tropical architecture

1. Author: Siti yaumilia salsa (13.036)
Tropical architecture
Architecture and climate
 Effect of buildiing on local climate
BUILDING DOES AFFECT MICRO CLIMATE SURROUNDINGS. IT
RAISESAMBIENT TEMPERATURE, CHANGE ITS RELATIVE HUMIDITY
AND AIRMOVEMENT SURROUNDING THE BUILDING. IN A LARGE
SCALE IT COULDCHANGE PRECIPITATION VARIATIONS
Buildings have a major impact on the environment over their
entire life cycle. Responsible for 40% of worldwide energy flow and
material use, conventional buildings have been identified as the largest source of green-house gas emissions, even more than
that of the transport and industry sector. They affect urban air quality and contribute to climate change. They are also
hazardous to health at times. During their lifecycle, conventional buildings harm the environment in many ways.
http://hubpages.com/forum/topic/4367

2.  Urban Heat Island (UHI)
What is an urban heat island?
"Urban Heat Island" (UHI) refers to the tendency for a city or
town to remain warmer than its surroundings, by as much as
10 deg. F or more. This effect is caused mostly by the lack of
vegetation and soil moisture, which would normally use the
absorbed sunlight to evaporate water as part of photosynthesis
(a process called "evapotranspiration"). This is also the reason
why forests are cooler than deserts.
Instead, the sunlight is absorbed by manmade structures -- roads, parking lots, and buildings. With little or no water to
evaporate, the sunlight's energy goes into raising the temperature of those surfaces and the air in contact with them. As
the day progresses, a dome of warm air forms over the city asconvection transports heat from the surface to higher in the
atmosphere.
(http://www.weatherquestions.com/What_is_the_urban_heat_island.htm)
Over the last decade, heat waves have claimed an increasing number of casualties among the elderly - particularly in
southern Europe. Prolonged periods of high temperatures also put a strain on medical resources and place an additional
financial cost to society as a whole. High densely built-up areas trap the heat, especially at night, causing what is called
Urban Heat Islands (UHI) in which city centers can be up to 10° C warmer than surrounding rural areas. Another
consequence of UHIs is that energy consumption rises with the increased use of air conditioners and refrigeration appliance.
http://www.urbanheatisland.info/
As urban areas develop, changes occur in their landscape. Buildings, roads,
and other infrastructure replace open
land and vegetation. Surfaces that were once permeable and moist become
impermeable and dry.1 These changes cause urban regions to become
warmer than their rural surroundings, forming an "island" of higher
temperatures in the landscape.
http://www.epa.gov/hiri/about/index.htm

3. CAUSES
There are several causes of an urban heat island (UHI). The principal reason for the nighttime warming is that the short-
wave radiation is still within the concrete, asphalt, and buildings that was absorbed during the day, unlike suburban and
rural areas. This energy is then slowly released during the night as long-wave radiation, making cooling a slow
process.[2] Two other reasons are changes in the thermal properties of surface materials and lack ofevapotranspiration (for
example through lack of vegetation) in urban areas. With a decreased amount of vegetation, cities also lose the shade and
cooling effect of trees, the low albedo of their leaves, and the removal of carbon dioxide.[7][8] Materials commonly used in
urban areas for pavement and roofs, such as concrete and asphalt, have significantly different thermal bulk properties
(including heat capacity and thermal conductivity) and surface radiative properties (albedo and emissivity) than the
surrounding rural areas. This causes a change in the energy balance of the urban area, often leading to higher temperatures
than surrounding rural areas.[9]
Other causes of a UHI are due to geometric effects. The tall buildings within many urban areas provide multiple surfaces
for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. This is called the
"urban canyon effect". Another effect of buildings is the blocking of wind, which also inhibits cooling by convection and
pollution from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the
UHI.[4][10][11] High levels of pollution in urban areas can also increase the UHI, as many forms of pollution change the
radiative properties of the atmosphere.[9] As UHI raises the
temperature of cities, it will also increase the
concentration of ozone in the air, which is a greenhouse
gas. Ozone concentrations will increase because it is a
secondary gas, aided by an increase in temperature and
sunlight.[12]
.
Vancouver's downtown (source :
http://www.aboutvancouver.co.uk). Vertical surfaces
absorb the energy reflected from most of the three-
dimensional built-up surface.
http://en.wikipedia.org/wiki/Urban_heat_island

