Keeping Cool

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By 2017-04-12

BY MICHAEL GREGSON

The current hot spell across Sri Lanka brought to mind something once said by the founding father of Singapore, Lee Kuan Yew. When Lee was asked by the Wall Street Journal in 1999 to name the twentieth century's most influential invention, he gave a characteristically unconventional answer. Other luminaries who were asked the same question came up with fairly predictable choices like television, antibiotics, the transistor and the internet.

Those suggestions were much too obvious for the Singaporean leader. Instead he chose the air-conditioner, arguing that before air-con, people living in the tropics were at a disadvantage because the heat and humidity damaged the quality of their work.

It is a topical thought as the sun blazes down directly over the latitudes of the island from now until the 15th of April. The Department of Meteorology has warned of temperatures as high as 35 degrees Celsius, especially in the North of the country.

That's hot enough for me and certainly has me reaching for the on switch of my AC, despite the big electricity bill that will inevitably follow.

But if you think it is hot in Sri Lanka at the moment, the current temperature here is nothing compared to the highest ever recorded. According to the World Meteorological Organization, the aptly named Furnace Creek in America holds the record.

Furnace Creek is in the notoriously hot Death Valley in California, close to the border with Nevada. The hottest air temperature ever recorded there was a staggering 56.7 Celsius (134°Fahrenheit) on July 10, 1913.

In more recent times, Death Valley set more temperature records. In July 2012, the day's lowest temperature was 42° C (107° F), tying the record for the world's hottest low temperature ever recorded. On the same day, the average temperature was 47.5° C (117.5° F), which is the world's hottest temperature, averaged over 24 hours on record.

Parts of the Middle East are almost as hot as Death Valley. I used to live in Qatar in the Arabian Gulf, where it regularly tops 45° C. and in July 2010 the temperature was recorded at over 50° C at the old Doha airport.

Sun-baked Cookies

It's so hot in Qatar that cars literally turn into ovens. During the summer months residents have been known to bake cookies inside their cars. They preheat their vehicles by leaving them out in the open with the windscreen pointing towards midday sun.

They then place a baking tray below the windscreen – and after an hour or so the cookies are cooked to perfection.

The Gulf countries would be virtually unliveable in the summer without modern air-conditioning. The desert Bedouin tribes were nomads and would move to cooler hill areas in the summer. They had no other way of avoiding the scorching heat until the arrival of electric fans and later Lee Kuan Yew's favourite 20thcentury invention; the air conditioner.

In chillier parts of the world, like northern Europe and India, snow and ice were used for cooling since ancient times. In the winter, ice would be harvested and stored in insulated boxes, often lined with straw, for use in the heat of the summer.

Evaporation is the basic concept behind air conditioning and refrigeration. The principal was apparently understood in ancient Egypt, where reeds were hung in windows and then moistened with trickling water. The evaporation of water cooled the air blowing in through the window. This process also made the air more humid, which can be an advantage in a dry desert climate, but probably not in Sri Lanka.

In Ancient Rome, water from aqueducts was sometimes circulated through the walls of buildings to cool them. In medieval Persia they used a combination of water filled cisterns and wind towers to cool buildings during the hot season.

The 2nd century Chinese inventor Ding Huan is reputed to have invented a rotary fan for air- cooling, with seven wheels of 3 metres in diameter and manually powered by prisoners.

The idea was taken much further by the Emperor Xuanzong in the 8th century. He ordered the construction of the Cool Hall (Liang Tian) in the imperial palace, which was described as having water-powered fan wheels for circulating the air as well as rising jets of water rising from fountains.

In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that evaporation of highly volatile liquids, like alcohol or ether could be used to drive down the temperature of an object past the freezing point of water.

Franklin concluded: "From this experiment one may see the possibility of freezing a man to death on a warm summer's day."

Some hotels and shopping malls prove his point.

The great English scientist and inventor Michael Faraday discovered in 1820 that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate rapidly.

The pioneering research of Franklyn, Hadley and Faraday were developed a crucial stage further by James Harrison in Australia.

He developed a system that constantly re-circulated the cooling vapour – the same basic method still used in fridges and air conditioners today.

Refrigeration & Air-Conditioning

His first commercial ice-making machine went into service in 1853, and his patent for an ether vapour compression refrigeration system was granted in 1855. Harrison's system used a compressor to force the refrigeration gas to pass through a condenser, where it cooled down and liquefied. The liquefied gas then circulated through the refrigeration coils and evaporated again in a continuous process. The machine produced an impressive 3,000 kilograms of ice per day.

It took almost another 50 years for this cooling technology to be applied to buildings. The first modern electrical air conditioning unit was invented by Willis Carrier in America. His first device was used to control the temperature and humidity inside a printing works in Buffallo, New York. His air conditioner worked – but little interest was shown at first. It took another 20 years and the boom in building skyscrapers for it to really take off in America. The rest of us had to wait until after the Second World War for the technology to spread beyond the US.

Nowadays air conditioners are commonplace around the world – though in Sri Lanka their use is somewhat limited by the high cost of electricity and occasional power shortages. Last year government offices were told to reduce the use of air conditioning and set the thermostats at no lower than 26° C to reduce the strain on the electricity grid.

It is also possible to use entirely natural methods to reduce the air temperature.

Strategically placed trees in urban areas can cool the air by between 2 and 8 degrees C. Be thankful if you live in a tree lined street. Mother Nature is helping to keep you cool.

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