Natural Ventilation Through Effective & Efficient Facade Design Using CFD Tools

Chhatrapati Shivaji Maharaj Terminus is a terminal railway station for the Suburban and long-distance node railway lines and lies in the Western Railways zone. The site is located in the capital city of Maharashtra. It is also a major landmark in the city. In 2004, UNESCO designated the building structure and its annexe as a World Heritage Monument. CSMT is a major transportation hub, connecting Mumbai to various parts of India. 14 lakh passengers (approx.) are handled at this station through the operation of over 500 (approx.) trains daily. The building has distinctive architectural value. Over the years, the terminus has become not only a transportation hub but also a popular tourist attraction.

The entire project shall have Green Building (Super ECBC) features with facilities for the reduction in energy consumption during construction as well as Operations & Maintenance. This is designed with passive energy-saving features, which promote the use of local materials and reuse the existing materials to the maximum extent possible.

How Does Natural Ventilation Work?

Natural ventilation relies on natural forces, like wind and temperature differences, to circulate air within a building/space, promoting fresh air intake and reducing indoor pollutants.

Here’s how it works:

1. Wind Pressure: When wind blows against a building, it creates pressure differences. Air enters through openings on the windward side and exits on the leeward side, facilitating cross-ventilation. In our design, a wind scoop has been proposed through the roof to intake fresh air for natural ventilation. Openings in the wall also have been considered.
2. Stack Effect: Warm air rises because it’s lighter than cool air. In a multi-story building, warm air from lower levels can escape through vents at higher levels, drawing in cooler air from below. This is particularly effective in taller structures.
   We have designed the naturally ventilated concourse based on the stack effect principle. Fresh cold air comes from outside the building, while hot air rises through the atrium and is released into the atmosphere due to the stack effect.
3. Thermal Buoyancy: Sunlight can heat parts of a building, causing air in those areas to warm up and rise. This movement creates a cycle where cooler air from outside is drawn in to replace the rising warm air. To counter such an issue, we considered openings on the wall in the design.
4. Design Features: Effective natural ventilation often depends on design elements like window placement, ceiling height, and the orientation of the building. Features like operable windows and ventilated atriums enhance airflow.
5. Climate Considerations: The effectiveness of natural ventilation varies based on local climate conditions, including temperature, humidity, and prevailing winds, however, we have captured the climatic data in our design.
   By applying the above principles, we have maintained a comfortable indoor environment and reduced the need for mechanical ventilation systems.

How CFD Tools Can Assist In Designing The Façade And Fenestration For Natural Ventilation?

Computational Fluid Dynamics (CFD) tools are invaluable for designing façades and fenestration to optimize natural ventilation in buildings. Here’s how they assist in the process:

1. Airflow Simulation

   • Visualizing Air Movement: CFD allows us to visualize airflow patterns around and within buildings, helping identify how air enters, circulates, and exits.
   • Understanding Ventilation Paths: By simulating different window configurations and orientations, we can pinpoint the most effective openings for cross-ventilation.

2. Performance Analysis

   • Evaluating Design Options: CFD can model various façade designs and fenestration strategies, enabling comparison of their effectiveness in promoting natural ventilation.
   • Identifying Hotspots: Simulations can highlight areas of stagnant air or overheating, guiding modifications to improve airflow and thermal comfort.

3. Wind Impact Assessment

   • Assessing Wind Patterns: CFD can analyze how wind interacts with the building shape and surrounding landscape, informing the placement and size of windows and vents to maximize natural airflow.
   • Simulating Different Conditions: We can test how different weather conditions (e.g., varying wind speeds and directions) affect ventilation performance.

4. Stack Effect Analysis

   • Vertical Airflow Dynamics: CFD tools can simulate the stack effect, showing how warm air rises and how it can be effectively expelled from higher openings, drawing cooler air in from lower levels.
   • Optimizing Ceiling Heights And Vent Locations: By analyzing the impact of ceiling heights and vent placements, we can optimize building layouts for better natural ventilation.

5. Thermal Comfort Evaluation

   • Indoor Climate Modeling: CFD can be used to assess how natural ventilation strategies impact indoor temperature and comfort levels, considering factors like solar gain and thermal mass.
   • Predicting Air Quality: Simulations can help predict the movement of pollutants or stale air, ensuring effective strategies for maintaining good indoor air quality.

6. Design Iteration and Optimization

   • Rapid Prototyping: CFD allows for quick iterations of design changes, enabling us to test multiple scenarios and optimize designs before physical implementation.
   • Cost-Effective Solutions: By identifying the most effective design solutions early in the process, CFD can reduce the need for costly modifications later in construction.

