Ebo
Registered Users
Posts:6
 |
| 09/18/2008 5:31 PM |
|
This may sound crazy but has anyone ever tried putting a coil or loop in a septic tank? Assuming that your loops are sealed as they would have to be in any geo therm system, what would be the problem? I am thinking (all guesing) that the temps in your sh.. tank might be higher than the average ground water temp. My other crazy idea is a ditch filled with wood & brush chips surrounding a ground loop. This is some heate source! I just don't know how long it would last before it just rotted, any ideas? The property that I bought has an area where they burried some woody debris as a result of the timber harvest, I imagine it to be brush and tops (of trees) and maybe some chips and stumps but when the weather is cold it steams out of a small crack in the earth where it has settled some, and this has been going on for over a year! If I could get a year or better out of my "heat ditch" I have my own excavation equipment so a replacement would be a cheap weekend job that even if I had to do it annually, It's do-able. What I am trying to achieve is avoiding the costs of the well(s) or hundreds of feet of ditching associated with "traditional" GWHP systems. I am learning about all of this (alternates to the oil, elec. and even fire wood) heating sources, and common sense tells me that 1. the hotter the water that you supply your heat punp the better. 2 If you slowed down the flow rate thru a higher temp heat source (80deg. wood chips or the ? deg. septic tank) rather than 50 deg. ? Maine earth at 5'/6' down, that you would be way better off. Thanks for any help. |
|
|
|
|
|
|
senecarr
Registered Users
Posts:158
|
| 09/18/2008 6:04 PM |
|
I would think that would increase your odds of the septic tank overflowing, and that it's fairly like the septic tank wouldn't have enough room.
You are correct that the septic tank has higher heat content. One of the things mentioned in the septic guide the county sent me when I bought my new house stated that if you have problems finding your tank, the first snowfall will tell because the snow will melt there first. Although, I imagine since it's connected to the house via plumbing, pulling heat out of it might end up pulling it back out of the house. Not sure how quickly a septic tank exchanges heat with the rest of the ground if you started freezing.
|
|
|
|
|
senecarr
Registered Users
Posts:158
|
| 09/18/2008 6:05 PM |
|
http://www.patentstorm.us/patents/5730208/description.html
Says it's an idea, but it looks like the corrosion to the equipment is a draw back. |
|
|
|
|
cnygeo
Registered Users
Posts:68
|
| 09/18/2008 6:25 PM |
|
I've never been lucky enough to own a septic system, so I'm largely ignorant of how tolerant they are to temperature swings. However, I believe it is not recommended to install a ground loop too close to the septic system as the colder temperatures will slow down the decomposition of the waste causing the system to fail. I've seen pretty strong language cautioning against doing this somewhere, I'm not sure if it was in an ISGHPA manual or some other literature.
It would be easy and cheap enough to try, though the consequences of failure would be somewhat severe unless you had a backup plan! |
|
|
|
|
engineer
Registered Users
Posts:394
|
| 09/18/2008 10:18 PM |
|
I've read of helical heat exchangers connected to heat pumps designed to recover heat from departing gray water to heat domestic water. It makes especially good sense in a high flow application such as a laundromat - it makes perfect sense to pump heat out of clothes washer drain water and into warm water for the next clothes washer cycle. I can even envision some kind of recovery device for clothes dryer exhaust preheating either or both of inlet water or air for washing / drying clothes.
But, I digress. Calculating 'out loud' into cyberspace: Flow into a domestic septic tank might run on the order of 150 GPD at 80 F (average of warm and cold water) Cooling 150 GPD from 80 to 40 (wouldn't want to freeze the septic bugs) yields right at 50K Btu, nominally enough for a 4 ton system for 1 hour of heating. Not much, and hardly worth the dubious joy of plumbing in a septic tank. Septic bugs might not like being chilly and could react by going on strike...let's not go there. |
|
Without data, you only have an opinion. |
|
|
geodean
Registered Users
Posts:590
|
| 09/18/2008 10:26 PM |
|
| There was an article in our newspaper a few years ago about a guy who talked the city into letting him put a helical heat exchanger in a section of the city sewer out in the road. As I recall, it worked quite well. |
|
Dewayne Dean
PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
|
|
engineer
Registered Users
Posts:394
|
| 09/18/2008 10:30 PM |
|
In the case of a city sewer line the flow is probably much more usefully higher. Assuming one works through any corrosion issues and / or obstructing the sewer with the helix, I can see that working.
