Danfoss AK-CC 421 User guide

User Guide

Controller for Condensing unit

AK-CC 421

Introduction

Application

Condensing unit control

Advantages

•Condensing pressure control in relation to outside temperature

•Fan variable speed regulation

•On/off or variable speed regulation of the compressor

•Heating element control in crankcase

•Day/night controller operation

•Built-in clock function with power reserve

•Built-in Modbus data communication

•Monitoring discharge temperature td

•Oil return management control at variable speed control

Principle

The controller receives a signal for demanded cooling, and it then starts the compressor.

If the compressor is controlled by variable speed, the suction pressure (converted to temperature) will be controlled according to a set temperature value.

Condenser pressure regulation is performed again following a signal from the ambient temperature sensor and the set reference. The controller will then control the fan, which allows the condensing temperature to be maintained at the desired value.

The controller can also control the heating element in the crankcase so that oil is kept separate from the refrigerant.

For excess discharge temperature, the liquid injection will be activated in the suction line.

Functions

•Control of condensing temperature

•Control of fan speed

•On/off control or speed regulation of the compressor

•Control of heating element in crankcase

•Liquid injection into economizer port

•Raising the condenser pressure regulation reference during night operation

•Safety cut-out activated via signal from automatic safety control

Regulation reference for condensing temperature

The controller controls the condensing temperature in relation to the ambient temperature. A set point is entered for how much

higher the reference must be. The reference can be raised at night.

Day/Night

The controller has an internal clock function which changes between daytime and night operation.

During night operation, the reference is raised by the 'Night offset' value.

This day/night signal can also be activated in two other ways:

•Via an on/off input signal - DI2

•Via data communication.

Reference

Night offset

Set Point

Tamb

Day

Night

Day

User Guide RS8KF102 © Danfoss 2019-03

AK-CC 421

Fan operation

The controller will control the fan so that the condensing temperature is maintained at the desired value above the outdoor temperature.

The user may select from different ways to control the fan:

• Internal speed regulation

Here the fan is speed-controlled via terminal 5-6.

At a need of 95% and above, the relay on terminal 15-16 are activated, while 5-6 are deactivated.

• External speed regulation

For larger fan motors with insufficient internal outlet, an external speed regulation can be connected to terminal 54-55. A 0-10 V signal indicating the desired speed is then sent from this point. The relay on terminal 15-16 will be active when the fan is in operation.

In menu 'F17' the user can define which of the two controls to use.

Fan speed at start

When the fan is re-started after an idle period, it will be started at a speed that is set in the 'Jog Speed' function. This speed is maintained for 10 seconds, after which the speed changes to the regulation need.

Fan speed at low loads

At low loads between 10 and 30%, the speed will remain at that which is set in the 'FanMinSpeed' function.

Fan speed at low ambient temperatures

To avoid frequent start/stops in low ambient temperatures in which the fan's capacity is high, the internal amplification factor is lowered. This provides a smoother regulation.

The 'Jog speed' is also lowered in the area from 10°C and down to -20°C.

At temperatures below -20°C the 'Jog Low' value can be used.

Speed

Jog

Min.

Required

capacity

Speed

Jog

Jog low

AK-CC 421

User Guide RS8KF102 © Danfoss 2019-03

Compressor control

The compressor is controlled by a signal at the DI1 input. The compressor will start once the input is connected.

Three restrictions have been implemented to avoid frequent start/ stops:

- One for minimum ON time - One for minimum OFF time

- One for how much time must elapse between two starts. These three restrictions have the highest priority during regulation, and the other functions will wait until they are

complete before regulation can continue. When the compressor is 'locked' by a restriction, this can be seen in a status notification.

If the DI3 input is used as a safety stop for the compressor, an insufficient input signal will immediately stop the compressor. The compressor can be speed-controlled with a voltage signal at the AO2 output.

If the compressor has been running for a long period at low speed, the speed is increased for a short moment for the purpose of oilreturn.

Maximum discharge gas temperature

The temperature is recorded by sensor Td.

If variable speed control is chosen for the compressor, this control will initially reduce the compressor capacity if the Td temperature approaches the set maximum value.

If a higher temperature is detected than the set max. temperature, the fan's speed will be set to 100%. If this does not cause the temperature to drop, and if the temperature remains high

after the set delay time, the compressor will be stopped. The compressor will only be re-started once the temperature is 10 K lower than the set value. The above mentioned re-start restrictions must also be complete before the compressor can start once again.

If the delay time is set to '0', the function will not stop the compressor. The Td sensor can be deactivated (o63).

Liquid injection into economizer port

The controller can activate the liquid injection into economizer port if the discharge temperature is approaching the maximum allowable temperature.

Note: Liquid injection function use the Aux Relay.

High pressure monitoring

During regulation, the internal high pressure monitoring function is able to detect an over the limit condensing pressure so that the regulation can continue.

However, if the C73 setting is exceeded, the compressor will be stopped.

If, on the other hand, the signal comes from the interrupted safety circuit connected to DI3, the compressor will immediately be stopped and the fan will be set to 100%.

When the signal is once again 'OK' at the DI3 input, the regulation will resume.

Low pressure monitoring

During regulation, the internal low pressure monitoring function will cut out the compressor upon detecting a suction pressure that falls below the lower limit, but only once the minimum ON time

is exceeded. An alarm will be issued. This function will be time delayed, if the compressor starts at low ambient temperature.

Pump down limit

The compressor will be stopped if a suction pressure that falls below the set value is registered, but only once the minimum ON time is exceeded.

