Dxgshpwh (ground source heat pump water heater)
Howdy! I begin by saying thank you, thank you to all who take the time to read my thread, who comment on it, who give advice, who save me money by keeping me from making stupid mistakes, and those of you who just want to see something created. My name is Jake, (I am very bad Dyslexia so I apologize if things get mixed up) my project is a DXGSHPWH that in English is a Direct Expansion (DX) Ground Source (GS) Heat Pump (HP) Water Heater (WH). I will give as many details as I break this all down. My idea is to use an electric hot water heater with the HX coil from a window AC unit coiled inside, with the DX line running 30 feet deep into a 2 inch bore hole. My outline will be broken down into sections of the system as follows: Section 1 Water Heater, the tank, thermostat, HX coil, and back up elements; Section 2 Main AC Systems, heat pump, refrigerant, accumulator, expansion valves, housing, and controls; Section 3 DX System, bore hole drilling, DX coil, bore hole replacement medium, and thermometer.
Section 1 WATER HEATER I have sourced a used 50 electric hot water heater. I would like to have to already existing thermostat control the compressor I have read on this forum about how to do that and fill like it should work fine. The HX coil is probably the biggest question mark in my head. I’m thinking 25 feet or 3/8 refrigeration copper tubing coiled into either the top or bottom 1 inch element hole. If I can get it the coil correctly would do it in the bottom be best? Also the fitting like on the Air Tap A7 looks perfect but can I just buy that fitting somewhere? Should I consider coating the coil in something to keep it from building up with calcium and other terrible water things? I have seen people electroplate copper with Nickle before, comments? Whatever hole I don’t use with have a 120 volt 1,800 watt element for when the heat pump can’t keep up (I hope that never happens). Section 2 MAIN AC SYSTEM I am hoping to basically just cut existing lines to the heat exchangers and braze with 15% silver rods the coils going to the WH and the DX bore hole on. The only control I should need is the thermostat on the WH because I shouldn’t have to deal with defrost. I was thinking about running a temperature probe to the bottom of the bore hole and if it drops below 45F or so to cut off the compressor until the ground can warm back up. I can easily get a 5,000-7,000 BTU window unit, what size would be best? I will be using BBQ propane frozen and then double line dry filtered as my refrigerant. Section 3 DX SYSTEM I plan to use 2 inch PVC pipe with a metal cutting head hooked to a 2 inch mud pump from my large pond, and add pipe until I get to 30 feet. I have done this before and gone to 36 feet. I’ll post pictures as I drill and give a run down on the set up. Then I will feed the DX coil down and refill the hole. What are ya’lls thoughts on how deep the bore hole is? What diameter DX coil, I’m thinking ¼ or 3/8? My biggest concern is the lubricant getting stuck at the bottom of the DX loop, could I just put a bigger compressor and get more flow if the first one is too small? It is much easier to replace a compressor than to bore another hole. Should I paint or electroplate the coil? What should I refill the hole with; I was thinking sand as it would let water in. Should I run a thermometer probe to the bottom? Should I cover the bore hole with concrete? Or should I maybe do 2 bore holes at 20 feet? I can hit water 75% of the year at less than 10 feet. Ground temperature is normally around 55-62F. I will post some simple drawings and pictures as soon as I get a chance. Thank you again for reading |
First off, welcome to the site!