Was it a storm or sanitary sewer? |
|
Without data, you only have an opinion. |
|
|
geodean
Registered Users
Posts:590
|
| 09/18/2008 10:48 PM |
|
Posted By engineer on 09/18/2008 10:30 PM
Was it a storm or sanitary sewer?
Sanitary
I could never figure why they are called sanitary....seems quite unsanitary to me.
|
|
Dewayne Dean
PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
|
|
joe.ami
Registered Users
Posts:370
|
| 09/18/2008 10:52 PM |
|
Heard about a septic loop last week, worked well in heating season...not sure about cooling season or in bacterial breakdown of waste season.
J |
|
|
|
|
geodean
Registered Users
Posts:590
|
| 09/18/2008 11:28 PM |
|
I found a link
|
|
Dewayne Dean
PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
|
|
engineer
Registered Users
Posts:394
|
| 09/19/2008 7:41 AM |
|
Interesting - I wish they'd been more specific.
I did see a shot of some large diameter copper pipe$ and a humongous pool of water in the basement - probably an expensive system. |
|
Without data, you only have an opinion. |
|
|
rlacasse
Registered Users
Posts:2
|
| 09/19/2008 9:25 AM |
|
I would not extract heat from a septic tank. This will slow down (and possibly kill) the bacteria in your tank. The bacteria are the key component that makes a system work. Plus -- depending on winter temps, snow cover, etc. -- you might lower the temp enough to allow frost to penetrate your tank/drain field and freeze it up.
I recommend anyone with a septic system read "The Septic System Owner’s Manual" by Lloyd Kahn. Preferably before you experience problems like drain field failure (such as I did several years ago)
While on the subject of utilizing waste water...
I plan to utilize gray water to help moisten a horizontal loop field. Water from everything but toilets and kitchen sink will drain to a small baffle tank buried in the yard that will be monitor for sand/dirt/lint accumulation over the years. Post baffle tank a leach field will trace atop the GSHP loop field - at a much shallower depth. There’ll be a small layer of sand or gravel around the leach pipe.
Per the book mentioned above, diverting gray water from septic system allows it to function more efficiently by removing flood cycles of laundry/showers/softener purge/etc. This can reduce septic system maintenance needs and possibly prolong the life of the septic system.
Ray... |
|
|
|
|
senecarr
Registered Users
Posts:158
|
| 09/19/2008 9:31 AM |
|
It looked like in one of the links I saw, one of the ways to do it to make it work right only really works for new construction. Basically you dig your geothermal pipes first, cover them partially, and then build the septic system on top. This avoids corrosions issues as the waster water going into the general field part should already be bacteria-ed at that point, but still at a higher point.
Engineer- your back of the envelope calc ignores the fact that the septic bacteria actually produce heat as well - ever had the misfortune to feel the temperature inside a compost heat with your hands (I hope not, I haven't either, it's something I prefer knowing second hand)? |
|
|
|
|
engineer
Registered Users
Posts:394
|
| 09/19/2008 12:01 PM |
|
I concur with the beneficial effects of diverting grey water, especially to soak a loop field - a nifty twofer
As for the heat generated by decomposition, I considered it while posting but figured it to have a negligible effect. I'm not even sure it is applicable to a septic tank. Here is why:
Compost piles generate heat by slowly burning (oxidizing) the material. The reaction is not combustion in the sense of providing a visible flame (unless the heat buildup gets out of hand) but does release the same amount of energy. A similar reaction (heat without flame) via oxidation occurs in our bodies as we 'burn' chemical energy in food.
