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stmbtwle

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Reply with quote  #41 
Latest pix: 

Front view with new HEX.


Rear view
[

unfinished duct showing HEX, plumbing, and fans (note unit is upside down here)


Preliminary tests indicate a MUCH greater air flow through the larger HEX.  Will have to test it to see how this relates to heat transfer.

The whole thing (with the pump) draws about .6 amps or 10 watts.   



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Willie, Tampa Bay

stmbtwle

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Reply with quote  #42 
First actual test today was a lot better though still not what I would like.  Air temperature rise in the collector is about 20-24° F, half what it was with the other HEX, so I'm getting much better air flow.  water temp rise is 1-2°, about the same as before.  I left it out in the yard, tomorrow I'll play with the fan speed and see if it makes a difference.  



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Willie, Tampa Bay
Thor

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Reply with quote  #43 
lookin good wille... getting closer to what I was thinking about, so you get 1 degree of temp rise in water flow at what gpm?
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stmbtwle

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Reply with quote  #44 
Thanks!

Actually I think get more than that, something on the order of 1.5° or 2°, at about .7 gpm. I determined one night that the output sensor was reading low, so today I put a correction constant into the software. I also changed it so it would read to two decimals for more accuracy. Another test soon.

I know it doesn't seem like much but it adds up fast, and I think it's enough for my purposes. If I get too much heat it will just have to be shut off anyway, and then it will stagnate.

I've also installed a snap switch, so once I get it installed I can remove the Arduino and connect the switch. The hot tub runs at a pretty constant (and relatively low) temperature so I think it'll work.

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Willie, Tampa Bay
stmbtwle

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Reply with quote  #45 
Well it's temporarily hooked up to the hot tub, running off a solar panel and the snap switch, pretty idiot proof (I think).  We'll see how well it does.  I need to redo the duct in the back, but otherwise it's ready to go.

Generally a snap switch doesn't work that well with a water collector, but I think it will in this case as the hot tub has a lot of mass and runs at a pretty constant temperature.  Also the snap switch is measuring the AIR temperature inside the collector, not the water temperature.  And it's solar powered so I KNOW it will shut off when the sun goes down.


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Willie, Tampa Bay
stmbtwle

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Reply with quote  #46 
Raised my 250 gal hot tub 2° yesterday, and I only lost 1° overnight, so it's at least gaining. I'd like to see more, but it's a start.
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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #47 
Willie, you got any way to measure the water flow rate through the HEX?

You got 4000 BTUs yesterday, how many hours did it take you to do that?

The automotive motor and fan that matches the heater core, should provide enough pressure to get a correct air flow through the heater core, and you would have variable speed.

When considering an HEX, look up the motor and fan that matches it. It will give you an idea what its is going to take to make that HEX work.

Have you checked the collector for air leaks using soap and water? A lot of little ones add up.

Rick H Parker

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Rick H Parker
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stmbtwle

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Reply with quote  #48 
I can check it easily enough by running it into a measured bucket and timing it, though probably around a gallon a minute. It doesn't really make much difference. A smaller pump will get a higher temp rise in the HEX but at reduced flow. The BTUs into the tub are the same.

Probably around 8 hours, but for part of that the input would have been minimal, realistically say 6.

The heater fan is out of the question, it draws 5 amps. No problem when you have a V8 providing the power, but for PV?

No attempt was made to make the collector airtight, and there are holes drilled for wires, hoses, sensors, etc. It's a closed system though and not under any pressure or vacuum. Leakage would be minimal.

Turned out to be little less than a gallon a minute, works out to 53 gph.

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Rick H Parker

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Reply with quote  #49 
"The heater fan is out of the question, it draws 5 amps. No problem when you have a V8 providing the power, but for PV?"

12V*5A = 60 watts.

A 100 watt panel and 10 amp charge controller to shape the output should do it. ~$100 - $120 total.

Rick H Parker

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Rick H Parker
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stmbtwle

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Reply with quote  #50 
That's as much as I have invested in the entire collector. What's the point? The PV panel would be bigger than the collector.

I could buy two such panels and a resistance heater and probably heat the tub directly. It would be a whole lot simpler.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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