What does the coefficient of performance (COP) indicate in heat pumps?

The coefficient of performance (COP) is a key indicator of the efficiency of heat pumps, representing the ratio of useful heating or cooling provided by the system compared to the amount of work input, typically in the form of electrical energy. A higher COP value signifies that the heat pump is performing more efficiently, delivering more heat or cooling while using less energy. This metric allows consumers and technicians to assess how well a heat pump converts energy input into heating or cooling output, making it integral in evaluating system performance.

The other options don't correctly define what COP measures. While efficiency of the refrigerant may impact overall performance, it is not what COP directly indicates. Similarly, annual energy consumption refers to the total energy used over a year, not the efficiency ratio at a given moment. Finally, the size of the heat pump unit can affect capacity but is not a measure of efficiency or performance. Hence, the correct understanding of COP focuses on its role in reflecting the useful output relative to energy input, confirming choice B as the accurate answer.