Why are more circuits required in outdoor coils of heat pumps compared to condenser coils of cooling-only units?

More circuits are required in the outdoor coils of heat pumps primarily to lower the pressure drop across the outdoor coil. In heat pump applications, the outdoor coil serves both as a condenser and evaporator, depending on the mode of operation (heating or cooling). When the heat pump is in heating mode, the coil must effectively extract heat from the outdoor air, which can be colder, leading to varying pressure conditions.

By incorporating more circuits in the outdoor coils, the refrigerant can distribute more evenly and flow more smoothly through the system. This design minimizes restrictions and helps maintain an optimal refrigerant flow rate, which is essential for efficient heat transfer. A lower pressure drop results in better system performance, helping to maximize the heat pump's overall efficiency and effectiveness in both heating and cooling modes. This is particularly important in heat pump applications where maintaining performance in colder outdoor temperatures is crucial.

The other options, while they may seem plausible, do not fully capture the fundamental reason for the requirement of additional circuits in heat pump outdoor coils. Increasing heating efficiency is a goal but is not the direct reason for the additional circuits; similarly, facilitating faster refrigerant flow is an outcome of reducing pressure drop rather than a primary justification. Reducing the overall size of the unit also does