North Carolina Freeze Warning on Bosch SM036

Discussion in 'General Discussions' started by KaiserSoze, Feb 17, 2015.

  1. KaiserSoze

    KaiserSoze New Member

    I've had my GeoThermal system running for about a year now. I live in central North Carolina. It was installed in Dec 2013. It is a Bosch SM036 - 3 Ton - 2 Speed unit with 2 5k aux strips. The loop is a closed loop system with 1" pipe, 2 - 250 ft vertical wells in parallel and only water in the loops. Everything is 5 ft underground and comes into my crawl space under the footer and foundation, well below any freeze problems. The pipe is also completely insulated from the ground to the unit and back (pump in between).

    Last year, it ran perfectly and when the temps hit 9 deg it only needed to run stage 2 periodically to keep the house at 68 deg. This year, however, has not been smooth at all. Any time the temps drop into the 20's the unit will kick into stage 2 as normal when needed. However, after a while (5 to 15 min), the compressor will shut down. The aux strips kick in when the temps drop 2 degrees and I have strip heat from then until I shut the system off and back on. It then returns to normal, running mostly stage 1. The unit displays a freeze error.

    I had a tech from my contractor come out on a Sunday. He didn't have the right equipment with him but speculated that maybe my loop temps were hitting 30 deg. and the system was in protect mode. However, today around 4pm (around 34 deg outside), they were able to get back over here. We measured the temps of the loop. The input temp was 46.5 deg and the output temp was 40 deg when running at stage 2. I am now going to try to get it to fail tonight when the temps drop into the 20's again to see if the loop temps drop to 30 deg.

    1) Does this much drop in temps for the loop seem reasonable? It would take the output of the unit to drop 10 deg from 40 this afternoon to 30 overnight. That seems like I would have a capacity issue with my loop if this occurs.

    2). The loop installation is suspect to me. It is a parallel loop, however, both the first loops input and return are closest to the heat pump. The second loop is T'd off the first loop for both the input and the return. This means the water has to flow an extra 30 ft to the second loop and an extra 30 ft back. I would think the extra resistance would cause an uneven flow between the loops and a loss of capacity.

    Any thoughts on this would be more than welcome!

  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    So it is not a reverse return header?
  3. KaiserSoze

    KaiserSoze New Member

    I had to look up the term, but it is not a reverse return. I guess it would be called a direct return. I took pictures of the connections that show the 2 T connections at the first well for the second well. If it were a reverse return, the return side would have a 90 deg connection to the loop and a T connection at the second well.
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yeh, generally the reverse return can be thought of as first out = last back. Helps manually balance a header.

    I'm wrapping my head around the effects of your header layout. I can't see it being easy to purge.

    Sounds like you do need to get some antifreeze in your loop and ensure there is no air in it.

    edit: I guess I should ask the obvious. Is there a way to manually isolate your circuits?
  5. KaiserSoze

    KaiserSoze New Member

    Reverse return seemed to be intuitive to me. I even mentioned it to the guys in the trench and they said they do it all the time. So, even though it didn't seem right to me, I deferred to the experts.

    I talked with the owner who sold me the system and designed it today about the layout. If it turns out the loop is the issue, he isn't opposed to having his contractor come out and change the loop. He didn't specify reverse or direct to the guy probably because the guys drills and installs many of the loops in this area. He told me he figured he knew what to do. But, with the input temps at 47.5 deg and 40 deg output, I guess I would be surprised if it draws down to 30 deg even with this setup. Evne though I'm sure I am losing capacity. I didn't even think about the difficulty purging. By the way, the pressures were 48 lbs in and 44 out ( I think, may have been 45).
  6. heatoldhome

    heatoldhome Geo Student Forum Leader

    How long was the unit run in 2nd stage before the Temps where measured?
  7. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    O.K. Get some accurate temperature monitoring going and see if water temps ever dip to freezing.
  8. KaiserSoze

    KaiserSoze New Member

    We measured them at around 30 minutes. They didn't vary at all. I kicked the Tstat up 5 degrees to force stage 2.

    Urthbuoy, I intend to do that tonight. I am running the system without aux backup enabled. The temps have dropped to 27 outside now. It will take another degree or two before the system is in the zone where it fails. Then, after it kicks into stage 2, I am going under the house, insert the temp gauge in the return and watch the temps. It usually doesn't take more than 15 min for the compressor to disengage. I want to make sure the readout says that it's a freeze error.

    ETA: the current thought is that the sensor may be reporting temps on the low side and the system is locking off at a higher temp than 30 degrees.
  9. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yes sensors can read wrong.

    And flows can encounter problems. The longer that water is in the coil, the colder it gets. Low refrigerant can lead to these type of faults as well.

