Minnesota GeoThermal heating issues

Discussion in 'Maintenance and Troubleshooting' started by Brett, Jan 6, 2015.

  1. Brett

    Brett New Member

    New member here, and barely a novice when it comes to GeoThermal systems - please bare with me! We bought a new home in September that already had a GeoThermal system installed. I don't have access to the original installer, and the HVAC company I have been working with has been somewhat helpful, but I don't get the sense they are "experts". I will do my best to explain what we have, and the problems:

    Equipment: Econar GW770-1 Heat pump with PumpPak, Econar GeoSource 2000 AirHandler, 75 gallon holding tank, small buffer tank.

    My understanding from the previous home owner is the loop field is horizontal, due to the water table in our area so they couldn't do vertical. But I have no idea how long the loop is.

    First problem we had was the circulation pump for the ground loop fried (literally started on fire). I had that replaced, and found out from the HVAC technician they had replaced the other circulation pump last year. Looking at the pumps, the pump on the ground loop is larger than the other pump. Seemed odd to me.

    Second problem is compressor lockouts. When trying to raise the temperature of the holding tank, I cannot go any higher than 115F, or the compressor locks out with a "high pressure" error light. The HVAC technician said he thinks the problem is the buffer tank is too small, when I try and raise the temp too high the buffer tank cannot handle it, and it locks out - sounds reasonable, but I am not educated enough to know if that's just a guess, or most likely the problem. I noticed the last time it locked out that the holding tank pressure was 45PSI

    Third problem - The system cannot keep up once the temperature goes below 20 degrees. I recently turned the hydronic floor heat off, re-balanced all the ducts and opened vents, and it seems to be able to keep up if I am just running off the air handler. I noticed when I made this change, the pressure in the holding tank dropped below 10PSI. I've also noticed that it does not hold this pressure, i've seen it go as low as 5PSI. This doesn't seem right to me. I am not sure if the problem is the holding tank temperature is not high enough to keep up during the cold MN winters, or?

    I don't know what the ground loop pressure is, nor do I know what the in/out temperatures are. But I want to buy a guage, and temp probes so I can at least validate what these values are.

    I don't want to keep dumping money into possible fixes, without a better understanding of the system, how its operating, and the right data to better pin point what the problem(s) is/are. The HVAC technician suggested that the pump may be undersized, and the best solution long term would be to split the heating source between the air handler and watts hyrdronic in-floor heat. Which will cost thousands and this seems like a guess.

    I am sure I am leaving out details, please let me know what other information would be helpful. Appreciate any help!
  2. Tamar

    Tamar Member Forum Leader

    Brett, where in MN are you? I can steer you toward a couple of local resources who may be able to help. Boots on the ground is always good.
  3. Brett

    Brett New Member

    Hi Tamar, I'm located in the Faribault/Northfield area. I had a new service company come out today, they seemed far more knowledgable, but a second opinion in this case would be a good idea. They found several issues with how the system was piped, under-sized buffer tank, issues with the direction of flow, etc. The estimated repair costs are in the thousands..

  4. Brett

    Brett New Member

    I should mention, the buffer tank is actually 50 gallons, not 75 as I previously said. He told me the rule of thumb is 10 gallons per ton, and its a 7 ton heat pump I believe.
  5. Tamar

    Tamar Member Forum Leader

    Brett, I'll send you my email address and phone number, and let you know what I know about the local lay of the land (I'm in St. Paul)
  6. Tamar

    Tamar Member Forum Leader

    PS, I believe your well driller would have had to file a report with the MN Dept of Health if they did any drilling. I guess I'm not sure if that applies to horizontal loops.
  7. dgbair

    dgbair Just a hobby Forum Leader

    Brett, these system don't produce super hot water like a oil or gas furnace. 115F is probably the max you would want to go. Looking at the unit's manual, that seems to be the highest temperature they show in the performance spec. Most units have a outdoor reset on them so the water temps can get turned down even further when the heat load drops due to warmer weather.

    From your problem description it would seem you have forced air and radiant heat in all rooms? Seems like the system was setup such that the radiant heat would only carry part of the load? You need to understand your heat loads... I'm guessing the old homeowner didn't leave any of the docs behind?
  8. Brett

    Brett New Member

    dgbair - Good to know on the buffer tank temperature, thank you! We have forced air throughout the house (all rooms) and then we have hydronic in-floor heat on the main level, and garage. The home is built on a slab, so no basement, and the in-floor heat is split into three zones - main floor except for one room is one zone, "man" room is another zone, and the garage. All three zones are on their own thermostat's.

    The way the previous owner had things setup, and you are correct, that the in-floot heat would carry part of the load (main floor) and forced air to carry the rest (up stairs). So he had all the ducts blocked off on the main floor to force all the air up. The problem is that as soon as it hit say 20F the system could not keep up. I think the warmest I could get the main floor was 67, zone 2 was worse, around 65, and upstairs was a couple degree's warmer. During this time the compressor would run for long periods of time, turn off briefly, and then start back up again. Our November heating bill we used 3159 kWh's, which is 1050 more than October - I can only imagine what December will be. I ended up turning the in-floor heat off completely except the garage (Geo system is stored in a small room out there so need to keep that above freezing), opened ducts in rooms I needed heat and balanced things. Its able to keep the home at 70F, even now when its ridiculously cold out. But its definitely working hard to do it. The new HVAC tech that came out yesterday measured 34.5 amps on the compressor which is its max load from what he said. So according to him the compressor is running at peak load every single time it kicks on.

    Yeah, the previous owner didn't leave me a single piece of documentation. I was able to dig up who installed the system though.

