• Introduction to Environmental/Climatic Design Climatic Design Factors• History and Background : Types of Climates and Corresponding Characteristics• Climatic Data and Analysis• Comfort: Concepts, Indices and Analysis• Climatic Concepts, Elements and Factors • Microclimatic Considerations• Tropical Design Theories• Tropical Climates: Hot, Humid Climates• Tropical Climates: Hot, Dry Climates• Shading: History and orientation• Fixed Shading Devices• Movable Shading Devices• Shading Designs for south windows• Design guidelines for fixed overhangs• Design guidelines for movable overhangs• Shading for east and west windows• Design of east and west horizontal overhangs• Interior Shading devices• Passive cooling; history• Passive cooling systems• Basic principles of air flow• Comfort ventilation• Building materials used in tropical design• Discussion on tropical design problem

History and Background : Types of Climates and Corresponding Characteristics

• Arctic- characterized by long,

cold winters and short, cool summers.

- nearly all parts of the Arctic experience long periods with some form of ice on the surface

- Average January temp. range : −40 to 0 °C (winter)

- Average July temp. range

: −10 to +10 °C (summer)

• Temperate- lie between

the tropics and the polar regions.

- changes in these regions between summer and winter

are generally relatively moderate, rather than extreme hot or cold.

• Tropical & Subtropical

- tropical temperature remains relatively constant throughout the year

- seasonal variations are dominated by precipitation.

• Equatorial- is a tropical

climate usually (but not always) found along the equator

- climate typically feature tropical rainforests

- Tropical rainforest climate is a type of tropical climate in which there is little or no dry season – all months have mean precipitation values

• TROPICAL DESIGN - concerned with countries where discomfort is due

to heat and humidity are the dominant problems.

Classification of Tropical, Sub-Tropical and Equatorial Climates• Warm Humid

- Tropical Islands, one where the air is very moist- lot of water in the air. Usually hot and steamy.

• Hot Dry- Maritime Desert- Minimal rain all year

• Composite- Tropical uplands, where heavy rains alternate with dryer

periods

Characteristics of Tropical Climates• Warm Humid

DBT – High temperature during the day, low diurnal change

RH – relatively highPrecipitation – heavy rains

especially during monsoon season

Sky – cloudy and glaringGround – less vegetation

• Hot DryDBT – Very high temperature

during the day. Large diurnal range which can be quite low during winter.

RH – Low and very constant throughout the year.Precipitation – often very lowSky – little or no cloud. Cold and non-glaring skyGround – sparse and often bare

• Composite-This is a mixture of

warm/humid and hot/dry climate.

-1/3 to 2/3 ratio of monsoon period

-Can be quite cold in winter.

Elements of Climate Needed in Design• Macro Climate – climate of a region and/or the entire country.

It provides the basis upon which micro-climate can be estimated.

• Micro Climate – climate of a site and its immediate environs.

• Dry Bulb Temperature(DBT) – measurement of air temperature measured under a shade.

• Relative Humidity (RH) – amount of moisture in the air.

• Sky – (or celestial dome) is everything that lies a certain distance above the surface of Earth, including the atmosphere and the rest of outer space. It is here defined as only the denser portions of the atmosphere. Some of the natural phenomena seen in the sky are clouds, rainbows, and aurorae. Lightning and precipitation can also be seen in the sky during storms. Due to human activities, smog during the day and light pollution during the night are often seen above large cities.

The design of buildings that respond to the environment involves the use of principles of solar

design as also a detailed understanding of the complex interrelationship between architectural design, building

materials, human behavior and climatic factors. This kind of design, not restricted just to the use of solar

energy but including the utilization of all forms of natural energy to provide required comfort conditions

within the built-up space may be defined as climatic design. Before elaborating on the ways and means to achieve human comfort in the built-space, it would be

useful to define what exactly constitutes comfort.

Thermal comfort criteria

Comfort levels are influenced by three main factors:

• Mean radiant temperature (MRT):• Humidity :

• Air Movement :

Modifiying Factor• Air Temperature

Mean radiant temperature (MRT): Temperature is one of the main parameters on which comfort of the inhabitants depends. In summer the acceptable temperature is considered to be 24-25 degrees C while in winter/cold season it is 22-23 degrees C. maintaining a temperature of 24 degrees C within the structure when the outside temperature is 35-37 degrees C puts a huge strain on the HVAC system leading to huge energy costs. Therefore, it would be wise to revise our criteria for thermal comfort and accept a standard for thermal neutrality instead, i.e. the person feels neither too hot nor too cold, nor feels any local discomfort due to asymmetric radiation, drafts, cold floors and furniture, non-uniform clothing, etc. At same time there has to be a willingness to adapt to the local weather conditions so as not to make unrealistic demands from the air-conditioning system. We should realize that the days of wasteful spending are now over and a measure of austerity has to be there in our energy spending.

