Geothermal air in line science question

aconred

<span style="font-size:12pt">Trying to learn some science to understand, goggled and did not find ran across this site an thought **** I’ll ask and see if anyone has insight can’t hurt. The basics of the question are how does air get into your geothermal loop without a leak? I’m assuming it has something to do with the chemical makeup of the loop liquid i.e. some of the H2O is broken down and got some O in the line. I am a general contractor. I am early riser when I get up all is real quite about a year ago when all was real quite I was hearing what sounded like a faint heartbeat slowly got louder. It’s been slow getting louder. I investigated and found it was my loop making a small noise, but only done it with the upstairs unit. My loop downstairs is exposed, I could hold my hand on the line to the upstairs and it pulsed with the noise, downstairs had no problem. Called geo installer what he said made sense, even though he did not know the science. Said I had air in my line my problems up high is why you don’t have the problem down low. OK how do I fix? Do I have you come more juice in it. He said no you can do it; turn off both systems hook a garden hose to the loop and to your domestic water. Turn it on make sure all is tight no water leaking from hose etc. then after pressurized open the loop valve and let it stay on for 10 – 15 minutes then reverse procedure then I asked the questions, WATER will it not freeze he said no you have plenty of stuff in there to keep from freezing your only talking a small amount of water probably less than a cup full. OK second question if I got air do I have a leak, he said no it just develops, said why he did not know. So I am here. </span>

<span style="font-size:12pt">thanks in advance </span>

<span style="font-size:12pt"> </span>

icesailor

Bumps in the loop:

There's a hole in the "expert's" knowledge.

There isn't enough pressure in the system. If the pressure isn't high enough in the system, the top of the upper loop can fall into a negative pressure or vacuum. It will allow circulators to cavitate and make steam at lower pressures. The pressure must be at least 12# PSI or higher.

Higher system pressure will compress the bubbles.

It is possible that you have a leak but it is more likely that you have no "spring" in the system. That is what the expansion tank does.

Show pictures of the near piping of the system.

hot_rod

air in loops

it could be the air was never completely purged out at the initial fill. It takes a large flow rate to purge an entire loop field if you cannot isolate individual loops. I think in some cases the installers do not have enough pump capacity to fill and purge large loop fields properly.



Everytime you add additional water you add some air into the system. I like to see an automatic air elimination device installed on GEO loops just as you would on a hydronic system. Small air bubbles can reduce the heat transfer in the tube and the heat exchangers, it takes time to purge the small microbubbles that come out of solution as the fluid is heated. it is almost impossible to remove the micro bubbles and enrtained air at the first fill and purge.



Remember also as you heat or cool water it will cause the system pressure to change, an expansion tank on the system wiull provide for a constant pressure and assure the pump has sufficient NPSH to prevent cavatation and the forming of additional air pockets.



Here is a link to a tech journal that clearly explains the how and why of loop purging and air removal, expansion requirements, etc. Page 60 and on explains purging and air issues.



http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_9_us.pdf



Another good source for loop field information is the IGSHPA site www.igshpa.okstate.edu



hr

icesailor

Air in systems:

Hot Rod,

You are absolutely correct in what you say.

And I NEVER have any problems with air in a system. I drain houses and turn them back on in the Spring. I purge into a bucket and when the water comes back hot on the return, I stop. I can hear water moving in the pipes but as long as it stays hot or gets hotter, I leave it alone. I've done multi-zone houses with no recurring air problems.Once purged, I close all the 400's down tight. Spirovents are capped. because I blow the water out in the fall. I never have a zone go down. I set the pressure at 16# to 18#.

Last year, I took out some radiators in an old house with an old pumped gravity system. Someone had re-piped a radiator and it was a long flat straight shot from the main to the radiator. It was working when I drained it. It wasn't working when I re-connected it. I was ready to change the flow control valve on the radiator. I set the system pressure at 20# and went home for the night. The next AM, I was planning on changing the valve. But the radiator was now working. Once I squished the water in the long pipe, flow started. Then, the air was absorbed. Overnight

The biggest cause of air in the systems that I run into is open air vents on upper floors, and the fill valve not adding water and the pressure dropping to below 10# and the upper level of the system goes negative or cavitation from over pumped systems.

That's what works for me. It always has. But I'm starting to think I am dreaming it. No one agrees with me.

acon

Icesailor / hot rod

Lol, this is aconred don’t know **** all that e mail passwords good for this site? Never had a sight that didn’t e mail you something to let you in first time! Anyways I’m back in for a second but not how I registered I just made up something and got back on site. If they email aconred password reset I’ll be back. I typed the below a while ago, figured I would send Monday. Did not really expect to get back on now._______________________________________________________________________________

Thanks I read at 2:30 Saturday then by mistake x’d of the browser, **** no problem I just open back explorer and sign back in only registered only done it a zillion places (ever one makes you, I sure hate it). Did not like my password! Shot I must of hit wrong key had it send me password, waited, waited. Went to the yahoo server to check and no password reset ever sent, I tried to re-register, nope that e mail was already register send password again, nothing. Anything’s possible but thinks site has problems, typing this in word and will paste on site when and if I get back in – the good with the bad – I was fine with black screens, green lines and DOS. Then this new thing window came along, 2.9 I think.

