What type of system typically requires separate supply and return pipes?

An all-water system is correctly identified as typically requiring separate supply and return pipes. This system is designed to carry heated or cooled water through distinct piping paths—one for supply and one for return. By maintaining separate lines for supply and return, the system can effectively manage thermal energy transfer, ensuring that heated or cooled water is delivered directly to the intended areas of a building, while used water is efficiently returned for reheating or recooling.

In comparison, a fan coil system usually utilizes a single loop or a fan to move air over the coil and distribute it throughout the space, not needing dedicated supply and return pipes for water. A hybrid system may incorporate both all-water and alternate methods of heating or cooling, potentially complicating the piping requirements further, while a single pipe system, as the name suggests, shares a common pipe for both entering and returning water, which typically does not meet the need for separated flow paths required for optimal efficiency and performance.

Understanding the requirements of piping configurations is crucial for effective system design and energy management in HVAC systems.