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inverter compressor 2
- Thread starter siuli
- Start date
Understanding of the oil pressure at reduced speeds.
Understanding of the loading at different speeds.
Understanding of cooling at different speeds.
Keith Cress
kcress -
Understanding of the loading at different speeds.
Understanding of cooling at different speeds.
Keith Cress
kcress -
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1
- Thread starter
- #6
Actually, the question is that how can i modify a conventional air conditioner into an inverter-controlled air conditioner.
1.Can I use the original compressor of the air conditioner? Or, must I buy an inverter compressor?
2.Actually, how the inverter compressor differ from the conventional compressor? I would like to know more about it, especially in the structural point of view. However, I cannot find related technical materials about them. Can anyone give me some reference materials (for example, web pages, papers, etc)
3.The motors of the conventional air-con cannot provide enough power output for compression of the refrigerant when their operation speeds are reduced by inverters. Is this statement true? The motors of the inverter compressor maintain the same level power output for compression of the refrigerant when their operation speeds are reduced by inverters. Is this statement true? If they are true, can anyone explain to me how the compressor maintains its power for compression, even its operation speed is reduced by inverter?
4.If I connect the original compressor to the inverter and (of course with a modification of the circuit board) then control it by PWM method, is it possible? Would this performance be better than using an inverter compressor?
5.One more question about the digital scroll compressor. When the fixed-scroll is "fixed", the compressor compresses the refrigerant. When the fixed-scroll is "not fixed", the compressor would not compress the refrigerant. Is this one kind of PWM control? Why people achieve this PWM control by hardware(compress)? Why don't we just control it by PWM signals? I mean that controlling the input signals by PWM is much simple than inventing a hardware (compressor) to work in PWM way.
Thank you very much.
1.Can I use the original compressor of the air conditioner? Or, must I buy an inverter compressor?
2.Actually, how the inverter compressor differ from the conventional compressor? I would like to know more about it, especially in the structural point of view. However, I cannot find related technical materials about them. Can anyone give me some reference materials (for example, web pages, papers, etc)
3.The motors of the conventional air-con cannot provide enough power output for compression of the refrigerant when their operation speeds are reduced by inverters. Is this statement true? The motors of the inverter compressor maintain the same level power output for compression of the refrigerant when their operation speeds are reduced by inverters. Is this statement true? If they are true, can anyone explain to me how the compressor maintains its power for compression, even its operation speed is reduced by inverter?
4.If I connect the original compressor to the inverter and (of course with a modification of the circuit board) then control it by PWM method, is it possible? Would this performance be better than using an inverter compressor?
5.One more question about the digital scroll compressor. When the fixed-scroll is "fixed", the compressor compresses the refrigerant. When the fixed-scroll is "not fixed", the compressor would not compress the refrigerant. Is this one kind of PWM control? Why people achieve this PWM control by hardware(compress)? Why don't we just control it by PWM signals? I mean that controlling the input signals by PWM is much simple than inventing a hardware (compressor) to work in PWM way.
Thank you very much.
- Thread starter
- #7
I want to have some modification to the question 3.
3.The motors of the conventional air-con cannot provide enough power output for compression of the refrigerant to the level that can reject required amount of heat in the condenser when their operation speeds are reduced by inverters. Is this statement true? The motors of the inverter compressor maintain the same level power output for compression of the refrigerant to the level that can reject required amount of heat in the condenser when their operation speeds are reduced by inverters. Is this statement true? If they are true, can anyone explain to me how the compressor maintains its power for compression, even its operation speed is reduced by inverter?
3.The motors of the conventional air-con cannot provide enough power output for compression of the refrigerant to the level that can reject required amount of heat in the condenser when their operation speeds are reduced by inverters. Is this statement true? The motors of the inverter compressor maintain the same level power output for compression of the refrigerant to the level that can reject required amount of heat in the condenser when their operation speeds are reduced by inverters. Is this statement true? If they are true, can anyone explain to me how the compressor maintains its power for compression, even its operation speed is reduced by inverter?
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1
- #9
MikeHalloran
Mechanical
The device you are calling an inverter is a VFD, which includes an inverter, and other stuff.
