OPERATING CHARACTERISTICS
I A
Temperature control
Control is performed based on the system water return tem-
perature.
The set points refer to the water return temperature.
The water outlet temperature depends on the difference
between inlet and outlet, usually 5°C (rated).
This temperature difference may change depending on the
type of water circuit.
For example, if the HEAT set point is set to +30°C, the outlet
temperature will be +35°C.
The return temperature is also used to activate the
resources inside or outside unit (e.g. electric heaters).
The controller features Full Floating technology that optimis-
es, when the scan time elapses, the water temperature set
points (COOL/HEAT/DHW) in relation to the compressor
operating time and the water temperature.
To display the actual set point, select directory Sr and the
active operating mode (Cool, Heat, DHW), as described in
the paragraph "Displaying installer parameters ".
Cooling set point
(factory setting) = 12°C, Hysteresis = 3°C.
The compressor starts at outlet water temperatures above
12°C+3°C (15°C).
The compressor stops at water temperatures below 12°C.
Heating set point
(factory setting) = 40°C, Hysteresis = 3°C.
The compressor starts at outlet water temperatures below
37°C.
The compressor stops at water temperatures above 40°C.
In the event of temporary power failure, when power returns,
the mode set previously will be retained in the memory.
COMPRESSOR START UP DELAY
Two functions prevent the compressor from starting up too
frequently:
- Minimum time since last shut-down 3 minutes.
- Minimum time since last start-up 5 minutes.
CIRCULATING PUMP
The electronic board has an output for managing the circu-
lating pump, always on in COOL and HEAT modes, and off
with a 1 minute delay when unit shuts down (standby).
After the first minute of pump operation when the water flow
is at full speed, the water flow alarm functions are activated
(differential pressure switch and flow switch).
FAN SPEED CONTROL
To enable the unit to function correctly at different outside
temperatures, a microprocessor with pressure reading via
temperature sensor controls the fan rotation speed. This
allows the exchange of heat to be increased and/or
decreased, maintaining condensing or evaporation pres-
sures essentially constant. The fan operates independently
of the compressor.
FROST ALARM
The frost protection function is always active even if the con-
troller is standby.
To prevent the water freezing and damaging the plate heat
exchanger, the microprocessor shuts down the compressor
if the temperature measured by the heat exchanger outlet
temperature sensor is less than +4°C.
The frost prevention temperature set point can be modified
by an authorised service centre only and only after verifying
that the water circuit contains antifreeze.
Tripping of this alarm shuts down the compressor but not
the pump, which remains active.
To reset normal functions, the water outlet temperature must
rise to more than +7°C. Reset is automatic.
If the frost alarm is tripped more than 3 times in one hour,
reset becomes manual.
DOMESTIC HOT WATER FROST PROTECTION
The domestic hot water frost protection function is only
active if an auxiliary resource is installed for the domestic
hot water storage (parameter CL61=28).
The auxiliary resource is activated if the water temperature,
measured by sensor BT4, is less than +5°C, and is deacti-
vated at +7°C.
FROST PROTECTION WITH UNIT IN STANDBY
Version AWR MTD (complete with built-in heaters)
The frost protection function is guaranteed by the activation
of the heating element inside the unit and the start of the
system pump.
The pump and the first stage of the electric heater (see Tab.
1) are activated if the water temperature (measured by sen-
sor BT2 at the heat exchanger outlet) is less than 4.5°C,
and are deactivated when the water temperature reaches
+7°C.
Version AWR MTD/B
The frost protection function is guaranteed by the activation
of the 200W electric heater used to protect the heat
exchanger, and by the activation of the system pump.
The pump and the electric heater are activated if the water
temperature (measured by sensor BT2 at the heat exchang-
er outlet) is less than 4.5°C, and are deactivated when the
water temperature r7°C.
WATER FLOW ALARM
The microprocessor manages a water flow alarm controlled
by a differential pressure switch installed as standard on the
unit, and a flow switch to be installed on the water outlet pip-
ing.
This safety device may trip after the first 60 seconds of
pump operation, if the water flow-rate is not sufficient.
The alarm shuts down the compressor and not the pump,
which remains active if the alarm lasts less than 20 sec-
onds, otherwise the unit is shut down completely.
DYNAMIC DEFROST
The unit manages the defrosts by reversing the refrigerating
cycle, switching the position of the reversing valve and oper-
ating the circuit in cooling mode for a few minutes with the
fans off.
The defrost cycle removes the ice that forms on the surface
of the outdoor heat exchanger external at low temperature
and high humidity.
The unit controller features smart defrost management in
relation to the temperature read by the outside air tempera-
ture sensor and the pressure in the refrigerant circuit.
The graph of the function is shown below.
25
GB 01/2009
AWR MTD - AWR MTD/B
