The Homemade Heat Pump Manifesto

[AC_Hacker]

Originally Posted by Nikolai

AC Hacker, have you considered a Dx variant of geothermal heating?

It can be done by direct burial copper pipes in the ground (cold end)...

Nikolai,

Yes, I am familiar with the DX GSHP approach. It certainly has attractive features.

[* NOTE: for those readers who are unfamiliar with "DX", it stands for 'Direct Expansion' or 'Direct Exchange'. It is an approach to GSHP wherein the the expansion loop (AKA: the evaporator loop, cold side loop, etc) is buried directly in the ground where it draws in heat from the ground. *]

Here's what I was able to learn:

DX was the very first form of GSHP. If I have the story straight, a basement experimenter/inventor in New Jersey noticed how much heat was present in the condenser coils of his basement freezer, and had the idea to bury the evaporator coils (AKA: cold side coils) in the ground, and blow air over the condenser coils (AKA: hot side coils) to warm his house. It worked.

DX is more thermally efficient, so the loop field can be reduced by 15 to 25 percent. This is due to:

• Better thermal conduction of copper as compared to polyethylene.
  
• No secondary heat exchanger (no water > refrigerant heat exchanger) inefficiencies
  
• No efficiency losses due to the water pump work. The compressor IS the fluid pump for the evaporator section.
  
• No danger of freezing the working fluid in the loop field, since the working fluid is refrigerant and lubricant, which have a very low freezing point.

But there are also disadvantages:

• The copper loops are subject to degradation due to corrosion. This is less of a problem if the soil pH is on the alkaline side. The area I live in has acid soil so this would be a bigger problem. I understand that using a sacrificial anode can reduce this. I also recall that there may also be an approach wherein a small current is applied to the copper tubing to stop the corrosion. If there were a failure of the loop field, there would be a problem of loosing the refrigerant. There would also be a problem, perhaps more serious, of contaminating the soil with refrigeration lubricant. The corrosion problem was discussed previously in this thread at this posting. Two pages from a Swedish study are reproduced there, you should read them carefully.
  
• There are also issues of circulating the refrigerant along with the lubricant over long distances. I studied enough DX patents to know that the problem was solvable, but the solution was not trivial.

As attractive as the DX approach was, what really made the difference for me was the fact that this is an experiment. I want to see if it is possible for a person to make their own GSHP system. I also realize that the loop field may have to be enlarged. It will be much easier to enlarge the field if it is water circulating in plastic pipe. I also want to do some experiments with circulating water directly in an air heat exchanger for summer cooling. Also I want to experiment with storing heat from my refrigerator in the ground, also drawing heat from the ground to pre-heat water for the water heater.

So to boil it all down, the features that tilted me to favor a water/polyethylene loop field me are:

1. Very long life of the loop field (quite possibly > 200 years).
   
2. Flexibility of possible future uses.

Best Regards,

-AC_Hacker

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[AC_Hacker]

Originally Posted by cold in Maine

Hello AC Hacker! I am fascinated by your work! I also have an old house and have been researching geothermal heating, and I am a teacher and want to have students explore some of these ideas as well. Could you give me an idea of what you have spent on materials? I would like to try to duplicate some of your experiments and need to look into obtaining supplies. As I digest the postings further I will probably have more questions. Thanks for your work!

cold in Maine,

Welcome aboard!

Well, from a teaching, learning point of view, I suppose that the heat pump I built from an old de-humifdifier and tested holds the most bang for the buck.

The standards for that are much lower than the standards for a system that you might build to heat your home and keep you from freezing to death in the Maine winter.

So here's a list of equipment:

1. Used air conditioner or de-humidifier = $10 to $40, maybe free, Since You Are A Teacher (hereafter abbreviated as "SYAAT")

2.Water-to-water heat exchangers. Brazed plate exchangers = $40 to $70 each. If you wanted to make your own tube-in-tube exchangers, new copper costs would be about the same as for brazed plate. But you could scrounge copper or get donations SYAAT.

3. Brazing tourch = $15. You might have one already. or maybe the school mantainance man might let you borrow his SYAAT.

4. Silver brazing rod (DO NOT USE SOLDER!!!): Very expensive, 6 sticks for about $35 was what I last paid. You might schmooze with some local HVAC companies, however and get donations SYAAT.

