Any experience with a DC-powered mini-split air conditioner?

[nwdiver]

...getting accurater refrigerant charge loaded takes special skills and a borrowed or rented tool/equipment if expected EER rating is to be achived.

The tolerance for refrigerant loading would have to be very wide for it to be able to operate in cooling and heating mode. When it's cooling the line set has liquid in it. When it's heating it has gas in it. So the volume of refrigerant will shift A LOT depending on mode. Most mini-splits I've seen come with a certain pre-charge and that charge is good for up to usually ~115' or so. I doubt there's any benefit to efficiency to removing some refrigerant if you're only running 20' of line.

[neweclipse]

The tolerance for refrigerant loading would have to be very wide for it to be able to operate in cooling and heating mode. When it's cooling the line set has liquid in it. When it's heating it has gas in it. So the volume of refrigerant will shift A LOT depending on mode. Most mini-splits I've seen come with a certain pre-charge and that charge is good for up to usually ~115' or so. I doubt there's any benefit to efficiency to removing some refrigerant if you're only running 20' of line.

Yeah, but, your way of thinking leaves out the all important 3 way reversing valve...otherwise you might of had it correct...
Liquid line always has liquid in it and gaseous line always has gas in it when in operation.

[nwdiver]

Yeah, but, your way of thinking leaves out the all important 3 way reversing valve...otherwise you might of had it correct...
Liquid line always has liquid in it and gaseous line always has gas in it when in operation.

Even in heating mode? I think the liquid line is too warm for liquid refrigerant in heating mode. Pretty sure the phase change happens in the condenser when in heating mode.

But... even beyond that... there would need to be an allowance for how many indoor units are in operation. The shutoff valves for the indoor unit is located in the condenser so the amount of liquid refrigerant in lines would vary depending on how many are in use. The amount of refrigerant in the unit doesn't need to be exact... just enough for operation. I've DIY'd 4 mini-splits. I just used to the included refrigerant and they're all doing great. It's super-easy. You just need a vacuum pump and a gauge set which I think you can find now for <$400.

[neweclipse]

Okay, Thanks for adding your success stories,

Wouldn't the phase change start at the expansion valve outlet near the reversing valve and the compressor?
The reversing valve changes the role of condenser and evaporator back and forth...

[nwdiver]

The reversing valve changes the role of condenser and evaporator back and forth...

Exactly. So the 'right' amount of refrigerant needed is going to vary A LOT depending how how many indoor units are in use and whether it's cooling or heating => 'precision' on how much refrigerant is in the unit is irrelevant... you just need to have enough.

If a unit comes pre-charged for up to 110' of line and your lines are only 10' there's no efficiency benefit to removing refrigerant.

[neweclipse]

Not disagreeing with you about refrigerant volumes being precise, in these pre-charged units, don't care to argue that with you.
I do take exception with your misinformation in refrigerant circuits...don't claim your victory on misinformation there.

[nwdiver]

Not disagreeing with you about refrigerant volumes being precise, in these pre-charged units, don't care to argue that with you.
I do take exception with your misinformation in refrigerant circuits...don't claim your victory on misinformation there.

Wrong terminology. I'm not a HVAC tech. When I said 'condenser' I meant 'outdoor unit'; Am I correct that when heating the phase change occurs in the outdoor unit? Not arguing... just curious.

[bcroe]

I am waiting for an explanation of just how the reversing valve and the rest manage
to turn the system around, with coils and pipes still in place. I could certainly hear
that valve CLANK when my older equipment needed to defrost itself. Not so on the
mini split, though I might have detected cooling when it was set for heat. Bruce Roe

[NochiLife]

Here's a simple yet concise explanation of how a heat pump works: http://www.refrigerationbasics.com/R...eat_pumps1.htm

"Central" heat pumps use a reversing valve as described in the above link (and yes, it does CLANK); I haven't opened a mini-split to see what happens in there--but I'm pretty sure it doesn't run the compressor backwards for heat mode (like I read someone insisting elsewhere. Wonder if their car runs the internal combustion engine backwards when they want to reverse, too!)

[bcroe]

"Central" heat pumps use a reversing valve as described in the above link (and yes, it does CLANK); I haven't opened a mini-split to see what happens in there--but I'm pretty sure it doesn't run the compressor backwards for heat mode (like I read someone insisting elsewhere. Wonder if their car runs the internal combustion engine backwards when they want to reverse, too!)

Thanks, more study material. If that compressor is 3 phase, reversing it would be easy. There
have been vehicles built that reverse their engines to back up, starting with locomotives.
Bruce Roe

[neweclipse]

Nice detailed illustrations there. Perhaps they help to see that in either mode that system volumes are fixed and equal...no gross difference in system volume when mode cycles.

Liquid lines always move liquid and gas or vapor lines always move gas...reversing valve handles the mode cycles..compressor within never changes flow direction.

[nwdiver]

Nice detailed illustrations there. Perhaps they help to see that in either mode that system volumes are fixed and equal...no gross difference in system volume when mode cycles.

Thank you. That is informative. Answers my question. When in heating mode there is subcooled gas in the indoor unit but no phase change and the only place liquid exists is in the outdoor unit.

There's going to be a HUGE change in volume when the system cycles. The indoor coil includes the volume of the lineset.

[NochiLife]

Thank you. That is informative. Answers my question. When in heating mode there is subcooled gas in the indoor unit but no phase change and the only place liquid exists is in the outdoor unit.

There's going to be a HUGE change in volume when the system cycles. The indoor coil includes the volume of the lineset.

Afraid I'm not getting your point. It's not possible for refrigerant to simply "disappear" one way vs. the other way. When the system starts, pressures on both sides of the compressor will be the same, and no matter which way the refrigerant is directed, it will always have the same amount in the system. You could basically turn a window A/C around in your window (cold air outside, hot air inside) if you want a very crude heat pump--but it won't change the volume of refrigerant in the system.

[nwdiver]

Afraid I'm not getting your point. It's not possible for refrigerant to simply "disappear" one way vs. the other way. When the system starts, pressures on both sides of the compressor will be the same, and no matter which way the refrigerant is directed, it will always have the same amount in the system. You could basically turn a window A/C around in your window (cold air outside, hot air inside) if you want a very crude heat pump--but it won't change the volume of refrigerant in the system.

Yes. Same mass. Different volume. There's more liquid when cooling than heating due to the volume of the line set. If there's more liquid when cooling then there's less volume.

[neweclipse]

Yes. Same mass. Different volume. There's more liquid when cooling than heating due to the volume of the line set. If there's more liquid when cooling then there's less volume.

Might want to get your crayons out and color in on two identical copies the linked illustration...one with cooling circuit, and the other with the heating circuit.

Pipes or their capacities of the line-set are not growing and/or shrinking anywhere...

Smaller line is always pressure liquid, and larger line is always gas suction...The 4 way valve and the TXV (thermal expansion valve) make this so no matter which mode is selected.