Compressor Efficiencly at Pressure Ratio 2:1

[wzal]

HI, Everyone,

I am working on an mobile air conditioning system and needs an R134a compressor that has best efficiency when pressure ratio is 2:1.

Is a scroll compressor more efficient than piston at the pressure ratio?

Thanks,

 

[imok2]

Wzal: Copeland makes fine scroll compressors. Scroll compressors achieve high efficiencies due to 100% volumetric efficiency during the compression process. The scroll design operates under continuous flank contact, maintained by centrifugal force. This minimizes gas leakage and maximizes efficiency and th're more efficient then piston. Piston comp loose eff. because of the required clearence at top dead center; because this causes re-expansion of the clearence gas on the suction stroke.

 

[wzal]

Thank you for your input, imok2.
I don't have the performance data of the scroll and pistion compressor I am comparing. They are a little special (open drive and small displacement for automotive). That's why I ask the general question.
I am sure scroll compressor will have much higher volumetric eff. than piston at the designed pressure ratio. But for low pressure ratio application, is it possible for it to over-compress the gas (say designed ratio 3:1 but actual duty 2:1 determined by condensing and evaporating pressure)?
I am not sure if this will happen to a piston compressor.

 

[ClydeMule]

A scroll will over compress. That is one of the downsides of a scroll.


Clyde

 

[imok2]

Wzal; You can try a variable displacement scoll compressor witch utilizes an internal control valve to reduce capacity
during low load condtions; this also eliminates clutch cycling.The control valve is set to a spcific lowside pressure so when air cond demand is low the control valve opens and by passes discharge gas to the suction side of the compressor allowing the comp to keep operating.
Take a look here

http://www.visteon.com/technology/automotive/media/compressors_spec.pdf

 

[boyceg]

I am new...

Copeland has a compressor selection system that you can download and look at compressors all sorts of ways. Careful, it can eat up a lot of time...

Scroll compressors from Copeland come in high temperature, medium temperature and low temperature designs. Looks to me like you would be most interested in the high temperature designs. However, I have found the #ZR18K4E- compressor hard to beat over a very wide range.

I also have experience with electronic expansion valves and would not consider using anything else if conditons vary or the design is not nailed down.
Boyceg