Temperature Adjustment Considerations; Management Of The Limits Of The Cooling Setpoint - Mitsubishi Electric Evolution+ s-MEXT Technical Manual

TEMPERATURE ADJUSTMENT CONSIDERATIONS

4
The heating and cooling resources are managed on the basis of the temperature values measured by the return or delivery
probe depending on the parameter settings. This temperature is compared with the set value (setpoint), and based on the
difference, the devices may activate. The proportional band selects the working area and may assume (as for the setpoints)
different heating and cooling values.
The software can be used to manage three temperature adjustment types:
•
Purely Proportional adjustment;
•
Proportional + Integral adjustment;
•
Proportional + Integral + Derived adjustment (only in units with inverter compressor).
The basic programme setting (default) features Proportional + Integral adjustment with an elevated integral time constant,
therefore very close to purely proportional adjustment.
INFORMATION:
All the adjustment diagrams shown in this manual refer to a purely proportional adjustment.
Compared with the diagrams described further on, Proportional + Integral adjustment can reduce (with respect to the distance
between ambient temperature and setpoint) the activation time of the cooling and heating devices and consequently delay
shutdown. This effect is more marked the longer the "permanent off-balance" phenomenon continues, that is, the immobility of
the ambient temperature in a different point from the set setpoint.
In any case, the delay/anticipation of the unit enable/disable never goes beyond the limit of the opposite proportional band.
Integral adjustment is always disabled (and therefore pure Proportional adjustment is involved) in three circumstances:
•
Setting the two cooling and heating setpoints so as to create a neutral zone (when the two setpoints are different).
In this case, no adjustment resources must ever be enabled in the temperature zone between the two setpoints. The
integral adjustment delay must therefore be disabled.
•
Direct expansion unit with just one compressor.
In this case the integral component has no sense as, even if a permanent off-balance condition is established
following activation of the compressor, there is no other resource that can allow the system to leave that condition.
•
In case of dehumidification.
In this case, inhibition prevents the delay from making the operation of the second compressor overlap with the
activation of the active heating resources for post-heating.
It is also possible to manually disable the integral component by setting the integral time constant to zero.

4.1 Management of the limits of the cooling setpoint

The parameter for setting the setpoint according to the selected type of unit is automatically limited to specific, default values.
The set values are given in the table below:
Direct expansion to be used in combination with the Mr. Slim condensing unit
The parameters P20.24 and P20.25 are in the "Regulation" menu, which can be accessed by entering the "Service"
password.
OBLIGATION:
Although the parameters P20.24 and P20.25 can be accessed with the "Service" password, please contact
MEHITS before setting different values.
When the unit is equipped with heating resources (electric heaters or hot water coil) and return adjustment is enabled, the
minimum allowable setpoint value is limited by the value of the heating setpoint value.
The chart below illustrates the limitation described in the previous page:
Version 38
Description P20.24 (°C) P20.25 (°C)
20 32
133