Automatic Controls for Industrial Refrigeration Systems-DANFOSS

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Automatic Controls

for Industrial Refrigeration Systems

Application HandbookREFRIGERATION &

AIR CONDITIONING DIVISION

MAKING MODERN LIVING POSSIBLE



Application Handbook Automatic Controls for Industrial Refrigeration Systems

2 DKRCI.PA.000.C1.02 / 520H1623 Danfoss A/S (RA Marketing/MWA), 12 - 200 6

Contents Page

Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

2. Compressor Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

2.1Compressor Capacity Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Discharge TemperatureControl with Liquid Injection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.3 Crankcase Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.4 Reverse Flow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.6 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3. Condenser Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.1 Air Cooled Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2 Evaporative Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.3 Water Cooled Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26


4. Liquid Level Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.1 High Pressure Liquid Level Control System (HP LLRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.2 Low Pressure Liquid Level Control System (LPLLRS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35


5. Evaporator Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.1 Direct Expansion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.2 Pumped Liquid Circulation Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.3 Hot Gas Defrost for DX Air Coolers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.4 Hot Gas Defrost for Pumped Liquid Circulation Air Coolers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

5.5 Multi Temperature Changeover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5.6 Media Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50


6. Oil Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6.1 Oil cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6.2 Oil Differential Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

6.3 Oil Recovery System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61


7. Safety systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

7.1 Pressure Relief Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

7.2 Pressure and Temperature Limiting Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

7.3 Liquid Level Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

7.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68


8. Refrigerant Pump Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698.1 Pump Protection with Differential Pressure Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

8.2 Pump Bypass Flow Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

8.3 Pump Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

8.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73


9. Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

9.1 Filter Driers in Fluorinated Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

9.2 Filter Driers in CO2Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

9.3 Water Removal for Ammonia Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

9.4 Air purging systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

9.5 Heat Recovery System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85


10. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8810.1 Typical Refrigeration Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

10.2 ON/OFF and modulating controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Reference Literature - Alphabetical overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101




Danfoss A/S (RA Marketing/MWA), 12 - 200 6 DKRCI.PA.000.C1.02 / 520H1623 3

Foreword This Danfoss application guide is designedto be used as a reference document by allthose involved in the workings of industrialrefrigeration systems.

This guide aims to provide answers to the variousquestions relating to industrial refrigerationsystem control: - Why a type of control methodis necessary for the refrigeration system? Whyshould it be designed in this way? What type ofcomponents can be used? How to select controlmethods for different refrigeration systems? Inanswering these questions, the principles of thedifferent control methods are introduce followedby same control examples, comprising DanfossIndustrial Refrigeration products.

The main technical data of the components isalso provided. Finally, comparisons betweendifferent solutions for each control method are

made, so that the reader should know how toselect a solution.

In this application guide, the pilot-operated servovalve ICS is recommended as a pressure andtemperature regulator. Please note that the wellestablished PM valve could also be applied whereICS is used.

For the final design of the installation it isnecessary to use other tools, such as themanufacturers catalogues and calculationsoftware (e.g. Danfoss Industrial Refrigerationcatalogue and DIRcalc software).

DIRcalc is the software for calculation andselection of Danfoss Industrial Refrigerationvalves. DIRcalc is delivered free of charge.Please contact your local Danfoss sales company.

Please do not hesitate to contact Danfoss, ifyou have questions about control methods,application and controls described in this

application guide.





1. Introduction Refrigeration System with Pump Circulation

Oilseparator

Compressor

Condenser

Evaporator

Expansion valve 1

Oil cooler

Refrigerant pump

Receiver

Liquid separator

Oilliquid/vapour mixture of refrigerant

HP liquid refrigerant

HP vapour refrigerant LP vapour refrigerant

LP liquid refrigerant

1

2

3

5

4

6

Dan

foss

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Compressor Control

Why?

Primary: to control the suction pressure;

Secondary: reliable compressor operation(start/stop, etc.)

How?

Control the compressor capacity accordingto the refrigeration load by means ofbypassing hot gas from the HP side back intothe LP side, compressor ON/OFF step control orcontroling the rotating speed of thecompressor;

Install check valve on the discharge line inorder to prevent reverse flow of the refrigerantto the compressor;

Keep pressures and temperatures on the inletand outlet of the compressor within theworking range.

Oil control

Why?

Keep optimal oil temperature and pressurein order to guarantee reliable compressoroperation.

How?

Pressure: maintain and control the pressuredifferential across the compressor for oilcirculation, maintain the crankcase pressure(only for piston compressors);

Temperature: bypass some oil around the oilcooler; control the cooling air or water to theoil cooler;

Level: return the oil in ammonia systems andlow temperature fluorinated systems.





1. Introduction(continued) Condenser Control

Why?

Maintain the condensing pressure above the

minimum acceptable value in order toguarantee sufficient flow through theexpansion devices;

Ensure the right distribution of the refrigerantin the system.

How?

On/off operation or control the speed of thecondenser fans, control the flow of the coolingwater, flood the condensers with liquidrefrigerant.

Liquid Level Control

Why?

Provide the correct flow of liquid refrigerantfrom the high pressure side to the low pressureside according to the actual demand;

Ensure safe and reliable operation of the

expansion devices.

How?

Control the opening degree of the expansiondevice according to the change of the liquid

level.

Refrigerant Pump Control

Why? Maintain the pump running in trouble free

mode by maintaining the flow through thepump within the permissible operating range;

Maintain a constant differential pressure acrossthe pump in some systems.

