Danfoss Controller for capacity regulation of brine Installation guide

REFRIGERATION AND

AIR CONDITIONING

Controller for capacity regulation

of brine installation

AKC 25H7

Manual

2 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

This function description is make out in February 2004 and applies to AKC 25H7 with code numbers

084B2022 and 084B2023

Validity

Contents

Introduction ..................................................................................

Application ....................................................................................................3

Systeminformation .....................................................................................4

Operation ......................................................................................................4

Language .......................................................................................................4

Application .................................................................................... 5

Control of cold brine temperature ..............................................6

General description ...................................................................................6

Control reference ........................................................................................6

Capacity regulation of compressor ......................................................9

Signal from the compressor's safety controls ................................ 12

Hourmeter .................................................................................................. 12

Forced control of compressor capacity ........................................... 12

Other functions belonging to the compressor operation ......13

Peak load limitation ................................................................................ 13

Accumulation of ice ................................................................................ 13

Compressor control, - but not condenser control ....................... 13

Injection signal ......................................................................................... 13

Start-up procedure .................................................................................. 14

Defrost ......................................................................................................... 14

Pump control ..............................................................................16

Cold side ..................................................................................................... 16

Warm side ................................................................................................... 17

Control of warm brine temperature ..........................................18

General description ................................................................................ 18

Control of condenser temperature ................................................... 18

Control of heat recovery ....................................................................... 20

Limitations ................................................................................................. 21

Examples of setup of references and limitations ......................... 21

Capacity regulation of condenser .............................................23

Choice of system structure ................................................................... 23

Regulation .................................................................................................. 24

Neutral zone .............................................................................................. 25

Fan deﬁnition ............................................................................................ 25

Time delays for cutins and cutouts ................................................... 25

How to prevent that fans get stuck ................................................... 25

Signal from the fans’ safety controls ................................................. 26

Hourmeter .................................................................................................. 26

Forced control of condenser capacity .............................................. 26

Condenser control, but not compressor control .......................... 26

Use of special functions .............................................................27

Thermostat function ..................................................................27

Monitoring ..................................................................................28

Monitoring of maximum discharge pressure ............................... 28

Monitoring of minimum suction pressure .................................... 29

Monitoring of temperatures ................................................................ 30

Monitoring of ON/OFF functions ....................................................... 31

Sensor failure ............................................................................................. 32

General information ...................................................................33

Supply voltage .......................................................................................... 33

Function switch (Main Switch) ............................................................ 33

Clock function ........................................................................................... 33

Access codes .............................................................................................. 34

Refrigerant ................................................................................................. 35

Service ........................................................................................36

Measurements .......................................................................................... 36

Forced control of outputs ..................................................................... 36

System measurements/data ......................................................37

AKA 21 operation ..................................................................................... 37

PC operation .............................................................................................. 37

Forced control of outputs ..................................................................... 37

Alarms and messages .................................................................38

The importance is indicated by means of the follow ................. 38

This is how the various messages are transmitted: ..................... 38

Who are the alarm receivers? .............................................................. 39

Example of setup of controller ..................................................40

Connections ................................................................................44

Survey of the controller's terminals .................................................. 44

Brief description of the individual terminals ................................. 45

Technical data .............................................................................46

Dimensions .................................................................................46

Ordering ......................................................................................47

Installation considerations ........................................................47

List of literature ..........................................................................47

AKC 25H7 Function description RC1NP402 © Danfoss 04/2005 3

Introduction

Application

AKC 25H7 is a complete brine cooler control unit that has been developed for indirect refrigerating

systems in supermarkets.

AKC 25H7 can be used together with other controllers from Danfoss’ programme of ADAP-KOOL®

refrigeration control system.

The controller’s main function is to control compressors and condensers in such a way that the

required brine temperature is maintained on the cold and warm side of the compressor system.

The controller contains all the functions required for the control of a brine cooler:

• The cold brine temperature can be controlled according to the shop temperature or the enthalpy

• Day/night programmes for the temperature reference (economy control)

• Displacement of the cold reference via override control function

• Alarm limits and delays on forward and return ﬂow temperatures

• Capacity control and monitoring of compressors distributed on one or two groups

• Sequential control or time equalisation of compressors

• Frost cutout for monitoring of suction pressure P0

• Peak load limitation via external signal

• Central defrost control or weekly programme (stop based on temperature or time)

• Signal given when injection is permitted

• Control and monitoring of single pump or twin pump on cold and warm brine

• Built-in rotation between twin pumps

• Automatic pump change when pump is defective

• Control and monitoring of air-cooled or brine-cooled condenser

• Condenser can be controlled based on pressure (Pc) or warm brine temperature (S7)

• Monitoring of max. condensing pressure

• Step regulation or speed regulation of fans

• Condensing pressure can be controlled according to outdoor temperature and an external

voltage signal

• Control of heat recovery temperature with built-in safeguard against too low condensing pressure

• Heat recovery temperature can be controlled according to outdoor temperature and an external

voltage signal

• Monitoring of the compressors’ safety circuit can be supplemented with alarm module type

AKC 22H

The controller’s terminals are shown at the end of the document.

