DX Geothermal Pond 4 ton Heat Pump
 

Greetings and welcome to my largest project yet, and by far the most expensive. I currently have a old 10 seer 4 ton air source heat pump that is on its last leg. I had plans to replace with a new unit but considering the cost and how doable this build looks I plan to build a DX (thats right no water pumps) geothermal heat pump (R290 of course) that uses a 3 acre, 17 feet deep pond/lake that is 40 feet from the edge of my house.
I currently have NO parts for this build. Of course I will be buying the copper tubing and I have all my sources out looking for a suitable compressor.
I really don't know where to start with all the data so might as well give a diagram of the house and 3 options I have thought up.

This is the distance that everything thing is apart. The pond at its deepest is 17 feet deep, and I get average temps in the 60's.
http://ecorenovator.org/forum/attach...1&d=1436929629

This is just a few ideas I had. No numbers are solid just guesses based on just a little math.
http://ecorenovator.org/forum/attach...1&d=1436929629
1 is 2 long loops buried deep (I have free access to a back hoe, so as deep as I need to go) that come out into the pond about 6 inches from the bottom.

2 is taking 2 larger lines out to the edge of the pond and brazing in a manifold that splits into 3 (or more/less) loops.

3 is long lines from the house to the compressor/s at the pond with a manifold/or long loops.

I'm really open to any and all suggestions.

I am thinking that about 800' of 5/8 copper tubing would be about right. So the smaller runs will be longer.

Also should I have 2 compressors, one 4 ton sized, and one 2.5 ton sized and hooked up with reversing valves so I can only use the 2.5 ton on mid days and for dehumidifying.

Thanks in advanced for all warnings/ideas/designs/complaints/or general help.

Oh boy! One amazing project after another!!

Personally, I think that the pond scheme could put you right up against the maximum limits of DX feasibility, what with lubrication issues, etc.

I have seen schemes where GSHP systems of the size you are talking about have worked.

Here is how they do it:


The advantages are that all of the copper loops, return to a central manifold. Also, since they are on a slant, the vertical distance (head loss) is reduced, while the linear exposure to the earth (water) is the same.

You might be able to use parts of this general scheme for your mega project.

If it were me, I would go with HDPE piping, which is not such a beast to weld as it might first appear.

In the grand scheme of things, going from copper to plastic results in about 15% reduction of heat transfer per linear foot. The remedy is to put in more plastic pipe.

Once welded, HDPE is eternal. It is very tough, and totally immune to corrosion.

You could run your HDPE up to your compressor shed, and go through a HX. Since it will be closed loop, a correctly sized brazed plate would be a perfect choice.

Also, please note that a 4-Ton compressor unit (and associated copper if you go this route) will contain a non-trival amount of propane and you do not want that to be in, or even up-hill of your house. Definitely outside, definitely downhill, preferably at a modest distance.

Them's my thoughts...

Go for it, however you will.

Best of luck,

-AC_Hacker

AC, yeah I was wondering about the head of the system. But I've seen buildings that are more than 50 feet high with the site handler on the to floor. I wonder if they are special compressor or over sized to make the climb. I plan to research more about the max head pressure of different compressors and their ability to keep lubricate moving. But it does look like a manifold style system is most common. Even if not at the eaters edge I can go crazy deep 6+ feet and not have much temputure fluxuation.
I have thought of doing it with hdpe and pumps. I just really don't want the extra power cost and the freeze potincial. But as I'm probably looking at over 2 grand for copper it might just be the best option. And doing it in a small pump House would be a great idea.
Yes propane in the set up would all be down hill but still a large risk. In willing to get it charged by a local guy that uses the new stuff called MO99. Seems to work better than R22 but acts more like propane in that in lowers head pressure.
Thanks for your thoughts AC!

Memphis91

What a great project. I wouldn't be able to find it again but I saw the amount of copper/
ton of heat was 100ft. so a loop of 50 out and 50 back to the manifold. For HDPE its 600ft/ton. I believe for the residential installation they had used 3/8 copper tube brazed to a manifold. When I was installing a ground loop with HDPE 1" the cost was $1.00/ foot and I see that 3/8 tube is about that cost/foot and you will use a lot less.

Look at it this way an outside unit (residential) uses 5/16 and 3/8 Dia copper in their aluminum fins.

There is a copper product now that has a thin plastic skin that will mediate corrosion.

