Protection And Safety Equipment - comatec AQWL Installations- Und Wartungshandbuch

6.4 Protection and Safety Equipment

Defrosting System (only for AQWH models)
The AQWH units are provided with an automatic defrosting system,
which prevents the formation of excessive ice banks on coolant/air
exchangers during heat pump operation.
This system, which is part of the electronic control system, 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 defrosting cycle stops after the coil has
been defrosted, and at this point the unit can work in heating mode
again.
For safety purposes, fans are started also during
defrosting, if the discharge pressure reaches
considerable values.
NOTE
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/circulating 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 frosting.
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.
6 - Control (continued)
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 provided with a
thermal protection.
For AQW 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 electrical flow switch
must be installed, to prevent the unit working in case of insufficient
circulation of the chilled fluid.
WARNING
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.
25
The electrical flow switch must be carefully
installed, according to the instructions given by
the Manufacturer.