Compression Ratio

[Deano240]

Hey my engineer has asked me to do home work..

He wants me to find out whats the best compression ratio like 2:1 any help and if its good or bad for the system ?

cheers

[NoNickName]

Best compression for what?

[US Iceman]

The best compression ratio is one that allows you meet the desired temperature for cooling at the lowest possible power input or total cost for electricity.;)

[Deano240]

So in other words If I chase my head pressure up. Il be changing my compression ratio. Is this more energy efficient and visa verca ie dropping head pressure ?

[desA]

Oh dear... :)

[1torr]

Give him a chance, got to start somewhere.

[US Iceman]

If the suction pressure remains constant and the discharge pressure increases, the compression ratio increases.

If the suction pressure decreases and the discharge pressure remains constant, the compression ratio increases.

If the suction pressure remains constant and the discharge pressure decreases, the compression ratio will decrease.

If the suction pressure decreases and the discharge pressure also decreases, the compression ratio will decrease.

Compression ratio = Discharge pressure divided by suction pressure

Note: pressures are in absolute pressure (not gauge pressure).

Someone is not helping you by asking questions like your original post.

You can only change your suction pressure within a narrow band since it determines the pressure in the evaporator (unless you are using back-pressure regulators. They control evaporator pressure if used). The pressure in the evaporator controls what the evaporating temperature is, which in turn essentially controls the desired space temperature. In effect, there is not much you can do to this without affecting the storage temperatures.

The discharge pressure is one you can change a lot, since this essentially determines the total power input for the compressor.

There are however some practical limits. The compressors have maximum compression ratios to prevent long-term damage from heating.

And there can be minimum compression ratios also, which typically fall into the range of 1.5:1 to 2:1.

[Magoo]

Calculate your compression ratios in absolute.

[desA]

The Copeland website gives some excellent performance information on their scroll compressors.

From the charts, you'll be able to see the effect of changing pressure ratios.