How? Design a bypass loop so that the flow can be

maintained above the minimum permissibleflow;

Shut off the pump if it fails to build up enoughdifferential pressure.

Install a pressure regulating valve.

Evaporating System Control

Why? Primary: maintain a constant media

temperature; Secondary: optimise operation of the

evaporators; For direct expansion systems: guarantee

that no liquid refrigerant from the evaporatorsenters the suction line of the compressor.

How?

Change the flow rate of the refrigerant intoevaporators according to the demand;

Defrost evaporators.

Safety Systems

Why? Avoid unintended pressure of the vessels; Protect the compressor from being damaged

by liquid hammering, overloading, oil shortageand high temperature, etc;

Protect the pump from being damaged by

cavitation.

How?

Install safety relief valve on vessels and othernecessary places; Shut off the compressor and pump if the

inlet/outlet pressure or differential is out ofpermissible range;

Shut off the system of part of the system when

the level in the liquid separator or the receiverexceeds the permissible level.





2. Compressor Controls The compressor is the heart of the refrigerationsystem. It has two basic functions:1. Maintain the pressure in the evaporator so

that the liquid refrigerant can evaporate at therequired temperature;

2. Compress the refrigerant so that it can becondensed at a normal temperature.

The basic function of compressor control,therefore, is to adjust the capacity of thecompressor to the actual demand of therefrigeration system so that the requiredevaporating temperature can be maintained.

If the compressor capacity is bigger thanthe demand, the evaporating pressure andtemperature will be lower than that required, andvice versa.

Additionally, the compressor should not beallowed to operate outside of the acceptabletemperature and pressure range, in order tooptimise its running conditions.

2.1Compressor Capacity Control

The compressor in a refrigeration system isnormally selected to be able to satisfy the highestpossible cooling load. However, the cooling loadduring normal operation is usually lower than thedesign cooling load. This means that it is alwaysnecessary to control the compressor capacity sothat it matches the actual heat load. There areseveral common ways to control the compressorcapacity:

1. Step control.This means to unload cylinders in a multi-cylindercompressor, to open and close the suction portsof a screw compressor, or to start and stop somecompressors in a multi-compressor system. Thissystem is simple and convenient. Furthermore,efficiency decreases very little during part-load.It is especially applicable to systems with severalmulti-cylinder reciprocating compressors.

2. Slide valve control.The most common device used to control thecapacity of a screw compressor is the slide valve.

The action of the oil-driven slide valve allowspart of the suction gas to avoid from beingcompressed. The slide valve permits a smoothand continuous modulation of capacity from100% down to 10%, but the efficiency drops atpart load.

3. Variable speed control.Variable speed regulation. This solution isapplicable to all kinds of compressors, andis efficient. A two-speed electric motor or afrequency converter can be used to vary thespeed of the compressor. The two-speed electricmotor regulates the compressor capacity byrunning at the high speed when the heat load ishigh (e.g. cooling down period) and at the lowspeed when the heat load is low (e.g. storageperiod). The frequency converter can vary therotation speed continuously to satisfy the actualdemand. The frequency converter observeslimits for min. and max. speed, temperature andpressure control, protection of compressor motoras well as current and torque limits. Frequencyconverters offer a low start up current.

4. Hot gas bypass.This solution is applicable to compressors withfixed capacities and more typical for commercialrefrigeration. In order to control the refrigerationcapacity, part of the hot gas flow on thedischarge line is bypassed into the low pressurecircuit. This helps to decrease the refrigerationcapacity in two ways: by diminishing the supplyof liquid refrigerant and releasing some heat intothe low pressure circuit.





Application example 2.1.1:Step control of compressorcapacity

Step Controller

Pressure Transmitter

Oilseperator

SCA

EVRAT+FA

SVA

FIA

Piston compressor

AKS 33

EKC 331

Tocondenser

From liquidseparator/

evaporator

SVA

MDanfoss

Tapp_0016_02

04-2006

HP vapour refrigerantLP vapour refrigerantOil

Step control solution for compressor capacity canbe achieved by using a step controller EKC 331 .EKC 331 is a four-step controller with up to fourrelay outputs. It controls the loading/unloadingof the compressors/pistons or the electric motorof the compressor according to the suctionpressure signal from the pressure transmitter AKS33or AKS 32R. Based on a neutral zone control,EKC 331 can control a pack system with up to fourequally sized compressor steps or alternatively

two capacity controlled compressors (eachhaving one unload valve).

EKC 331T version can accept a signal from aPT 1000 temperature sensor, which may benecessary for secondary systems.

Neutral Zone ControlA neutral zone is set around the reference value,in which no loading/unloading occurs.Outside the neutral zone (in the hatched areas+zone and - zone) loading/unloading will

occur as the measure pressure deviates awayfrom the neutral zone settings.

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

For more details, please refer to the manual ofEKC 331(T) from Danfoss.

