Essential Psychrometric Processes

→ Horizontal right movement

• DBT increases, W constant
• RH decreases
• Example: Electric heaters

← Horizontal left movement

• DBT decreases, W constant
• RH increases
• Example: Dry cooling coils

↑ Vertical upward movement

• W increases, DBT constant
• RH increases
• Example: Steam injection

↓ Vertical downward movement

• W decreases, DBT constant
• RH decreases
• Example: Desiccant wheels

↙ Down-left diagonal movement

• DBT and W decrease
• RH may increase or decrease
• Example: Standard AC units

↖ Up-left diagonal movement

• DBT decreases, W increases
• RH increases significantly
• Example: Swamp coolers

⇄ Straight line between states

• Final state lies on mixing line
• Position depends on mass flow ratio
• Example: Return + outdoor air mixing