A four-pipe system for chilled water and hot water requires:

A four-pipe system for chilled water and hot water requires:

• A. Changeover control valves
• B. Separate cooling and heating coils
• C. Only one pump
• D. A longer time for changeover than a two-pipe system

Answer: (B)

Four-pipe systems are designed to provide both heating and cooling simultaneously by keeping the chilled-water and hot-water circuits completely separate. Because an air handling unit must be able to deliver cooling and heating at the same time, it includes both a cooling coil connected to the chilled-water loop and a heating coil connected to the hot-water loop. This separation is why separate cooling and heating coils are required. Changeover valves aren’t needed to switch modes in a four-pipe setup—the coils are already independent, so you don’t rely on changing over to meet current loads. Likewise, having only one pump isn’t a defining requirement; many four-pipe designs use separate pumps for each loop or a redundant-pump arrangement. The notion of a longer changeover time doesn’t apply here, since there’s no single mode to switch between; both loops can operate independently as needed.

Four-pipe systems are designed to provide both heating and cooling simultaneously by keeping the chilled-water and hot-water circuits completely separate. Because an air handling unit must be able to deliver cooling and heating at the same time, it includes both a cooling coil connected to the chilled-water loop and a heating coil connected to the hot-water loop. This separation is why separate cooling and heating coils are required.

Changeover valves aren’t needed to switch modes in a four-pipe setup—the coils are already independent, so you don’t rely on changing over to meet current loads. Likewise, having only one pump isn’t a defining requirement; many four-pipe designs use separate pumps for each loop or a redundant-pump arrangement. The notion of a longer changeover time doesn’t apply here, since there’s no single mode to switch between; both loops can operate independently as needed.