Geothermal HVAC

Discussion in 'Off-Topic' started by inwo, Jan 8, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    Are there any HVAC guys on here that like to talk shop with hobbyist?
    (most don't):(

    It would be like me talking residential wiring.:cool:

    I put in my own Geo. system when building about ten years ago.

    Took me about this long to get it the way I want it. :p

    I researched it before building and I've learned a lot since.
    What I don't have is experience. This is the only one I've done except my daughters add-on.

    As it is going on 10 years, what can I expect?

    I'd love to go into detail as it's been my hobby over these years.
  2. #12


    Nov 30, 2010
    What? This post has been up for 3 minutes and nobody has pointed at me?
  3. MrChips


    Oct 2, 2009
    Try #12.....

    Edit: You beat me to it.
    #12 likes this.
  4. #12


    Nov 30, 2010
    What can you expect in regards to what? Good efficiency? Year round effectiveness? Finding out you buried stainless steel tubing clamps but the screws weren't?

    Edit: Just a coincidence that I happened here at this moment. Posting about the availability of the Bluetooth Catfinder.
  5. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    I gathered that you did AC service, but what about geothermal in the North?

    I guess you could address some concerns.

    My system runs on AB plc. It's really nice to watch it and fine tune it from this pc.

    I'm sure that seems silly to you. It's "something completely different" (m.p.)
    for me.

    Run times in the winter are about 20-30 minutes out of each hour.
    When it's -20° it can run for over 60 minutes.

    I like to limit the 20kw electric.
    So I use a run-time limit that shuts down compressor, waits 5 minutes to settle, then brings on aux. heat.

    Generally set to 50 minutes.
    I just bumped it to 60 and its kept the aux. off during these -20° days.

    What kind of life can be expected? Much over 10 years?
    Average winter use (6 Mo. here) must approach 40% on time.
  6. #12


    Nov 30, 2010
    I don't work in the north country and I've never done a geothermal, but I know the physics of the operation from 40 years of experience and the schooling required to get a State License. However, I don't know what an AB plc is.

    If you did the buried part right, 50 years is easily achieved. Of course, busted pipes caused by freezing is a real danger! It's the usual failure modes that will getcha. Even copper rots when constantly exposed to water. I hope you have a stainless steel heat exchanger.

    You don't need to, "let it settle" after you turn the compressor off. (I don't even know why you would shut the compressor off.) The electric heat should be after the AC coil (in the airflow). That allows the air to suck the last of the heat out of the coil just because the fan is running air over the electric heaters.

    The usual guarantee on compressors right now is 10 years. I nursed the last A/C on my house to 30 years of life. Long past due for a high efficiency replacement! However, you already have a very good efficiency machine. You will use up a couple of fan motors every 15 or 20 years. Contactors, capacitors, the usual stuff will go wrong. Fearsome is the Freon leak because the government keeps changing which Freon you can buy. I have an unopened can of R-22 for my home, and the customers will just have to buy the R-410 systems. They are not getting my private stash!
    Last edited: Jan 9, 2014
  7. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    See if my run times show in print screen.

    The columns alternate on off on off etc.

    There are some 60 minute run times from last night -20°.
    Aux. heat is just tracked as season total. 294 minutes as of now.
  8. #12


    Nov 30, 2010
    How you play with the controls makes no never mind to me. The water fed system should run until it can't keep up, then stay on while the second stage of the thermostat kicks in the electric heat to get the building up to only 2 degrees F below the set point.

    Again, I don't know why you would turn off the most efficient system and run the least efficient source known to James Watt.
  9. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    I could go on all night. I'm retired.:) Feel free to bug out anytime. We can pick it up later.

    On the buried part:
    Chapter 1
    The fun begins.

    Got in a pinch when building. Local suppliers would not sell to me. Quoted prices double to protect there pros. That's fine but no help.

    A buddy offered to get me a FHP brand 6 ton for $500 over cost. Not my first choice but it's still going.

    Pressed for time I hired the local pros to do the loops.
    They are the go to guys for all the shops in tri state area.
    Even had "Hi Tech" in the name.

    Two monkeys came ready to work. The first promise of 7' depth was down to about 5' and I think they barely did that.

    They were able to throw 6 slinky loops in the back yard in half a day.
    They backed over one coil that was leaning against a tree, then worked another 6 hrs digging it up and fixing leaks.

    Needless to say I was plenty nervous!
    In fairness, they must have done ok. Although I still wonder whether I have 5 loops or 6?

    All proper tubing and welded joints.

    I had two 10" pvc pipes stubbed out with plans for manifold and valves inside.

    That was a no-go and the pre-made manifolds are buried. Just two 1 1/2" tubes into my pump/valve box.

