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Old 10-03-11, 08:57 AM   #1
Xringer
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Default Desuperheater add-on for Mini-Split?

Aquefier R6K-HP-V-F-410 Hot Water Energy Saver Used With 1.5 to 5 Ton R-410A Refrigerant AC or Heat Pumps

I wonder what's under that insulation? Is it just two copper pipes, touching each other?
Or, do they solder them at the contact points?




PDFs over here:
Aquefier R6K-HP-V-F-410 Installation Instructions and Product Brochures

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Old 10-03-11, 09:50 AM   #2
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I've used some of those where the two pipes are simply bonded together and wrapped in insulation like the one you show. I have one that looks just like yours except the entire coil is encased in a foam block. All of those I've autopsied after failure had the tubes bonded together.

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Old 10-03-11, 10:02 AM   #3
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I was thinking along the lines of a DIY project to make one of these boxes.

One idea was to lay out both pipes side-by-side and wrap them tightly
together with metal flashing. Maybe 1/16" thick copper or aluminum.
And then pack them with sand and bend them into a neat coil. & insulate..

When you did the autopsies, what was the most common cause of failure?
Mineral deposits?

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Old 10-03-11, 08:23 PM   #4
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How about one of these DIY?

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Old 10-03-11, 09:22 PM   #5
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That looks pretty hard to make. I'll bet they have a machine that makes those bends!
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Old 10-03-11, 09:31 PM   #6
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That looks pretty hard to make. I'll bet they have a machine that makes those bends!
I used a conduit bender to bend one of these things... not so difficult.

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Old 10-04-11, 08:50 AM   #7
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Surprisingly, the failures are almost always on the freon loop. Generally a pin hole or split next to the joint where the tubes bond together. Heat, I assume exacerbated a fault in the tubing itself. I have also seen a similar fault in the cooling tubing. But remember, we use them for research applications here, so they're not always well treated or operated within factory specifications. The ones I use myself are all used purchased at surplus auctions and removed from salvage equipment. I have three in operation that have never caused a problem.

If I were to attempt to make one of these myself I'd snake a smaller tube through a larger one and roll it up. I have seen a successful homemade one however in a friends automated beer brewing system. He laid the two tubes side by side flat on a table, soldered them every foot or so, smeared them up with heat transfer compound and wrapped them in some rubbery tape of some kind. He then rolled it up and stuck it in a 5 gallon steel bucket and filled it with foam. The tubing was simply rolled around a piece of sonotube and zip tied together. Seems to work.
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Old 10-04-11, 10:09 AM   #8
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That DIY HX method seems sound, but wouldn't solder break during the bending?
And, if you brazed, the joints might be so stiff they would stress the tubes.
Plus, the area of contact between the two tubes is very small.

IMHO, if you put them side-by-side and wrapped (like you would tape) them
together using a roll of thin sheet metal (copper or aluminum),
the conductive 'tape' would really enhance the transfer rate.

The rubber insulation tape over the outside, would hold the conductive wrap
tightly to the tubes as they would being bent.
Some durable heat transfer compound under the foil might help also.
But, it should be some long-life stuff, that won't dry up and turn into insulation..

That Bucket-o-Foam idea is a good one.. I was thinking of building a box
out of blue foam insulation (that's what we use at work).
I would leak test for pin-holes before starting, and also before shooting the foam into the bucket..

Cheers,
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Old 10-04-11, 10:32 AM   #9
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Quote:
Originally Posted by Xringer View Post
That DIY HX method seems sound, but wouldn't solder break during the bending?
And, if you brazed, the joints might be so stiff they would stress the tubes.
Plus, the area of contact between the two tubes is very small.

IMHO, if you put them side-by-side and wrapped (like you would tape) them
together using a roll of thin sheet metal (copper or aluminum),
the conductive 'tape' would really enhance the transfer rate.

The rubber insulation tape over the outside, would hold the conductive wrap
tightly to the tubes as they would being bent.
Some durable heat transfer compound under the foil might help also.
But, it should be some long-life stuff, that won't dry up and turn into insulation..

That Bucket-o-Foam idea is a good one.. I was thinking of building a box
out of blue foam insulation (that's what we use at work).
I would leak test for pin-holes before starting, and also before shooting the foam into the bucket..

Cheers,
Rich
Before you start buying copper and brazing and bending and foaming, you might want to re-check small brazed plate HXs on ebay.

When I built my tube-in-tube HX, the cost of the copper alone was nearly as much as a complete stainless brazed plate unit. The brazed plate was smaller and more efficient, too.

If you're doing de-superheat, you won't need a very big HX.

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Old 10-04-11, 11:03 AM   #10
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I've seen the copper prices.. Not good!
But, as I've said before, these types of HXs aren't super safe, if a pin hole develops in the barrier.
In the case of 4.3 pounds of R410A, that could dump ~500 PSI into my heating system.

The gas would bubble into my HS Tarm boiler, expanding in the heat and possibly
building up damaging pressure, before the T&P valve popped open.
The pressure would also be felt in the baseboards upstairs. Thin copper.
In the case of R-290, the risk of an HX cross leak would be unacceptable to most people.

So, the Bucket HX's double-wall construction seems most suitable to me.
The chances of high pressure refrigerant getting into the water loop are a million to one.
IMHO, Double-wall would be the only way to go, if you wanted to connect directly to your drinking water lines.

Cheers,
Rich

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