Very interesting project Memphis91. I look forward to see what you come up with. |
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Regarding the vertical bore hole and the lubricant issue, when I cited it as a potential problem, I was acting as a 'devil's advocate', and was (am) trying to visualize possible problems. I was not saying that a 30 ft deep DX hole will not work... it might work just fine. We have heard from other folks from MS here on EcoRenovator, and from all reports, making vertical boreholes is comparatively easy in MS, compared to some other parts of the country. So in that regard, nature has been very kind to you. So, I guess what I'm trying to say is that I hope your project doesn't get tied up in knots over my comment about the possibility of lubricant starvation in a 30' vertical hole. Your initial vision is clear and good, and quite likely to work exactly as you originally envisioned it. & & & & & Having said all that, only if your vertical idea doesn't pan out, you might want to consider the illustration below: This is a typical diagram of a DX loop field as it is often implemented commercially. I always thought that this method was used because it resulted in the minimum disturbance to a suburban landscape, which is a very common reason that many people do not want to do a GSHP installation, even knowing the much greater efficiency (my girlfriend being one of them). But thinking about a potential lubrication issue, and remembering this diagram, I see that a horizontal borehole would give good exposure to the soil, and reduce the vertical vertical lift. It would also be much harder to dig unless you had specialized diagonal digging equipment, as seen below: Just in case you didn't see it already, I just came across a Wikipedia entry on DX heat pumps HERE that indicates that vertical DX boreholes have been drilled to depths as great as 100 ft. so do not be discouraged, do not be confused. Push on!! Best, -AC |
Thanks Doax!
AC, Yeah you just pointed out my biggest concern at the very beginning. The show WILL go on. Oh the ground here is AMAZING! Plus in about 40-50 feet from a large 2 acre pond. So hitting water will ALWAYS happen. I already have 500 feet for HDPE 3/4 poly pipe in the pond for a geothermal loop idea I was already working on to heat my greenhouse (aquaponics) in the winter. I have about 10 hours of reading ahead of me. I did find some good sites though. http://welldrillingschool.com/course...geothermal.pdf "copper has sq.ft-hr-°F per inch of wall thickness, whereas that of HDPE pipe is only 2.7 Btu/sq.ft-hr-°F per inch" And another forum mentioned using a oil separator, i guess like this one 1 3 8" HVAC Oil Separator 559011 | eBay Looks from what I can tell the line coming from the HX coil is larger on the way down and smaller on the way up. So I'm thinking 3/8 down, 5/16 up. I will try one 30 foot bore hole and if it doesn't work I'll just drill another hole. Are there any people with experience with DX installs on this site? |
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I just did some searching on the web, and on THIS page I found an interesting article, which had this picture: The tubing sizes are different going up and down, and are used for a bigger compressor. -AC |
AC,
Yes I was just on that page myself. I love diagrams. Those bore holes are at 120 feet. Boy that is deep. Random thought, if acid is the problem why can I not dump some powdered line into the bore hole as im filling it with sand? Maybe even some sea shells that will release lime over a long period of time? DX - Direct Exchange Equipment Options This site claims it 25% better than water loops. NO ONE does DX around my area even though we have awesome ground for it, strange. |
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I was also thinking about where your expansion device (cap tube) should go... Maybe at the top of the hole, before the entire trip... maybe at the bottom of the hole, before the trip back to the top? If you went for the bottom, the cap tube is pretty fragile, but once you were certain that there were no leaks, you could cast the bottom assembly in plastic or tar... concrete might be too corrosive. -AC |
AC,
That is something I have yet to ponder on. What would be the advantage of top vs bottom? I now have an idea to run 2 loops of 1/4 tubing 30 deep feet coming off a common manifold at the top, both sharing the same bore hole. It might be a bit trickier to get all that in 2-2 1/2 inch bore hole, but it will completely solve the lubricant issue. |
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I initially imagined that there might be a condensation problem, but then I realize that condensation will not happen in the low pressure side. Another aspect would be that the temperature of the liquid-flashed-to-gas that is exiting from a high-pressure tube into a low pressure area will be the very lowest in it's trip back to the the compressor, so the delta-T will be greatest and the heat migration into your vaporized refrigerant will be maximum at that point. The delta-T will decline as the vaporized refrigerant gathers more heat. So there could be an advantage to having all that take place at the deepest, most wet, most temperature-stable part of the bore hole. The opposite scenario would be that if the liquid-to-gas transition happened at the top of the hole, the vapor would have a longer distance, and longer time to gather heat. The construction and maintenance would be much easier. Also, if you went for a TXV, it would need to be at the top of the hole. But I think that a TXV for such a tiny compressor would be just too much techno for what should be a simple, elegant project. Quote:
In the IGSHPA manual (CLGS Installation Guide (#21020)), in the section on the loop fields, it looks at various ways of doing loop fields, both trenches and boreholes. There was even a small discussion on putting two loops in the same hole, and I believe that the performance increase was about 3% to 5%. I'm afraid I don't understand how two loops would remedy the lubrication issue? -AC P.S.: This manual is a tad expensive ($45.00), but it is so amazing in the breadth and depth of information regarding Ground Source heating and cooling, that you should seriously consider getting a copy. It can sometimes be found used, sometimes in libraries. But considering the information, it is a miracle. As I recall, the manual does not directly address DX, but most of the principles are the same. |
I will being looking for a cheap used manual. Thanks for the advise.
