Heat exchanger coil material

[Lumberjack]

OK I will first admit I am a cheap skate and copper is expensive.

I was looking at plastic tubing and wondering if anyone has tried to make exchanger coils from it. Also if anyone might have an idea of how efficient the heat transfer of plastic compares to copper.

[Capt Slog]

I'm cheap too, but I don't think that plastic is going to make a good heat exchanger.

I suppose it depends on the application though, and how much area you can afford space wise.  If you want to transfer a lot of heat across a small area then you will have problems.

[GaryGary]

Hi,

STSS ( http://www.stsscoinc.com/ ) make open heat storage tanks and large, copper pipe coil heat exchangers.  I understand that they are now starting to offer pipe coil heat exchangers from PEX.

The thermal conductivity of copper is much, much, much greater than PEX, but this does not mater as much as one might think, because there is a slow moving layer of water just outside the pipe coil that limits the overall conductivity to much less than the copper itself.  So, copper is better, but not better by the ratio of the conductivity of copper and PEX.

Here is a little test I did on a coil of black poly tubing as a heat exchanger:

http://www.builditsolar.com/Experimental/DHWPond/Proto3/Performance/Performance.htm

But, as was mentioned, it depends a lot on what you want to use it for.

Gary

[electronbaby]

I would think it depends on the heat source fluid flow rate, and if the tubing was totally immersed in the secondary fluid to get a more complete transfer.  You will not come close to the performance of copper or stainless.

[Lumberjack]

I was planning on 4 - fifty foot copper loops in a two foot cube , Increasing the size is not really a problem. I did notice the stss coils are a lot longer - up to 180 foot. Back to the drawing board.

[scorman]

I would recommend wrapping cylindrical coils of 1/2"x50ft aluminum tubing

http://www.plumbersurplus.com/Cat/Aluminum-Utility-Tubing/269/List?attribute_value_string|Brand=D.O. +Smith

Easy to use compression fittings to connect to each other or copper water lines

A fraction of the cost of copper

Stew Corman from sunny Endicott

[scorman]

sorry , bad link:

http://www.plumbersurplus.com/Cat/Aluminum-Utility-Tubing/269/List?attribute_value_string|Brand=D.O.
+Smith

[Jon Miller]

Not sure what you plan to do with it,

But a good place to find well made CHEAP and somtimes FREE heat exchangers is in a gas combi boiler.

Not sure where you are but in the UK they are thrown away all over the place.

The internal heat exchanger is stainless steel!

have a look at it!

[BigBreaker]

Watch out for galvanic corrosion when you mix copper and aluminum.  It's best to stick with one metal if you can.

[steve82]

I agree with the above comment about gas combi boiler heat exchangers. We have recovered some 304 and 316L stainless steel heat exchangers from gas combi boilers and used for solar panels with good results. 304 offers little corrosion protection when compared to 316L exchangers.

[goodlifer]

We are moving to rural France in a year or so, and in order to keep costs down (we will be "nearly pensioners") I want to design a system which will incorporate the benefits of a compost heating system (sited in a greenhouse) with a solar water heater.We anticipate having an acre or two of land for growing vegetables and especially grass cuttings for the compost heap.

My idea is to use an old hot water cylinder with a secondary heating coil (copper) inside. The water in the cylinder would be heated by the compost, and the water in the secondary system (to heat old/2nd hand radiators) by a solar heater. A small pump (solar/battery powered?) in each circuit would ensure even heat distribution and enough pressure for a shower or bath.The secondary water system would need to be "treated" to prevent scaling.I would also put in an immersion heater connected to the mains for really cold weather.

The compost heater would need to be wide enough and deep enough to heat the water, but in any case the solar water heater circuit should help boost overall temperature.

I read about a system like this many years ago in an early US alternative energy magazine.I have read recently of others using coils of plastic pipe 1 1/2" diameter in a compost heap with excellent results, but I think if you can get hold of a HWC it makes connections easier and more manageable. Using different metals could cause other problems!

I would be grateful for comments,suggestions, potential problems etc.

You can post on the blog or directly to me at johnwinlow@talktalk.net

Thanks

[GaryGary]

Hi,

You may have seen these already, but here are a couple links to compost heat generation:

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#GreenhouseHeat

The compost ones are down the page a bit -- look for New Alchemy, Sustainable Urban Living, and Jean Pain.

The New Alchemy one is very complete with a lot of data from experiments they did.

I'm not clear on how you plan to use the radiators?

Its seems like solar heating is a bit less fussy a source of heat than compost, but I guess if you have a good steady supply of compost available it should work.

Not that I know a lot about this, but I would consider making your solar collector for hot water on the large side, which should give you 80+% solar heated water, and then use the compost just for greenhouse heating (rather than trying to combine the two)?

Gary