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Old 02-24-16, 05:51 PM   #1861
Mobile Master Tech
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Hello All,

I've updated my heat storage/GSHP thread with some helpful insights and am asking for a little Phase Change Material help in post #15 of this thread:

http://ecorenovator.org/forum/geothe...aste-heat.html

Thanks in advance!
The MMT

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Old 02-24-16, 08:33 PM   #1862
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Last edited by jeff5may; 03-14-16 at 08:20 PM.. Reason: off topic babble bish
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Old 02-25-16, 02:50 AM   #1863
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That's interesting information. FWIW The refrigerant in my system is R407C. I have no idea whether that is in any way better or worse.

I may have given the wrong idea when I said that my system just about copes in the coldest conditions. What I mean is that when it is very cold out the heat pump has to work at the limit of how much heat it can extract from the ground. I normally keep its additional resistive heating turned off, and let the GSHP run hard. If that is not sufficient I do turn on the resistive heating function of the GSHP. I don't sit in the cold adding another horse hair shirt and letting the house grow cold.
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Old 02-26-16, 06:29 PM   #1864
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Deleted at AC's request.
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Old 02-27-16, 05:56 PM   #1865
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Quote:
Originally Posted by Mobile Master Tech View Post
Slightly off topic for small scale applications, but here is some interesting historical background on soda locomotives and ammonia motors, which then has interesting bearing on using low exergy waste heat for useful purposes via the Kalina Cycle.

Enlightening!
This is not slightly off topic, it is completely off topic. This thread is here for people who are interested in building their own Homemade Heat Pump systems. There is no other place on the Internet where this topic is discussed. You are diluting and abusing a very valuable resource.

Please delete your post and start another thread if you think it is important.

Sincerely,

-AC_Hacker
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Old 02-29-16, 03:10 PM   #1866
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Sorry AC,

We have all discussed numerous refrigerants and heat exchange/storage methods in great depth in this thread. I thought a one-liner on thinking outside the box in this area might have been helpful.

Part of the reason your thread has nearly 1 million views (congratulations!) is because of this willingness to discuss related topics.

Will delete post!
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Old 02-29-16, 11:29 PM   #1867
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Quote:
Originally Posted by Mobile Master Tech View Post
Part of the reason your thread has nearly 1 million views (congratulations!) is because of this willingness to discuss related topics.
Thanks for deleting. I have spoken to other people who have gone off-topic here, who have less integrity than you do, and their off-topic drifting is, like highway litter, still here.

But I disagree with you about related topics being a key to the thread's success.

The name of the thread, "Homemade Heat Pump Manifesto," is precisely descriptive. It's name is exactly what it is about. It is for people who have already made their mind up to make a homemade heat pump, hopefully to use in a heating or cooling application.

This thread is successful because it is strictly about a topic that is not being openly discussed at length any where else on the web, namely how to successfully build a homemade heat pump. There are related issues, such as loop field design and construction, heat exchanger discussion, etc. that also apply.

I want to insure that people who come here get what they are looking for, and not a swamp of free-association.

So far it is working. The 'Manifesto' is not only nearing a million hits, it has been the top ranking Web Address when anyone Googles, "Homemade Heat Pump Manifesto", since the first week of its existence.

I'm just trying to keep it clean.

Best,

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Old 03-01-16, 02:18 AM   #1868
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Old 03-02-16, 05:25 PM   #1869
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I'm posting here because this thread is more relevant concerning getting higher temps from a GSHP efficiently and Mike's comments HERE:

I answered most comments already in the hydronic floor thread but wanted to elaborate concerning limits of the refrigerant and equipment.

Not that we are going to, but you actually can use a refrigerant in its supercritical region as described HERE for CO2. Many new systems are doing this, including most upcoming cars.

The refrigerant doesn't liquefy, so the condenser is thus a "gas cooler" and the expansion valve is now a controlled High Pressure Expansion Device. Despite the fact CO2 is not as efficient as a refrigerant and has ludicrous operating pressures, it is still being used effectively. Where there is a will, there is a way. This tidbit and my deleted post aren't meant to dilute the intent of the Manifesto but rather to encourage out of the box thinking as we hack common equipment and think of new ways to store and use energy from it. We don't recognize that we don't know something if we haven't been exposed to it. AC, you said correctly that hackers and experimenters are often more on the cutting edge of what's possible than the industry as a whole is.