Any ways I seen the first two reply’s some great info, the pdf  looked full of info I skimmed it lot of reading, I understand all that stuff, I just got read it soak it in. I’ll get it. I know what an expansion tank is seen hundreds of them now little about the science of them but will. I’m gona learn, take some pictures of my loop in basement, and ask some more if needed. I think adding an expansion tank seems like it can be done. I’d have to get someone with pump to put more juice in it. I watched them do it, several 55 gallon drums of stuff in then after full it had one drum that it sucked out of and the other house filled up, ran through the lines for long time I think a few hours I think there was a gage on pump? Not sure, 2008 been running 4 years and 1 month now. MY biggest concern does not want to burn something up on the unit, which I am assuming is the pumps, which are really separate from the unit. I’m bad about doing my own stuff but learn before I start.



Thanks......assuming I get back on I’ll make a new email address if I got to I’ll try off and on till thin.

 



okokok! 6th try for a nick name  7th bob 8th oh my 9th tired of trying 10th acon



 

hot_rod

mysterious air

air can be a elusive creature in a closed loop system. Often raising the fill pressure will cause large bubbles to compress and work through the system. I feel you want 5 psi at the uppermost heat emitter to seal any air vents.



If you raise the fill pressure and keep it raised it would be good to adjust the expansion tank pressure to the fill pressure.



A central air eliminator is a wise investment I feel. Caleffi has an option hygroscopic cap for the Discal air separators. This gives you a second seal if the vent valve should stick.



We also have a check valve cap for our air vents to prevent air being sucked into a vent, should the system be pulled below atmospheric.



I've wondered how those converted, large pipe, gravity systems maintain enough flow velocity to push the air ahead of the water. Generally 2- 4 feet per second is required to shove the air along and back to the vent.

Mark Eatherton

GSHP industry versus Hydronics industry

That particular industry has a lot of catching up to do with the hydronics industry. When I first got involved, over 10 years ago, and to a great part many manufacturers today, did NOT require expansion tanks, air eliminators etc. Bear in mind that the bulk of the development work on GSHP systems was done by farmers. Nothing derogatory towards THAT industry. I actually envy farmers/ranchers because they are required to have a good working knowledge of ALL mechanical systems. But there are some things that they don't understand or take into consideration until a problem develops.



It has not been until recently that manufacturers, like Caleffi, have introduced the GSHP industry to labor/trouble saving devices like air elimination, dirt elimination, expansion tanks balanced manifolds etc. The primary reason they didn't feel that these extra components were necessary was because they felt that if the system were perfectly tight (yeah right, in your wildest dreams) as the tube was heated or cooled, the fluid pressure would remain relatively constant, hence no need for those additional components that drive the prices higher.



On larger commercial jobs, air elimination and expansion compensation is a requirement on the loop field, but for some reason, they ignore the needs of residential systems, which in reality have to go through the same temperature changes that commercial systems do, but on a smaller scale basis.



Do yourself and your system a favor. Install an expansion tank near the loop pumps inlets, and install an automatic air eliminator (take your pick) on the top of the system. You will not regret doing so. We've proven their effectiveness for many years. If you are a GSHP contractor, as HR has said, consider the use of these device in your GSHP loop system and your system will operate trouble free for many years without breaking the bank.



ME

Mark Eatherton

Mysterious air in larger pipe systems.

HR, it is obviously not being swept back down to the mechanical room. It ends up trapped in the upper floors radiators, that are oversized anyway, so it doesn't really cause any issues. You can find the air by doing a manual bleed with all pumps off.



I have been told by certain MBR manufacturers that their air elimination devices work SO well that it will remove any trapped air in the system by getting it back into suspension, and getting it back down to the MBR where it will "agglomulate" on the coalescing materials, and then gather in a larger bubble and be discharged through an auto vent... And if you believe that, I have some land I'd like to sell you off the coast... ;-) It just doesn't pass the sniff test, and I have found many air bound systems on upper floors that had an MBR installed, thereby proving their theory wrong.



I once had one of their salesmen tell me that their product was so effective that it could suck oxygen off the next planet... REALLY? These guys will tell you anything to get you to buy their products.



MBR's are absolutely more effective at removing free air, but there are still limitations to their ability.



ME

zacmobile

loop expansion

Thankfully the geo industry is catching up with the rest of the HVAC world and now considering these things in their loop design and providing products for their implementation. I have been installing expansion tanks & occasionally air separators on all my groundloops for the past 5 years or so, with much chiding and regarded as overkill by my comrades in the geo installation biz. but I have had zero loop air & pressure problems since making the switch and they have had many. I have also been told by a manufacturer rep that it was a bad idea to put pressure gauges on the loop because it would just be inviting callbacks.

Mark Eatherton

I'd find a new rep...

Kind of silly way to do business in my book. If you ignore the problem, it will go away...NOT !



Keep on doing the right thing regardless of what your competition says, and add value to your proposal over theirs by telling the consumer that you DID include these problem saving devices in your loop field piping design and estimate.



ME