4 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

Systeminformation

Controller type AKC 25H7 is a unit in the ADAP-KOOL® refrigeration control system. The controller

can be linked up with other controllers in the system via a two-core connection - the DANBUSS Data

Communication. Through this connection information can be transmitted between the units, like

settings, measurements, alarms etc.

Remote service

The diﬀerent messages and alarms can, via the telephone network, be transmitted by modems to, say,

a service company.

Address coding

An address code must be set by means of a number of switches on the controller’s front plate. There

are seven switches for the coding. How coding is performed is explained in the installation instructions

for the data communication cable (literature No. RC0XA).

Connection of control panel type AKA 21

A plug for the connection of control panel AKA 21 is mounted right on the front plate of AKC 25H7.

(If the control panel is to be used in any other place, a terminal box will have to be installed (cf. the

installation instructions for the data communication cable, literature No. RC0XA).)

Data communication

To obtain correct data communication it is important that the installation instructions for the data

communication cable be adhered to (literature No. RC0XA).

Operation

The controller can be operated in two diﬀerent ways. Either by using control panel type AKA 21 or by

means of a PC with system software type AKM.

AKA 21 operation

Setting of the diﬀerent functions is performed via a menu system. The menu system is built up on

several levels where you change around between the diﬀerent menus by means of arrow keys.

The complete list of menus is contained in the document “Menu operation via AKA 21”.

(Cf. list of literature).

PC operation

Operation takes place from a PC where Microsoft-Windows and System Software type AKM have

been installed. (The PC is connected to the system via Gateway type AKA 243/244).

Setting of the diﬀerent functions is performed by means of rolling menus and dialogue boxes.

Settings can either be made via the keyboard or by using a mouse.

For users of AKM system software the complete list of menus is found in the document “Menu

operation via AKM”. (Cf. list of literature).

Language

There are three languages in the controller. Depending on the code number selected, the languages

are either: English, German and French

or English, Danish and Swedish.

When the required language has been selected, the individual functions will be shown in this

language, both when there is operation via AKA 21 and system software type AKM.

NB! When you operate system software type AKM it is important that the language code is set before

an upload of the controller’s data is carried out to the AKM programme (it is the set language that will

be picked up by the AKM programme). Select one of the controller’s three languages by means of the

following settings:

0: English

1: German

2: French

3: Danish

6: Swedish

Activate the selected language by pushing "Enter" and then push "Clear".

AKC 25H7 Function description RC1NP402 © Danfoss 04/2005 5

The control has been designed for one of the following three applications:

1 Control of one compressor group based on “S4” and one condenser based on “Pc”

(Appl. Mode = 1).

Used where the condenser is air-cooled, or where there is one brine-cooled condenser.

2 Control of one compressor group based on “S4” or one or two condensers based on brine

temperature “S7”. Pc used for monitoring (Appl. Mode = 2).

Used where one or more condensers are brine-cooled and connected to the same brine circuit.

3 Control of two compressor groups according to “S4” and two condensers based on brine

temperature “S7” (Appl. Mode = 3)

Used where there are two separate compressor groups.

In addition to the three basic applications, further functions may be selected, as mentioned earlier in

the introduction.

Setting: INPUT Conﬁguration - Application mode - Appl. Mode_____

Application

Hint!

The controller can also be used in systems with direct expansion and application modes 1 and 2.

The heat exchanger and S4 are not mounted, so regulation will take place based on P0.

(S4 must not be used and the alarm destination for S4 must be set to 0).

6 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

General description

AKC 25H7 controls the cut-in compressor capacity, so that the temperature at the sensor (S4 or P0)

corresponds to the reference temperature. The actual regulation of the compressors takes place by

means of a neutral zone controller which adjusts the cut-in compressor capacity to the actual load

of the connected cooling/freezing points.

• AKC 25H7 can control and monitor one or two compressor groups with max. 11 compressor steps

distributed on max. eight compressors.

• The suction pressure is constantly monitored and protects the evaporator against freezing.

• AKC 25H7 can control and monitor two twin pumps.

• AKC 25H7 contains functions that will ensure a correct correlation between compressors, pumps and

injection when the system is started.

• Central defrost.

Control reference

Regulation of the cold brine temperature (S4 or P0 in connection with DX application) takes place on

the basis of a reference value comprising a set value plus a number of functions that will be added to

this value. Displacement functions are used for adjusting the reference temperature to the actual load.

Cold Ref = Cold SP

Set value (setpoint)

+ DT.Night Contribution from day/night function

+ K1 x (U Cold - UrefCold)

Contribution from external voltage signal, if applicable

+ K2 x (S3 - Tref Cold) Contribution from S3 temperature, if applicable

+ contribution from a override function

All changes of the reference (except for the night setback function) are ﬁltered over a period of time,

so that there will be no “leaps” in the reference.

