Code of practice for natural ventilation of residential buildings

IS 3362: Scope - Key Specifications and Tables

• Scope Definition (Clause 2.0): Defines terms relevant to the standard's application.

• Thermal Comfort Wind Speeds (Clause 4.2):
  Table 1 lists desirable wind speeds (m/s) for various combinations of dry bulb temperature (28°C to 35°C) and relative humidity (30% to 90%).
  Example excerpt:

  Temp (°C)	30% RH	50% RH	70% RH
  28	+	*	.
  32	0.20	0.94	2.26

• Minimum Wind Speeds for Acceptable Warm Conditions (Clause 4.2):
  Table 2 provides minimum wind speeds (m/s) for comfort at given temperature and humidity ranges.

• Indoor Wind Velocity (Clause 21.2):
  Average indoor wind velocity = 0.265 × (1 - 20/100) × outdoor wind velocity
  = 21.2% of outdoor wind velocity

• Rounding Off (Clause 0.5):
  Final values must be rounded per IS:2-1960, retaining the same significant figures as specified.

Summary Formula for Indoor Wind Velocity:

[ V_{indoor} = 0.265 \times (1 - 0.20) \times V_{outdoor} = 0.212 \times V_{outdoor} ]

For detailed design, refer to Tables 1 & 2 for wind speed recommendations based on temperature and humidity to ensure thermal comfort as per IS 3362.

IS 3362 - Key Definitions & Tables Summary

Definitions (Clause 2.0 & 2.6)

• Openings: Openings in buildings provided specifically for ventilation.

Thermal Comfort Tables (Clause 4.2)

• "+" indicates values higher than acceptable in practice.
• Wind speeds increase with temperature and humidity for comfort.

Minimum Wind Speeds for Warm Conditions (Clause 4.2)

• "*" indicates no minimum wind speed required.
• "+" indicates values higher than acceptable in practice.

Indoor Wind Velocity (Clause 21.2)

• Formula:
  [ V_{indoor} = 0.265 \times (1 - 0.20) \times V_{outdoor} = 0.212 \times V_{outdoor} ]
• Average indoor wind velocity is approximately 21.2% of outdoor wind velocity.

Summary Table Example (Desirable Wind Speeds)

For full tables and detailed values, refer to Clause 4.2 of IS 3362.

flowchart LR
    OutdoorWindVelocity -->|0.212 x| IndoorWindVelocity[Indoor Wind Velocity]
    IndoorWind

IS 3362: Essential Factors Necessitating Ventilation

Key Points from IS 3362:

• Purpose of Ventilation: To ensure removal of indoor pollutants, control humidity, and maintain thermal comfort.
• Factors Necessitating Ventilation:
  • Removal of moisture and odors
  • Dilution of indoor pollutants (CO2, smoke, gases)
  • Control of temperature and humidity
  • Health and comfort of occupants

Design Guidelines (Clause 6 & Appendix A):

• Wind Direction for Design: Assume wind within ±30° of prevailing direction.
• Wind Speed for Wet Bulb Temp Measurement: ≥ 4.5 m/s (Clause 2.9).
• Natural Ventilation Rate Calculation:

[ Q = A \times V ]

Where:

• (Q) = Rate of airflow (m³/s)
• (A) = Effective opening area (m²)
• (V) = Indoor wind speed induced by outdoor wind (m/s)

Formula for Indoor Wind Speed (Simplified):

[ V_i = C_d \times V_o ]

Where:

• (V_i) = Indoor wind speed
• (V_o) = Outdoor wind speed (from prevailing direction)
• (C_d) = Discharge coefficient (typically 0.6 to 0.7)

Typical Ventilation Rates:

Summary Diagram of Natural Ventilation Concept:

flowchart LR
    Wind[Outdoor Wind] -->|Wind Pressure| Openings[Ventilation Openings]
    Openings -->|Air Flow Q = A × V| Indoor[Indoor Space]
    Indoor -->|Air Exchange| Outdoor[Outdoor Air]

Note: Refer to Appendix A of IS 3362 for detailed calculation steps and empirical coefficients.