    But really getting a grasp on how your T's are performing will narrow much of it down.
  10. KaiserSoze

    KaiserSoze New Member

    Refrigerant pressures were good (110 low and 293 high IIRC). The delta T's also were good. I was getting 25 to 27 delta T in stage 2 and about 23 in stage 1. Those delta's held consistent and didn't drop until the compressor shut off. So, my thought was they would start to collapse if I were approaching 30 deg in the loop. I'm not sure what the flow rate was, but the pressures were right in line with what Bosch says.

    The temp outside is 27 right now and the unit is cycling on and off normally, never leaving stage 1 so far.
  11. KaiserSoze

    KaiserSoze New Member

    ETA: sorry Urthbouy, I just saw the edit with the question and statement on antifreeze. First, I think it would cost between $400 and $500 for inhibited Ethylene Glycol for the loop. If the temps aren't approaching 30 deg I am not sure why I would need to do it. We are at record cold right now. Do you agree?

    Second, there is really no way to isolate the loops as everything is buried.
  12. Bergy

    Bergy Member Industry Professional Forum Leader

    What was the measured Heat of Extraction?
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Ok if the system worked fine last year then something has changed and it's not your loops or the lack of antifreeze. Loop and refrigerant pressure looks good, I'd try a low pressure switch.
    waterpirate likes this.
  14. KaiserSoze

    KaiserSoze New Member

    Bergy, I'm not sure on the HoE since we didn't measure the flow. The delta T of the water was 6.5 deg.

    Update: The tech just left. I spent an hour or so at about 4am this morning under the house watching water temps. With the system running stage 1 the output water temp was a pretty steady 40.1 deg overnight. When I kicked it to stage 2 the output temp dropped steady and hovered around 37.8 deg. It never approached 30 deg. So, I finally gave up, pulled the temp probe and went to leave when the compressor kicked out. It happened another 6 or so times today. The code "3" meaning freeze lockout. We checked the thermistor and found the resistance reading was right in spec. So, they are ordering another main control board and swapping it out. I sure as hell hope it gets here tomorrow. Friday temps are supposed to be 0 for a low and 18 for a high.

    The loop installation, correction and whether to add antifreeze to the line are next on the list.
  15. heatoldhome

    heatoldhome Geo Student Forum Leader

    Just water in the loop? Any treatment?

    Maybe your system in growing things inside the pipes/exchangers??

    Maybe a expert can chime in not sure of what the signs of growing things in the loop are.
  16. TheDude

    TheDude The Dude Abides

    the unit monitors the REFRIGERANT temperature and shuts it off at 30*. Not the LOOP temp. I would not be surprised if it shuts down with loop temps approaching 35*. That would mean it is operating properly.
  17. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    The way to test for growy things is to test. Find a Furnox rep, they will test for free if you buy their fix. Great products. I do not know why it took them so long to cross the pond.

    My product of choice.

  18. KaiserSoze

    KaiserSoze New Member

    That is correct and why I mentioned the antifreeze and loop rework will probably be next. We know the board is failing, the water temps were over 40 deg with the system shutting down. The resistance of the freeze sensor was correct for the water temp as well. So, Bosch recommended replacing the main control board.

    But, I don't think this saga is over. I think I will get legimate freeze errors over the next two days. The system will need to have antifreeze added in order to allow the temp sensor to be set to 15 deg (cutting a resistor). But, before that, I want the loop corrected. More to come.
  19. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Before I dug the yard up I would see if the "Y" strainers called for in the small print of the I/O manual have been installed and pull a strainer. That is how we found out the freeze fault, was caused by low flow, caused by snot looking stuff growing in the fluids.

  20. Bergy

    Bergy Member Industry Professional Forum Leader

    "Refrigerant pressures were good (110 low and 293 high IIRC)"

    The heat of extraction/rejection (HE/HR) MUST be measured BEFORE refrigerant gauges are connected to the unit. If the measured
    HE/HR is within factory specs there is no need to connect a gauge set. Every time a gauge set is connected to, and removed from, a system a small amount of refrigerant is lost. It doesn't take a lot of uneducated techs loosing refrigerant to start affecting system performance. The next time your tech shows up with a gauge set in hand, tell them to put it back in the van and LEARN how to properly service a Ground Source Heat Pump.

    To measure the HE/HR you measure the Entering Water Temp (EWT), Leaving Water Temp (LWT), Entering loop pressure and leaving loop pressure.
    (A single Temp probe and a single pressure gauge are used to measure BOTH entering and leaving values.) With the EWT and Pressure diff. you can look in the spec manual to find the GPM. Multiply Temp Diff. X GPM X 485 w/antifreeze or 500 w/ water. this gives you how many BTU's are being extracted from the loop or rejected to the loop. Again, the spec manual will show what the HE/HR should be at the given EWT and GPM. IF it is within 10% of spec the unit is operating fine.

    Edited per docjenser's catch of a typo.... original post was 485 w/water or 500 w/antifreeze.
    Last edited: Feb 18, 2015
    waterpirate likes this.

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