In order to prevent that the reference value becomes too high or too low, limiting factors can be put

in.

Below we give you a description of the individual contributions and the limitation function:

Set value

Setting of setpoint value for S4 (P0) temperature:

Setting: Compressor Capacity Ctrl. - Cold Temp. Control - Cold SP__

Contribution from day/night function

With this function the reference can be displaced by up to 25 K in positive or negative direction.

When a night lid is placed on the appliances, the load will drop considerably, and the function may

therefore be used for raising the brine temperature during the night.

The function can also be used for cold accumulation when the brine temperature has to be lowered

during periods where the price of electricity is low.

The relay output DO9 can be deﬁned to follow the controller’s day/night function. During the night

the output will be activated.

(The function should not be used if there also is regulation with contribution from a override function.)

Setting: Compressor Capacity Ctrl. - Cold Temp. - Dt.Night K ___

If the function is not to be used, arrange setting = 0.

Control of cold brine

temperature

AKC 25H7 Function description RC1NP402 © Danfoss 04/2005 7

The function can be activated in two ways:

1) Signal on NIGHT input

When 230 V is fed to this input, the night setback function will be activated.

2) Internal time schedule

The controller contains a clock function that can transmit a signal that will activate the night

setback function.

Start and stop times must be set for each day of the week.

Deﬁnitions:

Night: Time when the night setback starts.

Day: Time when the night setback stops.

Night = 0 or Day = 0:

When one of the two times is set at 0, or when both are set at 0, there will be

no night setback the day

and night in question.

Night = 1 and Day = 1:

When the two settings are set at the same time, there will be night setback throughout that day and

night.

Setting: Day/Night Clock - Day/Night Setting - Mo day h ___ (+more)

8 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

Contribution from an external voltage signal

With a 0 - 10 V d.c. voltage signal on the U COLD input the reference can be displaced by up to 50 K in

positive or negative direction.

The signal may be supplied from a transmitter or another general control giving a signal on the air’s

enthalpy or relative humidity.

Setting: Compressor Capacity Ctrl. - Cold Temp. Control - K1 ___ , UrefCold V___

If the function is not to be used, set K1 at 0.

Example:

- Brine reference to be displaced based on the air’s relative humidity.

- A transmitter is mounted in the shop which measures the air’s relative humidity in the range

0 - 100%, corresponding to an output signal of 0 - 10 V d.c.

- At 60% relative humidity no displacement of the reference will be required (60% relative humidity

corresponds to an output signal of 6 V, i.e. Uref Cold = 6).

- For each 10% increase of the relative humidity (corresponding to 1 V), the reference should be

lowered by 2 K, that is to say, K1 = - 2

The contribution to the reference will therefore be: -2 (“voltage signal at Ucold input” - 6).

Contribution from a temperature signal

With this function it is possible to displace the reference on the basis of a measured temperature

S3. The sensor can for instance be placed in the brine’s return ﬂow temperature or on the business

premises. A reference is obtained in this way which should be adjusted to the actual load.

Setting: Compressor Capacity Ctrl. - Cold Temp. Control - K2 ___ , TrefCold °C___

If the function is not to be used, set K2 at 0.

Example:

- Brine reference temperature to be displaced based on the shop temperature.

- At 18°C no displacement of the reference is required, i.e. TrefCold = 18.

- For each 1°C increase of the shop temperature the reference should be lowered by 1 K, i.e. K2 = -1.

The contribution to the reference will therefore be: -1 (“S3 signal” - 18).

Contribution from override function ("P0" optimization)

The controller has been designed so that a displacement of the reference can take place if a signal is

received from a gateway’s override function.

AKC 25H7 Function description RC1NP402 © Danfoss 04/2005 9

Limitation of reference

To prevent that the sum of the contributions from day/night, voltage signal and temperature signal

will result in a too big displacement, a permissible working range must be stated for the reference.

This is accomplished by setting a max. permissible reference and a min. permissible reference.

Both the max. value and the min. value are set as absolute values.

Setting:C ompressor Capacity Ctrl. - Cold Temp. Control - Cold Max°C ___ , Cold Min°C___

Capacity regulation of compressor

The step regulator can control up to 11 capacity steps distributed on max. eight compressors.

This controller has been designed, so that the connected compressor steps are the same size, but this

is not a requirement.

The cut-in compressor capacity is controlled by the actual brine temperature measured with the S4

sensor and based on whether the temperature is rising or falling. Or with the P0 pressure transmitter

if S4 has not been mounted, for instance in connection with control of a system by means of direct

expansion.

The control is performed by a neutral zone controller.

- In the neutral zone there is no cut in/cut out of capacity steps.

