Homemade spiral heat exchanger?

[jimnorth]

I was looking at the spiral tube copper heat exchangers sold by TARM / STSS for use in their heat storage tanks. Judging only by the pictures, it seems making one of these is doable for someone with experience sweating copper. Has anyone ever attempted to do this? Is there more to these than meets the eye?

Thanks,
Jim

.... forever looking to save $$$

 

[Eric Johnson]

They're just regular copper coils. Not much sweating involved, other than the connections. However these days, "save $$$" and "copper" don't belong in the same sentence.

 

[jimnorth]

I know copper is expensive, but I was just quoted $935 for a 180 foot DHW coil from the rep at HS TARM. Last I checked, copper tubing wasn't quite that expensive. Maybe I should check again?

 

[Eric Johnson]

Last time I checked, last fall, 1" soft copper tube (I believe it was Type M) was $5.50 per foot. I bet 3/4 is close to $3.

Four years ago I paid $1 a foot for 1" Type M rigid copper. Now it goes for around 3 times that.

 

[Bob Rohr]

I believe this tank and coil is what you are looking for. www.stsscoinc.com.

Consider a few shorter loops headered together. Like two 1" header pipes with four 50 foot coils of 1/2" copper. Similar to how a solar panel is built. Or the way Thermomax and Ergomax build their indirect tanks. That should bring the cost down, flow just as well a one 180' loop and actually have better heat exchange.

hr

 

[wsurfer49]

I have not priced copper lately either. I had planned on trying to make my own coils though and may still. Will have to see how much the manufactured runs vs the price of the pipe.

I found a few books on the subject a few years ago and the way they described making the coil was to fill the tubing with sand and seal off the ends, the sand will prevent the copper from kinking. Sounds like a good idea to me.

Rob

 

[bbb123]

Mine has 2 180' x 3/4" for HX and one for DH. As far as DIY there is nothing to them just bend them around something solder ends and 3 or 4 1/2 inch supports up middle.

 

[jimnorth]

Mine has 2 180' x 3/4" for HX and one for DH. As far as DIY there is nothing to them just bend them around something solder ends and 3 or 4 1/2 inch supports up middle.

Did you make you own coils, or buy them with the tank?

 

[bbb123]

They came with the tank from Tarm I would have made them if I had known what they were. Heat storage was a foreign language to me 2 years ago (no hearth.com/boilerroom). Knowing what I know now I would build a tank and HX (wish I put solar in to). If I remember the copper coils were not alot more than the going copper price so it wasn't that big of deal.

 

[Bob Rohr]

Skip the sand, save it for the kids sandbox, or liter box You really don't want any residual sand in your pumps or components. Soft copper will easily bend around a barrel or drum for instance.

Actually it comes in a nice coil. Just pull it apart and make some brackets to hold the spacing you want.

hr

 

[mikeyny]

Master of Sparks,

DITTO,

That's just too easy.

 

[Nofossil]

I just made a wooden form and bent it around that. I used 4 pieces of 1/2" type M as vertical supports. I attached the verticals by lashing with copper wire and soldering.

 

[Tarmsolo60]

I just made a wooden form and bent it around that. I used 4 pieces of 1/2" type M as vertical supports. I attached the verticals by lashing with copper wire and soldering.

Same thing i did pretty much, 22" diameter is what the coils are as per tarm, I used 3 pieces of 3/4 L for vertical supports and utilised one of them to feed the bottom of the coil. Pretty easy to make.

 

[WRVERMONT]

I made a wood form and wrapped copper around them. Worked really well! Just a note about spiral coils. If there is enough space in your tank, make more coils (piped in parallel) each having a shorter length. The same heat transfer can be accomplished with less head pressure. Better heat exchange efficiency. You can also put one coil within another to save space. For example you could make three 60' 3/4" soft copper coils that nest together then pipe them parallel to each other. You end up with a higher flow exchanger. The real challenge for these exchangers is the PRICE OF COPPER!

 

[drizler]

I think the price of copper has come down some lately. A couple years I was marveling at the cost of a stick of 3/4 copper at Lowes for around 22 and tax. I saw it was down to something in the neighborhood of 18 bucks. Still sucks .

 

[cguida]

Does anyone have any thoughts about the trade-offs between copper coils and flat plate heat exchangers?

SSTS reports that their 120 foot coil costs about $660, and the 180 foot coil costs about $830. They recommend two coils, plus shipping.

So it adds up pretty fast.

On the other hand, a 12x5inch 40 plate heat exchanger on ebay costs about 270, including shipping.

That is a pretty compelling cost difference. So why do people still use copper? What am I missing?

 

[drizler]

I just swung by Lowes last night and its now $16 and some change for a stick, definitely coming down.

 

[Eric Johnson]

Does anyone have any thoughts about the trade-offs between copper coils and flat plate heat exchangers?

SSTS reports that their 120 foot coil costs about $660, and the 180 foot coil costs about $830. They recommend two coils, plus shipping.

So it adds up pretty fast.

On the other hand, a 12x5inch 40 plate heat exchanger on ebay costs about 270, including shipping.

