The first recognized cases of Legionnaires' disease occurred in the summer of 1976. Among 4,400 attendees of the 58th American Legion Convention held at the Bellevue-Stratford Hotel, the occurrence of a large-scale respiratory tract infection in the hotel caused severe panic. This is the origin “Legionnaires' disease”.
It has been found that the pathogen of Legionnaires' disease is polymorphous bacillus. The bacterium exists naturally in warm and humid water or air, such as cooling towers, swimming pools, drinking water, showerheads and faucets. It is even found in rivers, lakes, swamps, well water and other liquid environments. The bacteria grow best at temperatures between 35 and 46 °C. It cannot proliferate under environment temperature less than 20°C but is still dormant. The bacillus can proliferate in the cooling tower and can even survive in the heat exchanger. In the above case, the main source of bacterial pollution is the cooling tower of the building air conditioning system. The bacteria entered the air conditioning system through water vapor, and were then spread by the air to all the people in the venue.
In the planning stage of the TIAA MRT stations, the water chemical treatment equipment is designed to be installed in the cooling water and ice water pipeline device of the water-cooled central air-conditioning system. In addition to automatic monitoring of air conditioning system water quality, its functions include automatically adding chemicals in the cooling water and ice water to prevent microbial and bacterial proliferation. This equipment not only can eliminate the polymorphic short bacillus (the source of Legionnaires' disease), but also prevents proliferation of moss and other microbial that results in pipeline pollution or obstruction. The equipment can also balance the chemical composition of the water, inhibiting fouling and corrosion occurrences in the air conditioning equipment pipelines in order to avoid reduction of heat exchange rate and to improve the efficiency of air conditioning system operation. This will reduce station water and electricity expenditure and extend equipment life to achieve the purpose of reducing maintenance costs.