- In the “+zone” and “-zone” bands cut in/cut out will depend on whether the temperature is rising

or falling. Cut ins/cut outs takes place with the selected time delays.

- In the “++zone” and “--zone” bands cut in/cut out takes place with the selected time delays

, whether

the temperature is rising or falling.

Settings:

Neutral zon is set

+ Zone and - Zone bands are set

Time delay in +Zon e and - Zone band is set

Time delay in ++Zone and –Zone band is set

Compressor Capaciy Ctrl. - Compressor Step Control - NZ___ , etc.

Compressor deﬁnition

All the relay outputs can be used for compressors and fans, but you may also select a third function

which is speciﬁc for the given output.

It is necessary, for example, to clarify which of these special functions are to be used before outputs

for compressors and fans can be selected. Reference is made to the paragraph about the use of

special functions.

The controller can control one or two compressor groups with up to 11 compressor steps distributed

on max. eight compressors.

When relay outputs for compressors are ﬁtted, it must be deﬁned by means of the setting:

DO Type = “1” (fan deﬁned with “2” and special functions with “3”).

10 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

Each compressor must be deﬁned with a number, and this is done with setting DO Dev. No.”_”

(“1” is used for compressor number 1, “2” for compressor number 2, and so on).

For compressors with several steps the relay outputs belonging to the same compressor must be

deﬁned with the same number. The controller knows in this way which step belongs to a given

compressor. Based on the same settings the controller will then use the relay output with the lowest

number for starting and stopping the compressor.

Setting: OUTPUT Conﬁguration - DO Relay No.1 - DO1Type___

- DO1Dev.No___

Example:

A system consists of three compressors. One compressor with three steps and two compressors with one step each. Deﬁnition is carried out, as follows:

OUTPUT Conﬁguration DO Relay No.1 DO1 Type = 1 (1 = compressor)

DO1 Dev. No = 1 (compressor 1, step 1)

DO Relay No. 2 DO2 Type = 1 (1 = compressor)

DO2 Dev. No = 1 (compressor 1, step 2)

DO Relay No. 3 DO3 Type = 1 (1 = compressor)

DO3 Dev.No = 1 (compressor 1, step 3)

DO Relay No. 4 DO4 Type = 1 (1 = compressor)

DO4 Dev.No = 2 (compressor 2, step1)

DO Relay No. 5 DO5 Type = 1 (1 = compressor)

DO5 Dev.Nro= 3 (compressor 3, step1)

If the controller is to control two groups of compressors (A and B), there are two things to be

considered.

- The controller’s use must be deﬁned for two groups (“Application mode” must be set at “3”).

- The compressors’ numbers must be deﬁned on the basis of the following requirements:

Odd numbers must belong to group A (DO Dev No. = 1, 3, 5 etc.).

Even numbers must belong to group B (DO Dev No. = 2, 4, 6 etc.).

Example:

System consisting of two groups. Each group consists of two compressors. One compressor with two steps and one compressor with one step.

The deﬁnition can be made, as follows:

“Application mode” to be set at “3”.

OUTPUT Conﬁguration DO Relay No.1 DO1 Type = 1 (1 = compressor)

DO1 Dev. No = 1 (compressor A1, step 1)

DO Relay No.2 DO2 Type =1 (1 = compressor)

DO2 Dev. No =1 (compressor A1, step 2)

DO Relay No.3 DO3 Type = 1 (1 = compressor)

DO3 Dev. No=2 (compressor B1, step 1)

DO Relay No.4 DO4 Type = 1 (1 = compressor)

DO4 Dev. No=2 (compressor B1, step 2)

DO Relay No.5 DO5 Type = 1 (1 = compressor)

DO5 Dev. No=3 (compressor A2, step 1)

DO Relay No.6 DO6 Type = 1 (1 = compressor)

DO6 Dev. No=4 (compressor B2, step 1)

Time delay for cutins and cutouts

To protect the compressor motor against frequent cutins and cutouts two time delays can be put in.

- A minimum restart time (min. time between two starts).

- A minimum ON time (min. operating time before the compressor can be stopped again.

The time delays only apply to start and stop of the compressor motors. The outputs controlling the

cutin and cutout of the unloaders will not be aﬀected.

The setting range is 0 - 25 minutes.

Settings:

OUTPUT Conﬁguration - DO Relay No.( ) - DO( ) Recy m____ , DO( )ON m___

AKC 25H7 Function description RC1NP402 © Danfoss 04/2005 11

Sequence for cutin and cutout of capacity

The sequence for cutin and cutout of compressor capacity can be deﬁned in two ways. Either

with a ﬁxed sequence or automatic equalisation of the operating time between the compressors.

1) Sequential cutin and cutout (Step Mode = 1)

Cutin

Cutin of compressor capacity will take place in the sequence deﬁned for the compressors. The

compressor with the lowest “DO() Dev. No.” number will be started before the compressor with the

subsequent number.

