Question

With reference to air conditioning units

(a) With the aid of a sketch, explain the operation of a unit that includes means of dehumidifying, humidifying, and refrigerated cooling.

(b) (i) Describe the conditions that could lead to legionella growth.

(ii) List the precautions necessary in the maintenance of air conditioning systems to reduce the risk of legionnaires disease being contacted.

Answer 1

Part (a)

Part (b)

Accumulated or standing water provides a breeding ground for the bacteria.
Legionella thrive in water temperatures between 20°C and 45°C.
Dust, debris, and other particulate matter in aerated water provide nutrients for bacterial growth.
Water mist, generated by cooling towers or humidifiers, allows Legionella bacteria to become airborne and potentially inhaled.

Part (c)

Regularly drain and clean areas where water could accumulate, such as air handling units (AHUs).
Ensure proper cleaning and maintenance of drains and traps to prevent stagnation.
Regularly clean or replace air filters in the system.
Treat humidifiers with super-chlorinated water to inhibit bacterial growth.
Ensure that duct and equipment insulation remains dry to avoid damp conditions.
Perform routine cleaning of air ducts to remove dust and debris.
Use approved disinfectants periodically, especially after any maintenance activities.
Regularly clean AHU components, such as cooling coils and drain pans, to eliminate potential bacterial habitats.

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