Author Topic: Adventures in Thermo-siphoning  (Read 11934 times)

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Greg_M

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Adventures in Thermo-siphoning
« on: September 26, 2012, 04:29:46 PM »
I looked at many ways to build an enclosure for my temp sensor and finally came up with this idea. I have used thermo-siphoning in the past to heat a boiler full of water from a wood stove, so I knew that the technique worked. Here's what I did...

I got 2' of 4" abs from Home Depot and mounted the sensor holder inside it using 1-1/2" threaded nylon standoffs from McMaster-Carr. That puts the sensor right in the middle of the tube at the bottom. This is looking at it from the bottom end.




I couldn't find any little chunks of 6" thin wall pvc so I had to buy a whole length and cut off a foot. I put 6 stainless set screws around the top and bottom to act as standoffs. The pvc would provide shade for the bottom of the abs.




I found a little smoke stack hat at Coast To Coast to keep the rain out. I used 3" bolts and some conduit hangers for mounting, to hold the whole thing to the pole. I got those at HD

So here it is mounted with the sensor in it. The idea is that as the sun heats the upper part (ABS) it causes the warm air to rise, which draws cool air in from the bottom and exhausts it at the top.




I can always add a little more ABS if there's not enough suck power. Or if it just refuses to work I can put a solar powered fan in the top.
Even if it doesn't work it was fun trying it.

http://www.datilcam.com/

« Last Edit: September 26, 2012, 04:37:41 PM by Greg_M »

Offline casa manana

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Re: Adventures in Thermo-siphoning
« Reply #1 on: September 26, 2012, 04:56:37 PM »
It also looks like a good design for a bat house.   :grin:

Offline DanS

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Re: Adventures in Thermo-siphoning
« Reply #2 on: September 26, 2012, 06:25:45 PM »
That is a good design and a proven one. A couple years ago I saw where someone built one using a ~5 foot section of white PVC. It was mounted vertically and the top third of the PVC was painted black. Sensor was mounted at the very bottom. Same principle but yours looks a lot neater. :-)

Greg_M

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Re: Adventures in Thermo-siphoning
« Reply #3 on: September 26, 2012, 09:03:43 PM »
The wife and I are both surprised at how well it draws.
No fan needed.

Offline SlowModem

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Re: Adventures in Thermo-siphoning
« Reply #4 on: September 26, 2012, 11:24:48 PM »
Now that's a better mousetrap!
Greg Whitehead
Ten Mile, TN USA

Offline Randall Kayfes

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Re: Adventures in Thermo-siphoning
« Reply #5 on: September 28, 2012, 02:41:48 AM »
I am impressed with the fit and finish!



Greg_M

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Re: Adventures in Thermo-siphoning
« Reply #6 on: September 28, 2012, 09:31:20 AM »
Thanks!
I think I might re-do the ABS part with a piece 3' long

No real reason other than it will make me feel better  :-)

Offline NeverDie

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Re: Adventures in Thermo-siphoning
« Reply #7 on: July 23, 2013, 12:42:00 AM »
Nice concept.  Thanks for posting the photo. 

How did you convince yourself that it's working adequately?  Or that wind gusts or turbulence isn't forcing hot hair down on occasion, creating overheated measurements in a possibly unforeseen way?

One way to find out empirically might be to temporarily mount a fan beneath it, but turned off most of the time.  Then, from time to time switch it on and see if the temperature changes.  If it does change, then use a longer piece of ABS and repeat the testing.

Or, alternately start with a really long tube of ABS, and keep cutting it down until the temperature changes.  Then, the length before the last cut (oops!  too late) was the right length.

Likewise, for the white pipe, how long is long enough?

Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #8 on: July 25, 2013, 08:59:08 PM »
I built one myself to try. I have two sections of PVC, the larger section on top is painted black and has a large number of holes drilled to let the hot air out at the top. The bottom of the smaller section (reducer adapts it to the larger upper section) is open at the bottom and the sensor is just inside. (Davis sensor on the Temp/Hum channel of my Anemometer Transmitter via Envoy 8x).

I too am pondering how to see that it is working. The temperatures seem reasonable for rooftop temps in the sun. (an experiment, not reported data)

I could borrow an IR camera and see if I can see the heat plumes coming out of the holes. Another possibility I was contemplating is some kind of water manometer (U-tube) between the top and bottom. This might show a pressure differential, maybe it would be sensitive enough to show a delta pressure.

Greg H.


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Offline DanS

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Re: Adventures in Thermo-siphoning
« Reply #9 on: July 25, 2013, 10:48:15 PM »
Get two small cheap thermometers, one at inlet of the white bottom PVC pipe, other at outlet of the black top PVC pipe.



I was thinking the same thing or those little digital thermometers that are a dime a dozen.