If compressors with several steps are included, all steps of one compressor will be cut in before the

next compressor is started.

If the controller has been set to control two compressor groups, cutin of the compressor capacity will

take place alternately between groups A and B, so that there will be an even distribution of capacity

between the two groups. Within the individual group cutin of compressor capacity will still take place

in the sequence deﬁned for the compressors.

Cutout

The sequence for cutout of compressor capacity will depend on the compressor type:

- Compressor with one step

Last step cut in will be the ﬁrst cut out.

- Compressors with several steps

At cutout the steps on the border between the two compressors will be reorganised. This function

sees to it that the last cut-in compressor will not stop until the previous compressor has cut out one

unloader.

- Compressor groups

If two compressor groups are used, cutout of the steps will take place alternately between group

A and group B. Within the individual group cutout of compressor capacity will follow the rules

described above.

2) Automatic equalisation (Step mode = 2):

With this setting the controller will perform an automatic operating time equalisation between

the compressors.

- The compressor with the lowest number of operating hours will be cut in ﬁrst.

- The compressor with the highest number of operating hours will be cut out ﬁrst.

Cut in Cut out

12 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

- For compressors with several steps there will be no reorganisation of the steps, as the case is for

sequential coupling. The result is that there will only be one compressor at a time with cut-out

unloaders.

- If two compressor groups are used, equalisation of the operating time will take place within each

group, but not between the groups.

Settings:

Compressor Capacity Ctrl. - Compresssor Step Control - Step Mode___

Signal from the compressor's safety controls

All digital alarm inputs (DI1 - DI8) can be used for monitoring of compressors and fans, or for the

individual inputs a third function. This third function is speciﬁc for a given input. In other words, the

use of these speciﬁc functions must be clariﬁed before inputs for the compressors (and fans) are

selected. Refer to the paragraph about special functions).

The controller must have a signal on the status of each individual compressor’s safety circuit. The

signal is taken directly from the safety circuit and connected to a digital alarm input (DI1 - DI8). The

digital alarm inputs DI1 - DI8 are all 230 V a.c. inputs.

If the compressor’s safety circuit is cut out, the controller will cut out all output relays for the

compressor in question and give alarm (for the sake of safety the safety circuit must stop the

compressor without the assistance of AKC 25H7). Regulation continues for the remaining compressors.

When a digital alarm input is mounted, the purpose must ﬁrst be deﬁned. When a compressor has to

be monitored, the setting must be “1” (i.e. “DI( )Type” =

1 for the input in question).

Then the compressor’s number must be set:

DI( )Dev. No. =

1 (Here the input will monitor compressor No. 1).

DI( )Dev. No. = 2 (Here the input will monitor compressor No. 2).

Thirdly, a time delay has to be set. The time delay counts from the time the safety circuit is cut out and

until AKC 25H7 reacts to the alarm.

Settings:

INPUTConﬁguration - Setting of Alarm input 1..8 - DI( )Type___ , DI( )Dev.No___ , DI( )Del. s___ etc.

Hourmeter

An hourmeter is attached to all relay outputs. The hourmeter registers the time the output in question

has been activated since it was last zeroset. The hourmeter range is from 0 to 30,000 hours.

Readout/Setting:

OUTPUT Conﬁguration - DO Relay No.( ) - DO( ) Time____

Forced control of compressor capacity

There can be forced control of the capacity where the normal regulation and the safety function are

disregarded. The capacity is set in per cent of the regulated capacity.

Setting:

Compressor Capacity Ctrl. - Compressor Step Control - Man.Cap___, Man Cap. %____

AKC 25H7 Function description RC1NP402 © Danfoss 04/2005 13

Peak load limitation

This function may limit the energy consumption during certain periods where the cut-in capacity

must be kept below a certain level. The level is set as a per cent of the total compressor capacity.

The limitation is active when the LOAD SHED input is shortcircuited.

This activation of the input must be performed by other controls which monitor the actual energy

consumption.

Setting:

Compressor Capacity Ctrl. - Compressor Step Control - LoadShed. %____

Accumulation of ice

The analog “AO” output will provide a 0 to 10 V signal, if the output is not used for controlling the

condenser capacity. The signal will then represent the cut-in compressor capacity (0 to 100%).

The signal may be used by other automatic controls, e.g. for controlling the accumulation of ice.

In periods where the price of electricity is low and the compressor capacity not fully utilised, for

example, other automatic controls may allow accumulation of ice.

Compressor control, - but not condenser control

The controller is normally used for controlling both the compressor and the condenser.

However,

if the controller is only used for controlling the compressor, a lack of signal to pressure transmitter

input PcA may produce the result that the alarm will sound. But the alarm function may be

cancelled by setting the alarm destination for “PcA/P0B” and “HP Max” at 0. Please refer to the

section named alarms and messages.

