Architectural Elements

Introduction

In designing and planning for the hot arid and warm humid zones, two of the main problems confronting the architect are to:

(i)ensure protection against heat ; and

(ii)provide adequate cooling.

The built environment produces changes in the microclimate. The configuration of buildings, their orientations, and their arrangement in space create a specific microclimate for each site. To this must be added the building materials, surface textures and colors of exposed surfaces of the buildings, and the design of open spaces, such as streets, courtyards, gardens, and squares.

These man-made elements interact with the natural microclimate to determine the factors affecting comfort in the built environment: light, heat, wind, and humidity.There is no doubt that certain configurations create better microclimates than others. For each site, there is an optimum arrangement in space that the designer should seek and use as a standard of reference in the process of deciding upon a certain design.

Where it can be avoided, it is inappropriate and irresponsible to implement a design that adds even one degree of temperature or reduces air movement by one centimeter per second, if this would negatively affect thermal comfort. This obviously includes defective designs which require energy intensive mechanical means for their rectification.

1. The sun factor

Orientation
In hot climates, the sun is the major source of heat. To plan any site, the position of the sun must be determined for all hours of the day at all seasons as well as the direction of the prevailing winds, especially during the hot season.

For an ensemble of buildings forming a sector, there will be reflection from adjacent buildings and wind screening by clusters of buildings, which contribute to a specific microclimate for each location in the sector. Wind movement and humidity also are important and should be considered simultaneously with the direct and indirect effects of the sun.
The main objective is to establish the optimum orientation with regard to the sun and the prevailing wind. The problem is complex, and it is useful to begin by considering the simple case of a block consisting of a single row of buildings. On the basis of this, more complex cases can be understood.

Shading
Although the optimal orientation for single buildings and blocks of row houses is with the long side aligned from east to west, for many reasons this cannot always be applied so simply over the entire plan of a city or sector. Some single buildings or row houses must face streets and squares that may be oriented at any angle from the north, with each case requiring an appropriate means of shading, depending on its orientation.
Generally, a building with a facade opening to the west is the worst case encountered, owing to the heat gain of the surrounding environment during the day and the angle of altitude, which allows the sun's rays to penetrate into the interior.

However, for a sector with the long facade facing west and east, blocks of buildings can themselves shade one another. To ensure this, the height of the blocks must be designed according to the width of the street and the angle of altitude of the sun.

Facades

Northern Facade
This facade is least exposed to the sun. In fact, exposure occurs only in the early and late hours of summer days when the angle of altitude is low and the angle of declination is such that the sun's rays are almost tangential to the surface of the wall. An advantage to rooms opening on this facade is that their illumination is always evenly distributed, making them ideal for hospital operating rooms and for school classrooms.

Southern Facade
With regard to the sun factor, an advantage of southern exposure in the Tropics and Subtropics is that the sun is high over the horizon in summer and can be shaded using a relatively small overhang.

In winter it is low, allowing the sunshine to penetrate when it is most desirable. However, with regard to the wind factor, a disadvantage of the southern exposure is that it receives no wind, since the cool prevailing winds generally blow from a northerly direction in the Northern Hemisphere.

Eastern and Western Facades
The eastern facade is exposed to the sun's rays only from sunrise to noon. The walls cool down considerably by evening, making this exposure more suitable for bedrooms than the western exposure.
Shading of the facades of buildings can be achieved by covering the streets, as is often found in older cities and oasis villages of West Asia and North Africa.

For a single building, shade can be provided by architectural elements such as balconies, covered loggias or open galleries, and verandas to shield the facade, or by introducing special devices such as the Venetian blind, the brise-soleil, and the mashrabiya to shield the openings.

Openings

Window openings normally serve three functions:

(i) to let in direct and indirect sunlight,

(ii) to let in air; and

(iii)to provide a view.

In hot arid climates it is rarely possible or desirable to combine these three functions in a single architectural solution, several solutions were developed which concentrate on each function separately.

The Venetian Blind

• One device which can be added directly to the window is the venetian blind.
• This blind is made of small slats, about 4-5 cm (1.6-2 inches) wide, closely set in a wooden frame at an angle that will intercept the sun's rays.
• The slats are often movable so the angle can be changed. This feature of adjustability renders venetian blinds very useful in regulating solar radiation and wind flow into rooms.
• The sun's rays can be blocked out without obstructing the breeze, which generally blows from the northwest in most hot arid areas, including Egypt, Iraq, and North Africa.
• When the blinds are drawn, they completely obstruct the view to the outside as well as considerably dim the light reaching the interior.
• However, sometimes the venetians blind is not a satisfactory solution to the problem of adjusting radiation and airflow.
• In summer, the blind can be adjusted to deflect the wind downward onto the occupants
• Also, if the slats are made of metal, they then absorb some incoming radiation and reradiate it into the room as heat.