Randen

How about a compromise (copper pipe vs plastic)? Use plastic for the runs out to and from the pond. Then only use the amount of copper at the bottom of the pond for the true exchange loop.

Seems a waste to use expensive copper for the long runs to and from pond bottom.

One thing is certain, you need to measure the temp at the bottom of this lake. I suspect it is 65-70 F even though the surface water is 95 or so. This allows you to calculate the delta T across your heat exchanger and then work backwards to figure out how much copper pipe to put in. It may be cheaper to buy thinner (1/4 inch) copper and do a few parallel loops to get your total surface area.

The ratio of surface area to volume gets much higher in smaller diameter pipe. That maximizes your BTU transfer.

I second AC's warning about propane. This gas has a density higher than air and when (not if) you have a leak, it could get . . . . . interesting. Well know situations in basements of a propane bottle slowly leaking, collecting in a "pool" on the floor, and then someone turns on a light switch.

In the absence of a dielectric contact, copper does not corrode per se, but develops a surface green copper oxide. In the trade, this is known as "patina". Acid water will corrode copper, but that is a different issue as a pond will not have a pH of < 5!

This sounds great, but look carefully at the costs of this large amount (800 feet, 250 meters) of copper tubing.

I have consulted on several projects that have used closed loop pond loops for geothermal units. If I recall, all of them were HDPE plastic and about 300 feet per ton. Inexpensive to purchase, but would take a LOT of gas to fill the entire volume. I sure would use inexpensive propane to test this out, then use a higher priced gas.

How is the water heater going? What temp can it get the tank water up to?


Steve

It would be a good idea to get several verified sources for these estimates.

When I was tracking this kind of thing down, I found a Canadian GSHP company that was doing vertical holes, and their practice was that DX in copper had a 15% advantage over HDPE & water, in other words, a DX bore hole (copper) could be 15% shorter than the same configuration with HDPE and water and deliver the equivalent heat.

Six-to-one advantage of DX & copper sounds extreme to me. I suppose some testing would be in order here, before ordering materials and hoping for the best.

-AC

I think that using HDPE for refrigeration gas would be a very, very bad idea.

I have serious doubt about the permeability of HDPE to pressurized refrigeration gases.

I'm concerned about how it would hold up to extreme temperature cycling.

And I also have concerns about how HDPE would hold up to the ravages of pressurized lubricants and refrigerants, whether hydrocarbon or proprietary global warming gases.

If this was a viable idea, it would be possible to find thousands of success stories.

Do they exist?

-AC

AC, that is why I suggested it - a hack! Good points on permeability.

Steve

Just run a pump and dump system, using your endless supply of pond water as heat transfer fluid. You could still run a dx coil indoors if you wanted to. Pipe your suction line underground, and if the pond water is cold, it would pick up some heat underground on the way in. You could even use copper pipe if you wanted more heat transfer. Much safer, less refrigerant, way less expensively accomplished. Spend some extra money on a hx and pump.

Wow good suggestions and ideas. I'm looking into the good and the bad of all that's been said. But Jeffs ideas of pump and dump just took the cake I think. I didn't like the idea of closed loop with water but I never thought about open loop. This would be so easy that it's almost wrong for me not to do it. I would need a pump probably 8 GPM but that is the only down side. I'm thinking a super insulated 1 inch or bigger PVC pipe run out of the pump straight down 7 feet deep all the way to the pond edge and then 17 feet down to the bottom where the coolest/hottest water should be. And then the dump can just be maybe 2 feet deep to the edge of the pond.
How about building my own 4 ton hx?

Steve hull , the water heater is set to only 120. I'm very sure it could go higher though

Which ever way you go, oversize the refrigerant to water heat exchanger! Much like the evap coil you revised in your dehydration unit, too much is almost enough. This is your heat transfer mechanism, and with more transfer comes higher efficiency. Just a few degrees less drop from inlet to outlet on either side saves you money on your power bill.

You also have the freezing point of water to stay on top of. During the winter, when you need heat the most, your pond water may be precariously close to freezing. A few extra square feet of transfer area could keep you from using a backup heat source. A few less could spell disaster due to a rupture.

Well if i'm going to be saving so much money not buying so much copper, I don't mind building it over sized. I've done some looking but can't seem to find where anyone has build a coax coil for 4 ton. Any bookmarks ya'll have stashed away that could save me some hours on google?

