3.3 Design for warm-humid zones
The main points
• Provide maximum ventilation and free air movement by large openings.
3.3.1 Climate and design in general
The climate of warm-humid zones is characterized by high rainfall and high humidity. The temperature range is relatively high at around 30 - 35°C and is fairly even during the day and throughout the year. Due to minimal temperature differences, winds are light or even non-existent for longer periods. However, heavy precipitation and storms occur frequently.
Design objectives and response
The solar radiation is intense and to a great extent diffuse due to haze. It therefore demands generous shading devices. The haze may cause sky glare which can also be reduced by large shading devices.
Vegetation is rich and provides an excellent means of improving the climatic conditions. Its surface does not heat up and it provides efficient shading at low cost. However, it has to be arranged in a way that does not impede air circulation.
The principle of heat regulating measures by thermal mass and heat storage is not applicable for this climate, because the temperature difference between day and night is minimal. The designer is limited to measures which avoid heat absorption and heat storage. The use of low thermal mass, high reflective outer surfaces or double-skin structures are the result.
The indoor temperature can hardly be kept much below the outdoor temperature. However, by efficient design the indoor temperature can avoid exceeding the outdoor temperature and inner surfaces can remain relatively cool. Together with proper ventilation, comfortable conditions can be achieved in most cases.
Existing air movements should be utilized as much as possible to provide evaporative cooling and to avoid mould growth.
3.3.2 Settlement Planning
The main points
• Topographical location with maximum air velocity and shade.
18.104.22.168 Topographical location of settlements
Settlements should be placed preferably on southern or northern slopes, ideally facing away from the equator. The warm-humid climate zones are generally located near the equator. As a consequence, east and west slopes receive more radiation compared to north and south slopes and are, therefore, disadvantageous. (see Chapter 3.1.5 and 22.214.171.124)
Ideal sites are windward slopes near the crest or near the beach, where regular winds exist. The ventilation effect of winds can be improved by effective arrangement of vegetation. (see Chapter 126.96.36.199 and 188.8.131.52).
Although the wind velocity is generally low, occasional storms (hurricanes) can occur. Therefore, a firm structure is required. Floods are common in lowland locations and have to be kept in mind.
184.108.40.206 Urban forms and external space
An open settlement pattern is the appropriate response to the climate.
To provide sufficient air circulation, buildings should be scattered and have a low population density.
Buildings should be separated with large, free spaces between them. This allows airflow which provides ventilation for cooling and a hygienic environment.
On the other hand, the walking distance to public spaces should be minimal and the footpaths shaded.
Groups of buildings should not be built in too compact a manner. Extended settlements, arranged in a line across the prevailing wind direction give low resistance to air movement and are, therefore, the ideal solution.
In cases where settlements consist of several rows of buildings, the houses should be staggered to avoid windshaded buildings in the downwind rows. (also see Chapter 220.127.116.11)
Settlement pattern, street network
The settlement pattern should allow for a loose open street network.
External public spaces, streets, squares and footpaths should be protected from sun and rain.
Squares and passages should be covered, but cross-ventilation should not be impeded. Generous and well distributed areas of vegetation help to improve the microclimate.
Street spaces should be long and straight to facilitate air movement and lined by high, shade-providing trees.
Street space formed by trees
Certain species of trees (e.g. rain trees) form an extraordinary outdoor space by creating a canopy effect. They should not be planted too far from each other, so that the crowns form a wide hall-like space, creating a comfortable microclimate.
Landscaping with vegetationAn unshaded pavement exposed to the sun heats up and can reach very high temperatures. A vegetal cover of the ground, however, keeps it comparatively cool and contributes much to a cooler outdoor microclimate.
Landscaping with vegetation
An unshaded pavements should be avoided as far as possible and air should not be allowed to pass over such hot surfaces before reaching buildings.
High trees with wide, shading crowns provide significant protection from solar radiation and should be incorporated as much as possible into any landscape planning.
High bushes, however, should be avoided near buildings because the space between the ground vegetation and the high crowns of the trees should remain open, providing free access for the wind at the level of the living spaces.
