New Geothermal system questions

Discussion in 'Maintenance and Troubleshooting' started by Dan Dillner, Jan 20, 2014.

  1. Dan Dillner

    Dan Dillner Member

    OK a newbie here to this forum. This summer I took on the challenge to build my own house here in Vermont. We are on Lake Champlain and have a 2000sqft 1.5 story home. Very tight construction with foam insulation and triple glazed windows. We have been finishing the inside and living in it. We have been heating the building with 2-3 (1500W) electric space heaters comfortably to 70Deg even in the worst blast of -13 Deg F. Getting the GEOHP up and heating has been a bit lower priority to making the place liveable. Now I have the heat pump up and running, duct work in place and insulated but have some questions.

    1) I thought I would get a larger Delta T on both the EWT/LWT and the EAT/LAT. I can decrease the LWT by throttling down the exit valve. We measured the Wattage the well pump was using and it is around 500W so I have been focusing on reducing the run time of the heat pump which brings me back to the EAT/LAT delta. The most I have ever been able to measure is 13Deg F. Is this reasonable? In 20 Degree F outside air temp the HP is running about 50% of the time. Any thoughts or suggestions would be appreciated. Thanks Dan

    Here is my best at the list of background questions
    ) Where you live -- Vermont
    2) Heat loss/gain calculations for your home -- Not sure, I built the house myself. 2000sqft, 6" walls, closed foam insulation 7" up and 4" walls. Windows are triple pane. My estimated manual J was 40-50 Thousand BTU so I bought a 58,000 BTU unit (It might be too large)
    3) Brand, size (model) and type of heat pump Coldflo dual air cfx060
    4) Type of loop field (open/closed/vertical/horizontal) size and design parameters Standing column well with porter schroud 420ft deep. Pump is a variable constant flow capable of 18-20GPM.
    5) Average cost/Kwh of electricity and consumption .15c/kWh
    6) Entering and leaving air temperatures (EAT, LAT) measured immediately upstream and downstream of the heat pump EAT 67deg, LAT 82Deg
    7) Entering and leaving water temperatures (EWT, LWT) measured at the heat pump(s) I have a valve to adjust flow, Lower flow Higher temp delta. 2 deg to 4 deg delta EWT 50 Deg F, LWT 46 Deg F at about 15GPM
    8) Percent of load to be covered by geo and balance point 100% Geo, no aux heat
    9) Installers assessment of your systems operation. I installed unit my self
    10) Projected operating costs, actual operating cost and previous heating and cooling costs. Not sure yet
     
    Last edited: Jan 28, 2014
  2. Dan Dillner

    Dan Dillner Member

    Well I have a bit more detailed information now that I have installed better sensors. I added a Water flow meter and Cu temp wells on the in/out water pipes as well as digital probes on the EAT/LAT. Now I have accurately set the flow to 15GPM and I now have EWT of 49 deg, LWT of 47 deg. EAT 69 and LAT 80. I spoke with the tech support folks today and they agree that the delta T's were off. They said they would get back to me on what I should do next.

    I will wait for that but I suspect the reversing valve. Any body on this forum know how to check this? I suspect this because the refrigerant has a low and high pressure cut out switch and the unit has never cut out. Any other ideas would be welcome.
    Thanks

    Additions: I had a refrigeration contractor over to check the fluids and to have a look. He did not think anything was way out of wack. The low suction side was at 100psi and the high side was 285psi. The compressor sounded normal to him and was drawing 14.1Amps. The current draw seems a bit low. So no big smoking gun, still waiting for the technical support team to call me back.

    Any question or suggestions I would be welcome. Thanks
     
    Last edited: Jan 28, 2014
  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    If you were able to heat to 70 at OAT of -13*F with three 1500W space heaters operating continuously then voila! - Your load would be handily met by a nominal 1.5 ton unit. Design day condition for Burlington, VT is -6*F, so performance at -13*F is valid data. An old and dear friend lives

    Sounds like you are oversized by a factor of 3-4!

    Refrigerant pressures seem OK, maybe a tad low on high side. Airside Delta-T is quite out of whack, should be at least 25. Are you measuring right at unit's air handler inlet and outlet (return and supply)? Just a bit of chilly unconditioned air sneaking in to return ducting will throw it off.

    I don't follow your line of reasoning in re the reversing valve.

    15 GPM at 4*F delta -T works out to 30 kBtuh heat extracted.
     
    Last edited: Jan 28, 2014
  4. Dan Dillner

    Dan Dillner Member

    Thank you for taking the time to reply.
    Yes I agree that I oversized but when I ordered it we had no idea the house would heat so well. Normally a 2000 sq ft house here with open lake conditions and with lots of glass on the lake side, would need a lot more than we turned out to need. My Manual J calculations suggested a 4 Ton so I added a little extra. Also we were only heating our sitting area with the strip heaters so I would say if I could order it again I would order a 3 Ton unit. As it is now I have what I have and so we will see if we can optimize. It is very comfortable throughout the whole house even as it is. We have been in the single digits OAT and the unit runs about 60% of the time.

    The reason I was suspicious of the reversing valve is that one of the tests I did was to reverse it and see if it would get cold. I ran it that way for a short period of time and then switched it back to heat. After the delay it started up and I measured the largest delta T on the air that I have to date. It was more like 18deg. So I thought that might be a clue. I discussed this with the contractor that I had come and check the refrigerant and he thought the valve was a low probability. I have not run it much on the cooling side but it does not give me any measurable drop in air temp.
    I am measuring the air temp right in the exit plenum and in the return air duct at the heat pump. I am using a simple return air duct that is Central to the stairs and house so there is not much chance of any of the crawl space air in-filtering.

