I have continued to gently (uncommon for me) voice my DX concerns but feel obliged to sum them up given recent rebirth of the topic.

Want a DX system? Ask yourself these questions:

1) Do I want a system that is not recognized by the International Code Council?

   It is true, in Michigan for instance if you install a geo-loop system the code requires a hydrostatic test of loop system......show of hands, who wants to run water in a refrigerant circuit hundreds of feet long? How do you get it all out to avoid damage to the compressor?

2) Do I want a system in my home that (often) the same code requires an industrial type machinery room for?

   Also true. Though the International Mechanical and Residential Codes apparently haven't heard of Direct Exchange Heat Pumps, they do identify that once over X lbs/ft3 of  X refrigerant, one must have a machinery room with ventilation, refrigerant leak alarm etc. Let's say it again, the quantity of refrigerant in your DX system if leaked, could be injurious to the occupants of your home- therefore industrial measures (and related expenses are required).

3) Do I want a system that eliminates an inexpensive circulator pump, simultaneously increasing the workload of an expensive compressor?

   While seldom mentioned, don't you think adding (sometimes) 1,000 extra feet to a refrigeration circuit might tax a compressor a little more?

4) Do you want to put geo loops in the yard that very seldom corrode (if proper protocols are followed) or the ones that never do?

   I grow weary of water source guys hype of loop corrosion or refrigerant leaks in the ground. A Good DX installer will mitigate the possibility to almost nothing. That said, HDPE fears only impact and sunlight.

5) Do you want a system that is 3% of the market, or 97%?

   Seriously if you were buying a car- one to take you to work everyday, are you going to get the one that often costs more, has a smaller dealer/tech/part network just because the salesman says you might save $90 a year in gas (based on laboratory tests not actual driving)?

6) Do you want a system where most manufacturers, license holders etc have not held the product line for 10 + years?

   Go ahead check some domain registrations etc. and please don't bring up the sale of FHP to Bosch, I don't think Bosch is in the same catagory as XYZ DX, LLC.

7) Do you want a system where most dealer/installers have spent less than 5 years with the product?

8) Do you want a system that attracts more new guys since they don't have to buy new tools?

   Watersource manufacturers aren't particularly better at vetting new dealers, but extra tools and less finicky installations suggest greater financial security and less opportunity for mishap on installation.

9) Do you want a system with 5 times the refrigerant in it?

   Things made by people and installed by people do fail. If you get a leak on a your system do you want the one that has less or more- like maybe $800 more to leak out?

10) Do you want the system that tears up more of your lawn?

   While DX boasts of smaller foot prints, what they mean is less pipe. Sometimes this is more holes however or longer trenches etc.

11) Do you want the system with less loopfield flexibility?

   DX loopfields are refrigeration circuits that ave a prescribed length and pitch- coloring outside those lines may interfere with compressor's oil recovery harming the equipment. Water loops can follow the grade (saving excavation on hilly lots) or be increased where dry soil is present.


Do you have DX in your home now? Do not despair. 

Systems in my AO have been up and running more than 20 years.

Efficiency while ultimately hindered by ground thermoconductivity is still quite good.

Everything that has refrigerant in your home is potentially Injurious to the occupants. That a DX system has more suggests no greater risk of leak occurance, and injury is unlikely.

Greater sales today will hopefully keep some of these guys around for parts etc.

Who sells DX? With all this in mind why would anyone want to sell DX equipment? There are essentially 3 types of companies:

A) Tax credit band wagon guy- 

   Often low bank prefering system with less business start-up costs (i.e. fusion tools, flush carts etc.)

B) Marketing minded guy-

   "everyone is selling those systems for X price, if I'm the only one selling this system I can charge a more premium price."

C) Old geo guy trying out new technology, perhaps thinking of a distributorship opportunity down the road.

Or it may be some combination of the 3. My decision after training in 2 different systems (kinda a combination B and C guy)- I made friends in that industry in MN that I trust and would like to support but for now I must wait and see. I have not decided not to ever sell DX.
I had to ask myself "why is the biggest dealer of the biggest distributor of X brand, dropping the product in favor of water source?....and why did that same distributor just take on a water source product?" Geo systems are fairly expensive, eating a few lemons can really hurt a small shop. 

About your DX dealer you will have to ask yourself:
"is he ignorant of the code- following the code- subject to a different code or ignoring the code?" and "why is the aggravation of selling the least popular product worth it to him". There can be very good answers to the questions, but you won't know until you ask. 

Then of the manufacturer you have to ask why an organization as big as the International Code Council is not worth approaching to get the equipment recognized and maybe the refrigerant detector waived by exception or at least a reduction of measures required for compliance.

All that said, the best geo heat pump is still "whatever is sold by the best dealer in your town." This does not rule out DX.

There are always exceptions.

I welcome rebuttal from a DX manufacturer.

I think I may contact the ICC myself to see if they have been approached and if there is something new in the pipe line.

Joe Hardin

Posted By DGF on 11 Mar 2012 08:51 PM
It's nice that you can be meticulous and retain a genuinely open mind. I appreciate your help.

Here's my take

1. ICC endorsement is something I don't really care about much, personally. I was going to write about it myself, but instead I'll just link to someone else who has already summed it up very well: http://www.greenhomebuilding.com/building_codes.htm. Thats just me, though.
Yes just you. Because I am unaware of a DX system sold to anyone other than a contractor you are suggesting you want  to spend thousands with someone who blatantly breaks the rules. What other business rules will they not follow while executing your contract?

