Homemade Heat Pump Water Heater (R290)

[AC_Hacker]

Originally Posted by Ron342

So I will put a receiver before the cap tube (and a filter/dryer too ? and where?)

In my opinion, you should just try it out as is. I recently had lunch with a retired refrigeration tech, with 40 years experience on all systems including cascade systems for cryogenic applications, who told me that a receiver was not required on a cap tube system. I think you should keep it as simple as possible, try to get it working and introduce improvements as you go.

Originally Posted by Ron342

Use R290 instead of R22 when I charge it up. Do I do anything about oil?

R290 is not exactly the same, but very similar to R22 in terms of output and in terms of the metering device and in terms of oil.

Originally Posted by Ron342

And I charge slowly looking for frost at where the cap tube enters the evap (will the frost remain as it reaches full charge?)

You should look for frost to form right at the end of the cap tube, where it enters the evaporator. For now, the point at which frost is forming is full charge.

Originally Posted by Ron342

...and for the right temp pressure (120 - 140f) at the high side just before entering the condenser?

Since this is a hack-job (in the most favorable sence of the word), and not a rigorously designed system, you'll just have to see what you get.

For now, let frost be your guide.

Originally Posted by Ron342

Thanks so much guys - I hope each of you realizes that this is akin to voodoo to the rest of us!

Well, it may be voodoo to you, but remember that you are messing with dangerous extremely flammable gas, and if you introduce R290 into a system that contains air, you have a bomb, so vacuum well before gassing. Also remember that R290 is heavier than air, and will collect in low places. Only work outside or in an open garage with forced fresh air circulating.

May the blessed saint of refrigeration, Saint Frosty, be there to guide you to success.

-AC

[randen]

Ron342

I had found that there is the sweet spot (quantity of R290) in the system. As you add the refrigerant the pressure-vapour mechanism begins to function. Along with this increase in the volume of R290 the resultant current draw increases (amperes increase).

Remember your goal. Harvest the most amount of heat for the least amount of power.

Monitoring three items Current draw, Condenser temp, Evaporator return temp. I was able to have some success. It took some time to tune.

The condenser temp increase is the one we want with a low current draw and the evaporator working efficiently. Its a balancing act. You may want a little frost on the evaporator tube were the capillary tube enters. By the time this R290 enter the evaporator it is absorbing heat as it flashes from a liquid to gas. If the gas can return to the compressor at near ambient temp the refrigerant has absorbed a quantity of heat. Remember you want to heat the water not air-condition the room.

I had found the following results: (your mileage may vary)

Condenser temp from the compressor 150-160 Deg F
Evaporator temp returning to compressor 50-65 Deg.F
Current draw 2.2-2.5 amp.

For my system I had actually overcharged the thing and had to reduce the charge slowly monitoring the two temperatures and current. (tip the use of a Kill-O-watt meter is a most valuable tool) The reduction of charge was very linear to the digital display of wattage on the Kill-o-watt meter. The clamp type amp-meter jumps around a bit.

My hacked system is very simple with a capillary tube and no TXV. or filter/dryer or liquid receiver or over/under pressure switches. (compressor has built in over-temp safety switch) Wall receptcal has 15amp panel breaker. Remember some of the best machines are the simplest.

End result total run wattage via Kill-o-watt 375 watts including evaporator fan. The daily use of hot water by two retirees is about 4Kwh. I believe this is very close performance to what is expected by the Geo-Spring GE unit.

Best of luck

Randen

[jeff5may]

No worries here. If you're using a standard a/c compressor, they have a mini-suction-accumulator built into the muffler on the suction line. If the evaporator burps, the foamy froth goes into the bottom section of the muffler, rather than being ingested by the compressor. So unless the evaporator is vomiting, you should be OK.

Another thing to remember is that the regular, blow torch or bbq propane has "stink oil" mixed in (it is somewhat soluble/miscible with propane) the bottle. So if you don't want lots of oil, charge slowly with the bottle upright. Oil is heavier than propane, so it will sink to the bottom. If you shake the bottle, guess what happens? Lots of oil leaves with the gas.

[davismltc]

Wow, last post to this thread was 3 years ago! Where are all the hackers? On to bigger and better I suppose...

