11,000 BTU DX GEO Heating

[Ron342]

Just finished reading this thread and wanted to say thanks and merry xmas to Jeff for his incredible help & patience to all of us who struggle with understanding what is really happening inside these dark copper tubes and also the same to Memphis for his willingness to share his efforts and what he's tried and learned.
I know this has to take a lot of time you could be devoting to making money or chasing whatever else floats your boat but the time and effort you give is such a help and encouragement to so many others.
All that rump rubbing aside any updates??

[MEMPHIS91]

Ron, thank you. Yes I am still looking for a slightly larger compressor. But seeing as I can't find one right now, I am going to go ahead and braze on the txv I have. I was kinda worried that I would have to much pressure drop in the DX loop field for an internal equalized, but after running some numbers it looks like I'll be fine.

[jeff5may]

Originally Posted by MEMPHIS91

Ron, thank you. Yes I am still looking for a slightly larger compressor. But seeing as I can't find one right now, I am going to go ahead and braze on the txv I have. I was kinda worried that I would have to much pressure drop in the DX loop field for an internal equalized, but after running some numbers it looks like I'll be fine.

Check out the attached document. For an external vs internal equalized valve, as long as you don't have a huge pressure drop, the extra superheat is not that significant. Unless you have a double digit psi drop, for R-22 or 290 the added superheat (aka loss of effective surface area) is going to be less than 7 degF. Figure 4 and figure 5 illustrate the difference. If you have a straight-through evaporator that's not seriously clogged or undersized, at the flow rates we use in nearly all of the builds on this forum, there will be pressure drops well below the example. For a 1 ton unit, a 5% drop in capacity is like 180 Watts on the refrigerant loop and like 50 Watts on the compressor side. The somewhat mismatched txv still beats the holy moly out of a perfectly matched cap tube in real life.

Now if we were talking about a 40 or 50 ton machine, the loss of capacity would make a difference. 5 or 10 percent of half a million BTU per hour is a lot of lost capacity. In large systems like that, cap tubes are not even considered due to the economics of scale. These systems are often regulated to target superheat values within a few inches of water column to save operating dollars. FWIW, there are 28 inches of w.c. in 1 PSI. The powers that be have moved on in the direction of electronic valves and programmable controllers to tackle this realm (think Tyson foods, Sysco, Smithfield, etc.) since every penny they can save effects their profit margins.

[MEMPHIS91]

Jeff, yes I looked over that article. I had in on my phone already for the spare time reading. I think I have 20 more PDFs left to read but anyway, I have been studying hard and understand a lot more now. I posted a few articles in the pond geothermal build as well.
Thanks for putting all those facts into numbers so I could really understand how little it matters on a straight evap.

[jeff5may]

This rig you have going will be an awesome test bed to aid you in understanding all the different factors at play in the system. You already have some time under the hood with different compressor capacities and the effects of changing cap tube size on the system as a whole. These pieces of the puzzle are of great importance, and knowing what to expect when changes happen is vital.

When you swap out that cap tube for a txv, try not to forget about watching those temperatures and pressures in the various places in the system. The constant flow properties of a cap tube make it fairly easy to get the system charge close to where it needs to be with some trial and error. With a txv in the system, it automatically changes its flow to keep the evaporator happy. This behavior is not always good for the rest of the system.

With the heat pump water heater, you had a design goal of a certain high temperature the unit built up to slowly. As the water tank temperature rose, the COP of the unit fell. You found a cap tube length that didn't flood the evaporator and adjusted the charge to produce hot discharge gas. Not so difficult, right?

With this setup, you should have a large enough evaporator to move as much heat as the compressor is able. The txv will make sure the compressor is always getting fed well. However, on the condenser side, the goal is not necessarily high discharge temperatures and pressures. Changing the system charge upwards (adding gas) will yield you higher discharge temperatures that you may not need or want. After a certain point, your compressor will be drawing extra power without moving any more heat.

The thing is, the txv can sense the extra pressure from the added gas, and adjusts the flow rate to compensate. It doesn't care how much energy is being wasted on the high-pressure side, it is taking care of the evaporator.

[MEMPHIS91]

I am looking forward to testing it out. The weather has been crazy warm so I have been working on insulation stuff lately.

I will have all my test equipment that I own hooked up when I start charging the system. That makes sense about just using more power without moving anymore heat.

I'll post some more when I get it swapped out.
Thanks again Jeff

[MEMPHIS91]

So I got the txv put in. Sorry for the bad pictures, I was working in the dark/ grow lights.

