I bought an older home (1964) it has the original windows (single pane w/ storm windows) and the walls are not insulated (Outside is brick). The A/C is more than 12 yrs old. The heat is an oil fired furnace(hot water baseboard). I live in central Virginia. I am planning to insulate the walls and replace the windows, Lastly, I want to install a geothermal heating/cooling system. From what I can tell so far, DX requires a smaller horizontal loop footprint and is more efficient than water. I am planning to install loop field myself, I would like opinions on the pros and cons of the two types of systems and degree of difficulty of installation. Thank you!!! Tod

The best geo system is the one installed by the contractor in your area with the best references.
good luck,
Joe

I've settled on a Water Furnace system, but I'd still like to resolve an open question I have: could someone please contrast the pros and cons of the Freon/copper tubing closed-loop system [as DX] with the water/antifreeze of the WaterFurnace closed-loop system. The Joule-Thompson effect [on which I am not an expert] which drives the Freon exchange system isn't present in the water/antifreeze loop [is it?]. How does that affect heat exchange and efficiencies. I know someone attempted to answer this for me a couple months ago. I'm a bit more eductaed now [disproven by the fact that I just misspelled 'educated'], and a rehash should be more illuminating.

  The DX systems uses the refrigerant carrying copper in direct connect with the ground to achieve its latent transfer of heat.  As for the water- based systems, an internally installed heat exchanger inside of the package unit, is where the the water solution is pumping from the ground loop and transferring its heat, to the refrigerant cycle.

I have to go back to science class for the Joule-Thomson AKA Kelvin effect

To clear up the mantra that DX has a smaller footprint; it is true that DX puts less pipe in the ground, but it could actually require more excavation. Earthlinked for instance has us run 125' long down and backs pushed to the sides of a 4' trench (that's 250'/ton) while our slinkies use 600' pipe/ton in a 30" by 110' long trench.
Therefore the DX has a smaller "ground loop" footprint, but it's a little disingenuous if someone is trying to make you believe they'll tear up less of your yard.
J

From the above, it sounds like all things being equal DX probably uses less pipe, but can take just as much or more excavating. Individual system sizes might be limited due to oil return issues.

I was wondering, is the DX system theoretically more efficient as it has 1 less energy tranfer involved? A water source unit in heating modes transfers energy from earth to the water in the closed loop, and then rom the water in the closed loop to refrigerant and finally from refrigerant to the air circulted in your unit. DX system transfers energy from the earth to the refrigerant and then from the refrigerant to the air. Just a thougt....

In theory, yes and even on paper in some situations.....however;
DX swiftly changes the ground temperature around it, soils don't move heat as quickly and this means that COP's/EER's begin to fall.
Water source puts more loop in the ground and changes surrounding soil temps. more slowly. This means COP's, EER's fall more slowly.

Both work, but as a practical matter boasts of greater efficiency from any system are disingenuous.

J

I should add that open loop on both systems offers highest and most stable cops and eers but does not factor well pump kw consumption.
J

Joe,

Does adding more copper line to the DX system make it more efficient?  Is there a maximum length that copper lines can be for the DX system?

There isn't 1 less energy transfer cycle as I look at it , but please correct me if I'm wrong. Both DX and WaterFurnace have 3 sites of heat exchange.

Considering the heating cycle:
1} the heat exchange between the warmer ground transferring heat to the coolant in the ground piping [either Freon for the DX or water/antifreeze for the WF]. This coolant left the house cold and needs heat added back to it. There is some heat added back through the ground, and the efficiency of geothermal systems comes from this elevated ground temperature relative to ther colder ambient outside air temperatrures for air based heat exchangers. Emerging from the ground loop at 55 deg F [in my region] (or approaching that temp) before re-entering the 'unit' is better than being circulated through the open ambient air at 20, or 10, or zero deg F.  The next stage of heat transfer needs to add less heat for the ground systems as compared to air-exchange heat pumps.