You seem to be asking if it's possible to modulate the capacity of a generic air conditioner with a VFD.
Generic air conditioners use a small piston compressor driven by a PSC motor, with everything except the capacitors hermetically sealed inside a steel can.
Generic air conditioners also typically include a double-shaft PSC motor that drives both internal and external fans.
Some, not all, VFDs are capable of driving PSC motors.
The air conditioner may modulate its capacity as the apparent line frequency changes, a little. It may not respond linearly. The PSC motors may not care for frequencies other than those for which their quadrature capacitor was tuned.
You may be able to modulate the capacity, just enough to say that you can, but not enough to be useful. Efficiency will not improve with operation off design conditions.
You are even less likely to be satisfied using PWM based modulation, which will basically just reduce motor torque until they slow down, overheat and/or stall.
Keep a fire extinguisher handy.
Inquiring by stating a complex postulate and then asking if it's true is a bizarre method. Is this statement true?
Mike Halloran
Pembroke Pines, FL, USA
You seem to be asking if it's possible to modulate the capacity of a generic air conditioner with a VFD.
Generic air conditioners use a small piston compressor driven by a PSC motor, with everything except the capacitors hermetically sealed inside a steel can.
Generic air conditioners also typically include a double-shaft PSC motor that drives both internal and external fans.
Some, not all, VFDs are capable of driving PSC motors.
The air conditioner may modulate its capacity as the apparent line frequency changes, a little. It may not respond linearly. The PSC motors may not care for frequencies other than those for which their quadrature capacitor was tuned.
You may be able to modulate the capacity, just enough to say that you can, but not enough to be useful. Efficiency will not improve with operation off design conditions.
You are even less likely to be satisfied using PWM based modulation, which will basically just reduce motor torque until they slow down, overheat and/or stall.
Keep a fire extinguisher handy.
Inquiring by stating a complex postulate and then asking if it's true is a bizarre method. Is this statement true?
Mike Halloran
Pembroke Pines, FL, USA
- Thread starter
- #10
I hope that I do not miss-understand your points.
Do you mean that I cannot regulate the power consumption and work load of the PSC motor and thus the compressor, even I vary the input frequency, current and voltage by using VFD?
Do you mean that PWM is used to regulate the torque of the motor, rather than regulate the work load and power consumption of the compressor?
How does the digital scroll compressor save the energy? It seems to work in the way of PWM.
Sorry, I am still confused.
Do you mean that I cannot regulate the power consumption and work load of the PSC motor and thus the compressor, even I vary the input frequency, current and voltage by using VFD?
Do you mean that PWM is used to regulate the torque of the motor, rather than regulate the work load and power consumption of the compressor?
How does the digital scroll compressor save the energy? It seems to work in the way of PWM.
Sorry, I am still confused.
- Moderator
- #11
MikeHalloran
Mechanical
>>>Do you mean that I cannot regulate the power consumption and work load of the PSC motor and thus the compressor, even I vary the input frequency, current and voltage by using VFD?<<<
No. I mean that you _can_ control the speed of a PSC motor by varying the line frequency. I'm not so sure that you can do it to two differen PSC motors connected in parallel with one VFD. That's your first uncertainty. Your second uncertainty is that either of the motors may 'fall out of quadrature' as you drop the line frequency, and either stop, or fail to restart. Additionally, it does not follow that the refrigeration system will scale nicely with compressor speed. Because generic units typically use capillaries instead of expansion valves, it's probable that the high side pressure and temperature will just fall off as the speed comes down a little. As you drop the speed more, the oil distribution may be affected, or there may be other effects that were not anticipated in system design.
>>>Do you mean that PWM is used to regulate the torque of the motor, rather than regulate the work load and power consumption of the compressor?<<<
"Regulate" is the wrong word here. PWM on AC just steals part of every cycle, which reduces motor torque. It also introduces nonsinusoidal waveforms that may manifest as heat or acoustic noise. PSC motors typically do not respond in linear, or even usefully predictable, fashion, to PWM power.
>>>How does the digital scroll compressor save the energy? It seems to work in the way of PWM.<<<
I am aware that there is such a thing as a scroll compressor, and that its design is protected by patents and its manufacture is protected by secrecy.
