I found a grossly oversized Hx here:

copper refrigerant pipe: $113
TURBOTEC | COILS, STEAM & WATER | 3-1/2 TON COAX COIL | Surplus City Liquidators

cupronickel refrigerant pipe: $208
TURBOTEC | COILS, STEAM & WATER | 4 TON COAX COIL | Surplus City Liquidators

Both are rated at 450 PSI working pressure (burst pressure much higher). Your water-source setup should run at much lower working pressure in cooling mode (450 PSI = 125 degF saturation temp, 100 degF Tsat = 317 PSI). In heating mode, pressure is not an issue (freeze-up is related to pump sizing).

OR

You could look into China and have one custom built for cheap. Some suppliers will pretty much design and build a single one-off part for you, given pertinent performance specs. Not very expensive, either.

http://www.alibaba.com/product-gs/15...Exchanger.html

Thanks Jeff,
I've been looking at those before, but, with shipping and tax they end up half what I paid for my heat pump. Looking for a more budget friendly option. Secondly, I understand that a grossly oversized single hx will destroy my precious compressor due to low speed/flow of R410a. I read that there are minimum flow rates for 410 due to lubrication issues. This is why my hx has 3 circuits with thin lines among other things. Can anybody comment on the minimum flow rate ? At least this is what I read and I am trying to avoid lubrication problems.

Indeed it looks like the Chinese market is a good candidate even price wise, some offer this hx with free shipping:
Aliexpress.com : Buy free shipping fish piano music game carpet Fashion Children's Educational Toys fish Music crawling mat, baby toys blanket from Reliable carpet stair suppliers on Ningbo Haishu Chosen Trade Co., Ltd.
Not sure if the specs are ok. Will keep looking.
If oversized, I understand it is better to have several smaller hxs in parallel due to min flow rate required for 410a.
Cheers,
F

Oil carrying problems are unlikely in a condenser due to liquid refrigerant being a good solvent. You can add a little R290 (refrigeration grade propane) to act as an oil carrier.

Many thanks for the input Mike. It is good know, however what if the coil becomes an evaporator ? I actually try to refrain from using those designations since they switch around. My outside hx will also be used for cooling/dehumidifying, therefore there will be gas flowing through it too, not just liquid. Should I still be concerned ?

The multiple paths and thin lines are a method used in r410 units because they can tolerate more pressure drop in the lines. Since the high side is so high pressure, the smaller lines do not hinder flow like in r22 systems. By using more smaller lines, the mfr's can maximize the surface area of active piping.

How do you know that this is true?

-AC

One of those Purdue research papers. I commented on and maybe cited the article in a past thread somewhere. It had to do with micro-tiny, rifled tube construction and performance optimizing specifically for r410a. I had commented "How will I hack a heat exchanger made out of cap tubes?"

I found some literature in a hurry: Micro-groove

main page

specific paper
http://www.microgroove.net/sites/def...6755_final.pdf

If I may expand somewhat on Jeff's comments:

R410A has roughly 40% greater saturation vapor density than R22. The higher working pressures allow smaller cross section in the same sense that high voltage lines permit smaller wire cross section.

This has multiple benefits. Smaller tubing has lower hoop stress for a given pressure, allowing for thinner walls. Thinner walls increase heat transfer and lower cost. More tubes in a given HX area further increase heat transfer. Higher fluid velocity also increases heat transfer.

R410A gets a bad rap because it doesn't work in old equipment. Systems designed for R410A can outperform R22 and R290.

Ref. " Effects of refrigerant properties on refrigerant performance" Prapainop and Suen. 2012

I'm still having trouble with this notion. I just don't see how higher pressure equates to lower friction ("the smaller lines do not hinder flow like in r22 systems").

The electrical metaphor isn't doing it for me either.

The rest makes perfect sense.

A well-thought response.

I tried to find a copy of the Prapainop and Suen paper you mentioned, but none of the links I tried were live.

Do you have a working link to the paper?

-AC