The psychrometric chart illustrates how air is processed from the Mixed Air (MA) state to offset room loads. To achieve this, the air must be cooled and dehumidified by a cooling coil.
In a typical summer peak-load scenario, the cooling coil is selected to deliver air at a leaving condition of approximately 90% Relative Humidity (RH). The intersection of this coil process curve and the Room Sensible Heat Ratio (RSHR) line establishes our Supply Air (SA) —in this case, 13°C dry-bulb (DB). As this supply air enters the space, it simultaneously absorbs the room’s sensible and latent heat loads, moving along the RSHR line until it reaches the design Room Air (RA) condition. To maintain a continuous cycle, a portion of the RA is exhausted, while the remainder returns to mix with Outdoor Air (OA), creating the MA state before re-entering the coil.
This path represents the system operating at peak load. At part-load conditions, the process path shifts significantly, a topic we will explore in detail in a later post.
Related notes:
Chilled water cooling coil characteristic
Psychrometric process – cooling and dehumidification, mechanical based
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