Compressor Volumetric Efficiency (Clearance Re-Expansion)

The fraction of swept volume it draws in as fresh suction vapor, the number compressor-displacement names as a gap. Trapped clearance gas re-expands on the down-stroke before the suction valve opens, cutting the intake: VE = 1 + C - C x (Pd/Ps)^(1/n), with C the clearance ratio (~0.03-0.06), Pd/Ps the absolute compression ratio, and n the re-expansion exponent (~1.11 R-22, 1.16 R-410A). A 0.045-clearance machine at a 300/70 = 4.3 ratio (R-22) is ~88%; a higher head pressure raises the ratio AND the re-expansion loss, so VE and capacity fall -- why a compressor pumps less on a high-ratio day. CLEARANCE VE only; suction superheat, valve/ring leakage, and valve pressure drop lower the actual VE further. Multiply displacement by VE for the pumped suction volume. A recip model; the rated capacity at the operating condition governs.

compression_ratio = discharge_pressure_psia / suction_pressure_psia; volumetric_efficiency = 100 x (1 + C - C x (Pd/Ps)^(1/n)), C = clearance ratio (~0.03-0.06), n = polytropic re-expansion exponent (~1.11 R-22, 1.16 R-410A).

Reciprocating compressor clearance volumetric efficiency (clearance-volume re-expansion; ASHRAE Refrigeration / Dossat Principles of Refrigeration), by name; the compressor's rated capacity at the operating condition governs.

The clearance re-expansion relation is public thermodynamics; the clearance ratio, the suction and discharge pressures, and the polytropic exponent come from the compressor and the operating condition.

Estimate. AHJ and licensed professional govern.

Field names used by the API: clearance_ratio, suction_pressure_psia, discharge_pressure_psia, polytropic_exponent, compression_ratio, volumetric_efficiency_pct

• Clearance re-expansion VE = 1 + C - C x (Pd/Ps)^(1/n); C ~0.03-0.06, n ~1.11 R-22 / 1.16 R-410A; a higher compression ratio lowers VEASHRAE Refrigeration / Dossat
• Clearance VE only the actual VE is lower -- suction superheating, valve/ring leakage, and valve pressure drop each subtract more; actual pumped volume = displacement x VE; the rated capacity governscompressor engineering practice