    Does a delta T of 13deg seem right considering a delta T on the water side of 2deg @15GPM? Somehow is seems like the unit is not extracting enough heat out of the water. I'm not sure where to look next but welcome any suggestions.

    Today I will work on my automatic water dump system, I'd like the EWT to stay closer to 50.
     
  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    You can certainly bring down your water flow. If this is a 2 stage heat pump, you may not be in second stage. 30,000 BTU's extracted suggests you are in first stage. If there is a call for second stage, then the fan would run faster but without additional BTU's your Delta T would drop.
    Reversing valve is a red herring.
    A heat pump this grossly oversized will cost more to run than right sized and pump 100's of thousands of gallons more water than a right sized unit. You would be better off picking up a 1.5-2 ton and sell this thing on Craig's list (a 3 ton is not indicated either).
     
  6. Dan Dillner

    Dan Dillner Member

    Thanks for your comments and replacement may well be the end result. This unit is a single stage but as you point out acts more like it is running like a 2 ton and do not know why. The fan is running full speed producing 1900 CFM which is moving comfortably through the house with tight air ducts (no complaints from the wife). When I reduce the flow it also reduces the Air delta T. I may be wrong but I have been working to increase the Air delta at the expense of pumping water since the well pump is using 250 - 500W and the heat pump is using 14A (3 KW) + the fan. Do you think I am heading in the correct direction?
    Oh BTW, there is another reason I was checking the reversing valve is that there is no delta T on the air when in cooling mode.
    Thanks,
     
    Last edited: Jan 29, 2014
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Last edited: Jan 30, 2014
  8. Dan Dillner

    Dan Dillner Member

    Yes that is what their chart says. Not sure what I should look at next. Any suggestions?

    I guess if there is a consolation it would be that it is taking only 3KW to run instead of the 4.6KW in the chart to produce the reduced amount of heat. So we don't seem to be putting a load on the compressor. Not sure what I will do next, it is keeping us comfortable and is cheaper than running the strip heaters. Don't think anyone on CL would want this as is either. It may just drive me crazy........but I will be wiser when I purchase my next model. It is almost like I have the CFX041 instead except it is pushing air at the 1900CFM rate keeping the air delta T low.
     
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Slow the fan down and test again.

    Mark
     
  10. Dan Dillner

    Dan Dillner Member

    Well I had a call from the technical support folks and the agreed with me that the unit is not putting out what it should. They think it is about 8oz low on 410a. They asked me to take a "super heat" measurement to confirm. I'm not sure where to take this measurement but I am sure my refrigeration guy will know. The tech support person also mentioned that I could take a temp measurement on the suction line and it should be in the 36-41 deg range. I'll probably do this tomorrow.

    This seems odd to me that a new unit would be "low on refrigerant." but if that solves it I will be happy but wondering why or how a new unit could be shipped out of a factory performing so far from the specs unless it is leaking? Is it normal to check the level when a new unit is installed?

    I am very pleased now with how everything else is running. I had a nasty water hammer with the solenoid valve that was supplied with this unit but after I found a motorized one capable of the volume and pressure it is very quiet and my wife is happy!

    Oh BTW Mark, I have not looked at the fan to see if the speed could be reduced. The system was advertized as having a variable speed fan but I have not seen anything that would give me any control.
     
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    An amp draw can offer clue to a low charge as well. They should offer superheat and subcool values to your refrigeration buddy. New units are sometimes low on charge and sometimes leak.
    MO is not to add 8oz or whatever it is to evacuate charge and weigh in new refrigerant. If you weigh it on the way out you can establish whether or not that was the problem.
     
  12. Bergy

    Bergy Member Industry Professional Forum Leader

    How in the HELL could they say the unit is EIGHT OUNCES low?????
     
    ChrisJ likes this.
  13. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

  14. Bergy

    Bergy Member Industry Professional Forum Leader

    More like... WAG!!
     
  15. Dan Dillner

    Dan Dillner Member

    Thanks Joe, Good idea I will discuss this when we take the measurements later this week. I would like to establish cause.
     
  16. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    One way they might know it's 8oz low is if they have seen it before........as in an assembly goof where someone didn't get the memo to up the charge from 72 to 80 oz or someone didn't read the model number and thought they were gassing up a 4 ton.
     
  17. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I noticed a change in labeled factory charge on otherwise identical models awhile back...made me wonder which was correct.
     
  18. Dan Dillner

    Dan Dillner Member

    Well I am not sure how this got out of the factory with the water delta of 2 deg and the air at 13. Meanwhile the compressor is drawing about half the power that they spec the system at. I suspect it will start loading the compressor if we add some more refrigerant. Should see this happen this week. Meanwhile it is actually keeping us nice and warm, just runs a bit longer. I wish I could reduce the fan speed first and see what CFM it uses to have about a delta T of 20 on the air. I suspect it would be in the 1000cfm range. It is a GE Genteq X13.
     
  19. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    "Well I am not sure how this got out of the factory with the water delta of 2 deg and the air at 13."
    A factory run test would generally consist of closing the contactor to see if the compressor works.....if any at all. Not aware of an appliance manufacturer that runs their equipment for an hour to test parameters.
     
  20. Dan Dillner

    Dan Dillner Member

    Update, Well since we were heading south for a couple of months I decided not to make any changes to the refrigerant till we got back. The system kept the temp in the house a perfect 60 degrees while we were gone but still had the same delta T's. Well now it is getting warm here so I decided to try the cooling side for a while and low and behold we have the correct numbers. on the water side it is EWT=53 and LWT=61 (8 deg delta). On the air end it has been EAT 70 and 48 LAT (22 delta). I am pleased with this but wonder if the water coil just can't work at the 49-50 degree range. Continues to use only 3 KWs (14A @220VAC).
    Thanks for all your comments, I have and continue to learn a lot about the technology.
     

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