Danfoss AK-PC 560 User Manual page 22

Appendix
The regulation functions are explained in more detail below.
The PC reference
You may choose between four different regulation modes.
Basically 1 or 2 are recommended. But if the plant is unstable it
may become necessary to change over to 3 or 4.
1. PI regulation. Fixed reference i.e. constant condensing pressure.
2. PI regulation. Floating reference with outdoor temperature i.e.
variable condensing pressure.
3. As "1", but with P regulation. A somewhat higher condensing
pressure than indicated by the reference must be accepted here.
4. As "2", but with P regulation. A somewhat higher condensing
pressure than indicated by the reference must be accepted here.
1. PI regulation with fixed reference
Ref
The reference at any time, on the basis of which the controller
regulates, can be seen in "r29".
A reference (r28) is set here which with certainty can cope with all
kinds of loads.
2. PI regulation with floating reference
Ref
The reference follows the outdoor temperature Sc3. If the outdoor
temperature drops one degree the reference will also drop one
degree. The reference is adjusted according to the compressor
capacity with max. Xp value.
If you need to raise the condensing temperature for, say, heat
recovery, the setpoint (r28) must be set to this temperature.
22 Manual RS8GE202 © Danfoss 01-2016
To limit the variation in the reference, if floating reference is
chosen (mode 2 & 4), two limit values will have to be set. A max.
limit (r30) and a min. limit (r31). The total regulation reference (r29)
will not be able to go beyond these limits.
As a safeguard against too high condenser temperature a Pc max.
value (A30) also has to be set. If the temperature approaches this
value a cutout of the compressor will be started.
The different regulation modes are as follows:
Setpoint
If you need to raise the condensing temperature for, say, heat
recovery, an offset value (r34) has to be set.
The DI5 function must be defined to 1.
When a signal is subsequently received on the DI5 input the
reference will be raised.
The DI5 function must be defined to 1.
When a signal is subsequently received on the DI5 input the
reference will be changed to the r28 setting.
The reference at any time, on the basis of which the controller
regulates, can be seen in "r29".
If there is sensor failure on the outdoor temperature sensor the
reference will change over to the r28 setting.
AK-PC 560