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Old 05-26-13, 09:25 PM   #1
keachier
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After reading heatpump manifesto,and searching everywhere,the best thing to do is probably using propane gas in buried copper tube, in my place five foot deep and you have water. Can we install a hacked heatpump outside in a small cabin to avoid propane in the house,I need approx 5 ton heating system base on electricity bill. This site is fantastic.

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Old 05-27-13, 08:11 AM   #2
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5T for a 'small cabin' ? Even in lower lattitudes of Quebec, it would appear that a few $$ spent on insulation would be a better first investement in effort.

Given the cost of Cu these days, you may want to do a trade on building a tube in tube evaporator (about 70 ft of 3/4" Cu inside 1-1/2 ply for 5T) to use water from a poly loop to your HP source. Unless you are on a hillside and the ground water is flowing, you will still need a few hundred (or thousand) of feet of buried line for 5T.

If water is only 5 ft deep, how about a pump and dump or 2 shallow wells on opposite corneres of your property (if only a small parcel) for a pump and return system (using the same type tube in tube DIY evaporator)
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Old 05-27-13, 09:57 AM   #3
keachier
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I have and old water well at the corner of my house that can be used to pump water,how much flow is needed,and how big the exanger will need to be?
René,
Thanks to you .This is a formidable place to exchange.
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Old 05-27-13, 01:10 PM   #4
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If you can pump 8 gallons per minute out of that well, you can do a 5T system if the ground water is 50F (9C) or higher. All you need to do then is find a place to dump it (mine goes back into a pond, creek works well too) or dig another well to dump it in*. 1 pound water = 1 BTU deg F, etc. for the calculations on needed flow and temp drops, etc.....

My own system cranks out 59,000 BTU hr on a 9 gpm flow. COP = 5.6. I use 75 feet of 3/4" Cu pipe inside 1-1/4" pvc pipe for the evaporator. TXV with 7 deg F superheat setting feeds the evaporator. Condensor is an reclaimed 7-1/2T carrier AC coil.

Be sure you build yourself a cutoff switch that will shut down if evap outlet water temp hits freezing. Before I had my cutoff switch wired in (temp sensitive resistors and a LM139 comparator and relay) my valve failed closed and froze the whole evap and split a bunch of the pvc pipe.

* There are MANY different local rules on being able to do (or not do) this, best to check it out but keep your mouth shut at the same time if you know what I mean<G> Here, we need water rights, etc to withdraw ground water even though it is pumped back in, but that is the US western lands.
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Old 05-27-13, 06:24 PM   #5
keachier
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I had check for a pump able to flow 8 gal a min and it's not that big.Suppose the pump is controlled with a thermostat in the water of the well and exchange water as needed,prior to ice-up .I will try to post you some pics .
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Old 05-27-13, 06:27 PM   #6
keachier
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You exchange water to gas in the plastic pipe,can it be copper pipe running gas direct in the well.
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Old 05-28-13, 08:44 PM   #7
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If you pump lots of warm-ish well water through a pipe to your heat exchanger, you are constantly exposing your heat exchanger to fresh warm water. Not the same as hanging your heat exchanger down a borehole! Unless your well opens up into a cavern or underground river, you will quickly draw all the available heat from the well due to stagnation. After that, the borehole will freeze, with disastrous consequences. The ground is not a good conductor of heat, many orders of magnitude less than flowing water.

Running the chilled water back down the well you draw from will have the same effect: the ground surrounding the loop will quickly cool off and your heat extraction will quickly diminish. Since no fresh warm water will be extracted, your underground heat capacity will be limited by the volume of recirculated water. This method in particular is highly frowned upon by the government (what if something gets in the water? it would contaminate the aquifer.) in any and all locations on Earth. Pump and dump systems are a gray topic in general, but would likely be accepted if profesionally installed.

Consider this from an economic perspective as well. The least expensive option is the one mejunkhound described. Let's just say your well is right under your heat pump. You may be able to plumb the refrigerant line with only 100 feet of 3/4 inch tubing, building a coaxial exchanger with an inner copper tube only. The copper tubing will cost around $200 US, the PVC pipe and fittings will likely be under $50. A manufactured coaxial exchanger of comparable capacity will cost over $1000, and a plate heat exchanger will likely cost upwards of $2000.

Last edited by jeff5may; 05-28-13 at 08:48 PM..
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Old 05-28-13, 11:05 PM   #8
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Fifty feet distance of two wells enough or will need to scale down the projects.
Thanks for your precious help.

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