Yes condensation was a good friend of mines first words when I told him the idea. I now see it as you do, it should not be a issue. TXV would get complicated for sure. But would be awesome in a future system. I was thinking a bigger line, being maybe 3/8 or 5/16. But if I went with 2 1/4 I would be getting good enough flow and not loosing as much pressure to get the lubricate up. Plus I think it would help to spread the temperature out a little better. A random idea I had today, how cool would it be if you could pipe all your hot water users (dishwasher, showers, sink) into a special holding tank that had the DX loop in it. It would be recovering some of the heat from the already heated water. I know that would probably be against code in most places, but here in MS as long as that water makes it back into your septic system its legal. Just an idea. Back on topic, I like the cap tube being at the average water table, maybe 15 feet down? With the water table being so high I think I will be better off than all the way at the bottom. Now I need to look into running a DX line into my 2 acre pond (17 feet deep) from my 4 ton central heat pump. I'm going to have to start up a copper factory soon. I am also trying to get in contact with a DX installer in Memphis, TN. He said he would answer some questions for me. |
Tips for building
I have been off the forums for awhile, life to do and such... sounds like you are all-in on this project! Post lots of pics of what you do.
The heat exchanger in the water tank will do its best at the bottom. When cold water enters, it naturally sinks, so that's your best spot for heat transfer efficiency. Many DIY people have left the heating elements alone, by either inserting the hx loop through an existing fitting (inlet, outlet, or drain), or by bringing the water to the hx and back with pipe and pipe fittings. The big purpose is to have "less custom" fittings that don't take machining tools to fabricate. You can then buy a prefab, pretested hx that will be a proven winner. Less guesswork for the wary. With a hermetic compressor and just a single refrigerant path, oil control is a non-issue. The smallish compressors have a copious sump built into the shell. The built-in muffler also acts as a suction line accumulator. With the evaporator dropping way down into the ground, I would size the tubing small to maximize velocity to keep the oil from pooling in the bottom of the hole. A curly-q every ten feet of height would trap the stuff stuck to the walls. Might not need it, but it's cheap insurance. |
Jeff,
I've been all in on a long list of crazy home improvements that I have not posted to a forum about. So I am REALLY all in on this one. Thank you for your awesome advice. I will look at more post on the site to see what people have done. I believe I have only looked at two so far. (Got suck on the bore hole problems) Prefab sounds like an excellent option. Bottom of the tank it is then. ---"With a hermetic compressor and just a single refrigerant path, oil control is a non-issue. The smallish compressors have a copious sump built into the shell. The built-in muffler also acts as a suction line accumulator. With the evaporator dropping way down into the ground, I would size the tubing small to maximize velocity to keep the oil from pooling in the bottom of the hole. A curly-q every ten feet of height would trap the stuff stuck to the walls. Might not need it, but it's cheap insurance."--- In your opinion would two lines of 1/4 inch 30-35 feet deep be ok? And can you explain your curly-q idea a little better? I think I get the basic idea, you are giving the lubricant a small place to -get a foot hold(kinda like rock climbing)-. Is that right? Awesome info and food for more thought. Thank you |
For the tubing, check Xringer's thread on the airtap A7 HPWH he installed. He successfully integrated a solar/ashp/oil furnace powered water heating rig into his house for hot water no matter what. Last I heard, his solar was doing most all of the water heating, with the Airtap kicking in during high demand. Since the tank was rigged in, he has burned very little fuel oil at all. Way down from thousands of dollars a year.