Offline piconut

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Re: Adventures in Thermo-siphoning
« Reply #10 on: August 05, 2013, 05:37:50 PM »
Doesn't the black tube artificially preheat the air inside of it and thus increase the temperature readings?
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Offline piconut

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Re: Adventures in Thermo-siphoning
« Reply #11 on: August 05, 2013, 05:49:19 PM »
I understand the "hot air rises" thing, the part that I'm not understanding is the fact that your temperature readings will be higher than normal.  Right?
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Offline DanS

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Re: Adventures in Thermo-siphoning
« Reply #12 on: August 05, 2013, 06:39:44 PM »
I understand the "hot air rises" thing, the part that I'm not understanding is the fact that your temperature readings will be higher than normal.  Right?

correct if the temp sensor is mounted up top in the black section. Being mounted near the bottom in the white section the sensor sees the ambient outside air as it's drawn in from the bottom. The heated air is only up in the black section and rises out the top causing a slight vacuum in the bottom.

Offline Skywatch

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Re: Adventures in Thermo-siphoning
« Reply #13 on: August 05, 2013, 08:38:43 PM »
Doesn't the black tube artificially preheat the air inside of it and thus increase the temperature readings?
I believe it's a convection factor. The Davis solar and UV sensors do something similar where the outer housing heats up and a gap between the outer housing and the sensor creates a convection pathway which allows natural cooling without the use of a fan. The joys of physics.  ;) At least that's my guess.
I live in an apartment and for the moment am not a home weather watcher.

I am a storm chaser.

Offline piconut

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Re: Adventures in Thermo-siphoning
« Reply #14 on: August 05, 2013, 10:20:43 PM »
D'oh!  Greg did say the sensor was at the bottom.  Although I read that, the first picture stuck in my head and I was thinking the sensor was at the top!  I guess if the sensor is at the bottom then the shading provided by the white PVC is enough to keep the bottom portion cool.   

From the physics perspective, I wind might cause air to flow downward.  Bernoulli's principle would imply that air blowing across the top and bottom openings of the unit would force air in the opposite direction (downward) due to the larger opening at the bottom (creating a lower pressure relative to the top) which would draw heated air downward toward the sensor.  Maybe the "rain cone" at the top also helps in that situation by creating slightly more lift than the larger bottom opening.

Interesting idea though.
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Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #15 on: August 05, 2013, 10:38:20 PM »
I'll try to get a better photo, the pic I posted for the GPS antenna (part of Blitzortung) doesn't show the tube very well. It is blocked by the mast but you can just barely see it poking above the Davis anemometer transmitter. (just to the left of the mast)



The vertical tube is the thermo-siphon. The top is painted black with the holes near the top just under the cap. The sensor is about 2" up from the bottom of the white section. During direct sunlight, it does get hotter. The sensor is about 18 inches above the shingles, which is closer than I would like. I also blocked off the ridge vent just under this area so that garage rafter heat doesn't get to it.

The main culprit here is probably the roof heat, not anything to do with the thermo-siphon. It can run several degrees hotter than my Temp/Hum station in the shade and the ISS also in the shade. 10F is the worst that I have seen so far. I can generate Excel plots from the data to show this.

Greg H.



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Offline DaleReid

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Re: Adventures in Thermo-siphoning
« Reply #16 on: August 05, 2013, 10:53:52 PM »
Greg,
For the amount of money you'll lose by blocking off that attic vent, you can buy another tripod and stick it up a ways, or move it a few more feet away.

Wow, I have found a tremendous difference in attic temps when we unblocked a vent that was pretty well closed off by some shoddy workers (the new kids on the crew got sent in where it was sweltering, and they really wanted out, so to heck with being neat, no one is going to see it up there anyway, right?)

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Offline piconut

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Re: Adventures in Thermo-siphoning
« Reply #17 on: August 05, 2013, 10:57:44 PM »
Greg...

What is the diameter of your thermo-siphon tube?  It appears to be much smaller than the 4" ABS plastic in the pictures at the top of this thread. 

Scott
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Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #18 on: August 06, 2013, 06:52:53 AM »
Greg,
For the amount of money you'll lose by blocking off that attic vent, you can buy another tripod and stick it up a ways, or move it a few more feet away.

Wow, I have found a tremendous difference in attic temps when we unblocked a vent that was pretty well closed off by some shoddy workers (the new kids on the crew got sent in where it was sweltering, and they really wanted out, so to heck with being neat, no one is going to see it up there anyway, right?)

I blocked about six inches worth of vent right under the siphon. The ridge vent runs the entire length of the garage, so the reduction in area is minimal.

Greg H.



Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
CWOP: CW4114 and KE8DAF-13
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Amateur Radio Callsign: KE8DAF

Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #19 on: August 06, 2013, 06:55:32 AM »
Greg...