    The new HVAC tech spent about 1.5 hours dissecting and checking things, and the conclusion he came to is that we have several issues going on:

    1) The buffer tank is undersized, and does not have a large enough inlet port (its 3/4"). He said I need a 70 gallon buffer tank, and the inlet should be more like 1"
    2) Some piping is 1", and some is 3/4", creating bottlenecks trying to move water.
    3) The in-floot heat was piped wrong - the supply line is pulling water from the bottom of the buffer tank (cold) rather than from the top (warm).
    4) The circulation pumps between the heat pump and buffer tank are different (one is larger than the other) and one is not 230v which its supposed to be. He said if the system was piped right I should only need one pump (the bigger of the two) and that they used two to compensate for poor piping.
    5) There was also an issue he said, with how the system was piped to the air handler .
    6) He checked the ground loop pressure (20 PSI), and the in/out temps of the ground loop - in was 34F and out was 28F (if i remember right). The delta was 6F - 6.5F. He said for this time of year in our climate those numbers were within range.

    He talked to Enertech tech support to confirm some of his findings, and it was on speaker phone. The rep came to the same conclusions on the buffer tank, piping, and agreed that the compressor is working way too hard.
  9. dgbair

    dgbair Just a hobby Forum Leader

    Brett, these systems are design for long run times.... that is not a bad thing.

    (Keep in mind I'm not a pro...)

    Circulator pumps can have a huge negative effort on the efficiency of the system... every pump you have eats up power, and if you have large pumps or many pumps it can waste alot of power. Any fixes/changes in this area needs to be geared towards saving pump power. (ie increasing all piping to 1" and making it look pretty isn't going to save anything unless it enables you to remove or reduce you pump power)
    What circulators do you currently have?

    Given the system is running a long time kind-of says BTUs are being removed fast enough from the buffer tank.... I would think a undersized buffer tank would result in short run time which would be bad for the compressor. (This may be more of a issue when the weather is a bit warmer)

    If you still have your target temp set at 115F, then the unit will be working hard.... Heatpumps hate creating 'high' temperatures. Lowing the target temp to 105- 110 would help... but that may not be a option for you. (ie you may need the extra BTUs to heat the space)

    Maybe consider posting some pictures of the setup? I'm sure the pros will chime in at some point.
  10. dgbair

    dgbair Just a hobby Forum Leader

    Brett, how is the air handler piped in?
  11. Bergy

    Bergy Member Industry Professional Forum Leader

    How many tons do you have? 6.5? 6.5 tons X 3gpm=19.5 gpm That is the flow rate of your loop field and MUST be the flow rate between the unit and buffer tank. That flow rate requires 1 1/2" copper.

  12. dgbair

    dgbair Just a hobby Forum Leader

    I did a bit more looking at the spec for this unit.. Looks like they recommend 15 GPM for the loop and 12 GPM for the hydronic...

    (In looking thru the doc again, I did notice some performance number for 130 degrees HYD LWT, about a 20% drop in COP over 115F water)
  13. Brett

    Brett New Member

    Bergy - its a 7 ton system. The piping that is wrong according to them is the piping between the buffer tank and hydronic system (grundfos circulation pump and manifold), and between the heat pump and air handler - some is 3/4", some is 1". According to the documentation he sent me from Enertech, its supposed to be 1.25" based on my heat pump model, and size.

    The other issue they found was the hydronic supply line is connected to the buffer tank in a way that its pulling cold water from the dip tube at the bottom, rather than hot water from the top. And of course the buffer tank is only 50 gallons. The documentation from Enertech calls for 70-80 gallons I believe for this model.

    dgpair - Let me see if I can explain this right. The air handler has two pipes coming out of it -

    1) 1 Pipe goes from the air handler and T's

    a. One goes to a grundfos pump hanging off the return manifold of the hydronic system
    b. The other goes up to the thermal expansion tank, and then to the buffer tank

    2) The other pipe coming out of the air handler runs to an inlet port on the side of the buffer tank and is also T'd

    a. One goes directly into the buffer tank, inlet on the middle of the tank
    b. The other goes down to a grundfos pump hanging off the heat pump

    This new HVAC company is telling me that the way the air handler is T'd off the return manifold of the hydronic system, cold water is being pushed up from the hydronic system return manifold, and can run to the air handler circulation pump, which is trying to pull hot water out of the buffer tank.

    Based on the installation manual of the buffer tank, which is really an electric water heater they cannibalized, the supply line for the hydronic system is indeed piped into the Cold inlet on the top of the buffer tank. The return side of the hydronic system is being pushed up to the hot inlet on the buffer tank. So its piped backwards.
  14. dgbair

    dgbair Just a hobby Forum Leader

    yeah, 1.25" copper would support the flow needed.

    Sounds pretty messed up... I tried drawing out your description... but I failed.

    "b. The other goes down to a grundfos pump hanging off the heat pump" - bypassing the buffer tank all together... seems like they tried to feed the air handler partially directly via the geo?
  15. kkl

    kkl New Member


    I have an 8-ton Econar system that sounds similar to yours, other than the undersized buffer tank and connections. I haven't had any significant problems with it. What kind of controller do you have? Is it a Terra-Therm Geothermal Hydronic Control Module? They're right in your neck of the woods and did a lot of design and distribution of Econar systems. You might consider contacting their tech support for information and they would know of local dealers familiar with Econar. I've found them to be very helpful in the past when I needed to get info about my system, which they designed. Attached is a conceptual plumbing diagram for a Geosource 2000 which you can use to compare to your system. I also have many Econar documents if you need them.

    As others have said, 115 deg F is the absolute max for Econar heat pumps, and they run less efficiently at such a high temp. Don't try to push it above that.


    Attached Files:

  16. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    One needs to know flow.

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