Air Conditioning through the ages

Air conditioning

Origins date back to 2nd Century China and Ancient Romans

The term air conditioning most commonly refers to the cooling and dehumidification of indoor air for thermal comfort. In a broader sense, the term can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air.^[1] An air conditioner (AC or A/C in North American English, aircon in British and Australian English) is an appliance, system, or mechanism designed to stabilise the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time) , typically using a refrigeration cycle but sometimes using evaporation, most commonly for comfort cooling in buildings and transportation vehicles.

The concept of air conditioning is known to have been applied in Ancient Rome, where aqueduct water was circulated through the walls of certain houses to cool them. Similar techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season. Modern air conditioning emerged from advances in chemistry during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by Willis Haviland Carrier.

History

While moving heat via machinery to provide air conditioning is a relatively modern invention, the cooling of buildings is not. The ancient Romans were known to circulate aqueduct water through the walls of certain houses to cool them. As this sort of water usage was expensive, generally only the wealthy could afford such a luxury.

The 2nd century Chinese inventor Ding Huan (fl. 180) of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered.^[2] In 747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the Cool Hall (Liang Tian) built in the imperial palace, which the Tang Yulin describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains.^[3] During the subsequent Song Dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.^[4]

Medieval Persia had buildings that used cisterns and wind towers to cool buildings during the hot season: cisterns (large open pools in a central courtyards, not underground tanks) collected rain water; wind towers had windows that could catch wind and internal vanes to direct the airflow down into the building, usually over the cistern and out through a downwind cooling tower.^[5] Cistern water evaporated, cooling the air in the building.

Ventilators were invented in medieval Egypt and were widely used in many houses throughout Cairo during the Middle Ages. These ventillators were later described in detail by Abd al-Latif al-Baghdadi in 1200, who reported that almost every house in Cairo has a ventillator, and that they cost anywhere from 1 to 500 dinars depending on their sizes and shapes. Most ventillators in the city were oriented towards the Qibla, as was the city in general.^[6]

In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida.^[7] He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities.^[8] Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterwards when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer Vivian M. Sherlock, he blamed the "Ice King," Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.

Early commercial applications of air conditioning were manufactured to cool air for industrial processing rather than personal comfort. In 1902 the first modern electrical air conditioning was invented by Willis Haviland Carrier. Designed to improve manufacturing process control in a printing plant, his invention controlled not only temperature but also humidity. The low heat and humidity were to help maintain consistent paper dimensions and ink alignment. Later Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time air conditioning came to be used to improve comfort in homes and automobiles. Residential sales expanded dramatically in the 1950s.

In 1906, Stuart W. Cramer of Charlotte, North Carolina, USA, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning," using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company. This evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.

The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928. The refrigerant was much safer for humans but was later found to be harmful to the atmosphere's ozone layer. Freon is a trademark name of DuPont for any Chlorofluorocarbon (CFC), Hydrogenated CFC (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (R-11, R-12, R-22, R-134). The blend most used in direct-expansion comfort cooling is an HCFC known as R-22. It is to be phased out for use in new equipment by 2010 and completely discontinued by 2020. R-11 and R-12 are no longer manufactured in the US, the only source for purchase being the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone depleting refrigerants have been developed as alternatives, including R-410A, known by the brand name Puron.

Innovation in air conditioning technologies continue, with much recent emphasis placed on energy efficiency and improving indoor air quality. As an alternative to conventional refrigerants, natural alternatives like CO₂ (R-744) have been proposed.^[9]

