Variable Speed Scroll Compressors?

[mkadyz]

Has anyone worked with, or know of a manufacturer that makes a variable speed compressor for residential applications?

[Crazy4thenucks]

Anything with an Inverter compressor.....Panasonic, LG, Mitusbishi, Sanyo etc...

[SBKold]

I believe any inverter type compressor to be a rotary.

Copeland has a unloader scroll that can modulate all the way to 10% capacity but that is not a variable speed design.

And then there is the Copeland scroll Ultratech which is much more common.

These unload to 67% capacity in low stage.

They are usually coupled with a variable speed indoor unit.

[mchild]

Daikin makes an inverter driven scroll compressor. Other Asian manufacturers of VRF system may also.

[mkadyz]

Sorry for the bad terminology. By compressor I meant just outdoor unit in general. Those brands mentioned earlier all seem to be mini-splits, correct? Are any of the major American manufactures making a variable speed outdoor unit for central air? I know of guys making two stage units, but I haven't seen anything that was fully modulating. Just curious, I was thinking of trying to make my own, if I cant find one.

[SBKold]

Nordyne...see huge thread a few back

[Mike67]

Daikin and Nordyne are the only options I know of. As other posted noted, Nordyne thread exists. It looks like nice stuff, and the Maytag branded products looked to have a better warranty. For Daikin AC do a google search for "Inverter Unitary Ducted System" and Daikin AC. No mater which - these are true systems, which require outdoor component, and indoor component - be it air-handler, or furnace, and system specific T-stat. I was looking into this system for family, but we already had a furnace.

[BaldLoonie]

Nordyne uses a rotary, not a scroll.

[mchild]

Sorry for the bad terminology. By compressor I meant just outdoor unit in general. Those brands mentioned earlier all seem to be mini-splits, correct? Are any of the major American manufactures making a variable speed outdoor unit for central air? I know of guys making two stage units, but I haven't seen anything that was fully modulating. Just curious, I was thinking of trying to make my own, if I cant find one.

The description 'mini-split' seems to get applied to anything made in the Pacific Rim. Mini-split is nothing more that a smaller capacity (thus the phrase 'mini') split system. All of the Asian manufacturers offer theses systems but they also offer full sized split systems from 3 tons up to 100 tons. The larger sized of these system are normally for commercial use only, but the smaller 3, 4, and 5 ton systems are used in residential applications too. Daikin and maybe some of the others have inverter scroll compressors.

No American manufacturer makes such a system. The closest would be the Nordyen product but as BaldLoonie noted it is a rotary compressor.

Good luck on making your own system.

[compressor9000]

Hello, I see you have a problem of not being able to find what you need, and you want to solve the problem. I find this to be venerable, so I will help. Firstly, the variable output copeland scroll compressors work by reducing the pressure between scrolls, and thus, reducing the sealing ability, reducing compression ability. I would surmise that this method is not the most efficient way for "variable compression" due to essentially forcing compressor to essentially be leaky, but it will reduce the workload on compressor nonetheless.

Now for inverters...they are probably going to be more efficient. If you want to make your own, look up "astable multivibrator circuits", there are a few out there. Variablele resistors/capacitors will allow one to tune to desired frequency and speed. Note that there are a few tricks involved, since you will probably need to vary voltage with frequency output. Likely lower frequencies will need higher voltages so that higher voltages can induce faster change in magnetic field, generating more powerful field in rotor, increased speed, and thus, increased back "EMF" so that windings on motor will not draw too much current and overheat. I think a regular square-wave inverter drive is good enough for most motors since they tend to smooth out the voltage once they turn, though starting may be an issue.
I am no expert, but I know some of this stuff because I read up on it so that I could learn about the subway railcars and railroad locomotives with "AC" inverter traction. It is the same thing you need, except you need it for a compressor instead of a railcar. NYC MTA subway cars have three phase motors with "smooth wave" start up to a few MPH, and then they go to square waves. But maybe a good compressor/capacitor combination would do the trick for you.

Note that the astable multivibrators I speak of are different from "AM" type oscillators invented by the great american genius Mr. Armstrong who got cheated out after inventing FM...anyway... It is also perhaps possible to make an "ideal" AC oscillator using Inductor/Capacitor resonance (check LC tank circuits). But you would need larger capacitors and inductors than usual.

I am not completely sure how one canmake a smooth output astable multivibrator, but it most likely involves a large inductor to smooth out the current...

Also, all input going to the oscillators (astable multivibrator and LC tank) has to be DC, so you will need a "bridge rectifier" to convert household AC to DC.

hope this helps... again, I am no expert, but I have studied these subjects before. Would make for an interesting project. Hopefully others here can help, or can verify info. You may need to do your own research too. Maybe you could start a company so that we could buy a window/wall AC made in the USA. I need a replacement for my fedders B chassis, and I do not want to buy chineese junk.(compressor on old fedders (rotary, not legendary fedders piston unit, however) seems to have burnt out after a few evaporator freeze ups. Purchased bullet piercing valve, some gas, and eventually when I burped a bit of gas from AC, burnt smell arose, and some black sludge came out...unit still cools, not as well as it used to, compressor is very hot, and it cuts out due to overheat/overload during hot days.)

[mkadyz]

Thanks for the help guys. Unfortunately I didn't find quite what I was looking for. I think im going to play around with adding a drive to a standard compressor and see what happens. That shouldn't be a problem since controls are what I do (not HVAC though), but I might need some help understanding what the compressor and refrigerant can and can't do. Right now Im thinking maybe a Powerflex 70 drive running off of an old Allen Bradley SLC. Throw in some code to make it run and see what happens. But Ill start a new thread for that. Could be an interesting experiment.

[jbeckham]

as mchild stated, daikin makes an inverter scroll......they use the rotary units in their lighter tonnage applications. i imagine there is less involved in machining the rotary components when compared to a scroll. if you have ever seen one of these rotary comps, you will notice how similar the compression cycle is compared to a scroll.

i imagine diakin, mitsu, fuji, etc. have looked into exactly what you are planning. they just did it about a decade or so ago. i am in no way trying to discourage you from tinkering with your gear. i feel that we're in short supply of that attitude, and i encourage it.

i believe the altherma, skyair, and vrf systems use their scroll comp. i'm pretty sure their inverter scrolls can be sized for a residential application.

you-tube hosts a lot of vids on these topics.

[junkhound]

play around with adding a drive to a standard compressor and see what happens

Very easy to do with a 3 phase compressor, the control loop stability is what is trouble for most folks.

Get your count up and post in the pro tech section, one of my favorite topics. This type discussion too easily evolves into diy.

From and engineering standpoint (e.g. ground up design, not buying a manufactured unit), my own opinion is that variable speed has no efficiency advantage for a well designed fixed system such as GSHP where the temperature differentials are pretty fixed. You have a given flow rate of the compressor and you design the rest of the system to be optimal within your design cost limits. Draw a few Mollier diagrams and vary the compressor speed - all you get is different overall thermal capability due to # of refrigerant per unit time circulated (constant enthalpy per # ).

Granted, there will be secondary minor savings such as lower core losses in the motor, lower piping pressure losses with lower flows, etc, but the piping design for the fixed speed compressor should account for those losses.