Significant frost heave from horizontal loops

Discussion in 'Geothermal Loops' started by Rogero, Mar 27, 2017.

  1. Rogero

    Rogero New Member

    I live in Bellevue, WA and have a ClimateMaster system (3 ton, I think). The first few years after my system was put in I let the yard go to weeds while I waited for it to settle. I noticed a few times that there was a depression down the middle of my yard but really didn't think much about it. I have since had my rear yard landscaped and a nice flagstone deck and retaining wall installed. Last winter, everything was fine. This winter, I developed significant mounding of the ground over the loop runs on the lawn as well as the deck. The rise in the lawn is close to 4 inches if not more. When I installed my system, I was aware that it was on the lower margins for loops size, but I have not had any issues keeping the house warm.

    I have setup a DIY version of welserver using a RPi and some Dallas one wire sensors. As you can see from the chart, the loop temp is in the high 20's during the winter months.
    Anyone have any advise. The loops are minimum 4 feet down in the ground and closer to 8 feet under the deck. I asked my installer and he suggested adding the AUX heating unit and setting it to go to complete AUX heating if the loop temp drops to much. That could be several months of all electric heat in the winter, even though the Puget Sound is relatively moderate. I am wondering if it would make more sense to drill a few more vertical holes and tie into the current loop in my crawlspace. I have some space on my side yard where I could drill some wells. EWT<>LWT delta is about 5 degrees last I remember. My monitoring system quite working a few weeks back and not sure why.

  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Loop temps in the high 20s are not the end of the world, but you have to ensure that the sensors are calibrated, and in realty your loops are not much colder. Here you display 26 F minimum, and 112F maximum, both together indicate a a too short of a loop, especially in mild Washington state climate. Yes, you can add ore loop, but no need to turn on the aux heat. Your loose some % efficiency with your geo system, but that's it. Still much better than electric resistance heat (aux heat). The geo heatpump should have some operating range, and you are well within it. Again, not the most desirable, but also not the most detrimental either.
    Last edited: Mar 27, 2017
  3. Rogero

    Rogero New Member

    Thanks for the response. My biggest concern is not really the efficiency of the system. I just don't want to pay my landscaper $1000+ every year to reset my deck. It appears that my in soil heat transfer is not very good. The pipe was set in some pretty wet dirt that we hit 4 feet down. IS wet soil a bad conductor of heat? I would think that would be pretty good. Would extending the loop vertically go down into more stable temperatures and keep the horizontal section from getting so cold so fast?

    As for the sensors, the ones on the loop are wrapped to the pipe with a copper band then covered back up with the foam pipe wrap.. I think they are pretty accurate compared to the one measuring air temps. They all come to the same temp when the system is off and at room temp.

    Last edited: Mar 27, 2017
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    A thermal break between the lines and infrastructure will help. Assuming the lines close to the deck are just header lines, I would insulate them.
  5. Rogero

    Rogero New Member

    Unfortunately the flagstone deck is built over the loop field in 1/2 the back yard. Would adding additional vertical loops get down to more uniform temperatures and help mitigate the temperature extremes I am seeing in the current design?
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    likely. your is running to hot in the summer and too cold in the winter, all being relative here. adding loop capacity will decrease the extreme temperatures in the loop.
  7. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    You need more loop. Do you have any idea how much pipe is in your current loop and how it is laid out. Could you easily add a loop. It is likely that another ton of capacity in a vertical loop could resolve much of your problem. A loop in moist ground will tend to stay near 30 degrees or so for some time as it takes significant energy to turn water to ice (that eneergy is visualized in the heaving of tons of earth) With occasional dips into the 20's a ring of expanding ice is forming around your pipe. In moist soil, that will quickly remelt if no further cold is added. Sustained temperatures in the 20s will allow that cylinder of ice to grow and heave.
    Thinking you may have 3 ton system, adding another ton of vertical loop may resolve the problem wholly.
  8. Rogero