I just lost out on a dead water cooled unit with a 5 ton coax coil. The unit this was in got sent to the dumpster as the scrap value was too low. Was about two hours too late . . .

My suggestion would be to find a ClimateMaster or WaterFurnace dealer in your area and then bring over goodies to allow you to scrounge through their boneyard. This is how I got my one ton unit that I rebuilt.

I took the shop guys out to lunch today for their help and they will be looking for all kinds of goodies for me. Cost me about $57.

Worth EVERY penny . . . .

Steve

Totally doable BUT there are ZERO local installers for those systems. My closest bet would be Memphis, TN..... and I really don't like going there much less making friends. I do have tons of friends in the HVAC business, maybe they know people from areas that use them more. It would be worth a road trip I think.

But if I did make it this is what I was thinking. Pipe in pipe. Center pipe is for water with larger pipe around it filled with R290. Do several of these tied together.
http://ecorenovator.org/forum/attach...1&d=1437014715

There have been several DIY HXs similar to your drawing, done here at ER.

Acquario did a very interesting unit, that used a plastic shell and had multiple copper coils running inside, for the refrigerant. His first try had insufficient copper tubes, so he rebuilt it with more tubes, and got the results he wanted.

http://ecorenovator.org/forum/40959-post9.html


Also, randen did an interesting one wherein he used large flex pipe for the shell and copper inside for the refrigerant. You'll need to search for that one. The part that made that one work was machined brass end plugs that he could braze the refrigerant lines to, and ot also had fittings for water. With your amazing hack brain, you'll likely come up with an off-the-shelf solution.

Your biggest problem will be maintaining a hermetic seal of the refrigerant carrying portion.

The pressure involved in the water portion will be in the very low psi range, whereas the pressure of the refrigerant will be very high, and will be subject to severe temperature cycling.

So, if you're gonna do tube(s) in shell, think through your tube structure, and how it must be constructed, then think how you will need to wrap a metal or non metal structure around it, that will allow your water flow and maintain a seal at 10 psi or so.

Also, there is some flexible pipe material that is intended for connecting natural gas to a stove or something. This stuff is interesting because it has a high surface area, and would encourage turbulent liquid flow, which will increase efficiency. I have seen it in stainless and also in copper. The copper variety should be easy to braze. The stainless could be brazed also, with care, high-silver brazing rod and proper flux.

Rave on!

-AC

Here is a guy who is building a counterflow tub in tube, with some interesting additions.

Please note that this HX is for liquid-to-liquid not refrigerant-to-liquid, so the issue of hermetic-sealed refrigeration-grade quality doesn't come into play.

https://www.youtube.com/watch?v=DVf-lTFpR2c

-AC

Thanks AC!
So after a bunch of brain storming this is what I have come up with. I suck at drawing 3d so bare with with as I explain.

I have 100 feet of 1 inch rubber industrial hose. Its rated for high pressure and high heat. My idea is to run 3/8 (or smaller/bigger) copper tubing inside of it and then coil the entire thing into nice loops. The ends are threaded so I would use a metal female 90 and drill a 3/8 hole so that the inner tube can come straight out and then braze that. It really would be like a tee, with the water flow making a 90 degree turn and the copper continuing straight out. I would do that on both ends of the hose. Giving me 1 inch of water flow over 100 feet of 3/8 copper tubing.
When I thought about it, it really is simple. My first idea that I posted had the refrigerant on the outside therefore the crazy pressures where acting on the copper tubing as well as the water pipe. When you put the water on the outside you only have to make the outer tubing water tight. I think this could even be done with pex, only downside is the pex is a pain to loop into tight loops, but if size didn't matter than pex should work great.

The main question is now (and what I am currently researching) how much surface area of copper tubing do I need with how much flow of water at 55-65F temp water.

EDIT: I just watch the youtube video. This is very very close to what I was thinking. Awesome idea with the wire on the outside. I wonder what would be better, parallel or counter flow? More research to do.

Question about flow answered. COUNTERFLOW
Parallel and Counter Flow Designs Heat Exchangers | Engineers Edge | www.engineersedge.com

Counter flow always better.

I can't tell you right out of the gate how much surface area, but if you are looking at examples, you may come across water-to-water examples. You might be able to do an extremely general estimate from those examples, but refrig-to-water will require more surface area.

