DX Geothermal vs closed loop
Does anyone have experience in DX Geothermal? We are sincerely interested in this type of Geo application.
I have no direct experience with DX but I know they have been around 20+ years. The stories I have followed on them have been a mixed bag and they are few and far between. For all the claims DX has made of being superior to water source one has to wonder why DX has not kept pace with water source sales. Some claim they are just too complicated and difficult to troubleshoot.
Having a refrigeration background and looking at a Nordic DX installation manual I can see why many would make that statement.
Just giving my opinion.
Having had experience installing Nordic DX systems, both DX-To-Air and DX-To-Water, I can tell you that they are excellent and VERY reliable machines. As an owner of a Nordic DX HP in my own home I can tell you that we are now in our 7th heating season with no break downs or service calls required. These things are simple and bullet proof if you know what you’re doing!
In residential applications, the best way to compare the 2-systems is liquid is like a PC and DX is like a Mac… Take you pick.
BTW: I design and install systems using both methods. What’s complicated about the Nordic DX Installation Manual? (This post was written on a Mac)
Referring to the refrigeration diagram of the Nordic DX as compared to a water source Geo I don't think the average HVAC Tech would call it "simple".
Of course it's all about training and proper installation with any system.
That's an interesting comparison PC vs Mac.
Lots of problems with DX systems - when they leak or are mischarged - catastrophic problems. They also tend to have oil migration problems. I have seen many blown compressors on DX systems - very rarely on "water-based" Geo units. It takes a lot more care to braze field joints cleanly on a DX system. If a tech over-does a joint, you get a restriction and loose a lot of capacity.
The DX systems are NOT any more efficient than water based systems. The only potential benefit/advantage they have is lower loop field installation costs. In fact, in the hundreds of systems we have studied - we have yet to see a DX system actually break a COP of 3.0 in steady state!
I have also seen a few DX systems leak - and they hold a LOT of refrigerant. We prevented them from earning utility incentives in several NE states because a leak would constitute a fineable EPA offense and we didn't want customers exposed to that possibility.
If oil migration (loop design issue) and field brazing is done correctly - then they can theoretically work fine.
FWIW - I've seen too many botched DX installations too recommend them to anyone.
I installed an Earthlinked DX heatpump, it has an oil seperator coming off the compressor so I don't see a potential for migration issues. Its a 3.5 ton system and held 27 lbs of refrigerant...I think you're wrong about an EPA violation when leaks occur. This system runs like a dream!
I'm glad your system works like a dream.
Originally Posted by air2spare
We've seen leaky systems leak their entire 27 lbs of refrigerant multiple times. The "Law" says fix it. Second time you let it leak it IS a finable ($10K) offense (unless it leaks for a different reason).
I've been working on several Earthlinked systems - as well as a few other OEM's (at the request of building owners) where contractors have replaced multiple compressors. We've seen the ACC's work well as often as not to protect the compressor. On one job - now 8 years, 3 complete units, and 5 compressors later, the Mfg. finally agrees with me that there must be something wrong with loop field installations and their ACC cannot protect the compressor. Solution (per the OEM's engineer) - dig up the header pits, find/fix restrictions OR install new loop field. He was actually pushing up for a new loop field as he thinks maybe they used the wrong loop field design for the load...contractor says they installed the loop design specified by OEM.....and round and round it went.....
I am very PRO geo, and have been directly involved in studies for utilities as well as several OEM's and the EPA where we worked as hard as we could to get the DX systems to work favorably and hopefully even more efficiently than water-based GEO units. As such, I get to hear about almost all the failures. When these systesmn fail, they fail hard (expensive). When water-based systems fail, we can usually isolate the problem pretty quickly although loop-field repairs are still prohibitively expensive.
Can they work - when properly designed and installed (that is 2 very high percentage strikes against most contractors right there) - yes, but given the choices, I would recommend water-based well before a DX system at this point.
EPA 608 law starts comfort cooling at systems that have a charge of 50 pounds or greater. There is no law that covers systems with less than 50 pounds, they can be topped off legally indefinitely. It may not be cost effective, but there is no law against it.
Originally Posted by Buck_Taylor
I have mixed felling on the DX systems. I installed a few US power systems that worked well, looked at a few that did not work so well. We (myself or previous employers) would never take on a DX system we did not install, for that matter the same rule applied for closed loop Geo systems.
Open loop which is what we prominently have in my area we'd work on anyone's.
Time will only tell if ours will be a problem but short of an oil return problem or a ground loop leak I don't know why it would have any problems. I think the key point with this equipment is proper installation. Many companies can't install air source correctly muchless geo. The success is in the small but often neglected details.