Danfoss AK-PC 551 User Manual page 4

Condenser
Fan control
The fans can be controlled incrementally using the controller's
relays, or they can be speed-controlled via the controller's
analogue output.
Speed control can be via a frequency VLT-type transformer.
If the fans have EC motors, the 0-10 V signal can be used directly.
Step and speed simultaneously. (Parallel signals in step with each
other.) This function is primarily used to control a frequency con-
verter, but if the frequency converter fails, external wiring will
switch over to step control.
During night operation, the noise level of the fans can be kept
down. This is done by limiting the cutin capacity.
For speed control, keep the number of revolutions low.
Omit step cutin for step-by-step activation.
The limitation is bypassed if safety functions Sd max. and
Pc max. start to function.
Control
Regulation is carried out based on a signal from the Pc pressure
transmitter or an S7 media temperature sensor. The signal is com-
pared with the regulation reference.
The regulation reference can originate from one or more of the
following functions:
• Fixed reference
• Variable reference, which follows the outdoor temperature.
When the outdoor temperature drops, the reference will drop
by a corresponding amount.
This variable reference requires the installation of an Sc3
outdoor temperature sensor. The sensor must be positioned
so that it registers the correct outdoor temperature. In other
words, it must be shielded from direct sunlight and located
near the airway of the condenser.
This regulation requires setting a min. and max. reference,
so that the regulation process is kept within the given limits.
• Increase the reference for heat recovery.
Here the reference is raised to a fixed value when a signal is
received on a DI input. The reference value can be higher
than the set max. reference.
When the temperature of the heat recovery has been reached
and the DI signal disappears, the reference will drop once again,
though it will do so over the course of a few minutes to prevent
abrupt changes in the reference.
Media temperature
If controlling a media temperature, the control sensor
must be set to S7. This temperature sensor must be located
in the desired medium.
The Pc pressure transmitter must also be installed. It is used for
high-pressure monitoring.
4 User Guide RS8GY302 © Danfoss 2015-06
Max. ref.
Min. ref.
Ref. for heat recovery
Temperature sequence for
heat recovery
AK-PC 551