Efficiency of geothermal system as temperature of propylene glycol decreases

Discussion in 'General Discussions' started by jcottrel, Mar 14, 2013.

  1. jcottrel

    jcottrel New Member

    Greetings.

    Last summer, we had installed a 4-ton ClimateMaster heat pump in our house. The unit seemed to run pretty well until last month. At that time, instead of heating the house, the unit started to blow cold area in the house and the heat pump generated an error code indicating that there was a temperature issue. It was discovered that the incoming temperature of the propylene glycol was 25 degrees F. After some inspection of the unit, it was discovered that one of the connections on the board was not fully cut to allow colder temperatures to come into the house. This connection was fully cut back and the unit seems to be working okay now.

    However it seems that the efficiency of the unit itself has went down a lot. I have been reading my electric meter just about every day. Before this issue occurred during the middle of the winter, we were using at most 75-80kW a day on average and now it seems to be around 125 kW a day. (Note: I think we may also be having refrigerator problems too).

    Anyways, I was wondering if there is a time when the geothermal units are not as efficient as just running the electric backup heater? What do you all think? I'll be happy to hear what everyone thinks.

    Thanks,
    Jon
     
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    No. Elec auxiliary heaters are a 1 COP your geo on it's worst day likely still gets over 3 COP.
    While it is true the efficiency decreases as EWT drops has it occured to you that it is not the efficiency, but the cold weather of deep winter that is causing greater consumption?

    25 degree entering water is outside usual design standards but your system should run fine. Since it's your first year you may not have full compaction of the earth around your ground loops yet.
     
  3. jcottrel

    jcottrel New Member


    Yes that is what I was wondering about. We still haven't finished off the yard after the excavation. As you have mentioned we have had quite a bit of settling of the yard. The trenches were dug 6 ft deep and the piping for the loop field was laid in there. However the ground where some of the trenches were dug has probably sunk about 1 ft in some areas. Sometime later this spring we plan on leveling off the yard and reseed the yard. So I would think in ensuing years later in the winter, the entering temperature ought to go up. Is that a correct assumption?

    We have had some cold weather thus far where I am living however the temperatures seemed to moderate some but now it has gotten a little colder than average.

    Thanks for the information!
     
  4. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    "So I would think in ensuing years later in the winter, the entering temperature ought to go up. Is that a correct assumption?"

    It is my assumption, but understand that design standards are 30F-90F, so it won't necessarily go up much and it can dip lower than 30. Disparity in thermometers can impact by a few degrees as well, so you are darned close already.
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    So where did you measure the glycol temp. In the incoming or outgoing line?
    Usually the cutoff threshold is for the antifreeze setting is 30F, and the loop does not drop 5 degrees that quickly. Besides the lack of compaction, you also see higher EWTs when you put heat into the ground during A/C season.
     
  6. jcottrel

    jcottrel New Member

    Thanks for the timely comments.

    I went back through my paper work again just to see what was recorded. The service company was out here 3 different times. The first time they were out here the temperature of the glycol concentration was measured with a refractometer from a sample in the pump and that is when it came back with a temperature of 25F.

    In the last visit when they came out, the incoming water temperature was 39F and leaving temperature was 36F. They mentioned there should be a 4 to 8F difference in the entering and leaving water temperatures. After they left, they got an SLBP (not sure what this means) of 33F and an SLT (not sure what this means either) of 41F.

    Are there better liquids or mediums out there to use in a geothermal heat pump? In other words are there ones that maintain their temperatures better during the coldest of winter months?
     
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

     
  8. jcottrel

    jcottrel New Member

    I was curious about the incoming and outgoing temperature numbers that we are seeing. So it sounds like my numbers are okay and the unit ought to be working as expecting.

    The service folks that fixed my system want to flush out my system and replace the glychol with mythenol. Is there really any benefit to doing so? Is it really worth the investment to do so?
     
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    The heat pump should protect itself from freezing.

    I do not think it wise to change the chemicals used to provide antifreeze protection. How will they get the old stuff out, all of it?

    I like prop as one could eat it if needed. It will not kill cats and plants or the people that eat the plants if it gets loose.

    Prop needs more pump, but is safe.

    Mark
     
  10. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    It transfers heat better and will offer a higher reynolds number with current pump. What is their reason?
     
  11. jcottrel

    jcottrel New Member

    Actually they told me the glychol is NOT as efficient as the methanol and does not transfer heat as well. They also mentioned that glychol breaks down more readily (which is probably a good thing in terms of being more environmentally friendly) and that it doesn't travel as far. They also stated that methanol is lighter and is more efficient at transferring heat.