5. Manifold gauge set = $35 to $140. You'll want to get one that has 1/4" flare connectors. There is an ungodly spawning of specific, proprietary equipment going on, so get the old stuff or 'regular' flare fittings. Again, you might schmooze with some local HVAC companies, however and get donations SYAAT. I have an old gauge set that was given to me by Bruce-the-Pirate, it's maybe 40 years old and works good. There are little gaskets at the end of the fittings, replace them if in doubt. NOTE, your manifold gauge set will not read accurately into the deep vacuum levels, but is ok for experimenting & teaching. If you want to do a serious system, get a micron gauge ($150) so you can tell exactly what's going on. SYAAT probably will not help you get a free micron gauge.

6. Refrigeration vacuum pump. For experimentation & teaching, this could be marginal or home-built. HVAC folks might have an old one laying about and might help you here SYAAT. Bruce-the-Pirate gave me a vacuum pump that he had no faith in, for free. I changed the oil, let it run for a few hours and did a pump-down to < 75 microns. I'm set.

7. Tubing cutter = $3.95. Save your SYAAT capital for the big stuff.

8. 2 water pumps. I got some very high quality plastic magnetic impeller water pumps for $40 each, such a deal!. There's a Chinese tool store called Harbor Freight that has a biggish decorative fountain pump for about $12 each that should do the job. You might have to get a little creative with it to make it work, but that should be no problem, SYAAT.

The last bit is kind of a sticky wicket...

In the beginning there were many substances that were recognized to have value as refrigerant. They were all naturally occurring organic substances, such as ammonial, sulfur dioxide, propane, butane, and many more. These organic refrigerant did have the problem that if a leak occurred, in a confine space, there was a potential of fire, explosion or death from inhalation of a poisonous gas. As far as I can determine, these serious problems were rare.

The other problem was that corporations could not patent naturally occuring substances, so their profit potential was limited.

The fear of accidents happening through the use of organic refrigerant was used as a wedge to drive through legislation that mandated the use of custom-created synthetic (CFC & HCFC, like R-12 & R-22) refrigerants, and the prohibition of organic refrigerants. The profits resulting from this change were almost beyond comprehension.

Unfortunately, these synthetic refrigerants causes destruction of the ozone layer, which protects us from excess high-energy solar radiation. and makes life as we know it possible.

To fix this, new synthetic refrigerants (FC and HFC, like R-134a and R-401a) were created. While these new refrigerants have solved the ozone problem, they are amongst the most powerful and longest lasting of all global warming gasses, and are part of the cause of rapidly increasing planetary heating.

Common sense, a sense of ethics, and a wish to survive, would dictate that these gasses should be eliminated immediately, and that we should return to the use of organic refrigerants. After all, the technology is very well understood.

So, the sticky wicket is this: that you either obey the law, or you destroy the planet... which to choose?

Additionally. many refrigerants, R-12, R-22, R410a, etc. are illegal to use unless you are a licensed HVAC tech. Obviously this is a creation of a trade lobby, to protect their profit turf.

So in the USA (home of the brave, land of the free) our choices have been walled off by trade groups and corporations.

I think that R-134a is legal to buy and use, you can get it from auto parts stores in most states.

There are other substances that can be used as refrigerants that are not legal in the US, but are legal in other parts of the world. For instance, I have found some 'over-clockers' forums where German children are re-configuring AC Units to function as powerful chillers for their video game consoles, allowing them to play faster. I understand that they are using Propane (AKA: barbecue gas) as a refrigerant, because it is cheap and available. It is also compatible with R-22 lubricants.

So, I would not recommend that anyone break their local laws.

Since this blog is hosted on the Internet, it has an international audience.

Readers from all counties should use this information as part of their total information mix, should fully understand the personal safety, technical, legal, environmental and ethical implications of their actions and decide well.

BTW, you might be able to get a local HVAC guy to put on a demo for the class that would result in a functioning heat pump, SYAAT.

Best Regards,

-AC_Hacker

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[Nikolai]

AC_Hacker:

Here's why I'm asking: My goal is to achieve a system with maximum heat gain, so I came up with the idea to remove the second stage of heat exchange too, and to get so-called "direct-direct system".

I have no knowledge about the need for the return of oil in the compressor (in details), but I suppose that if I could achieve that the compressor is at lowest point in system.

I think it would be main problem, but if we could resolve it we could get one very efficient system.



// on second picture should be shown a water running trough underground heating, not refrigerant

[Xringer]

Okay.. Propane is R-290. And it looks like a lot of work has been done on that gas..