Settings:

Alarm destinations Sensor Alarms PcA/PoB = 0 (0= No alarm)

Other Alarms HP Max = 0 (0=No alarm)

Injection signal

Injection into the evaporator must be synchronised with the compressor operation. The injection

must start at the same time as the ﬁrst compressor starts, and it must stop at the same time as the last

compressor stops.

The DO7 and DO6 outputs have been prepared for synchronisation of the injection.

DO7 is used for compressor group A (one or two compressor groups).

DO6 is used for compressor group B (only two compressor groups).

A voltage signal is via output DO connected to either the solenoid valve or the relay activating the

injection control on an AKC 24P (or AKC 24P2).

But in those cases where the controller’s outputs are used for other functions, the signal may be

generated in other ways.

- Either directly from the compressor relay, if sequential cutin and cutout of the compressor is used.

- Or in the following way, if time equalisation is used between the compressors (when there is time

equalisation, it is not known which compressor will start ﬁrst/stop last:

All relays that start/stop the compressor must have an auxiliary switch

All auxiliary switches from the same compressor group must be connected in parallel.

Other functions belonging

to the compressor

operation

14 Function description RC1NP402 © Danfoss 04/2005 AKC 25H7

A voltage signal is via the in-parallel connected auxiliary switches connected to the solenoid valve or

to the relay activating the injection function on AKC 24P/AKC 24P2.

The outputs are deﬁned, as follows:

DO6 is set to Type = 3 (injection signal B)

DO7 is set to Type = 3 (injection signal A)

Start-up procedure

The controller contains functions ensuring a correct interaction between pumps, compressors and

injection during start-up.

Pumps

During start-up the pumps must accelerate a large amount of brine to normal ﬂow velocity, before the

compressors are allowed to start.

A time delay of 60 seconds has therefore been built into the controller, the time delay required before

the ﬁrst compressor can start.

The time can only be changed via software type AKM.

Capacity limitation

If too much compressor capacity is cut in during the start-up phase, the compressors will drop out on

low pressure. To prevent this, a time delay of 120 seconds has been placed between the ﬁrst and the

subsequent capacity step.

The time can only be changed via software type AKM.

Injection

The signals from DO6 and DO7 will not release the injection until the suction pressure has dropped to

a value which will ensure that the compressors are not overloaded. The injection will only be released

at a suction pressure corresponding to a value of 5 K above the reference value for the cold brine

temperature.

The value can only be changed via software type AKM.

Defrost

The controller can carry out central defrost of the whole cold brine circuit. When a defrost is initiated,

the compressors will stop, but the pumps will continue to circulate the cold brine.

Defrost can be stopped based on time, or when the cold brine has reached a set temperature. When

the defrost has stopped, the compressors will start again.

Relay output DO8 can be deﬁned to follow the defrost function. The output will then be activated

during the defrost:

Deﬁne relay output DO8 to follow the defrost function by means of the setting: Type = 3.

Defrost start

Defrost can be started in three ways:

1. Manual defrost

Manual defrost is started via control panel AKA 21 or a PC. The setting automatically returns to OFF

when the defrost has been completed.

Start with the setting: Man.Def. = ON

2. Signal on input DEFR

When 230 V a.c. is received on input DEFR, the defrost will start. The signal must be a pulse signal

of at least 2 sec. duration. If the external signal remains active 30 minutes after the resumption of

refrigeration, there will be an alarm. The alarm is cancelled, when the defrost signal is removed.

3. Internal time schedule

Defrost is started via a weekly programme which has been set in the controller. The times relate to

the controller’s clock function.

Use of the time schedule is deﬁned with setting: Def.Sched. = ON.

Three individual time schedules with up to four defrosts each may be programmed. Next, deﬁne

which weekdays are to follow which schedule.

Schedule 1 No. Per Day.

Def 1 Sc1 Hour

Min

Def 2 Sc1 Hour

Min

etc.

Schedule 2 No. Per Day.

Def 1 Sc2 Hour

Min

etc.

Schedule 3 No. Per Day.

Def 1 Sc3 Hour

Min

etc.

Def. Schedule Day selection Mon Sched. 1/2/3

Tue Sched. 1/2/3

etc.

Defrost stop

You may choose between two kinds of defrost stop:

1. Stop based on temperature with time as a safety factor.

The temperature of the cold brine is measured here. When the temperature is equal to the set

stop temperature, the defrost will stop, and cooling will be resumed.

You may choose whether defrost stop is to be based on the S4 or the S3 temperature.

If the defrost time exceeds the set max. defrost time, the defrost will stop. This will happen, even if

the temperature for defrost stop has not been reached. At the same time as the defrost is stopped,

the alarm message “Defrost time exceeded” will appear. The alarm will stop automatically after ﬁve

minutes.

Settings:

Defrost Control -Defrost stop Method Temp/Time____ (1= stop on temperature)

MaxDef Time___

Def.Stop °C___

DefStop Sx___

2. Stop on time

A ﬁxed defrost time is set here. When this period of time has elapsed, the defrost will stop and

cooling will be resumed.

