Recommendations for orientation of buildings, Part 1: Non-industrial buildings

IS 7662 Part 1 (1974) – Scope & Key Specifications

• Scope: Defines solar radiation data computation under standard atmospheric conditions:

  • Cloud-free sky
  • Dust particles: 300 particles/cm³
  • Precipitable water: 15 mm
  • Ozone: 2.5 mm
  • Altitude: Sea level

• Solar Radiation Data:

  • Direct solar radiation intensity is given in calorie/cm²/hr normal to the sun.
  • Solar altitude angles and solar geometry are defined for calculation of incident radiation on surfaces.
  • Data is tabulated for different latitudes and hours, based on Climatological and Solar Data for India (CBRI, Roorkee).

• Rounding Off: Values should be rounded per IS 2-1960, retaining significant digits equal to the specified values.

Key Formula (Solar Intensity on Tilted Surface)

[ I = I_n \cos \theta ] Where:

• (I) = solar intensity on tilted surface
• (I_n) = solar intensity normal to sun rays (from tables)
• (\theta) = angle of incidence between sun rays and surface normal (from solar angles figure)

Solar Angles (Fig. 2)

• Solar altitude
• Solar azimuth
• Surface tilt and orientation angles

graph LR
A[Sun Position] --> B(Solar Altitude)
A --> C(Solar Azimuth)
B & C --> D[Angle of Incidence θ]
D --> E[Calculate Incident Solar Radiation]

For detailed tables and solar intensities, refer to IS 7662 Part 1 figures and CBRI data.

Climatic Factors Influencing Building Orientation (IS 7662 Part 1)

Key Climatological Factors (Clause 3.1)

• Solar radiation & temperature
• Clouds & rains
• Humidity
• Prevailing winds

Orientation Principle (Clause 3.2.6)

• Maximize solar gain in winter and minimize in summer.
• Use solar load data on vertical surfaces for design.

Important Table: Daily Total Direct Solar Radiation (g.cal/cm²/day)

IS 7662 Part 1 - Solar Radiation & Temperature: Key Points

1. Standard Atmospheric Conditions (Clause 2.5)

• Cloud-free sky
• 300 dust particles/cm³
• 15 mm precipitable water
• 2.5 mm ozone
• Sea level

2. Solar Radiation Data

• Solar intensity (cal/cm²/hr) given for:
  • Direct solar radiation normal to sun (Fig. 1)
  • Vertical surfaces at various orientations
• Solar angles defined (Fig. 2)

3. Solar Load Tables (Clause 3.2.6 & Table 1)

IS 7662 Part 1 - Clouds, Rain, and Humidity Considerations

Key Points from IS 7662 (Part 1):

• Cloud Coverage (Clause 2.1):

  • Expressed in "tenths of sky" covered by all clouds and low clouds.
  • Monthly tabulated data available from meteorological sources (e.g., CBRI Roorkee).

• Standard Atmospheric Conditions (Clause 2.5):

  • Cloud-free sky
  • Dust particles: 300/cm³
  • Precipitable water: 15 mm
  • Ozone: 2.5 mm at sea level

• Effect of Clouds and Rain (Clause 3.3 & 3.3.1):

  • Clouds reduce direct solar radiation significantly.
  • Cloudy periods may negate the effectiveness of sun protection devices.
  • Design must consider coinciding hot and cloudy periods to decide on sun protection strategies.

Important Formulas & Concepts:

• Direct Solar Radiation (I):
  [ I = I_0 \times \tau \times \cos \theta ] where:

  • (I_0) = Solar constant adjusted for atmospheric conditions (from Fig.1)
  • (\tau) = Atmospheric transmittance (affected by clouds, dust, humidity)
  • (\theta) = Solar incidence angle (from Fig.2 solar angles)

• Cloud Effect:
  [ I_{cloudy} = I_{clear} \times (1 - C) ] where (C) = cloud coverage fraction (0 to 1)

Reference Tables (Available in Meteorological Data):

(Exact values depend on location and must be sourced from CBRI or IMD data)

flowchart LR
    A[Sunlight] --> B[Atmosphere]
    B --> C{Cloud Coverage}
    C -- Low --> D[High Direct Radiation]
    C -- High --> E[Reduced Radiation]

IS 7662 Part 1: Prevailing Winds & Ventilation Key Points

1. Prevailing Winds (Clause 3.5)

• Purpose: To utilize wind direction and velocity data hourly/monthly for optimal building orientation.
• Effect: Enhances natural ventilation, improving comfort especially in high humidity.
• Data Source: Hourly wind data from Climatological and Solar Data for India (CBRI, Roorkee).

