The Coefficient of Performance (COP) is a key metric that describes the efficiency of heat pumps and refrigeration systems. It represents the ratio of heat output to the input energy required—typically electricity. Simply put, the COP measures how many units of heat energy a heat pump can generate per unit of electrical energy consumed. For example, a COP of 4 means that a heat pump produces four kilowatt-hours of heat per kilowatt-hour of electricity used.

Calculation and Importance

The COP is measured under standardized conditions, but it can vary depending on external temperature and operating conditions. The higher the COP, the more efficiently a heat pump operates. A high COP indicates that a large amount of heat is generated with minimal electricity consumption, leading to lower operating costs and improved economic efficiency.

Typical COP values for modern domestic heat pumps range between 3 and 5, but they can be lower and, under optimal conditions, even higher. Industrial heat pumps typically achieve COP values between 2 and 7. In applications with high temperature lifts for process heat, COP values can fall below 3, but they still offer a significant advantage by cutting electricity consumption in half compared to electric boilers.

Key factors influencing COP

1. Temperature lift:

The difference between the heat source temperature and the required supply temperature (heat sink) significantly impacts the COP. A lower temperature lift results in a higher COP, whereas a larger temperature lift reduces efficiency. For instance, with a temperature lift of 60 K, realistically a COP of 3 to 4 can be expected.

2. Efficiency factor:

The efficiency factor indicates how close the actual COP of a heat pump is to the theoretical maximum COP (Carnot efficiency). In practice, high-temperature heat pumps typically achieve efficiency factors between 40% and 60%.

3. Temperature level:

For an ideal thermodynamic cycle, the COP for the same temperature lift is proportional to the absolute temperature of the heat sink. This means that at 150°C, the COP is about 15% higher than at 100°C. However, for real-world heat pump cycles, this improvement depends on the system’s efficiency factor—so the increase in COP diminishes as efficiency decreases at higher supply temperatures.

Conclusion

The COP is a fundamental indicator of a heat pump’s performance and is crucial for assessing energy efficiency. The COP of high-temperature heat pumps depends on various factors, primarily temperature lift and system efficiency. By optimizing these parameters, industrial heat pumps can efficiently provide process heat, making a significant contribution to energy efficiency and CO₂ reduction in industrial applications.