In a chilled-water system, what is circulated to fan coil units?

In a chilled-water system, the primary function is to cool the air within a space. The system circulates conditioned water to fan coil units, which can either be chilled or heated depending on the season and the specific needs of the environment. The fan coil units utilize this conditioned water to either absorb heat from the air (in the case of chilled water) or impart heat to the air (in the case of heated water) before it is distributed back into the space.

This circulation of conditioned water allows for efficient temperature control and comfort within a building, making it a critical component of many HVAC systems. By utilizing water as a medium for heat transfer, chilled-water systems can achieve more efficient cooling compared to air-only systems. Therefore, focusing on the nature of the fluid being used, it's clear that conditioned water—whether chilled or heated—is the correct answer as it highlights the fundamental operation of the system.