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5.2 Minimum delivery temperature limit
5.2.1
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 cooling demand is reset, and subsequently the compressor
turns off in the direct expansion unit or the valve in the chilled water unit closes.
5.2.2
Adjustment logic
In specific, the adjustment is as follows: when the value of the delivery temperature is nearer to the setpoint (minimum limit)
than the cooling demand, the adjustment automatically switches to the cooling demand of the ramp for the adjustment of the
delivery temperature.
For example, if cooling demand is 90%, while the delivery temperature adjustment ramp requires 50%, the cooling 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 unit is set as a Free Cooling unit, the programme will automatically enable this function.
Version 38
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
T
(°C)
delivery
T
(°C)
ambient
Ramps T (%)
142
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