4. IMPACT OF HEAT ISLAND
It has been largely demonstrated that cities with variable landscapes and
climates can exhibit temperatures several degrees higher than their rural
surroundings (i.e. UHI effect), a phenomenon which if increases in the future,
may result in a doubling of the urban to rural thermal ratio in the following
decades. Hence, assessment of the UHI and strategies to implement its mitigation
are becoming increasingly important for government agencies and researchers of
many affected countries.
As it would be expected, the characteristic inclination towards warming of urban
surfaces is exacerbated during hot days and heat waves, which reinforces the
air temperature increase, particularly in ill-ventilated outdoor spaces or inner
spaces of Source: PD.PHOTO.ORG
residential and commercial buildings with poor thermal isolation. This increases
the overall energy consumption for cooling (i.e. refrigeration and air-
conditioning), hence increasing the energy production by power plants, which leads to higher emissions of heat-trapping
greenhouse gases such as carbon dioxide, as well as other pollutants such as sulfur dioxide, carbon monoxide and particulate
matter. Furthermore, the increased energy demand means more costs to citizens and goverments, which in large metropolitan
areas may induce significant economic impacts. On the
other hand, UHIs promote high air temperatures that
contribute to formation of ozone precursors, which
combined photochemically produce ground level ozone.
A direct relationship has been found between UHI
intensity peaks and heat-related illness and fatalities,
due to the incidence of thermal discomfort on the
human cardiovascular and respiratory systems.
Heatstroke, heat exhaustion, heat syncope,and heat
cramps, are some of the main stress events, while a
wide number of diseases may become worse,
particularly in the elderly and children. In a similar way, respiratory and lung diseases have shown to be related to high
ozone levels induced by heat events. Several of the above mentioned impacts have been addressed by the US EPA (for
further information see links in the “External link” section of this website).
The anomalous warm of the city creates relatively low air pressures that cause cooler, rural air to converge on the urban
center, thus forcing warm air to ascend (i.e. convection), which at higher altitudes condensates and precipitates. Studies
carried out in several cities of the United States such as Atlanta, New York, Chicago and Washington, have shown that
urban-induced precipitation and thunderstorm events are mainly initiated by the UHI. Other meteorological impacts of the
UHI are associated with reductions in snowfall frecuencies and intensities, as well as reductions in the diurnal and seasonal
range of freezing temperatures. Lastly, high temperatures may produce physiological and phenological disturbances on
ornamental plants and urban forests.
Although in wintertime the UHI can result in energy savings (i.e. winter penalty), there is a great consent among
researchers that this benefit is outweighed by the detrimental effects that ocurr in summertime.

5. Mitigation of heat island effects
Figure 5. Workers apply a cool roof coating on a rowhouse in
Baltimore, Maryland. (Source: EPA)
There are a number of steps that communities can take to lessen the
impacts of heat islands. These heat island reduction strategies
include:
1. Installing cool roofs or vegetated green roofs
2. Installing green roofs
3. Switching to cool paving materials.
4. Planting trees and vegetation
The extent to which urban areas can benefit
from heat island reduction strategies depends on
several factors. Some of these factors, like prevailing weather patterns, geography, and pollution
transported from upwind regions, are largely beyond the influence of local policy.
However, factors such as land-use patterns, materials used in road and building construction, and the
coverage of urban trees and vegetation can be directly affected by decision makers. This is where
policies and programs to reduce the impacts of heat islands – and achieve related environmental and
energy-savings goals – can be most effective.
http://www.eoearth.org/view/article/153461/