Kelvin

Set up a two-stage or cascade cycle

Two suction groups with a flash tank between the stages, or two refrigerants coupled through a cascade heat exchanger.

Heat load and the cycle · Updated 7 Oct 2026

Both cycle types add their own sections to the Cycle sheet. Everything else is set up as in Set up a refrigeration cycle.

Two-stage compression

  1. 1

    Choose Two-Stage Compression (Flash Intercooler) as the Cycle type.

  2. 2

    Under Conditions, fill in the Low temp suction group and the Medium temp suction group. Each takes its own SST, Superheat and Load, or a preset.

  3. 3

    Enter the Condenser temperature, the Subcooling and the isentropic efficiency. The Design ambient comes from the project location.

  4. 4

    Under Flash tank / interstage, choose the Interstage mode.

  • Auto solves the interstage at the medium-temperature suction pressure.
  • Manual P takes the Interstage pressure you type.
  • Manual T takes the Interstage temperature you type and works out its pressure.

The results list both suction groups under Suction groups, with the flash tank's states among the State points.

Cascade

  1. 1

    Choose Cascade System (Two Refrigerants) as the Cycle type. Kelvin pairs a high-stage refrigerant so the cascade solves straight away; change it under Refrigerant · high stage.

  2. 2

    Choose the low-stage refrigerant under Refrigerant · low stage. It evaporates at the load and condenses in the cascade heat exchanger.

  3. 3

    Under Conditions, the Cooling load, Evaporator temp, Superheat and Subcooling are the low stage's. Condenser temp is where the high stage rejects its heat to ambient.

  4. 4

    Under Cascade coupling, enter the LT condensing temp and the Cascade HX approach TD.

  5. 5

    Enter any MT load carried directly on the high stage, with its MT evaporating temp, or leave it at zero if the high stage only condenses the low stage. The high stage carries both on one suction pack.

  6. 6

    Under High stage circuit, set the high stage's own Superheat, Subcooling and isentropic efficiency.

The high stage evaporates at the LT condensing temperature less the approach, or at the MT load's evaporating temperature when that is colder, and the sheet shows the figure.

The results start with Combined cascade performance, then give each circuit, the Low temperature circuit and the High temperature circuit, with its own state points and readings, and a P–h diagram for each, each against its own refrigerant.

Note

If the temperatures can't work, for example the LT condensing temperature at or below its evaporating temperature, Kelvin shows “Cascade not solvable” with the change to make, and the design can't be saved until it solves.