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Old 10-07-14, 10:31 AM   #11
AC_Hacker
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vwhead77,

I admire your project, and the ingenuity with which you are solving the problems involved.

Great photos, by the way. I wish everyone was as generous with their photos as you are with yours.

It will be interesting to see how your approach compares with other approaches, where the condenser HX tubes are actually placed inside of the water heater.

Did you mention if you will be using a small circulation pump in your approach? If you do plan on having a pump, your approach could have better heat transfer because of improved fluid flow (maybe even turbulent) around the heat transfer surface. However, since your HX will be external to the water that is being heated, you will have heat loss. Insulation of your HX will reduce that.

The DIY heat pump water heaters that have internal coils, don't have the HX heat loss issue, on the other hand, they are relying on the slow movement of thermal water currents in the water tank to help with heat transfer. A pump that forces circulation could make a big, advantageous difference.

In any case, you will eventually need a Heat Pump Controller for your project...

Quote:
The Homemade Heat Pump concept has had some notable success.

However, one link in the chain that is missing is an open-source general-purpose heat pump controller.

If such a controller existed, it could increase the success of people who undertake a homemade heat pump project.
It would be most excellent for you if the rest of us could complete and contribute at least a rudimentary, open source, controller for your project. The General Purpose Controller thread has made some progress, but as yet, we don't have anything, even rudimentary, that is tested that we could offer you.

Good luck,

-AC

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Old 10-17-14, 03:50 PM   #12
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My Heat Pump/ compressor is activated via 24V relay to (disconnected) Circ Pump at 115V. The Hot Water Tank activates its own circ pump. I may use an aquastat to be more precise.
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Old 10-17-14, 04:20 PM   #13
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Cool Update :

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This is the prototype and what I ended up with. Although I did finally decide to thread the 'insert' fittings, I messed up and dropped the end cap trying to glue it all together and caused a leak - the only solution I can think of is to have the seams all 'plastic welded' and / or (really) make it entirely out of copper - which I am in the process of doing. I'll post the next idea in a different thread - using the same fittings I used for this project.
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Old 10-17-14, 05:29 PM   #14
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OK, a couple of issues. I am assuming this is a thermosyphon system so all my comments are based on this assumption.

First, thermosyphon systems work when the the fluid path is like a circle with the heat source (HX) at about 5 o'clock and the tank is between 7 and 11.

The liquid must be able rise in the HX to the top of the tank and draw the cold from the bottom of the tank. Correct me if I am wrong but you seem to have a tank with both the cold and hot at the top. This won't work (unless it is a pumped system).

Second, the HX must be placed at the bottom of the tank. If it is not, it will stop thermosyphoning when the HX temp is equal to the tank temp AT THE LEVEL OF THE HX. If it is high, it will not heat the bottom of the tank.

If it is a pumped system, you will have to have a very slow pump to equal the heat produced by the system. It is hard to control.
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Old 10-17-14, 09:54 PM   #15
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Definitely a good first time effort. Your concept is not wrong, but there is a lot of room for improvement.

Look around for the best way to plumb the tank. It has been proven that plumbing in the cold water inlet at the drain fitting on the bottom saves energy over the stock configuration. It is also the best way to rig up a thermosiphon. Like Mike said, hot water rises and cool water sinks. Let mother nature be your pump.

Don't get discouraged, this is how great things get done in the way of the world. Any awesome creation goes through a process of evolution before it is finished. Keep on doing what you're doing; before you know it the thing will be done.
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Old 10-18-14, 05:09 AM   #16
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I agree with Bernie. As currently built, only a small fraction (10%?) of the water will flow over the copper coil. But a simple solution exists. Just block off the interior central hole with a PVC plug made of tubing and end caps. This will force the water to flow over the coil and will result in much better heat transfer.

I am concerned about the material used to plug the holes where the copper tubing comes out. Time will tell.

Great start however!


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Old 10-18-14, 08:48 AM   #17
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Question; Since I have had some issues with the plastic/copper seal, I was thinking of a different design. Tempted to wrap 1/4" tubing tightly around the OUTSIDE of a 2' length of 2 5/8" Copper. The 1/4" would be my heat pump source and the water would running through the 2 5/8" (metered by ball valves) IF I took that configuration and placed inside a piece of 4" PVC then filled it all with foam insulation, then piped it inline with the Passive Water Heater - what do you think my end result would be? Thanks in advance - advice appreciated
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Old 10-18-14, 10:23 AM   #18
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Having the coil inside the copper tube is way better than outside. It is a function of surface area needed for heat exchange. If you can braze with silfos, you can drill the holes just big enough for the 1/4" tube and seal it that way but you will need a powerful torch to get a big piece of pipe hot enough.

Then just put reducers on the copper on each end. You had the right idea the first time.
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Old 10-18-14, 04:32 PM   #19
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I can definitely make this particular design out of all copper but I'm looking at an investment of almost 150.00 and that is just a bit much at this point for an 'experiment' I like the helpful hints like capping the center of the HP coil to force the water to wrap the coil (rather than shooting right up the middle) I believe this is something I would like to pursue but want ot make sure my money is spent well. I am offering this next design - as I have bits an pieces already lying around.
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Old 10-18-14, 04:42 PM   #20
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That will not help in this situation. Remember that the system will only move the water when it gets hot enough to rise. It needs the time to heat up so it becomes more buoyant. That is what will start the circulation, and the hotter the water delivered to the top of the tank the faster the flow. It is a self limiting system. Your coil is fine. It also needs to have very little resistance from bottom to top so a center blockage may be counter productive.

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