Yikes indeed. Nordyne is claiming these performances at 58 degree F earth temperatures.
What is even more alarming is their earth loop sizing criteria. Balanced loads are taken into effect in designing your earth loops. The fact that some loops can be drilled to 400' has me scratching my head.

As for Nordic getting out of the business, I understand finances.

Yikes again. Let me ensure everyone that, as always with DX, the performance is great, but after one hour of sending refrigerant through the pipes the earth surround the pipes is not 58F anymore. The inherent problem with DX, if you want to extract the same amount of BTUs than a water sourced close loop system from lesser ground, you need to cool down the ground further, increase your delta T between the ground and the heat transfer medium, which results in significant lesser efficiency.

Not sure Nordyne has the juice to cover what appears to be the next-former DX system.

Docjenser, I agree with everything that you are saying.
The inherent problem with DX is that it rapidly cools the ground, and the ground is the bottleneck.
If the ground can not keep up, we increase delta T, which decreases efficiency.

It gets to the point that one must oversize the compressor in our area, heating dominant region, such that we never match the maximum heat loss with the "output capabilities" of the heat pump.

I know of some geothermal DX installers that size their heat pumps at a lower ground temperature just to add some buffer into the equation.

But of course, this adds costs, as compressor sizes are larger, more holes are needed, more ductwork is required.

Not sure if Nordyne knows what they are getting involved in. I for one would steer clear of this product, as there is does not exist sufficient engineering data to prove that their system is capable of delivering the btu's required.

This past summer we have seen a problem with the DX systems in cooling mode.

The ground is saturated with heat and the compressors are working extremely hard to circulate refrigerant to evaporator coils that are at distances of 100'.

Even though the manufacturer's installation instructions were followed to the letter T, these loop configurations are not dissipating the heat fast enough.

Note, that we had 18 days of 90 degree F plus weather, this phenomena makes me believe that DX fields are too aggressive in their heat exchange to efficient long run times.

The compressors are tripping off on high pressure and high temperature.

You can try soaking the loop area to increase heat transfer rate away from the loop.

jonr, I suggested that since we are having quite the dry spell in this area. However, the installer refuses to believe that installing soaker lines will do any good. He is stubbornly refusing to understand the phenomenon is occurring because these HP's have been running hard for long periods of time and the consolidated ground exchanger can't dissipate the heat fast enough. I keep explaining to him that it is the earth's ability to transfer heat that is needle here, not the copper tubing.

In any case, the installer believes that by installing more ground loops in the consolidated area will hopefully remedy the situation.

We shall see.

I would argue that fact that your installer installs DX systems is also a sure indication that he stubbornly refuses the phenomenon of comprehending efficient heat transfer, and heat pump operating conditions.

It's been over a year since this thread was created.

Was wondering if anyone has heard of 2-stage DX installations and their performance?

It is my understanding the Earthlinked , the major proponent of 2-stage DX technology, is taking their single-stage equipment offline at the end of the year.

Yes, I've installed several of the Earthlinked Prime Series two stage systems. The performance has been as advertised and promoted. During this years Dealer meeting in Florida it was announced that the single speed equipment would be gradually phased out. No time line was given at that point.

MI, where your installations DX-to-air, or DX-to-water?

I've installed 2 speed DX-TO-AIR as well as their combo unit which does both air and water in the same unit. I've not done DX-TO-WATER only as of yet.

Curious as to what your AO is. Having successful experience in the design/installation of DX-Geo equipment, I am interested in understanding where these units have been installed. My conservative nature has me apprehensive of using a "triple-function" unit for fear of overloading the unitary equipment with a diverse load. In short, one unit that makes both forced air & hydronic is still connected to a unitary geo-loop field. So, how does one correctly apply this technology knowing that we have a diverse load, but a single field sized for the "capacity" of the unit? How did you size the triple function unit? Thanks.

Tesh, I've installed these types of units in Michigan and Minnesota. Your apprehension is well founded, given the misunderstanding and misapplication with this type of unit in the past. However, Earthlinked and their application of modern technology have "almost" idiot proofed their machine. (And yes I said almost, as I feel given the opportunity there are those individuals that seem to go out of their way to push the boundaries of common sense let alone proper design). With that said, if you follow the simple rule of not under sizing your Geo system, it'll work flawlessly. Much of the diverse load you speak of is dealt with several different methods: Use of a buffer tank on the hydronic side; Proper sizing; And best of all, the idiot proof technology add. Earthlinked has added a programmable logic controller to all of their two speed equipment to protect and maintain system integrity. This logic controller will cycle on the auxiliary heat after a predetermined length of compressor run cycle; track staging and run a maintenance cycle to assure oil return; and will allow for priority settings. btw, if you count the domestic water heating assist, the unit is a true four function machine. Hopefully I've answered all your questions. If not, feel free to hit me back up again.

