Mitsubishi Electric ecodan EHST20C- TM9HB Operation Manual page 13

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Customising Settings for your Home
explanation of legionella Prevention Mode operation
• At the time entered by the installer 'Start time' flow of useful heat from the sys-
tem is diverted to heat the water in the DHW tank.
• When the temperature of the stored water exceeds the 'Hot Water temp.' set by
the installer (above 65°C) primary circuit water is no longer diverted to heat the
DHW tank.
• Whilst LP mode is in operation hot water is not directed to the space heating
/cooling circuit.
• Directly after LP mode operation 'Duration of max. temp' will operate. The dura-
tion of this feature is set by the installer and during its operation stored water
temperature will be monitored.
• If stored water temperature should drop to LP restart temp, LP mode will restart
and primary water flow from the heat source(s) will be directed to the DHW
tank to boost the temperature. Once the set time for Duration of Max. temp has
passed LP mode will not recur for the set interval (set by installer).
• It is the responsibility of the installer to ensure the settings for legionella preven-
tion are compliant with local and national guidelines.
Please note that LP mode uses the assistance of electric heaters (if present)
to supplement the energy input of the heat pump. Heating water for long
periods of time is not efficient and will increase running costs. The installer
should give careful consideration to the necessity of legionella prevention
treatment whilst not wasting energy by heating the stored water for excessive
time periods. The end user should understand the importance of this feature.
alWayS CoMPly WitH loCal and national GUidanCe For yoUr
CoUntry reGardinG leGionella Prevention.
Forced dHW
The forced DHW function is used to force the system to operate in DHW mode. In
normal operation the water in the DHW tank will be heated either to the set tem-
perature or for the maximum DHW time, whichever occurs first. However should
there be a high demand for hot water 'Forced DHW' function can be used to pre-
vent the system from routinely switching to space heating/cooling and continue to
provide DHW tank heating.
Forced DHW operation is activated by pressing button F and Back button in the
'Option Screen'. After DHW operation finishes, the system will automatically re-
turn to normal operation. To cancel forced DHW operation hold down button F in
the 'Option Screen'.
The heating/cooling menus deal with space heating/cooling using normally either
a radiator, fan-coil, or underfloor heating/cooling system depending on the instal-
There are 3 heating modes
Heating room temp. (Auto adaptation) (
Heating flow temp (
Heating compensation curve (
Cooling flow temp (
<room temp (auto adaptation) mode>
This mode is explained in detail in 'Overview of Controls' Section.
<Flow temp mode>
The temperature of the water flowing to the heating circuit is set by the installer
to best suit the space heating/cooling system design, and user's desired require-
explanation of compensation curve
During late spring and summer usually the demand for space heating is reduced.
To prevent the heat pump from producing excessive flow temperatures for the
primary circuit the compensation curve mode can be used to maximise efficiency
and reduce running costs.
The compensation curve is used to restrict the flow temperature of the primary
space heating circuit dependent on the outdoor temperature. The FTC4 uses
information from both an outdoor temperature sensor and a temperature sensor
on the primary circuit supply to ensure the heat pump is not producing excessive
flow temperatures if the weather conditions do not require it.
Your installer will set the parameters of the graph depending on local conditions
and type of space heating used in your home. It should not be necessary for you
to alter these settings. If however you find that over a reasonable operating pe-
riod the space heating is not heating or is overheating your home, please contact
your installer so they can check your system for any problems and update these
settings if necessary.
dHW tank temp.
Stop temp.
hot water temp.
Restart temp.
LP mode
Duration of Max. temp.
(LP mode: Legionella Prevention mode)
LP mode

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