HVAC Psychrometric Chart Practice Questions Carrier Handbook Key Points

Carrier Handbook Critical Points

1. Load Calculation Essentials

Sensible Heat Gain Formula: Q_s = 1.08 × CFM × ΔT
Latent Heat Gain Formula: Q_l = 4840 × CFM × ΔW
Design conditions: 1% dry bulb/mean coincident wet bulb temperatures
Safety factors: 10-15% for duct heat gain/loss

2. Air Distribution Fundamentals

Application	Air Velocity (fpm)	ΔT (°F)
Residential	500-700	18-22
Commercial	800-1200	20-25
Industrial	1200-1800	25-30

Throw calculation: 50-75% of terminal velocity at design flow

3. Equipment Selection Rules

Chiller sizing: 0.65-0.85 kW/ton for water-cooled
Approach temperatures: 7-10°F for cooling towers
Coil face velocity: 400-600 fpm for comfort cooling
Minimum airflow: 350 CFM/ton for dehumidification

4. Psychrometric Design Standards

System Type	Supply Air RH	Leaving Air Temp
Constant Volume	85-95%	52-55°F
VAV	90-95%	50-55°F
Dual Duct	80-90%	Cold deck: 50°F Hot deck: 85-100°F

5. Piping Design Guidelines

Chilled water ΔT: 10-12°F standard, 16-20°F for low-flow
Pipe velocities: 4-6 fps for supply, 2-4 fps for return
Expansion tank sizing: 6% of total system volume
Pump head: 40-60 ft for typical systems

6. Control Strategies

System	Primary Control	Reset Strategy
VAV	Duct static pressure	Reset based on zone demand
Chiller Plant	Supply water temp	Outdoor air reset
CAV	Discharge air temp	Night setback

7. Energy Efficiency Measures

Economizer cycles: 55°F outdoor air lockout
Optimum start/stop: 30-60 min pre-conditioning
Heat recovery: 50-70% effectiveness target
VSD applications: Fans >10 HP, pumps >15 HP