[Greenbuilding] Ground-source heat pumps

[Rob Tom]

On Thu, 11 Jan 2007 11:36:23 -0500, Leslie Moyer <Unschooler at atlasok.com>  
wrote:

> Steve Tripp wrote:
>> One thing I have noticed after talking to several General Contractors  
>> about geothermal systems is that there is not a lot of good information  
>> out there about reliability and performance.  10 years seems to be  
>> average that they give these systems to last before requiring major  
>> repairs.
>
> This just doesn't seem accurate to me--it goes against everything I've
> heard about them. I'm not connected to the industry at all


I'm not connected to the HVAC industry either but I can attest to the  
accuracy of Steve's assessment.

When I built my home about 20 years ago, I considered installing a GSHP.

Ultimately I decided that the $10-$20k initial cost (which included the  
cost of drilling a second well through bedrock for the discharge) for an  
auxiliary heating system that wouldn't see much use wasn't a very prudent  
investment.

One of my neighbours who built a couple of years after me did install a  
GSHP, the brand touted as being *the* most advanced and best in North  
America. The heat exchanger failed less than three years after the unit  
was installed. I think the repair cost was ~$2-3k IIRC. (Gimmee a break.  
It was almost 2 decades ago eh ?) Apparently there was some galvanic  
incompatibility with some of the components resulting in premature  
corrosion. We'll assume that problem has since been resolved.

Not long after I heard about that failure, I encountered a fellow on the  
other side of town (where they actually has a soil overburden) who had  
ripped out his GSHP in disgust and was offering it free to anyone who  
wanted it. The heat exchangers had failed three times at intervals not  
exceeding three years, at $#### each pop. The third failure was the straw  
that broke the camel's back for him.

I then started looking around for similar experiences and theirs was not  
unusual.

One failure might be a freak incident. Two heat exchanger failures might  
be a coincidence. Three or more has the indications of a pattern.

The most common explanation for the HX failures (according to the  
installation/repair contractors) is that the hard water in this area is to  
blame. I never got a more in-depth explanation as to why the hard water  
would be the culprit. Interestingly, an engineer in this area who was  
connected to the industry denied ever having heard of such failures. I  
introduced him to the GHSP owners that I had encountered and I'll bet his  
hearing improved.

In retrospect, my decision to install a big toaster (ie electric furnace @  
less than $400) as the Code-required, automatic auxiliary heating system  
seems to have been a good one. Never mind the fact that it has never been  
fired up in the over 20 years that it has been "in service".

To be fair, GSHP technolgy and design has undergone changes in the 20  
years since I first looked at them and no doubt, a lot of the bugs have  
probably (hopefully) been resolved satisfactorily.


=== * ===
Rob Tom
Kanata, Ontario, Canada
<A r c h i L o g i c   at  c h a f f y a h o o   dot   c a >
winnow the chaff from my edress in your reply