In dense settlements it is difficult to provide privacy as well as allowing the free flow of air. Various systems of paling fences and screen walls have been devised consisting of louvred or overlapping timber boards or planks. They do not permit a direct view and allow breezes to penetrate, but reduce the air velocity quite substantially. A suitably spaced, scattered settlement pattern helps to avoid fences, yet provides privacy.
3.3.3 Building design
The main points
• The main elevations and rooms should be placed facing north and south and towards the prevailing wind.
• The form should be spread out.
• Provide generous shade for direct and diffused radiation.
• Provide effective cross ventilation.
18.104.22.168 Orientation of buildings
Shading of the east and west elevations is difficult because of the low sun, and may require special devices; whereas the south and north sides can easily be protected by an overhanging roof.
Thus the best orientation for protection from the sun is along the east-west axis.
Where a predominant wind direction can clearly be identified, long-shaped buildings should be arranged across this direction.
Often the above two parameters are contradictory. In this case, a reasonable compromise should be made based on a detailed analysis of the specific situation, considering the possibilities for diverting the wind direction by means of vegetation and structural arrangements, such as parapet walls within the external adjoining space.
As a general rule, with low rise buildings, where the walls would not receive much radiation, orientation according to the wind direction is more advisable. With high-rise buildings the opposite holds true and protection from sun radiation should be the decisive factor.
22.214.171.124 Shape and volume
Forms with large surface areas are preferred to compact buildings. This favours ventilation and heat emission at nighttime.
126.96.36.199 Type and form of buildings
The main goal is the reduction of direct heat gain by radiation through openings and of the internal surface temperature. The building should therefore be designed not only with protected openings, but also with protected walls. This task will be much easier if the building is kept low. In addition, the roof should extend far beyond the line of walls, with broad overhanging eaves and other means of shading.
The height of the buildings should, in general, not exceed 3-storys. Higher buildings receive too much radiant heat and give wind obstruction to neighbouring buildings.
The intense diffuse solar radiation calls for buildings that have large overhanging roofs and wide shaded verandahs.
Row houses elongated along the east-west axis provide the best shading of the critical east and west walls.
These critical east and west walls are best protected if the house is covered with a hipped roof.
The arrangement of rooms depends on their function. Since the thermal load is related to the orientation, rooms on the east side are warm in the morning and, if not built with much thermal mass, cool down in the afternoon. Rooms on the west side are cooler in the morning and heat up in the afternoon. Rooms facing north and south remain relatively cool if provided with adequate shading. Thus, the rooms can be arranged according to their functions and according to the time of the day they are in use.
It may not always be possible to arrange all the main rooms in an ideal manner. In this case, special care must be taken for the disadvantaged rooms.
Bedrooms can be adequately located on the east side, where it is coolest in the evening. Good cross-ventilation is especially important for these rooms because, at rest, the human body is more sensitive to climate. On the other hand, stores and other auxiliary spaces can be located on the west side.
Provided the kitchen is mainly used during morning and midday hours, it can be located on the west side as well.
The main rooms which are in use most times of the day, such as living rooms, should not be located on the east or west side.
Rooms with internal heat load
Rooms where internal heat occurs, such as kitchens, should be detached from the main building, although they can be connected by a common roof.
Special attention should be given to the arrangement of rooms with a high humidity (bathrooms). Here a proper cross-ventilation is especially important to avoid mould growth.
The high humidity and warm temperatures require maximum ventilation, which leads to very open buildings. This is valid not only for the design of the elevations, but also for the floor plan.
Free passage of air for cross-ventilation through the interior is important. This can be achieved by large openings, not only in the outer walls but also in the internal partitions. An even more efficient solution is that of single-banked rooms with access from open verandahs or galleries.
The floor is preferably elevated above the ground to allow for a better ventilation. Houses are best built on stilts or at least on raised platforms.
188.8.131.52 Immediate external space
The same principles of maximum shading and maximum ventilation also apply to the design of the outdoor space. Tall shading trees and reduced ground vegetation are important elements.
