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Posted by geothermaljones on August 7, 2007, 11:36 pm
Wow...
First off, here in Minnesota, if we talk about re-injection wells on a pump
& dump system, the DNR folks start running around flailing their hands,
slapping temples & tush like their crevice & cranium are on fire...
then they stop & say something to the effect of " we don't allow that"
Hence, I'm not too familiar with the systems.
Sound like your suffering from the effect best explained by...
"It's easier to pull a chain than push one"
Reducing the flow through the GSHP's makes sense to control the reinject
issues, & 38dF is a good temp to maintain as a minimum out. What are your in
& out water temps? pressures?
If your flow rates are increased, you'll compound the issues with more water
forced into the ground.
If your opening the prv's & the bubbles disappear, why not leave them open?
Your pumps may run a bit wild, but it might be solving your issues... short
term.
The depth of your frost line in Winnipeg might be a source of your problems.
Here in MN they talk of 48", but we've been setting footing at 5' as the
last few years, we've been cold w/no snow.
75% of the septics in my home county froze out 3 years ago...
If your dumping 38dF water into a casing & expecting it to siphon down
through the lime stone, maybe a string of "heavy flow days" in the winter is
starting to back up the casing & freezing when it rises above the frost
line.
Opening the prv's increases the flow of warmer water thawing the ice etc...
just a theory of course.
Would a heat trace down the output casing help? Possibly cycling on based on
outdoor temp. or run time in heat mode.
maybe with sensor in discharge pipe.
In Winnipeg, I have to imagine your ground water has to be coming up around
45dF year round, correct?
@ that temp your cooling comes cheap, but in heat mode your only getting a
7dF delta T.
ROT say's you should have a 15dF delta T across a GSHP @ 3-4 GPM per ton...
Thus, you should be running twice that to cover a 7dF DT for 8 tons = 24-32
becomes 48-64...
I'm scratching my head w/ your 21 gpm,
unless your ground water is coming up much warmer (about 53dF min...), you
need
more flow, which your getting by opening the prv's.
As for dumping to the river to clear sand, that's what's allowed in MN.
You can't dump directly to a lake, river, or pond, you have to dump no
closer that 18" from the water...
Go figure? My brother dumps 3-5 ton GSHP out a 4" PVC pipe on the rock
retaining wall of the beach.
He likes to tell the local inspectors it's the shower & laundry waste, & he
often spends time showing them the real source... They don't like his sense
of humor, but they can't find a reason to shut the system down.
We suffer from tons of iron in our area, & the snotty rust colored filters
do need replacing quite often.
But that sure beats the price of the propane option available...
Magnesium makes for a nice black buildup as well.
As for chlorinating the wells, I'm at a loss.
I'd advise against it, especially if you domestic water is coming from the
same source as your GSHP feed, such as many I've worked with.
The infections you talk about are something I've never heard of, but I'd
want to be rid of.
Is this a summer or winter thing?
Would longer term dumping to the river lessen this? I doubt there's a water
shortage in your area?
p.s. I once rode the bike to the Winnipeg folk festival, on to Banff, Coeur
De Laine, Yellowstone, Black Hills & Home.
Winnipeg to Medicine Hat in one day, Rapid City to St. Paul in another
day... lots of low mile days in between.
Took a month, & met the "now wife" with in a week of getting back.
I'm still longing for a month off to ride the Great lakes perimeter, but she
laughs & hands me the honeydew list...
Man oh Man, I really enjoyed the Beat Farmers, John Prine, the Cowboy
Junkies, Corky & the Juicepigs...
sweet jane, i'm a happy enchilada and i think i'm gonna drown.
good luck
geothermaljones
st.paul,mn.
> I have a new house with an open-loop geothermal system. The house is two-
> storey with two heat pumps; a 5 ton unit for the first floor, basement
> and crawlspace and a 3 ton unit for the second floor. Used since last
> fall. Got great heat in winter with no red lights for the auxiliary heat,
> even on coldest windy nights (-35 degrees Celsius). Cools even better in
> recent heat wave (35 degrees Celcius). I am in Winnipeg, Canada where it
> gets pretty cold but only gets very hot for a few weeks.
>
> I have two problems, perhaps partly related.
>
> Most serious is that the injection well was overflowing by the end of
> winter. Normal static level is about 25 feet down casing with about 8
> foot rise when both units are running. When it overflowed I could see
> that there were a lot of bubbles, more than a pot at full boil.
>
> My pump rate is 21 USgpm.
>
> The bubbles were caused by pressure reducing valves (PRV's) that were
> installed downstream of each unit. When I cranked the PRV's wide open the
> bubbles stopped and then came back when I reset the PRV's. I did this
> several times and definitely isolated the bubbles to the PRV's.
>
> I was told that the PRV's were necessary because the installers adjusted
> the flow rate through each unit to limit the leaving water temp to 38
> degrees F so that there would be no risk of freezing the exchangers. This
> seems exactly incorrect to me since slowing down the flow would allow the
> unit to draw more heat from each gallon of water and thus reduce the
> leaving water temp. To prevent freezing you should speed up the flow so
> each gallon gives up less heat and the leaving water temp would be
> higher.
>
> The bubbles air locked the well, at least part of the problem was solved
> by installing a pump down the injection well and pumping out for a while.
> Then going back to the main house pump in injection mode. A lot or air
> was discharged, quite violently, from the well. A few cycles of this and
> I solved most of the problem - the mound up is 2 or 3 feet higher than
> last summer.
>
> I don't know if the remainder of the capacity loss is more air in the
> formation that I can't get out or possibly calcium or iron precititation
> partially plugging the limestone formation. I acid treated these wells
> after they were installed and that really increased the capacity so I can
> always do that again.
>
> The wells are both open holes in limestone formations, no screens at all.
> Sometimes I get a small amount of sand plugging the filter in the
> basement but not much - about a tablespoon of sand once every 3 to 6
> months. When I get the sand I just run the main pump on high to a pipe to
> the river for a few hours and the sand goes away for a few months. I may
> have to borrow a larger pump so I can over-pump the well to get rid of
> more of the sand. It's not the main problem anyway.
>
> My biggest problem is iron bacteria infection. I have been getting red
> slime on the filter to the extent that I have to clean it every 2 to 4
> weeks. I have also learned that the bubbles could have caused both iron
> and calcium to precipitate out of solution. The water tested high for
> calcium hardness and maxed the iron bacteria colony counts.
>
> I have researched well disinfection both from local experts and internet
> googling. I learned that the infection usually comes back. I figure that
> is because the methods used for domestic water wells are not adequate, or
> more accurately not enough, for geothermal open-loops. Since we have been
> pumping for a year now the bacteria has been spread through the limestone
> formation between the wells. Testing shows a 4-inch drop at one well when
> pumping the other well and discharging to ground. This is a good dis-
> connection from the point of view of geothermal heating or cooling but
> any connection at all will lead to spreading the infection. So I figure
> that the reason the infections always return may be that you have to
> disinfect the whole flow path between the wells to get all of the
> bacteria. If you just disinfect each well then as soon as you go back to
> normal operation you will suck the bacteria that were out of range of the
> chlorine into the system and you are back at square one.
>
> I am thinking of siphoning chlorine into the discharge pipe in the
> injection well for two weeks or so. This should get chlorine into the
> flow path between the wells and hopefully solve the problem once and for
> all. My concern is that I calculate the chlorine ampount as over $1500
> for just 50 to 100 ppm, more for the higher concentrations.
>
> Has anyone done any well disinfection? If so, was it successful and, if
> so, what did you do?
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