    Rogero New Member

    Contract says "Furnish and install a horizontal geothermal ground loop heat exchanger with four
    circuits of 3/4 HDPE 3408 geothermal ground loop pipe, trench to be 300 feet." The HP itself is a 3 tone dual capacity Climate Master. My walls are insulated with foam in 1/2 of the house, the attic is encapsulated in foam on the underside of the roof and the floor is foamed on the crawlspace side. How must additional vertical loop would I need. I have space on the side of my house next to the street where I could sink a vertical well or 2 especially if they slant drilled them in a V shape.
  9. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    Is this one 300' trench or 4 separTe trenches. If four, are they all heaving. If not you may have one or two loops not flowing.
  10. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    If you have 4 x 600' (?) circuits together in one shallow trench, you are definitely capable of producing ice lenses in the ground.

    The steps I'd take if this was my house.

    1. Figure out my Heat Loss/Heat gain
    2. Figure out my ground parameters (soil type, etc.)
    3. Design a ground loop with #1 and #2 and being hooked to the existing heat pump
    4. Figure out what % the existing ground loop actually is
    5. Determine if the load can be reduced somehow
    6. Decide on how to supplement this ground loop cost-effectively:
      1. Additional ground loop (horizontal, drilling)
      2. Solar hot water system feeding loop
    The short answer is, yes, you can definitely fix this, but don't guess at this stage. Get the proper numbers sorted.
  11. Rogero

    Rogero New Member

    Have attached a couple pictures of the loop installation. The frost heaves basically follow the trench footprint. No room on the roof for solar hot water. It already is covered with Solar electric panels. DSC_4770.JPG DSC_4776.JPG
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You loop is not deep enough, and the pipes are too close together. 4x600ft gives you a pressure drop of 18.6 ft/hd at 9 gpm.
    Please confirm your loop pump (model number).
    If you put in a single 350ft well with 1.25" pipe and good grout, you should more than double your capacity of your loop field.
    With a single 26-99 pump your flow will go up to 11 gpm. Your Reynolds number will not be great, meaning your are a bit short on velocity, but you will have a good performing and nicely balanced loop field.
  13. arkie6

    arkie6 Active Member Forum Leader

    Very poor loop design - pipes are way too close together and not nearly deep enough. No wonder the ground is freezing around them!
  14. Rogero

    Rogero New Member

    Pump is a Geolink FC2-FPT Geothermal Flow Center Variable Speed 2 pump. The installer stopped digging when we hit saturated dirt. there has been a few feet of fill added on top of the area under the deck since it was installed.
  15. IronOak

    IronOak New Member

    It appears you’ve already been well advised on your next steps. But I think your unfortunate situation and the hashing out of it might be helpful to those in the future that might knowingly or unknowingly try to cram too much pipe into a given area and/or naively try to cut cost, so thanks for sharing your story.

    Were you even advised this layout could possibly have this type of issue? Did you get multiple contractor quotes? Did they all visit and look at the yard? Where you quoted vertical or directional boring by any? Did any the other contractors suggest/quote/question this same layout? Did you subcontract/do the trenching yourself?

    What is the overall distance (measurement) between the right wall of the right trench and the left wall of the left trench looking towards the CAT? They have installed 16 (including supply & return circuits) runs in a X-foot-wide area. The pipes appear to not even be an average of a foot apart in the pictures!

    Is the 300’ (quoted or ended up as) in actuality 2 trenches @ ~150’ long located right next to each other within a foot or so? (8X150’X2=2,400LF)

    What is reason (or design) your LWT readings consistently show higher (warmer) than your EWT this past Winter on the graph?

    And unless you specifically signed off on a knowingly questionable Loop Field design the GEO contractor needs to come to the cost-to-fix party!

    Best of luck with your system.

