HVAC Psychrometric Chart Practice Questions Cooling & Dehumidification Psychrometrics

Cooling & Dehumidification Psychrometrics

1. Key Process on Psychrometric Chart

Process Direction: Moves left and downward from initial condition

Critical Points:

Point A: Initial condition (DBT/WBT)
Point B: Apparatus Dew Point (ADP)
Point C: Final condition after reheating (if applicable)

2. Performance Parameters

Sensible Heat Factor (SHF) = Q_sensible / (Q_sensible + Q_latent)

Parameter	Ideal Range	Calculation
Bypass Factor (BF)	0.1-0.3	BF = (T_out - T_ADP) / (T_in - T_ADP)
Contact Factor	0.7-0.9	CF = 1 - BF
Dehumidification Efficiency	60-85%	η = (W_in - W_out) / (W_in - W_ADP)

3. Design Conditions

Application	DBT (°C)	RH (%)	SHF Range
Comfort Cooling	24-26	45-55	0.75-0.85
Data Centers	21-23	40-50	0.90-0.95
Industrial Drying	35-40	30-40	0.50-0.65

4. Equipment Selection Guide

ΔT (DBT)	ΔW (kg/kg)	Recommended System
5-8°C	<0.003	DX Cooling Only
8-12°C	0.003-0.006	Chilled Water + Reheat
12-15°C	>0.006	Dedicated Dehumidifier

5. Troubleshooting Chart

Symptom	Psychrometric Cause	Solution
High RH but correct temp	Process line too horizontal (high BF)	Increase coil rows or reduce airflow
Low RH but cold air	Process line too steep (low SHF)	Add reheat or reduce dehumidification
Inconsistent conditions	Unstable ADP position	Check refrigerant charge/water flow