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Natural Ventilation Calculator — Cheat Sheet
Quick-reference cheat sheet for the Natural Ventilation Calculator tool.
Published 27 May 2026
CHEAT SHEET
Natural Ventilation Calculator
Quick-reference companion for the free Portal tool
What This Tool Does
The Natural Ventilation Calculator is an essential online tool for South African architects on the Blind Solutions Architects Portal. It helps you quickly estimate the effectiveness of natural ventilation strategies in your building designs, ensuring compliance with thermal comfort standards and energy efficiency goals.
This tool is crucial during the early design phases to inform decisions on window placement, sizing, and building orientation. It assists in achieving SANS 10400-XA compliance by demonstrating adequate passive cooling and ventilation, reducing reliance on mechanical systems, and ultimately lowering operational costs for your clients. Use it when designing residential, commercial, or institutional buildings where natural ventilation is a primary cooling strategy.
Architects, environmental consultants, and sustainable design specialists will find this tool invaluable for optimising designs for South African climatic conditions, from the highveld to the coastal regions.
Step-by-Step Usage Guide
Step 1: Project & Location Details
Start by entering your project name and selecting the closest South African city. This helps the tool pull relevant climatic data (e.g., prevailing wind directions, average temperatures).
Start by entering your project name and selecting the closest South African city. This helps the tool pull relevant climatic data (e.g., prevailing wind directions, average temperatures).
Example Input:
Project Name: "Rosebank Office Block"
Location: "Johannesburg"
Project Name: "Rosebank Office Block"
Location: "Johannesburg"
Step 2: Building Type & Occupancy
Specify the building type (e.g., Office, Residential, School) and expected occupancy density. This influences the internal heat gains and fresh air requirements (per SANS 10400-O).
Specify the building type (e.g., Office, Residential, School) and expected occupancy density. This influences the internal heat gains and fresh air requirements (per SANS 10400-O).
Example Input:
Building Type: "Office"
Occupancy Density: "10 m²/person"
Building Type: "Office"
Occupancy Density: "10 m²/person"
Step 3: Room Dimensions & Orientation
Input the dimensions of the room or zone you are analysing (Length, Width, Height) and its primary orientation (e.g., North, East). This is critical for wind pressure calculations.
Input the dimensions of the room or zone you are analysing (Length, Width, Height) and its primary orientation (e.g., North, East). This is critical for wind pressure calculations.
Example Input:
Room Length: "8 m"
Room Width: "6 m"
Room Height: "3 m"
Primary Orientation: "North"
Room Length: "8 m"
Room Width: "6 m"
Room Height: "3 m"
Primary Orientation: "North"
Step 4: Window & Opening Specifications
Add details for all ventilation openings (windows, louvres, doors). Specify their dimensions (Width, Height), type (e.g., Casement, Sliding, Louvred), and whether they are inlet or outlet. The tool factors in effective opening areas.
Add details for all ventilation openings (windows, louvres, doors). Specify their dimensions (Width, Height), type (e.g., Casement, Sliding, Louvred), and whether they are inlet or outlet. The tool factors in effective opening areas.
Example Input:
Opening 1 (Inlet): Width "1.5 m", Height "1.2 m", Type "Casement", Located on "North" wall.
Opening 2 (Outlet): Width "1.0 m", Height "1.0 m", Type "Top-Hung", Located on "South" wall.
Opening 1 (Inlet): Width "1.5 m", Height "1.2 m", Type "Casement", Located on "North" wall.
Opening 2 (Outlet): Width "1.0 m", Height "1.0 m", Type "Top-Hung", Located on "South" wall.
Step 5: External Conditions & Internal Gains
Adjust external temperature, desired internal temperature, and any specific internal heat gains (e.g., equipment, lighting). The tool uses default values based on location, but you can refine them.
Adjust external temperature, desired internal temperature, and any specific internal heat gains (e.g., equipment, lighting). The tool uses default values based on location, but you can refine them.
Example Input:
External Air Temperature: "28 °C"
Desired Internal Temperature: "24 °C"
Internal Heat Gains (Other): "5 W/m²"
External Air Temperature: "28 °C"
Desired Internal Temperature: "24 °C"
Internal Heat Gains (Other): "5 W/m²"
Step 6: Calculate & Interpret Results
Click "Calculate" to generate the ventilation rate (ACH - Air Changes Per Hour), air velocity, and a comfort assessment. The tool will indicate if the design meets recommended ventilation standards for the chosen building type.
Click "Calculate" to generate the ventilation rate (ACH - Air Changes Per Hour), air velocity, and a comfort assessment. The tool will indicate if the design meets recommended ventilation standards for the chosen building type.
Expected Output:
Ventilation Rate: "6.5 ACH" (e.g., "Meets SANS 10400-O requirements for offices")
Average Air Velocity: "0.25 m/s"
Ventilation Rate: "6.5 ACH" (e.g., "Meets SANS 10400-O requirements for offices")
Average Air Velocity: "0.25 m/s"
Common Scenarios & Expected Results
| Scenario | Input | Expected Output |
|---|---|---|
| Cross-Ventilation in Coastal Home (Cape Town) |
Location: Cape Town Room: 5x4x2.8m, East-West orientation Inlet: 1.5x1.2m Casement (East) Outlet: 1.5x1.2m Casement (West) Wind Speed: 3m/s (default for summer) Desired Temp: 23°C |
High ACH (e.g., 8-12 ACH) due to effective cross-ventilation and coastal winds. Good thermal comfort, minimal overheating risk. |
| Single-Sided Ventilation in Highveld Office (Pretoria) |
Location: Pretoria Room: 7x5x3m, North orientation Inlet/Outlet: Two 1.2x1.0m Top-Hung (North wall) Wind Speed: 1.5m/s (low, typical for calm days) Desired Temp: 24°C |
Moderate ACH (e.g., 2-4 ACH), potentially insufficient for peak summer heat without additional strategies. May indicate a need for stack effect or larger openings. |
| Stack Effect in School Hall (Durban) |
Location: Durban Hall: 15x10x6m, Multi-orientation Low Inlets: Four 2x1.5m Louvred (East/West) High Outlets: Two 1.5x1.0m Roof Vents External Temp: 30°C, Desired Temp: 26°C |
Good ACH (e.g., 5-7 ACH) driven by temperature difference. Effective in hot, humid climates for heat expulsion. |
Pro Tips
Consider the SANS 10400-XA Context:
Remember that natural ventilation is a key component of passive design strategies for energy efficiency. Use this tool alongside other considerations like shading, insulation, and thermal mass to achieve holistic compliance. It's not just about air changes, but comfortable air changes.
Wind Rose Data is Your Friend:
Always refer to local wind rose data for your project's specific location. While the tool provides defaults, understanding prevailing wind directions and speeds throughout the year will allow you to orient openings optimally for maximum effect. For Johannesburg, north-easterly winds are common in summer.
Stack Effect vs. Wind-Driven Ventilation:
Distinguish between these two mechanisms. Wind-driven ventilation relies on pressure differences, while stack effect relies on temperature differences (hot air rises). For taller buildings or areas with consistent temperature differentials, ensure you have well-placed high and low openings to maximise stack effect.
Don't Forget About Air Quality:
While this tool focuses on thermal comfort and airflow, good natural ventilation also dilutes internal pollutants. Ensure your inlets are not drawing air from undesirable sources (e.g., busy roads, industrial areas) and consider filtration for urban sites if necessary.