3.3.4 Building components
The main points
• Heat storage and time lag should be minimal.
Due to the relatively narrow diurnal temperature fluctuation it is not possible to achieve much cooling by utilization of the thermodynamic properties of building components. The main goal is, on the one hand to store as little heat as possible in the structure in order to obtain the maximum benefit of the cooler night temperatures.
On the other hand, maximum ventilation throughout the day enables cooling by perspiration.
A third important point is the reduction of radiation and its reflection, by which is meant direct and diffuse solar radiation as well as radiation by the surface of heated-up parts of the building and the surroundings.
Heat storage and time lag
Constructions with a high thermal storage capacity and a long time lag are to be avoided. It would cause undesirable re-radiation of heat at night. Due to the high relative humidity, problems of condensation could also appear in the morning hours because the surfaces would be somewhat cooler than the air.
As an exception, in buildings used in the daytime only, a certain heat storage capacity may be advantageous. Depending on the diurnal temperature differences, a reduction of the daytime indoor temperature by a few degrees may be possible. A relatively short time lag of some 5 hours may be adequate.
Thermal insulation has very little effectiveness. Due to the free flow of air, the ambient air temperatures inside and outside the building are very much the same. Insulation may be justified only in places where sun radiation is received, e.g. for roofs and sun-exposed walls. The use of reflective materials and surfaces is, however, more important. These measures keep the temperature of the inner surface low. The same effect can be achieved with properly ventilated double skin constructions.
Reflectivity and emissivity
High reflectivity and high emissivity are required properties for keeping the indoor temperature and the inner surface temperature low.
184.108.40.206 Foundations, basements and floors
Direct contact with the ground does not necessarily provide cooling because the temperature of the shaded surface is about equal to the mean air temperature. A certain cooling may only be possible by conduction for barefooted persons or persons sitting on the floor.
As a consequence, it is better to raise the floor and ventilate the space underneath. The floor should be of low thermal capacity (e.g. timber floor with void). The advantages are better ventilation due to the elevated space and maximum benefit of the slightly lower night temperature.
Walls, both external and internal, should be as light as possible with a minimal heat storage capacity. These should obstruct the airflow as little as possible and should reflect radiation, at least in places where solar radiation strikes the surfaces.
The outer surface should be reflective, light colored.
Walls should be shaded as much as possible. If, however, exposed to the sun, they should be built in the form of a ventilated double leaf construction, the inner leaf having a reflective surface on its outer side and perhaps with thermal insulation.
Light and thin materials such as timber or, even better, bamboo matting are recommended. Other materials forming light panels can be used, together with a frame structure to take care of the structural requirements.
220.127.116.11 Openings and windows
Design and placement
In warm humid areas openings are important elements for the regulation of the indoor climate. They should be large and fully openable, with inlets of a similar size on both sides of the room allowing a proper cross-ventilation. Windows are preferably equipped with flexible louvres allowing a regulation of ventilation. Door shutters may also incorporate louvres or grills. Windows with fixed glass panes are of no advantage and should be avoided.
To avoid direct solar radiation and glare, openings should be shaded by an overhanging roof, screens, lattices, grills etc.
All these measures have to be designed to give minimal resistance to the airflow. Mosquito-screens, which are essential in these regions, but reduce the airflow considerably, are therefore best installed away from windows, e.g. around the verandah or balcony.
Openings should be placed according to the prevailing breezes, so as to permit a natural airflow through the internal space. This airflow is most effective if concentrated at body level.
A difficult problem is the design of large openings which at the same time protect from driving rain.
Ordinary louvres direct the wind upwards above body level. Furthermore they are not safe against driving rain.
Modified louvres keep the wind at lower level (living area) and provide protection from driving rain, but reduce the airflow to a certain extent.
Another alternative is the use of a second set of louvres to direct the air down to the occupants.
In warm-humid areas the roof is preferably pitched to allow heavy rains to run off.
