geothermal chiller

[Cuby2k]

<a href=showthread.php?s=&postid=7352578#post7352578 target=_blank>Originally posted</a> by salty joe
Marc, if only that heat exchanger were titanium, it would be looking good. I don't think aluminum will do a reef tank much good.

Would a standard di-electric (I think that is what it's called) fitting make a problem free transition from copper to titanium? Also, to be safe, the titanium would have to extend out of the tank and down the outside of the tank before connecting to copper.

So PVC is not an option because it allows O2 into the system??? Do I have that right?

Joe

No Joe,
The PVC is OK except for it's ability to transfer heat. It would also serve the purpose of the di-electric coupling.

I would run PVC (or PEX) from the ti heat exchanger to and through all of the above pumping and above ground apparatus. Then to the outdoors and at a point about 18" below the surface of the ground I would transfer to copper.

If you are in an area that is subject to winter freezing you will need to isolate the portion that goes outdoors and then below grade from freezing. Maybe through a basement wall. In my area I will probably have to bury the piping about four feet below the surface to get the necessary cooling.

Just make sure you have a vent at the high point, a means of expansion, and a means to fill and maintain static pressure.

 

[salty joe]

Thanks, I could have sworn that someone said that PVC allows O2 into the system and can't be used if the pump has an iron impeller.

Joe

 

[Cuby2k]

<a href=showthread.php?s=&postid=7352656#post7352656 target=_blank>Originally posted</a> by salty joe
Thanks, I could have sworn that someone said that PVC allows O2 into the system and can't be used if the pump has an iron impeller.

Joe

Well it may have been me. PEX without an oxygen barrier will eventually corrode a cast iron impeller. While that remains true I am not sure how long this would take.

I would make sure the impeller is stainless at a few dollars more expense - or - get your PEX with an oxygen barrier.

Domestic water grade PEX does not have the oxygen barrier typically because the water is already laden with oxygen. But that is why black iron pipe will rust so fast in a domestic water system. And in closed loop HVAC water systems black steel pipe is a norm.

 

[salty joe]

What is PEX made of? Would a di-electric connector be neccessry between the copper and PEX and between the titanium and PEX?

Doesn't copper resist further corrosion after corroding to a green color? Or is that not true for submerged applications?

 

[Cuby2k]

<a href=showthread.php?s=&postid=7353008#post7353008 target=_blank>Originally posted</a> by salty joe
What is PEX made of? Would a di-electric connector be neccessry between the copper and PEX and between the titanium and PEX?

Doesn't copper resist further corrosion after corroding to a green color? Or is that not true for submerged applications?

PEX is crossed link polyethylene and does not require a di-electric coupling..

As far as copper's resistance to corrosion after the green has started, jeeze I am not sure. I would guess that to be true . Isn't that what the Statue of Liberty skin is made of?

 

[ChemE]

As long as the oxide layer is tightly adhered, it will prevent water and oxygen from reaching the uncorroded copper. In fluid flow applications the flow can wash away this oxide layer and expose fresh copper to a corrosive environment. This process is referred to as erosion corrosion.

 

[douggiestyle]

<a href=showthread.php?s=&postid=7353960#post7353960 target=_blank>Originally posted</a> by cseeton
I am in no way saying that you can not use copper, I jsut don't recommend it because it costs too much and every solder connection you have in the ground better be a good one. If you can get 5/8 copper coil 75ft for $70, that is a good price, the cheapest I have found recently for a 50ft coil is $150.

You nailed the reason to use PEX in two statements:





The low conductivity of the earth means that you can use just about any tubing you want because you will not be able to push heat into the soil faster than the soil will accept. PEX or copper behave the same with surronded by an excellent insulator - good ol' mother earth.

You will need much more that 75 feet of tubing to reject any appriciable amount of heat; 200-500 ft would be a better starting point.

a typical horizontal ground loop is sized at about 400-600 fet per 1 ton of cooling.

