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stmbtwle

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Reply with quote  #1 
I've been fascinated by the Zero Pass concept so decided to try an Aretha version.
This one is a center-feed with the back screen (solarshade screen) laying right on the polyiso.  The front screen is a bit more than an inch above the back one.  The airflow is out-and-back sort of a split dual pass.  See diagram.
zero pass Aretha.png 
Sorry I don't have more photos, but the camera was misbehaving yesterday when I took most of them.  

IMG_0596.JPG 
under construction with adjustable mount

IMG_0597.JPG 
HEX and fan 


IMG_0598.JPG 
Complete less glazing...

The unit is going to be mounted on the roof of my screen room which is white metal, so I expect to get some reflected heat from that, especially in the winter.  The adjustable mount is so I can orient the collector in the winter and put it near vertical in the summer.  It will be used to heat my hot tub.




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Willie, Tampa Bay

gbwillson

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Reply with quote  #2 
Looks good Willie!

Just a thought...Assuming the collector box is 4x8, isn't the flow air of air somewhat limited to one side as the air flows as if the unit were 2 separate 4x4 units sharing a single fan and hex?
Like this:OO


I think the idea of having the hex and fan perpendicular to the collector box, with a longer path through the collector was mentioned a while back. A longer flow path would allow the air to get hotter before being transferred to the water via the hex. 

In any case, I'll be watching closely to see how your numbers compare to previous units.

Greg in MN






stmbtwle

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Reply with quote  #3 
True, the shorter path might not heat the air up hotter than the long path, but then again the air is moving more slowly. The total surface area is the same, and the CFM is the same or possibly a little higher (same fan, less resistance) so I expect the heat capture to be about the same. Heat transfer into the water may not be as good though, as this unit is using a heater core instead of 2 oil coolers. We'll see.

Again this a proof-of-concept. I'm trying out the ZP concept as well as the "vortex" circulation pattern. I had noted that the later model Italian Arethas were roughly square, with the input to one side. I never could get any info on how well they worked, though.

Having the HEX and fan perpendicular to the collector box probably would be better, but it would mean a deeper box to accommodate them, which I'm trying to avoid. Then there is the Aretha Molinari, which is an air collector with a remote HEX assembly.

One thing about the Arethas is that they are not single-pass collectors. The air is recirculated, so any heat not picked up by the air or transferred to the water on first "pass" simply goes around again... sorta like a traffic roundabout. Eventually it reaches equilibrium.

The HEX in my previous Aretha was destroyed by the pool chemicals in the water, so I still have to make a HEX to go in the tub, probably just a couple lengths of cpvc along the side of the tub.

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gbwillson

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How fast will the air be moving through this collector? 
stmbtwle

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Beats me. I think the fan is rated at 70 cfm. The entire working air space of the 2 x 4 collector is only about a cubic foot, so a "change" about once a second. Air channel is 11" x 1.5" (x 2). That works out to what?

A problem with an ARETHA: You can get higher air temperatures with a LOWER air flow as with all collectors, but the HEX works best with a HIGHER air flow. I'm not sure how to address that, or if it even matters. Suggestions?

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gbwillson

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Reply with quote  #6 
Bigger fan to move more air? The ZP works more efficiently with higher flow rates as this helps keep the temps down. As you said earlier, the air path may be short, but the air is constantly recirculating, so the air could get really hot unless the HEX can draw off enough heat. And since the HEX works best with high flow, your collector should do well. Do you have a same-sized ARETHA with a different absorber design for comparison? In any case too much heat produced is always a good problem to have. 

Greg in MN
stmbtwle

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Reply with quote  #7 
Yes my experiments a couple years ago indicated that without airflow through the HEX it gets really hot really fast. Water flow doesn't seem to matter as much since water holds so much more heat.

It's pretty much ready for testing, just need to get some hose so I can hook the pump up. Probably next week, and go from there.

No I don't have another one to test against.

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Willie, Tampa Bay
gbwillson

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Reply with quote  #8 
How much of a water temp increase were you getting?

Greg in MN
stmbtwle

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Reply with quote  #9 
One picture is worth a lot of words:
https://simplysolar.supporttopics.com/post/show_single_post?pid=1286697333&postcount=78&forum=268126

I still have that Arduino control unit, so I'll simply hook it up to the new Aretha.

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gbwillson

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Reply with quote  #10 
Good to have! Does it log data too?

Greg
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