How does a two-pipe HVAC system differ from a four-pipe system?

In a two-pipe HVAC system, there are indeed only two pipes used for both heating and cooling, which means that the same set of pipes is utilized to either distribute hot water or chilled water throughout the building, depending on the season or the specific demand at any given time. This design allows for simpler installation and reduced material costs since it involves fewer pipes compared to a four-pipe system.

However, this configuration also means that a two-pipe system cannot provide simultaneous heating and cooling. Instead, the system must switch between the two modes, making it less versatile in applications where both heating and cooling are needed at the same time in different areas of a building.

In contrast, a four-pipe HVAC system has dedicated pipes for both heating and cooling, allowing different zones or rooms to be conditioned simultaneously without the necessity to switch modes. This flexibility is advantageous in commercial settings or environments with varying thermal loads.

With this understanding, it is clear why the option stating that a two-pipe system uses the same pipes for heating and cooling accurately represents the fundamental difference between a two-pipe and a four-pipe system.