    Warm Regards,

  16. Rogero

    Rogero New Member

    Hi IronOak,
    I had multiple contractors come out when I was starting the project. The one guy said he thought he could get enough loop in my restricted space but it would be pushing the limits. Every one else said the site was too small. Not sure if we discussed vertical wells, but might have been a cost question at the time. So I went in with my eyes open. Marginal performance was acceptable to me at the extreme ends of the temp spectrum. The frost heaving is the real issue. I am away this week, so not able to get the measurements you are looking for till next week.

    As to the EWT vs LWT temperature charts, I might have the labels wrong. When I wrote my app, my definition might be relative to the pump instead of the loop. Never seen the exact definition of LWT vs EWT. That chart is very cluttered. Need to look at the hourly chart when I get my RPI working again.

  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    He could have easily gone deeper or come up with some creative loop designs which would have helped you with the performance. He also added 2 pumps when 1 would do the job fine, which means you are now paying for twice as much pumping.
    I would sit down with the contractor since you have an underperforming system with some side effects which are not industry standard.
  18. Rogero

    Rogero New Member

    I solicited a bid from a local company to add additional capacity to my system. Due to the lot size and layout, my only option was drilling a 350 ft. borehole. Bid came back around $22,000. I believe that leaves me with installing the AUX heater and turning on freeze protection as the better option. Is it a correct assumption that the climate master has a freeze protection setting that will turn on the AUX heater if it detects low loop temperature?
    Assuming it is feasible, I have been reading the documentation for the AUX heater (AGL15AAG) and installation looks pretty straight forward. I had a bit from a climatemaster dealer for 6 hours labor which based on the documentation, looks way high. Am I missing something? Their estimate did not include the electrician running the circuit.

  19. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What happened to your contractor? Having a 2 pump flow center on a 3 ton system is a very poor design, in addition with a short loop with temperatures outside the design parameters. Putting your loops deeper would have solved some of the issues.
    I don't think any manufacturer has an algorithm build in their boards to start aux heat at low loop temps. The installer might try an external control solution. But given the install and device thus far, my confidence in him would be questionable at best that he can come up with a good and efficient solution for you.
  20. lugster

    lugster New Member

    Hey roger, I'm looking at your temp chart, pics, and the average monthly temp chart in your area and things just don't add up. These pro's (no disrespect meant) who have posted links to designs they've used aren't much different then yours, so I have a few questions. You said 1/2 the house has foam insulation on it. Should one then say the other half has none? And what temp are you trying to maintain in the house? Are you a chill baby, trying to keep the basement or 3 season porch at 85 degrees? Looks like you're framing in some big windows in the back; You may suffer from OVERLOAD! do a heat loss calculation before condemning the design. And if you're trying to hit 90 degrees inside, turn it down and get some long johns.
    Turning down the T'stat in cooling mode to 55 and the A coil will freeze up, same can be said for a heat pump in heating mode, the low side of the system is now the loop side and will get it colder then designed.
    One thing that confuses me is your temp chart and it could be just because I'm not in this business and ignorant, but Late Apr, may, and jun the average loop temp shoots up to 70 degrees, about the average outside ambient temperature in your area, and the months you don't really call for heating or cooling. A pro could address this but does the circulating pump run continuously even when there isn't a demand for heating or cooling? I've never seen that before with radiant heating systems.
    Bottom line, make sure everything else is right before condemning the loop field. You get enough rain to wet the ground for good thermal transfer over dry ground, most loops look a foot apart just as other designs I've seen on this form, and you don't have a problem with ground frost, so eliminate the simplest causes first. Like overload, controls incorrectly set, ect. A good HVAC contractor would be a good choice to pinpoint the problem. I would check ground Temperature, because a loop with no circulation should read the ground temperature and not the outside temperature. I'd strap a temp probe on both main lines to the house and look at the differential and compare that to the ground temp. You should have a defined temp. gain based on ground temp I would think. Have a pro tell you if it is normal. It could be as simple as over or undercharged refrigerant system in the heat pump. Or everything could be fine and accept the fact your yard is going to move a little. Good day.

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