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Old 05-16-11, 05:53 PM   #21
Xringer
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The outside shell of Nigel's HX design is PVC type pipe. I think my HX will only run at
30 to 50 PSI on the water side. But, if case of a pressure regulator failure, it could go up to 90 PSI.
So, I'm a little reluctant to use the PVC design.
However, it's only water and it's loss wouldn't be a big deal..

I wonder how important the ID of the refrigerant tubing is.?.
Because, since I have a lot of room to work in,
I could use large ID PVC and build a much larger
version of the Nigel MK2 EX. Both fatter and longer.

That way, I could use standard 1/2" copper pipe and fittings, for the refrigerant. Makes building it easier. (If I have a very hot torch).

~~~~



I've noticed that many of the flat-plate EX units on Ebay have a max pressure limit of 435 PSI..
That kinda makes me wonder about using R410A, with it's high pressure.
Have you seen any that are rated to 800 PSI??

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Old 05-17-11, 10:46 AM   #22
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Quote:
Originally Posted by Xringer View Post
I've noticed that many of the flat-plate EX units on Ebay have a max pressure limit of 435 PSI.. That kinda makes me wonder about using R410A, with it's high pressure. Have you seen any that are rated to 800 PSI??
That would certainly be an issue.

Good to remember that R-290 runs at pressures LOWER than R-22 which runs LOWER than R-410a.

Too bad it's so darn flammable...

-AC
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Old 05-17-11, 12:16 PM   #23
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Not sure I'd be too keen using a plate hx. I did think about it at the beginning but discarded the idea due to the pressures involved. The other thing to bear in mind is the velocity the gas travelles through the system - I've no idea what that is mind, but reading anything written re refrigerants and they frown upon anything that impedes refrigerant flow.

I did start looking for a titanium or stainless steel hx designed for use with refrigerant/water but in the end opted for my own design. There are a few Chinese manufacturers but I didn't find any supplier of sensibly priced units.

Why not put a cheap pressure release valve in the water circuit to prevent over pressure or make the body out of some steel tube - a fire extinguisher or gas bottle springs to mind.

Nigel
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Old 05-17-11, 01:57 PM   #24
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I have a bunch of work to do on my old boiler. And replacing T&P relief valves is on the list.

Now that you mention it, I have seen some advice on how not to impede refrigerant flow. Good point!

There is a video of a 7,000 BTUh ASHP being installed here:
http://www.airgenerate.com/installation_demo.php
About 3/4 into the movie, they run a copper loop down inside the tank..

As you can see from this picture, it's a fairly long loop..


Just guessing, but if used this method, I would need a much longer R410A loop..
Maybe 3 or 4 times as long.?. Maybe too long for small ID tube.?.

I do have a few large access ports on the boiler that are not being used.
It might not be very difficult to install a large loop inside..

It would have to co-exist with the existing hot water coil.. Which isn't real small.


If it were possible to remove the coil hatch, maybe a refrigerant loop could
be hung in the center of the hot water loop.?. I wonder if they still sell
the hatch gasket for this thing?

Edge of hatch.
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Old 05-17-11, 02:24 PM   #25
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It's suprising what you can thread through a small hole! My latest, ongoing project is using a 100 litre electric water heater as the body of a heat exchanger.
So far I have made a coil (same form as MK2 heat exchanger, 3 coils 1/4" etc....) but with both entry and exit protruding from where the heating element used to live.


I have it piped up to a 5Kw Mitsubishi external unit. It works but at the moment suffers from overheating of the compressor. I'm planning to install a TXV to better control it. I may not progress much though until the autumn as it's getting pretty warm here in the day and I'd have to be out working on the roof in the sun... maybe a (rare!) cloudy day.






My idea is to have this exchanger in series (and before) my oil boiler as an 'accumulator'. My thinking is that I can pre-heat the water going to the boiler thereby reducing the consumption of oil.

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Old 05-17-11, 07:49 PM   #26
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Quote:
Originally Posted by Acuario View Post
Not sure I'd be too keen using a plate hx. I did think about it at the beginning but discarded the idea due to the pressures involved. The other thing to bear in mind is the velocity the gas travelles through the system - I've no idea what that is mind, but reading anything written re refrigerants and they frown upon anything that impedes refrigerant flow.
Nigel,

I think you are right to be cautious about pressures in a Brazed Plate HX. Pressure information is readily available from selection literature on the manufacturer's web site.

But I don't think that Brazed Plate HXs would be a problem, regarding friction losses... they're pretty well designed.

The main impediment I see is cost... I've been able to locate some pretty good deals on ebay.

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Old 05-17-11, 10:17 PM   #27
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Hey Nigel, that brazing job on the 3-into-1 is amazing.
It seems like the filler has to be filling some really large gaps between the cluster of tubes.


What equipment did you use to make those connections and what kind filler metal was used?

I have a thread about brazing already going at:
http://ecorenovator.org/forum/tools/...html#post13527

If, you have time to donate some of your expertise those of us interested,
some of us might want to copy your work.

Thanks,
Rich

Soldered many a pipe & cable, but never Brazed..
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Old 05-18-11, 01:13 AM   #28
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The connection comprises: 3 x 1/4 inch tubes and a 1/2 inch to 3/8 inch reducer. It takes a bit of effort to get the 3 tubes into the reducer but they will go eventually with a bit of persuasion!

The great thing about brazing rather than soldering is that you have much better control over the metal. Soldering using a normal blow torch and plumbing solder gives you very little control as the solder runs way too easily. With brazing you don't seem to have the same problems so it's much easier to fill voids, which is basically what I did.

I don't have any particularly specialised equipment - just a MAPP Gas blow torch. I generally start with a pre-fluxed solder rod to get the metal flowing then finish off with a non-fluxed rod to fill in.

I'm no expert, just determined!

Nigel
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Old 05-18-11, 08:05 AM   #29
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Thanks for the encouraging words Nigel. I have some MAPP and I'll try out some
silver filler when I can find some that's not too expensive.

This is the best price I could find so far.. Might even be useable too..
4.4 OZ. SILVER BRAZING SOLDER RODS 5% 15% 36 IN. LONG - eBay (item 200609174825 end time May-21-11 21:03:50 PDT)
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Old 07-14-11, 12:42 PM   #30
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I know I'm a bit late to this but Nigel's pool heater page doesn't seem to be there anymore. I just copied and pasted the address he put into Firefox with no luck. Anyone else have this problem?

Thanks,
Adam

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