Technical data Pressure transmitter-AKS 33 Pressure transmitter-AKS 32R

Refrigerants All refrigerant including R717

Operating range [bar] 1 up to 34 1 up to 34

Max. working pressure PB [bar] Up to 55 >33

Operating temp. range [C] 40 to 85

Compensated temp. range [C] LP: 30 to +40 / HP: 0 to +80

Rated output signal 4 to 20 mA 10 to 90% of V supply





Application example 2.1.2:Compressor capacity controlby hot gas bypass

Stop valveCapacity regulator

Stop valve

From receiver

Tocondenser

EVRAT+FATEA SVASVA

EVM

CVC

ICS

SVA

SVA

SVA

EVRAT+FASVA

ICS

CVCOilseperator

Compressor

SVA

SCA

FIA

Evaporator

Danfoss

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HP vapour refrigerantHP liquid refrigerantLP vapour refrigerantLP liquid refrigerantOil

Hot gas bypass can be used to control therefrigeration capacity for compressors with fixedcapacity. The pilot-operated servo valve ICSwith a CVC pilot valve is used to control thehot gas bypass flow according to the pressureon the suction line. The CVC is a back pressure

controlled pilot valve, which opens the ICS andincreases the flow of hot gas when the suctionpressure is below the set value. In this way, thesuction pressure ahead of the compressor is keptconstant, therefore the refrigeration capacitysatisfies the actual cooling load.

Technical data Pilot-operated servo valve - ICSMaterial Body: low temp. steel

Refrigerants All common refrigerants, incl. R717 and R744

Media temp. range [C] 60 to +120

Max. working pressure [bar} 52

DN [mm] 20 to 80

Pilot valve - CVC

Material Body: stainless steel

Refrigerants All common refrigerants

Media temp. range [C] 50 to 120

Max. working pressure [bar] High pressure side: 28

Low pressure side: 17

Pressure range [bar] 0.45 to 7

Kvvalue [m3/h] 0.2





Application example 2.1.3:Compressor variable speedcapacity control

FIAFrom liquidseparator/evaporator SVA

M

AKD 5000

SVA

M

From liquidseparator/evaporator SVA

FIA

PLC/OEM

controller

VLT 5000

To oil separator

To oil separator

SVA

AK2

AKS 33

AKS 33

Danfoss

Tapp_

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08-2006

Frequency converter

Controller

Pressure transducer

HP vapour refrigerantLP vapour refrigerant

Frequency converter control offer the following

advantages:Energy savings

Improved control and product quality

Noise reduction

Longer lifetime

Simplified installation

Easy to use complete control of the system

Technical data Frequenc y conver ter AKD 2800 Frequ ency conver ter AKD500 0

Enclosure IP 20 IP 20 or IP 54

Ambient temperature

KW size 0.37kW to 18.5kW 0.75kW to 55kW

Voltage 200-240V or 380-480V 200-240V or 380-500V





2.2Discharge TemperatureControl with Liquid Injection

Compressor manufacturers generallyrecommend limiting the discharge temperaturebelow a certain value to prevent overheating ofvalues, prolonging their life and preventing thebreakdown of oil at high temperatures.

From the log p-h diagram, it can be seen that thedischarge temperature may be high when:

the compressor runs with high pressuredifferential.

the compressor receives highly superheatedsuction vapour.

the compressor runs with capacity control byhot gas bypass.

There are several ways to reduce the dischargetemperature. One way is to install water cooledheads in reciprocating compressors, anothermethod is liquid injection, by which liquidrefrigerant from the outlet of the condenser

or receiver is injected into the suction line, theintermediate cooler, or the side port of the screwcompressor.

Application example 2.2.1:Liquid injection withthermostatic injection valve

Stop valve

Solenoid valve

Thermostatic injection valve

Stop valve

Thermostat


Compressor

To oilseparator

RT 107

EVRA+FA

TEAT

SVAFrom receiver

From liquidseparator/evaporator

From oilcooler

SVA

SVA

FIA

RT 1A

RT 5A

Danfoss

Tapp_0018_02

04-2006

When the discharge temperature rises abovethe set value of the thermostat RT 107, RT 107will energise the solenoid valve EVRA whichwill start liquid injection into the side port of thescrew compressor.

The thermostatic injection valve TEATcontrols the injected liquid flow according tothe discharge temperature, which prevents thedischarge temperature from rising further.

Technical data Thermostat - RT

Refrigerants R717 and fluorinated refrigerants

Enclosure IP 66/54

Max. bulb temp. [C] 65 to 300

Ambient temp. [C] 50 to 70

Regulating range [C] 60 to 150

Differential t [C] 1.0 to 25.0

Thermostatic injection valve -

TEAT


Regulating range [C] Max. bulb temp. 150P band: 20

Max. working pressure [bar] 20

Rated Capacity* [kW] 3.3 to 274

* Conditions: Te = +5C, p = 8 bar, Tsub = 4C





Application example 2.2.2:Liquid injection with motorvalve

Stop valve

Solenoid valve

Motor valve

Stop valve

Controller

Temperature sensor


An electronic solution for liquid injection controlcan be achieved with the motorised valveICM. An AKS 21 PT 1000 temperature sensorwill register the discharge temperature andtransmit the signal to the temperature controller

EKC 361. If the temperature reaches the setvalue, the EKC 361 sends a control signal to theactuator ICAD which will adjust the openingdegree of the motor valve ICM so that thedischarge temperature is limited.

