Handbook on Functional Requirements of Buildings (Other than Industrial Buildings)

IS SP Part 41: Scope - Key Formulas, Tables & Specifications

Scope Summary:
The code addresses daylighting, ventilation, and thermal performance of buildings, focusing on louvers, sky components, glazing, and building layouts.

Key Terms (Clause 3.4.3.1)

• P: Outward projection of louver perpendicular to wall (base dimension).
• B: Angle of louver inclination from wall normal (0° = normal).
• Spacing: Distance between adjacent louvers, increases with B.

Important Tables & Parameters

Sample Formula for U-Value (Clause 5.2)

[ U = \frac{1}{R_{si} + \sum \frac{d_i}{k_i} + R_{so}} ]

• (R_{si}), (R_{so}): Internal and external surface resistances
• (d_i): Thickness of ith layer (m)
• (k_i): Thermal conductivity of ith layer (W/m·K)

Visual: Louver Parameters

graph LR
A[P: Projection] --> B[Wall]
B --- C[Louver at angle B]
D[Spacing] --> C

Summary

• Use P, B, and spacing to design louvers.
• Refer to Tables 3 & 4 for sky component penetration and spread.
• Use Table 8 for window maintenance

IS SP Part 41 - Terminology & Definitions Key Points

1. Louvers (Clause 3.4.3.1)

• P: Outward projection of louver perpendicular to wall (base dimension).
• B: Angle of inclination from normal to wall; B=0 means louver normal (vertical/horizontal).
• Spacing: Distance between adjacent louvers; increases with B for same P, reducing louver count.

2. Thermal Spaces (Clause 1.88)

• Closed space: ≥1.88 cm wide, bounded by ordinary materials or reflective insulation.
• Open space: ≥1.88 cm wide.
• Variations include corrugated surfaces and plane-to-corrugated contact.

3. Surface Properties (Table 5 - Clause 4.1.3.6)

4. Daylight & Ventilation (Tables 7, 8, 9)

• Daylight availability depends on block layout and spacing.
• Window maintenance factors vary by location, window position, and time.
• Diffuse transmittance of glazing materials ranges from 0.40 (glass fiber sheets) to 0.85 (clear glass).

Summary Diagram: Louvers Geometry

graph TD
  Wall -->|Normal| Louver
  Louver -->|Projection P| Outward
  Louver -->|Angle B| Inclination
  Louver -->|Spacing| Adjacent Louvers

Use these definitions and tables for design calculations related to ventilation, daylighting, and thermal performance as per IS SP 41.

IS SP Part 41: Climatic Data for Buildings - Key Points

1. Climatic Data (Clause 1.4 & 1.5.2)

• Provides hour-wise design dry bulb (DB) and wet bulb (WB) temperatures for representative Indian cities (Jodhpur, Bombay, New Delhi, Hyderabad).
• Essential for thermal comfort and HVAC load calculations.

2. Design Dry Bulb & Wet Bulb Temperatures (Excerpt from Table 1)

(Refer full table for all hours)

3. Building Index & Comfort Conditions (Clause 9.4, Table 18)

• Building Index quantifies cooling load based on construction type, orientation, insulation, and shading.
• Comfort conditions classified as:
  • SW: Slightly Warm
  • H: Hot
  • C: Cool
  • C-SW: Cool to Slightly Warm

Key Formulas, Tables & Specifications for Daylighting (IS SP:41 Part 4)

1. Daylight Factor (DF) Concept

• Daylight Factor (DF) = (Indoor illuminance / Outdoor illuminance) × 100%
• Target DF typically ranges from 1% to 5% for adequate daylighting.

2. Window Area as % of Floor Area (From Fig. 14 & 15, IS 7942-1976)

• Window area depends on:
  • Room floor area and depth (up to 12 m)
  • Window location (shorter or longer wall)
  • Window type:
    • (a) Open aperture
    • (b) Glazed with 3 mm glass
    • (c) Wooden window (more daylight cut-off)
    • (d) Metal window (less daylight cut-off)

3. Assumptions for Design Curves (Clause 3.6.1)

• Ceiling, walls, floor reflectance: 70-75% (white finish)
• Light finish: ~40% reflectance

4. Diffuse Transmittance of Glazing (Table 9)

5. Window Maintenance Factors (Table 8)

• Varies by location and window orientation, e.g., vertical windows in clean offices: 0.83 average over 6 months

6. Design Aids

• Use sky component protractors and nomograms for internal reflected components (from IS 2440-1975).

Thermal Performance of Building Elements (IS SP 41)

Key Formulas & Definitions

• Overall Thermal Transmittance (U-value):
  [ U = \frac{1}{R_{total}} = \frac{1}{\sum \frac{d_i}{k_i} + R_s} ]
  Where:

  • (d_i) = thickness of layer (i) (m)
  • (k_i) = thermal conductivity of layer (i) (W/m·K)
  • (R_s) = surface thermal resistance (assumed constant for design)

• Thermal Damping (D %): Percentage reduction of temperature amplitude through the element.