The Brise-soleil

• The brise-soleil or sun-breaker is a new shading device that requires a special sophisticated support.
• It is generally used to shield entire facades of glass-wall and concrete or steel frame buildings.
• A brise-soleil properly designed to intercept the sun's rays reduces the heat gain to at most one-third, which although an improvement is still inadequate.
• There is the additional disadvantage of using the brise-soleil with regard to the view to the outside.
• The brise-soleil is a transposition of the venetians blind, with the slat width increased from 4 to about 40 cm (1.6 to about 16 inches) to suit the scale of the entire facade instead of just the window opening in a solid wall.
• When the angles of altitude and declination for screening direct sunlight are calculated, the required space between the slats is much larger than for the venetians blind. The result is a view slashed by large dark stripes interspersed by offensive glare.
• It may be used advantageously in some cases of modern architecture if comprehensively articulated in the facade with due regard for reduction of physical glare and for aesthetics.

The Mashrabiya

• The name mashrabiya is derived from the Arabic word "drink" and originally meant "a drinking place."
• This was a cantilevered space with a lattice opening, where small water jars were placed to be cooled by the evaporation effect as air moved through the opening.
• Now the name is used for an opening with a wooden lattice screen composed of small wooden balusters that are circular in section and arranged at specific regular intervals, often in a decorative and intricate geometric pattern.
• The mashrabiya has five functions. Different patterns have been developed to satisfy a variety of conditions that require emphasis on one or more these functions.
• These functions involve: (1) controlling the passage of light, (2) controlling the air flow, (3) reducing the temperature of the air current, (4) increasing the humidity of the air current, and (5) ensuring privacy. Each mashrabiya design is selected to fulfill several or all of these functions. In the design, it is the sizes of the interstices (spaces between adjacent balusters) and the diameter of the balusters that are adjusted. Different names identify certain of these patterns.

The roof
If the outdoor air temperature is higher than the indoor temperature, the outer surface of the roof exposed to the sun is heated as it absorbs radiation, and, being in contact with the outside hot air, also is heated by conduction.

The roof then transmits this heat to the inner surface, where it raises the temperature of the air in contact with it by conduction. At the same time, it radiates heat that is absorbed by people and objects indoors, thereby affecting thermal comfort.Therefore, the reflectivity of the outer surface of the roof and the thermal resistivity of its materials are of primary importance.

Shade can be achieved by using a double roof with a layer of air between or by covering the roof surface with hollow bricks. Insulating materials such as fiberglass, styrofoam, and lightweight blocks are often used. This solution, however, requires special commercial materials and increases the cost of the building beyond the means of most inhabitants in hot arid zones.
A useful idea is to shade the roof more naturally by designing it to suit popular traditions. In hot arid countries, since the air temperature drops considerably during the night, the inhabitants have arranged the roof architecturally into loggias or open galleries and lightweight roof covers. These loggias and roof covers have the double function of shading the roof during the day and providing physiologically comfortable living and sleeping spaces at night.

The shape of the roof is also of considerable importance in a sunny climate.

• A flat roof receives solar radiation continuously throughout the day, at a rate that increases in the early morning and decreases in the late afternoon due to changes in both solar intensity and angle of the sun.
• Pitching or arching the roof has several advantages over a flat structure :

(i) the height of part of the interior is increased, thereby providing a space far above the heads of the inhabitants for warm air that rises or is transmitted through the roof.

(ii) the total surface area of the roof is increased with the result that the intensity of solar radiation is spread over a larger area and the average heat increase of the roof and heat transmission to the interior are reduced. (iii) for most of the day, part of the roof is shaded from the sun, at which time it can act as a radiator, absorbing heat from the sunlit part of the roof and the internal air, and transmitting it to the cooler outside air in the roof's shade.

• This latter effect is particularly effective for roofs vaulted in the form of a half-cylinder and those domed in the form of a hemisphere since at least part of the roof is always shaded except at noon when the sun is directly overhead.
• Domed and vaulted roofs also increase the speed of any air flowing over their curved surfaces due to the Bernoulli Effect rendering cooling winds more effective at reducing the temperature of such roofs.