Interesting reading.

http://www.icarma.org/green/document...nal-030404.pdf

[AC_Hacker]

Originally Posted by Nikolai

AC_Hacker:
Here's why I'm asking: My goal is to achieve a system with maximum heat gain, so I came up with the idea to remove the second stage of heat exchange too, and to get so-called "direct-direct system".

I have no knowledge about the need for the return of oil in the compressor (in details), but I suppose that if I could achieve that the compressor is at lowest point in system.

I think it would be main problem, but if we could resolve it we could get one very efficient system.

Nikolai,

OK, pictures really help...

I think the DX systems save 8% to 10% per heat exchanger, so your thinking is along a good line.

I had thought about just such a system, with copper in the concrete floor and in the ground.

The advantages of such a system are obvious.

You might want to do some patent reasearch. There is a web site called Free Patents Online that requires you to register, but then gives you access to a huge number of patents, so you can see what kind of work has been done before. It's not legal to manufacture something that has been patented, but it is legal to build your own. One of the really good things about this patent search is that you can see what previous patents were referenced by a particular patent, and you can track ideas backward through time. Very interesting...

If you can solve the problems associated with this approach, you win the prize!

One of my research areas has been hydronic radiant floors. There was a mass-housing development right after World War II called Levettown, in New York state. Many houses were built on the same pattern for cost saving. The houses were heated with hydronic floors. As I recall, steel pipe was used. Steel has just about the same coefficient of thermal expansion as concrete, which is favorable. Unfortunately, over time, in many of the houses it started to leak. I'm not sure what the corrosive potential of concrete is on copper, but it is something you should look into.

I also considered the heat carrying capacity of refrigerant over long distances, like a serpintine path in a concrete floor. I wasn't able to locate information on that and I also didn't do any experiments to try to determine it. But I do know that water is a very good heat carrier, and the diameter of the water-carrying tubing in concrete is large, compared to what would be likely for refrigerant. But it could be engineered to work.

I 'm still not totally satisfied with how I'm going to do the hydronic floor in my house. My house is old, and the foundation is not up to modern standards. I looked into light weight aggregates for concrete, but came to see that lighter weight usually means lower thermal conductivity. I did some work on this issue this summer and will report on it later in this blog. A thin concrete floor with many closely-spaced copper tubes would be a bit expensive, but is very attractive.

The advantage of polyethyene pipe in the ground and PEX pipe in the floor is that it is relatively inexpensive, essentially leak-proof and has a very long life. It doesn't have a high index of thermal transfer like copper, but the medium from which it draws heat (earth) and to which it releases heat (concrete) is low and very large, so having an excellent conductor like copper in earth or copper in concrete doesn't, by itself, yield a large advantage. But eliminating heat exchanger losses is where the advantage is.

I wish you the best of luck in your work, you have identified some signifigant areas of higher efficiency and are addressing very important problems to be solved!

Best regards,

-AC_Hacker

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[AC_Hacker]

Originally Posted by Xringer

Okay.. Propane is R-290. And it looks like a lot of work has been done on that gas..

Interesting reading.

http://www.icarma.org/green/document...nal-030404.pdf

> Interesting reading.

Boy, I'll say!

Good find.

Regards,

-AC_Hacker

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[NiHaoMike]

Most window A/Cs use R-22. There is Enviro-Safe 22a which is a HFC mixture that replaces R-22.
22a Refrigerant Details and Online Ordering at Enviro-Safe, Inc
I have actually used it in a central A/C and it works well. The TXV needs to be adjusted slightly for optimum efficiency.

[AC_Hacker]

Originally Posted by NiHaoMike

Most window A/Cs use R-22.

You may want to update your database on that info...

Here's a page of info regarding the Montreal Protocol and R-410A, R-134a, R-22, etc.

http://www.epatest.com/R410A/manual/manual.jsp#po

But it's good to know of other refrigerant outlets.

Curious how they can call this stuff "Enviro Safe" when it's global warming dangers are so well documented.

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Here's a link to a mega-plex of refrigeration-related "MATERIAL SAFETY DATA SHEETS".

It's good to be informed.

Regards,

-AC_Hacker

[Daox]

What did you use, and how did you insulate the tubing that is in the troughs?

[AC_Hacker]

Originally Posted by Daox

What did you use, and how did you insulate the tubing that is in the troughs?

I used 'pre-split' plastic foam water pipe insulation. In most cases, I didn't open the shallow cut in the foam that was the 'pre-split' feature, I just slid the foam over the pipe and cinched the ends with nylon tie wraps.

There wasn't any science to it, just a hunch that it would help.

Regards,

-AC_Hacker