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Old 02-09-12, 07:36 AM   #1
mrd
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Default A better heat pump

I consider a traditional heat pump setup to be a split system with the compressor outdoors, a heat exchanger indoors, and refrigerant running between the two. I wonder if a reverse-cycle chiller isn't a better system?

First, it maintains a factory seal of the refrigerant in the outdoor unit. Faulty installations only result in leaked water, not refrigerant. Better for environment, check. Safer install failures, check. Cheaper leak detection and correction, check. This would also make old, discarded units more useful to impoverished areas.

Second, the system can easily be adapted to radiant floor heating, which permits higher efficiencies due to the lower temps involved.

Third, it can be easily adapted to heat thermal storage mass for emergencies, off-peak electric advantages, or possibly excess heat for an off-grid pv-powered system.

So why are these systems so uncommon? It seems the big expense might just be the additional heat exchanger in the outdoor unit, but the pros seem to outweigh that small cost.

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Old 02-09-12, 08:38 AM   #2
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Quote:
Originally Posted by mrd View Post
the pros seem to outweigh that small cost.
This thread is misplaced, it should go in the 'Geothermal' section. I know that Geothermal might seem a bit misnamed, but all of the vapor-compression stuff goes there.

It would be useful if you could post a picture, or a drawing, or a diagram of a reverse cycle chiller. This would help those of us who may think that Reverse Cycle Chiller is really just a Heat Pump under a different name.

* * *

And have you seen the excellent work that Acuario (AKA: Nigel) has done in converting air conditioners into water heating machines, that he is using to heat his swimming pool in Spain, and now his house, too. His work can be found in the Geothermal section, in a thread called, "Air Source Heat Pump (ASHP) Hacks & Mods".

He took existing air conditioners, re-arranged the refrigerant flow a bit, and built a refrigerant-to-water heat exchanger out of copper tubing and ABS waste pipe. He has good descriptions, and useful photos.

Also, please note that he switched his machines from R-22 to a hydrocarbon refrigerant... better for the environment.

Overall, a very impressive accomplishment.

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Old 02-10-12, 10:17 AM   #3
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A chiller is a system that cools a fluid. A reverse-cycle chiller can also heat the fluid. See wikipedia:
Chiller - Wikipedia, the free encyclopedia

I consider the main distinction being that a fluid, typically water, is used to transfer the heat to and from the system. A typical 'split system' uses refrigerant. Hence all the benefits I described above.

I don't have a diagram, and I believe there are a variety of configurations. My original point was to highlight all of the advantages of a commercial product with a sealed vapor-compression refrigerant circuit and open water connections. From the perspective of a hacker or DIY-er, it doesn't much matter as one can build any kind of system they please

Acuario's thread here:
http://ecorenovator.org/forum/geothe...heat-pump.html
references a Danfoss DHP-A, which is very similar to what I've described. This system takes the isolation of the vapor-compression stage one step further, and provides a plumbable fluid connection for both sides of the heat equation.
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Old 02-10-12, 11:42 AM   #4
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Originally Posted by mrd View Post
I consider the main distinction being that a fluid, typically water, is used to transfer the heat to and from the system. A typical 'split system' uses refrigerant. Hence all the benefits I described above.
OK, I get it... I would describe it as an air source heat pump with a refrigerant-to-water heat exchanger located in the outdoor unit.

Yeah, this is just what Acuario has built.

There is a Japanese/European designed unit that is paralyzingly expensive that fits this description called the Daikin Altherma (monobloc configuration).


I even went to a product introduction seminar and learned all about it. They have done their homework on these units. But when the entry-level price is about $18,000, only the wealthy can afford to save money.

Quote:
Originally Posted by mrd View Post
From the perspective of a hacker or DIY-er, it doesn't much matter as one can build any kind of system they please...
Yeah, hacking/DIY is what this forum is all about, and that is why I am here.

In fact, I have come to realize that when I think and speak about various heat pump and air conditioning machines, I tend to think in structural terms rather than in product terms or commercial terms, since it better assists me in understanding so that I can rip apart and re-structure these assemblies to suit my purposes.

Product loyalty bad, re-purposing good!

I am very intrigued by the possibility of getting an inverter mini-split outdoor unit and hacking it so that it goes refrigerant-to-water. This would allow you to use it in a radiant floor configuration. There has been a lot of development in mini-splits and their efficiency is very high now... getting close to GSHP standards. The inverter technology seems to be key. It would be ever so useful if someone could 'break the code' on inverter technology to the point that an ordinary hacker could re-purpose one of these babies for use in low-temperature hydronic heating.

This would be a very favorable combination of technologies, as low-temperature hydronic heating would lower the 'temperature lift' requirements on an already very efficient heat pump and increase its efficiency even further. ASHPs lose efficiency as they heat higher. R-22 units had a tough time getting above 120F, R-410a goes a bit higher... but the lower you go in required temp, the higher the efficiency, and a few degrees lower in temperature, means a large increase in efficiency over time.

In fact, it was in anticipation of and to accommodate such a development that I started the "Air Source Heat Pump (ASHP) Hacks & Mods" thread. This was before Acuario posted his work... so, because of his posts we are part way there, but we have a way to go yet.

I recently acquired (yesterday) a 2 Ton ASHP, not a mini-split like I would like to work with, but a COP 2 R-22 York, for $75. It has never been put into use, still has the un-brazed refrigerant fittings, and is reputed to have a full charge of refrigerant inside.

