Active systems utilize which of the following to increase heat transfer?

Active systems are designed to enhance heat transfer through mechanical means. Fans and pumps are integral components in these systems, as they facilitate the movement of fluids, either air or liquid, which is essential for transferring heat efficiently. For instance, fans help circulate air within a space, thereby distributing warmth or coolness more uniformly, while pumps move liquids through a heating or cooling system, enhancing heat exchange in processes like hydronic heating or cooling setups.

The other choices, though they have functionality related to heat transfer, do not focus on the active mechanism of moving heat. Pipes and valves contribute to the system's structure and flow regulation but do not actively enhance heat transfer. Heaters and coolers are devices that generate heat or coolness but rely on active components like fans and pumps to effectively distribute that energy. Radiators and condensers serve specific purposes in heating and cooling systems but generally rely on the movement of fluids facilitated by pumps to optimize heat transfer. Therefore, fans and pumps represent the dynamic forces that actively improve the efficiency of heat transfer in active systems.