 

[douggiestyle]

<a href=showthread.php?s=&postid=7353960#post7353960 target=_blank>Originally posted</a> by cseeton
I am in no way saying that you can not use copper, I jsut don't recommend it because it costs too much and every solder connection you have in the ground better be a good one. If you can get 5/8 copper coil 75ft for $70, that is a good price, the cheapest I have found recently for a 50ft coil is $150.

You nailed the reason to use PEX in two statements:





The low conductivity of the earth means that you can use just about any tubing you want because you will not be able to push heat into the soil faster than the soil will accept. PEX or copper behave the same with surronded by an excellent insulator - good ol' mother earth.

You will need much more that 75 feet of tubing to reject any appriciable amount of heat; 200-500 ft would be a better starting point.

a typical horizontal ground loop is sized at about 400-600 feet per 1 ton of cooling.

 

[douggiestyle]

according to aqualogic

apx. 3080 btu of heat removal (cooling) should handle a tank of 125g-175g
this equates to apx 1/4 ton
so 100-150 feet for ground loop with an apx. size tank of 150g

obviously the smaller the tank, the smaller the ground loop.

with a 90g tank, 75 feet of ground loop would be right on target.

horizontal is the way to go. vertical ground loop is pretty extreme. gotta have a hole apx. 40 feet deep.

not sure of the spacing or recomended depth. i havent gone there yet.

if someone had a well there are some pretty awesome and efficient designs if the well is not to deep.

noticed a trend. would it be safe to say 1' of ground loop per gallon?

 

[cseeton]

I just bounced over here because douggiestyle pointed this thread out to me.... I will catchup.

In the meantime, the 400-600 ft of groundloop coil per ton is for a heat pump (GSHP) application where your DT (earth to loop) is larger, not direct cooling which requires longer lengths.

 

[Cuby2k]

Hey I agree that the issue is the conductivity of the Earth and not necessarily the piping. That never hit me until cseeton pointed it out. That does mean that 400 to 600 LF that Doug suggested in very close, and it may take more.

Your DT is still around the 20 deg range but the problem is that you really need another heat exchanger in your sump. Titanium might be a great thermal conductor but water is not, so 1 to 2 feet of ti in your sump just isn't going to cut it. The one thing helping us out is that the water is moving fairly fast so the heat transfer improves inside of the sump.

No doubt a little more thought is required before sinking a bunch of piping.

 

[Cuby2k]

Well cseeton I guess I have to eat crow once again. I guess I have not priced copper lately, I just had a roll left over from a job that I did last summer and I remember that for both the scution and the liquid line it was around $115 for 75'.

Well I just got off the phone with my supplier and I guess copper has gone through the roof. In fact the price that he would quote was good for only three days!!!

Sooooo, it is looking like we are back to PEX for the buried loop. Thank you for clearing that up for us (me).

 

[cseeton]

Agreed, copper prices have skyrocketed and I don't see them coming down any time soon.

Ground sourced heat pumps (GSHP) have a temperature difference of about 40F for cooling since they use fluid to cool the condensor and go into the ground around 90F (average ground temp around here is about 50F) - hence can have a shorter loop for the same capacity 400-600 ft per ton for GSHP. GSHP also operate year round utilize what I call "heat banking" - you deposite heat into the ground in the summer and withdraw it in the winter. This gives you some additional capacity over a deposite only design (your direct cooling loop).

 

[RCragg]

2 closed loops?

2 closed loops?

