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Old 12-20-10, 02:47 AM   #411
bigsmile
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Thank you very much for the detailed answer. Mean while, during the hours I posted my question and now, I have roughly gone through this thread. One thing I'm curious about is that early on (in about the first post), you conducted some experiment with the heat pump you built. It had rather good cop numbers. Why now when you connect it to the ground loop, the COP drops so much?

Also, you mentioned the compressor has a leak. Are you sure it's the compressor, not the other parts of the refrigerant circuit? The reason I ask is because I have the feeling that the plate exchanges may not be for refrigerant, so it may be them that are leaking.

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Old 12-20-10, 12:24 PM   #412
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Quote:
Originally Posted by bigsmile View Post
One thing I'm curious about is that early on (in about the first post), you conducted some experiment with the heat pump you built. It had rather good cop numbers. Why now when you connect it to the ground loop, the COP drops so much?
Great question...

This test is different from what would be encountered in actual practice, because the source temp is declining continually and the sink temperature is rising continually and there is no steady state. But it does give many snapshots of what to expect at various stages of temperature difference between the heat source and the heat sink.


Above is the ending part of the original heat pump test, with my new addition which is the fat red line that approximates the COP. As you can see, the COP is declining. In all of the subsequent tests I have done, I see the same thing. What is going on there is that the "source" temperature is getting lower and the "sink" temperature is getting higher. One way to look at it is that the heat pump has to "lift" the heat a greater distance and therefore has to do more work (a more scholarly explaination can be found here). This would account of a declining COP. In the early test I should have let it run longer so that the source temperature was well below what I would expect my loop field temperature to be.

(* I'm still testing for optimum refrigerant charging levels, and I may have some additional testing to do on heat exchanger sizing. If I want to strangle all of the COP possible out of my system, I may need to go to larger heat exchangers. *)

So I now know that my initial loop field temperature is close to 51, in December and I can expect it to decline somewhat as winter progresses, and the more I use the heat pump. I'm still not sure what the rate of decline might be, and I'll just have to use the heat pump under normal conditions to find out.

So, some lessons from all this are:
  • a shallow loop field will work, but a deeper loop field will work better, because it is less affected by seasonal fluctuations (less heat when you need it most).
  • a larger loop field will decline more slowly than a smaller loop field.
  • a larger heating load will cause any loop field to decline more rapidly.

Step numbers one through three are still insulate, insulate, insulate.

Quote:
Originally Posted by bigsmile View Post
Also, you mentioned the compressor has a leak. Are you sure it's the compressor, not the other parts of the refrigerant circuit? The reason I ask is because I have the feeling that the plate exchanges may not be for refrigerant, so it may be them that are leaking.
I mis-spoke, I should have said that the system has a leak. The very last part I suspect of leaking is the compressor. The part I most suspect is the refrigerant-to-brazed-plate connection.


These particular heat exchangers are really meant for water-to-water use. And I had to get some adapters to fit water pipe threads to refrigerant tubing. I didn't appreciate it at the time I got the heat exchangers, how important it is to braze the whole system so that it is hermetically sealed.


Here is a heat exchanger I bought subsequently, which is meant for refrigerant use and has "sweat" fittings. Don't be confused by the name... in the refrigeration trade, they often say "solder up a system" and the name "sweat" would make you think that they are referring to sweat solder, but in practice, brazing is the method used, because it is stronger and more able to withstand decades of vibration. The construction of both exchangers is the same high quality, the connection is the difference.

I also may have a pinhole failure in the brazed joints I did... I didn't know what I was doing, and was really flailing about just trying to get something together so I could do some testing.

What I need to do is over-charge the system, remove the electrical connecting parts, and submerge the whole frigging thing in a water tank and look for bubbles...that would do it.

Hope this helps...

Regards,

-AC_Hacker
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Old 12-20-10, 04:55 PM   #413
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Default HP test - 4 (Dec 20, 2010)

I'm still having a heck of a time with the data logger, so here is more manual data logging...

Logging Improvements
  • I have started using a digital clock (the one on the Kill-a-Watt) and the time is more reliable.
  • I have insulated under the bottom of the blue bucket, so heat is not being lost through conduction into the basement floor.
  • I've started logging the cumulative kw-h with the Kill-a-Watt, and using that in the COP calculations.
  • I have started using a thermometer that responds in tenths of a degree to measure the loop water temp.

Below is the chart for this test, as in the prior tests, the energy used by the pumps is not being considered.


I've made the lines easier to read.

Due to the automatic scaling,the kw-h line is at the very bottom of the chart.

The COP*100 line looks pretty favorable (even pushing over 400%!), especially when the heat-sink temperatures are down below 100 degree range (when the "lift" isn't so high). This really speaks volumes about the advantage of radiant floor heating (huge radiating area, lower feed temperature), where feed temperatures are in the range of 85 to 95 degrees, compared to forced air (smaller radiating area, higher feed temperatures) where the feed temperatures are in the range of 120 degrees.

Below is the logged data for this test.


