HVAC
AIR PURIFICATION
IN A SUBWAY
Automatic analyses by our NablaHVAC software
CLIENT
An Italian customer in the air purification sector
CHALLENGE
Analyse the impact of an air purification system in a subway station
SUCCESS
The results let the client position the machinery in the optimal amount and location, for maximum yield in pollutant reduction and air purification, and contained cost
01
CHALLENGE
A customer needed a set of HVAC analyses to investigate the impact of an air purification system in a complex closed environment: a subway station in Milan.
Running HVAC analyses with computational fluid dynamics in a subway station presents several challenges that have to be addressed for the work to succeed:
01
Complex geometry of subway stations — underground spaces have intricate layouts with multiple levels, platforms, tunnels and entrances. That irregularity makes airflow patterns hard to model accurately, and capturing the interactions between ventilation, train movement and passengers is crucial for reliable analysis
02
Passenger behaviour — stations are high-traffic areas with a constant influx of people, whose movement significantly affects how contaminants disperse and how well a purification system works. Modelling it needs detailed analysis of crowd dynamics
03
The presence of various pollution sources — exhaust fumes, dust particles and airborne contaminants. The analysis has to account for their distribution and dispersion and their interaction with ventilation and purification devices, and the placement of filters and units must be optimised for maximum removal
02
SOLUTION
NablaHVAC is an automated tool for designing and verifying the HVAC system of a closed environment — such as a multilevel subway — and checking the effect of the ventilation setup on air recirculation. Running an analysis takes these steps:
01
Simplifying the subway geometry by removing every detail unnecessary to the CFD analysis. These have to be chosen carefully: they are the geometrical features that burden the numerical analysis without affecting the final air distribution
02
Importing the geometry into NablaHVAC
03
Placing air purification systems into the 3D model
04
Modelling pollution by including a source of the species considered (CO2, PM10), and calibrating the dispersion model against the most accurate data in the literature
05
Considering passenger behavior and train movement, optionally
Simulating an air purification system in a subway station also requires transient analysis, which is computationally expensive and takes considerable time. NablaHVAC can be parallelized across all the physical cores of the server the simulations run on.
03
RESULTS
The simulation phase can take several hours, depending on the hardware resources required. A sensitivity study was carried out beforehand to simplify the model without affecting the results, which greatly reduced the computational time.
The CFD models implemented in NablaHVAC estimate:
01
the percentage removal of pollutants and their spatial distribution
02
the time required to achieve given purification goals
03
the optimal positioning of the machines within the 3D space
An automatic report of the analysis, containing the most important results, can also be generated. On that basis the customer can decide the correct number and position of air purification systems to match the time required to reduce pollution across the whole subway environment — and a cost analysis and market study can be built on the same data.