    They mentioned they would flush it with a flush cart with the town water and then clean out the reservior. They stated it would take about 8 to 10 hours to do so at a cost of $1700-$2200 depending on much the mythenol would cost. It would take about 25 to 30 gallons of methanol they thought.

    So it sounds like they are just trying to sell me something that is not really needed or are hoping to find other problems to "correct". That is why I asked the question out here just to get some more opinions on this particular issue.

    Thank you Joe, Mark, and docjenser for your great assistance to me. It is greatly appreciated!

    Thanks,
    Jon
     
    Last edited: Mar 20, 2013
  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Jon:

    If you gave us what was pumping the loops, I missed it.

    Most contractors use a pump center or flow center, which I consider to be a one size fits all approach. Most flow centers use a pair of pumps, one pushing and one pulling. The issue I have with that system approach is it has no point of no pressure drop. That point is the expansion tank hook up.

    What I like to do is treat the loop side of a system just like any hydronic heat transfer system and I include a pump sized to the flow and head loss of the loops, the head loss of the heat pump, the loss of the near heat pump piping, an expansion tank, make up water equipped with a pressure reducing valve and a back flow preventer and some times a bit of add chemicals piping in case a leak develops. My plan is like putting the correct engine and transmission in a car or truck for the best gas mileage for the job it is doing, or installing TWO of the biggest V-8s one can find and forget about MPG.

    When I size the correct, just enough pump I factor in the type of antifreeze my educated customer wants to use when choosing the size of the pump.

    I mention this in case you would like to give me the money they want to charge you to change antifreeze. I could use a road trip.

    Mark
    aka 1/2 of geo-gypsies.
     
    Last edited: Mar 20, 2013
  13. methanol, propylene glycol
     
  14. jcottrel

    jcottrel New Member

    Hi Mark,

    No I did not give that particular info in my earlier posts. We have a flow center in our loop field. I think I understand what you are saying after reading your post a few times. You size the loop side of the system appropriately based upon the type of antifreeze you are pumping through the loop field. That seems to make sense to me.

    Thanks,
    Jon
     
  15. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader


    Woah!

    You asked:

    The service folks that fixed my system want to flush out my system and replace the glychol with mythenol. Is there really any benefit to doing so? Is it really worth the investment to do so?



    I replied:
    It transfers heat better and will offer a higher reynolds number with current pump.
    "It" = methanol.
     
  16. jcottrel

    jcottrel New Member

    Ohh okay, I misinterpreted what you meant by "it". I thought "it" was still referring to the glycol. Sorry for my misunderstanding. You probably figured that out :) So it does seem like there maybe a benefit to doing this and the service company in your opinion is correct. If I go ahead and do this, I just wanted to make certain that is worth the investment to do so.

    Thanks for the clarification!
     
  17. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I want to know why they want to make the change.

    It is easy to monitor conditions of the gylcol.

    I do not get the cost/benefit.

    Mark
     
  18. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I'm still not convinced we aren't getting good enough numbers to leave this alone.
     
  19. jcottrel

    jcottrel New Member

    I went back and looked to see what I have posted in the past on this thread. I forgot to mention one thing that I had thought I had already mentioned. When the service folks were out here the 3rd time after getting the low temperature code on the ClimateMaster 4-ton heat pump, they did some cleaning of the QT pump. There were some small shavings from the PVC pipe that is inside the house. This was probably just from not being careful with the joints on the PVC pipe. Also the service tech found a small rock in the QT pump. I do not know if the installation company flushed the system properly when they brought it up online. I would think there would be more than one little rock in the QT pump if there were loop field issues. I asked the service tech if finding a rock was an indication of loop field issues and he said no. But the installation manager from the service company seemed to be concerned about there being a possible loop field issue. I am wondering if the installation manager from the service company is just trying to scare me in order to drum up more business.

    As I had already mentioned in previous postings when they do the flushing they want to replace the glycol with the methanol because that is what they prefer to use. It seems there are 2 schools of thought on the methanol vs. glycol debate. The glycol is more environmentally friendly and easier to monitor the temperature of. While the methanol is slightly more toxic but is more efficient.

    The service tech seemed to be okay with the temperatures after he left. I do not have any more temperatures other than those listed earlier in this thread. He may have verbally told me the temperatures but I did not write them down.
     
  20. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Again you have not posted temps that compell me to suspect the loop field.
     

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