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Old 06-09-15, 07:33 AM   #121
stevehull
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Memphis,

Now a few things are making sense. I bet that tiny flakes of oxide are partially plugging the cap tube. No big deal - just braze with an inert gas.

The funny thing with small particles in the system, is that the set up will not work predictably. Sometimes all is fine and then a bit of oxide flake gets in there. Because of the tiny tube diameter a smaller flake can restrict flow. It only takes an 11% change in tube diameter to decrease flow by 50%.

PLEASE do not get discouraged. This is great stuff!

Steve

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Old 06-09-15, 10:50 AM   #122
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This product will take care of the contamination issue if it exists.
Supco

Supco model no. Sud111 or sud115

Cap tube is no. Bc1, BC2, bc3, ETC. BIGGER NUMBER IS LARGER I'D.

They also come with cap tubes already attached. Under ten bucks on eBay every day.

I have learned to install some kind of filter on all my experimental units. Don't ask how. Dirt cheap insurance.

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Old 06-09-15, 11:19 AM   #123
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I have a large drier on the system now. Same one I used on the propane drier. There is a picture of it way back toward the beginning of the thread. That might be too big, if it is I will order the one you suggested.

Is this to big to help? This is same one that is on mine.
http://www.rexxindustrialparts.com/p...38qu16338.html

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Old 06-09-15, 09:33 PM   #124
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If you trust your filter, then by all means use it. The cap tube is a predictable metering device with no moving parts. If it clogs, you can tell pretty easily. If it does clog, just chop off a couple inches (as you did) on the high-pressure side. Contaminant will lodge in the upstream end pretty quick if it is going to.

Watch this and be well informed:


No matter what the scientists tell you, cap tube sizing is a trial and error affair. With a perfect charge, with brand new everything, a calculated value will get you somewhere in the operating range. Where in the range the unit works best depends on many variables that change against each other when you shorten or lengthen the cap tube. This includes the system charge.

With a manufactured unit, this allows the designer to rapidly prototype and optimize a unit that can be blueprinted once and be copied easily. At the factory, they build it to the print, weigh in a charge from deep vacuum, do a quick function check, then It's done. Nothing to tweak, so the thing does what it does consistently until something breaks.

What this means for you is once you get the cap tube optimized in your running range, there is not much else to optimize. Making some test runs after a major change (cap tube or charge in your case) will provide the key performance indicators to tell you if what you changed did any good or not. Just make sure you take enough readings and notes while your rig is in a certain configuration. You may reach a point where you went too far and want to backtrack.

From your posted testing, you have increased your heat flow by a substantial amount by removing just a short piece of your cap tube length. I don't imagine you will have to remove much more before the compressor finds its happy place.

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Old 06-09-15, 10:27 PM   #125
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Jeff - excellent You tube video. Thanks for posting . . .

In the current situation that Memphis has, a evaporator temperature of 65 F is far more than the typical situation where it might be 20-30 degrees less. I read the graph in the video and was surprised at the long lengths of cap tube (1/3 hp, R-22) for this temperature.

Was I reading this wrong?

I don't recall the total length of cap tube that Memphis started with.

The video makes a big point that disconnecting gauges causes a significant amount of refrigerant loss. I guess the best way to start is with a pressure at the high end of the specs, allow equilibration, make all your readings and then let out some gas and repeat.

Memphis has been doing this, but shortening the capillary length (less pressure drop) has me confused. Just taking out a few inches will make a big difference in latent heat?

Steve
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Old 06-09-15, 10:59 PM   #126
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Jeff, That is some great info. I think my filter/drier is working well, but I will save the info for the SUD111, especially if I mess up my cap tube. I took the cap tube totally out today and gave it some blast of 150 psi dry air. I also cut off 3 more inches. I ran 100 psi propane blast into the borehole and into the water heater lines. Every thing seems open. I got a chance to make a quick test
tonight here are the numbers.

