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Building Technologies
Modular Heating Controller RMH760B
CE1P3133en
HVAC Products
10 DHW heating
05.02.2007
Further setting choices for the circulating pump are described in subsection 10.11.3
“Circulating pump”.
The cold water must join the DHW from the circulation pipe right by the heat exchanger.
If, for plant reasons, this is not possible, the “Min stroke with flow signal” must be set to
0 %.
10.5.4 Maximum
charging
time
The maximum charging time is also active with direct DHW heating. Subsection 10.4.3
“Maximum charging time” contains additional details on this function.
The controller is supplied with the function deactivated.
10.5.5 Legionella
protection
with direct DHW heating
During the time the legionella program is active, the circulating pump must operate.
For direct DHW heating, the information given in the following section “Legionella
protection”.
If no circulating pump is used, it is recommended to deactivate the legionella function.
In that case, the legionella protection frequency must be set to “Never“.
10.6 Legionella
protection
The “Legionella protection” function
can be
an important measure aimed at preventing
the growth of legionella viruses.
However, the legionella program is
no guarantee
for preventing the growth of legionella
viruses because these might occur in plant sections that the function cannot reach.
10.6.1 General
Legionella viruses develop significant growth in the temperature range of 35…45 °C. At
temperatures above 50 °C, they stop growing.
Legionella viruses are killed at temperatures above about 55 °C; the higher the tem-
perature, the shorter the time required to kill them.
There are different opinions regarding the effectiveness of thermal disinfection.
Control measures, such as the legionella function, are only effective in connection with
other measures (primarily building construction measures, but also chemical disinfec-
tion and UV radiation).
The legionella function ensures thermal disinfection of the storage tank. It is important
here that the entire DHW storage tank will be brought to the required temperature. This
poses problems in connection with certain types of storage tanks (with electric immer-
sion heater or coiled heat exchanger) where cold water accumulates beneath the heat
exchanger. These problems can only be solved by taking adequate measures.
In addition to the legionella function, it should be made certain that the DHW setpoint
and the switching differential are adjusted such that the switch-on point will not be too
low (e.g. 55 °C).
It is also important to thermally disinfect not only the storage tank but also the entire
piping network. It must be made certain that there are no dead pipes or piping that has
not been used for longer periods of time.
If possible, the circulating pump should run during the legionella program.
Ideally, during the legionella program, the taps are in use.
Note
Notes
Thermal disinfection
Piping network
Circulating pump
