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Old 12-29-13, 12:49 AM   #1
RB855
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Default Another DIY HP Waterheater (pics and info)

First new thread from a lurker, this is mostly a documentary to spread what I have learned. I have been slowly poking at a heat pump waterheater project for years now. Iv lost count of how many alterations have happened along the way. The quick and dirty info of its current state: 12k r-410A heatpump window unit. Swapped to r-134a for better working pressures. TXV evap control, series/parallel piped BPHE r-410a rated, small 4-8gpm taco pump, chinese heatpump waterheater controller, and some fancy pipe work.

My design goal is a outdoor remote piped unit (funny to think cold air is a byproduct!), at least a 2.0 COP, maximum water temp 130*F (115-120* desired), and totally automatic.
The current iteration is achieving about 2.5COP at 115*F water temp at 80*F ambient, moving approx 5800btu. I literally just charged it with 2lb of gas and let it run. There may be some improvement to be found in a proper subcooling adjusted charge as it felt like only the desuperheater exchanger was doing all the work.

(Please be patient with links, my server is underpowered for what I demand of it)
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I have updated my site and images have moved. Please use this link

I understand the cautions of using BPHE in a potable water circuit, but they saved a lot of space, and just one could handle the full load. They are "wired" in series on the gas side as a desuperheat/condenser, so even if one fouls, it will still operate fine. The BPHE are piped in parallel on the water circuit, counter flow of the gas circuit. I have also included a fine mesh strainer on the inlet of the unit. I had trouble deciding to stay with hot gas defrost as it does show some loss of hot gas temp when running, and I'm not sure how low an ambient this unit will still be efficient. The controller has inputs for safety disables, so I have included a high and low pressure cutout, as well as a water pressure cutout (no sense in it running if the waters off! Also prevents dry run, and shut down on plumbing failure). The filter dryer acts as a receiver for the txv in this arrangement, convenient! I decided to use the original evaporator in the recent variant for a few reasons. This gave me a 3 speed lower wattage motor, a much quieter blower, separates the condensate from the components, allows me to seal up the component side and insulate the box, instead of every component by itself. The unit is a 12k unit, and I'm only moving about 6K of heat, so the evap should be capable of lower ambient temps. It has significantly reduced unit noise, and also offers the ability to duct the cooled air. Im seeing about a 25-30*F delta coming out of the cold side on full speed.

Here is the growing gallery of photos of *invalid url*
Please excuse the lack of any naming scheme. I know what is in my head lol.

I have updated my site and images have moved. Please use this link

The previous phase of this project, you will see in the gallery I was attempting to use the old condenser as the evap. Trial and error showed some need to change the coils circuitry, which resulted in some very messy brazing, mistakes, unbalanced circuits, and other things that made things not very nice. The fan was also loud, single speed, and some 150watts by itself. It also *invalid url* drew the air around all the components[/URL], wasting significant heat. Also resulted in a lot of *invalid url* un-tamed piping jumbled into one corner [/URL]around the compressor. And further, all the components were sitting in a pan of condensate. While this arrangement worked ok, after a couple years of fooling with it, I decided to go the route of the original evap. I work on PTAC and windowshakers these days, so getting another of the same model was a matter of going out back to the scrap pile lol. The first version is a mess of a learning curve and years of fiddling. The newest version was put together in 2 nights, and tested in an afternoon. Yay experience!

I will update this thread as things advance, and feel free to ask anything you may have questions about. The spreadsheet pictured is just something I slapped together, ment for limited data calcs. But if there is interest, Ill buff it up and post a link. You feed it time, temp, amps, volts, and water capacity, it does the rest. Iv spent enough time fooling with this thing to learn a thing or two. Just don't expect an expert reply lol.


Last edited by RB855; 01-19-15 at 11:49 PM..
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