Technical data

Compressor

To oilseparator

SVA

Fromreceiver

From oilcooler

ICAD

ICMEVRA+FA

EKC 361

AKS 21

SVA


SVA

FIA

Danfoss

Tapp_0019_02

04-2006

Motor valve - ICM

Material Body: Low temperature steel

Refrigerants All common refrigerants including R717 and R744


Max. working pressure [bar] 52 bar

DN [mm] 20 to 65

Nominal Capacity* [kW] 224 to 14000

* Conditions: Te = 10C, p = 8.0 bar, Tsub = 4K

Actuator - ICAD

Material Housing: aluminium

Media temp. range [C] 30 to 50 (ambient)

Control input signal 0/4-10mA, or 0/2-10

Open-close time 3 to 13 seconds depending on valve size





Application example 2.2.3:A compact solution for liquidinjection with ICF

Valve station with:

Stop valve Filter Solenoid valve Manual opener Motor valve Stop valve

Controller

Temperature sensor

HP vapour refrigerant

HP liquid refrigerantLP vapour refrigerantLP liquid refrigerantOil

For liquid injection, Danfoss can supply a verycompact control solution ICF . Up to sixdifferent modules can be assembled into thesame housing. This solution works in the sameway as example 2.2.2, and is very compact andeasy to install.

Technical data

SVA

Compressor

To oilseparator

Fromreceiver


From oilcooler

EKC 361

AKS 21

FIA

ICFS

ICF

ICFM

ICFF

ICM ICFE ICFS

DanfossTapp_0020_02

04-2006

ICF control solution



Media temp. range [C] 60 to 120Max. working pressure [bar] 52 bar

DN [mm] 20 to 40

M





2.3Crankcase Pressure Control

During start-up or after defrost, the suctionpressure has to be controled, otherwise it canbe too high, and the compressor motor will beoverloaded.

The electric motor for the compressor may bedamaged by this overloading.

There are two ways to overcome this problem:1. Start the compressor at part load. The

capacity control methods can be used tostart compressor at part load, e.g. unload

part of the pistons for multi-pistonreciprocating compressors, or bypass somesuction gas for screw compressors with slidevalves, etc.

2. Control the crankcase pressure forreciprocating compressors. By installing aback pressure controlled regulating valve inthe suction line, which will not open untilthe pressure in the suction line drops belowthe set value, suction pressure can be keptunder a certain level.

Application example 2.3.1:Crankcase pressure control withICS and CVC

Crankcase pressure regulator

Stop valve


In order to control the crankcase pressure duringstart-up, after defrost, or in others cases whenthe suction pressure may run too high, thepilot-operated servo valve ICSwith the backpressure controlled pilot valve CVC is installedin the suction line. The ICS will not open until

the downstream suction pressure falls belowthe set value of the pilot valve CVC. In this way,the high pressure vapour in the suction linecan be released into the crankcase gradually,which ensures a manageable capacity for thecompressor.

Technical data

Tocondenser

SVA

EVRAT+FA

SVA

ICS

CVC

Oilseparator

CompressorSCA

Fromevaporator

Danfoss

Tapp_0021_02

04-2006

Pilot-operated servo valve - ICS

Material Body: low temp. steel

Refrigerants All common refrigerants, incl. R717 and R744



DN [mm] 20 to 80

Capacity* [kW] 11.4 to 470

* Conditions: Te = 10C, Tl= 30C, p = 0.2 bar, Tsub = 8K

Pilot valve - CVCMaterial Body: low temperature steel



Max. working pressure [bar] High pressure side: 28

Low pressure side: 17

Pressure range [bar] 0.45 to 7

Kvvalue [m3/h] 0.2





Application example 2.3.2:Crankcase pressure control withICS and CVP - (P > 17 bar)

Pilot-operated servo valve

Hand regulating valve


Constant pressurepilot valve

Stop valve


For refrigeration systems with a suction pressure

above 17 bar (e.g. CO2system), the pilot valveCVC can not be used. Crankcase pressure controlcan be achieved using the constant pressure pilotvalve CVP instead.

The maximum suction pressure required is set onthe pilot valve CVP. When the suction pressurereaches the set value, CVP opens. Hence thehigh pressure vapour on the servo piston of themain valve ICSis released into the suction line,the pressure over the servo piston drops, andthe valve begins to close. This will prevent thesuction pressure from rising above the set value.

After operating for some time, the compressor

will pull so much vapour from the evaporatorthat the evaporating pressure drops below thepressure set on CVP. When this has happened,CVP will close, and the main valve ICS will open.During normal operation the ICS valve will becompletely open. The manual regulating valvesREGandshown are set for an opening whichresults in a suitable opening and closing time onthe main valve.

Note:The CVH for the pilot CVP should beinstalled against the main flow direction, asshown in the diagram.

Technical data

To condenser

SVA

EVRAT+FA

SVA

CVP(HP)

Oilseparator

Compressor

SCA

Fromevaporator

CVH

REGREG

ICS

Danfoss

Tapp_0022_02

04-2006

Constant pressure pilot valve - CVPMaterial CVP (LP) Body: steel

Base: steel

CVP (HP) Body: cast iron

Base: stainless steel

CVP (XP) Body: steel

Base: steel



Max. working pressure [bar] CVP (LP): 17

CVP (HP): 28

CVP (XP): 52

Pressure range [bar] CVP (LP): 0.66 to 28

CVP (HP): 0.66 to 28

CVP (XP): 25 to 52

Kvvalue [m3/h] CVP (LP): 0.4

CVP (HP): 0.4CVP (XP): 0.45





2.4Reverse Flow Control

Reverse flow and condensation of refrigerantfrom the condenser to the oil separator andthe compressor should be avoided at all time.For piston compressors, reverse flow can resultin liquid hammering. For screw compressors,

reverse flow can cause reversed rotationand damage to the compressor bearings.

