I should also note that, I have so much condenser surface area, the liquid leaving temp has a almost 0* delta to water inlet temp. Something on the order of 2 tons capacity, pushing 1/2 a ton of heat lol. Once I correct the charge, Ill recheck my vapor temperature. The last iteration of this system was 150-160*F vapor, but I could be completely mistaken. I recall seeing about 250psi vapor/discharge the other day, which relates to 146*F (at 130*ish water temp). The controller Im using also has a discharge vapor temp sensor that will shut it down if it goes beyond a set variable (Think i have it set to 180*, since thats well above expected conditions). Previously, I had also experimented with water flow rates, with surprising results. I had to dial it all the way back to about 0.4gpm before I started seeing liquid temps more than 5*F Delta. The taco pump Im using now is for sure overkill at the moment, but once I factor in 20-30ft worth of pipe and fitting restrictions, I suspect ill be down in the 1-3gpm range. As for the suggestion of using it as a heat loop, that is a great idea. The unfortunate part, my heater is in a optimal position... right in the middle of all the fixtures. Would need to run 2 loops. And with a setup like this, I would want a dedicated feed or return instead of using the cold line (because then your bleeding hot water to get cold water! lol).

Couple other specs, 80*F Ambient runs about 50-55psi low side. Highside vapor pressure varies a lot by water temp. 80* water is only some 110psi, 115* water is about 150-175, and 130-135* water is about 250*. I will make more accurate notes next time. Total system current never exceeds 3.25amps, comp only pulls about 2.5, well below the LRA 6something its rated for. Lots of overhead. The previous system had an accidental excursion, pushing the water temp all the way to 195*F ! before I found it and turned it off. Wish I could have ampped that lol. Hi-side was around 475psi (200*F), just barely under critical temp (213*F) lol.

It will not excessively heat the cold water line. If you use a reversible pump, the control circuit stops the pump as soon as it senses that the hot line has become hot. (That's how most hot water recirculating systems work.) If you just run the unit, the water coming out the bottom of the tank would be warm at most until the tank is full, at which point it should turn off as there's no point in continuing to heat a full tank.

Trouble is, this unit only adds a couple/few degree rise to the water, requiring multiple passes. Dialing back the flow would overcome this, but that sounds like quite a balancing act (perhaps only suited to a such mentioned ECM pump with temperature feedback). Not sure how that would effect my COP as well, since a depleted tank has a much lower condensing temperature, than trying to maintain 115-120*f outlet temperatures. Something to mull over, maybe up for experimentation.

Still need to decide an optimal way to tap the tank. I dont Want to tap the tank drain as thats a sure source of sediment. I could pull the water from the inlet dip tube, but there will be conductive heat gain on its way up. I considered removing the lower element and install a short dip tube to the bottom, or possibly a coax'd tube in through the drain with a slight rise to get it off the bottom. Im going to push the heated water in through a Tee with the T&P valve in the top. That will ensure that cold water cant bypass the tank through the heatpump. The budget for this unit is about at its limit for feasible returns, so the ECM pump is out of the picture for this round... (and I got the taco for 25$ lol)

I'm not quite clear on the adapting strategy of these ecm circulators. Are they constant head/constant flow, or are they temperature feedback? Building a simple pwm dc drive with temp feedback for a DC pump wouldn't be too difficult. Not sure I want to try to venture into driving a split capacitor ac motor with a scr drive. But I guess that will depend on what kind of returns I get out of multipass vs constant control output.

I think you have a very interesting water heater going on here.

Thanks for sharing all the charts and photos, very useful. I wish more people were as good at describing and documenting their efforts as you are.

I don't think we've had anyone substitute R134a for R410a before. Interesting swap and an interesting reason for doing so.

When I first looked at your machine, I had to blink a few times, I thought I was looking at an old VW engine... but then I dialed it right in!

As I recall, one of the comments was a question about why didn't you consider air conditioning? Well... isn't the output from this beast cool air? I think that just a bit of ducting and you would have killed two birds with one stone.

My question is tube length... Most of the commercial units I have examined have longer copper loops that would seem necessary, but they are that way to reduce vibration strain by spreading the strain out over a longer length. And then fair-sized chunks of rubber are put on those loops as vibration dampers. I believe that jeff5may ran into the problem of a too-short loop giving out due to vibration strain.

BTW, with reliably warm Florida air temperatures, and the modest level to which you are heating your water, I think that COP 3.5 is not too much to expect from a Heat Pump Water Heater.

If you get the urge to do another one, you might try a R22 compressor and filtered BBQ gas... I really like that combination. Your skill set is such that anything you build now will go together fast.

But, all-in-all, this is a great effort. You have tried quite a few interesting ideas... and you have them working. That's a good thing, right there. No doubt.

Congratulations!

-AC

In my hurry to reply before bed, I forgot to explain some of the bigger deciding factors of choosing r-134a. Using a constant of 54* evaporating, 150* condensing temperatures.
R-410a pressures would have been pretty extreme, 155/610psi. R-22 a bit more acceptable 90/370, but not oil compatible. R-290 was considered for some time, given 85/327, but seeing as r-134a was 51/260 which are much more manageable, and available in bulk right out of the bottle. It also works with the existing POE, and mixing a little PAG in wont hurt it as well (using automotive charging equip that has PAG in it, as well as the use of dyed oil for leak finding). I didnt bother considering R-12, since its becoming so expensive. Something you may get a kick out of, is look up the blends in Freeze-12 (a "dropin" replacement that we used. I feel very ripped off). And speaking of which, AC-Hacker, you will like this link. The epa did something useful! Composition of Refrigerant Blends | Alternatives / SNAP | US EPA And to all you r-290 supporters, you may be entertained knowing I dissected a hotel minifridge to discover the compressor was rated for r-290, r-134a, and blends (USA Model)

R22 works fine with POE oil. I believe the issue with PAG oil is its low breakdown voltage, so it's best to avoid any of it in a high voltage compressor.

Iv heard that mentioned before concerning hermetic hybrid car compressors. They strongly suggest not charging prius without purging your equip, for example. Fortunately I only have traces of pag residue from my equip. Maybe I was thinking r 22 wasn't a good mix because it's normally used with mineral, and just simplified it in my head to prevent contamination.

This list is rather dated. As you may or may not know, there are oodles of "new and natural" refrigerant blends on the market now. The OEM suppliers have now crossed the line of including "highly flammable" hydrocarbon refrigerants in the circuits of small appliances. The powers that be have been granted permission to do so below a certain mass of charge, and the mini-split and window-shaker market falls within the boundaries.

This trend has yet to penetrate the USA market, mainly confined to European and Asian markets. I believe it is just a matter of time until hydrocarbon refrigerants start appearing in refrigerators, dehumidifiers, and portable A/C units in the Americas. Your experience with the mini-fridge is living proof that at least a FEW of these units are being sold here now. But I can't help but believe that the r134 and r410 units are on borrowed time.

For some reason, most US HVAC techs freak out about the "danger" of hydrocarbon refrigerants, yet have little concern about the even more flammable Lithium batteries everywhere. I have a clue it has to do with the pinkwashing (their push for R410a as the future refrigerant) by the fluorocarbon industry...

Personally, flammability doesn't bother me. If you vac out the system, it's not flammable without air. So what might happen while brazing on the system, a surprise candle? As long as there isn't any saturated oil anyways. Anyways, topic has wandered a ways from the threads intentions.