http://ecorenovator.org/forum/geothe...er-heater.html Randen also turned a 5000 btu window aircon unit into an air-source water heat pump, with much custom work done throughout. He is just a mechanical master genius. Everything he does comes out looking awesome, even the stuff that doesn't work! I hate to see a good-looking piece of machinery destroy itself, but it looks ALMOST as good dead... kind of like taxidermy. http://ecorenovator.org/forum/geothe...heat-pump.html If you look at a larger split-unit install manual, the manufacturers have pictures and guidelines for where and when to put the oil traps in the lines. They work just like a p-trap in a drain. When the flow stops, the extra oil gets stuck in the trap instead of finding the bottom of the plumbing. When flow starts, the oil is carried back to the compressor much quicker. http://www.daikinac.com/content/asse...ds/FAQ-req.gif Rather than jog the line laterally for the trap, you can loop it once for the same effect. With natural refrigerants (propane, propylene, butane, etc.), the oil is much more soluble and miscible in the refrigerant, so oil flows much easier and better through the system than with "modern"(r134a, r410a, r407c, etc.) refrigerants. As a result, it is usually ok just to size the tubing small enough to get decent velocity, so the foamy froth can make it a decent way back up the tube before the gas and oil separate completely. |
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I have read each of the other threads completely now. I'm a plumber by trade so p-traps I can understand. Do I need loops going down and coming back up or just on the way back up?
I'm think maybe just one run of 1/4 down the bore hole then, with the cap tube at the top. I'm sure this time of year the water table is at maybe 6 feet down. Should I not fill the bore hole? If water is best then filling with sand will only make it worse? I'm sure some dirt will fall in over time though. I made a sketch up of what I am thinking. Any thing I'm totally forgetting? http://ecorenovator.org/forum/attach...r-img_0584-jpg -- Next project, running my 4 ton heat pump in a loop in my pond. -- |
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In the lower right corner you will find instructions regarding the desired way to backfill a bore hole that passes through an aquifer. I saw this graphic quite some time ago, and it was from a site that may not exist anymore, but the site was in Canada, and the distances for fill that they describe were specifically suited to that part of Canada where they were operating. If you scale their advice to your knowledge of your location, you'll be good to go. The gravel fill principle is to put the larger gravel (pea gravel) at the bottom, up to the level of the top of your aquifer. Then graduate to finer granularities by following with a small (6" or so) layer of finer gravel, then a similar layer of some coarse sand above that, and then finish off with whatever you want... dirt, bentonite, etc. -AC |
The lines in your sketch are backwards. As a general rule, the liquid line should be smaller than the suction line. In your sketch, the borehole loop is part of the suction line. It would be better to use 5/16" from the cap tube to the compressor muffler and 1/4" everywhere else, if you even need it. The only tubing I have used over 1/4" in my beasts has been used to adapt up in size to fit compressors and txv fittings. The situation changes rapidly with long distances and larger capacity systems.
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AC, Somehow I didn't read the diagram I just looked at the pictures..... Pea gravel it is then.
Jeff, Really? 1/4 inch all the way? In the water heater and bore bore? That would make things SO much easier. |
The newer minisplit units are using long parallel runs of small diameter, thin wall, ribbed tubes in their heat exchangers. The superconducting supercomputers have led them in this direction. Apparently, some pressure drop is a good thing. More surface area is always better, as is turbulent flow.
