HVAC Psychrometric Process Calculator

Use this preliminary calculator page to review common HVAC psychrometric processes, including sensible heating, sensible cooling, cooling and dehumidification, humidification, outdoor-air mixing, return-air mixing, and ERV/HRV leaving-air conditions.

This tool is intended for preliminary HVAC engineering reference only. Final equipment selection and psychrometric analysis should be verified using project design conditions, manufacturer data, applicable codes, and professional engineering judgment.

What This Calculator Will Help Estimate

• Humidity ratio from dry-bulb temperature and relative humidity
• Moist-air enthalpy
• Dew-point temperature
• Mixed-air dry-bulb temperature
• Mixed-air humidity ratio
• Sensible heating and sensible cooling processes
• Cooling and dehumidification across a cooling coil
• ERV/HRV leaving-air temperature and ventilation-load reduction
• Supply-air and room-process relationships

Typical Air Conditions

• OA: Outdoor air entering the HVAC system
• RA: Return air from the occupied space
• MA: Mixed air after OA and RA combine
• SA: Supply air delivered to the space
• ADP: Apparatus dew point on the saturation curve

Basic Formula References

Mixed-Air Dry-Bulb Temperature:

T_MA = (CFM_OA × T_OA + CFM_RA × T_RA) ÷ (CFM_OA + CFM_RA)

Mixed-Air Humidity Ratio:

W_MA = (CFM_OA × W_OA + CFM_RA × W_RA) ÷ (CFM_OA + CFM_RA)

Total Cooling Load:

Q_total ≈ 4.5 × CFM × Δh

Sensible Cooling Load:

Q_sensible ≈ 1.08 × CFM × ΔT

Latent Cooling Load:

Q_latent ≈ 4,840 × CFM × ΔW

Common HVAC Processes

• Sensible Heating: Dry-bulb temperature increases while humidity ratio remains approximately constant.
• Sensible Cooling: Dry-bulb temperature decreases while humidity ratio remains approximately constant.
• Cooling and Dehumidification: Both dry-bulb temperature and humidity ratio decrease through the cooling coil.
• Humidification: Moisture is added to the air stream.
• Air Mixing: Outdoor air and return air combine before entering the HVAC equipment.

Related HVAC Training

• Psychrometric Chart Training Series
• Room Sensible Heat Ratio and Supply-Air Condition
• Cooling and Dehumidification on a Psychrometric Chart
• Mixed Air and ERV/HRV Processes

Download the Excel Calculator

Use the downloadable Excel workbook to evaluate common HVAC psychrometric processes, including sensible heating, sensible cooling, cooling and dehumidification, humidification, air mixing, and preliminary ERV/HRV leaving-air conditions.

This workbook is intended for preliminary design reference. Final psychrometric analysis and equipment selection should be verified based on project design conditions, manufacturer data, applicable codes, and professional engineering judgment.

Download Psychrometric Process Calculator

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