My thinking is to run the refrigerant lines just inside the house and make the refrigerant-to-water exchange happen there. This would keep the water part of the circuit safe from freezing, and easily get me into hydronic heating.

So, do I have a reverse cycle chiller? I don't know, but I certainly have a hell of a project on my hands!

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Old 02-10-12, 01:00 PM   #5
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Sounds like a very fun project

In regard to hacking an inverter-based system, I suppose the targets would be the compressor and the digital expansion valves. So first you need a "brain" to run the system, maybe an arduino or a pic or whatever is desired. Then you need to interface it with the compressor and valves. The thermistors and what not can be ignored and use your own if that's easier, rather than reverse engineering them as well.

The compressor may have its own dedicated hardware controller, as I'd imagine the compressor manufacturer wants to sell its unit to other vendors, and the simplest way would be to dedicate a cheap controller and provide a simple interface for controlling the compressor. In that case, you need to decode the communication protocol to that controller. This is probably the most difficult hurdle. Maybe something here..?
Inverter Control Module : Hitachi Appliances, Inc.

The valves should be really simple to decode, I think a youtube video described them as acting like stepper motors. They probably just have a reset command and positioning commands.

Once you have that down, I'd start the software with safeguards to protect the compressor. Then write up a test suite to go through various possible control schemes, and use sensors to measure efficiencies of each. Developing good theories and automating testing here will get the setup optimized quickly. Sensors can be integrated as desired to meet theoretical operation..
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Old 02-10-12, 02:46 PM   #6
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Quote:
Originally Posted by mrd View Post
Sounds like a very fun project

In regard to hacking an inverter-based system, I suppose the targets would be the compressor and the digital expansion valves. So first you need a "brain" to run the system, maybe an arduino or a pic or whatever is desired. Then you need to interface it with the compressor and valves. The thermistors and what not can be ignored and use your own if that's easier, rather than reverse engineering them as well.

The compressor may have its own dedicated hardware controller, as I'd imagine the compressor manufacturer wants to sell its unit to other vendors, and the simplest way would be to dedicate a cheap controller and provide a simple interface for controlling the compressor. In that case, you need to decode the communication protocol to that controller. This is probably the most difficult hurdle. Maybe something here..?
Inverter Control Module : Hitachi Appliances, Inc.

The valves should be really simple to decode, I think a youtube video described them as acting like stepper motors. They probably just have a reset command and positioning commands.

Once you have that down, I'd start the software with safeguards to protect the compressor. Then write up a test suite to go through various possible control schemes, and use sensors to measure efficiencies of each. Developing good theories and automating testing here will get the setup optimized quickly. Sensors can be integrated as desired to meet theoretical operation..
Maybe it wouldn't be required to completely re-engineer the control system of the inverter type heat pumps. They do seem to do a pretty good job as they are.

I'm thinking that instead, it might be possible to build a refrigerant-to-water heat exchanger and pump that can convince the outdoor unit that it is actually a factory-built air handler.

The existing air-handler (AKA: indoor unit) has:
  • An air flow redirecting vane & motor system (useless)
  • A variable-speed air circulating fan (useful... there are available variable-speed water circulation pumps that respond to external control)
  • An IR receiver module (useful with the IR remote control)
  • Air filtration system (useless)

I don't know if there is any intelligence in the air-handler or not. I do know that there are four wires that connect it to the outdoor unit. I assume that two are power...

This approach seems much more direct, and likely to succeed. In addition, it probably would apply to most inverter heat pumps and require little modification.

So, if you're really itching to do an Arduino project, maybe it could do some arbitration between the hydronic unit and whatever part of the system is sending signals, and perhaps looking for status signals.

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Old 02-15-12, 10:25 AM   #7
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NOTE - mrd posted a very useful document that explains the theory of operation of an inverter-type Fujitsu mini-split in the 'R290' thread, but this discussion thread seems to be an ideal place for this information.

http://www.goductless.com/v/vspfiles...lq_service.pdf

This kind of information is vital to being able to succeed in re-purposing an inverter mini-split (air-in-air-out) into a highly efficient machine for heating water that could be used for hydronic radiant floor heating.

...now, if we can just get one for the AOU12RLS, (which is a 12,000 BTU cooling / 16,000 BTU heating unit, and also has the highest HSPF) then we'd really have something.

[EDIT] here is URL (from Internet archive) for the above unit:

http://web.archive.org/web/201010071...lq_serivce.pdf

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Old 02-15-12, 05:00 PM   #8
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Here is the engineering data on Altherma I think this is the Low temp unit, They are making a HT as a direct replacement for boilers. The hydrobox concept is very simple.
The smallest unit produces 17.16 kbtu/hr @FLA of 17amps, so maybe a 1.5-2 ton compressor
Thoughts?
trying to hack a day
http://www.daikinac.com/DOC/DACA-EED...ing%20Data.pdf

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Old 02-15-12, 07:07 PM   #9
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Thoughts?
Not quite sure what you have in mind here...

I think this is a very well designed machine.

It's also a very expensive machine.

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Old 02-23-12, 09:04 AM   #10
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ACH,
is there a way to post PDF files here? I found some info on the Daikin from REHVA Journal 9/2011, which might be informative on how they work, and would like to share
k

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