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Old 01-29-2009, 12:27 PM   #1
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thermostat controlled Solenoid valve ?


I need to come up with a way to purge off water from my Geothermal heating well when the water gets too cold... so when it hits like 40 degree's I need to purge off like 1000 gal of water for it to boost up the temp to like 42 so it doesnt go in to Aux heat mode.

So I kinda need something to sense the incoming water is at 40 and then
open up the valve that purges off the water.. then when it gets back to
another temp.. like 42 it then closes...

how hard is it to build something to do that ? anyone got any ideas ? or
other suggestions ?

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Old 01-29-2009, 01:48 PM   #2
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thermostat controlled Solenoid valve ?


Is pumping off 1000 gallons of water really cheaper than heating it 2 degrees? I'm not sure I understand the concept here. Why does pumping heat it up?

Could you use a recirculating loop instead?

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Old 01-29-2009, 02:21 PM   #3
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thermostat controlled Solenoid valve ?


How about this?
http://www.honeywell.be/DocsAdobePDF.../L641AB_pd.pdf
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Old 01-29-2009, 02:55 PM   #4
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just to answer Gigs... Geothermal heat pumps use the water heat to heat the home.. they work great if the water stays above 40.. I have a pump and dump well that is not deep enough.. so during a long cold snap the well temp
will go down and down.. if it gets to 40 the water after it leaves the unit will be around 35.. which is close to freezing.. and then the unit will shut off and go all electric.. the well will return to 45 in like 6 hours.. but if you start to purge off the returning water to somewhere else than the well, the water from the surrounding aquifer will flow into the well and start raising the water temp in the well.. making my unit run normal.
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Old 01-29-2009, 03:00 PM   #5
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thermostat controlled Solenoid valve ?


I guess that thermostat may work.. I guess the Frost protection one..

now I would just need to understand all those specs.. fun fun..
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Old 01-29-2009, 03:33 PM   #6
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Alright I think I get it now, normally it recirculates but when it gets too cold you are saturating the well, so purging the cold water brings in new warmer ground water.

Just brainstorming, it's probably possible to use something in your existing system to trigger it. You could possibly make a small current transformer to sense when the aux coils come on and start purging then. It wouldn't require any permanent modifications to the existing system since it's just coiled around the existing wire.
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Old 01-29-2009, 05:35 PM   #7
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I need to kick it off before then.. I think.. once it goes into "trouble mode" the only way get it out is to reset from the thermostat. So I want
to stay one step ahead of the situation.. I assume it shuts off the pump when it hits like 38.. so I want to start the purge before it even gets to
that point...
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Old 01-30-2009, 12:04 AM   #8
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thermostat controlled Solenoid valve ?


The differential temperature of this thermostat looks like 10 degrees. It says 10 K, but I'd bet it means 10 C. It's not adjustable.

What this means is when the thermostat opens the solenoid valve, it will keep it open until the temperature rises 10 C.

Keep in mind that this thermostat is degrees C, not F. The lowest setting is 10 C (50 F) on, and 20 C (68 F) off. This might be too high for your application.

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Old 01-30-2009, 01:19 AM   #9
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Quote:
Originally Posted by ksauerwald View Post
I need to kick it off before then.. I think.. once it goes into "trouble mode" the only way get it out is to reset from the thermostat. So I want
to stay one step ahead of the situation.. I assume it shuts off the pump when it hits like 38.. so I want to start the purge before it even gets to
that point...
How much of this do you want to build yourself? I can imagine myself making something with a custom PCB and some thermocouples and maybe an AVR microcontroller, but I'm a nerd like that.
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Old 01-30-2009, 08:39 AM   #10
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thermostat controlled Solenoid valve ?


I have no clue how to build it.. I was hoping for a product that kinda does it
already and I would just need to attach the thermostat to the solenoid valve power it and be on my way... but sounds like it will need to be custom.. then that would be out of my league ..

so Gigs you build these things... gimme a price...
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Old 01-30-2009, 11:13 AM   #11
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All electronic temperature controllers will accept two types of inputs and will output (relay) the voltage required to turn on or shut off any pump that is controlled by a contactor. It can also be used to operate a solenoid valve. This is accomplished by using "for example" a thermocouple to sense water temp and one or two output relays in the instrument to control the motor starter or solenoid.