I don't plan on using a refrigerant near it's critical temp, such as R410a, in my GSHP. Most likely I will use R290 with a brazed plate condenser and short piping to minimize the refrigerant amount, since about 60% of the refrigerant in a system is in the condenser when running.

HERE is a plain English guide helping with refrigerant and equipment selection. Most important: compressor inlet temps up to 90F and discharge temps up to 250F are ok as long as you consider the compressor envelope, especially compressor cooling and pressure ratio. FYI, the units we are likely to hack from are the high temp/pressure variety, not medium or low.

You don't want to maintain operation outside the compressor's envelope with the refrigerant in question as explained HERE. "Pull down" temporary operation can vary outside the envelope a bit but has to be kept in check if excursions are extreme.

The pressure ratio and thus efficiency is mainly affected by the temperature spread, not the actual temperature. COP falls off at a pressure ratio greater than 3.5 and most compressors max out around 7.5. Newer Copeland scroll compressors optimized for heating and DHW production can go up to 9.5, and even up to 11.5 with vapor injection.

Pressure ratios are graphed in a straight line on envelopes. I might have to limit flow if the PV panel collectors got especially warm, but my geo/solar/PV/GSHP proposed system temps of approx. 73F source and 140F output are within the envelopes of several compressors. Best of all, they are at a very efficient pressure ratio of 2.8, the same pressure ratio and therefore approximate efficiency as 104F output from a 41F source.
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Old 03-03-16, 12:28 AM   #1870
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I've been doing research to understand the potential risk of flammable refrigerants for our heat pumps, such as R290 we've discussed here. The automotive industry is phasing in R1234yf which is mildly flammable. Daimler originally said they wouldn't use it in their cars because they could repeat fires and a corrosive acid cloud during their testing. Other manufacturers were satisfied with their tests, the SAE and others decided the risk was so small even airbags posed much more risk, and Daimler has since backed down.

So just how much extra risk does a flammable refrigerant pose? A small leak will never amount to a fire risk. A catastrophic leak even with a nonflammable refrigerant still has a fire risk because of the aerosolized oil cloud that escapes with the refrigerant. I found a few documented cases of oil fires happening this way, including one in the report below. Anyone who has ever loosened (accidentally) a gauge set hose that had not been evacuated knows the cloud I mean.

I've personally witnessed an AC system fire with a flammable refrigerant, but it was uncertain whether the refrigerant was to blame. The disintegrating compressor caused a hot spot and the system was full of air instead of all refrigerant.

THIS report was done after Australia allowed flammable refrigerants in vehicles and many in the USA put flammable refrigerants such as OZ12 in their R12 vehicle systems.

They found that the average automotive charge of R290 (most have 1 to 2 tons cooling capacity) was about 200g, less than half what you are carrying around in that green cylinder for your portable grill. They compared the number of predicted refrigerant fires (49 per year in Australia alone) to the number of actual fires: zero in both countries through multiple years.

They found that small leaks were easier to detect and drivers would address them because flammable refrigerants have odorants. They found that even if 200g is released in a catastrophic 1 second release, the gas is hard to ignite due to its velocity and concentration (ever try to light a torch while the valve is wide open?) and it is diluted below the level of flammability within 10 seconds. Even though mobile systems, unlike stationary systems, can be catastrophically damaged in a crash actual risks are clearly much lower than expected and far lower than many other things we should worry about.

Nations are now approving flammable refrigerants in larger quantities, allowing "those who must comply with the IBC" more equipment choices. Gasoline is more dangerous than R290 as I detailed IN THIS POST. The 315 cubic feet I described is the equivalent volume of a cramped 5x8' equipment room, not a large room or basement.

We've lived with gasoline's extensive use and spillage for a century and think nothing of putting a car, or a lawnmower, or a gas can in the garage. Me? I'll take the most effective refrigerant. The risks of flammable refrigerants are small and overblown.

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