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Old 11-22-14, 06:52 PM   #1
jeff5may
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Default homemade mini split

I just had an idea. This could be very easy to accomplish.

A couple of small units could be connected to each other with a lineset so that the compressor in one unit would operate in heating mode and the compressor in the other would operate in cooling mode. For this setup to work, all that would really be necessary would be some check valves.

What do you think?


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Old 11-23-14, 07:15 PM   #2
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Originally Posted by jeff5may View Post
What do you think?
Sounds gloriously straight forward.

A general purpose heat pump controller would tie it all together with a bow.

-AC
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Old 11-23-14, 07:19 PM   #3
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Since the parts list is so low the idea certainly has merit from that stand point.

I am curious if it is possible to plumb two compressors in series for a boost in the heating Btu ?
If it was possible I 'think' it would be a better use of the compressor as any window ac will keep you cool but not many keep you warm.


In short I think AC is readily available were as heat pumps are some what scarce.
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Old 11-23-14, 08:34 PM   #4
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Originally Posted by ecomodded View Post
Since the parts list is so low the idea certainly has merit from that stand point.

I am curious if it is possible to plumb two compressors in series for a boost in the heating Btu ?
If it was possible I 'think' it would be a better use of the compressor as any window ac will keep you cool but not many keep you warm.


In short I think AC is readily available were as heat pumps are some what scarce.
It is not difficult to "reverse cycle" a window a/c unit. You use a "piercing valve", recover the charge, and substitute it with inert gas. You simply switch lines on the compressor (suction line to discharge of compressor, discharge line to suction of compressor), bending or lengthening tubing if necessary, and braze everything back up. Replace the piercing valve with a permanent access valve while you're at it. Pressure test, pull a deep vacuum, and recharge the unit with what you recovered. This will yield you a heater that works well down to about 40-45 degF.

To get into "frost territory", a method must be used to allow the unit to operate in heating and cooling modes. Hot gas defrost is merely "air conditioning" with the outdoor fan not running.

To get more raw BTU's through a system, it is better to plumb two compressors in parallel with each other. The series method requires a "booster" compressor that is rated at a lower compression ratio and higher displacement than the "primary" compressor. usually, some sort of economizer or intercooler is used between the two compressors to desuperheat the intermediate pressure gas before it is run through the second compressor. This is where certain manufacturers have somewhat warped the law of physics, making all manner of grandiose claims about their systems.

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Old 11-23-14, 08:39 PM   #5
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Sounds gloriously straight forward.

A general purpose heat pump controller would tie it all together with a bow.

-AC
I'm working on the defrost control logic and sorting out assignment of onewire sensors as we speak. I posted a rough alpha sketch (on github - see our other thread) that I have working today. It works in heating, cooling, and auto changeover modes as it sits. Please feel free to collaborate. Without a whole lot of help, progress will be slow.

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