Time in Minutes - Water Temp F - Watts - Borehole F - COP
00 - 85 - 00 - 55.5
30 - 89.5 - .17 - 52.5 - 3.22
60 - 93.7 - .36 - 53.6 - 2.69
90 - 97.7 - .55 - 54.5 - 2.57
120 - 101.5 - .74 - 55.4 - 2.44

5.1 oz (by weight) Charge
Water temp in tank:85.6
Discharge line temp at entrance of tank:164.7
Line temp at exit of tank:93
Discharge temp at compressor: 166 @230 psi
Suction line temp at compressor: 67 @ 54 psi
Amps: 3.35 Borehole temp: 54.5

Water temp in tank:96.5
Discharge line temp at entrance of tank:171.5
Line temp at exit of tank:102.7
Discharge temp at compressor: 173 @ 250 psi
Suction line temp at compressor: 66 @ 50 psi
Amps: 3.48 Borehole temp:54.3

As you can see my borehole started getting really cold which to me says, "ITS WORKING".
And I was very happy to see it start warming back up.
I will finish out the test soon and see if I might still need to trim just a hair off the cap tube. If I understand it right I can keep making it shorter until my evaporator can't keep up, but so far it has handled everything I have tried to do. then it will just be playing with the charge.

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Old 06-10-15, 09:46 AM   #127
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Quote:
Originally Posted by MEMPHIS91 View Post
I got a chance to make a quick test tonight here are the numbers.

Time in Minutes Water Temp F Watts Borehole F COP
0 85 0 55.5
30 89.5 0.17 52.5 3.22
60 93.7 0.36 53.6 2.69
90 97.7 0.55 54.5 2.57

I will finish out the test soon and see if I might still need to trim just a hair off the cap tube. And then it will just be playing with the charge.
I thought you'd be interested to see what a graphic representation of your data looks like:



Y = temp, X = time



Y = COP, X = temp

Looking at your Temp vs. Time plot, it is very linear, with no down-turn in the range of data. This tells me that your system is not approaching any limit. This is a very good thing, to be operating within a linear range. It also indicates that it would be quite possible to reach higher temperatures, but the second graph indicates the COP-reduction penalty you would pay.

Awesome work from everybody involved!


Best,

-AC

P.S.: If you separate your horizontal data with tabs, it make it much easier to plot.
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Old 06-10-15, 11:59 AM   #128
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*duplicate of post below before editing*

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Old 06-10-15, 01:16 PM   #129
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Quote:
Originally Posted by stevehull View Post
Jeff - excellent You tube video. Thanks for posting . . .

In the current situation that Memphis has, a evaporator temperature of 65 F is far more than the typical situation where it might be 20-30 degrees less. I read the graph in the video and was surprised at the long lengths of cap tube (1/3 hp, R-22) for this temperature.

Was I reading this wrong?

I don't recall the total length of cap tube that Memphis started with.

The video makes a big point that disconnecting gauges causes a significant amount of refrigerant loss. I guess the best way to start is with a pressure at the high end of the specs, allow equilibration, make all your readings and then let out some gas and repeat.

Memphis has been doing this, but shortening the capillary length (less pressure drop) has me confused. Just taking out a few inches will make a big difference in latent heat?

Steve
The real deal with capillary tubes, as has been stated previously, is that a small difference in diameter drives a huge change in pressure drop. As the charts depict, the mass flow at a certain delta t will get you in the right ballpark for diameter. A tiny cap tube cannot flow a large mass, no matter how short it is. A somewhat larger diameter cap tube than necessary would have to be super long to drop enough pressure.

Within the operation ballpark, the cap tube will find equilibrium with the compression ratio the compressor is working to supply. A cap tube is a fixed restriction, so as you go up in length, the resistance increases and less mass flows. This drives down your evaporator pressure with respect to discharge pressure. If you are trying to cryogenically freeze something, a long cap tube is your best bet. It might take a long time to get there, depending on how much insulation the cooler has.