2. A significantly larger volume of refrigerant would certainly pose a greater risk in scenarios (whether sensible or silly) in which a leak occurs inside the home. A valid point, one of the most compelling I've come across on the this subject.

Anyone have a rough estimate of the amount of refrigerant a typical water source system would use, compared to the same for a typical DX system?

 Loosely 5Xs.

3. Good question, one which I was trying to bring up in the other thread. I assumed previously, that adding a water pump would add to the total workload, regardless. Now I'm wondering how a water pump's work-footprint compares with the work added to a compresser by making it cycle an entire ground loop.

I think the electric usage for each would clarify that greatly. This doesn't address the issue of having two mechanical systems versus one, and thus having more potential failure points. However, I suppose this may well be trivial; especially if this avoids or rectifies other issues that are of greater significance.
 
The significance of design plays a terrific role in op cost here. We know for instance adding one ton in a heating dominated climate may save 50 to 100 bucks/yr though cost thousands extra to install. One of may dealer training courses in DX taught me to load heavy to allow ground thaw (down time) and indeed the trainer appeared hear once and commented that without downtime he would see radial cuts on the loop pipe from frozen earth. So saying it comes down to cost is an oversimplification. Doc is showing performance exceeding the boasts of one manufacturer.

4. I agree with your sentiment. The possibility of corrosion occurring with copper is worth taking note of, but it seems (from what I've read) both rare for for this to be a problem, and easy to determine if it will be in advance. Non-issue if handled appropriately.

 You might also agree with part 2 of the sentiment......material where trouble virtually never occurs beats material where trouble occasionally occurs. Let's not forget, many airsource products begin to have trouble after 20 years or so with brazed joints. I am unaware of a socket fusion leak (if done correctly) after 20 years.

5. I do not care if it's only a small percentage of the market, as far as merit is actually concerned. Ad absurdum, geothermal itself only currently represents a small percentage of the overall heating market. This doesn't say much of course - one way, or the other - about an idea's merit. However, this does have a real effect (good or bad) on whether the idea can be implemented in reality, at the time and place you find yourself in.
You might care if you find the warranty on your equipment has no backer because the company folded. There is no comparison between the solvency Climatemaster, Bosch or Research products and most any DX manufacturer. 
 
6 & 7. Experience can be a worthwhile trait, so yes, it is worth considering. Not the end-all-be-it-all, but a meaningful variable. A DX line which has lasted 10 years would indeed be nice. It's hard to say what the lack of this indicates, exactly. Perhaps it proved to be a problematic system, or maybe its just simply the fact that its new, immature, and needs more exploration. Perhaps these businesses were never able to sustainably reach critical mass. Dunno.
ding ding ding.........

8. I honestly don't know enough about this. Might help if you explained this one to me, if you're up for it.
Aside from the obvious excavation, DX uses tools that any heat/AC tech already owns...so if you want to jump into geo, wouldn't you do it as inexpensively as possible. In fact when a dealer inquires a point is made to let them know they can get in the geo biz on the cheap.
9. Maybe this answers the question I had in up in #1

10. Myself - I'll be looking for a lot of land with, at minimum, 3 acres or more, and doubt I'll have a lawn of any sort. Still, quite a valid, important question for many, I'm sure.

11. Great point I was not aware of before. Ground loop flexibility might very well turn out to be something valuable down the road. I'd like to know more about the "compressor's oil recovery harming the equipment" - not an issue I am currently familiar with. Once again, if you're up for it.

All refrigeration has a maximum reach where oil pumped away from the compressor can not be recoverd by the compressor.

I think one of the most disturbing things (deserving or not) I've have heard about, and wasn't brought up yet, is that a DX system is more susceptible to freezing/thawing issues then a typical water source system. Presumably, this is because of a DX's smaller underground footprint, with more heat being taken from every cubic foot of dirt involved then a system with a larger footprint, and where the load is more spread out. This would seem to indicate that a DX will routinely freeze the ground around it, and in turn produce seasonal/variable ground heaving. Can this be avoided in a water loop system? It also sounds as if refrigerant leaks through copper are more problematic, and likely to happen in this scenario, then water/brine leaks through HDPE. Can this be elaborated on?

see #3 above. water source EWTs have a minimum design temp of 30f (below freezing). ground freeze will occur with either though the HDPE is less concerned with it. It can be designed out in water source with more loops (though it often doesn't pay). One can not simply add loopage to DX.

Posted By DGF on 11 Mar 2012 08:51 PM
I think one of the most disturbing things (deserving or not) I've have heard about, and
wasn't brought up yet, is that a DX system is more susceptible to freezing/thawing
issues then a typical water source system.

A second way to circumvent the code (which is quite routine) is to have an engineer sign off on the design. Author said he didn't mind spending a little more so he need simply to pay an engineer to sign off on his hay bale house.

Posted By DGF on 13 Mar 2012 10:07 PM

A second way to circumvent the code (which is quite routine) is to have an engineer sign off on the design. Author said he didn't mind spending a little more so he need simply to pay an engineer to sign off on his hay bale house.

Exactly what I've been doing.