2} Still, more heat needs to be added to the 'coolant' prior to being distributed to the house by the air handler. The temp of the 'coolant' must be brought up significantly above room temp inside the house in order to be able to heat the house.  In the DX system this is done in the compressor [or condensor]. This is where the classic thermodynamic Carnot cycle is carried out. The gaseous freon is compressed by a mechanical pump driven by electricity. The compression of a gas introduces heat into the gas [there are some exceptions, but the exceptions aren't used for this purpose]. The freon liquifies and is transported from the compressor to the indoor air handler [I'm not an expert on refrigeration --- maybe the freon is always in dense gas state]. For the WaterFurnace 'unit', the heat exchanger is not a Carnot cycle as at these temps and pressures water is always liquid. There is a heat exchanger in the WF unit serving thwe same purpose as a comprerssor in the DX system, transferring the additional heat needed to the coolant prior to the air handler. I assume an electric resistance element of some nature [either internal or external to the coolant system] is being used, which I'll figure out now that I have my new unit sitting in the basement.

3}  At the indoor air handler, the 3rd heat exchange takes place as the blower blows room temp air from the system's return ducts over the heat exchanger within the air handler with the coolant [freon or water/antifreeze] flowing through its vanes, extracting heat from the  freon or water/antifreeze and thus warming the house. The freon or water/antifreeze then returns to the 'unit' [compressor for the DX] and is routed  to begin the cycle again. In the case of the DX/freon system, the freon is allowed to expand and gasify again prior to entering ther ground, completing the Carnot cyle. The freon cools significantly here before re-entering the ground. This is why the DX systems cool the surrounding ground so rapidly.

Joe, I don't know how you would have an open loop with a DX system. Am I missing something? As I understand todays DX technology, when a DX loop exceeds a depth of about 100' oil seperation may occur and begin collecting at the "U". Son't as me why because I don't know. Also, I've heard there is work being done to extend this depth but haven't heard more than that or how it will be done. As always, spacing is critical to having the correct volume of heat sink for each loop, water or DX. Not enough earth volume is begging trouble. It's the couple of pipe to earth that makes this whole GSHP thing work! Loose that and you're sunk.

I'm quite certain Joe was comparing conventional open loop water source systems TO DX.

You are correct - the phrase "open loop" is irrelevant to DX.

KJ - in both DX and open loop the majority (~90%) of the heat transfer occurs upon phase change of the refrigerant - liquid to gas and back to liquid. All systems have both a condenser and an evaporator. In winter, condenser heats indoor air. In summer, evaporator cools indoor air.

The only diff between DX and water source is in how the heat is transferred to / from refrigerant

A heat exchanger may be employed to use well water with a DX system. Much like a reversed on demand water heater.
Re add to the length to improve DX efficiency, as was already mentioned recovery of the refrigeration oil becomes difficult after X feet (varies by brand and refrigerant). This is one of the limitations of DX, water source's reach is quite a bit longer which really matters if customer wants the field further away from the house to avoid landscaping repair.
J

I'll throw in my non expert .02 here based on the original question. Any heat pump will be working hard in the above mentioned house. Like most energy efficeint devices they work better under ideal conditions. Such as a well insulated home. No heat pump is ging to be as susccessful at heating an old drafty house as your oil burner. The oil burner gets hotter it just uses more energy to do it.
That being said I'm seeing a couple of different things being thrown about above. DXs can be built using 3 kinds of coils. horizontal. vertcial. diagonal. (i'm not getting into Water based systems much as I have little experience with them).
My understanding is that verticals have never worked well.
Horizontal coils don't have the issue with the oil return(if installed correctly) but can get a "thermocline" (my description) problem. This is when the soil gets dry and will not readily take the heat from the coils and returns hot gas to the compressor. You get a hot layer in the soil. This is not an everyday problem but does show up in times of extreme prolonged heat and no rain. I have this type of system. My solution has been to turn on the soaker hose that was installed with the coil to help with soil compaction. Run it a little bit every couple of days to keep the soil moist in dry weather. This has worked for me for 15 years. Horizontal coils are also much cheaper to install. It's a much cheaper to dig a swimming pool than 8-12 70' wells. In my case a 50'x50'x6' deep hole. Far more practical for the DIYer. The diagonal coils(in well holes) solve the "thermocline problem by sreading out the heating area both horizontal and vertically. This also adds more cooling ground water into the equation.

