Design a transcritical CO₂ booster

• –Auto holds the receiver at a fixed set point, shown under the control, kept above the MT suction pressure.
• –Manual P and Manual T take the Flash tank pressure or Flash tank temperature you type. Whatever you type, Kelvin keeps the receiver above the MT suction and below the critical pressure.
• –Flash tank subcooling cools the receiver's liquid below its saturation temperature in an external subcooler. Its duty shows as Liquid subcooler in Derived readings. It is not in the rack's total power, so size whatever provides it separately.

• –FGBV → MT suction: the flash vapour bypasses through the flash gas bypass valve into the MT suction line.
• –HT suction group: the flash vapour feeds its own suction line with a separate compressor. The results add a High Temp (HT) suction group.

When the gas cooler exit is above CO₂'s critical temperature, the high side is a gas cooler, and its pressure comes from a published optimum. Below it, the same exchanger can condense. There Kelvin solves the rack both ways, condensing and held above the critical pressure, and takes whichever needs less compressor power. Just below the critical temperature, holding the head up can be the cheaper of the two.

The heading of the state points says which mode the rack is in, “condensing” or “transcritical”. The high-side readings say Condensing pressure and Condenser heat, or Optimal discharge pressure and Gas cooler heat, and the basis beside the pressure says how it was set. A condensing head never floats below the receiver pressure, and the basis says when it is held there.

Kelvin holds no manufacturer's ejector data. It takes the entrainment ratio your own selection gives, and uses it only at the conditions it was read at.

1. 1

   Set Flash vapor routing to HT suction group. An ejector needs parallel compression: the vapour it lifts into the receiver is taken by the parallel compressors.

2. 2

   Under Ejector, choose Vapour ejector.

3. 3

   Choose Copy this cycle's conditions. It fills Read at with this cycle's gas cooler outlet, gas cooler pressure, MT evaporating temperature, MT superheat and receiver pressure, as the page shows them.

4. 4

   Select the ejector at those conditions in your selection tool, then enter the Entrainment ratio it gives: entrained ÷ motive mass flow.

5. 5

   Under Source, fill in Document or tool, and the Edition or version and Page or date.

6. 6

   Read the status line under the entry: “Applied”, or “Not applied” with the reason.

Copying the conditions clears the ratio, so a ratio read at other conditions is never carried over. When the entry is applied, an Ejector block in the results gives the entrainment ratio, the motive and entrained flows, the lift, the outlet quality, an implied efficiency (a check, never an input), and the power and COP against the same rack with the high-pressure valve alone.

The entry is not applied, and the rack is solved with the high-pressure valve alone, when any of the five conditions differs from where the ratio was read (each is listed with both figures), when the flash gas goes to the MT suction, when there is no MT load, or when the figure can't hold: an all-vapour outlet, more vapour drawn than the MT evaporators make, or entropy destroyed, which no ejector can do.

• –Kelvin takes the whole gas cooler flow as motive flow and reports it as Motive flow, so you can check it against the ejector block's rating.
• –An ejector switched on must be complete before the design can be saved, and the entry lists what it still needs. Switched off, it is kept as typed.
• –The energy analysis is worked without the ejector, because its ratio was entered at the design conditions only and each month runs at others.

For a booster worked from heat load to issued report, see the transcritical CO₂ supermarket worked example, and for R-744's properties, its refrigerant page.