I added a service valve right before the condenser in order to get a more accurate pressure reading in order to calculate subcooling.

I filled her up with propane and the finished measurements were, 205psi Discharge/at condenser, 70 psi suction, 102F liquid line temp right before txv. 690 watts.
So 205 on R290 PT chart shows 112F, so 112F - 102F = 10F subcooling. Not bad at all. I will get more numbers and see how well she runs tonight. Gonna get down to 36F.
More soon

[jeff5may]

DID YOU MEAN TO TAKE AN OPTICAL ILLUSION OF A PICTURE??
I had to look close to see that your equalizer line wasn't actually connected to the sensing bulb...

Then I had to use my imagination to convince my eyes that the dx field and the accumulator wasn't just one big loop! My brain trusts it is connected to the second pic somehow...

Pressures look awesome for a water-to-water rig. I would expect more subcooling if the immersion coil is large enough and the fish tank is not above 90. If the air condenser is big enough, and it can move lots of air, it may be worth running at this dP. Otherwise, you might be better off heating with a huge mass of tepid water and humidity. Depends on what you are growing to a large extent.

[MEMPHIS91]

HAHA WOW, sorry jeff after looking at it again I see what you mean. Thanks for having the faith in me to know I didn't do something that crazy. lol Here is a better picture for you.

On to more test data, So this is a 40% R290, 60% R1270 mix. ONLY because I was out of R290. SO I need to look at the PT chart for R1270 as well to get closer guess as to the saturation temp. http://www.gas2010.com/pdfs/care45_pt.pdf

First Subcooling,

So 210psi equals 113.8F for R290 and 94F for R1270 so a good guess would be 105F saturation temp. My line temp was 97.7 was that's 7.3F subcooling. I really should have just stayed with R290 because it going to be very hard to know exactly what is going on with mixed pt charts. Plus I was using my cheap temp meter, I will use my nice one next time as well.

Next Superheat,

So 75psi equals 48F for R290 and 25F for R1270 so a good guess 38F saturation temp. My line was 62.2 so 24.2F Superheat.

So this clearly shows I'm still undercharged. I'll do more tuning tonight.
I know I am no where close yet, I just want to record my progress so others can learn as well.
More soon

[jeff5may]

Originally Posted by MEMPHIS91

HAHA WOW, sorry jeff after looking at it again I see what you mean. Thanks for having the faith in me to know I didn't do something that crazy. lol Here is a better picture for you.

On to more test data, So this is a 40% R290, 60% R1270 mix. ONLY because I was out of R290. SO I need to look at the PT chart for R1270 as well to get closer guess as to the saturation temp. http://www.gas2010.com/pdfs/care45_pt.pdf

First Subcooling,

So 210psi equals 113.8F for R290 and 94F for R1270 so a good guess would be 105F saturation temp. My line temp was 97.7 was that's 7.3F subcooling. I really should have just stayed with R290 because it going to be very hard to know exactly what is going on with mixed pt charts. Plus I was using my cheap temp meter, I will use my nice one next time as well.

Next Superheat,

So 75psi equals 48F for R290 and 25F for R1270 so a good guess 38F saturation temp. My line was 62.2 so 24.2F Superheat.

So this clearly shows I'm still undercharged. I'll do more tuning tonight.
I know I am no where close yet, I just want to record my progress so others can learn as well.
More soon

Your numbers are off for propylene. It looks like you translated bars to psi absolute instead of psi gauge. This throws your r1270 saturation temperatures off 1 bar low or about 15 psi. At condenser pressure, the effect is less than at evaporator pressure. My guess is 5 degF subcooling and maybe 19degF superheat. This mixture is very close to that of r22 as far as pt values go.

The puzzle piece missing here is your outdoor water temperature. If it is above say 45 degF, it is doing lots of boiling. If not, the ground is doing most of the work. Remember, now that you are running a txv, it can sense this kind of stuff as it happens. If it has a MOP charge, it isn't going to feed a lot more juice than it is now. Adding gas will just increase your subcooling.

For your convenience, and to boggle and amaze others, I highly recommend downloading the refrigerant slider app from Danfoss from the play store or the app store. It makes quick work of figuring out pt values for lots of gases. The only ones it doesn't do are the cfc "old school" gases, which can be found on an old gauge face anyway. I haven't actually ran through a chart for a while. The app just makes it too easy.