That is a pretty compelling cost difference. So why do people still use copper? What am I missing?

There are some interesting discussions here about using a flat plate heat exchanger instead of a coil or some other in-tank hx. Basically, you need to pump water through both sides of a flat plate, and then you have to pipe the tank so that you can both store and recover heat when you need to. It's easier with an in-tank hx but the price differential is, as you point out, a compelling consideration. Search "flat plate" and you'll find the threads I'm talking about.

 

[SteveJ]

I think the main advantages of copper coils over flat plate heat exchangers in storage applications are:
1. Heat stratification - see https://www.hearth.com/talk/threads/13844/
2. No additional pump required on the storage side - important for thos of us off-grid!!

As Eric points out there are several discussions on the flat plate versus copper coils - search on storage, stratification to get an idea.

Others can elaborate more.

Hope this helps

 

[chuck172]

Looking into building my own copper coil HX's coils. Current STSS price is $1,150.00 per 180' . Need 3. I can buy 100' type L copper coils for $300.00
Totals:
STSS- $3,450.00
540' copper- $1,650.00
Same material, Doesn't seem very hard to do.
I'd like to hear some success stories here:

 

[DaveBP]

I'm going to be building my own heat storage tank to go with my Tarm 40 (picking it up next week) and would like to build my own heat exchangers if I decide the copper coils are the way to go. STSS's markup seems pretty steep for the sort of work required. Comparing prices at CopperTubingSales.com it looks like a nearly 100% margin. I spoke to the owner at STSS about a year ago and he indicated that 3/4 dia. is the most effective compromise between friction, exchange surface per foot and cost of material. The tables I've looked at make me think he was being pretty candid about that. They have done a lot of research and serious testing over the years. One question I have is what are the trade-offs between the different grades of tubing in this kind of application. Refrigeration tubing is 25% thinner wall for 40% less cost (.045/.035,$300/$180). It's rated for 260 lbs. pressure at 400 F. That sure ought to be adequate. What I don't know from experience is how you solder it together. Standard fittings don't work on it because of the different O.D. Is it trickier to work with for those of us who don't have surgeon's fine touch? Flat plates are really cool looking but they require another circulator and a reversible one at that to use the same HX to extract the heat from storage and I haven't yet seen a definitive answer on how big they need to be. My intuition is that the fittings to and from the HX should be the same size as the pipe from the boiler, 1 1/4 in my case. Flat plate HXs that size aren't so cheap, even on Ebay. I like the simplicity of the copper coils, but I sure would like to spend as little as possible on precious metals. Anybody out there with experience working with the different tubings? Is type 'L' worth the extra cost? For my first post I've rambled a bit, haven't I?

 

[NHFarmer]

Dave, Welcome, I am also looking to have my Tarm Solo40,delivered next week.Also building my own storage,7' diam,1000 gal.I have been going between flat plates and coils.I haven't decided yet but the refrigeration tubing sounds interesting,sorry I can't offer any working experience but I am sure someone will.

 

[Chris S]

L tubing is a thicker wall than M , and usually easy to find in rolls which would very quickly become... your coil.

How about looking for some actual coils from discarded idirect water heaters, and using them? A good percentage of the time- the tank leaks but the coil Is sill good.
we usually sell them for scrap.... maybe a business venture is available here

 

[chuck172]

STSS uses L copper. I think I'd like to have that thickness. Pinholes can be a big problem that can occur if the water in the tank isn't properly conditioned. (acidic?)

I understand STSS uses 20" diameter coils at 43" high. I wonder if they use any type of stand or just sit them on their tank liner. They also have a way that automatically bleeds the coils of air.
Uncoil the 100' type L copper to 20" dia. Using a coupling or a swage tool to connect and come out to 180' Spreading out the coil vertically to 43" soldering straight copper tubing as stiffiners.
Sounds like a plan.

 

[jebatty]

I remain puzzled over the fascination with large (STSS style) coil hx's when the low relative price and high efficiency of plate hx's is so well known. Without repeating my prior posts on this topic, all I will add is that the cost of an extra circ pump appears to be the primary objection. Addressing that objection:

1) Plate hx on ebay about $225.
2) Taco 007 on ebay about $50.
3) Elec draw of 007 is about 85 watts. Assuming 6 hrs/day, which for my extreme northern clime and heating 1000 gal of storage would be average (some days longer, some shorter), that amounts to 15kwh/mo, or $1.40/mo at our $0.09 rate.

Chuck172 reports cost of copper (I assume 3/4", which I think is STSS) to make your own coils to duplicate STSS: 540’ copper- $1,650.00.

The math: $1650 - $225 - $50 = $1375 / $1.40 = 982 mos = 8.5 years of operation before payback on coils for my installation. If I take that $1375 and invest it at 3% (on average can do much better than this), that is $41.25/hr, and my electric cost (generous) is $1.40 x 6 = $8.40 per year (six months of heating).

Simplicity and time: a plate hx over making coils is no contest.

Seems to be that the cost and operation of an extra circ pump as an objection to the plate hx is based on erroneous assumptions.