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

The coefficient of performance (COP) is a critical metric in evaluating the efficiency of heat pumps. It specifically measures the ratio of useful heating or cooling output to the energy consumed by the system. A higher COP indicates that the heat pump is operating more efficiently, providing more heating or cooling per unit of energy consumed. This concept is fundamental for understanding the effectiveness of heat pumps in transferring heat compared to their electrical consumption and is essential for determining energy savings and operational costs.

The other options do not accurately reflect what COP measures. The amount of sound produced does not relate to performance efficiency; the type of refrigerant influences the thermodynamic properties but is not what COP assesses; and the size of the heat pump system might affect capacity but does not directly relate to the efficiency ratio defined by COP. Hence, option B clearly encapsulates what COP represents in the context of heat pumps.