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  1. #1
    Join Date
    Mar 2010
    Location
    North Louisiana
    Posts
    15

    What would expected EWT from well

    I live in northern Louisiana and have a 4 ton 2 stage geothermal system with a 4 ton plate coil in 15' deep water in a large lake. My mid afternoon entering water temp is running 93 degrees F with an outside air temp of 95 deg. I calculate an cooling EER of 13.8 which is not as efficient as I had expected. I am considering converting to a closed loop well system to replace the plate coil in the lake. Anyone have any idea what EWT I could expect with four 150 ft deep wells?

  2. #2
    Join Date
    Jul 2010
    Posts
    43
    Quailtrail Have you tried to clean your plate off? If you are in 15 ft. of water and your lines in and out of your havc are at least 4 or 5 foot underground you should not have this problem. Your plate may be covered in mud if that happens there is no heat transfer. Is this a new problem in an old system or is this a new system? Curtis

  3. #3
    Join Date
    May 2005
    Posts
    161
    What's the EWT after the system sits idle for a long time? What I'm getting at is.............is 93 the actual water temp that low? Doubtful. I'm betting you don't have enough loop or as the previous poster has mentioned, your heat transfer is poor.

  4. #4
    Join Date
    Mar 2010
    Location
    North Louisiana
    Posts
    15
    Good idea to clean the plate. I will do this next week and report my results.

  5. #5
    Join Date
    Jul 2010
    Posts
    43
    Quailtrail also be sure that the plate is not resting on the bottom it should be up about 1 foot so that water can flow all around it.

  6. #6
    Join Date
    Mar 2010
    Location
    North Louisiana
    Posts
    15
    After cleaning the lake coil ( It had a slime on the surface of the coil that easily brushed off) the EWT did not change. I have ordered a data logger and will investigate my problem with better information. The plate was standing upright on the bottom of the lake as it should be.

  7. #7
    Join Date
    Jul 2010
    Posts
    43
    Hi Quailtrail I had hoped that would work for you. How deep is your return line from the lake? what is the temperature of the lake at say 12 feet? It would be very nice if you can get this to work. If you have to dig wells it will be alot of dollars that should not have to be spent. I have a 3 ton 2 stage and a 2 ton with 6 200ft. wells that give me ewt of 74 in late summer and 46 in late winter. I live in Virginia on the water so I don't think that 4 wells at 150 ft. would be enough for your hot summers. Curtis

  8. #8
    Join Date
    Mar 2010
    Location
    North Louisiana
    Posts
    15
    I installed a Hobo u12-006 data logger on my system. For a five day period in July my EWT avg'd 95.7 deg and my LWT avg'd 98 deg. The avg outside temp for this period was 84 deg (High 98deg & low 77 deg). A spot reading at 9:30 in the morning of the lake temp at 7' deep was 90 deg and at 15' deep the lake temp was 85 deg (not near the lake plate heat exchanger). The air temp during these readings was about 93 deg. My calculated cooling EER runs about 12.8.
    Any comments would be appreciated.

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    We do a lot of systems up here in New England and we use standing column wells with great success. The wells are deep and always in bedrock. Using a sliding scale, we average 150 feet/ton for small systems up to about 6-tons and 120 feet per ton for larger systems. When drilled to the proper depth for effective heat transfer to the bedrock, we see pretty consistent temperatures that vary from 59F in summer to 46F in winter. For those who can't get the necessary depth due to aquifers or budget limits, bleeding water from the well is the fall back position. By bleeding some water out of the well, it becomes a mini pump and dump type system where fresh water from outside the well bore seeps into the well and it is always right at about 55F and so aids in controlling well temperature. Of course, the problem may be getting a well company that can drill to the depths needed for such wells.

  10. #10
    Join Date
    May 2005
    Posts
    161
    Quote Originally Posted by quailtrail View Post
    I installed a Hobo u12-006 data logger on my system. For a five day period in July my EWT avg'd 95.7 deg and my LWT avg'd 98 deg. The avg outside temp for this period was 84 deg (High 98deg & low 77 deg). A spot reading at 9:30 in the morning of the lake temp at 7' deep was 90 deg and at 15' deep the lake temp was 85 deg (not near the lake plate heat exchanger). The air temp during these readings was about 93 deg. My calculated cooling EER runs about 12.8.
    Any comments would be appreciated.
    This sounds like a textbook case of undersized loop. However, I'd like to ask again..... have you checked the EWT after the system has sat idle for about a day? I'd be curious if your EWT drops to whatever the lake water temp is for at least a few minutes of running.

    If you let the system sit idle, then turn it on and measure the EWT, and the temps come in reasonable (e.g. 80 F).........then clearly your loop's capacity is too low.

    There's only two explanations I can think of for this:

    1 - There is enough pipe, but it's plumbed wrong and you're only flowing through part of the loop.

    2 - There simply isn't enough pipe/area.

  11. #11
    Join Date
    Jul 2010
    Posts
    43
    Quailtrail It looks to me like your lake temperture is way too high. Like I said before I am not a pro just a homeowner that has studied geothermal systems. If I were you I would be mad at whoever sold me a lake plate on a 85-90 degree lake as they should know that won't work any better than an air source heat pump. It should be great for the winter though. If you do change to a loop with wells be sure you use someone that will guarantee you an ewt that is normal for your area. Good Luck! Curtis

    P.S. Sometimes it is better to cut your losses. If your system is working and keeping your house cool it might be cost effective to just leave it alone. your wells would cost several thousand dollars more than you will save in electricity.

  12. #12
    Join Date
    Mar 2010
    Location
    North Louisiana
    Posts
    15

    Confused

    I shutdown my geothermal system last night at 8pm and let it sit idle overnight. At 10am this morning I checked the temps before starting the system and the results on the Hobo system was EWT of 76.2 deg and a LWT of 83.6 deg with nothing running for 14 hours. The temp in my basement where the system is located was at 76 deg. I used a digital probe in the TP ports and got the same result. I switched the Hobo leads and got the same result. The Hobo temp probes are thermal epoxied to the bare line and heavily insulated so I don't understand why the LWT is over 7 deg hotter than the EWT with nothing running.
    At 10:43 I started the system with the following results:
    Time EWT LWT outside temp
    10:43 86 92 88
    10:45 86.4 92.8 87.8
    10:47 90.4 96.4 87.8
    10:50 92.6 98.7 88
    10:55 95.2 101.5 88.3
    11:00 97.0 103.4 88.3

    Your comments would be appricated.

  13. #13
    Join Date
    Mar 2010
    Location
    North Louisiana
    Posts
    15
    I specified the lakeplate system to save $$$. I assumed the water temp would be much lower in the summer. My mistake. The installer put in what I asked for.

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