HumidityThe moisture content present in the air is called ‘humidity’.

The level of humidity greatly influences evaporative cooling. Greater the moisture content in the air lesser is the effect of evaporative cooling.

Therefore efforts to reduce humidity levels within a space result in better conditions.

In the design of HVAC systems humidity level of 40-50% is considered acceptable, but one should also remember that this standard is not a law and human adaptability can be stretched to farther limits.

Air movement or ventilation can be used to considerably cool the interiors of a building.

Air movement over the skin results in Evaporative cooling- as the air moves over the skin, the perspiration on the skin surface evaporates leading to cooling of the surrounding area.

Air movement also affects conductive-convective heat transfer between skin and air. The velocity of the air is also important as stagnant air creates a suffocating effect as the air turns stale due to respiration, foul odors, smoke, etc.

Therefore removal of this air and its replacement with fresh air is very important which directly depends on adequate cross ventilation of the spaces, which results in proper air movement and velocity.

A combination of these three factors is responsible for the maintenance of proper living conditions within the

space.

It is therefore, possible to maximize the cooling effect of these factors by making use of proper design

elements and the principles of solar architecture

to reduce our dependency on external energy to maintain a comfortable living environment.

Principles and Strategies of Climatic Design

The objectives in the design of a structure that responds to the environment should be to maximize solar gain in winter and minimize heat gain in summer. Heat gain can take place in one of the following ways of natural thermal transmission-conduction, convection and radiation in addition to evaporation, which plays a major role in cooling of indoor environment. There is thus an inherent contradiction in the tasks that the building envelope has to perform in summer and cold season.

In a climate such as ours, cooling is the main factor affecting building design. Humidity levels are also quite high along with high summer temperatures in the high 30’s. Therefore the control of solar heat gain is the most important factor to be considered.

Sources of heat gainThe proper use of shading devices can prevent direct solar radiation from reaching all or part of the roof, walls or windows of a building. Natural vegetation, neighboring buildings or the surrounding landscape can provide shading - for example on the north-facing slope of a hill or valley. Shading devices on the building (fixed or movable, the latter being manually or automatically controlled) can prevent radiation from reaching critical parts such as windows, doors and even roofs. Indirect solar gain from the sky or reflected from the surrounding buildings or the ground and air heated by irradiated surfaces such as roads and pavements can also contribute significantly to cooling load.

A significant amount of heat is also produced by appliances, electric lighting and occupants, which during the overheating season can lead to uncomfortably high temperatures. The use of Natural Daylight to replace artificial light where appropriate and the use of high efficiency artificial lighting can reduce cooling costs drastically, especially in commercial buildings. Heat producing appliances should be placed such that the heat can be quickly removed from the building to reduce cooling load.

Control of heat gain

Solar control involves the prevention of unwanted solar heat gain taking into consideration the following factors in design:

Microclimate and site designBuilding envelope

Control of internal gains.

The Architectural Approach (Building Envelope)

Control of internal gains.

Creating Thermal Conditions of the EnvironmentAir temperature Relative Humidity

Air Velocity Mean Radiant Temperature

The Psychrometric Chart(s)

The Comfort Zone and various types of discomfort outside that zone are shown on the

Psychrometric Chart

“We must begin by taking note of the countries and climates in which homes are to be built if our design for them are to be correct. One type of house seems appropriate for Egypt, another for Spain… one still different for Rome… It is obvious that design for homes ought to conform to diversities of climate.”

VitruviusArchitect, first century B.C.

Microclimate and site designLandscaping can improve the microclimate in both summer and cold/stormy season, providing shading, evaporative cooling and wind channelling in summer, or shelter in cold season. Vegetation absorbs large amounts of solar radiation in summer helping to keep the air and ground beneath cool while evapotranspiration can further reduce temperatures.However some care should be taken in the choice and placement of vegetation on or near the building to avoid structural damage.

Grass and other ground cover planting can also influence the microclimate, keeping the ground temperature lower than most hard surfaces as a result of evapotranspiration and their ability to reduce the effect of solar radiation. This happens due to the shading provided by the grass which prevents radiation from reaching the ground resulting in a difference between asphalt and lawn being as much as 25 degrees F (figures taken from Climatic design, Energy efficient building principles & practises/ Donald Watson and Kenneth Labs).

Windbreaks can enhance air pressure difference around buildings and improve cross ventilation. Hedging, for example, can allow a gentle breeze to filter through the foliage, while a masonry windbreak can create a calm, sheltered zone behind it. Gaps in windbreaks, openings between buildings or openings between the ground and canopy of trees can create wind channels, increasing wind speeds by about 20%.

Water can also be used effectively for cooling of internal as well as surrounding environment. Ponds, streams, fountains, sprays and cascades can be used where water is available in summer. These are particularly effective in dry conditions where relative humidity levels are low.

