Section 5: Domestic Hot Water Page 19
5.3 Legionella
It is possible to use the heat pump to raise the HW cylinder to around
50 to 55°C.
For protection against Legionella the temperature can be periodically
raised to 60°C using the Grant Automatic DHW Boost Kit 2, available
from Grant UK (product code: HPDHWBK2).
This boost kit also allows the cylinder immersion element to be used
to raise the temperature to 60°C for one hour either daily or weekly to
sterilise the cylinder against Legionella.
For this system to operate, the existing immersion switch must
be left set permanently to ON.
To totally prevent operation of the immersion element, the
existing immersion switch must be set to OFF.
NOTE
!
5.3.1 Legionella Sanitisation Regime
Care must be given to vulnerable people who may be exposed to
potentially life-threatening legionella. This group of people include
the elderly, pregnant women, young children and those with breathing
difficulties.
Care must also be given to households who do not use a lot of water
on a daily basis. While this chart is not exhaustive, it is important that
you discuss any potential issues with the occupants before deciding
on the appropriate regime. It is important that this decision is based
on the welfare of the occupants and not on energy saving measures.
Table 5-2: Legionella group sanitisation regime
Uses less than 50
litres of hot water
per day
Uses more than 50
litres of hot water
per day
Vulnerable Group
Store at 50°C and raise
hot water cylinder to
60°C for 1 hour every
day
Store at 50°C and raise
hot water cylinder to
60°C for 1 hour every
3 days
Non-Vulnerable Group
Store at 50°C and raise
hot water cylinder to
60°C for 1 hour every
week
Store at 50°C and raise
hot water cylinder to
60°C for 1 hour every
2 weeks
If the hot water stored in the cylinder has not been used for a
prolonged period of time (e.g. a few days) and has not been
stored at 60°C, then it is important that the temperature is
raised to at least 60°C for a period of one hour before using the
hot water.
!
WARNING
5.4 Automatic DHW Boost Kit
This system uses both the existing cylinder immersion heater and
cylinder thermostat. This is switched via a contactor operated by a
small timeswitch, both enclosed in a separate unit to be mounted next
to the cylinder. Thus the immersion element can be programmed to
operate for the required period on either a daily or weekly basis.
Once set, this system is fully automatic but can be overridden by the
user if required. Also, the user can still switch the immersion element
off, via the immersion heater switch, irrespective of the programmer or
cylinder thermostat setting or whether the heat pump is operating.
5.4.1 Installation
The Automatic DHW Boost Kit 2 comes pre-wired within its enclosure,
ready for installation. The connections to the Immersion heater switch,
Immersion heater and cylinder thermostat must be made after it is
installed on site.
When installed, this kit interrupts the electrical supply between the
existing immersion heater switch and immersion heater. Refer to
Figure 5-4 for electrical connection details.
In order to connect and use this kit the existing cylinder thermostat
must have two output terminals; one ‘make on rise’ (normally open)
contact and the other ‘break on rise’(normally closed) contact. If not,
then the cylinder thermostat MUST be replaced with one that does
have two output terminals.
The use of any other type of cylinder thermostat, or any modification
to an existing thermostat, will invalidate the product guarantee and
may result in a potentially dangerous installation.
IMPORTANT
Do not alter the pre-wired connections within the enclosure
and only make the external connections as shown in the wiring
diagrams. See Figure 5-4.
Where a 3-phase supply is present, ensure that BOTH the
immersion switch and heating system controls are taken from
the same phase. If in doubt, contact a qualified electrician.
!
WARNING
To Next Page
Loading...
Need help?
General
