7. Legionella and General Advice
7.1 Legionella
The legionella bacteria is present in all source water. The concentration, however is normally too low to
be a risk to health. The growth of the bacteria and hence the concentration is dependent on stagnation
time, temperature and nutrient availability.
A domestic hot water storage cylinder in the UK is unlikely to remain stagnant in the cylinder for much
more than a day under normal occupation of the premises. In addition the mains cold water supply is very
low in nutrients, as it is often treated with chlorine which remains in the water and is toxic to the bacteria.
Nevertheless, if the premises are unoccupied for any length of time, such as absence on holiday, it is
good practice to sterilise the system using the immersion heater or an auxiliary heat source before using
any hot water. This applies whether or not a solar water heating system is fitted.
It is strongly advised that the hot water boost function, or existing hot water boiler controls be set
to ensure that the water is heated up to 60°C at least once a week.
7.2 Getting the most from your immerSUN
To get the most from your immerSUN there are a few things you will need to consider.
1.
Set your boiler hot water timer (or the immerSUN boost function) to ensure that water is only
boosted to full temperature after the water has been heated to the maximum extent possible
by the immerSUN. This is likely to be after the sunset. When you use hot water during the
evening and early morning, this will ensure that there is plenty of cold water in the cylinder for
the sun to heat the next day. Using back-up heat in the morning means less opportunity for
the immerSUN to contribute.
2.
Adequate insulation of cylinder and pipes is vital. Systems with poorly insulated cylinders can
suffer from inadequate hot water provision in the mornings.
3.
Electric showers heat water themselves rather than using the solar-heated water, using them
will reduce overall hot water use, meaning that you won't get maximum benefit from the
immerSUN.
4.
Allow the hot water temperature to vary. If you do not need high temperatures all the time, you
will have less need for back-up heating, heat loss from the cylinder will also be less. However,
it is important to make sure your cylinder reaches 60°C at least once a week to avoid risk of
Legionella.
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