Microclimate and site designOrientation to sun and wind

The orientation of the building on site is very important to achieve reduced heat gain and improved wind circulation and ventilation. The major openings in the building envelope should be placed on the North while the south face should be adequately protected from heat gain by using shading devices or vegetation. Prevailing wind direction should be taken into consideration while deciding the position and size of the openings to ensure proper cross ventilation. This can go a long way in improving comfort conditions within the building.

Building shape and PlanningThe configuration of the building and the arrangement of internal spaces according to function can help to influence the exposure to incident solar radiation, the availability of natural daylight and airflow in and around the building.In general, a compact building will have a relatively small exposed surface, or in other words a low surface to volume ratio (SVR). This can offer advantages for the control of heat gains through the building skin without conflict between design priorities for winter and summer months. There are a range of other options to improve thermal performance including courtyards, construction on pilotis, use of wing walls, etc. however the relationship between form and thermal transmission are not very critical as a number of strategies are available to counteract its negative effects. More important are the effect of building form on wind channelling and airflow patterns and the opportunities for enhancing the use of daylight.

Natural Ventilation

Ventilation provides cooling by using air to carry heat away from the building and from the human body. Air movement may be induced either by natural forces (wind and stack effect) or mechanical power. Airflow patterns are a result of differences in pressure patterns around and within the building. Neighbouring landforms such as slopes and valleys can be used to increase the exposure to summer breezes along with proper orientation to wind. Openings should be oriented to catch the prevailing summer breeze.

Air moves from high-pressure regions to low pressure ones. When the outside air temperature is lower than the inside air temperature, building ventilation can exhaust internal heat gains or solar heat gain during the day and cool air during the night if required. Indoor air movement enhances the convective exchange at skin surface and increases the rate of evaporation of moisture from the skin. Evaporation is a very powerful mechanism for cooling which may bring a feeling of comfort to the occupants under hot conditions. However, to be effective the surrounding air should not be too humid (relative humidity less than 85%). Turbulent air movement will hinder both of these mechanisms of heat removal.

Both the design of the building itself as well its surrounding spaces can have a major impact on the effectiveness of natural cooling through ventilation. The rate of air flow through the building will be affected by location, sizing and air flow characteristics of the openings (wing walls, louvers, overhangs can be used to direct summer wind flow into the interior), the effect of indoor obstacles to air movement (open plan spaces promote air flow), the effects of the external shape of the building in relation to wind direction, etc. The total airflow normally depends on a combination of buoyancy and wind pressure differences, and is affected by the size and location of openings.

Proper placement of openings along with the use of wing

walls can greatly enhance the effect of ventilation by

increasing wind pressure differences and consequently air velocity within the space.

Other strategies for improving ventilation are wing walls,

wind towers and solar chimneys.

Solar chimneySolar chimneys use the sun to warm the internal surface of the chimney. The buoyancy generated due to the temperature difference help induce an upward flow along the plate. The chimney width should be close to the boundary layer to prevent backward flow.

Wing walls

Many buildings having rooms with lust one external wall are difficult to ventilate naturally. Even rooms with two windows placed as far as possible will offer limited ventilation. However, research has found that airflow in rooms with two windows on one wall can be further augmented by the use of wing walls (small walls perpendicular to the main wall). These projections create positive pressure over one window and negative over the other, achieving cross ventilation of the room by drawing air in on one side and forcing it out on the other side.

Wind towersWind towers draw upon the force of wind to generate air movement within the building. There are various systems based on this principle. The wind-scoop inlets of the tower oriented toward the windward side capture the wind and drive the air down the chimney. The air exits through leeward openings in the building. Alternatively, the chimney cap is designed to create low pressure at the top of the tower, and the resultant drop in air pressure causes the air to rise through the chimney. A windward opening should be incorporated in the system as an inlet. The buoyancy of the warm air inside the building aids this process. Both these systems can be combined in a single tower providing both admittance and exhaust of air thus creating a self sustained system.

Microclimate and site designLimitations of wind induced ventilation

Wind induced ventilation would be an ideal strategy if winds were in a steady direction and intensity (greater than 3m/s). In reality, however winds are extremely variable and detailed weather data is not readily available for most sites. Also the rate of air changes in a naturally ventilated system will vary and therefore cause some inconvenience. Also a detailed study of the effect of measures taken to enhance ventilation has not been made due to which reliable information on the subject is not available.

