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How to determine the setting for FC23:
The boiler output is used to switch an external boiler ON / OFF to support the ESTIA system during
low ambient conditions. It is possible to estimate the switching temperature, required for the boiler
output, using the system/installation capacity graph generated by the ESTIA Sales Support Software
(see graph below).
On the graph above:
The heat pump output capacity is represented by the red line
The heat load for the installation / site is represented by the blue line
The point where the 2 lines cross, point A, represents the equilibrium point of the system.
This is where the capacity output from the heat pump is equal to the heat load requirements
of the installation / site. On the example above the equilibrium point is reached when the
outdoor air temperature (OAT) is approximately 1°C
The area to the left of the equilibrium point and between the red and blue lines represents
the area where an additional heat source is required to support the heat pump output
From the graph it can be seen that when the outdoor air temperature is -4°C there is a
requirement for an additional heat source (electric back up heaters, existing boiler etc.) to
supply the installation with approximately 3.5kW of heating
For the example above with FC23 set to 1°C then the boiler output will turn ON when the
OAT decreases to 1°C. The boiler will support the output of the heat pump if the OAT is 1°C
or less
There is a 5K temperature differential between the boiler output ON / OFF temperatures. If
the boiler output is set to turn ON when the OAT is 1 °C then the boiler output will not turn
OFF until the OAT has reached 6°C
It is possible to set FC23 lower than 1°C however this result in the electric back up heaters
supplying some of the heating capacity required from the additional heat source.
Required capacity supplied by
heat pump capacity only
Additional heat
source required
A