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stmbtwle

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Reply with quote  #41 
Just pulling your leg Hermit, sorry! Please keep us updated.
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Willie, Tampa Bay

mattie

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Reply with quote  #42 
No worries GH,
Its threads like this that keep my mind moving and help me understand the system better.
Stmbtwle one issue i see with a metal based collector is with thermal bridging and the resulting heat loss.Although a design to reduce this occuring could be thought out, all situations have a work around.
As for the glazing issue I have been working on an excel sheet regarding the use of argon,I mentioned this before but I haven't got it up to the standard of this site just yet as I been busy learning software, its something I have to wrap up properly
It may help with a few ideas in this area.
Regards Mattie


stmbtwle

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Reply with quote  #43 
Exactly Mattie, which is why I'm NOT doing it.  The temperatures you're talking about will wreck anything else.   Feel free to try it, but I have other things to do with my limited resources.

PS like the avatars!

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stmbtwle

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Reply with quote  #44 
Well as others have said today was a good day for testing (playing in the sun).  I've had my Aretha set in the back yard for days waiting for a break in the weather when I or the rest of the family wasn't sick.  (Seems it's been one or the other since Samhain.)

Anyway even though I had other plans Old Sol knocked on the window and told me to get my @$$ in gear, so I cranked everything up.  So here's the info:

Aretha collector with 2-stage HEX vs CPVC / flashing collector     Sq Ft7.27
      Water (lb)42
 Water Temp (F)  Insolation   
TimeArethaCPVC (btu/sq ft/hr)   
12:506670 390 Actual start, temps discounted 
13:208182 362 Start of calculations 
13:509595 368   
14:20106104 344   
14:50113111 311   
15:20120118 260   
15:50122120 224   
16:20124124 163 End of test 
        
Gain (F)4342Avg:295   
Water (lb):4242sq ft:7.27   
Total BTU18061764(calculated):2143   
Efficiency:84.27%82.31%   Something is NOT right here... 

The first set of readings were a bit odd so I ignored them and started my calculations with the second round.
Total temperature rise for 42# of water was 43°F, or 1806 BTU for the Aretha, and 42°F (1764 BTU) for the water tube.
Seems not bad for collectors just over 7 sq ft!

This is the first time my Aretha has outdone the reference water-tube collector!  Whoopee!  My idea of a two-stage HEX has apparently worked, as this is the same unit that kept coming close (but no cigar) before.  The fans are the same, the case is the same, the insulation and the absorber are the same.  The only change I made was the extra HEX.

What's really interesting though is the following readings taken midway through the test:

TimeAir inWater inAir outWater out
14:30135106109109

Note that while the input temperatures differ by nearly 30°F, the output temps are the same.  In the past I still had 10-20° of leftover heat in the air.  The second HEX (right behind the first) has now managed to scavenge that.   This is NOT an anomaly!  I took several readings to verify this and they all came out within a degree or so.

It works (I think) like this:  The heat exchangers are "stacked" one against the other, so as soon as the air leaves the first (hot) HEX it encounters the second (cooler) one,  which cools it down even further.  The water flows in the opposite direction, going through the second (cooler but still warm) HEX and is "preheated". Then it gets to the first HEX and meets the hot air just coming off the absorber plate.  Anyway whatever is going on it's working. This the first time I've gotten a 3° rise in water temperature in a single pass, too. I don't think I can do much better with the HEX (unless the auld Witch gives me a hand).

Now I have to address that big temperature difference in the air before and after the HEX.  Normally in an air collector if you increase the air speed you lower the output temp (that's the same as the INPUT to the HEX).  So I'm headed to the store tomorrow to pick up a couple 70cfm fans to replace the two 40s that are in there now.  That should give me about 50% more airflow I think, which will run the air around faster (and cooler) and it will go through the HEX more often, hopefully giving up more heat.  Weather being what it is, it may be a while but I'll get back with the results.

For those air guys that may be confused by my "inputs" and  "outputs", I'm talking about the HEX, not the collector.  The air NEVER leaves the collector, but it DOES enter and leave the HEX.  Think of an Aretha as two parts, the "absorber section" (the air part) and the HEX.  Air enters the absorber section just like any other air collector, gets heated, and leaves. It immediately goes "into" the HEX where it gives up its heat to the water and is then returned to the absorber section.  Just like an air collector on the side of your house, where the house is the HEX, exchanging the heat from the air to the people. There is NO ductwork (and no ductwork losses).

About the efficiency numbers:  To be honest I don't believe 'em and don't expect you to either.  They're what I got; something is not right, but what I don't know, yet.  Still working on that part.

Found it!  My insolation readings were in BTU/HR, but it was a THREE hour test.  So actual efficiency is 1/3, or 28% for the Aretha, and 27% for the CPVC.  Bear in mind this is the whole system, collector, tank, etc.


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Willie, Tampa Bay
mattie

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Reply with quote  #45 
What is your heat sink or HEX mainly composed of, is it aluminum fins and copper at the core? I have no doubts you know this already but ill mention anyway just in case,increasing the amount of copper should increase the cooling rate or heat transfer,is it then plausible to source radiators built with copper fins, do they exist or are aluminum fins the norm due to material costs?
Regards Mattie
stmbtwle

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Reply with quote  #46 
It is all aluminum. Here's a picture from an earlier model Aretha. This unit uses two of them, stacked.
http://rs71.pbsrc.com/albums/i133/stmbtwle/Solar%20collector/IMG_0142_zps6d9a1265.jpg~320x480

It's actually an oil cooler. A radiator assembly would never fit in my small experimental collectors.

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Willie, Tampa Bay
Garage_Hermit

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Reply with quote  #47 
Hey, Willie,  Nice Reading !

You are doing OK - 28% efficiency is almost as good as a coal-fired generating station (33%), so no sweat !

Also, very good results considering that the fans are not even matched for the HEX...

That is why I am hoping for great stuff from a Car Radiator
(but that is quite some way down the road...)

Have U considred getting a multispeed computer fan - like, with switch changing, say 3 speed, like this...
http://www.amazon.com/Antec-Tricool-Speed-120mm-Case/dp/B00314W992

Mebbe a bit more expensive than a fixed speed fan, BUT will allow you more freedom is selecting a speed (hi, medum or low...)
Just a thought !
 
G_H

just adding becos MUCH cheaper here...     http://www.newegg.ca/Product/Product.aspx?Item=N82E16835209005


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stmbtwle

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Reply with quote  #48 
Thanks! 

I chose the new fans big enough so I could put a speed control on them if need be (and probably will so I can experiment).  I've found several systems intended for computer cabinets, stereo cabinets, etc, even car fans like yours that will do it automatically.  All of them are DC which is fine.  It's AC controllers that are hard to find.  Maybe Julian will put his into production, I'd be interested.

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mattie

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Reply with quote  #49 
So with the ac fan you have greater output, the Italian's were using an arduino ,if you Google ac fan with PWM and arduino you should find the link I was about to send,Im on my phone here and cannot post it.
mattie

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Reply with quote  #50 
Hello again Stmbtwle
I dont have any experience working with Arduino
Would something like this help?

http://alan-parekh.com/projects/pwm-fan-controller/

Also i do not know if AC with the Arduino presents any unforeseen issues.I have seen other clips online like this where AC is used.



Seems to lots of info out there but nailing exactly what you need seems like it may require more looking.
I hope Im not taking up your time answering questions and instead some of this is useful to you [smile]

Regards Mattie
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