MI_GSHP_Guy, thank you for the additional information. You mention the "simple rule of not under sizing (your ) Geo system," yet that is why I revisited this thread; recent experience with Earthlinked's sizing Excel Spreadsheet & their approved Sizing Software platform indicates that "under-sizing" is almost encouraged through the data output. In short, and mind you the "produced suggestion" is merely based on economic analysis of a modeled performance bin, without actual experience of installation and monitoring of one's system designs, an installer lacks real world knowledge of how this technology performs under load.

Which is why I question the recent PLC implementation feature that stages compressor and Aux functions based on run times. This feature, from my experience, was/is used by Maritime Geothermal / Nordic, for their equipment. While an outstanding feature, I feel as though its global function HAS to be coupled with a terminal control function; we need to monitor actual system delivery in order to stage compressor function and Aux function in order to prevent aggressive cooling of the source.

And that is the direction I had hoped Earthlinked would look to. The technology of DX Geothermal is such that increased run times destroy performance efficiency, and, chills the ground to temperatures not suitable for compressor operation. The diminished refrigerant pressure and temperature characteristics which are a result of a long run cycle starve the compressor, increase electrical draws, and create terrible compression ratios. In short, and I'm quoting an Earthlinked representative here, "A happy (Earthlinked) Geo system, is a Geo system at rest." What they mean is SHORT run cycles.

So, MI_GSHP_Guy, I can tell that you are one of the good guys who knows his equipment, knows how to properly size and install units, and has figured out how to properly implement this type of technology in the real world. But, the danger in promoting this advanced DX technology+control platforms is that in heating dominant regions, under sizing can not ever be considered; ever. To freeze the ground 3/4 of the way into the winter is no situation any installer would want to be in. Until the technology has proven itself over the course of several winters, I remain apprehensive.

Hi Tesh,
My name is Gregor Vialette, I’m an Applications Engineer at EarthLinked Technologies. Saw your post and thought I’d jump in. You have some good questions regarding the best sizing methodology for DX.
The unit you are referring to is our PSDH unit, and it’s actually a four-function machine: it’s a two-stage system that provides forced air heat/cool, hydronic heating and domestic water heating (desuperheater).
What you call diverse load, we call Split Zoning. The correct sizing method for Split Zoning is to size the unit for 100% of the home’s total heating load. I imagine that’s what MI_GSHP-Guy was referring too when saying “simple rule of not under sizing (your) Geo system”. That way you are never “overloading the unitary equipment”.

Now I am not sure what your experience has been with our Sizing Software but rest assured that “under-sizing” is never encouraged. It doesn’t matter what type of geothermal system you are installing: laws of heat transfer say that if you undersize (whether it is in heating or cooling), you will not be able to properly satisfy the load of the home. EarthLinked has a custom version of LoopLink, one of the industry leading geothermal sizing software.

Now let’s not confuse undersizing (system installed cannot meet the load/demand) and optimizing the size of the geo equipment within a system. Depending on the dealer strategy and the wishes of the customer, it is perfectly acceptable to not size to a 100% of the heating load, as long as you size the supplementary heat properly. This is true for all geothermal systems, DX or water-based. Here I will just quote our Sizing Manual:
“when selecting an EarthLinked Geothermal System and sizing it to meet the loads of a house, one must resolve the tension between two opposing economic logic in order to choose the optimal system to install. The first logic wants to minimize the cost of operation of the system and recognizes geothermal as the most efficient solution and the cheapest to operate. The second logic wants to minimize the cost of installation of the system and resorts to auxiliary source of heat to find an optimal system mix. This second logic makes use of the fact that a geothermal system can be supplemented by an auxiliary heat source to meet the heating load.”

This comes down to the discretion of the installer and the customer, depending on what they are after. In both cases, whether it relies on supplemental heat (electric strip, dual fuel..), the system as a whole will not - and of course should not - be undersized.
The LoopLink software is an excellent tool to be able to select the optimal system because it shows you the $ impact on yearly cost of operation from going down or up a system size. This allows dealers and customers to make an informed decision.


Now, as far as “real world knowledge of how this technology performs under load” goes, all our two-stage systems ship with the EarthLinked Diagnostics & Monitoring board which allows you to remotely track things such as power, temperatures and pressures. So we are really giving installers all they need to size, install and maintain our systems in the most optimal way.
Everything we do (training, sizing, installation..) is based on real world performance. As for our PLC, it contains a proprietary program that optimizes the run time and staged based on and 35 years of installing DX system.

One more thing, you mentioned that “a long run cycle starve the compressor”. Now of course “long run cycle” is subjective, but again this comes down to proper sizing: a system will never overrun if sized correctly. DX done right, sized and installed correctly, works wonderfully. But any system that is undersized, whether it is geo, DX, water-base or otherwise, will run into issues.