2. Ventilation Design

• Natural ventilation depends on prevailing wind velocity and direction.
• Orientation should maximize exposure to prevailing winds during hot/humid periods.

3. Standard Atmospheric Conditions (Clause 2.5)

• Cloud-free sky
• 300 dust particles/cm³
• 15 mm precipitable water
• 2.5 mm ozone
• Sea level conditions

4. Wind Pressure Calculation (from general knowledge)

[ P = 0.6 \times V^2 \quad \text{(Pressure in N/m}^2, V in m/s)} ]

• Used to estimate wind pressure for ventilation openings.

5. Ventilation Rate (Q) Estimation

[ Q = A \times V \times C_d ]

• (A) = area of opening (m²)
• (V) = wind velocity (m/s)
• (C_d) = discharge coefficient (typically 0.6-0.7)

Summary Table: Wind Data Use for Orientation

flowchart LR
    A[Hourly Wind Data] --> B[Analyze Direction & Velocity]
    B --> C[Determine Building Orientation]
    C --> D[Maximize Natural Ventilation]
    D --> E[Improved Indoor Comfort]

**Use prevailing wind data hourly/monthly for orientation to optimize natural ventilation and comfort as per IS 7662 Part 1.

IS 7662 Part 1 - Orientation Recommendations by Climatic Zones

Key Concept (Clause 3.2.6)

• Objective: Maximize solar radiation in winter, minimize in summer.
• Use Table 1 for total direct diurnal solar radiation (g.cal/cm²/day) on vertical surfaces for two representative days: May 16 (summer) and Dec 22 (winter) at various latitudes.

Table 1: Daily Total Direct Solar Radiation (g.cal/cm²/day)

IS 7662 Part 1 - Planning & Layout for Building Orientation

Key Points:

• Objective: Maximize solar gain in winter, minimize in summer.
• Orientation Principle: Longer building faces should ideally face North-South (Orientation 3) for optimal solar heat gain across India.
• Latitude Impact: North of 23ºN, prefer orientation with smaller surface facing North-West; south of 23ºN, prefer smaller surface facing South-West to reduce summer heat load.

Key Tables & Formulas:

Table 1: Daily Total Direct Solar Radiation (g.cal/cm²/day)

(Refer full table for all directions and latitudes)

Solar Heat Gain Calculation (Example for Orientation 3):

[ \text{Total Solar Heat} = \sum (\text{Solar Radiation per face} \times \text{Area of face}) ]

• For orientation 3 (longer faces North & South):

Thermal Capacity & Shading Techniques per IS 7662 Part 1

Key Points from IS 7662 (Part 1):

• Tree Planting (Clause 6.7):

  • Use deciduous trees on southern & western exposures to block summer sun and allow winter sun.
  • Trees help reduce glare, create cool/warm pockets, and allow natural wind flow.

• Solar Load Calculation (Appendix A & Clause 3.2.6):

  • Solar load depends on orientation, latitude, and season.
  • Standard atmospheric conditions: cloud-free, 300 dust/cm³, 15 mm precipitable water, sea level.
  • Use solar intensity data (cal/cm²/hr) for vertical surfaces from graphs or tables.

Table 1: Daily Total Direct Solar Radiation (g.cal/cm²/day)

Practical Guidance:

• Orientation: Maximize solar gain in winter (south-facing) and minimize in summer (shade south & west).
• Shading: Use trees or architectural elements to block high summer sun but allow low winter sun.
• Solar Load Calculation Formula:
  [ Q = I \times A \times t ] Where:
  • (Q) = heat gain (calories)
  • (I) = solar intensity (cal/cm²/hr) from tables/graphs
  • (A) = area exposed (cm²)
  • (t) = duration of exposure (hr)

Design Considerations for Hot and Arid Zones
(IS 7662 Part 1 - Clauses 5.3, 5.3.1, 5.4.1)

Key Points:

• Objective: Minimize solar heat gain during daytime; maintain indoor temperatures close to ambient/shade temperature.
• Walls & Roofs:
  • Use materials with high thermal capacity and time lag to delay heat transfer inside.
  • Surfaces exposed to sun should be reflective or heavily shaded.
• Openings & Orientation:
  • Small openings with shading (e.g., chajjas) are effective.
  • Right building orientation is critical to reduce solar load.
  • Verandahs on east/west less effective due to low sun altitude.
• Ventilation:
  • Restrict air movement during day to reduce heat ingress.
  • Provide fresh air in evenings to cool the structure by radiation loss.
  • Air velocity: 50-100 cm/s recommended for cooling effect.