I'm new to the ecorenovator site and as an A7 owner, I thought I might share my experiences. I bought an A7 HWHP (new) off ebay and installed it on top of my electric HWH in my basement. A friend was helping me install it and through miscommunication the copper lines being fed into the tank weren't fed into the brass fitting correctly and the lines had to be removed. Removing the lines from the tank was awkward at best. Once the error was corrected, the rest of the installation went smoothly.

The unit worked great for a little over a year, and the HWH tank failed. I assumed the failure was caused by us possibly scratching the glass lining of the steel tank when we attempted to remove the copper lines during the initial installation error. The sacrificial zinc was still in pretty good shape.

I purchased a new electric HWH and was able to install the A7 without any problem. This time I was very careful about feeding the copper lines into the tank. A little over a year later the second tank failed, and I must say the sacrificial zinc had been doing its job and there was plenty of zinc still left.

I was about to give up on the whole HPWH when I got an idea on how to stop the corrosion problem. I decided to route the 1/4" heating lines into some 1" cpvc and create a heating 'U' loop instead of placing them inside the tank. Ebay provided me with a used brass Taco circulation pump. So now my (insulated) heating loop is outside my hot water tank and isolated from the glass lined steel tank. I use a digital thermostat (probe is snuggled against the hot water tank) to turn the heat pump and the Taco circulation pump on/off to maintain the desired temperature in the tank. My heating loop is insulated and strapped to the ceiling of my basement. I'm now going on year three without a tank failure.

As I side note, I rigged up some CPVC fittings so water for my heating 'U' loop is pulled and returned from the same fitting and it is installed where the tank drain was previously. Water is now pulled from the very bottom of the tank and heated water is returned there as well. I wanted to be sure I didn't induce any heat siphoning, and my 240v heating elements remain in the glass lined tank for backup. All I have to do is flip the breaker on...which I haven't had to do since the unit was installed.

I'm just wondering if anyone else has experienced problems with galvanic corrosion because of all the copper tubing introduced into the glass lined tank? I previously had zero problems with my power hungry resistance hot water heaters.

Thanks to all for their contributions....this site ROCKS!!

[Xringer]

My A7 AirTap has been running almost 5 years now. But, my tank is also heated by some solar PV, which is a nice assist.

Had some problems with frost and with the iron nipple on the cold water input.
We also lost one of the 200W panels. Only 3 left, 600w max.
But, the system is still providing enough hot water for two old folks..
It helps keep the basement dry too.

Now that it's still too cold to use the big dehumidifier, we have to rely on the A7.

I was gifted an old broken A7, so I might have to try your out-board HX idea..

Cheers,
Rich

[davismltc]

Xringer-

Getting the 1/4" lines back out of the tank was a bit challenging. If your unit is working fine, I'm not sure I'd convert it to an external loop unless I had a problem. (aka...If it ain't broke, don't fix it)

The external loop does work great for me, and my old dumb HWH is now high tech digital. LOL

Just an FYI, the 1/4" lines on the A7 are double walled...don't ask how I know

[Xringer]

The 'spare parts' A7 that I got from a forum buddy, does not have the external loop.
So, I will need to add on some connectors before it can be hooked up to a remote HX.

I saw those cut-off 1/4" lines, but didn't I guess it didn't click they were double walled.
I assume that was to get the two-walls of isolation to meet 'code' in some locales.
My junk pile contains a couple of Taco circulation pumps.. And, I have a brand new SS HX.

But, right now, my old A7 is still running fine.. It's been running a lot this year,
because of all the cover-cast and cloudy days we've had..
Maybe I'll be needing a new heat pump soon, and I would like to use this HX..

Cheers,
Rich

[Themitchells04]

i was also gifted a broken a7 recently im looking to do the same outside hx. did you have any luck on your rebuild xringer also what refrigerant did you use?

[Xringer]

Originally Posted by Themitchells04

i was also gifted a broken a7 recently im looking to do the same outside hx. did you have any luck on your rebuild xringer also what refrigerant did you use?

My A7 is still making hot water. I guess having the PV panels is helping to extend it's life span.
My free A7 is being stored as a source for spare parts. I also have the spare thermostat control unit NIB.. It looks like a bear to change out.

I was thinking of adding on an HX and preheat my oil burner boiler, but it has too much heat loss.
If I did decide to pre-heat that old boiler, I would install some standard 13 ohm hotwater tank heaters and hook them up to some PV panels..
No moving parts might last a long time..