Come to think of it, randen's first unit was about 2.5 or 3 Ton. He had a diy HX like you are considering. Check his specs... they worked.

If you are going with open loop (pump & dump), brazed plate will not do, it will quickly foul. But if you are going closed loop, Brazed Plate HX are very much worth looking into... but tube in tube will be OK, too.

-AC

Memphis & AC

I had limited success with the tube & shell That's why I turned to a brazed plate for the price I could not go that route. Memphis is right the refrigerant needs to flow around the outside of the water tube. There are commercial units avalible.

What about your new discovery DX.?? 5/8 or 3/4 copper out to the pond, some 3/8 loops with manifolds and return. No circ. pumps. No heat exchangers, no antifreeze a huge advantage.

One other detail depending how much heat your trying to sequester with a tube and shell you may need antifreeze.

Randen

Randen I agree that the DX system would probably be the best. But the cons way out weigh the pros right now. Cons are cost, tons of brazing/potential leaks, time consuming install, amount of refrigerant, and heat loss in the ground on the way back to the house. PVC is much easier to insulate.
I am reading your post now about the tube in shell. Why do you say the refrigerant needs to be on the outside? I can make the exchanger very large if need be to gain the efficiency needed. Not disagreeing just SO much data right now.

The heat exchanger boils down to a time and temperature model, one mass against the other. Water has much higher heat capacity and mass than refrigerant, so less of it (mass) needs to flow than the refrigerant per unit of time. With a coaxial hx, you can make the space between the tubes small, so the gas can flow through the middle. However, this reduces the surface area of water that is exposed to heat transfer.

The main advantage with gas in the center is cost reduction. Since the water is under much less pressure, the outer tube can be made of much less expensive material. PVC or pex is common, as well as cast iron.

With the water flowing through the center, both tubes must be made tough enough to withstand the pressure of the refrigerant. In this type of hx, the refrigerant can leak out to atmosphere or into the water line, so most are made with double walls to prevent an overpressure condition in the water line.

DX vs Glycol/HDPE loop
 

AC Memphis

From Wikipedia direct exchange geothermal:The boreholes are drilled to a length of 50, 75 or 100 ft (15, 22 or 30 m) with a diameter of 3 inches (76 mm). A total of 100 feet (30 m) to 140 feet (43 m) of drilling is needed for each ton (3.5 kWth) of system capacity. At 40' from your home a 60' line set is doable.

Its good your weighing all your options.

What are you brazing with?? Silphos brazing is one of the easiest.

What is your plan on the other end? Are you air conditioning and heating with a fan center??

One other thought. If your going to through the loops in the pond both systems will want to float so they will need to be weighted. There is a commercially made system for HDPE made for ponds but I have no idea their cost.

For a day I had a pond with HDPE is this what your thinking??

The shell and tube worked, but I had them freeze up many times even though my flow was good. It was a good thing the outside shell was a flexible plastic but even so it did fail badly. I could imagine inside the ice slowly forming around the tubes reducing the flow and ultimately freezing solid. The proper antifreeze to prevent the freezing isn't cheap either.

Randen

Jeff that does make sense, so basically as long as it's big enough both ways should work.

Randen, thanks for the pictures. I am not considering a hdpe loop. It's either DX or open loop. Open loop would mean no antifreeze.
The freezing problem does sound bad, that is why I'm now thinking 2 coils with water and refrigerant split between them. And I like the gas on the outside idea because I'm thinking it will limit how much refrigerant flow acts on the water as fast, hopefully helping with freezing as well.
I breeze with 15% sliphos.
The other end is a 4 ton older air handler.
I have a idea I'm going to see if even is possible. I'll post pictures soon.

Randen this most stable temps in the pond are about 50 feet or from the bank. So the line set would be about 120 feet long. Do you think 3/4 out and 5/8 return would work?? Then a manifold and 5 100 feet loops of 3/8. That really would not be to bad. Hmmmm.... More brain storming to do.

Randen, very good info there!

I was just looking on a table of Thermal Conductivity values of some common Materials and Gases. These values are to be used in equations to calculate the quantity of heat flow, when you know delta-T, and other factors. But I think it is useful to know what these values are, to guide intuitive judgment.