Furthermore, migration of refrigeration into theoil separator and further into the compressor atstandstill should be avoided. To avoid this reverseflow, it is necessary to install a check valve on theoutlet of the oil separator.

Application example 2.4.1:Reverse flow control

Stop check valve


The stop check valve SCAcan function as acheck valve when the system is running, and

can also shut off the discharge line for serviceas a stop valve. This combined stop/check valvesolution is easier to install and has lower flowresistance compared to a normal stop valve pluscheck valve installation.

When selecting a stop check valve, it is importantto note:1. Select a valve according to the capacity and

not the pipe size.

2. Consider both the nominal and part loadworking conditions. The velocity in the

nominal condition should be near to therecommended value, at the same timethe velocity in the part load condition shouldbe higher than the minimum recommendedvelocity.

For details on how to select valves, please refer tothe product catalogue.

Technical data

To condenser

SVA

EVRAT+FA

SVA

Oilseparator

Compressor

SCA

From

evaporator

Danfoss

Tapp_0023_02

04-2006

Stop check valve - SCA

Material Housing: special cold resistant steel approved for low temperature operation.

Spindle: polished stainless steel

Refrigerants All common non-flammable refrigerants, incl. R717.


Opening differential pressure [bar] 0.04


DN [mm] 15 to 125





Solution Application Benefits Limitations

Compressor Capacity ControlStep control of compressor

capacity with EKC 331 and

AKS 32/33

Applicable to multi-

cylinder compressor, screw

compressor with multiplesuction ports, and systems

with several compressors

running in parallel.

Simple.

Almost as efficient at part

load as at full load.

The control is not

continuous, especially when

there are only few steps.Fluctuations in the suction

pressure.

Compressor capacity controlwith hot gas bypass using

ICS and CVC PC

Applicable to compressorswith fixed capacities.

Effective to control thecapacity continuously

according to the actual

heat load.The hot gas canhelp the oil return from the

evaporator.

Not efficient at part load.Energy consuming.

Compressor variable speed

capacity control MApplicable to all

compressors with the ability

to run at reduced speed.

Low start up current

Energy savings

Lower noise

Longer lifetimeSimplified installation

AKD2800 cannot be used

for piston compressor

applications.

Compressor must be suitedfor reduced speed operation.

Discharge Temperature Control with Liquid Injection

Mechanical solution for

liquid injection with TEAT,

EVRA(T) and RT

TC

TSHL

Applicable to systems where

the discharge temperatures

may run too high.

Simple and effective. Injection of liquid refrigerant

may be dangerous to the

compressor. Not as efficientas intermediate cooler.

Electronic solution for liquidinjection control with EKC

361 and ICM

M

TC

Applicable to systems wherethe discharge temperatures

may run too high.

Flexible and compact.Possible to monitor and

control remotely.

Not applicable to flammablerefrigerants. Injection of

liquid refrigerant may

be dangerous to thecompressor. Not as efficient

as intermediate cooler.

Electronic solution for liquid

injection control with EKC

361 and ICF

Crankcase Pressure Control

Crankcase pressure control

with ICS and CVC

PC Applicable to reciprocating

compressors, normally

used for small and mediumsystems.

Simple and reliable. Effective

in protecting reciprocating

compressors at start-up orafter hot gas defrost.

Gives constant pressure

drop in the suction line.

Crankcase pressure control

with ICS and CVP

PC

Reverse Flow Control

Reverse flow control with

SCA

Applicable to all

refrigeration plants.

Simple.

Easy to install.

Low flow resistance.

Gives constant pressure

drop in the discharge line.

2.5Summary





2.6Reference Literature

For an alphabetical overview ofall reference literature please go

topage 101

To download the latest version of the literature please visit the Danfoss internet sitehttp://www.danfoss.com/BusinessAreas/RefrigerationAndAirConditioning/Products/Documentation.htm

Type Literature no.

AKD RB.8D.B

AKS 21 ED.SA0.A

AKS 32R RD.5G.J

AKS 33 RD.5G.H

CVC PD.HN0.A

CVP PD.HN0.A

EKC 331 RS.8A.G

EKC 361 RS.8A.E

EVRA(T) RD.3C.B

Type Literature no.

ICF PD.FT0.A

ICM PD.HT0.A

ICS PD.HS0.A

REG PD.KM0.A

SCA RD.7E.C

SVA PD.KD0.A

TEAT RD.1F.A

Technical Leaflet / Manual

Type Literature no.

AKD 2800 EI.R1.H

AKD 5000 EI.R1.R

AKS 21 RI.14.D

AKS 32R PI.SB0.A

AKS 33 PI.SB0.A

CVC RI.4X.L

CVP RI.4X.D

EKC 331 RI.8B.E

EKC 361 RI.8B.F

EVRA(T) RI.3D.A

Type Literature no.

ICF PI.FT0.A

ICM PI.HT0.A

ICS PI.HS0.A

REG PI.KM0.A

SCA PI.FL0.A

SVA PI.KD0.B

TEAT PI.AU0.A

Product instruction





3. Condenser Controls In areas where there are large variations inambient air temperatures and/or load conditions,it is necessary to control the condensingpressure to avoid it from falling too low. Toolow condensing pressures results in there being

insufficient pressure differential across theexpansion device and the evaporator is suppliedwith insufficient refrigerant. It means thatcondenser capacity control is mainly used in thetemperate climate zones and to a lesser degree insubtropical and tropical zones.