There are charts and formulas all over the web (and this site) that can help you predict how your design will act before you actually install it. I used coolpack and the SWEP literature a lot to make things jive. The literature ac_hacker cited is also awesome. For a 4 ton rig, you will need to do your homework to ensure the rig will be reliable. For this half ton build, it will probably work well without lots of modeling. However, it will be good practice to get your hands dirty and for measuring performance. I perfected my brazing skills on small systems and built up my tool set. |
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Coolpack looks like quite the learning curve for me, but I will already downloaded it and starting to play with it. Basically I just need to see how long my hx needs to be based on all the other data I have. Yeah the old 4 ton can wait. I got a water heater to build. Thanks for the info. |
So coolpack is something I will learn over time. I've never been good with computer programs and its quite overwhelming. I did find a few helpful charts, and some threads on here.
30 feet for the water heater HX, and a bore hole of 30 feet deep (60 feet of tubing altogether) with the cap tube at the top of the bore hole looks to be a good balance with everything being 1/4inch. Am I missing anything? I'm ready to buy some copper and get started making the coil. Pictures will start as soon as I do. |
Hope your project is developing well.
If you hit a snag & need help, give a holler! -AC |
Thanks man, a few set backs have slowed me down. On the way out the door to visit the in laws I noticed a water puddle under my existing water heater, needless to say I had to buy a new one. Just got back in town and plan to start back on the coil tomorrow after work.
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I got the propane dryers and adapter all brazed. And started making the coil, I post pictures soon. I don't have a smart phone so it takes a minute.
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Working on different coil sizes to see what works best
http://ecorenovator.org/forum/attach...1&d=1432335976 http://ecorenovator.org/forum/attach...1&d=1432335976 http://ecorenovator.org/forum/attach...1&d=1432335976 http://ecorenovator.org/forum/attach...1&d=1432335976 http://ecorenovator.org/forum/attach...1&d=1432335976 |
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So I found that with this new water heater the insulation is thicker therefore making the screw in coil much to long and causing it to make its way to the top of the tank. So i pulled it all out and just made it coil itself at the bottom of the tank. I used my inspection camera to make sure all was ok. Sorry for the bad quality its a picture of a live feed. 30 feet of 1/4 inch refrigeration copper is in!
http://ecorenovator.org/forum/attach...1&d=1432435339 |
MEMPHIS91
This water heater project is probably the best bang for buck on any DIY home efficiency radar. My parents are saving a pile of money with the one I had built for them. Its located in their finished basement an it purrs away in a small utility room. The heat it actually sequesters from the room is not at all noticeable. During the summer months when the air is humid they may get a quart of water (condensate) in a bucket beside the HPWH. But it evaporates as quickly as it collects. In fact there is a drain located only 4 ft. from the HPWH. But didn't bother to run the drain hose to it. With your DX you will not encounter this small problem. I have found that the amount of heat required by the evaporator is quite small (5000 BTU A/C window shaker) The amount of work required to drill the ground bore hole would be my issue. (As I age I'm getting lazy) However I'm on the edge of my seat to see how little energy you will use to heat the water as you have no need for a fan to force air through a finned HX. In fact it will be very quiet as well. I believe My creation ultimately used approx. 450 watts total. I know you will do a lot better with your efficiency not having the fan and only powering the compressor. I'm going to guess less that 300 watts!!! To charge the system I used propane and slowly added to get an appropriate condenser temp approx. 140 deg. F As adding more refrigerant just raised the amount of power required and no more heat was produced. I believe the suction side was only 18 psi. As far as the copper in the ground it will out-live both of us and 1/4" is all you will need there too. However if you are concerned HVAC suppliers (or Ebay) have a polyethylene coated copper tube that would last for an eternity in the ground. Its a very rewarding project. More should do the same!!! Randen |
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I have a fast quad-core computer, very fast Internet, 32 GB of ram, a very powerful video card, and a large monitor. Am I the only one having difficulties?? -AC P.S.: the max width for an image that doesn't get resized by the EcoRenovator robot is 640 pixels. |
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Sorry about that AC the pictures are much to big. I resized a few. Most the others are not important since I had to change up my design.