• Thermal Time Constant (h): Time lag in hours for heat to pass through.

Important Tables

1. Thermal Performance of Walls (U-values, Time Constant, Damping)

PL = Plaster

2. Solar Optical Properties of Glazing

3. Emissivity & Reflectivity of Surfaces

Lighting Design Principles & Methods (IS SP Part 41)

Daylighting Design

• Based on clear design sky for Indian conditions.
• Daylight indoors depends on:
  • Window size & location
  • Room size & interior finish
  • External obstructions (buildings, trees)
• Components considered:
  • Sky Component (SC)
  • Externally Reflected Component (ERC)
  • Internally Reflected Component (IRC)
• Use design curves (from IS:2440 & IS:7942) to find window area as % of floor area for required daylight factor.
• Tools:
  • Sky component protractors
  • Nomograms for IRC
  • Lux grids (IS:7942)

Artificial Lighting Design

• Methods:
  • Lumen method (for general lighting)
  • Point-by-point method (for local lighting)
• Supplementary lighting:
  • General supplementary lighting design curves based on window size % and floor area.
  • Local supplementary lighting designed by point-by-point method.

Key Formulas & Laws

• Inverse Square Law:
  [ E \propto \frac{1}{d^2} ] Illuminance (E) decreases with square of distance (d).

• Lambert’s Cosine Law:
  [ E = E_0 \cos \theta ] Illuminance depends on angle (\theta) of incidence.

• Cosine Cubed Law:
  Accounts for mounting height and angle effects on illuminance.

Reflectance Values for Interior Finish (Typical)

Supplementary Lighting (Table Extract)

flowchart TD
    A[Daylighting Design] --> B[Window size & location]
    A --> C[Room size & finish]
    A --> D[External obstructions]

Detailed content not available.

Key Formulas and Specifications for Solar Control & Shading Devices (IS SP Part 41):

1. Shade Factor (S)

Shade factor quantifies shading device effectiveness: [ S = \frac{\text{Solar heat gain through fenestration}}{\text{Solar heat gain factor through ordinary clear glass}} ]

• S is nearly constant for practical use.
• Used to compare shading devices.

2. Total Heat Gain (THG) through Fenestration

[ THG = S \times SHGF + U \times (T_o - T_i) ]

• SHGF: Solar Heat Gain Factor for 3 mm clear glass.
• U: Thermal transmittance (W/m²K).
• T_o, T_i: Outside and inside temperatures.

3. Thermal Performance Index (Table 6)

4. Shade Factors & U-values for Shading Devices (Table 15)

Energy Requirements for Cooling and Heating (IS SP Part 41)

Key Points from IS SP Part 41:

• Clause 4.3: Cooling and heating load must be calculated considering building characteristics and comfort conditions.
• Clause 10.8.3 (Tables 19 & 20): Defines inside design dry bulb and wet bulb temperatures for comfort air-conditioning.

Inside Design Conditions for Comfort Air-Conditioning

Cooling Load Estimation

• Consider building index (Table 18) based on construction type, orientation, shading, and insulation.
• Use factors like solar heat gain, internal heat sources, ventilation, and infiltration.

Typical Cooling Load Formula

[ Q = U \times A \times \Delta T + Q_{solar} + Q_{internal} + Q_{ventilation} ]

Where:

• (Q) = Cooling load (W)
• (U) = Overall heat transfer coefficient (W/m²°C)
• (A) = Surface area (m²)
• (\Delta T) = Temperature difference (°C)

Block Diagram Concept (from Fig. 7 & 8)

flowchart LR
    B[Outdoor Air Duct] --> D[Tempering Coil]
    D --> G[Heating Coil]
    G --> H[Cooling Coil]
    H --> L[Duct for Zone]
    L --> Room[Conditioned Room]
    Room --> TI[Heating Thermostat]
    Room --> T2[Cooling Thermostat]

Summary

• Use Tables 19 & 20 for inside design temperatures.
• Apply **building

IS SP Part 41: Air-Conditioning & Mechanical Ventilation Key Points

1. Inside Design Conditions (Clause 10.8.3)

Refer Tables 19 & 20 for detailed stepwise values.

2. Cooling Load Estimation (Clause 10.4.3)

• Consider building orientation, insulation, shading, and glass area.
• Use Building Index from Table 18 to adjust comfort conditions.
• Example:
  • Top floor, unshaded glass, South orientation → Building Index = 87, Comfort Condition = SW (Summer Wet)

3. Solar Heat Gain (Table 23)

• Solar heat gain = Coefficient × Area (A)
• Orientation affects heat gain significantly (East/West higher than North).

