Danfoss AK-PC 531B User guide

Design guide

Capacity controller

AK-PC 531B

ADAP-KOOL® Refrigeration control systems

Introduction

Application

The controller is used for capacity regulation of compressors and / or condensers in small refrigerating systems.

This controller can regulate up to ten compressors. The condenser capacity is step regulated via the remaining available digital outputs and external relay module or variable speed regulated via a frequency converter.

Advantages

•Patented neutral zone regulation

•Sequential or cyclic operation

•Possibility of suction pressure optimisation via the data communication

•Load shedding function

Regulation

Regulation is based on signals from one pressure transmitter for the compressor regulation and one pressure transmitter for the condenser regulation plus one temperature sensor for the air temperature before the condenser.

Functions

•Relays for capacity regulation

•Voltage output for capacity regulation

•Status inputs. An interrupted signal indicates that the safety circuit has been activated and the respective circuit stopped

•Contact inputs for indication of alarms

•Contact inputs for displacement of references or for indication of alarms

•Alarm relay

•External start/stop of regulation

•Possibility of data communication

Operation

All operation takes place either via data communication or via connection of a display type EKA 164. The display can be disconnected after the installation.

Manual RS8HG102 © Danfoss 11-2015

AK-PC 531B

Function

Capacity regulation

The cut-in capacity is controlled by signals from the connected pressure transmitter and the set reference.

Outside the reference a neutral zone is set where the capacity will neither be cut in nor out.

Outside the neutral zone (in the hatched areas named +zone and -zone) the capacity will be cut in or out if the regulation registers a change of pressure “away” from the neutral zone.

Cut in and cut out will take place with the set time delays. If the pressure however “approaches” the neutral zone, the controller will make no changes of the cut-in capacity.

If regulation takes place outside the hatched area (named ++zone and --zone), changes of the cut-in capacity will occur somewhat faster than if it were in the hatched area.

Cut in of steps can be defined for either sequential or cyclic operation.

Sequential (first in - last out)

The relays are here cut in in sequence – first relay number 1, then 2, etc.

Cutout takes place in the opposite sequence, i.e. the last cut-in relay will be cut out first.

Cyclic (first in - first out)

The relays are coupled here so that the operating time of the individual relays will become equalised.

At each cutin the regulation scans the individual relays’ timer, cutting in the relay with least time on it.

At each cutout a similar thing happens. Here the relay is cut out that has most hours on the timer.

Rx = random relay h = number of hours

AK-PC 531B

Suvey of functions

Function	Para-	Parameter by operation via
	meter	data communication
Normal display
If the two displays are mounted:		P0 b (bar)
P0 will be shown on EKA 165 / EKA 164 (the one with buttons)		Pc b (bar)
Pc will be shown on EKA 163
Compressor regulation reference		Compressor control

P0 setpoint	r23	Set Point b
Regulation is based on the set value plus an offset, if applicable. An offset can be
created from night setback r13 and/or from a master gateway’s override function.
Offset	r13	Night offset
The set reference may be displaced with a fixed value when a signal is received at
the DI4 input or from the function "Night setback" (r27).
(Cf. also Definition of DI4 input).
Night setback	r27	NightSetBack
OFF: No change of the reference
ON: Offset value forms part of the reference
Reference	r24	Comp ref. b
The regulation reference is shown here
Set point limitation
With these settings the setpoint can only be set between the two values.
(This also apply if regulation with "P0-optimisation function".)

Max. permissible setpoint value.	r25	P0RefMax b

Min. permissible setpoint value.	r26	P0RefMin b

Neutral zone	r01	Neutral zone
There is a neutral zone around the reference. See also page 3.
Correction of pressure measurement	r04	AdjustSensor
An offset adjustment of the registered pressure can be made.
Unit	r05	(In AKM only bar or °C is used,
Here you can select whether thedisplay is to indicate pressure in bar or in Psig.		whatever the setting)
And temperatures in °C or °F.
0: Will give bar and °C.
1: Will give Psig and °F.
Start/stop of refrigeration	r12	Main Switch
With this setting the refrigeration can be started and stopped. Start/stop of
refrigeration may also be performed with an external contact function connected
to the input named “ON input”.