Here are some of the values:

• Carbon Steel - 43
• Aluminum - 205
• Copper - 401
• Concrete, stone - 1.7
• HDPE - 0.42 - 0.51
• Water - 0.58

It's not surprising that aluminum would be a much better conductor than carbon steel. And that copper is much better than aluminum.

I have listed concrete & stone, because I have seen many tables that give the heat transfer of dry earth, damp earth, wet earth, etc. And the value of concrete and stone are very close to the cluster of values found in bore hole heat transfer conditions.

I was just about to make this entry, to suggest that the loops in water could be made much shorter than the loops in earth, but the thermal conductivity value for water really surprised me.

I would imagine that this value would be more favorable when the system is actually in use, because there would be at least some modest flow of water past the tubing due to temperature differences, whether they are copper or HDPE, but it would certainly not be anything like water that is driven through a HX by a pump.

Also, of interest is that when heat flow is calculated, the various factors that would inhibit thermal flow are all added together, for instance the resistance of flow from the refrigerant itself, the resistance of the boundary layer of refrigerant, the resistance of the transfer tubing (copper or HDPE), the resistance of the boundary between the tubing and water, and the resistance of water itself, there could be other terms added in like resistance due to moss, etc.

So the equation for the overall resistance would look something like:

TOTAL RESISTANCE = Rref + Rbdy1 + Rtube +Rbdy2 + Rwtr

So, although the heat transfer index for copper is a big number, and the heat transfer index of HDPE is a very small number, and the ratio of one to the other is something like 800 to 1, when the terms all get summed up and put into the equation, the difference in overall thermal transfer efficiency is nothing like 800 to 1, it is far more modest.

For example...

Gary, over at Build It Solar did has done a huge amount of testing on many aspects of solar heating, but there was one test that he did that I thought could relate to MEMPHIS91's current project...

HERE is the page that detailed the construction and test setup.

HERE is the page that detailed the test itself, and the results. The conclusion odf the test are quoted below:

Make of it what you will...

Best,

-AC

Awesome info AC. I had seen that table of thermal conductivity some where. And you are totally right, flowing water is much much better at giving off its heat. That is why coaxial coils can be so short, and why you have to pay a arm and a leg for all the DX copper. But water being so low also is what makes a pond a awesome thermal storage area.
I have no idea how much flow is at the bottom of the pond. I know that the great exchange will make it move some plus the pond is full of large fish, all that swimming has to move lots of water.
Great articles on the solar stuff to. That is a project for next year.
I got a quote on 150' of 3/4, 500' of 3/8 and 150 of 5/8. It's was right at $1,000. But that was from only one place. After the building of the coax coils and the extra pump cost doing pump and dump is not going to save to much money. And if I'm going to have to dig up my yard to the pond anyway it's not going to save me much work.

I did make sure that DX could handle the overall 30 foot head and it for sure can. Should move the oil around nicely.

I am eager to see how much energy can be saved by going dx with a pond loop. The increased heat transfer and lack of a circulation pump could be substantial. The added ground transfer will also come into play if you bury and do not insulate the lines. I would almost want yo run them together as in a refrigerator.

Yes I will be excited to. Gonna start saving up to buy some copper. You think I should not insulate? I'm thinking the ground will be more effected by seasonal temps. Maybe only insulate the return line?
Should 3/4 to and 5/8 be good enough? Also looking at doing more loops with 1/4. Per AC's post the more surface area I can get the better.

Running calculations on the copper pipe surface area. 500' of 3/8 =662 square inches.
1,000' of 1/4 = 590 square inches.

Randen I am very interested in the compressor you used in your 5 ton build.
I've been looking at the compressors and they look like they are worth the extra money for the vfd. Is it a high learning curve to program the set up?
EDITED TO ADD LINKS
New Top Quality 220V 4KW 5HP Variable Frequency Drive Inverter VFD | eBay

Sanyo 4 8 Ton Scroll Compressor 57K BTU R 22 208 230 V 3 Phase 60 Hz New | eBay

4.8 Ton DX build
 

Memphis

I have used this identical VFD. No they are not difficult to program. Sit down take your time and go step by step through their manual.

Now there are some less than clear indication whether or not you can operate these with single phase supply. As luck would have it I have one on the shelf I can test for your application if you are serious. I would only assume you do not have 3 phase power at your home??