Thermal Design Parameters:

Solar Radiation & Orientation:

• Use solar altitude and azimuth angles (Clause 3.2.6.2) to calculate solar load on surfaces.
• Formula for solar heat gain on a surface:

[ Q = I_b \times A \times \cos \theta ]

Where:

• ( Q ) = solar heat gain (W)
• ( I_b ) = beam solar radiation normal to sun (W/m²)
• ( A ) = surface area (m²)
• ( \theta ) = angle of incidence between sun rays and surface normal

Diagram: Solar Angles & Orientation

graph LR
A[Sun Position] --> B[Solar Altitude Angle (α)]
A --> C[Azimuth Angle (γ)]
B & C

Design Considerations for Hot/Warm and Humid Zones (IS 7662 Part 1)

Key Points from IS 7662:

• Indoor temperature should be close to ambient/shade temperature.
• Use lightweight construction with low thermal capacity for walls and roofs.
• External surfaces should have low solar absorption; internal surfaces should emit minimum long-wave radiation.
• Ensure air movement of 50-100 cm/s (0.5 to 1 m/s), natural or artificial.
• Use fans, forced ventilation, screens, and jallies to maximize ventilation and reduce glare.
• Evaporative cooling is effective only in dry zones, not in humid zones.
• Maximize use of prevailing winds for natural ventilation.

Practical Specifications:

Formula for Air Velocity Conversion:

[ 1 \text{ cm/s} = 0.01 \text{ m/s} ]

Recommended Construction Features:

• Use light-colored paints or reflective coatings.
• Incorporate jallies/screens to allow airflow but block glare.
• Design openings to maximize cross ventilation.

flowchart LR
    A[External Surface] -->|Low Solar Absorption| B[Lightweight Wall/Roof]
    B -->|Low Thermal Capacity| C[Indoor Space]
    C -->|Air Movement 0.5-1 m/s| D[Comfortable Indoor Temperature]
    D -->|Fans / Prevailing Winds| E[Ventilation]
    E -->|Screens/Jallies| A

This approach ensures thermal comfort by controlling heat gain and promoting air movement in humid climates.

Effect of Building Clusters on Wind Flow
(IS 7662 Part 1: Clauses 3.5.3, 3.5.6, 6.5)

Key Points:

• Wind eddies form on the leeward side of rows of buildings; their size depends on building height (H), length (L), and width (W).
• These eddies weaken prevailing winds, reducing natural ventilation behind building clusters.
• Orientation and spacing are critical:
  • Buildings facing wind block airflow to downstream rows.
  • Oblique orientation and gaps between blocks reduce wind obstruction.
• Study hourly and monthly wind velocity/direction for optimal building orientation.
• Street width and building height/depth should ensure air/light access and channel useful winds.

Practical Guidelines:

Simplified Wind Reduction Model:

Wind velocity behind building cluster (V₂) can reduce approximately as:

[ V_2 = V_1 \times e^{-\alpha \times (L/H)} ]

• (V_1) = approaching wind velocity
• (L) = length of building block
• (H) = height of building
• (\alpha) = empirical coefficient (~0.3 to 0.5)

flowchart LR
    Wind[Prevailing Wind] --> BuildingRow[Row of Buildings]
    BuildingRow --> Eddies[Wind Eddies on Leeward Side]
    Eddies --> ReducedWind[Reduced Wind Velocity]
    BuildingRow --> Gaps[Gaps between buildings]
    Gaps --> ImprovedFlow[Improved Wind Flow]

Summary: Design building clusters with adequate spacing, oblique orientation, and gaps to minimize wind blockage and maximize natural ventilation per IS 7662 Part 1.

IS 7662 Part 1: Use of Meteorological Data for Orientation

Key Points & Specifications:

• Climatological Factors (Clause 4.1):
  Use sun charts, solar loads, temperature, cloud cover, relative humidity, and wind data for building orientation.

• Standard Atmospheric Conditions (Clause 2.5):

  • Cloud-free sky
  • 300 dust particles/cm³
  • 15 mm precipitable water
  • 2.5 mm ozone
  • Sea level conditions
    These are hourly values available for different latitudes in Climatological and Solar Data for India by CBRI Roorkee.

• Solar Angles (Fig. 2):
  Defined by solar altitude and azimuth angles, essential for calculating solar radiation on surfaces.

• Solar Radiation (Fig. 1):
  Direct solar radiation normal to the sun varies with solar altitude; use this to estimate solar loads on vertical/horizontal surfaces.