BUILDING ENVELOPE

Design of OpeningsShading systems

GlazingFixed shading systems

Movable shading systemsVegetation

Thermal insulationAir infiltration

Design of openingsThe balance between heating, cooling and day-lighting is a critical consideration for the choice of orientation and size of opening. Building type and Building Regulations also influence this choice. However, the use of additional devices such as overhangs, shutters, blinds and louvers allow some scope to correct or limit the unfavourable orientations for large glazed areas. The sizing of north facing openings is less affected by seasonal variations and may be determined largely by day lighting and cross ventilation requirements. North facing openings can provide an almost uniform daylight source. Effective cross ventilation typically requires openings distributed across opposing facades, with minimal internal barriers to impede airflow. The proper treatment of south and west facing windows is therefore very important to prevent unnecessary heat gain. For single sided ventilation the shape of opening becomes important, horizontal formats being more economical in simulating internal air velocities. The design of openings should be undertaken in conjunction with the overall solar strategy.

The building envelope design strategy must encompass winter and summer conditions so that, for example, excessive solar heat gain can be avoided in summer while adequate daylight is available throughout the year, thus avoiding the need for artificial lighting during the day, consequently reducing cooling loads.

Shading systemsBlocking the solar radiation from reaching the building, particularly the glazed, but also the other opaque surfaces (including the roof) and reflecting the solar radiation is fundamental to the prevention of heat gain. While shading systems must provide good solar protection in summer, they should not reduce solar gain in winter, impede natural lighting or obstruct cross ventilation. Well-designed shading systems can actually enhance natural day lighting and ventilation. Shading systems can be either fixed or movable and placed internally, externally or between double glazed panels. Vegetation can also be used to provide shading.

Glazing

The type of glazing used can also affect the solar heat gain of the building. Glazing may be either clear or may have special coatings or treatments to enhance it’s reflective or heat absorbing properties. Electrochromic glass allows the radiation transmission properties to be altered by varying an electric current that is passed through the glass panel. Other new types of high performance glass called low-e glass are also now available which have low emission values compared to normal glass. The use of sun films can also reduce the penetration of solar radiation.

Fixed shading systemsFixed shading systems include structural elements such as balconies and projecting fins or shelves and non-structural elements such as canopies, blinds, louvers and screens. The orientation and shape of the opening to be shaded, relative to the position of the sun at different times of the day and year is critical to the design of fixed shading systems. Each orientation will need to be examined separately, taking account of direct and diffuse and reflected components of solar radiation throughout the day and year. Typically horizontal shading is used for south facades while vertical fins or louvers are more efficient for east and west facades. Fixed shading systems are generally used externally as when used internally heat build-up between the system and glazing can reduce the effectiveness of the system by as much as 30%.

Movable shading systemsMovable shading is use either internally or externally. Control can be either manual or power assisted and may be automated to respond to changing conditions such as current radiation levels and daylighting or thermal requirements.

Awnings can reduce heat gain by up to 65% in summer on south facades and up to 80% on east or west facades. The geometry of awnings is similar to that of horizontal overhangs but efficiency will also depend on how opaque the material is to both direct and diffused radiation and the presence of dust which might change the absorption and radiation characteristics of the awning. Normally, an air gap should be provided between the awning and glazing for air circulation. The efficiency of awnings may also deteriorate with age and weather damage.

Venetian blinds can permit simultaneous ventilation and shading which is controllable and may allow daylight to be reflected, to the ceiling, for example. With the exception of reflective blinds, curtains and blinds fitted internally are less satisfactory as they provide shade only after radiation has passed through the glazing. The use of curtains and internal blinds may often conflict with the daylighting or ventilation needs.

VegetationVegetation can be used effectively for shading of the building. A major advantage of natural shading using vegetation is that plants constantly rearrange and reposition their leaves for maximum solar exposure and therefore maximize shading, while artificial shading is generally inflexible.

A curtain of vines or creepers in the external walls will reduce heat penetration and help maintain cooler temperatures within the rooms.

Shady trees will control the light and heat reflected off the roads and pavements onto the walls and roof of the structure if it is within the shadow range.

Terrace gardens can further reduce heat transmission through the roof. As the roof is responsible for 50% of the heat load this can achieve temperature drops of 3 degrees C to 5 degrees C.

Thermal insulation

Thermal insulation may combine two physical processes; reducing the thermal transmittance of the envelope and maximizing long wave radiation. Usually, only the first is taken into consideration, but both these processes can be incorporated in the concept of radiant barriers. The development of higher quality foil products and research showing the most efficient way to install these, have resulted in major energy savings in hot regions, for example, a low emissivity material like aluminium foil, next to an air gap will impede radiation, thus reducing the temperature of the inner layer and also radiant room temperature. At night, the foil blocks radiant heat exchange, reducing night cooling. When properly installed, radiant barriers can reduce cooling loads by as much as 10%.

Air infiltration

Air infiltration represents a major cooling load in hot climates. By sealing areas or introducing air infiltration barriers where different building materials join together, summer heat gain and excessive use of mechanical equipment for cooling can be dramatically reduced.

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