Thanks for this very interesting discussion and sorry if my post is long; I can only congratulate you for putting so much thought in how to best size and install a geo system.

Gregor,

Let's address your points: "our PSDH unit, and it’s actually a four-function machine: it’s a two-stage system that provides forced air heat/cool, hydronic heating and domestic water heating (desuperheater). "

This machine is a triple function unit; it makes forced air heating and cooling and hydrnoic heating only. Coupling a desuperheater package to the refrigerant piping makes it a waste heat recovery system during cooling and a heat scavenging system during heating. Unsure of your controls for the heating operation of the DSH, I can only wish that latent energy of the refrigerant stream after the condensing coil (interior HX) is being used such that heat produced from the vapor compression cycle is being prioritized for interior condition prior to DW heating.


What you call diverse load, we call Split Zoning. The correct sizing method for Split Zoning is to size the unit for 100% of the home’s total heating load. I imagine that’s what MI_GSHP-Guy was referring too when saying “simple rule of not under sizing (your) Geo system”. That way you are never “overloading the unitary equipment”.

I would prefer that it be called diverse load in hopes that the designer would recognize the diversity of the block loads of the air/hydronic systems connected to the unit. Split Zoning infers that your equipment is connected to separate spaces, and if that is the application in which you are advertising this equipment type for, then you are in fact risking subjecting the equipment to long run cycles and potential ground freezing.

So let's further address my concerns of the triple function unit: you have a forced air heating/cooling system, which could in fact contain ducted zones in itself. These zones are spread throughout different spaces of the building's orientation. Therefore this ducted zone system is already subject to load diversity in that throughout the course of the day, the zones experience needs for conditioning at different times; possible/potential continual equipment run is likely. But now we also have a radiant load connected to this equipment. Our hopes is that the connected buffer tank is sized for the load in such a manner that there is adequate energy contained in the tank to handle the load and then some; giving our compressor both adequate run times for enerngy efficient heat transfer, as well as adequate rest time for ground recharge.

But the risk in this type of setup is that the ducted zones and the radiant zones are not in the same space; so we have to address priority, which is typically forced air systems are the priority to satisfy conditioning calls, and once satisfied the equipment can return to the buffer tank call. Knowing that our radiant zones rely on connected medium properties of thermal mass, we again have an issue of fast response mediums versus slow response mediums, i.e. how quickly can heat be put into the radiant panels versus how quickly is it being removed.

This type of equipment specification for a DX GEO is dangerous, as we subject the equipment to long run times. In my opinion, the BEST application of a triple function unit is one where we have a connected ducted system in the same space as the radiant system. Now, the designer can use radiant heating as 1st stage, and forced air heating as 2nd stage, with AUX/Backup kicking in as required in the ducted system. To take it one step further, and to add value to your product, your triple function should be able to make chilled water so the owner could truly benefit from the increased comfort of radiant cooling, and our unitary piece of equipment also performs the required latent air cooling/dehumidification process. To date, I know of no manufacturer who is providing this feature with their triple function units.

Correct me if I am wrong, but your sizing manual does not account for ground/soil types. It accounts for ground temperatures only. Your Loop Link software platform does not account for ground/soil types either. I can only hope that Loop Link predicts run times based on BIN data, and then linear interpolates the subsequent ground temperatures and equipment performance when a heating design day approaches.

A long run cycle does starve a compressor in a DX GEO system during heating. Someone in this forum once said that the bane of a DX GEO system is the connected ground source in that copper is TOO excellent at transferring heat energy; that it is the ground's conductivity which is truly the eye of the needle. Having a unit which rips heat from the ground faster than the ground can recharge has risks, especially when we have long run cycles.

So, until the DX industry recognizes that a global equipment control platform HAS to be intertwined with a terminal control platform, the technology will be subject to the limitations of the previous performance standards and limitations of its equipment. One of the greatest limitations of a DX GEO unit is that it is "unitary" in sense of its connected ground HX. We can only attempt to put as much pipe in the ground that the compressor can handle to circulate refrigerant without exceeding compression ratio. That is a limitation. When your installers realize that "recommended" installation methods limit the actual volume of ground one of Earthlinked's loop models can be placed into, you begin to realize that DX would really benefit from more loop length and more ground volume, not vice versa.

I commend Earthlinked for putting so much effort in its technology, I do. I appreciate all technologies in this industry, but I respect applications of equipment and do not push the envelope.

What I would recommend to you, Gregor, is to look into real quickly the idea of putting compressors in series or parallel. Acadia air source heat pumps tried this, and failed, but made great advances in testing the boundaries of that type of technology.

Regards.

Hi and thanks for you answer.

Usually it is considered that heating domestic water is a function, disregard of the mean used to achieve it, but that’s beside the point.