    I'll hope for lifetime from the loops then.:D

    On the settle time.
    I do some things for strange reasons.

    I try not to use electric at all!
    The settle time allows the last little heat in the system to reach the thermostat. It's often enough to keep electric off.
    It also allows me to notice the short cold air burst before aux heat comes on.

    This brings me to the next question.
    I really don't need the aux. Only use it because I worry about long run times wearing out the compressor.

    Should that be a worry?
    I'm thinking maybe the start cycles are worse than running for another 10 minutes each hour.

    How about running continuous? If it ever gets that cold.
    Is that a bad deal.

    It's a trade off between wear and the cost of aux heat.
  10. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    I'm going to keep prattling on while I'm thinking about this.:rolleyes:

    Had an early failure on one of the grundfos circ. pumps.
    Also the starting device. Can't think of what it's called right now.:confused:

    Turns out a pinched wire in the compressor terminal box was shorting out.

    It had the spot welded connector burned off the short brass pin coming out of the compressor.

    I didn't trust anyone to replace compressor under warranty, so I burnished it with a moto tool, put anti-ox on it and made some type of connection thats lasted ten years.

    I haven't found anyone in the area that I would trust with repairs. How big a job to replace a compressor? Can I trust Joe Nobody to do it?

    Do I just replace the whole heatpump?

    Refrigeration a weak spot for me. As is magnetics.
    I understand the theory. Talk of super heat baffles me. (even though I've read the theory)

    If I don't bore you completely I'll explain my system. I believe it's rather unique.

    Oh, AB plc is an Allen Bradley programmable logic controller.
    I use them for any little thing, and it grows into a hundred rungs.:)
  11. #12


    Nov 30, 2010
    "High Tech" in the name? I worked for a company called, "Design Air". The guy was a sheet metal worker and he couldn't design the ductwork! Thirty years later we still refer to a completely messed up wiring job as a "Kermit". It's faster to jerk it all out and start over than to try to trace out his mistakes.

    Depth is good. In Florida, 50 feet deep is common. But then, Florida is made mostly of sand. You can sink a pipe into Florida with a garden hose.

    "Settle time" means fan persist time to me. Standard modules are available to keep the fan running after the thermostat goes to off. Same mfg. as your timer cubes, I think.

    Long compressor run times are like highway driving compared to city driving. What's better, a steady 18 amps that is pumping Freon or a start surge of over 200 amps into a pretty much not moving crankshaft? Your priorities seem crazy to me. Trying to save wear on the compressor by defeating the purpose of the whole system is like neutering your bull because you're afraid having sex will make him tired.

    Cutting into the Freon system (replacing the compressor) is about the most skilled craft in air conditioning. Everything has to be done right if you're going to get it to last. It resembles a sterile surgical operation. The inside of the copper tubes will be pristine for decades if you keep the atmospheric humidity out, know exactly where to put the flux, and use a flow of dry nitrogen to suppress oxidation while brazing. A few months ago, my sister got a bid for a new air conditioner and it said, "Evacuate system to 500 microns of pressure". I take them to 50 microns! Therefore, I wouldn't trust anybody but me to replace parts in my Freon system. Maybe that's why her air conditioner is still running, with no system repairs, for over 20 years. Problem is, you can't buy that kind of quality unless you know your stuff and negotiate for the technician to spend the extra 20 or 30 minutes to do it right and make sure he knows about flux placement and dry nitrogen. With you demanding that level of quality, most techs will refuse to work for you.

    Replace the whole heat pump? Can you buy one with the water parts already installed in the Freon system? Factory standards are a lot better than field technician standards. Otherwise, you're paying a technician to do the Freon system work that you were trying to avoid by buying a new heat pump.
    Last edited: Jan 9, 2014
    inwo likes this.
  12. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    Ouch :eek:

    I was afraid of that.

    It actually has made little difference in practice. ie. mixed up priorities.

    I keep the run time limit so high that it rarely activates.:)

    With your good advice I'm cranking it up so it will only activate with a failure.

    Thanks for advice on replacement versus repair. That's exactly the reason I did my own compressor repair.

    I firmly believe most repairs are needed as a result of previous repair.
    Automotive is a good example. I don't let anyone tear into something for a minor problem. It just starts a death spiral.

    My new pickup had a dead battery issue 1st day.
    The service center spent 6 hrs monitoring current draw while switch was off.

    Couldn't find anything, so they ordered a whole new fuse/control panel.
    They were a little upset when I didn't go back to have it put in. (I'm sure they wouldn't get paid without parts)

    I'll take a minor inconvenience over a guessed at parts replacement.
  13. #12


    Nov 30, 2010
    Oh the horror stories.