Curiously, the temperature of the loop field (AKA: 'T(source)') starts to climb a bit toward the end of the test. I think this is due to the heat being produced by the quarter-horse sump pump.

So next on the agenda is looking for a much lower wattage pump that can still provide sufficient circulation through the loop field.

Regards,

-AC_Hacker
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Old 12-20-10, 09:14 PM   #414
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Thanks for the reply, and for the invitation to join. I also believe that when it comes to heating and cooling, GSHP should be the way to go. But the current situation is that the high cost spoiled the whole thing for most people. I really hope that something will be done in the future to bring the price down. But for the moment, I can't resist being drawn to thinking about DIY. What I have in mind is direct exchange setup. It's efficient and also it requires smaller ground loop. The only thing seems to be certain technical difficulties, such as the oil return issue.

If that's the case, I came upon a masters thesis on dx system, in which it is stated that as long as the wells are shallow (20' or so) and the velocity of the refrigerant fast enough, oil return isn't an issue. Does this sounds correct to you?

In your other post, you mentioned the patents on dx system. I guess it may be a good idea for me to read some of the patents. Actually I have came upon a couple of such patents during my random search, but the issue is that the website I read didn't have figures. Just reading the text didn't give me very clear idea. Does the site you mentioned (about patents) have figures?

BTW this is really a great thread. I've spent some effort searching about GSHP, this is the one single most informative result I've found so far.

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Old 12-20-10, 09:39 PM   #415
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One thing about the efficiency is that the compressor you use may not have very high efficiency to start with. I think most window AC units have EER value below 10. The compressors in central AC units or mini-splits should have higher efficiency.
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Old 12-21-10, 02:28 AM   #416
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Quote:
Originally Posted by bigsmile View Post
...The only thing seems to be certain technical difficulties, such as the oil return issue...If that's the case, I came upon a masters thesis on dx system, in which it is stated that as long as the wells are shallow (20' or so) and the velocity of the refrigerant fast enough, oil return isn't an issue. Does this sounds correct to you?
Yes, the oil return does seem to be the issue with DX systems.


Some DX companies drill a series of holes from a central header vault, that radiate out and down, this reduces the vertical travel but allows sufficient length.

Quote:
Originally Posted by bigsmile View Post
In your other post, you mentioned the patents on dx system. I guess it may be a good idea for me to read some of the patents. Actually I have came upon a couple of such patents during my random search, but the issue is that the website I read didn't have figures. Just reading the text didn't give me very clear idea. Does the site you mentioned (about patents) have figures?
By figures, I think that you mean illustrations... My favorite patent site is:

called freepatentsonline

...they have searchable text and you can also download a PDF of the whole patent, with pictures. I searched my files for a particular patent that would be very helpful to you, it was either taken out by one of the big air conditioning companies, or was assigned to them. Its real value was that it gave limits to certain proportions of tubing, like the length could not exceed 720 times the inside diameter (I just made these numbers up) in order for the lubricant to circulate properly. It had ratios like that for the whole system. Very useful.

Keep searching...

Also, there is a maker of GSHPs in Canada named Maritime Geothermal Ltd. and I have a PDF that I found previously on their website called, "Maritime Geothermal Installation Manual.pdf". That shows an installer (that could be you) how to build a DX loop field. I think this may be very, very useful for you. I just tried to find this document again, but no luck.

The document is about 1.5 Meg, too big for EcoRenovator to handle.

If you send me an email via the EcoRenovator thingie, I'll send you a copy.

Quote:
Originally Posted by bigsmile View Post
BTW this is really a great thread. I've spent some effort searching about GSHP, this is the one single most informative result I've found so far.
I'm very glad that I can help. If you happen to come across material you want to share, this is the kind of place where you can share it.

I especially encourage you and anyone else who reads this, to do some actual experiments, to try things out.

I say this because it was when I built that little heat pump (that I am still testing) that this whole thing really started to seem possible.

And I think that when a group of people start sharing information and experiences, then the snowball will really start rolling.


Let me know if I can be of further help.

Regards,

-AC_Hacker
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Old 12-21-10, 02:38 AM   #417
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Quote:
Originally Posted by bigsmile View Post
One thing about the efficiency is that the compressor you use may not have very high efficiency to start with. I think most window AC units have EER value below 10. The compressors in central AC units or mini-splits should have higher efficiency.
I think you may be right about that.

I actually have about a half dozen more compressors (people just keep giving me these things!) that came from equipment with better SEER ratings.

I'm also going to try a TXV valve on the next one.

Regards,

-AC_Hacker
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Old 12-21-10, 04:18 PM   #418
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I need to post this to be able to post email address.
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Old 12-21-10, 04:18 PM   #419
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It turns out that I need to have 20 post to send email on the forum. (I even need 5 post to be able to post email address.) I'm sure I'll get there sooner or later, but at the moment, if you don't mind, please send the document to whyharp@gmail.com.

I've been looking for something like an installation guide for DX for quite a while without success. So this is really something that I want to read. Thanks in advance.

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Old 12-21-10, 06:33 PM   #420
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...if you don't mind, please send the document...
Help is on the way...

-AC_Hacker

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