Liquid-Line Subcooling to Prevent Flash Gas
How much subcooling a system needs to keep the liquid line from flashing: dP_lift = 0.43 x lift (R-410A liquid), dP_total = dP_lift + friction, required_subcool = dP_total / P-T slope (~5 psi/degF R-410A). Techs credit only the friction and forget the vertical-lift static column that dominates on a tall riser. A design aid, not a commissioning measurement.
Formula and source
dP_lift = static_gradient x vertical_lift_ft (0.43 psi/ft R-410A liquid); dP_total = dP_lift + friction_dp_psi; required_subcool = dP_total / pt_slope (about 5 psi/degF R-410A near condensing).
ASHRAE Refrigeration Handbook / refrigerant piping guides liquid-line subcooling to prevent flash gas, by name.
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