Try www.automationdirect.com and search (temperature controllers).

You will need a sensor too. The controller does not come with one. If you use an RTD, you can use THWN to extend the leads to the length required. The controller can be programmed to consider and correct the resistance value of the additional wire required to extend the sensors length.
It's a snap to set up. You will need an enclosure for the instrument.

Last edited by J. V.; 01-30-2009 at 11:17 AM.
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Old 01-30-2009, 12:57 PM   #12
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thermostat controlled Solenoid valve ?


Quote:
Originally Posted by ksauerwald View Post
40 degree's I need to purge off like 1000 gal of water for it to boost up the temp to like 42 so it doesnt go in to Aux heat mode.
A thermistor driving an LM339 comparator with "2 degrees" of hysteresis, powered by a wall xformer, driving a relay which drives the valve. One adjustment for the setpoint, maybe another for hysteresis.
The guys on electronic forums already have the schematics; if not we can do a custom job for your case.
A long day assembling, testing and debugging (you'll need a VOM) plus $20 in parts should do it. For UL approval, add another five kilobucks. . .
What AC or DC voltage and current does the valve need?

Last edited by Yoyizit; 01-30-2009 at 01:30 PM.
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Old 01-30-2009, 02:58 PM   #13
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thermostat controlled Solenoid valve ?


I would love to try to built this myself.. but I just dont know if I have the know how.. I know basic home wiring.. but nothing like this stuff.. wish I did know how to do it..

so if I got someone to build this from scratch.. how much am I talking to get this built.. $$$ ?

as far as spec's..

would like to be able to change the temp controls on open temp and close temp.. around the 40 degree range.. power.. thats up in the air.. I can power
it however.. but it would be seperate power.. not off my hvac... and the solenoid valve is not purchased.. I was just thinking basic plastic. 1 inch that
I would pipe up for a hose fitting..
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Old 01-30-2009, 03:31 PM   #14
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thermostat controlled Solenoid valve ?


Here's a simple thermistor circuit. It drives a relay. With the thermistor used, it has a resistance value of 15 kOhms at 25 degrees C, and 45 kOhms at 0 C. The op-amp shown is a very reliable and very available 741. The transistor shown can be be almost any NPN type that can handle the load of the relay.

The 270 kOhm resistor provides the hysteresis to keep the circuit from rapidly switching. The 100 kOhm pot is used to adjust the temp the switch activates at.
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Old 01-30-2009, 08:44 PM   #15
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Quote:
Originally Posted by InPhase277 View Post
Here's a simple thermistor circuit. It drives a relay. With the thermistor used, it has a resistance value of 15 kOhms at 25 degrees C, and 45 kOhms at 0 C. The op-amp shown is a very reliable and very available 741. The transistor shown can be be almost any NPN type that can handle the load of the relay.

The 270 kOhm resistor provides the hysteresis to keep the circuit from rapidly switching.
for slowly changing inputs

The 100 kOhm pot is used to adjust the temp the switch activates at.
Yes.

I've used opamps as comparators; the output slew rate is not as high but you don't need it here. The 1N400x diode across the relay coil reacts too slowly; it should be a switching type but everyone uses them anyway.
As shown the thermistor needs to change 2k for 2 degrees with the 200 millivolts of hysteresis this circuit gives. Pick a cheap thermistor and the rest of the circuit can be mod'ed to suit the OPs specs.

That 741 just will not go away! It's a dinosaur.

We can tweak this thing to do exactly what the OP wants.
One thing: in this circuit the power supply voltage is also used as a reference voltage, so if you want 1% precision in the setpoint you need to keep this voltage stable.
To relax this constraint you can use REF01 or some of National Semi's voltage reference chips. Add 50 to the price (and $6 if you want a box around this thing).
You also need a single point ground; if the relay current flows through the same wires as the detect circuitry this thing can oscillate as fast as the relay armature can move. This subtle point only shows up on wiring diagrams, not schematics.


Last edited by Yoyizit; 01-30-2009 at 09:50 PM.
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