In the time of cholera

Exactly 150 years ago London was in the grip of a cholera epidemic but within the space of a week in early September a doctor changed medical thinking forever. Dr Snow was ridiculed for saying cholera was a waterborne disease Today cholera is indelibly linked with water. However, 150 years ago it was much different. At the end of August 1854 London's third big cholera outbreak was beginning. The accepted thinking was that it was an airborne disease. Within a week London physician John Snow had changed the perceived wisdom - but only after hundreds of people had died. Dr Snow, who was 41 at the time, had already set out his water theory at conferences in 1849 and 1853 but the medical establishment was still not convinced. During late August the outbreak was just beginning. Paralysed By the end of the month, the disease, which causes severe diarrhoea and vomiting, really took hold with more than 50 cases being reported on the night of 31 August. During the next four days another 400 came to light. With the public authorities paralysed by indecision, Dr Snow set about proving he had been right for years. Analysing the deaths, he soon realised the outbreak was centred around a water pump at the junction of Broad Street, renamed Broadwick Street in 1936, and Cambridge Street in Soho. He examined it on 3 September but only found minimal evidence of contamination. I guess he [Dr Snow] was a bit of a maverick, he was ridiculed by some, but stuck to his theory and was proved right Dr Ros Stanwell-Smith, of the John Snow Society Instead, he went to the register of deaths and started to research where the victims lived. Of the 89 who had died in the first two days of the outbreak all but 10 were served by the pump. But it was those that did not live near the pump that proved Dr Snow right. Two ladies from Hampstead, which was five miles away and was not hit by the outbreak, were among the victims. It turned out that the pair, an aunt and niece, had water regularly transported from the Broad Street pump to drink. Symbolic Allied with the information, Dr Snow met with the local parish board of guardians. On 8 September, in one of the most symbolic gestures in the history of public health, the pump handle was removed and within days new cases had dried up. A year later the physician published a 139-page text, On the Mode of Communication of Cholera, setting out how the disease spread. Vibrium cholerae, the cholera-causing bacteria He paid for the document, an updated version of one he first wrote a few years earlier, out of his own pocket. Dr Ros Stanwell-Smith, honorary secretary of the John Snow Society, said Dr Snow's work during the first week of September 150 years ago changed the way the world thought about cholera. "Before he proved it was waterborne, the general opinion was that it came from bad air, the miasma theory. "Using analytical methods, he was able to demonstrate that it was the sewage contaminating the water that was causing cholera. He probably stopped the second wave of the epidemic. 'Greatest' "For me he is one of the greatest doctors in history. He gave the UK a head start in cleaning up our water supply, which then lead to the developing of the sewage system. "I guess he was a bit of a maverick, he was ridiculed by some, but stuck to his theory and was proved right." But for some his legacy goes beyond the field of epidemiology. He became the first doctor to give a member of the royal family an anaesthetic during the birth of Queen Victoria's son, Prince Leopold, in April 1853. Cholera: The facts There are still more than 140,000 cases of cholera a year The symptoms include severe diarrhoea and vomiting Rehydration salts and clean water can cure cholera Cases in the UK are rare, barely more than a handful each year There have been seven cholera pandemics The latest started in Indonesia in 1961 Professor Martyn Evans, principal of the John Snow College at the University of Durham, named after the doctor who was born nearby in North Yorkshire, said his expertise crossed several medical fields. "For us he is an inspirational figure not just for his work in epidemiology but also obstetrics and as an anaesthetist. "He was one of the country's greatest doctors although he is now more well known in the US than here." Last year his achievements were recognised when he was voted the greatest doctor of all time in a poll by the Hospital Doctor magazine. However, it was his work on cholera that remains his lasting legacy. Killer Dr Snow died before the revolution in public health he had campaigned for for so long took place. There was another cholera epidemic in 1866 - eight years after his death. Fellow epidemiologist Dr William Farr, who had at first disputed Dr Snow's theory, provided further evidence water was carrying the disease. Within years great engineering projects were started in many cities to collect and treat sewage, ultimately eliminating the disease in industrialised countries, including the UK. A girl takes her first dose of the cholera vaccine in Sudan A spokeswoman for the Health Protection Agency said: "Cholera is not a really a problem in Britain now. There are only a handful of cases each year and these tend to be brought back by travellers." However, the disease still remains a killer in the developing world. The world has been fighting the seventh cholera epidemic since it was identified in Indonesia in 1961. It soon spread across Asia, Russia and the Middle East and Africa with cholera cases topping 140,000, including 4,500 deaths, in 2002, according to World Health Organisation figures. The WHO said: "Poor sanitation and food hygiene are the major causes of cholera in the developing world." And with vaccines now available, the 21st century tragedy is that people are still dying from cholera. Less than 1 in 100 cases result in death in countries with access to modern medicine but in some third world countries the death rate can top one in two.