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Old 09-06-2008, 09:30 AM   #1
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Geothermal Project


Hello.
I am looking a building a geothermal system from scratch and hopefully very cheap. I am fairly experienced with automotive ac. I built a large unit for a meat cooler with recycled auto parts. I farm and don't have a lot of money to throw around and do love learning and tinkering.
Right now I have a 10 year old 32000 btu window ac unit that was used very little. It is charged with r22 and has never been opened. It is still works very well. I was thinking of pulling the compressor (it will be sucked down first) and building a geothermal system. I use large amounts of water feeding livestock. I am looking at purchasing a couple of brazed plate heat exchangers and tapping into this water supply as it leaves the well before it is dumped to the livestock. The entire geothermal pump will be water to refrigerant and I will not need a reversing valve. I will simply draw hot or cold water off the appropriate side as needed for heating or cooling and circulate it through my unused floor heat and hydronic rad in my furnace. It will also supply my hot water. I know i will need to purchase a txv, heat exchangers, and filters. I normally work with automotive stuff and use redtek12a but I have a friend with r22 that can charge the system for me.

What do you think of my project and what do you think I should purchase? Thanks.





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Old 09-06-2008, 12:06 PM   #2
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Geothermal Project


When you get into refrigeration lines, remember that you're dealing with fairly high pressures and temperatures. As long as the heat exchanger can handle the pressure and temperature, and is COMPLETELY clean, your system will work well.

A few questions; 1) Are you using the heat exchanger as the only condenser, or will it be between the compressor and an air-over condenser? If it's the only one, you'll need some sort of electrical control scheme to prevent the compressor from running if there's no water flow.

2) What is the distance from the compressor to the heat exchanger, and from the heat exchanger to the expansion valve? Keep it as short as possible.

3) Since this is a non-standard installation, refrigerant charge level will be difficult to calculate. I'd suggest installing a sight glass somewhere near the expansion valve, and use this to determine the amount of refrigerant charge.

When I built my house, I did something somewhat similar. I have propane furnaces (2) with remote A/C units. I installed a hot water pre-heater (simply a 50 gallon electric water heater that's not powered) that feeds the regular water heater. I ran 1/2" copper from the top and bottom of this pre-heater out to the A/C units. There's a circ. pump that comes on anytime either unit is running. My heat exchanger is 1/2" copper tubing (type K) that is run along the compressor discharge line with heat-transfer tape. The net result is that the pre-heat tank is usually between 70 and 100 degrees during the summer. It costs a lot less to heat 80 degree water than 50 degree.

Depending on what you want it to do, I think your system will work pretty well.

Rob

P.S. My system is 11 years old, not the slightest problem so far.

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Old 09-06-2008, 03:51 PM   #3
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Most brazed plate heat exchangers are built to handle refrigeration process. I intend to use them to process the condenser heat and the evaporator chill. I will have all kinds of safeties built in to stop overheats and freeze ups. The electrical part is not the hard part for me. I just want to make sure I select the best and properly sized components to make this the most efficient as possible. I will also probably incorperate holding tanks as you have done. The water temp is about 10C .What size of the brazed plate heat exchangers do you think I should use? Would a thermal expansion valve sized for 3 t be right with these operating temps? What should I use for accumulator and filter?
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Old 09-07-2008, 06:19 PM   #4
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love your inovation but , first problem a txv need a ceritan amount of head pressure to operate properly ( usualy requires 60 degree ambiant) unless your water temp is that you will have problems . geothermal units usualy operate with the old school refrigeration metering device with a float acting on a metering device inside the accumultor. second is sizing for heat while 32000 may be your cooling btu output it wont be your heating . also the btu per liniar foot of baseboard will change dramaticly because the water temp will be closer to warm water radiant then hot water base board , if the house was designed for warm radiant its a muet issue . just so I clear you are talking about a simple pump and dump system not closed loop. if so the water purity is important and be prepared to stay on top of those heat exchangers
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Old 09-07-2008, 07:15 PM   #5
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I guess I got more research to do then. I see most new geothermal units are using txv. How are they accomplishing this?
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Old 09-08-2008, 04:43 PM   #6
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Geothermal Project


Quote:
Originally Posted by boozeboy View Post
I guess I got more research to do then. I see most new geothermal units are using txv. How are they accomplishing this?
there are txv that operate down to 55 ambiant but these are tough to get after market. I dont want to deture you from trying this out . but I dont want this to be your sole source of heat
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Old 09-08-2008, 04:45 PM   #7
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most geo system's end up bare min 25k for good reason
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Old 09-30-2008, 12:57 PM   #8
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Geothermal Project


Dig a large trench to about 6 feet deep. Put in 1000 feet (or more if you have a large home in a hot climate) of 3/8 pex. Get a small pump to circulate the water and use that for cooling. Very cheap and the pump will require about 60 watts when it is on. No compressing, no high pressures, no complicated wiring.

You can have an old car radiator and a box fan behind it or go for the sophisticated look and use an old A coil out of central air unit and a squirrel cage fan. Or if you have central heating already then put the A coil in the duct and use that.

If you really want to get fancy hook a thermostat to the pump and it will turn on by itself.

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