Condenser regulation reference		Condenser control
Pc setpoint	r28	Set Point b
Regulation is based on the set value plus an offset, if applicable. An offset can be
created via the “r34” function and/or from a master gateway’s override function.
Offset	r34	Press.offset
The set reference may be displaced with a fixed value when a signal is received
at the DI5 input. (Cf. also Definition of DI5 input).
Pc reference variation	r33	Pc mode
1: No change of the reference. Regulation based on set setpoint.
2: Outdoor temperature forms part of the reference. The outdoor temperature
is measured with Sc3. When the outdoor temperature drops one degree, the
reference is lowered one degree.
Setting 1 and 2 operate with a PI regulation.
If the system is unstable and the PI regulation not satisfactory the I element may
be left out, so there will be P regulation only.
3: As 1, but with P regulation
4: As 2, but with P regulation
The regulation reference is shown here.	r29	Cond ref. b

The mean temperature difference across the condenser at maximum load (dim tm K)	r35	Dim.Tm K

The mean temperature difference across the condenser at the lowest relevant com-	r56	Min tm K
pressor capacity (min tm K)
Set point limitation
With these settings the setpoint can only be set between the two values.

Max. permissible setpoint value.	r30	PcRefMax b
Min. permissible setpoint value.	r31	PcRefMin b

AK-PC 531B

Correction of pressure measurement	r32	AdjustSensor
An offset adjustment of the registered pressure can be made.

Compressor capacity		Compressor pack config.

Running time
To prevent frequent start/stop, values have to be set for how the relays are to cut
in and out.
Min. ON time for relays.	c01	Min.ON time
(The time is not used if the relay cuts an unloader in or out).
Min. time period between cutin of same relay.	c07	MinRecyTime

Setting for neutral zone regulation

Regulation band over the neutral zonen	c10	+ Zone b

Time delay between step cut-ins in the regulation band over the neutral zone	c11	+ Zone m

Time delay between step cut-ins in the regulation band over the "+Zone band".	c12	+ + Zone m

Regulation band under the neutral zone	c13	- Zone b

Time delay between step cut-outs in the regulation band under the neutral zone	c14	- Zone m

Time delay between step cut-outs in the regulation band under the "-Zone band"	c15	- - Zone m

Compressor configuration	c16	Compr mode
Here you set the combination of number of compressors and any unloaders.
1 = One compressor, 2 = two compressors, 3 = three, 4 = four....10 = ten.
See page 9.
Selection of coupling mode (See also the overview page 9)	c08	Step mode

1.Sequential: First relay 1 cuts in, then relay 2, etc. Cutout takes place in the opposite sequence. (”First in, last out”).

2.Cyclic: An automatic operating time equalisation is arranged here, so that all steps with motor connection will have the same operating time

Definition of condenser and number of fans	c29	No. of Fans
Here you set the number of fan steps with which regulation has to be carried out (but
max. eight).
1-8: All fans are cut in and out with relays. The first vacant relay number is assigned to
fan 1, the next to number 2, etc. Steps after DO10 must be executed through connec-
tion of a relay module type EKC 331 to the analog output. Cf. drawing on page 9.
9: All fans are controlled via the analog output and a frequency converter.
10: Not used
11-18: Total number of fan relays which are to be connected with alternating start-up.
Read temperature at sensor Sc3	u44	Sc3 temp
Read temperature at sensor Sc4 (sensor is only used for monitoring)	u45	Sc4 temp
Read temperature at sensor "Saux"	u03	Saux temp
Status on DI3 input	u87	DI 3 status
Status on DI4 input	u88	DI 4 status
Status on DI5 input	u89	DI 5 status
	-	- - - Comp. Cap %
		Read cut-in compressor capacity
	-	- - - Cond. Cap %
		Read cut-in condenser capacity
Regulation parameters for the condenser regulation
P: Amplification factor Xp (P = 100/Xp)	n04	Xp b
If the Xp value is increased, the regulation becomes steadier
I: Integration time Tn	n05	Tn s
If the Tn value is increased, the regulation becomes steadier
Cutin condenser capacity with manual control. See also “n53”	n52	FanManCap%
Manual control of condenser capacity (when ON, the value in “n52” will be used)	n53	FanManCap

AK-PC 531B

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