Dear Saxena ji,
Thank you for inquiry.
West facing windows can be a big source of heat, first measure which you...
Why all these are not applicable to Tuticorin port or the one planned in AP or WB ?
What an eye opener! As an environmental engineer,disposal of sanitary napkins has always been a concern during waste...
WHY is a city hotter than its surrounding
countryside? The first answer that
comes to mind is the availability of open
space and trees in the countryside. Now,
Haider Taha and his colleagues at the
Lawrence Berkeley Laboratory (LBL) in
Berkeley, California, and the University
of California, Los Angeles, say that
painting the roofs of houses in the cities
white can complement the cooling
effect of trees.
Taha and his colleagues simulated
the effects of adding moderate amounts
of trees and white roofs in a computer
model of Los Angeles (LA). They observed an amazing 4'c fall in the average
summer temperature. The reason -
white colour wards off heat by reflecting
the sunlight while trees add moisture to
the air, thus cooling it. The estimated
summer energy savings on air-conditioning amounted to us $100,000-
200,000 per hour (New Scientist, Vol 146, No 1970).
The model also revealed that altered
temperatures and increased reflectivity,
because of the trees and the white roofs
reduced the smog by about 10 per cent
which is "equivalent to getting rid of
about 3 million cars offThe roads," says
Arthur Rosenfeld, former director of
LIBL'S Center for Building Science,
Because chemical reactions slow down
as the temperature falls, ozone produced by pollutants reacting with each
other went down by 5 per cent due to
the VC temperature drop.
But these results are mere simulations, reminds Taha. However, scientists at the Florida International
University in Miami and the LBL'S
Urban Heat Island Project group, have
tried to find out how this theory would
work on real houses and buildings.
Hashem Akbari, leader Of LIK'S
Urban Heat Island Project, along with
his group measured the air-conditioning costs before and after surrounding
houses in Sacramento, California, with
trees carried in trucks and applying
reflective white plastic polymer paint on
the roofs, The study revealed that air-
conditioning costs went down by about
40 per cent, with more than half the savings owing to the reflective coating.
However, things are not as simple as
they seem. For instance, many trees emit
hydrocarbons, terpenes 'a class of
volatile aromatic hydrocarbons) and
isoprene which react with nitrogen
oxides and contribute to Smog. In LA,
trees account for about 10 per cent of
the hydrocarbon pollution. Now, scientists'are categorising the trees into low,
moderate and high emitters so as to
make a better selection possible.
Then there is the problem of fungal
and algal growth on the roofs in humid
places - they would hamper the reflectivity of the surface coating. But the scientists are working on developing zinc
oxide-based paints which act as a fungicide and an algicide.
And if the people do not want so
much white in the city, then the researchers offer a variety of reflective coating material using raw materials which
would reflect the infra red light rays. For
example, reducing the magnetite
amount in terracotta tiles, lowers the
amount of infrared radiation absorbed.
If these heat-reducing measures are
implemented in the whole of North
America, annual energy savings amounting to us $10 billion within 20 years
could be effected.
Though the measures offer a way to
reduce energy costs and pollution, what
about the winters and monsoon? Would
the houses have to be painted with light
absorbing colours or would the energy
bill double up to keep these cool houses
warm? The researchers, it seems, will
now have to develop 'smart' materials
which would keep the houses cool in
summer and warm in winter.