Settings:

Defrost Control -Defrost stop Method Temp/Time____ (2 = stop on time)

MaxDefTime___

Cold side

The controller can control and monitor one or two pumps circulating the cold brine. If two pumps are

used and equalisation of operating time is selected, the controller can also alternate between the two

pumps in case of operational alarms.

Connection and deﬁnition

- Cold pump 1 must be connected to relay output DO1.

- If a cold pump 2 is connected, it must be to relay output 3.

- The outputs must be deﬁned, so that the controller knows that they are used for pumps.

DO(1 and 3, if applicable): Type is set at 3 (3 = cold pump).

Choice of pump

It is possible to choose:

- whether one of the pumps should operate

- whether both pumps should operate, or

- whether you want to alternate between the pumps (then there will be equalisation of operating

time and change-over to the other pump, if the ﬁrst one fails)

Choice of pump is carried out with the following settings:

0: both pumps are stopped

1: pump 1 put into operation

2: pump 2 put into operation

3: both pumps put into operation

4: automatic change-over between pumps allowed

Setting:

Pump Control - Pump Cold Brine - CPump Ctrl___

Automatic change-over between the pumps (only when setting = 4). With this setting the operating

times of the two pumps will automatically be equalised. Set the required working period for the

pump. When this working period has elapsed, the other pump will be started. (At start-up is is however

always pump 1 which starts).

When you change over to the other pump, the inactive pump will be started before the active pump is

stopped. Set the required overlap time.

Setting:

Pump Control - Pump Cold Brine - CPumpDel.s___

Pump Control - Pump Cycle - PumpCycl.h___

Monitoring of pumps

General

If the controller is to monitor the pump operation, the controller’s digital alarm input DI1 must be

connected to a signal from, for example, a ﬂow switch.

It has to be input DI1, as this is the only input which can be used for the cold brine pumps. If the input

is used for monitoring the pumps, the input must be deﬁned by means of setting “4” (DI1 Type = 4).

A time delay for when the alarm is to be activated must also be set. The time delay is the period of time

between the moment the input loses the signal and the controller’s alarm.

Especially where there is equalisation of operating time when

the pumps are operating with automatic equalisation of operating time, the controller will carry out

a change-over between pumps when the ﬂow is insuﬃcient (the change of pump will however not

take place until the time delay for the alarm has expired). Depending on whether the change of pump

cancels the alarm situation or not, the following will happen:

1) Change of pump will cancel the alarm situation.

If the change of pump cancels the alarm situation, the fault- less pump now operating will

keep on running until the normal cycle has ended. Now change back to the “faulty pump”,

as it must be presumed that it has been repaired. At the same time zeroset the alarm

Pump control

situation (alarm is cancelled). If the faulty pump has not been repaired, another alarm will be

released, and there will be another change-over to the faultless pump. This process will be

repeated, until the situation has been remedied.

2) Change of pump does

not cancel the alarm situation.

If the alarm however remains active after the change of pump, the controller will also give an alarm

for the other pump. At the same time, both pump outputs are activated in an attempt to create

so much ﬂow that the alarm situation will be cancelled. The controller will now have both pump

outputs activated until the alarm signal disappears.

Separate alarm priorities can be set for drop-out of one pump and for drop-out of both pumps. Please

read the section named Alarms and Messages.

Warm side

The controller can control and monitor one or two pumps circulating the warm brine. The control and

monitoring is in principle the same as mentioned in the section about cold brine, but there are a few

exceptions as regards the connections - they are, as follows:

- Hot pump 1 must be connected to relay output DO2.

- If a warm pump 2 is connected, it must be to relay output DO4.

- The outputs must be deﬁned, so that the controller knows that they are used for pumps.

DO(2 and 4, if applicable): Type set at 3 (3 = warm pump).

- If the controller is to monitor whether the warm brine pumps are operating, the controller’s

digital alarm input DI2 must be connected to a signal from, for example, a ﬂow switch.

It has to be input DI2, as this is the only input which can be used for the warm brine pumps.

Setting:

Pump Control - Pump Warm Brine - WPump Ctrl___

Pump Warm Brine - WPumpDel.s___

Pump cycle - PumpCycl.h___

General description

AKC 25H7 can control air-cooled as well as brine-cooled condensers. Capacity control can take place

with various functions, e.g. step coupling or speed control of fans and control of a by-pass valve.

During normal operation the cut-in condenser capacity will then control the cut-in condenser

capacity, so that the condensing temperature measured with S7 or with Pc sensor will correspond to

the reference temperature.

During heat recovery the cut-in condenser capacity will then control the forward ﬂow temperature

(Saux), so that the warm brine is adjusted to the actual load in the heat recovery circuit.