The basic idea of control is to control thecondenser capacity when the ambienttemperature is low, so that the condensingpressure is maintained above the minimumacceptable level.

This condensing capacity control is achievedeither by regulating the flow of circulating air orwater through the condenser, or by reducing theeffective heat exchange surface area.

Different solutions can be designed for different

types of condensers:3.1 Air cooled condensers3.2 Evaporative condensers3.3 Water cooled condensers

3.1Air Cooled Condensers

An air cooled condenser is a condenser cooled byambient air drawn from bottom to the top acrossthe heat exchange surface (tubes with fins) byaxial or centrifugal fans.

Condensing pressure control for air cooledcondensers can be achieved in the followingways:

3.1.1 - Step Control of Air Cooled Condensers

The first method was using the required numberof pressure controls in the form the Danfoss RT-5and adjusting them to different set cut-in andcut-out pressures.

The second method of controlling the fans wasby using a neutral zone pressure controller in theform of the Danfoss type RT-L. Initially it was usedtogether with a step controller with the requirednumber of contacts for the number of fans.

3.1.2 - Fan speed control of air cooled condensersThis method of condenser fan control is mainlyused whenever a reduction in noise level isdesired due to environmental concerns.

For this type of installation Danfoss frequencyconverter AKD can be used.

3.1.3 - Area control of air cooled condensers

For area or capacity control of air cooledcondensers a receiver is required. This receiver

must have sufficient volume to be able toaccommodate the variations in the amount ofrefrigerant in the condenser.

Two ways this condenser area control can bedone:1. Main valve ICS or PM combined with the

constant pressure pilot CVP(HP) mounted inthe hot gas line on the inlet side to thecondenser and ICV combined with adifferential pressure pilot CVPP(HP) mountedin the pipe between the hot gas line and thereceiver. In the pipe between the condenserand the receiver a check valve NRVA ismounted to prevent liquid migration from the

receiver to the condenser.

However this system reacted too fast and timerswere used for delaying the cut-in and cut-out ofthe fans.

The Third method is todays step controller theDanfoss EKC-331.

2. Main valve ICS combined with the constantpressure pilot CVP(HP) mounted in the pipebetween the condenser and the receiver anda ICS combined with a differential pressurepilot CVPP(HP) mounted in the pipe betweenthe hot gas line and the receiver. This methodis mainly used in commercial refrigeration.





Application example 3.1.1:Step control of fans with stepcontroller EKC 331

Step controller

Pressure transmitter

Stop valve

Stop valve

Stop valve

HP vapour refrigerantHP liquid refrigerant

EKC 331is a four-step controller with up tofour relay outputs. It controls the switching of thefans according to the condensing pressure signal

from a pressure transmitter AKS 33or AKS 32R.Based on neutral zone control, EKC 331 can control the condensing capacity so that thecondensing pressure is maintained above therequired minimum level.

For more information on neutral zone control,please refer to section 2.1.

The bypass pipe where SVAis installed isan equalizing pipe, which helps balance thepressure in the receiver with the inlet pressure ofthe condenser so that the liquid refrigerant in thecondenser can be drained into the receiver.

In some installations, EKC 331T is used. In thiscase the input signal could be from a PT 1000temperature sensor, e.g. AKS 21. The temperature

sensor is usually installed in the outlet of thecondenser.

Please note:This solution is not as accurate asthe solution with pressure transmitter, becausethe outlet temperature may not correctly reflectthe condensing pressure because of subcooling.If the subcooling is too small flash gas may occurwhen fans are starting up.

Technical data

AKS 33

EKC 331

Fromdischarge line Condenser

To expansiondevice

SFA SFA

LLG

SVA

SNV

Receiver

SNVDSV

SVASVA

SVA

Danfoss

Tapp_0031_02

04-2006

Pressure transmitter - AKS 33 Pressure transmitter - AKS 32R



Max. working pressure [bar] Up to 55 >33








Application example 3.1.2:Fan speed control of air cooledcondensers

SVA

SVA

AKS 33

SVA

AKD

Fromdischargeline

Condenser

SFV SFV

To expansiondevice

Receiver

DSV

SNV

LLG

SVADanfoss

Tapp_0141_02

08-2006

Frequency converter

Pressure transducer


Frequency converter control offer the followingadvantages:

Energy savings

Improved control and product quality

Noise reduction

Longer lifetime


Easy to use complete control of the system

Technical data

* Larger kW sizes on request

Frequenc y conver ter AKD 2800 Frequency conver ter AKD50 00

Enclosure IP 20 IP 20 or IP 54

KW size* 0.37kW to 18.5kW 0.75kW to 55kW

Voltage 200-240V or 380-480V 200-240V or 380-500V





Technical data(continued)

Constant pressure pilot valve - CVP (HP/XP)

Material CVP (HP) Body: cast iron

Base: stainless steel

CVP (XP) Body: steel

Base: steel



Max. working pressure [bar] CVP (HP): 28

CVP (XP): 52

Pressure range [bar] CVP (HP): 0.66 to 28CVP (XP): 25 to 52

Kvvalue [m3/h] CVP (HP): 0.4

CVP (XP): 0.45

Overflow valve - OFV

Material Body: steel

Refrigerants All common refrigerants, incl. R717



DN [mm] 20/25Opening differential pressure range [bar] 2 to 8

3.2Evaporative Condensers

An evaporative condenser is a condenser cooledby ambient air combined with water sprayedthrough orifices and air baffles in counter flowwith the air. The water evaporates and theevaporation effect of the water drops adds muchto the condenser capacity

Todays evaporative condensers are enclosed in asteel or plastic enclosure with axial or centrifugalfans at the bottom or at the top of the condenser.