4. System Components (Figures 7 & 8)

• Typical central system includes:
  • Dampers (Return, Outdoor max/min)
  • Coils (Tempering, Heating, Cooling, Reheating)
  • Thermostats (Room, Duct, Outdoor air)
  • Valves (V1, V2, V3, V4)

Summary Diagram of Central AC System

flowchart LR
    B[Outdoor Air Duct] --> D[Tempering Coil]
    D --> G[Heating Coil]
    G --> H[Cooling Coil]
    H --> L[Duct to Zone]
    L --> Room[Room]
    Room --> TI[Heating Thermostat]
    Room --> T2[Cooling Thermostat]
    B --> T3[Outdoor Air Duct Thermostat]
    L --> T6[Duct Thermostat]
``

IS SP Part 41 - Surface Reflectance & Interior Finishes

Key Tables

Table 5: Reflectance of Common Finishes

Table 6: Desirable Reflectances of Room Surfaces

Important Notes on External Obstructions (Clause 3.5.5)

• External obstructions reduce sky component but increase external reflected component.
• External reflected component ∝ reflectance × illuminance × solid angle subtended.
• Obstructions ≥ 3× their height away from window facade are negligible.

Reflectance & Heat Flow Relation

• Reflectance affects daylight and thermal comfort.
• Use higher reflectance for ceilings and walls to maximize daylight.
• Lower reflectance floors reduce glare.

Formula for External Reflected Component (simplified):

[ E_{reflected} \propto \rho_{obstruction} \times E_{obstruction} \times \Omega ] Where:

• (\rho_{obstruction}) = Reflectance of obstruction surface
• (E_{obstruction}) = Illuminance on obstruction
• (\Omega) = Solid angle subtended by obstruction at point

Summary:

• Choose light colors (white, cream) for

IS SP Part 41 - Glazing Materials and Fenestration: Key Formulas, Tables & Specs

1. Thermal Transmittance (U-value)

[ U = \frac{1}{\sum \frac{d_i}{k_i} + R_s} ]

• (d_i) = thickness of layer i (m)
• (k_i) = thermal conductivity of layer i (W/m·K)
• (R_s) = surface resistance (assumed constant)

2. Shade Factor (S)

[ S = \frac{\text{Solar heat gain through fenestration}}{\text{Solar heat gain factor through 3 mm ordinary clear glass}} ]

• Used to compare shading efficacy.
• Total Heat Gain (THG): [ THG = S \times SHGF + U \times (T_o - T_i) ]
• (SHGF) = Solar Heat Gain Factor for ordinary clear glass
• (T_o, T_i) = outside and inside temperatures

3. Solar Optical Properties of Glazing (Table 7 excerpt)

4. Diffuse Transmittance of Glazing (Table 9 excerpt)

5. Thermal Performance Index (Table 6)

| Index Range (Non-AC)

Thermal Comfort & Performance Indices — IS SP Part 41 Key Points

1. Thermal Comfort Definition (Clause 2.3 & 4.3.1)

• Thermal comfort: Condition where body heat balance is maintained at normal temperature without sweating.
• Upper limit of comfort: 27.5°C effective temperature for everyday work.
• Air movement (wind speed) is critical for comfort in hot/humid climates.

2. Wind Speed for Thermal Comfort (Clause 4.3.1)

• Note: "*" = No wind speed needed; "+" = Higher than practical.

3. Air-Conditioning Design Conditions (Clause 10.8.3)

4. Building Index & Comfort Conditions (Table 18, Clause 9.4)

IS SP Part 41: Design Aids & Worked Examples Summary

• Appendix A contains detailed worked examples illustrating design computations step-by-step.
• Clause 5.2.1 references Figure 4, which provides typical construction values for components like walls, floors, and roofs.
• Clauses 3.7 & 6.3 include additional worked examples to clarify calculation methods.

Key Design Aids (from Figure 4 & examples):

Common Formula for Heat Transfer:

[ Q = U \times A \times \Delta T ]

• Q = Heat loss/gain (W)
• U = Overall heat transfer coefficient (W/m²K)
• A = Area (m²)
• ΔT = Temperature difference (K)

Visual: Simplified Heat Transfer Path

flowchart LR
    Inside[Inside Air] -->|Convection| WallSurface1[Wall Surface]
    WallSurface1 -->|Conduction| WallCore[Wall Core]
    WallCore -->|Conduction| WallSurface2[Wall Surface]
    WallSurface2 -->|Convection| Outside[Outside Air]

Use Appendix A and Clauses 3.7, 5.2.1, and 6.3 for detailed stepwise calculations and component-specific data.

IS SP Part 41: Special Considerations & Limitations - Key Formulas & Tables

1. Daylight Availability (Clause 3.5.5.1) - Table 7

2. Window Maintenance Factors (Clause 3.5.6) - Table 8

Values reduce over time; plan maintenance accordingly.

3. Diffuse Transmittance of Glazing (Clause 3.5.6.2) - Table 9