Composite or monsoon climate is neither consistently hot and dry nor warm and humid.
Their characteristics change from season to season, alternating between long, hot and dry periods to shorter periods of rainfall and high humidity.
There is a significant difference in air temperature, humidity, wind, sky and ground conditions throughout the year.
Physiological Objectives
The objectives set for warm-humid and hot-dry climates apply to the respective seasons of the composite climate.
During the cold season, effective temperatures are much lower than in the warmer seasons and the physical comfort will rely upon heat loss, especially through the night.
In the warmer season, heat dissipation is inadequate and designers try to increase it, the opposite happens during the cold season. The dissipation is excessive, hence heat retention is necessary.
Design Criteria
Solutions for one season are unsatisfactory for others.
Thermal design criteria recommended for hot-dry climates apply not only to the hot-dry season of composite climate but also to the cold season.
For the monsoon, buildings should be designed according to the criteria of warm-humid climate, which would require entirely a different solution. This duality of the problem has to be handled tactfully by the designer. An analysis of the site climate will help the designer prioritize the needs.
Form and Planning
A moderately compact internal planning of the house will be of benefit for most of the year.
Buildings should be grouped in a way to take advantage of the prevailing breezes during the short period when air movement is necessary.
A moderately dense, low rise development is suitable, which will ensure the protection of outdoor spaces, mutual shading of the external walls, shelter from the wind in the cold season. Shelter from dust and reduction of surfaces exposed to solar radiation.
Shading walls is desirable, provided the roof has a low transmittance and good thermal capacity.
External openings do require shade during the hot and warm seasons.
External Spaces
Brise-soleils, louvres and other sun break used to protect openings during the hot-dry period are also advantageous in the rainy season, serving as protection against rain.
During the cold season, when solar gain is essential, all shading is undesirable.
The high rainfall makes it easier to maintain vegetation, consequently also reducing dust. Deciduous plants are advisable.
A courtyard is the most pleasant out-door space for most of the year because it excludes the wind and raps the sun during the winter. The courtyard may even be covered by a pergola carrying deciduous plants.
Roof and walls
Roofs and external walls should be constructed solid masonry or concrete to have a 9 to 12-hour time lag in heat transmission. The thermal capacity will be beneficial for the cold and hot dry season.
Resistance insulation should be placed at the outer surfaces of the external walls or roof.
Low rise development is the greater contact of the walls with the ground, thus the ground will also act as thermal storage.
Surface treatment
The prevention of heat entering through the outer surfaces of the walls and roof is a fundamental rule.
Surfaces exposed to the sun during the hot and warm seasons should be light coloured or of shiny polished metal.
Variable surfaces may be devised, but the solar geometry may often permit permanent surfaces to be utilised in the appropriate seasons.
Ventilation
Orientation of the openings is determined by two factors- (1) towards the breeze prevailing during the warm-humid season, to utilise its cooling effects. (2) towards the sun during the cold season, to utilise the heating effect of radiation entering through the windows; If the two factors lead to a contradiction, the analysis of comfort will aid to reach a final decision.
Reasonably large opening in the opposite walls is suitable, preferably with solid shutters which can be opened when cross-ventilation is necessary, possibly during the hot and humid season or cool evenings in the hot-dry season.
The area of the openings should not exceed the area of the solid walls on the same elevation.
On the adjacent walls, the windows should not occupy more than 25% of the total area.
Traditional Shelter
The character of the houses in a composite climate depends upon the relative predominance of hot-dry or hot-humid conditions during a year.
The urban solution includes a ground floor with massive walls of earth or masonry, with large shuttered openings, laid out around a courtyard, and a first-floor structure of lightweight materials.
New Delhi experiences a composite climate
These cool quickly at night, to allow fairly comfortable sleeping conditions during the hottest parts of the year.
In such a hybrid structure, the family shifts its activities through the day with seasonal changes in the climate.
Conclusion
The composite climates are a culmination of the characteristics of hot-dry and hot- humid climate. The dominant prevailing climatic condition analysis helps decide on design solution priorities. The places which experience a composite climate are central India, central South America, south-eastern North America.
