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Fig. b) Unit operation with electrical heating
1
/
Band
2
Heating
Set point
Dead Band
1
/
Band
2
Heating
Set point
5.3 --- Unit with freecooling
5.3.1 --- Control logic
The control algorithm is based on single---stage regulation
for the heating and mechanical cooling (compressor), with
modulating proportional---integral control for the Freecooling
(see Fig. c). The control manages all of the compressor ac-
tivation delays, as we have seen in the 2 previous cases, in
order to guarantee the proper operation and to extend its life.
The activation of the Freecooling mode occurs as a function
of the difference (that can be set) between the inside tem-
perature and the outside temperature. This means that if the
difference between the two temperatures increases beyond
the set value, the unit automatically initiates the Freecooling
function; the compressor is deactivated and an analogue
output controls the 3---point servomotor of the damper. The
damper opening is determined as a function of the difference
between the outdoor and indoor temperatures and as a func-
tion of the intake air temperature, which cannot be lower than
a preset safety value. If the indoor temperature exceeds the
proportional band by more than 20% for over 10 minutes, the
unit reverts to compressor---aided cooling and the Freecoo-
ling mode remains de---activated for
temperature exceeds the proportional band by more than
50% for over 2 minutes, the Freecooling mode is de---acti-
vated for 1 hour, and the unit reverts to cooling by means of
the refrigeration circuit.
Fig. c) Compressor, heater and damper opening
operation
P Band
Heating
Set
P Band
Heating
Set
5.4 --- LAN local network management:
Stand---by and Cascade modes
The control of the units in stand---by can be completely auto-
matic, thanks to the possibility of connection with the Power-
Face control. A unit in stand---by is automatically activated in
case of an alarm causing the main unit to lock---out. This also
occurs if the main unit is switched off or disappears from the
system due to a failure on the control connecting network
(bus). Rotation of the stand---by units can be set to occur
automatically every 24 hours, so as to enable an even wear of
the system components. If the system is connected to a Hiro-
matic interface, it is possible to set timed daily or weekly rota-
tion functions. When the Cascade function is activated, if sev-
P Band
Cooling and
1
/
Band
heating unit
2
Cooling
°C
Cooling and
1
/
Band
heating unit
2
with Dead band
Cooling
°C
1
/
hour. If the inside
2
Freecooling
mode
Cooling
_C
Compressor
cooling mode
Cooling
_C
eral units are simultaneously on, with the same Set Point, the
temperature used for the control is the average of those de-
tected. In mechanical cooling mode, the proportional semi---
band is divided by the number of units in the system, in order
to share the total available cooling capacity. The activation of
the Freecooling mode (if installed) is sequential on the differ-
ent units forming the system, and precedes the possible ac-
tivation of compressor for mechanical cooling.
Fig. d) shows an example, illustrating the operation of a sy-
stem formed by three units.
Fig. d) System with 3 units in cascade ---
PowerFace control
3
2
Heating
Compressor cooling mode
3
2
Heating
5.5 --- Alarm control
Two sets of alarm contacts (each n.c. or n.o.) are available on
the terminal board of the electrical panel board for:
1) General Alarm (highest priority), including:
Compressor alarm (high and low pressure).
S
Sensor fault.
S
Memory fault.
S
Evaporator fan fault.
S
2) General Warning (lowest priority), including:
High temperature.
S
Low temperature.
S
A further General Warning is available in the unit equipped
with heating, signalling the following abnormal condition:
Electrical heater fault.
S
NOTE:
An alarm causes the unit to stop and the unit in stand---by
S
(if available) to intervene.
A warning does not stop the unit.
S
Both the alarm and the warning activate visual and aud-
S
ible indication (on unit with Hiromatic).
Both the alarm and the warning must be reset manually
S
on the PowerFace (or Hiromatic if installed).
Should the thermofuse intervene, the electrical heaters must
be replaced.
6 --- Settings
The air conditioner has already been factory---tested and
S
set as described below (see Tab. 8).
For the microprocessor control settings please refer to
S
the relevant manual (to avoid incorrect operation do not
use temperature and relative humidity set points or pro-
portional bands which differ excessively from the stan-
dard settings).
pag. 5
Freecooling mode
P Band
1
Set
Cooling
P Band
1
1
2
Set
Cooling
_C
3
_C
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