AK-CC 421

Heating element in the crankcase

The controller has a thermostat function which can control the heating element for the crankcase. Oil can thus be kept separate from the refrigerant. The function is active when the compressor has stopped.

The function is based on the ambient temperature and suction gas temperature. When the two temperatures are equal ± a temperature difference, power will be supplied to the heating element.

The 'CCH off diff' setting indicates when power will no longer be supplied to the heating element.

The 'CCH on diff' indicates when 100% power will be sent to the heating element.

Between the two settings the controller calculates the wattage and connects to the heating element in a pulse/pause cycle which corresponds to the desired wattage.

The Taux sensor can be used to record the temperature in the crankcase if desired.

When the Taux sensor records a temperature lower than Ts+10 K, the heating element will be set to 100%, but only if the ambient temperature is below 0°C.

Digital inputs

There are two digital inputs DI1 and DI2 with contact function and one digital input DI3 with high voltage signal.

They can be used for the following functions: DI1: Starts and stops compressor

DI2: Here the user can select from various functions Status notification from an external safety function External main switch

Night setback signal Separate alarm function Monitoring of input signal

DI3: Safety signal from low/high-pressure switch

Data communication

The controller is delivered with built-in MODBUS data communication.

If a different form of data communication is requested, a LON RS485 module can be inserted in the controller.

The connection will then be made on terminal RS 485.

Important

All connections to the data communication must comply with the requirements for data communication cables.

See literature: RC8AC.

Display

The controller has one plug for a display. Here display type EKA 163B or EKA 164B (max. length 15m) can be connected.

EKA 163B is a display for readings.

EKA 164B is both for readings and operation.

The connection between display and controller must be with a cable which has a plug at both ends.

A setting can be made to determine whether the Tc or Ts is to be read out. When the value is read out, the second read-out can be displayed by briefly pressing the lower button.

When a display is to be connected to the built-in MODBUS, the display can advantageously be changed to one of the same type, but with Index A (version with screw terminals).

The controllers address must be set higher than 0 in order for the display to be able to communicate with the controller.

If connection of two displays is required, one must be connected to the plug (max. 15 m) and the other must then be connected to the fixed data communication.

Override

The controller contains a functions which can be used together with the override function in the master gateway/system manager.

Address o03 > 0

Function via data communication	Day/Night schedule

Function in gateway/system manager	Day/Night control / Time
	schedule

Used parameters in AK-CC 421	--- Night setback

AK-CC 421

Survey of functions

Function	Para-	Parameter by operation via data
	meter	communication
Normal display

The display shows the temperature value for the suction pressure Ts or from the con-		Ts / Tc
densing pressure Tc. Enter which of the two are to be displayed in o17.
During operation, when one of the two is shown in the display, the other value can be
seen by pressing and holding in the lower button.
Thermostat		Thermostat control
Set point		Reference
The controller's reference Tc is the outside temperature + set point + any applicable
offset.
Enter the set point by pressing the middle button. A offset can be entered in r13.
Unit	r05	Unit
Set here if the display is to show SI-units or US-units		°C=0. / °F=1
0: SI (°C and bar)		(Only °C on AKM, whatever the set-
1: US (°F and Psig).		ting)

Start / stop of refrigeration	r12	Main Switch
With this setting refrigeration can be started, stopped or a manual override of the
outputs can be allowed. (For manual control the value is set at -1. Then the relay out-		1: Start
lets can be force-controlled by the respective reading parameters (u58, u59 etc.). Here		0: Stop
the read value can be overwritten.)		-1: Manual control of outputs allowed
Start / stop of refrigeration can also be accomplished with the external switch func-
tion connected to a DI input.
If the external switch function is deselected, the input must be shorted.
Stopped refrigeration will give a ”Standby alarm”.
Night setback value	r13	Night offset
The controller reference is raised by this value when the controller switches to night
operation.
Reference Ts	r23	Ts Ref
Here the reference is entered for the suction pressure Ts in degrees.
Reference Tc	r29	Tc Ref
Here the current controller reference for condensing pressure Tc can be read out in
degrees.
Minimum condensing temperature (lowest permitted regulation reference)	r82	MinCondTemp
Here the lowest permitted reference is entered for the condensing temperature Tc.

Maximum condensing temperature (highest permitted regulation reference)	r83	MaxCondTemp
Here the highest permitted reference is entered for the condensing temperature Tc.

Maximum discharge gas temperature	r84	MaxDischTemp
Here the highest permitted discharge gas temperature is entered. The temperature
is measured by sensor Td. If the temperature is exceeded, the fan will be started at
100%. A timer is also started which can be set in c72. If the timer setting runs out,
the compressor will be stopped and an alarm will be issued. The compressor will be
reconnected 10 K below the cut-out limit, but only after the compressor's off timer
has expired.
		Night setbck
		(start of night signal. 0=Day, 1=Night)
Alarm		Alarm settings

The controller can give alarm in different situations. When there is an alarm all the		With data communication the impor-
light-emitting diodes (LED) will flash on the controller front panel, and the alarm relay		tance of the individual alarms can be
will cut in.		defined. Setting is carried out in the
		“Alarm destinations” menu via AKM.
Delay of a DI2 alarm	A28	AI.Delay DI2
A cut-out/cut-in input will result in alarm when the time delay has been passed. The
function is defined in o37
High condensing temperature	A70	Air flowDiff
The limit value (difference over normal reference) to which the condensing tempera-
ture has increased, and at which an alarm must be issued. Can be set in K.
Delay time for alarm A70. Set in minutes.	A71	Air flow del
		Reset alarm
		Ctrl. Error

AK-CC 421

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