A septic tank is different - it is maintained in a sealed, airless state (otherwise it stinks and generates complaints) No air = no free Oxygen so no Oxidation. Bacteria do the work. The condition is referred to as 'anaerobic'
The perception of a septic tank or drain field being warmer than surrounding ground probably has more to do with the inputs (mostly lukewarm domestic water) being warmer than ambient dirt.
In keeping with my sig, this is only an opinion - I have no hard data in its support
|
|
Without data, you only have an opinion. |
|
|
senecarr
Registered Users
Posts:158
|
| 09/19/2008 3:16 PM |
|
While it would be true that the bacteria making the break down work in an anaerobic environment, they are still performing oxidation, they just can't use the most efficient oxidizing agent - oxygen.
http://en.wikipedia.org/wiki/Fermentation_(biochemistry)
Fermentation releases energy - meaning exothermic. |
|
|
|
|
engineer
Registered Users
Posts:394
|
| 09/19/2008 11:11 PM |
|
OK, I'll buy that. As I said, I'm out over my skis on this one.
But consider also the mass of solids - it really isn't much, just a few pounds per day, probably not over 5 (While researching flushing effectiveness of various toilets I came across a British study of average stool mass produced by adult males...I'll say no more)
Suffice to see that the BTU content of a day's few pounds of wet, already-digested solids wouldn't be much, and it would be overwhelmed by the heat content of the 100+ gallons of wastewater that accompanies the solids. |
|
Without data, you only have an opinion. |
|
|
joe.ami
Registered Users
Posts:370
|
| 09/21/2008 10:48 PM |
|
OK (with apologies if I missed the solution) but if we take advantage of gray water for heating, don't we lose something with the heat in gray water (say during a shower) during the cooling season? We're all here to build the best mouse trap, but I think gray water or sewerage offers diminished returns at best (lost edge during cooling season, possibility of plugged drain....etc).
J |
|
|
|
|
engineer
Registered Users
Posts:394
|
| 09/21/2008 11:02 PM |
|
I think (operative word - think) that in the case of soaking a horiz loop field that warmth of graywater in cooling season would be trumped by its aiding conduction, compaction and heat transport down from the field, especially in dry climates.
Whether this limited benefit is worth the extra expense and confusion (think of plumbers and building inspectors) of separating the gray water and getting out to the field is certainly subject to debate. In a cold climate the ground above the loop field could come to be an ice rink, another possibly undesireable result. |
|
Without data, you only have an opinion. |
|
|
joe.ami
Registered Users
Posts:370
|
| 09/22/2008 9:13 AM |
|
If the heat from summer usage has little impact then wouldn't that be true in the winter as well? I gues we're talking about more than one thing here. The "duty loop" I mentioned earlier was actually in the septic tank where yes summer showers impacted surrounding (and therefore EWT's) water temp's. To put the loops over or under the drain field is of course avoided do to the likely hood of damage if field repair is ever necessary, all manufacturers I know of want at least 10' from any plumbing (making it a code thing) and risk of freeze which shouldn't bother a new field with lot's of unimpeded openings, but could bother a partially plugged older field.
If we want to look at the soaker method/ improved compaction. It might be interesting to do research on the benefits of a soaker hose installed with the field and compare cost/vs savings for an occasional squirt of water.
J |
|
|
|
|
senecarr
Registered Users
Posts:158
|
| 09/22/2008 11:16 AM |
|
| Of course, you could always close the drain during your shower, and every time you have a shower or bath, you would let the water cool down to room temperature before you send it back outside. That's the cheapest install cost of all - a 10 cent bath tub stopper at best. You can even turn the functionality off in the summer - empty the drain as soon as possible. Of course, it only captures some of the degrees, but they are the ones that move freely. It's a tip that makes me like builditsolar other than the disagreement over if geothermal is a good investment economically and environmentally. |
|
|
|
|