This is the way I brazed on a propane valve for the small cooking bottles. http://ecorenovator.org/forum/attach...1&d=1432676093 This is the finished product and going into my gauges to test for any leaks. http://ecorenovator.org/forum/attach...1&d=1432676093 Here is where the change happened. I could not get 30 feet of 1/4 refrigeration copper to coil in the tank without going to the top. This really was a problem because I had planned on simply brazing on an old hacked element base and continuing to screw the coil in. So I just uncoiled the tubing and and ran in it the bottom element hole and got it to coil at the bottom. http://ecorenovator.org/forum/attach...1&d=1432676093 I used teflon tape and joint compound with a 36" aluminum pipe wrench to put it all together. I will finish the back half tonight. Idea is to braze the coil through a 1 inch bass cap then tighten the union down. I'll post more picture at the right size from now on. http://ecorenovator.org/forum/attach...1&d=1432676093 |
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And your solution to the problem of twisting the copper tubing, by using a pipe union is just awesome. Great stuff! Best, -AC |
Pictures have been showing up ok on my smartphone. HTC evo 4g running android 4.0.3, on WiFi only.
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Got to all brazed up last night. Its held house pressure with no leaks all night.
http://ecorenovator.org/forum/attach...1&d=1432725748 |
The project seems to be coming along great. :thumbup:
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Earth works...
It's going to be really interesting to see how the earth works part of the project goes.
I don't know how easy it is to dig where you are, but we have had reports from other Mississippians who reported that boreholes were not a huge problem. I hope that part goes well for you. -AC |
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Thanks so much for all the replies.
Randen Somehow I totally missed your post, thank you for your insight. Very encouraging to know you think it is going to work so well. I got to play with the compressor some today it was pulling 2.13 amps on 120 volts with R290 and 17 psi on the low side. So you estimate looks very accurate. http://ecorenovator.org/forum/attach...1&d=1432771847 Starting to plot out where everything is going to go. The bucket is the compressor housing and the compression coupling is the hole. I'm going to just put the paving stone back over the hole when I'm done filling it with the pea gravel. http://ecorenovator.org/forum/attach...1&d=1432771847 Question, should I wrap the tubing coming back from the hole around the compressor a few times? I think I could gain some heat and also keep the compressor cool. Also should I insulate the housing for the compressor? This is the updated drill head, as you can see it is going to be 3.5 inchs instead of 2. http://ecorenovator.org/forum/attach...1&d=1432771847 |
MEMPHIS91
Good point yes wrap the compressor with evaporator tube. These little rotor type compressors liberate a lot of heat while operating. You could wrap it from mid way up to the top where most of the heat is generated. Maybe after returning from the ground loop to the compressor wrap for additional heat. Good thought!!!! I wouldn't recommend insulating though. Any trapped heat could overheat the compressors windings burning out the motor. Leave it naked with only the copper tubing wraps. Randen Looks really good I like the tank/HX coupling solution!! |
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Your brass cap adapter is an awesome idea! Coupled with a common union it's ingenious. Common parts, simple construction methods, I love it!
This adapter idea would make it much easier for the average garage hacker to build one of these energy-savvy devices. I hope you start a trend with this piece of magic. |
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If you are going to use the cap tube that came with your A/C, it will be designed for the anticipated running environment of that air conditioner, using R22, and the condenser coils and evaporator coils that your unit came with. When you hack a unit, you are violating the original design in so many ways! Vlad, a real refrigeration tech, was absolutely beside himself when he first heard what we were doing... until he tried it for himself. It's kind of a miracle that after all these reckless mods, the new machines not only work, but work so well. It will be very interesting to see how wrapping the compressor in copper tubing will influence ultimate COP. Seems like it should be a good idea. Even without wrapping the compressor, which sounds like a good idea, I think that your COP is going to be very favorable, better than an air-source conversion. Your concept has very many features that favor high efficiency: ground source (conduction beats convection), direct expansion (no heat exchangers, each taking it's 10% toll), no pumps, no defrost cycles, no hassle with freezing conditions. Because you are heating a tank of water, it will be very easy to do an accurate assessment of COP. You really are on the cutting edge here. Best, -AC P.S.: Awesome drill bit you have there... DIY? |
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