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  1. #27
    Join Date
    Feb 2014
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    Cape Town, Western Cape, South Africa
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    Great discussion, you guys just opened my mind and gave me an idea to think about. Will do a research project on this system and see how it goes. It really sounds awesome.

  2. #28
    Join Date
    Feb 2004
    Location
    Pacific NW
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    Quote Originally Posted by SkyHeating View Post
    In my area we have to keep our geo lines a code required 10' away from a septic system so running through the system would instantly fail an inspection lol.
    +1, there is a reason for that code

    Interesting discussion, but would NEVER cool down my own septic system.

    digestion takes place optimally around 30 to 38 C, or at ambient temperatures between 20 and 45 C, where mesophiles are the primary microorganism present (copied from wiki)

    Of course, if one wants to subscribe to the 'pump septic tank every 3 years' philosophy (when about every 60 years per person per 500 gal of tank is all that is needed if there is no garbage disposal and separate washing machine grey water disposal) then it does not matter much. Have not pumped own tank in 45 years, and just checked it the summer, only 4" of sludge in 1200 gal tank. 4 people, no garbage disposal.

    If one work the thermodynamics, there is at most about 1000 BTU per pound of human waste decay energy injected into the septic system - so say you get the equivalent of 1 kW-hr after a heat pump. ALL the other heat of heat exchanger extraction in a septic system comes from ground heat coming INTO the septic tank.

    How much poo do you generate per day, eh? About 5 cents worth of heat per day vs. destroying your septic system and forking over $30+ a year for pumping?

    If you want to recover your shower and washing hot water energy, a heat exchanger on the sewer pipes would be more effective.

  3. #29
    Join Date
    Feb 2014
    Location
    Bloomsburg pa
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    24
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    My only question as a former co worker had the same idea had drawings an calcs and then got some engineer involved and was told that the unit would draw to much heat out of the tank and would kill off all of the bacteria is have you noticed any adverse effects in the tank. He was looking as sole heat source type using the heat generated by the bacteria breaking down the waste to go into a water to air heat pump

  4. #30
    Join Date
    Aug 2009
    Location
    Maine
    Posts
    8,073
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    Just had to crawl into a septic pumping station to replace pump. 12 out side about 70 in the pumping station. It was a ****ty job.
    However wouldn't you be able to reclaim heat from there?

  5. #31
    Join Date
    Jan 2016
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    1
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    Confused Heat reclaim

    Quote Originally Posted by snupytcb View Post
    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.
    Hi,
    Why not inserting the coil on the liquid side of the septic tank?
    When it is time to empty the tank, why not empty only the solid in the tank?
    ...the way I understand a septic tank, there is one reservoir for the solid and then the liquid goes into the other reservoir before draining into the bed.
    If the coil is in contact with the warm waist liquid, should I get better heat transfer?

    Thank you

  6. #32
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    17,864
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    Although I have a septic tank at property I own, I've never used it. So I'm still a bit of a rookie in this regard. But I think the biologic breakdown really slows down below 40 or 50*F.

    As far as the baffles go, that is to trap the solids, but biologic reactions are happening in all parts of the tank. Not just where the solids are trapped.

    And average ground temps around where I live are 55*F. So there's very little heat to be gained without compromising the septic system, or the drain field. Which is the 'really' expensive part to fix.

    Probably better just to use solar to warm a tank or pool, then use a heat pump to transfer the heat to the living quarters. At least in my part of the country.


    Quote Originally Posted by FLJ View Post
    Hi,
    Why not inserting the coil on the liquid side of the septic tank?
    When it is time to empty the tank, why not empty only the solid in the tank?
    ...the way I understand a septic tank, there is one reservoir for the solid and then the liquid goes into the other reservoir before draining into the bed.
    If the coil is in contact with the warm waist liquid, should I get better heat transfer?

    Thank you

  7. #33
    Join Date
    Sep 2002
    Posts
    22,525
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    Have you ever considered solar heating? A sun space structure maybe? My house here was not suited to that concept so I built active hydronic panels but a sun space is far superior of you can manage it.

    Google: Nick Pine if you like. You'll see some things you weren't expecting. <g>

    PHM
    -------



    Quote Originally Posted by mikeweber3 View Post
    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
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  8. #34
    Join Date
    Aug 2018
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    13
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    You don't want to remove heat from you septic tank. That heat is what is keeping your biomes from going into hibernation. If you just pump cold water out to your field without any pretreament from the septic tank, eventually you will have a breakout from your septic field, give it enough time. God forbid your system is close to an aquifer or a steam, if you poison someone from your system, you could be liable. What you don't want to do is mess with septic. It is very very expensive to fix once you screw it up

  9. #35
    Join Date
    Mar 2013
    Location
    Billington Heights, NY
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    Quote Originally Posted by Flezhen View Post
    You don't want to remove heat from you septic tank. That heat is what is keeping your biomes from going into hibernation. If you just pump cold water out to your field without any pretreament from the septic tank, eventually you will have a breakout from your septic field, give it enough time. God forbid your system is close to an aquifer or a steam, if you poison someone from your system, you could be liable. What you don't want to do is mess with septic. It is very very expensive to fix once you screw it up
    This is untrue.

    The heat is a byproduct of bacterial action. The bacteria create the heat. It doesnt come from elsewhere. Removal of that heat, down to just above freezing even, does not inhibit the decomposition action. There are many many systems and schools of hvac that teach better usage of residual heats recovery for a more efficient overall system.

  10. #36
    Join Date
    Sep 2002
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    But doesn't higher heat (within reason - not boiling heat <g>) accelerate the process of decomposition?

    I wonder what the optimal septic process temperature is?

    PHM
    ---------



    Quote Originally Posted by HVAC_Marc View Post
    This is untrue.

    The heat is a byproduct of bacterial action. The bacteria create the heat. It doesnt come from elsewhere. Removal of that heat, down to just above freezing even, does not inhibit the decomposition action. There are many many systems and schools of hvac that teach better usage of residual heats recovery for a more efficient overall system.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  11. #37
    Join Date
    Mar 2013
    Location
    Billington Heights, NY
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    Quote Originally Posted by Poodle Head Mikey View Post
    But doesn't higher heat (within reason - not boiling heat <g>) accelerate the process of decomposition?

    I wonder what the optimal septic process temperature is?

    PHM
    ---------
    the bacteria, like all others, have a range of "best operation" or a range of temperatures where they prefer to live. A septic tank has many kinds of bacteria, some go dormant as the temperatures in the tanks change and others come to life. This is why the tank doesnt go solid during harsh winters or get overcome with debris during harsh summers. There isnt one specific process temperature unless you're also uniquely identifying a specific bacterial species.

  12. #38
    Join Date
    Sep 2002
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    I mention it because I used to do a fair amount of sewer plant boiler service. They were gently heating the sewage to speed up the process. I don't know to what temperature though.

    PHM
    ----------------


    Quote Originally Posted by HVAC_Marc View Post
    the bacteria, like all others, have a range of "best operation" or a range of temperatures where they prefer to live. A septic tank has many kinds of bacteria, some go dormant as the temperatures in the tanks change and others come to life. This is why the tank doesnt go solid during harsh winters or get overcome with debris during harsh summers. There isnt one specific process temperature unless you're also uniquely identifying a specific bacterial species.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  13. Likes HVAC_Marc liked this post
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