Crazy Geo-Thermal Idea

[toivo1037]

I asked this question to a local installer. And he stated just as in that link, only claimed he had as client actually do it. Wrapped the piping around a 1000 gal septic tank, and it worked OK, until wintertime, when it froze that sucker solid. Good idea, but I guess they just pull too much energy out of the ground.

I have been doing my research, man I can't wait until I get far enough along to put one in.

 

[joe48]

Been thought of, been done. Against code, and screws up the anaerobic digestion so I've been told.

As a former sewage treatment plant operator with an anaeobic digester at the plant to reduce the sludge by 50-75% and produce methane for heating both plant water and the digester process. The digestion process is by 2 types of bacteria anaerobic acid formers and anaerobic gas formers. the acid formers like temps in the range of 50-100 F, the gas formers like 90-100 f, so to operate the most efficiently we would run the digesters at 90-100F. So a little warm water going thru a separate loop will not have much affect on the bugs and certainly less than sending hot dishwasher water into the tank. Even though the bugs like warmer temps they don't like sudden changes any more than you do.

I could be wrong but I don't know of any code in NY that says you can't put a heat recovery loop thru waste water , as long as its isolated, HOWEVER ,YOU CAN NOT PUT DOMESTIC / DRINKING WATER THRU ANY THING LIKE THAT.

all in all not a bad idea if your heat recover BTUs exceed the BTU input in KWatts to pump thru the loop. Need to do a bunch of math.

Good luck and keep us posted.

 

[atgreene]

My well guy and I are exploring the possibility of grabbing heat off a septic tank. The idea that it will freeze is a little off.

Personally when we do it, we are going to insulate the tank. Further, we are looking at putting a coil on top of the tank, or at least at the top of the tank as well as going with a 1500 gallon tank rather than the typical 1000. It would not supply all your heat, but a portion of it.

I will let you know, as we're slated to begin working on 3 different geo-therm set-ups this fall, the septic may be incorporated into one of them.

I say that until someone actually tries it, it's just a theory. Insulation would seem to be the key.

 

[excelagator]

Good link...I guess that answers the question although I am surprised the sytem could cool a septic that much. I have thought of putting a shallower loop (2-3 feet only) since I have muck soil which is extremely high in organic material. I have not seen it freeze more than an inch or two down--and then only in spots. I think the constant slow decompostion keeps it "warm." I understand that deep ground stays about 55 degrees in this area...but I wonder if muck soil is hotter. Maybe I should rig some sort of thermometer at 2-4-6 feet this winter and test out the theory. Muck is sort of like a huge compost pile with topsoil thrown in for good luck. Anyone have experience with this soil type? Peter

I have friend that has 160 parcel. some of it is swamp. He told me that that it rarely freezes. Now we are in Northern Wisconsin and I find it hard to believe. I yet find it very intriguing because it is decomposing and yes it gives off heat to a certain extent.

 

[excelagator]

I asked this question to a local installer. And he stated just as in that link, only claimed he had as client actually do it. Wrapped the piping around a 1000 gal septic tank, and it worked OK, until wintertime, when it froze that sucker solid. Good idea, but I guess they just pull too much energy out of the ground.

I have been doing my research, man I can't wait until I get far enough along to put one in.

I can see this working in the winter though.

If you insulated the sides and the top of tank it would retain the better. Natural earth heat will protect the bottom. I think am on the same latitude as you. My septic tank is down 7-8 feet.

I think insulation will work. I had my well line by the house freeze the 2 previous years. Last year I covered the area by the house with only 1 inch insulation board above the line. It did not freeze at all last year.

 

[joes_427_vette]

I have never seen a review of a geo thermal installation and usage for a number of years to see if it is cost saving or more expensive. Depends on the amount of electricity and replacement parts I would think. At any rate if they were that great they would be more popular. Would like to see a break down of cost on the install, parts, and comparison against a standard high efficiency gas furnace operation.

 

[Tig]

I don't have the numbers handy but I did the math in 1990 when I installed my Geothermal unit. A $2K government grant made it a no brainer for me. The unit paid off in a year as compared to my other options.
High efficiency gas was not an option at the time because gas was not available in my neighbourhood. The Geo unit was more efficient than gas but not by a significant margin. All rebates aside the pay back term for geo over gas approached the expected life of the unit. When I replaced the furnace in that house I put in high efficiency gas. I will take the geo unit with me to the country after a quick rebuild of the valves.
It is still the best alternative for me in my new home.

 

[Airic]

I had a friend just install a geo thermal system. It ran $10k + 2k for a new well for discharge due to local codes. Goverment rebate at $2K puts it at $10K. He has had it running for a few month now and has an electical savings of around $120 a month. His previous heating and cooling system was electric. His system runs at about 5gph.

 

[ampsucker]

hmmm... that's a payback period of about 7 years. pretty impressive.

our average heating and cooling bill (gas in winter, elec in summer) runs about $170 total each month. installing the same system and assuming a 25% improvement, we would see a payback period of nearly 20 years - approaching the life expectancy of the system.

that is assuming, of course, that energy rates do not go up significantly.

my BIL works for the electric company. he told me last week the government has put many new infrastructure requirements on their company "intended" to make service more reliable. the specific operation he cited was the requirement to drill test holes in each and every wooden pole to determine it's viability and replace them when substandard ones were found. the end result of this requirement is the hiring of a vast army of subcontractors overseen by about 200 new full time employees whose sole job it will be to drive around from pole to pole and drill test holes in them.

they anticipate rate case increases of around 30% across the board to meet this requirement.

look forward to all forms of energy going up significantly over the next few years....fossil or other otherwise.

wood heat and the associated work and mess is looking better and better...

amp

 

[afish]

I'm confused by the people saying that it will freeze the septic tank. I'm not saying to only install the loop in the tank but to use it to boost the temp of the loop by a few degrees. If the tank was at the end of the loop the temp of the water in the loop would already be around 55 degrees plenty above freezing. So how can that freeze the tank? I'm not sure how much it would boost the temp since I don't know how warm the tank gets in there I just know it melts the snow above it in the winter so its got to have some heat. The mulch isnt bad idea either but I wouldn't want to back fill the trenches with mulch since you would end up with ruts in your yard as the mulch decomposed. But if you excavated a large hole next the hose where the loop returns and coiled up some extra pipe and filled that with mulch maybe a some type of copper coil to help the heat transfer for a shorter coil but I'm not sure of the rules for joining the pex to the copper under ground or if that would be allowed