Considerations On Temperature Registers - IntesisBox FJ-RC-MBS-1 User Manual

4.2.3 Considerations on Temperature Registers

• AC unit temperature setpoint (R/W)
(register 4 – in Protocol address / register 5 – in PLC address):
This is the adjustable temperature setpoint value that must be required by the user. This
register can be read (Modbus function 3 or 4) or written (Modbus functions 6 or 16). A
remote controller connected to the Fujitsu indoor unit will report the same temperature
setpoint value as this register, but only will happen when no AC unit´s external
reference is provided from FJ-RC-MBS-1 (see detail for register 22/23 below).
• AC unit temperature reference (R)
(register 5 – in Protocol address / register 6 – in PLC address):
This register reports the temperature that is currently used by the Fujitsu indoor unit as
the reference of its own control loop. Depending on the configuration of the indoor unit,
this value can be the temperature reported by the sensor on the return path of the
Fujitsu indoor unit or the sensor of its remote controller. It is a read-only register
(Modbus functions 3 or 4).
• AC unit external temperature reference (Modbus) (R/W)
(register 22 – in Protocol address / register 23 – in PLC address):
This register allows us to provide an external temperature's sensor from the Modbus
side. Fujitsu indoor unit does not allow on devices like FJ-RC-MBS-1 to provide directly
temperature to be used as a reference of the control loop of the AC indoor unit. In order
to overcome this limitation and enable the usage of an external temperature sensor
(i.e.from Modbus side), FJ-RC-MBS-1 applies the following mechanism (only if "external
temperature's reference" is being used):
After a couple of values have been entered in the "AC unit external temperature's
o
reference" (register 22/23) and "AC unit temperature set point" (register 4/5),
FJ-RC-MBS-1 is going to estimate the temperature chosen implied (e.g. if a
"temperature setpoint (register 4/5)" of 22ºC, and an "external temperature
reference (register 22/23)" of 20ºC are entered, FJ-RC-MBS-1 will assume that
the user is demanding a +2ºC increase in temperature).
By knowing at any time the ambient temperature currently used by the indoor
o
unit to control its own operation (register 5/6), FJ-RC-MBS-1 can calculate the
required temperature setpoint needed to apply the decrease/increase on the real
temperature and reach the temperature chosen by the user (following the
example above, if FJ-RC-MBS-1 reads an "ambient temperature" (register 5/6) of
24ºC in the indoor unit, it will apply a final setpoint of 24ºC + 2ºC = 26ºC).
At this moment, each time that FJ-RC-MBS-1 detects a change on the ambient
o
temperature reported by the indoor unit (register 5/6), it will also change the
required setpoint, in order to keep the temperature required by the user at any
time. If we follow the last example, if FJ-RC-MBS-1 receives a new temperature´s
value coming from the indoor unit of 25ºC, FJ-RC-MBS-1 will automatically adjust
the temperature setpoint required of the AC indoor unit to 25ºC + 2ºC = 27ºC).
In general, FJ-RC-MBS-1 is constantly applying the "Virtual Temperature"
o
formula:
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This information is subject to change without notice
IntesisBox ® is a registered trademark of Intesis Software SLU
FJ-RC-MBS-1
S = S
AC
– ( T – T
)
u u AC
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