Natural Ventilation Study.

Introduction:

Natural ventilation - To keep the buildings cool and well ventilated, almost all old buildings in the past were built using this concept. Due to increase in the energy cost, it is once again a popular alternate method to provide an acceptable indoor climate. It is a method of supplying fresh air to a building or a room by means of natural forces, typically wind speed or differences in pressure internally and externally.

Objective

The main objective of the CFD project was to determine if the natural ventilation would be sufficient to obtain an optimum temperature in the human occupied zone of the Academic block and then suggest design changes. The primary purpose of the building design is to create an indoor thermal comfort environment for the occupants inside the building.

The thermal comfort depends on three environmental factors, i.e. temperature, relative humidity & air velocity. These environmental factors vary independently of each other but act simultaneously on the human body. So it is not possible to express the thermal response of the human body in terms of any single factor as the influence of any one depends upon the level of others. So, the combination of influencing environmental factors into a single parameter is called Index of Thermal Comfort. The CFD study was used to evaluate the Thermal Comfort with the help of Tropical Summer Index (TSI) inside the building for naturally ventilated areas.

Modeling and Analysis:

3D model of the building was modeled and appropriate meshing and boundary conditions were applied. There were few assumptions done like if the suggested design of the building is comfortable for humans in these 3 extreme conditions, it would also be comfortable for the remaining hot months. Thus, we have selected these 3 worst case months for carrying out the CFD simulations to evaluate the TSI levels inside the proposed design of the building. 

The results obtained were used to determine the airflow distribution in and around buildings. The velocity profile, temperature, humidity levels inside the human occupied area was studied in the initial design. In the initial analysis it was found that natural ventilation was not enough to maintain appropriate temperature and high temperature was found in few areas.

Conclusion

CFD analysis was carried for functional use of the building in hot summer & dry humid months. After conducting the CFD analysis for the initial design, it was found that 70% of the areas inside the academic block were not having any air circulation which would create the discomfort level to occupants. The maximum limit for easily tolerable TSI level is 34 degrees. Design modifications were done using the CFD analysis to improve the natural ventilation system inside the building. 

As per the modified design CFD analysis, the velocity profiles & TSI profiles inside the building were improved as compared to initial design. 

For the month of July evening, the TSI levels were slightly exceeding (i.e. 34 to 36 °C) in 15% area of the complete building and remaining 85% of the building is within easily tolerable. 

The TSI levels for August & September months were within easily tolerable range. Thus the design of natural ventilation of the building was optimized in the building for maintaining the “easily tolerable thermal comfort levels” in the academic block.