The heat exchanger surface in the wet air streamconsists of steel pipes.Above the water spray orifices (in the dry air) it iscommon to have a de-super heater made of steelpipes with fins to reduce the hot gas temperaturebefore it reaches the heat exchanger in the wet

air stream. In this way the building up of calciumscales on the surface of the main heat exchangerpipes is greatly reduced.

This type reduces the water consumptionconsiderably compared to a normal water cooledcondenser. Capacity control of an evaporativecondenser can be achieved by either two speedfan or variable speed control of the fan andat very low ambient temperature conditions

switching off the water circulation pump.

3.2.1 - Control of Evaporative Condensers

Controlling the evaporative condenserscondensing pressure or the condenser capacitycan be achieved in different ways:

1. RT or KP pressure controls for fan and water

pump control (as it was earlier).2. RT-L neutral zone pressure control for fan and

water pump control.

3. Step controller for controlling two speed fansand the water pump.

4. Frequency converters for fan speed controland water pump control.

5. Saginomiya flow-switch for alarm if watercirculation fails.





Application example 3.2.1:Step control of evaporativecondenser with pressurecontroller RT

Suctionline

Compressor

SCA

SNVDSV

Receiver

To oilcooler

LLG

SVA SNV

To expansiondevice

SFA

SVA

SFA

SVA

RT 5A

Condenser

RT 5A

SVAWaterpump

Danfoss

Tapp_0033_02

04-2006

Pressure controller

Pressure controller

Stop valve

Stop valve

Stop valve

This solution maintains the condensingpressure, as well as the pressure in the receiverat a sufficiently high level in low ambient

temperature.

When the inlet pressure of the condenser dropsbelow the setting of the pressure controller RT5A, the controller will switch off the fan, todecrease the condensing capacity.

In extremely low ambient temperature, when thecondensing pressure drops below the setting ofRT 5Aafter all the fans have been switched off,

RT 5A

will stop the water pump.

When the pump is stopped, the condenser andthe water pipes should be drained to avoidscaling and freezing.

Technical data


HP liquid refrigerantOil

HP pressure control - RT 5A


Enclosure IP 66/54

Ambient temp. [C] 50 to 70

Regulating range [bar] RT 5A: 4 to 17


Max. test pressure [bar] 25





Application example 3.2.2:step control of evaporativecondenser with step controllerEKC331 EKC 331

AKS 33

To expansiondevice

Suctionline

LLG

To oilcooler

SVA

Receiver

SNV

SNVDSV

Compressor

SCA

SVASVA

SFA SFA

Condenser

SVAWaterpump

Danfoss

Tapp_0034_02

04-2006

Step controller


Stop valve

Stop valve

Stop valve

This solution works in the same way as example3.2.1, but operated via step controller EKC 331.For more information on EKC 331, please refer to

page 7.Step control solution for compressor capacity canbe achieved by using a step controller EKC 331 .EKC 331 is a four-step controller with up to fourrelay outputs. It controls the loading/unloadingof the compressors/pistons or the electric motorof the compressor according to the suctionpressure signal from the pressure transmitter AKS33or AKS 32R. Based on a neutral zone control,EKC 331 can control a pack system with up to fourequally sized compressor steps or alternativelytwo capacity controlled compressors (eachhaving one unload valve).

EKC 331T version can accept a signal from a

PT 1000 temperature sensor, which may benecessary for secondary systems.

Neutral Zone ControlA neutral zone is set around the reference value,in which no loading/unloading occurs.Outside the neutral zone (in the hatched areas+zone and - zone) loading/unloading willoccur as the measure pressure deviates awayfrom the neutral zone settings.


HP liquid refrigerantOil

If control 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.For more details, please refer to the manual ofEKC 331(T) from Danfoss.

Technical data Pressure transmitter-AKS 33 Pressure transmitter-AKS 32R



Max. working pressure PB [bar] Up to 55 >33








3.3Water Cooled Condensers

The water cooled condenser was originally a shelland tube heat exchanger, but today it is veryoften a plate heat exchanger of modern design(for ammonia made of stainless steel).

Water cooled condensers are not commonlyused, because in many places it is not allowedto use the large amount of water these typesconsume (water shortage and/or high prices forwater).

Today water cooled condensers are popularin chillers, with the cooling water cooled by acooling tower and re-circulated. It can also beused as a heat recovery condenser to supply hotwater.

The control of the condensing pressure can beachieved by a pressure controlled water valve,or a motorised water valve controlled by anelectronic controller to control the flow of thecooling water according to the condensingpressure.

Application example 3.3.1:Water flow control of watercooled condensers with a watervalve

Condenser

Compressor

Coolingwater out

Coolingwater in

SCA SVA

To expansiondevice

Suctionline

SVA

SNV

SFA

DSV

SFA

SNV

WVS

Danfoss

Tapp_0035_02

04-2006

Stop valve

Stop valve

Water valve

This solution maintains the condensing pressureat a constant level. The refrigerant condensingpressure is directed through a capillary tube tothe top of the water valve WVS, and adjusts theopening of WVSaccordingly. The water valveWVS is a P-regulator.

