28
E
Flow temperature sensor, heating/cooling cir-
cuit 2
F
Indoor unit with 2 integral heating/cooling cir-
cuits:
Heating circuit pump, heating/cooling circuit 2
G
Integral buffer cylinder
H
Secondary pump
For indoor unit with 2 integral heating/cooling cir-
cuits, also heating circuit pump for heating/cool-
ing circuit 1
K
Flow sensor
The defrost process starts as soon as heating of the
integral buffer cylinder has finished. The 4-way revers-
ing valve in the outdoor unit switches to the "refrigerant
circuit reversal" position. The fans are switched off.
The actuators of the refrigerant circuit are initially oper-
ated for 10 s with fixed control variables, e.g. the com-
pressor with a specified speed.
The compressor speed is then slowly adjusted to as
constant a value as possible so that the suction gas
temperature (evaporator) reaches a higher tempera-
ture level. The compressor speed has its own max.
limit for the defrost process.
For the defrost process, the heat from the integral buf-
fer cylinder is fed into the refrigerant circuit. The
amount of thermal energy available is monitored via
the return temperature of the secondary circuit. If the
thermal energy in the integral buffer cylinder is not suf-
ficient, the return temperature of the secondary circuit
drops sharply.
If the return temperature drops too much, it is com-
pared with the flow temperature of heating/cooling cir-
cuit 1:
■
Return temperature of secondary circuit is lower
than flow temperature of heating/cooling circuit 1:
The 4/3-way valve moves to position
—
= > 25 % to < 50 %. This allows the defrost
process to continue with the thermal energy from
heating/cooling circuit 1.
■
Return temperature of secondary circuit is higher
than flow temperature of heating/cooling circuit 1:
–
Heat pump with integral instantaneous heating
water heater:
The instantaneous heating water heater is
switched on to reheat the integral buffer cylinder.
–
Systems with external heat generator:
The external heat generator is switched on to
reheat the integral buffer cylinder.
–
Systems with external heating/cooling water buffer
cylinder:
The thermal energy from the external buffer cylin-
der is used.
The 4/3-way valve moves to position = 50 %.
If reheating is required more often, the internal buffer
cylinder is heated to a higher temperature.
Note
The minimum flow rate for defrosting is 900 l/h.
What happens if the defrost process is aborted
The defrost process is aborted in the following cases:
■
The liquid gas temperature (condenser) is too low.
■
The suction gas temperature (evaporator) is too
high: High pressure fault
■
Fault message from refrigerant circuit is present.
The defrost process is automatically restarted after
being aborted. If the minimum return temperature is
below the actual return temperature, the refrigerant cir-
cuit cannot start. In this case, the return temperature is
raised.
■
Heat pump with integral instantaneous heating water
heater:
The instantaneous heating water heater is switched
on to reheat the integral buffer cylinder.
■
Systems with external heat generator:
The external heat generator is switched on to reheat
the integral buffer cylinder.
■
Systems with external heating/cooling water buffer
cylinder:
The thermal energy from the external buffer cylinder
is used.
As soon as the required return temperature is reached,
the refrigerant circuit starts. If the defrost process has
been interrupted up to 10 times in a row, the refrigerant
circuit is blocked and must be unlocked via ViGuide
(message F.864).
End of the defrost process
After successful defrosting, the heat pump switches
back to normal operation. To do this, the 4-way diverter
valve switches the refrigerant circuit to heating mode.
The defrost process ends when 1 of the following con-
ditions is met:
■
The min. defrost time has been exceeded and the
liquid gas temperature (condenser) has reached the
stop limit.
■
The max. defrost time has been reached.
Function description
Defrost (cont.)
6218234
Functions
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