NATE Air Conditioning and Heat Pumps Practice Exam

Why are more circuits needed in the outdoor coils used in heat pumps than in the condenser coils found in cooling-only units?

1. To keep the pressure drop across the outdoor coil high

2. To keep the pressure drop across the outdoor coil low

3. To provide more subcooling during the cooling cycle

4. To provide more subcooling during the heating cycle

The correct answer is: To keep the pressure drop across the outdoor coil low

The correct answer emphasizes the need for additional circuits in the outdoor coils of heat pumps to keep the pressure drop across these coils low. This design consideration is vital because heat pumps operate by extracting heat from the outside air in heating mode and expelling it from the indoor air. When the outdoor coil functions in heating mode, having a lower pressure drop allows for more efficient fluid flow, which is essential for effective heat transfer in varying outdoor temperatures. A low pressure drop means that the refrigerant can easily circulate through the coil, maximizing the heat exchange process and ensuring that the system can deliver adequate heating even when the outside temperature is low. In contrast, cooling-only units do not require the same amount of circuiting in their condenser coils, as they typically operate in a more stable temperature environment where the demands on the system are less variable. This difference in design reflects the unique operational requirements of heat pumps, which need to be efficient in both heating and cooling modes while maintaining optimal refrigerant flow. Therefore, the additional circuits in the outdoor coils of heat pumps are an intentional design choice, promoting efficiency and performance during the heating cycle.