Air purification in a subway

Automatic analyses by our NablaHVAC software

Riscaldamento, ventilazione e condizionamento dell’aria (HVAC): miglioramento della distribuzione dell’aria e del comfort negli ambienti chiusi

An Italian customer in the air purification sector


Alcuni clienti nel settore ventilazione


Performing an analysis of the impact of an air purification system in a subway station


Identificare le zone poco ventilate o con assenza di ricircolo di un determinato ambiente chiuso, allo scopo di migliorarne la distribuzione dell’aria


Thanks to the results generated by our software, the client was able to position the machinery in the optimal amount and location to achieve maximum yield in terms of pollutant reduction, air purification, and cost containment.


Una nuova configurazione dell’impianto di aerazione ha permesso di migliorare il comfort e al contempo ridurre il consumo energetico

Air purification system in a subway

A customer required a set of HVAC analyses to investigate the impact of an air purification system in a complex closed environment such as a subway station in Milan.

Running HVAC analyses with computational fluid dynamics (CFD) in a subway station presents numerous challenges that need to be addressed for successful implementation. Several factors must be considered to ensure effective performance and optimal air quality:

  • Complex geometry of subway stations: the underground spaces often have intricate layouts with multiple levels, platforms, tunnels, and entrances. The irregularity in design poses difficulties in accurately modelling and simulating airflow patterns using CFD. Accurately capturing the complex interactions between ventilation systems, train movement, and passenger behaviour becomes crucial for reliable HVAC analysis.
  • Passenger behaviour: subway stations are high-traffic areas with a constant influx of passengers. The movement and behaviour of individuals significantly impact the dispersion of contaminants and the effectiveness of an air purification systems. Modelling passenger behaviour and their impact on airflow patterns requires detailed analysis of crowd dynamics and human behaviour, adding another layer of complexity to the simulation.
  • The presence of various pollution sources in subway stations, such as exhaust fumes, dust particles, and airborne contaminants, creates challenges for air purification. CFD analysis needs to consider the distribution and dispersion of these pollutants, as well as their interaction with ventilation systems and air purification devices. The efficiency and placement of air filters and purification units must be optimized to ensure maximum removal of harmful substances.
Air purification system in a subway - geometry passengers pollution

NablaHVAC is an automated tool to design and verify the HVAC system of a closed environment such as a multilevel subway and verify the effects of the ventilation setup on the air recirculation.

In details, the required operations to run an HVAC analysis are reported in the following:

  • Simplifying the subway geometry by removing all unnecessary details for the CFD analyses. These details should be carefully selected: these are all the geometrical features that potentially burden the numerical analysis without affecting the final air distribution.
  • Importing the geometry into NablaHVAC.
  • Placing air purification systems into the 3D model.
  • Modelling pollution by including a source of the species considered (CO2, PM10), and calibrating the dispersion model with the most accurate data in the literature.
  • Considering passenger behavior and train movement (optional).

Moreover, simulating an air purification system in a subway station requires considering the transient analysis. These are usually computationally expensive and require a considerable amount of time to be completed. NablaHVAC can be parallelized to use all the physical cores of the server where the simulations are run.

Air purification system in a subway - CO2
Air purification system in a subway - pm2.5

The simulation phase can take several hours, depending on the hardware resources required. A sensitivity study has been previously carried out to simplify the model without affecting the results. This allowed to greatly reduce the computational time.

The CFD models implemented in NablaHVAC allow to estimate:

  • the percentage removal of pollutants and their spatial distribution
  • the time required to achieve given purification goals
  • the optimal positioning of the machines within the 3D spaces

An automatic report of the analysis, containing the most important results, can also be generated.

Based on the results of the analysis, the customer can decide the correct number and position of air purification systems that match the required time to reduce the pollution in the whole subway environment.

In addition, a cost analysis and a market study can be conducted based on these data.

La tua realtà ha esigenze uniche. 
Cosa possiamo fare per te?