I would like to install an open loop geothermal system where I use
domestic well water run through a heat exchanger before discharging into a
small "turtle" pond.
I need recommendations for the heat exchange unit (water to water) and a
source for purchase.
The building is essentially an insulated pole shed with 2x6 construction,
fiberglass batts for insulation, new Pella Energy Star windows and doors.
I will be installing radiant floor heat.
What I'd like to do is use the well water, run it through the exchanger
which in turn would transfer the water to the hyrdonic floor system.
It would be a plus to be able to heat domestic water as well. Right now
I have a 40-gal electric water heater.
This is open source, you can't treat the water and dump it into a pond, you
will have to chemically clean it when efficiencies decrease.
Also, sealed systems only need treatments if high phosphates, sulphur, and
excessively high/low ph is present. If you have sulphur it's best just to
bring the water in for the closed/sealed side that doesn't have it. Sulphur
and PH are really bad when it comes to brass and HX's. Very soft water isn't
that great either.
Franz you should investigate little more before you commit your
self to that project, I am not in that type of business and I do not
know you location however your expanse vs. benefits may be
some what small and perhaps negative, if you are going to use
this for heating as you say water coming out of ground will be
still cold and you will need to add heat to it so your expense
may out weigh the benefits.
the fluid is only used as a heat transfer fluid for the heat pump. You
don't actually use the loop water as the radiant loop fluid. In using it
for DHW, you will need to use an additional source to heat the water in
addition to the Desuperheater, especially in the winter.
The benefit to using the desuperheater is that it is free heat. You can
temper your potable water so that you are now only raising the temp 30 or 40
degrees rather than 80-100 degrees, depending on the time of year.
The hottest you are going to get your water is about 110 degrees, great for
radiant floor heat not so great for a shower.
Most Geo manufacturers make a Water to Water unit. You should first check
with your municipality will allow you to use an open loop. You should then
get your groundwater checked for compatability with the GEO unit. It is
more efficient to use the groundwater over a closed loop, but coil
maintenance will be more expensive.
In addition to having a borehole drilled you still have to have a well pump
and associated tanks and pumps inside.
Most manufacturers offer water to water heatpumps.
Make sure you get one with the Cupronickel Coaxial heat exchanger...
In addition you'll need a min. 60 mesh sand screen on the well water coming
into the unit, some add filters prior to the HP as well, I've seen water
softeners as well in areas with nasty water, but the cost of salt etc... in
that system would make me rethink the whole idea.
You'll want a 35-40dF freezestat to avoid freeze up... especially if you
should decide to use a brazed plate heat exchanger unit rather than the
coaxial tube type.
You'll also need a buffer tank equal to or larger than 1 Gallon per 1000
Btuh of the heatpumps size.
The heat pumps job will be to keep the tank at a desired temp. Most
geothermal units can maintain 100-110dF temps easily, some will state 120dF,
but the rating parameters used are usually suspect (for those of us in -20dF
The Buffer tank will prevent shortcycling the HP, allowing the unit to
operate for longer time spans & run in it's most efficient mode. The control
should allow for a few dF "anticipator" allowing the tank to drop 3-5 F
prior to starting the HP.
Avoid using waterheaters as buffer tanks unless you find one with 1" or
larger pipe connections.
I'd avoid a desuperheater in this type of application as your using the HP
Unless your chilling water in the summer & running it through a fan coil for
A/C, the "free heat" claims of desuperheaters is false as it'll just extend
run time to preheat your domestic hot water.
If your cooling water, then the HP's rejected heat can preheat you DHW,
otherwise it's a waste of $$.
Also, if desuperheating, check the added cost, & compare the warranties,
some are different if desuperheaters are added, due to added circuits &
reversing valves, controls, etc...
If you are using the HP to chill water, make sure you get a fully foamed
buffer tank, as condensation will occur on fiberglass insulated tanks &
corrosion will shorten tank life.
GPM through the unit needs to be looked at as well.
If your ground water is cold, 47dF or less, then increasing the flow will be
required to allow a 5-10dF temp drop rather than the 15F that is commonly
rated. Verify the TD with the manufacturers engineering data.
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