A dimensionless ratio measuring refrigeration system efficiency, calculated as cooling output divided by energy input. A COP of 2.5 means the system removes 2.5 kW of heat for every 1 kW of electrical or mechanical energy consumed. Higher COP indicates greater efficiency—but manufacturer COP ratings at sea level systematically overstate performance for South African highland operations.
Understanding COP
COP = Cooling Capacity (kW) / Power Input (kW)Typical transport refrigeration COP values:
- At sea level, mild conditions: 2.5-3.0
- At sea level, hot conditions (35°C+): 2.0-2.5
- At Johannesburg altitude: 2.15-2.3 (14% degradation)
- Johannesburg + summer heat: 1.8-2.0 (compound degradation)
Why COP Matters for Operating Costs
COP directly determines fuel consumption. Lower COP means more fuel to achieve the same cooling:
| Condition | COP | Fuel for 4kW Cooling |
|---|---|---|
| Sea level, 25°C | 2.8 | 1.43 kW input |
| Sea level, 35°C | 2.3 | 1.74 kW input |
| Johannesburg, 25°C | 2.4 | 1.67 kW input |
| Johannesburg, 35°C | 1.9 | 2.11 kW input |
The compound effect of altitude and high ambient temperature can increase fuel consumption by 50% compared to manufacturer specifications derived from European sea-level testing.
COP Degradation Formula
Our Technical Formulas Reference provides the altitude COP correction:
COP_altitude = COP_sea-level × (P_altitude / P_sea-level)^0.4At Johannesburg (atmospheric pressure ~82 kPa vs 101 kPa at sea level):
- COP reduction: approximately 7.6%
- Combined with capacity reduction: 28.6% total performance degradation
Variable Speed Advantage
Variable speed compressors maintain higher average COP by:
- Operating at partial capacity during light loads (higher COP)
- Avoiding inefficient start/stop cycling
- Matching output to actual demand continuously
This explains why variable speed systems achieve 20-40% fuel savings despite identical peak COP ratings—they spend more time operating in efficient partial-load conditions.
Industry COP Deception
Manufacturers publish COP at optimal test conditions: sea level, 32°C ambient, steady-state operation. Real-world South African conditions—altitude, 35-40°C summer heat, multi-stop thermal cycling—produce dramatically lower actual COP that operators discover only through excessive fuel bills.
Related Terms: Energy Efficiency (Cold Chain), Variable Speed Compressor, Altitude Correction Factor