TM_s-MEXT_ME28relC_00_12_19_EN
Technical manual
TRANSLATION OF THE ORIGINAL INSTRUCTIONS
72
4
NOTES ON TEMPERATURE ADJUSTMENT
The heating and cooling devices 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;
•
Propor Integral adjustment;
•
Propor In Derived adjustment (only in units with inverter compressor).
The basic programme setting (default) features Propor Integral adjustment with an elevated integral time constant, therefore very close to purely proportional
adjustment.
All the adjustment diagrams shown in this manual refer to a purely proportional adjustment.
Compared with the diagrams described further on, Propor 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 inhibited (and therefore pure proportional adjustment is active) when the two cold and hot setpoints are set, so that a dead zone is included (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 is
therefore disabled;
4.1
MANAGEMENT OF THE LIMITS OF THE COLD SETPOINT
The parameter for setting the setpoint is automatically limited to specific values set during the design of the units themselves.
The set values are given in the table below.
Unit code
Description
P20.24 (°C)
P20.25 (°C)
s-MEXT DX/DW
Direct expansion to be used in combination with the Mr Slim condensing unit
20
32
The parameters P20.24 and P20.25 are in the
“Regulation” menu
, which can be accessed by entering the
“Service” password
.
INFORMATION
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 sources (electric heaters or hot water coil), the minimum allowable setpoint value is limited by the value of the hot setpoint value.
The chart below illustrates the limitation described above.
T
ambient
(°C)
Set
P50.01
P20.24
P20.25
T
ambient
(°C)
Set
P50.01
Set
P50.02
P20.25
P20.24
Without Heating sources
WITH Heating sources
Figure 4-1:
Charts of management of the setpoint limits
4.2
REGULATION PROBE MANAGEMENT
For the unit, it is possible to define which probe to use for the adjustment, selecting from:
•
Intake air probe.
•
Delivery air probe.
The regulation with delivery air probe is allowed only if the heaters are not present.
