Simulation of naturally ventilated underground car park with CFD

Use your smartphone to scan this QR code and download this article ABSTRACT The basement car park is a popular solution to effectively use urban land, especially in commercial centers and apartments. However, the situation of apartment fire and explosion is a hot problem, partly due to the tunnel ventilation has not met the requirements of fire safety. Therefore, the design of the car park basement ensures fire safety as well as bring comfort to people. In this study, the computational fluid dynamics (CFD) method has been applied to determine the pressure and velocity intensity for buildings that detect residuals in architecture, thereby improving and providing an optimal solution. The Ansys CFX commercial software is used to simulate the ventilation process in a parking basement. In Ansys CFX, the Shear-Stress Transport turbulence model is used to determine the temperature and velocity of the tunnel and calculate the level of physical comfort according to ADPI standard. Firstly, a simulation problemof ventilation in theworkshop room is also performed to verify the reliability. Finally, the problem of basement temperature and wind velocity by natural ventilationmethod will be analyzed and evaluated in accordance with ADPI standard and carbonmonoxide concentrationwithWHO standard to identify areas of unsatisfactory temperature and velocity to reasonably adjust and propose other suitable ventilation options. The results from this study present a promising natural ventilation analysis procedure and technique for car parking basements of tall buildings in major cities.


INTRODUCTION
Nowadays, the speed of urbanization is increasing rapidly, so the urban land area is fully utilized to build high-rise buildings, apartments, and commercial centers and thus, the parking basement also become more popular. However, apartment fire and explosion, especially car fire and explosion is an extremely important issue that must be concerned in construction design. Therefore, it is essential to design an effective ventilation system in the parking basement when a fire occurs. When building up the car park, the importance is not only a reasonable architecture but also the ventilation and air quality of the tunnel because it directly affects human health. Decades ago, scientists had studied the solution to ventilate the car park. The computational fluid dynamics (CFD) method is also applied to determine the pressure and velocity intensity for buildings that detect residuals in architecture, thereby improving and providing a superior solution. Many studies related to this issue have been published internationally. Jiang 1 also investigated natural ventilation by using Reynolds Averaged Navier -Stokes turbulence model (RANS). Khalil 2 also examined the distribution of CO emissions from buses in a basement in Cairo using ANSYS FLUENT software.
In this paper, Ansys CFX commercial software is used to simulate the ventilation process in a parking basement. In addition, a simulation problem of ventilation in the office room is also performed to verify the reliability. In Ansys CFX, the Shear-Stress Transport turbulence model is used to determine the temperature and velocity of the tunnel and calculate the level of physical comfort according to ADPI standard.

Natural Ventilation
Natural ventilation occurs when the air in a space is exchanged outside without using mechanical systems such as fans. Common types of natural ventilation are made through open windows but can also be achieved through differences in temperature and pressure between spaces. However, opening a window or grounded structure is not a good choice for basement ventilation or underground structures.

Mechanical Ventilation
Mechanical ventilation or forced system is through an air handling unit or directly into space by fans. Local

Analytical Methods
Commercial software ANSYS CFX is the key tool for calculating velocity, temperature and then comparing it to the APDI standard 3 . The EDT (Effective Draft Temperature) indicator is calculated by the following formula: Where:

The Problem Model Room Study Problem
The problem is based on the Workshop Room Study of ANSYS CFX 5 as shown in Figure 1. The velocity and temperature field between the two models after re-modeling the sample problem on ANSYS CFX 19.1 is shown in Figure 2.

The Car Park Basement Problem
The

Room Study Model
Take the value of velocity and temperature at certain points from the results of the two problems to compare and evaluate the error. The degree of error of temperature and velocity of the two problems is shown in Figure 3. The difference temperature and velocity results between two problems is calculated according to the following formula: Where: X: The considered object It is easy to see that the temperature at 20 specific points between the two problems has no big difference, with the average error value of 0.080965%. While the speed at these points is quite different, the average error value is 8.724897%. This difference comes mainly from the version of Ansys software, due to the differences between the Reynolds coefficient and the other coefficients between the two versions 12.0 and 19.1.

Car Park Basement Model
The temperature and velocity fields and CO volume fraction are shown in the Figures 4, 5 and 6. Through simulation results from Figure 4 and Figure 6, it can be seen that the high temperature zone is also the area with high concentration of CO. Take 20 points in the entire air flow to calculate and compare the APDI standard, the velocity, temperature and EDT index of the points shown in are not yet achieved, equivalent to 85% of the APDI standard. Therefore humans can be comfortable in this air condition. Besides, the max CO concentration of this space is just 6.375e-6 which showed at Figure 6, so it is good for human health according to WHO standards 6 .

CONCLUSIONS
The present study has shown the safety and rationality in the design of the car park to ensure both mechanical and biochemical safety by considering factors related to APDI and WHO standards. Besides, the topic still has a number of points left unresolved, namely, only research on carbon monoxide concentration, not considering other harmful emissions and not yet diversified in vehicle types. The simulation results visually show the temperature and CO distribution in the parking basement. From there, better designs for ventilation can be made based on current standards.