The condenser pressure, expressed either by Pc or S7, is monitored constantly, and it is ensured that

the pressure will not exceed the min. and max. limits (also during heat recovery).

AKC 25H7 can control and monitor two twin pumps (refer to section “Pumps”).

Control of condenser temperature

Reference

The condenser temperature is controlled by the S7 or Pc sensor, depending on the application chosen.

Control takes place according to a reference value consisting of a set value (setpoint) and a variable

contribution from an external voltage signal.

Warm Ref.°C = Warm SP°C + K3 (U warm - UrefWarm).

When K3 is an ampliﬁcation factor, U warm is the voltage signal to the controller, and the last link is the

value against which the voltage signal should be compared.

The contribution from the voltage signal is ﬁltered over a period of time, so that there will no “leaps” in

the reference.

It is possible to have the condenser temperature follow the outdoor temperature, so that it as a

minimum will always have a ﬁxed diﬀerential above the outdoor temperature (measured with Sout).

(Warm Ref°C > Sout + Min tm K).

Finally it is possible to limit the condenser temperature with absolute max. and min. limits.

A description of the settings and limitations to the references is given below.

Set value (setpoint)

Set the basic value of the reference

Setting: CondenserCapacity Ctrl. - Warm Temp. control - Warm SP°C__

Control of warm brine

temperature

Contribution from an external voltage signal

With a 0 - 10 V d.c. voltage signal on input “U WARM” the reference can be displaced by up to 50 K in

positive or negative direction. The signal can be supplied from a transmitter or another general control

unit.

Settings: Condenser Capacity Ctrl. -Warm Temp. control - K3___ , UrefWarm V___

If the function is not to be used, arrange setting K3 = 0.

Limitation of reference:

Absolute max. and min. limits

To avoid that the condenser pressure becomes too high or low, max. and min. limits can be set.

These max. and min. limits will also apply to heat recovery.

Settings: Condenser Capacity Ctrl. -Warm Temp. control - Pc/S7 Max°C___ , Pc/S7 Min°C___

In relation to the outdoor temperature

It is possible to have the condenser reference follow the outdoor temperature, so that it as a minimum

will always be a few degrees above the outdoor temperature (measured with Sout). The result is that

if the outdoor temperature rises to the reference value for the condenser temperature, the reference

value will be raised by the set value. The value could for instance be the temperature diﬀerential

according to which the condenser or brine cooler has been dimensioned.

The advantage of this function is that it permits a smaller cut-in fan capacity in the range with

partload.

The function cannot displace the reference above the set max. limit.

Settings: Condenser Capacity Ctrl. -Warm Temp. control - Min tm K___

If the function is not used, setting should be -25K.

Control of heat recovery

During normal operation the condenser temperature is controlled according to S7 or Pc. When heat

recovery is activated, the reference is changed, and the controller will now control on the basis of the

Saux sensor.

Activation of heat recovery

The heat recovery function must be activated by a signal on input DI8 (230 V a.c.). The DI8 input must

be deﬁned, so that it can be used for the heat recovery function.

Setting: INPUT Conﬁguration - Setting of Alarm input 1..8 - DI 8 Type 4 (4 = heat recovery)

Deﬁnition of output

Relay output DO11 can be deﬁned to follow the heat recovery function. The output can for instance

start a pump in the heat recovery circuit when the heat recovery function is active.

Setting: OUTPUT Conﬁguration - DO Relay No. 11 Type

3 (3= Heat recovery)

Reference

When the heat recovery function is activated, the controller changes reference sensor to Saux.

At the same time the reference value is changed, as follows:

Heat Ref°C = Warm SP°C Set setpoint

+ Dt Heat K Contribution from heat recovery function

+ K4 (Uwarm - UrefWarm) Contribution from voltage signal

+ K5 (Sout - TrefWarm°C) Contribution from outdoor temperature

The contributions from the external voltage signal and the Sout temperature are ﬁltered over a period

of time, so that there will no “leaps” in the reference.

The reference value for the heat recovery is indirectly limited inasmuch as the limitations on the

condenser temperature are also active during heat recovery.

The three contributions are the following:

- Contribution from the heat recovery function

With this function the reference can be displaced by up to 50 K in positive direction.

Setting: Condenser Capacity Ctrl. - Warm Temp. control - Dt Heat K___

- Contribution from external voltage signal

With a voltage signal of 0 - 10 V d.c. on the “Uwarm” input the reference can be displaced by up to 50

K in positive or negative direction. The signal will typically come from an overriding control

unit. Please note: it is the same voltage signal which is part of the reference for the condenser

temperature (the only diﬀerence being the constant K4). The contribution can be expressed, as

follows: K4(Uwarm - Uref warm).

Setting: Condenser Capacity Ctrl. - Warm Temp. control - K4___ , UrefWarm___

If the function is not used, set K4 to 0.

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Danfoss Controller for capacity regulation of brine Installation guide

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