Ariston NSGA 500 Instructions Pour L'installation Et L'entretien page 52

GB
RECOMMENDATIONS FOR PREVENTING LEGIONELLA PROLIFERATION
(based on European standard CEN/TR 16355)
GENERAL INFORMATION
Legionella is a small rod-shaped bacteria that is found naturally in all sweet water. Legionnaire's Disease is
a serious pulmonary infection caused by inhalation of Legionella pneumophilia bacteria or other Legionella
species. The bacteria is frequently found in water supply systems of homes and hotels, and in the water used
in air conditioners or air cooling systems. For this reason, the main weapon against the disease is prevention,
to be eff ected by checking for the presence of the organism in water supply systems.
The CEN/TR 16355 European standard provides recommendations on the best method for preventing
Legionella proliferation in potable water systems, without supplanting the provisions in force at a national
level.
GENERAL RECOMMENDATIONS
"Favourable conditions for Legionella proliferation". The following conditions favour the proliferation of
Legionella:
• Water temperature between 25 °C and 50° C. In order to minimise proliferation of Legionella bacteria, the
water temperature should be kept between these limits so as to prevent or at least limit its growth, which is
nonetheless possible everywhere. Alternatively, the potable water system must be sanitised through heat
treatment.
• Stagnant water. To prevent it from stagnating for long periods, water must be used or made to fl ow
abundantly at least once a week in every part of the potable water system.
• Nutritional substances, biofi lm and sediments present within the system, including water heaters, etc.
Sediment may favour proliferation of Legionella bacteria and must be eliminated regularly from storage
systems, water heaters, expansion vessels with stagnant water (e.g. once a year).
With specifi c regard to storage water heaters, if:
1) the appliance is switched of for a certain period of time [months] or
2) the water temperature is kept constant between 25° C and 50° C, Legionella bacteria may develop inside
the tank. In these cases, the so-called "heat sanitation cycle" must be implemented to reduce Legionella
proliferation.
The electromechanical storage water heater is supplied with the thermostat set to a temperature above 60° C,
which allows for eff ecting a heat sanitation cycle to reduce Legionella proliferation inside the tank.
This cycle is suitable for use in domestic hot water production plants and complies with the recommendations
for preventing Legionnaire's Disease specifi ed in Table 2 of the CEN/TR 16355 standard below.
No storage
No hot
water
circulation
Reference
in Annex C.1
C
Tempera-
- -
ture
Stagna-
- -
tion
Sediment - -
a Temperature ≥ 55° C for the whole day or at least 1h a day ≥ 60° C.
b Volume of water contained in the piping between the circulation circuit and the valve with the greater distance with respect to the system.
c Remove the sediment from the storage water heater in accordance with the local conditions, but at least once a year.
d Heat sanitation for 20 minutes at a temperature of 60° C, for 10 minutes at 65° C or for 5 minutes at 70° C in all withdrawal points at least once a week.
e The water temperature in the circulation ring must not be below 50° C.
- Not required
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Table 2 - Types of hot water plants
Separate hot and cold water
Storage
With hot No hot With hot
water water
circulation circulation circulation
C.2 C.3
in storage
e
water
≥ 50 °C ≥ 50 °C
a
heater
b
- -
≥ 31
c
- -
remove remove
No storage upstream
of the mixing valves
No hot With hot
water water water
circulation circulation
C.4 C.5 C.6
heat sani- heat sani-
e
d
tation tation
b
- -
≥ 31 ≥ 31
c
- - - -
Mixed hot and cold water
Storage upstream of
the mixing valves
No hot With hot
water water
circulation circulation
C.7 C.8
e
in storage
≥ 50 °C
water
heat sani-
d
a
d
heater
tation
b b
- -
≥ 31
c c
remove remove
No storage upstream
of the mixing valves
No hot With hot
water water
circulation circulation
C.9 C.10
heat sani- heat sani-
d d
tation tation
b
- -
≥ 31
- - - -