OK I have been following along and am just wondering if it wouldn't be better to have two closed loops that run through a common cistern of some type. What I mean is have the copper loop with tap water or even antifreeze in it going through the ground and then to a water filled cistern to act as a heat dump. Insulate it so the water will stay cold. Have another closed loop with a titanium heat exchanger going through the same cistern and then back to the tank. I am not sure of the heat transfer but it seems like the two loops in the cistern could be put very close together (even interlocked so to speak) and you no longer have to worry about cross contamination. OK go ahead and poke holes in my ideas. I know the people who use the dorm fridges always say to put a bucket of water in it to run your coil through. Maybe not the most effecient way but I think this would work. By the way this is a great discussion and I plan on doing this when I return to the states. Thanks to all of the pioneers (guinea pigs??) out there who are trying this. Rick

 

[Marco67]

Arggggh

Arggggh

Thank for all the new input guys, Now I'm really FUBAR.
I need to back fill the week after next, and just when I was set on copper not using copper makes all to much sense.

OK so I understand there's no sense in using (paying for) a material that can give up heat faster than the ground can accept it, conversly it wouldn't make sense using one on the other end of the scale. So .... which material is that ? Pex?

If Pex, why is pex any better than the regular black plastic water line commonly used ?
I've called around and found I can get 100' coils of 5/8" ID "thin wall" tubing rated for burried drinking water at 100 psi for about $.20/ft

 

[douggiestyle]

so we need a direct use geo cooling model.

 

[douggiestyle]

Re: 2 closed loops?

Re: 2 closed loops?

<a href=showthread.php?s=&postid=7357866#post7357866 target=_blank>Originally posted</a> by RCragg
OK I have been following along and am just wondering if it wouldn't be better to have two closed loops that run through a common cistern of some type. What I mean is have the copper loop with tap water or even antifreeze in it going through the ground and then to a water filled cistern to act as a heat dump. Insulate it so the water will stay cold. Have another closed loop with a titanium heat exchanger going through the same cistern and then back to the tank. I am not sure of the heat transfer but it seems like the two loops in the cistern could be put very close together (even interlocked so to speak) and you no longer have to worry about cross contamination. OK go ahead and poke holes in my ideas. I know the people who use the dorm fridges always say to put a bucket of water in it to run your coil through. Maybe not the most effecient way but I think this would work. By the way this is a great discussion and I plan on doing this when I return to the states. Thanks to all of the pioneers (guinea pigs??) out there who are trying this. Rick

each time you move the heat you waste energy. so best would be to take it direct to the tank.

now say that you did this. you divert a spring into a cistern and let drain out. you run that water through your system to cool the tank. now you would have about the best system possible with geo cooling.

an old friend of mine has a spring that runs out on his property. he built a pond. then took a drain from the bottom of the pond and ran it into his house into the basement into a large concrete cistern that overflows into another drain that goes to a stream at the bottom of his property. in that cistern is his geo loop for his heat pump.

 

[RCragg]

I agree, but...

I agree, but...

Hey Doug I agree but the purpose for the two closed loops is to prevent cross contamination of the waters. A cistern would stop that from happening. I think you are right about the stream but not many people are so lucky. What is someone who doesn't have one supposed to do. Geo cooling to the earth is a viable option but having the water go directly to the sump through copper piping is asking for disaster. Pipes fail. If the water just went into a cistern only the cistern would become contaminated. Just MHO. Rick

 

[douggiestyle]

Re: I agree, but...

Re: I agree, but...

<a href=showthread.php?s=&postid=7358624#post7358624 target=_blank>Originally posted</a> by RCragg
Hey Doug I agree but the purpose for the two closed loops is to prevent cross contamination of the waters. A cistern would stop that from happening. I think you are right about the stream but not many people are so lucky. What is someone who doesn't have one supposed to do. Geo cooling to the earth is a viable option but having the water go directly to the sump through copper piping is asking for disaster. Pipes fail. If the water just went into a cistern only the cistern would become contaminated. Just MHO. Rick

didnt realize that this was what you were after.
i think the whole copper tubing concept has been buried (ha,ha)

no sense in having something that is more conductive than the earth its self. a very basic point that was originally missed.
so we are back to some sort of poly tubing.

 

[douggiestyle]

cannot find any direct use geo cooling models, only geo heating. found some software for geo systems with a free trial. will mess around with it, see what it does.