Minimum Delivery Temperature Limit; Objectives; Adjustment Logic - Mitsubishi Electric s-MEXT-G00 006 Technical Manual

TM_s-MEXT_ME28relC_00_12_19_EN
5.3

MINIMUM DELIVERY TEMPERATURE LIMIT

5.3.1

Objectives

Setting a minimum limit to the delivery temperature may be a request justified by the presence, very close to the unit delivery outlet, of devices that are sensitive to relatively
low temperatures.
The delivery temperature can only fall excessively if there is a sudden decrease in the temperature of the cold coil (evaporation temperature or, more likely, the temperature
of the chilled water coming from a chiller). This has effects on the room temperature that can only be measured after a certain period of time (the time required for the mixing
of the delivery air with the ambient air to decrease the temperature sufficiently for it to be measured by the probe on the unit).
As soon as the delivery temperature falls below the set value, the cold demand is reset, and subsequently the compressor turns off in the direct expansion unit or the valve in
the chilled water unit closes.
5.3.2

Adjustment logic

In detail, adjustment takes place as follows: When the value of the delivery temperature is nearer to the setpoint (minimum limit) than the cooling demand, adjustment
automatically switches to the cooling demand of the ramp for the adjustment of the delivery temperature.
For example, if cold demand is 90%, while the delivery temperature adjustment ramp requires 50%, the cold demand adapts to the seconds and considers the 50% value.
This function is managed by considering the ramp of the minimum values shown in the following figure.
The minimum delivery set parameter is in the "Regulations" menu, which can be accessed by entering the "Service" password.
For the default values, see the parameters table.
The minimum delivery differential is fixed, may not be modified, and is set at 4°C.
INFORMATION
If a Freecooling unit is selected, the programme will automatically enable this function.
Technical manual
100%
Ramp
T (%)
delivery
0%
P20.29
100%
Ramp
T (%)
ambient
0%
P50.01
R
cold
100%
Cold ramp (%)
0%
Figure 5-6: COOLING demand limit graph
Differential 4°C
(fixed)
P20.18
= Min (R ;R )
delivery ambi e nt
77
T (°C)
delivery
T (°C)
ambient
Ramps T (%)
TRANSLATION OF THE ORIGINAL INSTRUCTIONS