refrigeration plant capacity calculation

[VIVEK230]

Hi guys,

I want to know the connection between cooling capacity and the temperature that can be obtained.
For the same compressor what capacity in TR would it yield for a water chiller application @ +5 degrees and what would it produce for a refrigeration application @ -10 degrees.

[shaaf]

Definitely compressor will be on less capacity when it will be operate from +5 to - 10 degress

[mad fridgie]

A simple rule of thumb (which I do not really like to use), is 1C change is SST changes the capacity by 2.5% (increase up, decrease down)

[VIVEK230]

Definitely compressor will be on less capacity when it will be operate from +5 to - 10 degress

Dear shaaf,
Can you tell me by what extent the capacity will vary and what are the parameters that are to be considered to calculate the difference. Please mention any formula if available....:)

[VIVEK230]

Is there any explanation to this phenomenon. I am unable to understand cause the compressor has a standard output capacity of 356 KW so by changing the temperature how the TR is effected....?

[moideen]

I think there is not any formula to calculate compressor capacity at different stage. The performance data of the compressor which manufacture published be used to find out the actual TR at various stage of ambient (condensing temperature) and evaporator temp.

[sandybapat]

Vivek

Refrigeration compressor capacity varies with the refrigerant used, suction & discharge pressure. However the basic capacity of volumetric flow at suction port remains the same all the time. Depending upon the pressure and temperature condition at suction port the refrigerant specific volume changes and therefore the mass flow rate of refrigerant at suction port changes. Assuming refrigeration effect per unit mass of refrigerant is same at all temperature conditions the refrigeration capacity varies with mass flow rate of refrigerant.

Thus for the same swept volume compressor handles different mass flow rate at different evaporating temperatures and the refrigeration capacity varies with that.

Please see the attachment for more clarity

[shaaf]

A product contain 1 lbs weight 1F down temperature need 1 BTU reject its heat. So when you are going to down 15C (27F) need 27 BTU reject heat from having weight 1lbs. So this heat will boil more refrigerant and create more vapors/ mass flow. On which capacity compressor design( swept volume). How can handle load that compressor who designed for +5 but on less capacity. We have one screw compressor normally run on -10C/+35C with capavity 1106 KW But when we operate it on weekend mode at -35C/+35C it`s capacity down 635KW.. mass flow rate which creates in evaporator

[VIVEK230]

Thank you very much,
This helped a lot.....:)