Danfoss ADAP-KOOL AK-PC 781, Design Manual

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AK-PC 781 Capacity controller RS8GG602 © Danfoss 2015-03 111
The minimum temperature difference (min tm) at low load should
be set at approximately 6 K as this will eliminate the risk that all
fans will be running when no compressors are running.
Set the dimensioned difference (dim tm) at max. load (e.g. 15 K).
The controller will now contribute with a value to the reference
which depends on how large a part of the compressor capacity
has been cut in.
P-regulation
With P regulation the reference will be three degrees above the
measured outdoor temperature. The proportional band Xp indi-
cates the deviation with 100% condenser capacity.
Heat recovery function
(for all refrigerants except CO2. For CO2
see later section in the condensation description).
The heat recovery function can be used on the installation
when you want to make use of warm gas for heating purposes.
When the function is activated the reference for the condenser
temperature will be raised to a set value and the attached relay
outlet is used to activate a solenoid valve.
The function can be activated in two ways:
1. A digital input signal is received
In this instance, the heat recovery function is activated via
an external signal from, for example a building management
system. When the function is activated the reference for the
condenser temperature will be raised to a set value and the
attached relay outlet is used to activate a solenoid valve.
2. Use of a thermostat for the function.
This function can be used with advantage where the heat
recovery is used to warm up a water tank. A temperature sensor
is used to activate/deactivate the heat recovery function. When
the temperature sensor becomes lower than the set cut in
limit, the heat recovery function is activated and the reference
for the condenser temperature will be raised to a set value
and simultaneously the chosen relay outlet is used to activate
a solenoid valve which leads the warm gas through the heat
exchanger in the water tank. When the temperature in the tank
has reached the set value, the heat recovery is cut-out again.
Max
Min
PcRef
Pc ref
DI
In both cases it applies that when the heat recovery function is
de-activated, the reference for the condensing temperature will
then decline slowly in accordance with the set rate in Kelvin/
minute.
Limitation of the reference
To safeguard yourself against a too high or too low regulation
reference, a limitation of the reference must be set.
Forced operation of condenser capacity
Forced operation of the capacity can be arranged where the nor-
mal regulation is ignored.
The safety functions are cancelled during forced operation.
Forced operation via setting
The regulation is set to Manual.
The capacity is set in percent of the regulated capacity.
Forced operation of relays
If the forced operation is carried out with the switches at the
front of an extension module, the safety function will register
any exceeding of values and transmit alarms, if required, but the
controller cannot cut the relays in or out in this situation.