Large overhangs protect the walls and openings from radiation and precipitation.
Single leaf construction
The roof should be made of lightweight materials with a low thermal capacity and high reflectivity. Metallic and light colored surfaces have the best reflective capacity (see data in Appendix 5.1 ). Painting the surface in light colors, e.g. a yearly applied coat of whitewash, is an economical method to increase reflectivity. However, in most cases a single leaf construction will not satisfy the comfort requirements.
Ventilated double roof
A more efficient solution is the properly ventilated double roof. The inner layer (ceiling) may be well insulated and provided with a reflective upper surface. The inner surface of the ceiling should not exceed the air temperature by more than 4°C. This can be achieved by an insulation board with a U-value of about 1.5-W/m². Where such materials are not available or cannot be afforded, even the cheapest kind of ceiling would provide a substantial improvement.
A simple example can illustrate this effect. In two identical houses, roofed with corrugated asbestos sheets and with an outdoor temperature of 22°C, a difference of 14°C in the ceiling surface temperatures was monitored. In the first case where there was no ceiling, the temperature was 48°C; in the second case where there was a paper ceiling lined with aluminium on the upper surface, the temperature was 34°C. [ 8 ]
Air which has passed through a double roof space should not be allowed to enter the living zone (e.g. discharged towards a verandah), as this air will be much hotter than the normal outdoor air. (also see Chapter 18.104.22.168)
3.3.5 Special topics
22.214.171.124 Shading devices
Although the intensity of radiation is normally less than in hot-dry regions, it is nevertheless a significant source of heat, therefore its entry into the building should be prevented. In hot-dry climates the radiation is mostly directional and the shadow angles can be established with a high degree of accuracy. Here, due to the moisture in the air, much of the radiation is diffuse, coming from the whole of the sky.
Shading devices should therefore provide great coverage, obstructing most of the sky and not just the sun. Furthermore, the openings should be far larger than in hot-dry climates. This is another reason why the shading devices should be much larger.
Shadings with vegetation
The proper arrangement of vegetation, mainly of shade-providing trees, within the surrounding space is an important aspect for the improvement of the indoor climate.
Another efficient solution is to grow a green cover over roofs and walls. This cover functions as a second skin which provides
• protection against solar radiant heat,
A disadvantage may be a certain increase in unwanted insects. But since openings should in any case be protected by screens, this may not cause a problem.
Tile roofs and similar “soft” roofing materials may be destructed by certain plant species. In this case, the plants have to be selected carefully. Species with too aggressive root systems like certain Ficuses should be avoided. In dry locations plants should be selected which can acclimatize and stand dry spells.
126.96.36.199 Natural ventilation,
Basic principles and concepts
Efficient air circulation is one of the few possibilities for natural climatization in warm-humid zones. Because of the minimal temperature differences it can hardly be utilized to cool down the building components, but cooling is felt through the increased perspiration of the human body. However, this effect is only felt if the air is not fully saturated with humidity.
The flow of air can be influenced by topographical features, by the orientation of the building and by the position of surrounding buildings and other obstructions. Such obstructions may be built intentionally to divert the wind in a desired direction (see Chapter 188.8.131.52).
In this climate there is a need for both a frequent change of air and for an air movement across the body surface.
An exchange of air is also necessary because without it, both the temperature and the atmospheric humidity in the room will quickly increase above the values outside, due both to the heat and moisture output of human bodies and to various activities such as washing, cooking etc.
A simple active device for the improvement of the indoor climate may be the use of electric fans (see Chapter 184.108.40.206)
220.127.116.11 Passive cooling means
The possibilities for evaporative cooling in humid regions are limited. The potential of the air to absorb humidity, and with it the potential for cooling is minor.
In island climates, however, where the peak temperature is combined with approximately 65% relative humidity, methods of evaporative cooling are possible, although the efficiency is less than that in hot-arid climates.
Here, only indirect cooling using a heat exchanger is possible because in humid areas the relative humidity of the indoor air must not be further increased. (also see Chapter 18.104.22.168)
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