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Unit 6 — Refrigeration System Components
Section 5 — Compressor Performance Metrics

5.4 — Coefficient of Performance (COP)

Mastery of compressor terminology enables clear communication among technicians, engineers, and other professionals in the refrigeration and air conditioning field. This lesson defines the fundamental mechanical terms — compression ratio, displacement, and volumetric efficiency — along with refrigerant state terms, discharge temperature, oil charge, and the performance metrics used to rate and compare refrigeration equipment.

5.4.1 — Coefficient of Performance (COP)

The Coefficient of Performance is a measure of compressor and system efficiency, expressed as the ratio of the useful cooling capacity to the power consumed to produce it. A higher COP indicates a more efficient system that delivers more cooling per unit of electrical energy input.

Coefficient of Performance
COP = Cooling Capacity (kW) ÷ Power Input (kW)
Both values must be in the same energy unit (kW). COP is dimensionless.
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Typical COP Values

COP values for refrigeration systems typically range from 2.0 to 4.0, depending on operating conditions and equipment type. A COP of 3.0 means the system delivers 3 kW of cooling for every 1 kW of electrical power consumed. Higher evaporating temperatures and lower condensing temperatures produce higher COPs; harsher operating conditions reduce COP.

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COP vs. Compression Ratio

COP falls as compression ratio rises. Each additional unit of pressure difference across the compressor requires more work input per unit of refrigerant moved. This is why maintaining clean condensers (lower head pressure) and clean evaporators (higher suction pressure) has a direct, measurable impact on energy consumption — it reduces compression ratio and raises COP.

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COP and Maintenance

COP is a useful field diagnostic: if measured COP has dropped from a known baseline, the system is working harder than necessary. Common causes include fouled condenser coils, low refrigerant charge (lower suction pressure), non-condensables in the system (higher head pressure), and a worn compressor. COP can be estimated from measured pressures and temperatures using manufacturer data tables.

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