“Low stage pipework only” in Events means this layout covers the cascade's low stage: its drawn runs, its discharge into the cascade heat exchanger, and the liquid leaving it. The high stage's discharge and condenser liquid lines aren't sized here.
Why
A layout is drawn, sized and charged in one refrigerant, the system's own, and on a cascade that is the low stage's. The high stage runs on its own refrigerant. Sizing its lines on the low stage's properties would print a wrong figure without saying so, so Kelvin leaves them out and says so instead.
What to do
- 1
Size and charge the low stage on this layout as usual.
- 2
Size the high stage's discharge and condenser liquid lines separately, on the high stage's refrigerant.
- 3
When you total the system's charge, remember the pipework charge from this layout is the low stage's alone.