performances of inverter compressors at partial load

[p12i]

Hi

Where can I find tecnical informations (performances, COP,..) about inverter compressors (rotative, scroll, screw) at partial load ?

Thanks

[icecube51]

GOOGLE !!

ice

[Brian_UK]

GOOGLE !!

ice

Or the manufacturers of those compressors.

[NoNickName]

Nowhere, probably.

[icecube51]

thats why a said " Google" brian_UK, and as nonickname comes to say, probably nowhere.

Ice

[Brian_UK]

Fair enough.

[nh3wizard]

I would think the manufacturer would have / know this information.

[US Iceman]

The compressor manufacturer's will have this data however it is most likely to be in their software. Some of this software is not publicly available. And just as important, you need to know how to understand the data.

Compressors DO NOT work the same way as fans or pumps when operated at variable speeds.

Google may be able to find some limited material, but I think NoNickName is probably right.

[SteinarN]

A resiprocating compressor has normaly a higher volummetric efficiency at lower speed, say 30 to 40Hz than at nominal speed, 50 or 60Hz. This is mainly caused by the relatively high pressure loss in the reed valves of resiprocating compressors at nominal speed.

Compressors where the suction gas flows through channels in the rotor instead of in channels in the compressor body tends to show a higher decrease in cop and volummetric efficiency as the Hz increases. This is caused in part on static pressure loss in the relatively narrow channels in the rotor as vell as relatively high dynamic pressure loss in those same channels as the radial speed of the channel itself is considerable at nominal Hz. The volummetric efficiency may be 2 to 3 percentage lower at 60Hz compared to 50Hz. The COP experience a similar difference at 50Hz versus 60Hz.

However at very low speed the slip will cause a decrease in the efficiency as the slip in percentage of the rpm increases as the rpm decreases. At nominal speed, 50 or 60Hz, the slip may be 3 to 4 percent, that is the rpm is between 1440 to 1455 at 50Hz. At say 25Hz the slip increases to 6 to 8 percent since the slip is a stable rpm value at constant operating conditions. This lead to, at some point as the Hz decreases, decreased volummetric efficiency in relation to the Hz as well as decreased cop. This negative slip effect probably overcomes the positive effect of decreased pressure loss only at very low Hz, say below 25 or 20Hz.

Screws and scrolls has different properties, mainly because of the absence of reed valves and the high pressure loss they cause. The difference in the volummetric efficiency at 50Hz compared to 60Hz is often negligble if any difference at all. This leads to the negative slip effect becoming more important making it more likely with a decrease in the cop and the volummetric efficience as the Hz decreases, even when the Hz decreases from a relatively high value, say 35 to 45Hz. This is especially true in compressors where the suction gas do not flow through channels in the rotor as in hermetic scrolls.

[NoNickName]

I'm afraid that compressors have the highest fluid-dynamic efficiency at synchronous speeds. This is the result of years and years of development, because at these times 98% of the compressors are still used without inverters.

If I was to install an inverter, I would not be worried about the inverter itself, but the control logic that will pilot the inverter. Too fast acceleration and deceleration will cause a lower efficiency and reliability that no inverter.

And no, US Iceman, manufacturer don't have those data. No manufacturer can afford testing dozens or hundreds of compressors, with multiple refrigerants, at all to+tc conditions, at all frequencies.

[US Iceman]

No manufacturer can afford testing dozens or hundreds of compressors, with multiple refrigerants, at all to+tc conditions, at all frequencies.

I'm sure that is true. Not all of the compressors are tested. What I think happens is that one or two sizes are tested to develop a range of performance capability. This data is generalized into a set of curves which are applied in a general manner.

One point of caution I have on the word efficiency is this; while a few % points may be lost of gained depending on any number of variables, efficiency is not in itself the entire concern.

It is the cost of electricity and the amount used that determines the final effectiveness of operation. If you save more money by using an inverter, than by shutting of the compressor and re-starting it then the cost of operation is less. That is what the final concern is IMO.

The system may operate at points that are not efficient, but in doing so the cost operation is less.