Cooling coils are selected based on peak design loads; however, systems operate at part-load most of the time. In a constant air volume (CAV) system, the thermostat senses the room temperature and signals the control valve to modulate chilled water flow to the coil. As the system adjusts to meet the thermostat setpoint, it reaches an equilibrium where the coil’s sensible capacity matches the room’s sensible heat load. Because reducing the water flow raises the coil surface temperature, the system’s latent cooling capacity decreases, usually resulting in higher indoor relative humidity.
Refer to Chilled water cooling coil characteristic for cooling coil performance vs chilled water flow.
Related notes:
Psychrometric process – cooling and dehumidification, mechanical based
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