IS 3362: Minimum Standards for Ventilation - Key Points

1. Minimum Ventilation Requirements (Clause 4.1)

• Ventilation is primarily to control body odour and remove combustion products.
• Fresh air needed to maintain safe CO₂ and oxygen levels is minimal.
• Standards focus on adequate air changes to ensure comfort and safety.

2. Ventilation Rate Calculation (Clause 5.2 & Appendix A)

• Ventilation rate is determined by wind pressure and indoor wind speed.

• Probable indoor wind speed can be estimated using:

  [ V_i = C \times V_o ]

  where:

  • (V_i) = indoor wind speed
  • (V_o) = outdoor wind speed
  • (C) = coefficient depending on building design and openings

3. General Design Guidelines (Clause 6)

• Provide cross ventilation with openings on opposite walls.
• Minimum opening area should be at least 5% of floor area for residential buildings.
• Ensure unobstructed airflow paths inside rooms.

4. Typical Table: Minimum Opening Area for Ventilation

flowchart LR
    A[Outdoor Wind] -->|Wind Pressure| B[Window/Openings]
    B -->|Airflow| C[Indoor Space]
    C -->|Exhaust| D[Other Openings]
    D --> A

This cycle ensures continuous fresh air exchange maintaining indoor air quality as per IS 3362.

IS 3362: Calculation of Ventilation Rate and Indoor Wind Speed

Key Formulas (Appendix A)

• Ventilation Rate (Q):
  [ Q = K \times A_s \times V_o ] where:

  • (Q) = ventilation rate (m³/h)
  • (K) = coefficient of effectiveness (depends on wind direction and opening areas)
  • (A_s) = area of smaller opening (m²)
  • (V_o) = outdoor wind speed (m/s or km/h)

• Coefficient of Effectiveness (K):

  • Depends on:
    • Wind direction relative to openings (max when perpendicular)
    • Ratio of larger opening area to smaller opening area
  • Values given in Figure 1 for wind at 0° and 45°

Typical Values of K (from Figure 1)

Indoor Wind Speed

• Indoor wind speed is proportional to ventilation rate and opening geometry.
• Example:
  • Square openings of 0.36 m side, wind 5 km/h at 45°, yield ~194 m³/h flow, sufficient for a 4x4x4 m room.

Notes:

• Outdoor wind speed data: Refer Climatological and Solar Data for Design of Buildings for Comfort in India, CBRI Roorkee.
• Use K values carefully considering wind direction and opening sizes.

flowchart LR
    Wind[Outdoor Wind Speed \(V_o\)]
    Opening1[Large Opening Area \(A_l\)]
    Opening2[Small Opening Area \(A_s\)]
    K[Coefficient of Effectiveness \(K\)]
    Q[Ventilation Rate \(Q = K \times A_s \times V_o\)]
    IndoorWindSpeed[Indoor Wind Speed]

    Wind --> Q
    Opening2 --> Q
    K --> Q

IS 3362: General Rules and Design Guidelines for Natural Ventilation

Key Points from Clauses 4.2 & 6.0

1. Ventilation Rate Determination (Clause 5.2 & Appendix A)

• Ventilation rate is based on wind pressure and indoor wind speed induced by wind action.
• Appendix A provides the method to calculate these parameters.

2. Thermal Comfort & Wind Speed (Clause 4.2, Tables 4.3)

• Table 1: Desirable Wind Speeds (m/s) for Thermal Comfort

• Symbols:
  • + Higher than acceptable in practice
  • * Recommended values
  • t

IS 3362: Effect of Wind Pressure on Ventilation — Key Points

1. Rate of Ventilation (Clause 5.2, Appendix A)

• Ventilation rate depends on wind pressure and induced indoor wind speed.
• Formula involves coefficient of effectiveness K, wind speed, and opening areas.

2. Coefficient of Effectiveness (K) (Clause A-3.1.1)

• Depends on:
  • Wind direction relative to openings.
  • Ratio of areas of two openings (inlet & outlet).
• Maximum when wind is perpendicular to the opening.
• Increases with the size of the larger opening relative to the smaller one.

(Values approximate from Figure 1 in IS 3362)

3. Ventilation Rate Example (Note 2)

• For a square opening 0.36 m side with an equal outlet area,
• Wind speed = 5 km/h at 45°,
• Airflow ≈ 194 m³/h, adequate for a 4x4x4 m room.

