Climate and Design of Solar Radiation

CLIMATE AND DESIGN OF SOLAR RADIATION

Weather

The weather of a place denotes the state of the atmospheric environment over a period of time.

Climate

Integrated weather condition over several years is known as climate as climate.

The climate analysis of a particular region can be used to assess the seasons during which a period may experience comfortable and uncomfortable conditions. ytibimur

The orientation and openings of a building can be suitably arranged from this analysis.

For example, we feel hot due to intense solar radiation and high humidity.

Design of solar radiation

The building design should ensure to optimize the solar radiation, according to the different climatic conditions. The optimization can be achieved by the following ways.

• The building should be sufficiently shaded to prevent solar radiation from entering the house.

• It must be ventilated to reduce discomfort due to high humidity.

Basic Principle

Every location on earth receives sunlight at least part of the year. The amount of solar radiation that reaches any one spot on the earth's surface varies according to:

• Geographic location

• Time of day

• Season

• Local landscape

•  Local weather.

Since, the earth is round, the sun strikes the surface at different angles, ranging from 0° (just above the horizon) to 90° (directly overhead).

When the sun's rays are vertical, the earth's surface gets all the energy possible. The more slanted the sun's rays are, the longer they travel through the atmosphere, becoming more scattered and diffuse.

The polar regions never get a high sun light due to the tilted axis of rotation.

When the sun is nearer the earth, the earth's surface receives a little more solar energy.

The earth is nearer the sun when it is summer in the southern hemisphere and winter in the northern hemisphere.

Note:

• The altitude angle is the angle of the sun above the horizon, achieving its maximum on a given day at solar noon.

• The azimuth angle, also known as the bearing angle, is the angle of the sun's projection onto the ground plane relative to south.

Diffuse and Direct Solar Radiation

As sunlight passes through the atmosphere, some of it is absorbed, scattered, and reflected by:

• Air molecules

• Water vapor

• Clouds

• Dust

• Pollutants

• Forest fires

• Volcanoes

This is called diffuse radiation. The solar radiation that reaches the earth's surface without being diffused is called direct beam solar radiation. The sum of the diffuse and direct solar radiation is called global solar radiation.

Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days. (Fig. 1.23)

Solar radiation is the most important weather variable. It determines whether a place experiences high temperatures or cold.

Solar radiation design

There are two types of solar radiation design

1. Active solar design

2. Passive solar design

1. Active solar design:

It uses outside energy and equipment like electricity and solar panels to help capture and utilize the energy of the sun.

2. Passive solar design:

It doesn't use any outside energy or require much special equipment, but simply takes advantage of existing natural phenomena, like the direction of the sun properties of concrete.

Solar Passive Design

Solar passive buildings are designed to achieve thermal and visual comfort by using natural energy sources and sinks e.g. solar radiation, wet surfaces, outside air, vegetation, etc.

Architects and designers can the buildings by studying the macro and micro climate of the site. Designer can achieve a solar passive building design by the following steps.

• Modulating  the  micro  climate  of  the  site through landscaping.

• Optimizing the orientation and building form.

• Optimizing the building envelope and windows design to reduce the cooling demand.

• Applying day light integration to reduce the artificial lighting demand.

• Adopting low energy passive cooling strategies.

Design external shading for windows to cut heat gains from direct solar radiation and to protect against rain.

Site Specific Considerations during design

Following are the site specific considerations

• Latitude, sun path and insolation (sunshine).

• Seasonal variations in solar gain e.g. cooling or heating degree days, solar insolation, humidity.

• Micro-climate details related to breezes, humidity, vegetation and land contour.

• Obstructions/Over-shadowing-to solar gain or local  cross-winds.

Design elements for Residential Buildings in Temperature Climates

• Placement of room-types, internal doors and walls, and equipment in the house.

• Orienting the building to face the equator.

• Extending the building dimension along the east/west  axis,

• Adequately sizing windows to face the midday sun in the winter, and the shaded in the summer.

• Minimizing windows on other sides, especially western windows.

• Erecting correctly sized, latitude-specific roof overhangs, or shading elements (shrubbery, trees, trellises, fences, shutters, etc.)

• Using appropriate amount and type type of insulation including radiant barriers and bulk insulation minimise seasonal excessive heat gain or loss.

• Using thermal mass to store excess solar energy during moil an the winter day (which is then re-radiated during the night).