CFD Investigation of Vehicle’s Ventilation Systems and Analysis of ACH in Typical Airplanes, Cars, and Buses

Abstract

The simulation of the ventilation and the heating, ventilation, and air conditioning (HVAC) systems of vehicles could be used in the energy demand management of vehicles besides improving the air quality inside their cabins. Moreover, traveling by public transport during a pandemic is a concerning factor, and analysis of the vehicle’s cabin environments could demonstrate how to decrease the risk and create a safer journey for passengers. Therefore, this article presents airflow analysis, air changes per hour (ACH), and respiration aerosols’ trajectory inside three vehicles, including a typical car, bus, and airplane. In this regard, three vehicles’ cabin environment boundary conditions and the HVAC systems of the selected vehicles were determined, and three-dimensional numerical simulations were performed using computational fluid dynamic (CFD) modeling. The analysis of the airflow patterns and aerosol trajectories in the selected vehicles demonstrate the critical impact of inflow, outflow, and passenger’s locations in the cabins. The CFD model results exhibited that the lowest risk could be in the airplane and the highest in the bus because of the location of airflows and outflows. The discrete CFD model analysis determined the ACH for a typical car of about 4.3, a typical bus of about 7.5, and in a typical airplane of about 8.5, which were all less than the standard protocol of infection prevention, 12 ACH. According to the results, opening windows in the cars could decrease the aerosol loads and improve the low ACH by the HVAC systems. However, for the buses, a new design for the outflow location or an increase in the number of outflows appeared necessary. In the case of airplanes, the airflow paths were suitable, and by increasing the airflow speed, the required ACH might be achieved. Finally, in the closed (recirculating) systems, the role of filters in decreasing the risk appeared critical.

Risk of SARS‐CoV‐2 in a car cabin assessed through 3D CFD simulations

“…All the ventilation modes were tested considering outside air intake provided by a HVAC system, which is with no air recirculation; the windows were considered closed for the entire duration of the journey. Different HVAC flow rates (from 10% to 100% of the maximum flow rate), Q (m 3 h −1 ), were investigated: in particular, the intermediate airflow rate (flow rate at the 50% of the maximum fan capacity, hereinafter referred as Q 50% ) is set at 216 m 3 h −1 on the basis of the value adopted by Pirouz et al in their study 49 ; this value is consistent with the intermediate fan capacity reported by Ullrich et al 50 for a real car whose internal volume is comparable to that of the cabin model employed for the scenarios under study. We point out that the flow rate also affects the velocity ( u ) at the inlet sections and then the velocity field in the car cabin; moreover, in the simulations here performed a single angle of inlet air‐flow rate was adopted.…”

How opening windows and other measures decrease virus concentration in a moving car

“…The continuous development of computational fluid dynamics (CFD) theory and the associated simulation tools and the rapidly growing computing power have made it much easier than ever to analyse complex flow problems in various engineering applications. ANSYS Fluent is one of the most frequently-used CFD software, and it is also the main simulation platform for the aforementioned studies (Ibrahim and Mehta, 2018;Pirouz et al, 2021;Kale et al, 2007). ANSYS Fluent provides comprehensive modelling capacities for a wide range of incompressible and compressible, laminar and turbulent fluid flow problems, and more technical information can be found in its official user's guide.…”

Electric Bus Indoor Heat Balance in Cold Weather

“…Ventilation and ambient loads are functions of the temperature difference between the cabin and the ambient load. The air flow rate for the buses depends on the operating of the air conditioning system, with values between the 0.05 m 3 /s and 0.3 m 3 /s [28]. For the city buses with frequently stops, the fresh air supplied by ventilation is dominated by the air flow through the open doors, and the ventilation can be used for the lower value, which is 0.05 m 3 /s [28].…”

“…The air flow rate for the buses depends on the operating of the air conditioning system, with values between the 0.05 m 3 /s and 0.3 m 3 /s [28]. For the city buses with frequently stops, the fresh air supplied by ventilation is dominated by the air flow through the open doors, and the ventilation can be used for the lower value, which is 0.05 m 3 /s [28]. Heat transfer due to the ventilation can be estimated with Formula (8) and depends on the temperature difference (∆T), the specific heat, the air density (ρ air ) and the air flow rate ( .…”