4. Design Guidelines

• Use verandahs open on three sides to enhance air motion.
• Consider wind from ±30° of prevailing direction for design.

Simplified Ventilation Rate Formula (from IS 3362 Appendix A):

[ Q = K \times A \times V ]

Where:

• ( Q ) = Volumetric airflow rate (m³/h)
• ( K ) = Coefficient of effectiveness (depends on wind direction & area ratio)
• ( A ) = Area of smaller opening (m²)
• ( V ) = Wind speed (m/s)

flowchart LR
    Wind[Wind Direction & Speed]
    Openings[Two Openings: Inlet & Outlet]
    K[Coefficient of Effectiveness (K)]
    Q[

IS 3362: Recommended Values & Design Data Summary

1. Wind Speed for Thermal Comfort (Clause 4.2)

• Table 1: Desirable wind speeds (m/s) depend on dry bulb temperature (28–35°C) and relative humidity (30–90%).
• Values range from near 0 to >3 m/s; higher speeds marked with "+" are beyond practical comfort.

2. Minimum Wind Speeds for Acceptable Warm Conditions (Clause 4.2)

• Table 2: Minimum wind speeds required for comfort at given temperature and humidity.
• Speeds vary from 0 to about 3 m/s, with "*" indicating no minimum required.

3. Ventilation Rate Based on Wind (Clause 5.2 & Appendix A)

• Ventilation rate depends on wind pressure and indoor wind speed induced.
• Coefficient of Effectiveness (K) varies with:
  • Wind direction relative to openings.
  • Ratio of areas of two openings.
• Maximum K when wind is perpendicular and larger opening dominates.

4. Indoor Wind Velocity (Clause 21.2)

• Average indoor wind velocity ≈ 0.265 × (1 - 20/100) × Ve
  where Ve = outdoor wind velocity.

5. Coefficient of Effectiveness K (Appendix A, Fig.1)

• K values plotted against area ratios and wind angles (0° and 45°).
• Example: For equal openings and 45° wind, flow through 0.36 m side square opening ≈ 194 m³/h.

Key Formula: Indoor Wind Velocity

[ V_{indoor} = 0.265 \times (1 - 0.20) \times V_{outdoor} = 0.212 \times V_{outdoor} ]

Practical Notes:

• Use Table 1 & 2 to select wind speeds for design.
• Refer to Appendix A for detailed ventilation calculations.
• For design, consider wind direction and opening sizes to estimate K.

flowchart LR
    Wind_Speed(Outdoor Wind Speed Ve)
    Coeff_K[Coefficient of Effectiveness K]
    Opening_Area_Ratio[Area Ratio of Openings]
    Wind_Direction[Wind Direction]
    Indoor_Wind

IS 3362: Typical Building Layouts and Airflow Patterns - Key Formulas & Tables

1. Ventilation Rate & Effectiveness Coefficient (K)

• K depends on wind direction and ratio of inlet/outlet areas.
• Maximum when wind is perpendicular to opening.
• Values of K are given for different area ratios (Fig. 1).

2. Indoor Wind Velocity Calculation

• Average indoor velocity at 0.9 m sill height:

  [ V_s = V_{0.9} + 0.072(1 - S) V_o ]

  • (V_{0.9}) = indoor velocity at 0.9 m sill (from Fig. 2)
  • (S) = sill height ratio ((S = \frac{\text{sill height}}{0.9}))
  • (V_o) = outdoor wind velocity

• Adjust for inlet/outlet area ratio using Performance Efficiency (E) (Fig. 4):

  [ V = E \times V_s ]

• Adjust for wind angle (Table 3):

  Condition	Multiplying Factor (45° wind)
  Inlet > Outlet	1
  Inlet = Outlet	0.8 to 0.85
  Inlet < Outlet	0.7

3. Correction Factors

• Window location (Table 4): ±10% to ±40% changes in indoor velocity.
• Louvers (Table 5): Typical changes from -25% to +10%.
• Verandah effects (Table 6): Changes from -50% to +15% depending on location and type.

4. Typical Dimensions & Areas (Fig. 5 Example)

Summary Flow Calculation:

[ Q = K \times A \times V_o ]

• (Q