Air Handling Unit (AHU) Calculator

Airflow & Operation

3-10 m³/h per m² for offices
Select based on climate and requirements

Temperatures & Conditions

0% = 100% Fresh Air system

Heat Recovery

Fan & System Parameters

Ductwork + grill resistance
Fan + motor + inverter combined
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Air Handling Unit Design

Air Handling Units (AHUs) condition and distribute air for building HVAC systems. The calculator models the psychrometric processes: mixing of fresh and return air, heating/cooling coils, and fan power. Key design parameters are the airflow rate (based on heat loads and air changes), supply temperature (determined by heat emitter type), and fresh air percentage ( Indoor Air Quality requirements). Heat recovery is essential for energy efficiency when fresh air exceeds 30%. Specific Fan Power (SFP) is the key energy metric, with regulatory limits typically 1.8-2.5 W/(m³/h) for commercial buildings.

Key Points:
  • Airflow rate: 3-10 m³/h per m² for offices, 10-20 for labs, 15-30 for hospitals
  • Fresh air minimum: 10% or per occupancy (ASHRAE 62.1: 5-10 L/s per person)
  • Supply temp: 35-45°C heating (radiators), 30-35°C (underfloor), 12-16°C cooling
  • Heat recovery: mandatory for fresh air > 30% in EU EPBD, saves 30-50% energy
  • SFP limit: EN 13779 Class SFP 1 = <0.9, SFP 2 = 0.9-1.5, SFP 3 = 1.5-2.1, SFP 4 = 2.1-2.7, SFP 5 = >2.7 W/(m³/h)
  • Fan efficiency: EC backward-curved = 75-85%, AC forward-curved = 55-65%
  • Coil water ΔT: 10°C standard, 15-20°C for district heating, 5-7°C for chilled water
  • Duct pressure: 250-400 Pa typical, >600 Pa requires high-pressure fans (expensive)
Calculation Steps:
  1. Enter all required parameters
  2. Click "Update Calculation"
  3. Review results and analysis
Formula Variables:
V̇ Airflow Rate (m³/h)
ṁ_air Air Mass Flow (kg/s)
ṁ_water Water Mass Flow (kg/s)
T_mix Mixing Air Temperature (°C)
T_supply Supply Air Temperature (°C)
T_return Return Air Temperature (°C)
T_outdoor Outdoor Air Temperature (°C)
Q_coil Coil Capacity (kW)
Q_sensible Sensible Heat (kW)
P_fan Fan Power (kW)
SFP Specific Fan Power (W/(m³/h))
ΔP Pressure Loss (Pa)
η Fan Efficiency (%)