What is the diameter of your thermo-siphon tube?  It appears to be much smaller than the 4" ABS plastic in the pictures at the top of this thread. 

Scott

The upper portion (painted black) is 2.5" PVC. There is a reducer to 1.5". I bought 2' sections at Home Depot.The larger top section is 2', I cut the white smaller section to 1' (so it would fit). There is also a cap on top. A picture is worth a thousand words, I'll try to get one as soon as work/weather allow.

Greg H.



Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
CWOP: CW4114 and KE8DAF-13
WU: KMIROGER7
Amateur Radio Callsign: KE8DAF

Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #20 on: August 11, 2013, 06:05:46 PM »
Greg...

What is the diameter of your thermo-siphon tube?  It appears to be much smaller than the 4" ABS plastic in the pictures at the top of this thread.  

Scott

The upper portion (painted black) is 2.5" PVC. There is a reducer to 1.5". I bought 2' sections at Home Depot.The larger top section is 2', I cut the white smaller section to 1' (so it would fit). There is also a cap on top. A picture is worth a thousand words, I'll try to get one as soon as work/weather allow.

Greg H.


Here is the photo of the thermo-siphon mounted on the Wx mast. (hanging out the window to take it :shock:)



The intake is just below the point where the three tripod legs converge. The top of the black portion is as high as it can go without hitting the bracket that stabilized the mast to the house. The Davis temp sensor is about an inch or so above the bottom.

Here is today's plot. It runs about 10F high in the sun.



Greg H.

« Last Edit: August 11, 2013, 06:15:04 PM by miraculon »


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CWOP: CW4114 and KE8DAF-13
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Amateur Radio Callsign: KE8DAF

Offline piconut

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Re: Adventures in Thermo-siphoning
« Reply #21 on: August 11, 2013, 06:30:18 PM »
Thanks for the image Greg!

Do you think if you made the diameter of the siphon greater that it may not affect the temperature readings as much? 
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Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #22 on: August 11, 2013, 07:04:05 PM »
Thanks for the image Greg!

Do you think if you made the diameter of the siphon greater that it may not affect the temperature readings as much? 

The idea being more black solar collection area for a greater delta T? Or the entire works? I don't know how much bigger will still fit on the mast.

My idea was to use the Davis temp sensor plugged into the Anemometer Transmitter, so I have to keep it fairly close to where it is.

Greg H.


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CWOP: CW4114 and KE8DAF-13
WU: KMIROGER7
Amateur Radio Callsign: KE8DAF

Offline piconut

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Re: Adventures in Thermo-siphoning
« Reply #23 on: August 13, 2013, 12:59:55 AM »
The idea being more black solar collection area for a greater delta T? Or the entire works? I don't know how much bigger will still fit on the mast.
I am thinking that a larger diameter tube would draw more air and reduce the effect of causing an inflated temperature reading.  I think you would need at least 4" diameter to lessen the effect. Is yours 2" in diameter?   I hope you understand...I'm not questioning your work, just trying to learn so that I can figure out what is going to work for my next setup.  I appreciate your time and help.


My idea was to use the Davis temp sensor plugged into the Anemometer Transmitter, so I have to keep it fairly close to where it is.

You raise an interesting point here.  I was told by Davis Instruments that when using a wireless anemometer sensor, you could not plug any other probes into it because you have to set it as the wind station in the main display panel.  Is this something you are going to do, or have you done it already?   I wanted to do the same thing and that is when I called Davis tech support and they said that it wouldn't pass the temperature data through to the display or logger.
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Offline miraculon

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Re: Adventures in Thermo-siphoning
« Reply #24 on: August 13, 2013, 09:02:27 AM »
I am using it with an Envoy 8x. It is the only way to read this sensor, unless I temporarily set the Anemometer Transmitter as the ISS on a console or standard Envoy.
Even on the Envoy 8x, I tell it that the Anemometer Transmitter is an ISS.
What Davis is telling you is correct.

I think that the upper painted-black portion of the thermo-siphon is 2.5".
Without totally relocating it, I can't go any larger.
I am thinking about putting something to block the sunlight near the sensor to see if that helps. I also want to measure pressure differential, or air flow when I get around to it.
When I first put up my old Dallas Semiconductor station, it had the temperature sensor built into the wind instrument housing. The error with that (which led me to remote the temp sensor) is about the same as the sensor in the siphon if I remember correctly.

No problem on the questions, this is just kind of a "use the sensor" experiment". It was originally purchased to measure garage temperature hoping that I could directly read it with existing consoles. Learned the hard way that you can't.

Greg H.


Greg
« Last Edit: August 23, 2013, 12:41:09 PM by miraculon »


Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
CWOP: CW4114 and KE8DAF-13
WU: KMIROGER7
Amateur Radio Callsign: KE8DAF

 

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