Page 26
VLS-GB.indd 27
17-06-2009 15:56:45
Control
6.4 Protection and Safety
Equipment
Defrosting System
(only for VLH models)
The VLH units are provided with an automatic defro-
sting system, which prevents the formation of excessi-
ve ice banks on coolant/air exchangers during heat
pump operation.
This system, which is part of the electronic control sy-
stem, is of the time/suction pressure type, and when
the suction pressure detected by a sensor drops
below a fixed limit, once the preset time is over,
switches from heating to cooling the operation of the
unit, with the fans stopped.
During the defrosting cycle the compressor works
normally, but the coil’s fans remain off. The defro-
sting cycle stops after the coil has been defrosted,
and at this point the unit can work in heating mode
again.
Both circuits are defrosted at the same time.
For safety purposes, fans are started also
during defrosting, if the discharge pressure
reaches considerable values.
Frost Protection for the Chilled Fluid
These units are provided with frost protection for the
chilled fluid. This protection consists of an electrical
resistor positioned in contact with the coolant/circu-
lating fluid exchanger, which is activated (although
the unit is off) when the temperature of the fluid drops
below 5 °C - the standard value for a non-glycol unit.
If the leaving water temperature drops below 4 °C
(standard value for a non-glycol unit) the machine’s
antifreeze alarm is activated. If the circulating fluid
is water, before the beginning of the cold season it
is advisable to drain the circuit to prevent water fro-
sting.
If the circuit cannot be drained, it is essential to avoid
de-energizing the unit, so as to permit the activation,
when necessary, of the frost protection.
NOTE
WARNING
Compressor protection
Compressors are equipped with a heating element to
prevent oil dilution, which may result in remarkable
risks of failure of compressors.
The windings of the compressors’ motors are provi-
ded with a thermal protection.
For VLS/VLH/VLC/VLR models an accessory kit for
thermal protection is available, for any overcurrent
of scroll compressors, which shall be shop-mounted.
Electrical flow switch
To ensure the correct operation of the unit, a electri-
cal flow switch must be installed, to prevent the unit
working in case of insufficient circulation of the chil-
led fluid.
The electrical flow switch must be carefully
installed, according to the instructions given
by the Manufacturer.
The electrical flow switch must be installed on the
pressing side of the circulation pump for the fluid, just
upstream of the heat exchanger’s inlet. The electrical
flow switch must be installed in a horizontal straight
length of piping, in a position reasonably far (both
upstream and downstream) from localized pressure
drops (curves, valves etc.).
Continuous Regulation of the Fan Speed
The fans’ speed regulator, if installed, allows the unit
to work at an ambient temperature down to -18°C.
Differential pressure switch
This pressure switch halts the operation of the unit in
the event that it does not detect a sufficient pressure
drop through the exchanger.
VLS-GB.indd 26
17-06-2009 15:56:45
