Posted By DGF on 07 Mar 2012 01:40 PM
.... 2 mechanical systems (a water pump and a compresser) ought to be more
prone to fail, and lead to additional maintenance, then just a compresser alone.

That logic is fine IF the systems being compared have similar probability
of failure AND similar cost/consequences in the event of failure.

A heat-fused HDPE loop is about as inert as anything I can think of,
and certainly less susceptible to corrosion/leaks than buried copper
pipe. Yes, the circ pump is a potential point of failure -- but pump
replacement is a simple repair that won't break the bank.

Looby

Apprecitate the feedback, and explaining what you meant, docjenser

It really is not a big deal going through another heat exchanger and to have a circulation pump on it. Yes, there is an efficiency penalty, but again, the W-A heatpumps seem to run at a higher COP despite the addition of the second heat exchange. I don't think the ice is an issue. Water sourced systems freeze the ground all the time, too. The issue is that the ground cannot keep up and is not 25-30F but 15F or less, killing efficiency and possibly compressors.

A heat-fused HDPE loop is about as inert as anything I can think of,
and certainly less susceptible to corrosion/leaks than buried copper
pipe. Yes, the circ pump is a potential point of failure -- but pump
replacement is a simple repair that won't break the bank.

Copper pipe corrosion appears to be a non-issue the majority of the time. Thats what I've read anyway. Seems like it could be ruled out as a problem with soil acidity tests, whatever the case.

Your points, while fine, just point out why a water pump is "not all that bad". I'm curious to know where the water pump actually adds value. Or in other words, sure - maybe it simply will never be a problem - but I don't yet grasp why having it in the first place means anything, vs not having it at all.

I'm guessing there's some solid reason, and not just that 98% of everyone else does it. Underground refrigerant issues, or perhaps compressor issues on larger scales?.

Posted By DGF on 10 Mar 2012 01:04 PM
Copper pipe corrosion appears to be a non-issue the majority of the time.

HDPE pipe corrosion is guaranteed to be a non-issue ALL of the time.
No ifs, no ands, no buts, no pH tests, no contractor judgement calls.

I'm curious to know where the water pump actually adds value.

It eliminates a potentially catastrophic point-of-failure. IMO, a very
small price to pay for bulletproof reliability of the least accessible
subsystem. (Curiously, I've heard no one expressing "concerns"
about the circ pumps in old-school hot water radiator systems.)

I'm guessing there's some solid reason ...

- Limited in-ground heat exchanger size -- due to oil-return issues.
- Large quantities of refrigerant = code/safety/leak-detector issues.
- No possibility of factory-sealed, factory-tested refrigerant system.

Posted By DGF on 10 Mar 2012 01:04 PM
 
Copper pipe corrosion appears to be a non-issue the majority of the time.
With HDPE corrosion is a non-issue 100% of the time.

Your points, while fine, just point out why a water pump is "not all that bad". I'm curious to know where the water pump actually adds value.

I think it does, while no one discusses it, Looby touched on how inexpensive circ. pump replacement is. Would you expect a refrigeration circuit often 1,000 feet longer (than water source equipment) improves the life expectancy of compressor? Would you expect it costs more to replace a compressor than a fractional horse circulator?
DX does not take away the circulation of a transfer agent through ground loops it simply uses a larger more expensive (to purchase/replace/operate) pump (compressor).

I'm guessing there's some solid reason, and not just that 98% of everyone else does it. Underground refrigerant issues, or perhaps compressor issues on larger scales?.

DGF, I have created a seperate thread to once again sum up the short-comings of DX as it is lengthy.

It is easier (less pumping power required) to pressurize and send an incompressible liquid down a long pipe than to do the same with a compressible gas (refrigerant)

Maybe someday someone will make a DX system that uses HDPE or PEX pipe and a low cost propane mix refrigerant. All external to the home (for safety reasons).