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ENG
µchiller +0300053EN rel. 2.2 - 14.12.2021
Functions
5.20 Air/air unit management (Legacy model only)
The Chiller Legacy version can manage air/air units, both cooling only and reverse cycle. The type of unit is selected via param-
eter U077, which in the Legacy model can be set as Air/Air CH or Air/Air CH/HP.
On these units, the control probes have the following meaning:
Sensor Meaning
System water return temperature Room air return temperature
System water delivery temperature Air supply temperature
Air supply limit management in cooling mode
A function is used to limit the air supply temperature. When the air supply temperature falls below a certain threshold, set for
parameter F009, in the band defi ned by parameter F010, the control ramp is limited proportionally.
User Code Description Def Min Max UOM
S F009 Minimum air supply temp. limit: set point 14.0 0 99.9 °C
S F024 Manual control of heater 1 0=AUTO, 1=OFF, 2=ON 002-
S F025 Manual control of heater 2 0=AUTO, 1=OFF, 2=ON 002-
S F010 Minimum air supply temp. limit: proportional band 4 1 20 K
5.20.1 User fan
On air/air units, the user pump is replaced by a user fan. The water fl ow switch alarm is used as an air fl ow switch alarm.
Fan control is subject to the following conditions:
• parameter F017
If F017 = 0, it follows standard mode, i.e. unit on -> fan on.
If F017 = 1, the fan follows the temperature control request and remains off until there is a temperature control request.
• Hot-start and hot-keep functions
The user fan will be activated as shown in the following table:
Unit status Mode Control status Parameter F017 Hot-start Hot-keep Fan status
OFF Not considered Not considered Not considered Not considered OFF (switch-off delay after compressor
and/or heater off U048)
ON Cooling Not considered FALSE Disabled ON
ON Cooling Off TRUE Disabled OFF
ON Cooling On call TRUE Disabled ON
ON Cooling Not considered Not considered Enabled ON
ON Heating Off Not considered Enabled OFF
ON Heating On call Not considered Enabled ON on Hot-Start function command
Tab. 5.c
User Code Description Def Min Max UOM
S F017 Main fan: activation mode 0=always On, 1=ON from control 001-
Hot-start and Hot-keep functions
These functions are only active in heating mode.
The Hot-Start function is active on air/air units in heating mode only. The function keeps the fan off until the condensing tem-
perature reaches a set point (parameter F018) to avoid sending cold air into the room. If the condensing pressure or condensing
temperature probe is not fi tted, control is based on the air supply temperature. If the electric heaters are activated, the fan is
switched on immediately.
The Hot-keep function has two modes:
• in heating mode, if the compressors and/or heaters are off , the fan remains on until the condensing temperature is greater
than the hot-start set point (parameter F018) minus the diff erential set for parameter F019.
• in cooling mode, the fan will be switched off after the time set for parameter U048, after the compressor and/or heater has
been deactivated.
User Code Description Def Min Max UOM
S F018 Hot-start: set point 40.0 0 99.9 °C
S F019 Hot-keep: diff erential 5.0 0 99.9 K
Temperature set point for deactivating the compressors
To avoid energy effi ciency below that of electric heaters, the compressors are deactivated if the outside temperature falls below
F026, with a fi xed reactivation diff erential of 1 degree. The heaters are activated according to the corresponding set points. Set-
ting F026 to “-40°C” (default value) disables the function.
User Code Description Def Min Max UOM
S F026 Compressor deactivation due to low outside air temperature -40 -40 99.9 °C
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