Just to clarify: Split Zoning is one of the applications of our PSDH unit. Again, there is absolutely no risk of “long run cycles and potential ground freezing.” as long as the unit is sized and installed following our instructions. We wouldn’t be offering these systems if they didn’t work very efficiently in this type of application.

As a matter of fact, it strikes me that you keep using the word “risk” when there is no risk whatsoever with our equipment or this particular application. The only risk that exists - as in every HVAC system - is that the installer does not follow the sizing and installation guidelines for the application.

You said: “the zones experience needs for conditioning at different times”, this is not an issue since the unit is being sized to the total load of the home (based on a Manual J load calculation), meaning that you are always sizing to the worst case scenario.

I think you have a slight misunderstanding of how a hydronic (radiant heat) system works in a geothermal system: the whole point of a buffer tank in these applications is to provide buffer. That means that you don’t have to worry about the hydronic circuit, the only job of the system is to satisfy that buffer tank. Such a system, again designed correctly, completely eliminates the “issue of fast response mediums versus slow response mediums”

Yes, having the PLC is what gives us the possibility of prioritizing a zone over another.

You guessed how the LoopLink software works perfectly.

“A long run cycle does starve a compressor in a DX GEO system during heating. Someone in this forum once said that the bane of a DX GEO system is the connected ground source in that copper is TOO excellent at transferring heat energy; that it is the ground's conductivity which is truly the eye of the needle. Having a unit which rips heat from the ground faster than the ground can recharge has risks, especially when we have long run cycles.” --> This is probably one of the biggest myths regarding DX that I see out there. Not sure where it comes from, but it that logic does not hold when you look at the physics of thermal transfer. Of course, I have already explained how proper design along with our controls will prevent the system from long run cycles. But if you want a quick-read on the physics behind DX, I did write a one page about it in the GeoOutlook magazine (page 5, on the right): http://www.geooutlook.org/epub/GO2015No4/#4

The short of it is: yes, as with every geothermal system, the ground tends to be the eye of the needle: the soil conductivity is the limiting factor for thermal transfer (although HDPE pipes for water-based systems or grout can also be limiting if not properly selected). But that is not an issue; you get out of the ground as much as ground gives you. Saying that copper is “too excellent at transferring heat energy” or “rips heat from the ground faster than the ground can recharge” does not make physical sense. We just established that the ground is the eye of the needle. It does not matter how fast the energy is conducted by the pipe, since you are always limited by the ground and how fast it brings or takes energy. Conductivity is only a small part of why DX loops are shorter. The main difference between our systems and water-based, is that we used R-refrigerant in the ground, which is much better at heat transfer than water/antifreeze. That’s it.

Theoretically, you are right, the more sensors and the more intelligence in a system, the more refined the control of its running can be. But in real-world application you would really be over-engineering a system for marginal gains. Our current controls are based on decades of experience with these systems and perform extremely well.

A small correction: when it comes to thermal transfer, there is never a single limiting factor. It's not like material A has the lowest thermal conductivity and therefor material B doesn't matter. They all add up. At most you can say "material B has negligible effect".

...you are always limited by the ground and how fast it brings or takes energy.... DX loops are shorter.

The limiting factor is the ground but somehow you need less ground? Your geooutlook paper is clearer. Better heat transfer (compressor to ground) means more delta-T and allows shorter loops (with how much being the big question).

I recommend not using the phrase "limiting factor". Numerous geothermal "experts" have used it to incorrectly conclude "the ground limits the btu transfer therefor improving the thermal conductivity of the tubing or grout will make no difference".

Hi Jonr,
You are absolutely right, there are of course more than one factor that influence the rate of conductive heat transfer. The article (http://www.geooutlook.org/epub/GO2015No4/#4) was indeed clearer and lays a good foundation for this type of discussion. Here I was trying to say that the thermal conductivity of the soil is the limiting factor as in “the environmental factor that is of predominant importance”, meaning the only factor you do not have control over.

To sum up the article I referenced: according to Fourier’s law of conductive heat transfer, there are three factors that influence the total capacity of your loop: the overall thermal conductivity (soil+grout+loop), the surface area of thermal exchange (directly proportional to the length of your loop) and Delta T (temperature difference between inside the loop and outside, it’s basically the thermal equivalent of an electric tension). Pretty intuitive I think.

When designing a system to satisfy the load of a home, you do not have significant control over the overall conductivity of the ground (the limiting factor being the soil), although of course copper and a good grout will always be beneficial. Refrigerant-based geothermal (DX) is able to achieve a better Delta T thanks to R-410A refrigerant and copper (as compared to antifreeze solution and HDPE pipe). That means that DX needs less surface area (shorter loops) than water-based geothermal to achieve the same capacity. Just two different ways to solve for the same equation really.

Thanks, Gregor