CFD for analyzing pollutant dispersion in parking garage

Background

A HVAC consulting company was designing an underground parking lot for a shopping mall. The parking lot had to be designed ensuring proper ventilation, distribution of temperature and exhaust for gases.

There was a concern that traditional calculation approaches would not give the necessary accuracy and would cause excessive costs in changes after the installation of the ventilation system.

So CFD analysis was considered an an alternative.

Challenges

  • The indoor operation of automobiles presents many concerns such as the emission of carbon monoxide, nitrous oxide, and oil and gasoline fumes. However, it is generally accepted that the ventilation required to dilute carbon monoxide to acceptable levels can also control the other contaminants satisfactorily.
  • A secondary concern is maintaining sufficient draft on each underground floor to avoid mold growth.
  • The traditional approach to designing the ventilation system would have been to use hand calculations, where accuracy is reduced by several factors. First, these calculations do not take the geometry of the structure into account. Second, they determine only average carbon monoxide content but not the spatial distribution or gradients in the distribution which can have an important impact. The result is that engineers are unable to be certain about the performance of the design until the ventilation system is installed and tested.
  • This creates the possibility that expensive changes will have to be made after testing is performed.
  • It is for these reasons that CFD was used analyze ventilation system designs and predict indoor air quality in advance to avoid expensive changes later.

Technical approach for CFD Analysis

  • Appropriate Boundary conditions were considered for Ceiling, wall and floor, Supply air temperature, Exhaust & Entrance and ACH.
  • Standard boundary conditions were considered for diffusers.
  • The available commercial meshing tool was used to generate combined Tetrahedral and hex mesh.
  • Standard Navier-Stokes equation was used for Flow and heat transfer modeling.

Results of and Conclusions from the CFD Analysis

  • The velocity vector shows a well-mixed scenario with velocity uniformly distributed.
  • The ventilation system is capable of removing heat keeping the average temperature of the parking within the safety limit.
  • CO average mole fraction in the parking is close to zero ensuring safe environment.