    I hired a shop to replace a fuel pump. When they brought the car back, the catalytic converter had been cut open and the coat hanger welding wasn't holding it closed.:confused:

    I hired a shop to replace an engine. It came back with all the smog controls removed:eek:

    OK. That's the whole list. Now I have an engine crane and I rebuild my own transmissions. I still don't want to lower a gas tank to replace the fuel pump, but I will if the only other choice is to over-pay somebody else to screw it up.
  14. tcmtech

    Distinguished Member

    Nov 4, 2013
    You guys sound just like me! I would rather do it wrong my self and learn something than pay someone to do it wrong for me and learn nothing on top of it. :D

    Personally over the years I have come to know our local electrician and HVAC guys as being more idiots and crooks or crooked idiots than legitimate educated professionals. :mad:

    The auto mechanics I deal with are not so bad but then most of them are life one hands on guys not certified bone heads with a piece of paper hanging on a wall in someone elses office.
  15. #12


    Nov 30, 2010
    One of my criteria for do-it-yourself is: If I can buy the tools for less than the retail cost of the repair, I will. When I get done, I will still have the tools and the education, even if the job costs me the same as it would to hire somebody else.
    Metalmann likes this.
  16. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    Let me explain a little more about my system and how I got to where I am.

    I was very disappointed with the loop performance.
    By the middle of December, loop temperature was below 30°F.
    Run times were over 60 minutes and weather was in the teens. (that means warm)
    Made no sense to me, that I was running system continuous, trying to heat my home with 30° water.

    Water table is pretty high here, so I pushed a pvc casing down til I hit something hard. About 58'.

    Much more, involving sweat and tears, but got it done.
    This gave me ≈5gpm @ 53 degrees.

    I installed a large plate exchanger in my ground loop circuit. When loop temperature gets below 43°F, I dump 5gpm 53 degree water thru it.

    This has been very successful. I'm quite sure that the pumping penalty is easily offset by HP efficiency gains of 43° EWT versus below 30° previous.

    The hybrid system works well in that it has all the advantages of the closed loop system.

    Yet, Jan-Feb, I can pump and dump to supplement the loop.
    When loop gets below set point I also run a "loop warmer" program to keep the circ. pump and well pump on a few minutes extra. This keeps my EWT high.

    Yet it can now supply all my heating and hot water.

    Now, it could be that my loop system is undersized. My research shows that it's about average. 1 slinky loop per ton each in a 75 foot trench.

    Doubling or tripling it was not practical.

    This is what's accumulated so far this winter..:)
  17. tcmtech

    Distinguished Member

    Nov 4, 2013
    I see the problem you are running into is typical of most any single stage heat pump system.

    There is always going to be a temperature differential limit thats going to put your system into a running condition where the heat transfer efficiency bottoms out and no further heat can be transferred.

    In your system it would appear that when your ground loop hits about 30 F the pumping system maxes out and heat production on the hot side starts falling off.

    Thats the common problem with ground source heat pumps in my region of the country. With a normal ambient ground temp of some 45 - 48 F going 1000 - 1500 feet down it doesn't take very long to hit that lower limit point.

    The other problem I understand is if you take heat out of the ground at some point you have to put it back otherwise you hit that point of diminishing returns and there is nothing that is cost effective that can be done after that.

    I have had this argument with several people over the last 10 -15 years. They seem to be under the assumption that the ground is some infinite source of heat they can suck energy out of indefinitely.

    Its not. At some point that giant thermal battery they are drawing from has to be recharged. The recharging part escapes them and when told that doing so could be as simple as adding an adequately sized solar thermal heat collector to harvest and recharge their thermal battery during the summer for whatever reason seems totally unreasonable.

    In regions like where I live our summertime AC loads are not sufficient to recharge the thermal battery, most seasonal air conditioning demands are less than 10% of the winter thermal demand, so some sort of additional supplementary source is needed. Thats all.

    But what do I know. I don't have some piece of paper hanging on some guys office wall that says "I R A HVAC tech". :rolleyes:
    #12 likes this.
  18. Metalmann

    Active Member

    Dec 8, 2012

    Sounds like me, I must have enough tools and tooling, to start several businesses.

    However, I may have exaggerated a wee bit.;)
  19. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    I've talked to other geo owners during there costuction phase. They all expect to heat totally with geothermal.

    Never get a chance to see how it worked out. I have a feeling that it doesn't matter. They may get 50% from geo and don't know the difference.

    Now that the bugs are out, I love my system.

    The first year, total energy cost was about $100 a month average. That's 6k square feet in MN.

    Dec was cold and set a record of $313.

    Grandson stopped in after school...........................
  20. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    Same here.

    The exception is refrigeration.:(

    I have had people in the business say, "just get some gauges".

    That's all I need right #12?:D:D