I was not aware that there was such a thing as a variable capacity scroll compressor, or that it is or is not 'digital' in some way, as you alluded.
;----
Now, for the other reason why your idea won't make you rich:
It's already been done.
You can now buy an air conditioning sysem for your house that is otherwise conventional, but includes a variable speed air handler motor. It is actually a three phase AC motor, but it is fed from a special VFD that runs on single phase power and includes both an inverter and some means of measuring the motor current dynamically. ... from which it magically derives an estimate of the load on the motor. ... using which information it is able to both throttle the house airflow down to imperceptible but effective levels, and to tell you when the air filter needs changing.
The compressor is an ordinary high power PSC hermetic unit. The condenser fan motor is an ordinary low speed PSC unit. The compressor cycles on and off, only. There is no variable speed drive on the compressor.
Only the air handler motor is special, and maybe the thermostat, which now may include a filter change indicator.
What you can't buy is replacements for the damn magical energy saving air handler motors, is why I'm on my second such system in ten years. Well, belay that; I did get quotes on motors, which apparently can only be obtained by disassembling a complete air handler. It was easier, and not a whole lot more expensive, to just replace the entire system.
Yes, they do save energy, and lots of it.
Mike Halloran
Pembroke Pines, FL, USA
No. I mean that you _can_ control the speed of a PSC motor by varying the line frequency. I'm not so sure that you can do it to two differen PSC motors connected in parallel with one VFD. That's your first uncertainty. Your second uncertainty is that either of the motors may 'fall out of quadrature' as you drop the line frequency, and either stop, or fail to restart. Additionally, it does not follow that the refrigeration system will scale nicely with compressor speed. Because generic units typically use capillaries instead of expansion valves, it's probable that the high side pressure and temperature will just fall off as the speed comes down a little. As you drop the speed more, the oil distribution may be affected, or there may be other effects that were not anticipated in system design.
>>>Do you mean that PWM is used to regulate the torque of the motor, rather than regulate the work load and power consumption of the compressor?<<<
"Regulate" is the wrong word here. PWM on AC just steals part of every cycle, which reduces motor torque. It also introduces nonsinusoidal waveforms that may manifest as heat or acoustic noise. PSC motors typically do not respond in linear, or even usefully predictable, fashion, to PWM power.
>>>How does the digital scroll compressor save the energy? It seems to work in the way of PWM.<<<
I am aware that there is such a thing as a scroll compressor, and that its design is protected by patents and its manufacture is protected by secrecy.
I was not aware that there was such a thing as a variable capacity scroll compressor, or that it is or is not 'digital' in some way, as you alluded.
;----
Now, for the other reason why your idea won't make you rich:
It's already been done.
You can now buy an air conditioning sysem for your house that is otherwise conventional, but includes a variable speed air handler motor. It is actually a three phase AC motor, but it is fed from a special VFD that runs on single phase power and includes both an inverter and some means of measuring the motor current dynamically. ... from which it magically derives an estimate of the load on the motor. ... using which information it is able to both throttle the house airflow down to imperceptible but effective levels, and to tell you when the air filter needs changing.
The compressor is an ordinary high power PSC hermetic unit. The condenser fan motor is an ordinary low speed PSC unit. The compressor cycles on and off, only. There is no variable speed drive on the compressor.
Only the air handler motor is special, and maybe the thermostat, which now may include a filter change indicator.
What you can't buy is replacements for the damn magical energy saving air handler motors, is why I'm on my second such system in ten years. Well, belay that; I did get quotes on motors, which apparently can only be obtained by disassembling a complete air handler. It was easier, and not a whole lot more expensive, to just replace the entire system.
Yes, they do save energy, and lots of it.
Mike Halloran
Pembroke Pines, FL, USA
- Thread starter
- #13
MikeHalloran
Mechanical
You haven't told us what the 'original' compressor is, so even if there were such a thing as an 'inverter compressor' (there isn't, AFAIK), we couldn't answer the question.
Mike Halloran
Pembroke Pines, FL, USA
Mike Halloran
Pembroke Pines, FL, USA
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