometer they read the same.

Mine helped save alot of food when the fridge went bad, burnt out a freezer fan. It was great to check temps of milk, meat, veggies, etc in an instant. I wired in a couple 12V computer fans I had on hand with a 115 amp battery, worked pretty good till a got a correct fan. $100 for a new fan, no way!!! Got a scrap yard fan for about $1. But for awhile I ran the 12V and the non-contact thermometer saved about $50 or more in foods easy!
.
nothing to lose

Spelin and tpying are my strong points, not electronics.

Re: Passive Refrigeration and AC (3.00 / 0) (#5)
by ghurd on Wed Sep 06, 2006 at 11:34:52 PM MST

I have the "non-laser" HF thermometer.
Car remote size. Paid US$6. Retails around US$20? Thats all I can tell anyone.
Happy with it. More accurate than I can fault.
Sidewalk reads 62.5F, freezer is 10.8F, etc. About right.
Clear night sky reads 123F. That is the published upper limit of the unit, though I have seen 128F show up.
G-
Ghurd.info
[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#7)
by nothing to lose on Thu Sep 07, 2006 at 11:08:01 AM MST

I never saw one like yours, mine is a little less than 2 soda cans tall. I'll have to look for the smaller ones, didn't know they made them.

Mine does not seem to work on the sky, bright clear sky is still -18 or so, no clouds today so far so I can't check those yet to see if they show any temps.

Not sure where the book for mine is to check the limits, I used it for the alky still so it goes around 200F at least but I think alot higher. Not certain but I think I have used it on the wood burner and got readings over 500F also.
Hmm, ya pretty sure I did. I dried silica gel beads on top of the wood burner and remember I used the non-contact to make sure I did not get those too hot, around 300F I think for the beads.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.
[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#8)
by scottsAI on Thu Sep 07, 2006 at 03:40:15 PM MST

Thanks nothing to lose!

I have wanted to get one, have not found the justification. Then you need it and you don't have it...
I do have a thermocouple meter, has been handy a few times.

Did you get a chance to try it during the day? (my major interest are at night).

Your readings support black body radiation effects!

Sun should read 5,000 or there abouts. Did you try it? Or worried about damage?

Moon at 0000F is no big surprise, I though it might be higher.
Sun warms up the surface.
Open space should read 0004K, or -269C, the sensor was not designed to read numbers like that. Or the atmosphere reflects some of the ground temperature or even its own.
If that is the case then the cooling effect will be less than 100w/m2.

I expect a cloudy day to read the dew point temperature or higher, clouds may reflect the "temperature of the ground" With little to no cooling effect.

Based on your results, (need to confirm the clouds) looks like the sensor will work!
Have fun,
Scott.

[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#14)
by nothing to lose on Mon Sep 25, 2006 at 05:57:00 AM MST

Hi Scott.
I went to Chicago for awhile so I hadn't checked anything else yet. Been storming here now alot since I been home, maybe today I can check the clouds and sun. Looks like it might be a nice day today sofar.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.
[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#6)
by whatsnext on Thu Sep 07, 2006 at 09:57:47 AM MST

I'm pretty sure that option three is the correct one.

Water evaporation at night.
Black body radiation at night.
Ice delivered by lizard skinned aliens who arrive via some sort of wormhole transportation device.

Re: Passive Refrigeration and AC (3.00 / 0) (#9)
by Bruce S on Thu Sep 07, 2006 at 04:16:57 PM MST

I vote for number 3
:-]

[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#10)
by asheets on Thu Sep 07, 2006 at 05:13:05 PM MST

If you have 2 of these things, and aim them at each other from about 25 feet away, you can use them as an optical air thermometer for the airmass between. Same basic concept, but far less power, as a high-power laser vertical profiler (which can be used to determine air temp, pressure, and wind speed at discrete altitudes up to 100,000 feet).
_____________________________

Alan Sheets

Re: Passive Refrigeration and AC (3.00 / 0) (#11)
by asheets on Thu Sep 07, 2006 at 05:15:35 PM MST

Oh, and as an answer to your original question, my bet is a combination of evaporation, cooling throughs from the river, and high pressures.
_____________________________

Alan Sheets

Re: Passive Refrigeration and AC (3.00 / 0) (#12)
by asheets on Thu Sep 07, 2006 at 05:16:05 PM MST

and salt...
_____________________________

Alan Sheets
[ Parent ]

Re: Passive Refrigeration and AC (3.00 / 0) (#13)
by mikey ny on Sun Sep 10, 2006 at 06:44:57 AM MST

Scott,
try experimenting with a cad cell from an old oil burner. They sense the bright flame of the fire in the furnace and in the abscence of a flame it shuts down the burner for safty reasons. I know they will scence the sun because I experimented with one to make a solar tracker. Unfortunatly that experiment ( along with several others is on the back burner for now) never got completed.
Mike
Mr. Mikey... "I thought I made a mistake but I was wrong"

Passive Refrigeration and AC | 14 comments (14 topical)

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