By leveraging CFD tools, we have designed the façades and fenestration systems that not only enhance natural ventilation but also contribute to overall building performance and occupant comfort.

Approach To Designing The Façade And Fenestration For Natural Ventilation In The Redevelopment Of Railway Station Buildings

Designing a façade and fenestration for natural ventilation involves a strategic approach that considers airflow, thermal comfort, and aesthetics. Here are key considerations:

1. Orientation and Placement

   • Wind Direction: Analyze prevailing wind patterns to optimize window placement for effective cross-ventilation.
   • Sun Orientation: Position windows to take advantage of natural light while minimizing heat gain from direct sunlight.

2. Wind scoop

   • Wind Scoops: This is an effective way to enhance ventilation and cooling in hot climates, drawing on the power of natural wind patterns. A wind scoop typically has an open top and a sloped or angled surface. Air intake louvres have been considered in the design for natural ventilation for the Concourse.

3. Window Types And Sizes

   • Operable Windows: We have considered casement, sliding, or awning windows in our design that can be easily opened to facilitate airflow.
   • Size Variation: We have considered the different sizes of windows to balance aesthetics and functionality, allowing for both larger openings for airflow and smaller ones for controlled ventilation.

     

4. Façade Design

   • Shading Devices: We have considered the elements that can block excessive sunlight while allowing airflow, which helps reduce indoor temperatures.
   • Roof And Balconies: A wind scoop has been planned in the roof for natural airflow and to enhance indoor comfort conditions.

5. Stack Ventilation

   • High Ceilings And Transom Windows: Utilise vertical atrium space to allow warm air to rise and escape through higher openings, encouraging cooler air to enter through lower openings.
   • Atriums Or Light Wells: We have designed the central spaces that can promote the stack effect, enhancing ventilation across multiple floors.

6. Landscaping

   • Strategic Planting: We are using trees and vegetation to block wind or shade windows, which can enhance the effectiveness of natural ventilation.

7. Simulation And Testing

   • CFD Analysis: We have conducted computational fluid dynamics (CFD) simulations to predict airflow patterns and optimize the design.
   • Performance Monitoring: We have implemented strategies for monitoring indoor air quality and temperature to evaluate the effectiveness of natural ventilation.

By integrating these elements, we have created façades and fenestration systems that enhance natural ventilation and contribute to the overall sustainability and comfort of buildings.

Materials Used For The Façade And Roof

Materials used for the façade and roof are selected to achieve comfortable temperatures for naturally ventilated buildings. Selecting materials for façades and roofs in naturally ventilated buildings is crucial for achieving comfortable indoor temperatures and optimizing natural ventilation.

Here are some key material considerations:

1. Roofing Materials

   • Cool roof materials: These are designed to reflect more sunlight and absorb less heat, helping to keep buildings cooler. To enhance sunlight reflection, we will utilize light-coloured, highly reflective paint.
   • Through The Roof: Zink Sheet with Rock wool/XLPE Insulation.
   • Concrete Roof: Deck Slab with XLPE/PIR/EPS Insulation

2. Glazing Options

   • Low-Emissivity (Low-E) Glass: This type of glass reflects infrared radiation while allowing visible light to pass through, reducing heat gain while maintaining natural light.
   • Coated Reflective Glass: This helps to control solar heat gain while still providing views and daylight.

3. External Exposed Wall Materials

   • External wall: 32mm Granite with 100mm XPS Insulation & 200mm AAC Block
   • Overall Heat Transfer Coefficient Of Materials: The materials have been selected based on their thermal properties, reflectivity, and permeability, to create naturally ventilated buildings that maintain comfortable indoor temperatures while promoting energy efficiency.

Quick Facts:

• Project: Redevelopment of Chhatrapati Shivaji Maharaj Terminus (CSMT) Railway Station and construction of associated Infrastructure.
• Location: Mumbai (Maharashtra), India
• Name of Client: Rail Land Development Authority (RLDA)
• Typology: Railway Station
• Architect: M/s. ANA Design Studio Pvt. Ltd
• Principal Architect: Amin Nayyar
• Name of Contractor: M/s. Ahluwalia Contracts (India) Ltd.
• Design Team: Jawed Ali, Somjit Sahani, Manoj Mondal, Pratima Pandey, Vivek Kumar, Aakriti, Ritesh Sutar, Sana, Saquib, Anant & Aishwarya, Praveen, Rabia, Tikam & Purshotam.
• Total Site Area: 3,18,536 sq m Approx.
• Built-Up Area: 4,00,000 sq m Approx.