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The diagram is generated from the section and airflow model. Disabled sections are not drawn.
Outdoor air
-20,0 °C · 100 % RH · h -18,6 kJ/kg
Supply air
20,0 °C · 4 % RH · h 21,7 kJ/kg
Room air
20,0 °C · 40 % RH · h 34,8 kJ/kg
Base data
Calculation points
AHU sections
The calculator prepares an AHU balance for winter and summer: heater, cooler and humidifier capacity, heat recovery, fan power and SFP. The results form a design schedule with required operating parameters that can be compared with specific manufacturers' units.
Determine the required supply and extract airflow from occupancy, contaminant loads or air-change rates. This is the primary AHU size parameter.
Set the winter and summer design conditions and the required supply-air parameters. For Polish cities, the calculator fills in the climate zone.
Configure heat recovery, heater, cooler, humidifier, fans and silencers. The calculator determines section capacities, condensate, state points and SFP.
Compare the resulting design schedule with a manufacturer's catalogue. The selected unit must deliver the required airflow at the system pressure, section capacities and acceptable SFP.
The calculator supports rotary, counterflow, crossflow, heat-pipe and run-around coil recovery. Each type has separate temperature efficiency, moisture recovery and frost-protection parameters.
The PDF contains the AHU schematic, winter/summer capacity balance and air state points after every section. Excel provides the same data in Design schedule, PL climate and State points sheets for comparison with manufacturer selection software.
Psychrometrics uses ASHRAE relationships at 101,325 Pa. Air density is calculated at every state point, the cooling coil includes dehumidification and latent load, and heat recovery is corrected for unequal supply and extract airflows.
First determine the required supply and extract airflow, then the pressure needed to overcome system resistance. Select a unit that delivers this duty point at an acceptable SFP and has heater, cooler and heat-recovery capacities that satisfy the winter and summer balance.
No. It creates a manufacturer-independent design schedule containing airflows, section capacities, state points, condensate and SFP. Use this set of requirements to compare specific units in a manufacturer's catalogue or selection program.
Capacity depends on air mass flow and enthalpy rise. With heat recovery, the heater warms air from the temperature after the recovery section rather than directly from the outdoor temperature, so its required capacity is much lower.
Cooling capacity must be calculated from the enthalpy difference because it includes both sensible cooling and dehumidification. A temperature-only calculation omits latent heat and can underestimate the required capacity.
Specific fan power is the fan electrical power divided by airflow. It compares the energy demand of units at the same duty point and depends on system pressure, fan efficiency, filters and other resistances.
A supply-and-extract AHU balances both airflows and enables heat recovery. Supply-only units are used when separate systems provide the extract airflow, such as process exhaust fans or kitchen extract systems.
