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  1. #1
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    Septic tank heat reclaim

    About 2 years ago I built a new house. It is an all electric house and I'm trying to get the lowest energy footprint possible. I put a coil of 3/4 pex in my septic tank and circulate a closed loop antifreeze solution through it. I use this loop to bring heat from the septic tank to a tube in tube heat exchanger which is my evaporator. I then used a small airconditioning compressor to move this heat into another tube in tube heat exchanger which then sends the heat into my water heater. It runs about normal airconditioning pressures..... 40 degree low side and 130 degree high side.
    If I had it to do over the only change I would make would be to insulate my septic tank before back filling, as I'm sure I'm loosing heat into the ground before I reclaim it.

    It was a fun project, and has been working great. Please feel free to copy my idea.

    Thanks

    Mike

  2. #2
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    Thanks for the idea. I have considerd mulch type biomass for decomp heat but never a septic.

  3. #3
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    Thread Starter
    It's not really about bio heat as much as simple sensible. Most of the water down the drain is 75 degrees or higher which can get you over 3.0 COP

  4. #4
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    Thanks for sharing. This sounds like a great idea as long as you don't take out too much heat which could interfere with the biology of the septic system. I guess a water tank only uses about 40 kbtu or so per day, what is the capacity of the compressor and about how many hours per day do you run it?

  5. #5
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    It's about a 1 hp. Probably runs about 2 hrs/ day. It can't possibly cool tank below ambient ground , which in my area is 55.9. If you think about it, all heat I pull out goes back in through the drain. Also I get some heat from comp and pump electricity use. Also toilets warm water up from 55 to 73 before flushed. My tank usually runs about 65. I think if my tank was insulated it would run higher.

  6. #6
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    It's a great idea. Actually for tank insulation after the fact, consider the top is the warmest part so if you just insulate the top and the sides as far down as you can easily get to you will probably stop >1/2 of the heat loss.

  7. #7
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    Quote Originally Posted by terawatt View Post
    It's a great idea. Actually for tank insulation after the fact, consider the top is the warmest part so if you just insulate the top and the sides as far down as you can easily get to you will probably stop >1/2 of the heat loss.
    We just buried the over-under 4ft wide x 7 and 5ft deep geothermal lines around/very close to the septic, and on a 4ton rev cycle GHP with HW desuperheater, on 3700 sq ft B+ energy saving home; GREAT IDEA!

    loop is above 37 at coldest in 52 Earth-Coupled in 6600 ddays/ -14 usual, since 2002; (1994 -22 peak peak cold winter )
    Process cooling: NO COMPRESSORS Earth-Coupled since 1996
    ... however, much still needs to be hybridized energy transfer.

    CLOSED LOOP 2015 listed EER's
    even 49+ now; and "blended from low to high variable speeds" for 32deg.F ~ E-Star

    Perhaps you need a 32F Chiller/HW-Heat: buy a GEO-T Heat Pump (GHP with Heat-Recovery)
    http://www.energystar.gov/index.cfm?...mal_heat_pumps

    http://www.hydro-temp.com/products.html and Bosch/Carrier and AquasystemsInc.com

  8. #8
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    3-lines at 7ft 480ft runs horse-shoe around
    and another 3 at 5 ft rough filled, for odd style 6 lines ~under 3000 ft with 1.1/4" headers
    Process cooling: NO COMPRESSORS Earth-Coupled since 1996
    ... however, much still needs to be hybridized energy transfer.

    CLOSED LOOP 2015 listed EER's
    even 49+ now; and "blended from low to high variable speeds" for 32deg.F ~ E-Star

    Perhaps you need a 32F Chiller/HW-Heat: buy a GEO-T Heat Pump (GHP with Heat-Recovery)
    http://www.energystar.gov/index.cfm?...mal_heat_pumps

    http://www.hydro-temp.com/products.html and Bosch/Carrier and AquasystemsInc.com

  9. #9
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    This was one of my favorite ideas, " the poop loop " we called it. We gave up on the idea beased on capacity of the tank and falling temps. We never considered water heating as a more reasonable use of limited btu's. Good on you!
    Eric
    Eric Sackett
    weberwelldrilling.com
    Delta P= 8 ATA
    www.youtube.com/weberwelldrilling

  10. #10
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    An excavator owned the septic GTXtraheater set up, thought he'd save equipment rental T&M, etc, and did.

    11 yrs conductivity there seems well- OK.


    also:
    I believe the drillers and excavator contractors should sell btu's/quality/longevity like the ut'y co's.

    -believing designers should state minimal entering flows and temps and leave the btuh's to the Earth-Coupler''
    s to comply by performance contracting, like we expect of the ut'y co's.

    -Believing it would save testing/design-invested dollars in many instances.
    we regularly performance-contract with such-

    one installing OEM just proposed 250 tons to a 350 engineered blue print...
    they added 25 more... to that school ,
    like a strip-heater, -- but for peak cooling loaded- the next under 15 tons lastly added was just ultra eff heat pumps to air exchange for additional peak cooling/optional more efficient than certain-timed GTHP handling.

    Add- on designing and pricing to performance-flexible purchasing additions keeps a lotta-guessin' by the way side. When it can be so, this is proving the engineering without the up-front associated costs in planning, I believe. EARTHMOVERS' Utilities4U, Inc.
    Process cooling: NO COMPRESSORS Earth-Coupled since 1996
    ... however, much still needs to be hybridized energy transfer.

    CLOSED LOOP 2015 listed EER's
    even 49+ now; and "blended from low to high variable speeds" for 32deg.F ~ E-Star

    Perhaps you need a 32F Chiller/HW-Heat: buy a GEO-T Heat Pump (GHP with Heat-Recovery)
    http://www.energystar.gov/index.cfm?...mal_heat_pumps

    http://www.hydro-temp.com/products.html and Bosch/Carrier and AquasystemsInc.com

  11. #11
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    Back in the day (1974), we installed loops on top of the leach field for a geothermal system, before back filling. To my knowledge it is still in use today.......
    I came into this world with nothing, I still have most of it left....

  12. #12
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    25 years ago I did a similar thing except I put the coils on the outside of the septic tank and circulated the refrigerant through them directly, I also insulated on the ground side of the lines, it worked like a hot damn, all the waste water from the house and the energy produced by the bacteria were recovered and put back into the house, I was at first concerned that we might drop the temp of the tank down to far for the needed bacterial propagation but we never had a probem

  13. #13
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    Quote Originally Posted by Pendragon View Post
    25 years ago I did a similar thing except I put the coils on the outside of the septic tank and circulated the refrigerant through them directly, I also insulated on the ground side of the lines, it worked like a hot damn, all the waste water from the house and the energy produced by the bacteria were recovered and put back into the house, I was at first concerned that we might drop the temp of the tank down to far for the needed bacterial propagation but we never had a probem
    this seems like a better way to go. having the lines inside the tank will be great for a while but after time they cover with sediment and loose efficiency.

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