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INFECTION CONTROL


Figure 2: The experimental system.


evaporative and steam humidifiers, and a comparison of several measures for the pollution control of evaporative humidifiers. In the first step, three different


evaporative humidifiers and a steam humidifier were set in place. In the second step – to evaluate the performance of several measures for the pollution control of evaporative humidifiers – the steam humidifier in Figure 1 was replaced with an evaporative humidifier. A constant air volume (CAV) unit was installed to keep the passing air volume constant (800 m3


/hr) in each


humidifier. The hot water, which was produced by air source heat pumps, was supplied to the heating coil for air heating. The set point of outlet air dry-bulb (DB) temperature of the humidifiers was 24.2˚C. The humidifiers were also controlled at 50% relative humidity (RH). The hysteresis of the RH was set at 10% (RH 40%). This experimental air handling unit was operated continuously. Microorganisms were sampled at the positions shown in Figure 3 and evaluated as follows: • Airborne microorganisms – The air was sampled at three measuring positions;


Contact sampling 1 3


Sampling of humidified air


Humidified air


2


outdoor air, air before humidification, and humidified air. The sampling was performed three times at each sampling position, and each sampling volume was 1 m3


. The number of airborne


• AHU inner surface colonised microorganisms – Microorganisms on the


microorganisms was evaluated by the mean value of the three results. Trypticase soy agar was used for sampling the microorganisms and potato dextrose agar for the fungi.


• Contained microorganisms in humidification element – Contained


inside wall surface of the humidified air chambers were sampled three times; twice at the ceiling surface (material: galvalume steel plate wall) and once at the sidewall (material: steel plate wall). The evaluation was made by averaging the three results. Trypticase soy agar was used for sampling the microorganisms and potato dextrose agar for the fungi at each point.


microorganisms in the humidification element were evaluated by a method of petrifilm plate and a smear culture. The petrifilm plate method for microorganisms, 10 g of specimen


Sampling of air before humidification


EA Humidifier


Sampling of humidifier element


Detection of Legionella species


Figure 3: Measurement points and items. 72 Water supply QA


Sampling of outdoor air


Hot water coil Filter


• Legionelladetection in water supply and drainage – The presence of Legionella


element was mixed with 90 mL of disinfected diluted solution and 1g of this sample was cultured on the petrifilm plate. In the smear culture method for fungi, the same sample was smeared on potato dextrose agar.


species in the water supply and drainage of each humidifier was evaluated using the WYO-α agar.


Comparative experiment between steam and evaporative humidifier Three types of evaporative humidifiers (identified as 1, 2 and 3), which were the products of different companies, and one steam humidifier (identified as 4) were installed in the experimental AHU. The experiment was conducted from December 2008 through to March 2009. Sampling of microorganisms was


conducted at four periods during the experiment. Once in the initial state, when the humidifier elements are new. (Only air sampling and sampling microorganisms of the humidifier elements of evaporative humidifiers); twice during the operation of the humidifiers – First sampling, 29 January 2009: two months (15.00 hr) after the start of the humidifier operation and the second sampling on 5 March 2009: three months (23.00 hr) after the start of the humidifier operation; and once more one week after the operation stopped (season of ventilation operation without humidification), on 12 March 2009.


IFHE DIGEST 2014


‘No considerable difference in cleanliness was observed between evaporative and steam humidifiers.’


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