We reserve the right to alter specifications.
GB.FUNKRXHC.180907
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When defrosting is completed, the outdoor air damper
and the exhaust air damper open, the recirculation
damper closes and stabilization operations are run.
In order to reduce the risk of freezing, a termination
sequence is started at the same time when the recircula-
tion damper is opened and closed a number of times.
Electrical air heater RX/HC (accessory)
When there is a defrosting requirement, the electric air
heater is enabled immediately.
Overheating protection is installed. Post-cooling is car-
ried out if the air handling unit stops during or just after
defrosting.
Critical defrosting
If the evaporation temperature in the heating circuit drops
below a critical limit, defrosting starts.
If the control system discovers ongoing ordinary defrost-
ing, critical defrosting is adapted to the ordinary defrost-
ing sequence, e.g. recirculation starts.
3.10 Limitations
For operations outside the outdoor temperature limits
and/or below air limits, the reversible heat pump function
stops and the air handling unit acts as a GOLD RX.
Outdoor temperature limit, cooling
Operation of the reversible heat pump in cooling mode
is only permitted at an outdoor temperature above 15°C
(adjustable value).
Outdoor temperature limit, heating
Operation of the reversible heat pump in heating mode
is only permitted at an outdoor temperature above -25°C
(adjustable value).
Air flow limits
Operation of the reversible heat pump is only permitted
when the extract airflow and supply airflow exceed a
minimum airflow limit. Values can be set for the extract air
and supply air.
3.9 Defrosting
Freezing occurs when operations are in heating mode and
the temperature across the exhaust coil is below 0 °C.
Depending on the temperature, compressor speed, airflow
as well as moisture content in the extract air and fresh air,
freezing occurs with varying speed and behaviour.
The pressure drop across the exhaust coil is measured
to detect the defrosting requirement or stop ongoing
defrosting. Defrosting starts when the pressure drop
exceeds a specific limit. When the pressure drop falls
below another lower limit defrosting stops.
At defrosting with recirculation, the recirculation damper
have a finishing sequence for protection against freezing.
Phases
Defrosting occurs by reversing the heat pump circuit. The
exhaust coil then works as a condenser (as with the cool-
ing function) and heats.
Start delay
When the pressure drop across the exhaust air coil exceeds
the start limit, for a period longer than 60 seconds,
defrosting starts.
Initiation
When defrosting is detected the Initiation phase starts.
The recirculation damper then opens for recirculation, and
if there is an electric air heater this starts. For recirculation
the signal is sent with a delay of 60 seconds, if there is no
recirculation the signal is sent without a delay.
Pre-defrosting
When the defrosting process starts, a signal is sent to the
heating circuit which lowers the compressor speed and
turns the flow directions through the four-way valve.
Defrosting
The defrosting process continues through ramping up the
compressor speed and running until the control system
requests that defrosting stops or until the maximum
defrosting time has been reached.
Runoff
In the last part of the defrosting process, the compressor
speed drops and the flow directions through the four-way
valve are turned back.
Adaptive start and stop
Start and stop of the defrosting process is controlled by
calculations in the control system, which take a number
of different factors into consideration that are measured
continuously.
Adaptation is performed after each defrosting to optimise
the process.
Air recirculation section RX/HC (accessory)
When there is a defrosting requirement, the recircula-
tion damper opens, and the outdoor air damper and the
exhaust air damper close.
Recirculation operation is ensured before defrosting starts.