Desuper heaters also help and I love the free hot water.

I have lived with the same DX system since early '94. I would do it again tomorrow. I personally want nothing to do with water based sytems. In this state there are quite a few badly installed Water based sytems that have leaked antifreeze into the soil and fouled the owners wells. Granted the key here is BADLY INSTALLED. But if that does happen how do yo fix it? I don't want that potential problem. Plus in my opinion water based systems have more parts which equals more things to go wrong. More pumps to fail in the middle of the night. I'm a KISS principle type of guy.

Dx has 2 heat transfers=soil to refridgerant, refridgerant to air in home.
Closed loop water based has 3=soil to water, water to refidgerant, refridgerant to air in home.

It mainly boils down to who can do the best job for you WHERE YOU LIVE. Because this stuff is not as common and widespread as you would think. Even here in a very populated area most contractors don't want to be bothered with GEO systems if they can talk somebody out of it.

Hope this helps a little. There is some real good folks and info on this site, However sometimes people forget that alot of the new questions are posted by non technical newbies. Sometimes the answers can get a little confusing for the average joe.

Very helpful, and much appreciated!

Best regards,

Bill

In my previous post on this thread, I stated the WaterFurnace heat exchange at step 2, substituting for the compressor/condensor in a DX freon system, wasn't a Carnot cylce process, but instead I surmised it must be some resistive heater process, as I didn't know what exactly 'goes on' inside the WaterFurnace unit. I was wrong ... there is a compressor/condensor unit in the WaterFurnace system [at least the Envision]. Now that ours is somewhat installed and I have a manual and the real thing to investigate and prod, I have learned that the water/antifreeze re-entering the 'unit' after heat exchange with the ground [absorbing heat for winter heating] passes into a coaxial copper-copper tubing assembly [Cu-Ni for some open loop systems --- ours is closed loop]. The water/antifreeze mix runs through the inner coax tube, while the cold refrigerant [freon 410A] runs through the outer coax tubing. Heat exchange from the water/antifreeze of the inner tube gasifies the refrigerant in the outer tube [heat is absorbed by the freon at this point]. The freon 410A enters a scroll-type compressor whioch compresses the gas, evolving heat and raising the temperature of the freon 410A to approx. 165 deg F. The freon is then discharged into the air coils of the air handler for heat exchange into the house. I have paraphrased this explanation from the WaterFurnace Envision Owner's Manual.

Finally, I understand how this sytem works !! I wonder, does the DX system use separate ground source and compressor/air handler loops running through coax like this, or is the freon of the DX just continuous through the entire sytem ?

It is continuous throughout. Earthlinked has a nice animated schematic at the bottom of the page at http://www.earthlinked.com/residential/how-it-works -Adam

DX employs coax for DSH or on demand hot water. Otherwise the same refrigerant circulates through the ground and the fan coil.
joe

I've read this thread and still confused about DX and closed loop. BOTH are in direct contact with the ground......What I'm I missing?? You can tell that I'm a newbe tying to learn this stuff.

By chance....does anyone have a picture of a DX horizontal being installed?

In the Northeast the DX works good because the loops are only about half the length as water loops and
I live in NH ( We are called the Granite State for a reason , lots of hard rock ).....

A DX hole is 100 feet per ton...
A water loop is around 170 feet per ton...
( vertical bore )

A DX hole cost half of a water loop hole to drill
( because the hole iand drill rig is smaller )
It doesn't take long to realize the big difference in cost before you even get into the building......

I like both systems , DX or water , each has it advantages...

Think of DX this way ..... Take that coil off the back of your refrigerator , extend the lines and bury
that coil in the ground .... You have DX.....

Closed loop water is going to have a heat exchanger and pump to transfer that heat or cool
from the ground to the GEO unit .... An added cost to consider.....

Dave in NH