Operation; General Information; Cooling (See Fig. 8); Heating (Optional) - Liebert Hisp Service Manual

4 --- Operation

4.1 --- General information

The unit operation is completely automatic. The following se-
quence shows how the unit operates (see also Fig. 11 and
Fig. 12 --- Refrigerating circuit):
The temperature sensor, positioned on the intake inside the
room, gives information to the control about the state of the air
to be conditioned.
The control compares the received information with the Set
Point values (= min. indoor temperature required) and the Dif-
ferential programmed values, presetting the air conditioner for
the air conditioning with the following modes:

4.2 --- Cooling (see Fig. 8)

The compressor and the fans are started up when the tempera-
ture of the room to be conditioned exceeds the preset value.
The air, taken into the unit through the rear inlet (lower inlet for
unit with Freecooling option) by the centrifugal fan, goes imme-
diately through the filter and the evaporator. The cold refriger-
ant flows trough the evaporator, cooling the air flowing through
it. The conditioned air is conveyed into the conditioned ambi-
ent through the delivery opening. The heat taken from the room
and that generated by the operation of the conditioner motors
are disposed through the condenser placed in the motor ---con-
densing unit and blown, thanks to the fan, by the outside air.
The condenser fan speed is varied automatically (Variex, see
par. 4.5) as a function of the condensing pressure. For the con-
trol operation logic, see Chap. 5.

4.3 --- Heating (optional)

The air heating is achieved through armoured electric heaters
which are located in the air flow and activated according to the
logic set on the control.
The manual reset of the safety thermostat, located on the heat-
ers, is to be carried out by accessing from the air discharge
grille of the evaporating unit.

4.4 --- Freecooling (optional)

When the temperature of the outside air is lower than that of the
inside air by some degrees, it is possible to use this difference
to refresh the inside of the room by direct intake of the outside
air, i.e. without using the compressor. Thus it is possible to
achieve a considerable energy saving.
When the expected conditions occur, the servo---control, man-
aged by the Microface control, opens the moving damper sep-
arating the flow of the inside air and outside air. Outside air, tak-
en into the room by the fan, gets out through an overpressure
damper which is installed on the walls of the room (optional)
and is protected by an external rainproof grille.
The opening degree of the damper is determined as a function
of the set point value to be kept and of the intake air tempera-
ture (see Chap. 5).
4.5 --- Adjustment of the condenser fan
speed
A sensor is positioned so as to detect constantly the condens-
ing pressure of the refrigerating gas. On the basis of this infor-
mation, an electronic device (Variex) adjusts the fan rotation
speed in order to keep the condensing pressure within the al-
lowed values. In this way, besides optimizing the compressor
operation, you can have a remarkable reduction of the sound
pressure level (mainly during the night), an easier start---up of
the compressor at low temperatures and some energy saving.
For the calibration of the speed adjuster see chapter 8.

4.6 --- Emergency cooling (optional)

This option is available for all those applications where it is im-
portant to keep an airflow inside the room even in the event of a
mains power cut---out. In this case the units can be supplied by
the emergency batteries at 48 V dc (or 24 V dc).
The intervention mode of the emergency system depends on
the state of the automatic switch QS1:
English
QS1 = ON If the main power supply is not cut out, the
S
emergency system remains inactive; if there is no voltage
on the main power supply line, some energy is automatical-
ly collected from the emergency batteries at 48 V dc (or 24
V dc) and it supplies the fan of the evaporating section and
the electronic control through the 48 V / 230 V (or 24 V dc)
transformer. So all functions of the unit are still managed,
allowing the inside air to recirculate (or the outside air to
flow in, if the unit is provided with the Freecooling system)
if the temperature inside the room is not within the per-
mitted range.

5 --- Microprocessor controls

The machine is available in four different operating configura-
tions:
1) only cooling unit;
2) cooling and heating unit;
3) unit with freecooling, only cooling;
4) unit with freecooling, cooling and heating.
In all versions the control display is remoted on the metal box to
be installed inside the room.

5.1 --- Cooling only unit

5.1.1 -- Control logic
This option is managed by the Microface microprocessor con-
trol, which can be combined with the Hiromatic control to moni-
tor all the operation parameters of the unit (see the enclosed
manual). The control algorithm is based on a one ---step adjust-
ment for the compressor ---aided cooling: the control manages
all its lags in the activation, so as to guarantee its correct opera-
tion and to make it function as long as possible.
P Band
Set
Fig. I --- Operation of the cooling only unit.
5.1.2 -- Start-- Stop
There are 2 ways for starting or stopping the unit:
a) the digital input of the Microface card;
b) the ON ---OFF push button on the Hiromatic interface (op-
tional).
Priority with Hiromatic: a) and b) must be regarded as 2 series
contacts; the unit can operate only if all contacts are on.
5.1.3 -- Alarm control
The 2 alarm contacts available on the terminal board of the con-
trol panel can be used in this way:
1) General alarm:
compressor low pressure
S
compressor high pressure (reset on the pressure switch)
S
sensor fault
S
memory fault
S
fan fault
S
2) General warning --- signalling of various abnormal condi-
tions, among which:
high temperature
S
low temperature
S
Notes:
both the alarm and the warning must be reset manually on
S
the Microface.
An alarm causes the unit to stop and the unit in stand ---by
S
(if available) to intervene.
The warning doesn't cause the unit to stop.
S
4
Cooling only unit
Cooling
°C