HISTORY | AIR WASHERS MADE IN AMERICA Air washing technology was first developed in the US to protect building occupants from outdoor pollution. David Arnold says the technological advances made by Willis Carrier to enable humidity control then led to the development of air washers for movie theatres and film studios I n the second half of the 19th century, the air quality in large industrial cities was of concern in Britain and the US. Fog or smog (a mix of smoke and fog) from coal used for power and heating was prevented from rising by temperature inversions that trapped the smog near street level. After the pea soupers of 1879, the registrar general for London reported that mortality in London had risen 220%, causing the premature deaths of about 3,000 people. Most buildings were naturally ventilated, so the air indoors was the same, if not worse, than outside. Engineers designing the few mechanically ventilated buildings knew they had to clean the air drawn in to reduce soot deposits and the risk to health. Cheesecloth filters were tried initially, but they were soon discarded because of the resistance to airflow and the large areas of filter necessary in the supply ducts. Around 1900, several US inventors filed applications for patents for air washers, but the simplest and most popular was by Richard H Thomas, who lived in Chicago, one of the industrialised cities most badly affected by fog. His patent was for the Acme Purifying and Cooling System, which was intended to be installed at the intake to a mechanical ventilation system. It was simply a metal casing housing an air heater to prevent freezing, water sprays, and eliminator blades to remove droplets and soot. Dirty air hit the eliminator blades and sooty water drained down to a sump to drain away. The first Acme air washer was installed in the recently built Chicago Public Library, which was having problems with soot and dust settling on the books. It was so successful that the entire building was then treated. Sackett & Wilhelms, a fine art printer in Brooklyn, had problems of a different sort controlling humidity in summer and winter for its lithographic printing. The problem was taken to Buffalo Forge, a manufacturer of ventilation fans and air heaters, for a solution. One of the companys graduate engineers, Willis Carrier, was concerned at the lack of science for sizing heat exchangers and had been carrying out research work. Perhaps because of this, he was assigned to find a solution to the printers problems. His first attempt to control humidity was by passing moist air over a bed of calcium chloride brine, but he abandoned it because it resulted in undesirable odours and corrosive action. He then experimented with chilled cooling coils and realised the counterintuitive process occurring: moisture was being removed from the air by contact with water at a lower temperature on the surface of the coils. Why not then, he asked himself, spray the cold water into the air stream to increase the surface of contact and reduce the resistance to airflow? Unsatisfied with the air washers available at the time, Carrier decided to develop his own and set about making improvements. He thought the Acme air washer did an excellent job, but the type of spray couldnt provide the right conditions for the exact control of moisture content. His biographer, Margaret Ingels, relates the story of Carriers flash of inspiration while waiting for a train in the fog at a railway station in Pittsburgh. He realised, to obtain 100% saturation, he needed to create a fog-like atmosphere in the air washer. Achieving 100% saturation meant the air was at its dew-point temperature and no more moisture could be absorbed. Further, by raising or lowering the temperature of the spray water he could control the air to any given moisture content and, therefore, any relative humidity. It is a coincidence that achieving a fog-like atmosphere in Carriers air washer could also be used to remove fog by dehumidifying air drawn into the ventilation systems in film studios. Another coincidence is that one of the most successful markets for air washers in the 1920s was the expanding film studio and movie theatre market. The first Carrier air washer in a movie theatre was installed above the auditorium in Graumans Metropolitan Theatre in Los Angeles, in 1923. It was probably the same model installed in the Famous PlayersLasky film studio in 1922 referred to as a fog-dispersal plant by Farmer the only difference being that the spray water was cooled by a mechanical refrigeration plant. Air washers evolved into the first, most common, type of air conditioning installed in cotton mills, cigarette factories, theatres, hotels, offices, public buildings, and sports stadiums throughout the 1920s and 30s, including what is claimed to be the first fully air conditioned office, the Milam Building in San Antonio, in 1928. CJ CIBSE past President DAVID ARNOLD FCIBSE is a partner at Troup Bywaters and Anders, and author of 20th century air conditioning, published by ASHRAE The Milam Building in San Antonio was claimed to be the first air conditioned building in 1928 44 March 2022 www.cibsejournal.com CIBSE March 22 pp42-44 Film Studio Fog.indd 44 25/02/2022 18:32