• Wind Data (Clause 3.5.6):
  Hourly and monthly wind velocity and direction data are critical for natural ventilation and orientation.

Basic Formula for Solar Radiation on Tilted Surface:

[ I = I_b \cos \theta + I_d \left(\frac{1 + \cos \beta}{2}\right) + I_r \left(\frac{1 - \cos \beta}{2}\right) ]

Where:

• (I) = total radiation on tilted surface
• (I_b) = beam radiation on horizontal surface
• (\theta) = angle of incidence
• (\beta) = tilt angle
• (I_d) = diffuse radiation
• (I_r) = reflected radiation

Summary Table for Orientation Factors

flowchart LR
    A[Climatological Data]

Key Formulas & Specifications for Solar Energy Calculation (IS 7662 Part 1)

1. Solar Load Calculation Basics

• Solar radiation on surfaces depends on:
  • Solar altitude and azimuth angles (Fig. 2 in IS 7662)
  • Orientation of the surface (N, NE, E, SE, S, SW, W, NW)
  • Time of year (summer/winter representative days: 16 May, 22 Dec)
• Standard atmospheric conditions assumed:
  • Cloud-free sky
  • 300 dust particles/cm³
  • 15 mm precipitable water
  • 2.5 mm ozone
  • Sea level

2. Solar Intensity

• Direct solar radiation normal to sun is given in cal/cm²/hr (Fig. 1)
• Solar load on vertical surfaces is derived using solar angles and intensity.

3. Daily Total Direct Solar Radiation (g.cal/cm²/day) [Table 1]

• Use this table to calculate heat gain based on building orientation and latitude.

4. Solar Load Calculation Method

• Refer to Appendix A of IS 7662 Part 1 for detailed stepwise calculation:
  • Calculate solar angles (altitude, azimuth)
  • Find intensity normal to sun
  • Project intensity on the surface using angle of incidence
  • Integrate over daylight hours for total load

Summary Diagram: Solar Load Calculation Flow

flowchart TD
    A[Determine Latitude & Date] --> B[Calculate Solar Angles]
    B --> C[Find Direct Solar Intensity (cal/cm²/hr)]
    C --> D[Calculate Angle of Incidence on Surface]
    D --> E[Project Intensity on Surface]
    E --> F

IS 7662 Part 1: Recommendations for Road and Neighborhood Planning

Key Points & Formulas

• Road Layout Orientation (Clause 6.4 & 5.6):

  • Design road patterns to maximize good orientation for the maximum number of blocks.
  • Study climatological, topographical, and zonal factors to decide optimum orientation for the entire area.

• Tree Planting for Microclimate Control (Clause 6.7):

  • Use trees that shed leaves in winter and have dense summer foliage on southern & western exposures.
  • Trees should provide shade, glare reduction, and wind flow without obstructing natural ventilation.

• Solar Load Calculation (Appendix A):

  • Solar load on vertical surfaces depends on orientation and time of year.
  • Use solar geometry formulas to calculate incident solar radiation:

[ Q = I_b \times \cos \theta + I_d \times F_d + I_r \times F_r ]

Where:

• (Q) = total solar radiation on surface,
• (I_b) = beam radiation,
• (\theta) = angle of incidence,
• (I_d) = diffuse radiation,
• (F_d) = diffuse radiation factor,
• (I_r) = reflected radiation,
• (F_r) = reflection factor.

Summary Table: Orientation Effects

flowchart LR
    A[Layout Planning] --> B[Study Climatology & Topography]
    B --> C[Decide Optimum Orientation]
    C --> D[Design Road Patterns]
    D --> E[Maximize Good Orientation]
    E --> F[Plan Tree Planting]
    F --> G[Shade & Wind Control]

Use these guidelines to optimize road layouts and neighborhood planning for climate responsiveness and energy efficiency.

IS 7662 Part 1 - Summary & Implementation Guidelines

Key Assumptions (Clause 2.5)

• Cloud-free sky
• 300 dust particles/cm³
• 15 mm precipitable water
• 2.5 mm ozone
• Sea level conditions

Solar Radiation Data (Clause 3.2.6 & Appendix A)

• Solar load varies by surface orientation and latitude.
• Use Table 1 for daily total direct solar radiation (g.cal/cm²/day) on vertical surfaces for May 16 (summer) and Dec 22 (winter).
• Helps optimize building orientation for max winter and min summer solar gain.

Table 1: Daily Total Direct Solar Radiation (g.cal/cm²/day)