With this rig, the opposite is true. The ground is massive and a much higher temperature. It has just now begun to have enough heat drawn from it to force a temperature drop. It has not been taxed enough yet to see a close approach between the exiting suction line and the borehole. Memphis has done this by driving less pressure drop with a shorter cap tube. He will soon either flood his evaporator or drop his discharge pressure too far. After all, the compressor has only so much displacement.

I have my fingers crossed, hoping he runs out of compressor before either hx reaches its limit.

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Old 06-10-15, 01:48 PM   #130
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Quote:
Originally Posted by AC_Hacker View Post
I came across this very interesting document just now:


Table 1 is called:

Table 1. Recommended Lengths of Trench or Bore Per Ton For GCHPs

It adjusts for ground temperature, soil conditions, the whole thing.
When I made this post, I was not sure if the bore hole that MEMPHIS91 dug was up to the job of delivering heat to the water tank.

Thanks to all the good advice regarding optimizing the compressor, the bore hole was obviously not the problem, and incremental improvements are likely. But I am still intrigued by the information in the PDF that I found, because it has very useful information for GSHPs in general, and information that is particularly relevant for GSHPs in the South Eastern states.

I was wondering how 'close to the edge' is the bore hole that MEMPHIS91 dug, with regards to its ability to yield heat.

There were two tables that were of interest, Table 1 which indicated the depth of a 'standard' bore hole that will yield 12,000 BTU/hr with regard to soil temperature, and Table 4 which has correction factors for various factors, like water content of the soil. So the idea is to select a 'standard' bore hole length according to the ground temperature, and then correct the length for soil moisture, and other factors.




I ignored the horizontal loop-field data, and just concentrated on the vertical bore hole data. The first thing I notice was that there seemed to be an error in Table 1, because the warmer the soil, the deeper the hole needed to be... should be the other way around.


Apparently this chart is for a GSHP that is used as an air conditioner. Also, the data to the left of the 52 degree F column looked 'out of whack' (apparently Southern soil behaves in mysterious ways), so I ignored it. When I reversed the data left to right in the columns in the '52 degree F' to '68 degree F' range, everything began to make sense, and agreed with common knowledge regarding Oregon's soil temperature, so I decided to make that change, and proceed.



Next thing is that this chart is based on using water in HDPE tubing and MEMPHIS91 went with Direct Expansion, which is generally, 15% more efficient. So I tweaked the data for DX...


Then there is the correction factor from Table 4 that needs to be applied to adjust for soil conditions, and as far as I can tell, MEMPHIS91's soil conditions are a gift from heaven, so I applied the very most favorable possible factor, and came out with this:


I'm runnung close to the limit off images per post, so I'm leaving a few steps out...

This image indicates the sustainable heat extraction from a 30 foot DX hole, given MEMPHIS91's soil conditions.


Notice that I have added a 55.5 temp line because that is what MEMPHIS91 has. I did some regression analysis on the data, so that line is more accurate than interpolation would be.

Here is the heat MEMPHIS91 is actually extracting:




So, if this analysis is true, MEMPHIS91 would seem to be performing a miracle, because he seems to be extracting more heat than is possible to extract. But this is not the case, because the study from which this data comes from assumes continuing heat extraction, and MEMPHIS91's application is intermittent, and the bore hole can 'recover' between run cycles.

Continuous extraction curves have a general shape like this:



Although for GSHP heat extraction, they would not be so steep, but they will approach a limit, which the study has assumed.

CONCLUSION: From MEMPHIS91's performance date, and also from an analysis of the study, there is heat yield to spare, when the system is run intermittently. It also indicates to me that strapping a bigger compressor onto the existing bore hole might yield a larger heat output, but COP would most likely suffer considerably, because in the grand scheme of things, MEMPHIS91 called it pretty close.

Best,

-AC

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