A VFD is very nice and has some very useful advantages. They are only within a few dollars of a contactor/relay for a motor of this HP. The 3 phase motors are a little more efficient and usually a few bucks cheaper. I run my compressor at different speeds therefore different out-put (BTU) Case in point air-conditioning this week I was required to reduce the compressors out-put or possibly freeze the evaporator HX. My anti-freeze only protects me down to -15 Deg. C and -25 Deg. C is a few rpm away with this unit. The soft start or ramp-up is really nice as the lights don't flicker on start-up. The VFD has other low voltage contactors to integrate further controls like thermostats and circ. pump relays etc.

Be careful You may be able to find on ebay or others a 3 phase heat-pump with fan and controls inexpensively that you can hack. You many be able to just circumvent the in-put DX to your ground loop. All the safety switches TXVs and reversing valves etc. would be there. I've seen cheap R22 units.

For further discussion latter!! these VFD will operate on DC. You could run your system from a solar PV and or with a battery bank.

This is really exciting, the DX Heat-Pump could be the holy grail. For your application it seams perfect. I couldn't do DX because of my heated floors and solar hot water collection is a totally integrated system.

Randen

Randen. THANK YOU! Awesome info. Everything I have seen says that using one phase is totally doable as long as the unit (the one I linked) says it can handle 1 phase input. I do not have 3 phase at the house. I am VERY serious about this, I don't see the sense in spending tons of money going DX and not using the most efficient compressor.
Cool I will be watching ebay closely!
My last step before buying is the size of the DX coil. I have been looking for days and the best info I can find is the 100 feet per ton is a good size.
What I'm looking into now is normal closed loop hpde geothermal systems install into a lake. Are they the same size as the ground loops? Are the bigger smaller? Then I will apply that info to the DX sizing.
UPDATE:
"Most often, the same type of HDPE pipe materials that are used for earth loops are used for pond systems; however, pipe length requirements per nominal ton tend to be significantly shorter–and coils can usually be configured in a more compact arrangement–than with buried systems." http://minnesotageothermalheatpumpas...-loop-options/

On this site. 600 feet of 3/4 = $509.28 500 feet of 3/8 = $386 Total of $895.28 that includes shipping. That is using 3/4 to and from the manifold.

https://www.simplyplumbing.com/catal...SOFT+COPP+TUBE

You will want to check on fluid resistance in pipe.

The higher the resistance, the more pump power is required to keep your circulation moving at a rate that is acceptable.

The factors that you have control over that affect resistance are:

• tube diameter - larger diameter less resistance
• tube length - longer tube run means more resistance
• velocity - the faster the fluid flows through the pipe (ft per sec) the greater the friction

Fluid resistance is calculated in "head loss".

Taco is a manufacturer of circulation pumps, and they have very good infformation that will help you calculate and optimize your layout so that you will have minimum resistance and maximum flow.

Here are sources of information from different companies. I find that it helps to see the same information ffrom different sources.

• HERE
  
• HERE
  
• HERE

If you go with HDPE, you can heat-weld it. If you go with PEX you can't weld it, I tried. But you can use crimp fittings.

When I put in a small loop field in my back yard, I just had 720 feet of pipe. The pump required was 1/4 horse to get the required flow, which was really excessively high, compared to my little compressor.

When I laid out the loops, I had an idea that it might be too long, so I did my layout such that I could tap into the center of the array, and create two arrays, without undo difficulty.

Changing from one 720 ft loop to two parallel 360 ft loops, cut my power requirement by a factor of 4. So my pump only had to be 1/16 HP... huge difference.

You need to do these calculations before you buy your tubing. If I had done this, it would have saved me a day of digging.

-AC

With your dx outdoor exchanger, it depends where you install the txv or metering device. If you run a liquid and suction line all the way out to the pond, you will save money by having smaller tubing for it. If the metering device is close to the compressor, you need to run larger tubing to and from the pond.

Sorry I don't think I'm following either one of you. Ac are you saying I might need 2 sets of 3/4 lines run to the pond?
Jeff can you explain that a little more detailed. I was going to look into where the txv went next. My first guess was on the indoor coils. In your opinion what would be best?
Been in the sun too long today. Might have cooked my brains some.

Refrigerant Flow Controls How It Works | EarthLinked Technologies Earthlinked Technologies

Within the EarthLinked heat pump is a uniquely-innovative, patented technique that enables control of the flow and stability of the refrigerant without any electronic devices, thereby further improving efficiency and reliability. The refrigerant is efficiently managed by two simple proprietary flow control devices: the Active Charge Control and Liquid Flow Control.

These two mechanical controls respond directly to the temperature and velocity of refrigerant flow through the system. They modulate the amount of refrigerant in circulation to assure optimum efficiency at all times. By eliminating subcooling in the condenser, the system operates at lower refrigerant “head” pressures with increased mass flow, which reduces energy consumption, increases heat transfer, system reliability and useful life.


Q and A from DX Geothermal installation - Page 4

I am located in Argentina where absolutely nothing of this subject exists. I am studying a 5Ton system with 5 Vertical BHE, 100ft deep each. The following questions arise:

1) I understand some units have solenoid valves to limit loop operation when condensing. I also understand this is for the condensing pressure not to drop to much. They are really expensive. Not to consider the electronic controller. Do you see a way to avoid using those valves?

The DX systems that I install do not have any valves controlling refrigerant flow. The design is very simple. there is a patented flow control device that regulates the refrigerant flow through the circuit.

2) The boreholes could be at some 45ft away from the unit. What size tubing is recommended. Again, the oil return might be the problem.

Unlike water source systems, DX systems are limited to the total length of line set run and lift. The maximun length of run is 125 ft. This is from the manifolds to the compressor and to the air handler. The maximum lift from the manifolds to the air compressor is 20'. the maximum lift from the compressor to the air handler is 40'. This is standard design and could probably be extended if you contact tech support and have the line sizes resized. As long as these guidlines are followed, there is no problem with oil return to the compressor as the velocities are high enough to ensure its return.

3) When thinking of DX Vertical BHE, don't you have a problem with oil return if you have the 3/8"liquid - 1/2"vapor tubing with no oil traps?

As stated above, as long as you stay within the manufacturers specifications, you won't have a problem. If your local ground temperature is over 60°F, you would have to install 1.5 loops per ton of system capacity. 5 Tons of capacity would require 7 loops 100' deep. They can also be installed in a diagonal configeration as well as pit and trench loops. Depending on drilling cost and land available, it might be cheaper to install a pit or trench system. I have installed all of them with no problems. The customers love the comfort levels and energy efficiency. They are a great system. You can do hot water heating and radiant floor heating with these systems.

If you want to research it some more, go to : EarthLinked Technologies | Geothermal HVAC Systems Earthlinked Technologies. Hope this helps and good luck!
Your help will be appreciated. [/B][/QUOTE]

Questions remaining to be ansered.
Where and how should I control flow?
How long/size of pond loop

Check out this heat pump diagram:
http://www.iarc.org/~4z5ay/HVAC/tev_3.jpg

Since it is reversible, there is a txv for each coil. Whichever one is the evaporator (cold) coil will have its txv actively controlling mass flow to maintain constant superheat. Whichever one is the condenser (hot) coil will bypass the txv through a check valve.

The only difference with your unit and the picture is that you will have a dx coil outside, correct? With the pictured unit, it is obvious that the txv is located right next to the outdoor hx coil, since the sensing bulb is positioned very close to the coil. With a run of the mill outdoor unit, this prevents the coil from being saturated and possibly burping refrigerant foam, among other things.

Since you will have a decent distance between your reversing valve and the outdoor hx coil, the lineset will exchange some heat with the ground, whether you insulate it or not. You can put the outdoor txv and sensing bulb close to the reversing valve or close to your dx coil. With the txv placed close to the compressor, your lineset is utilized as part of the heat exchanger. Both lines would need to be able to flow low pressure vapor-liquid-oil froth both in and out. With the txv installed next to the dx coil, the line between the two txv's is a liquid line, and can be downsized since it will always contain slow-moving high pressure liquid.

Awesome diagram. Thank you. I think I understand what your saying now.
As I see it the compressor and reversing valve will be right beside the house. Then the copper 3/4 lines that go to the manifold will go straight down 6+ feet into the ground out to the manifold under water. So I really don't have a choice as to where I put the txv on the outside. Therefore both lines will have to handle the low pressure vapor-liquid-oil froth.Is 3/4 enough to handle that? 7/8 copper wasn't too much more expensive.

"the Active Charge Control and Liquid Flow Control" is a quote from the artical above. The TXV is the Liquid Flow Control. What is the Active Charge Control?