Technical data

HP vapour refrigerantHP liquid refrigerantOil

Water valve - WVS

Materials Valve body: cast ironBellows: aluminium and corrosion-proofed steel

Refrigerants R717, CFC, HCFC, HFC

Media Fresh water, neutral brine


Adjustable closing pressure [bar] 2.2 to 19

Max. working pressure on refrigerant side [bar] 26.4Max. working pressure on liquid side [bar] 10

DN [mm] 32 to 100





Application example 3.3.2:Water flow control of watercooled condensers with amotor-valve

Coolingwater in

Coolingwater out

Suctionline

Compressor

SNV

VM2

Condenser

To expansiondevice

SVA

SFA

SNV

SCA

SVA

SFA

DSV

AMV 20

AKS 33

Controller

DanfossTapp_0036_02

04-2006


Controller

Motor-valve

Stop valve

Stop valve

The controllerreceives the condensingpressure signal from the pressure transmitter AKS33, and sends out a corresponding modulatingsignal to actuator AMV 20 of the motor valveVM 2. In this way, the flow of cooling water isadjusted and the condensing pressure is keptconstant.

Technical data

HP vapour refrigerantHP liquid refrigerantOil

In this solution, PI or PID control can beconfigured in the controller.

VM 2 and VFG 2 are motor-valves designed fordistrict heating, and can also be used for waterflow control in refrigeration plants.

Motor valve - VM 2

Material Body: red bronze

Media Circulation water/ glycolic water up to 30%



DN [mm] 15 to 50

Motor valve - VFG 2

Material Body: cast iron/ductile iron/cast steel

Media Circulation water/ glycolic water up to 30%


Max. working pressure [bar] 16/25/40

DN [mm] 15 to 250





Solution Application Benefits Limitations

Air Cooled Condenser ControlStep control of fans with

step controller EKC331

Condenser

Receiver

PT

Used mainly in industrial

refrigeration in hot climatesand to a much lesser degree

in colder climates

Control of air volume in

steps or with variable fanspeed control; Energy

saving;

No use of water.

Very low ambient

temperatures; Fan stepcontrol can be noisy.

Fan speed control of air

cooled condensers

Condenser

PT

Receiver

Applicable to all condensers

with the ability to run at

reduced speed.

Low start up current

Energy savings

Lower noiseLonger lifetime


Very low ambient

temperatures;

Evaporative Condenser Control

Step control of evaporative

condenser with pressurecontroller RT

Fromdischarge line

Condenser

Receiver

PS PS

Industrial refrigeration

with very large capacityrequirement

Large reduction in water

consumption compared towater cooled condensers

and relatively easy to

capacity control; Energysaving.

Not applicable in countries

with high relative humidity;In cold climates special

precaution has to be taken

so the water pipe is drainedfor water during water pump

off periods.

Step control of evaporative

condenser with step

controller EKC331

Fromdischargeline

Receiver

Condenser

Waterpump

PT

Industrial refrigeration

with very large capacity

requirement

Large reduction in water

consumption compared to

water cooled condensersand relatively easy to

capacity control; Possible

to control remotely. Energy

saving.

Not applicable in countries

with high relative humidity;

In cold climates specialprecaution has to be taken

so the water pipe is drained

for water during water pump

off periods.

Water Cooled Condenser Control

Liquid flow control with awater valve

Condenser

Compressor

Coolingwater in

Coolingwater out

PCChillers, heat recoverycondensers

It is easy to capacity control Not applicable when wateravailability is a problem.

Liquid flow control with a

motor valveCoolingwater in

Coolingwater out

Compressor

Condenser

M

PT

PC Chillers, heat recovery

condensers

It is easy to capacity control

the condenser and the heat

recovery; Possible to controlremotely.

This type of installation

is more expensive than

a normal set up; Notapplicable when water

availability is a problem.

3.4Summary

3.5Reference Literature

For an alphabetical overview ofall reference literature please gotopage 101

Type Literature no.

AKD RB.8D.B

AKS 21 ED.SA0.A

AKS 32R RD.5G.J

AKS 33 RD.5G.H

AMV 20 ED.95.N

CVPP PD.HN0.A

CVP PD.HN0.A

Type Literature no.

ICS PD.HS0.A

NRVA RD.6H.A

RT 5A RD.5B.A

SVA PD.KD0.A

VM 2 ED.97.K

WVS RD.4C.A

Technical Leaflet / Manual

Type Literature no.

AKD 2800 EI.R1.H

AKD 5000 EI.R1.R

AKS 21 RI.14.D

AKS 32R PI.SB0.A

AKS 33 PI.SB0.A

AMV 20 EI.96.A

CVPP RI.4X.D

CVP RI.4X.D

Type Literature no.

ICS PI.HS0.A

NRVA RI.6H.B

RT 5A RI.5B.C

SVA PI.KD0.B

VM 2 VI.HB.C

WVS RI.4C.B

Product instruction

To download the latest version of the literature please visit the Danfoss internet sitehttp://www.danfoss.com/BusinessAreas/RefrigerationAndAirConditioning/Products/Documentation.htm





4. Liquid Level Control Liquid level control is an important element inthe designing of industrial refrigeration systems.It controls the liquid injection to maintain aconstant liquid level.

Two main different principles may be used whendesigning a liquid level control system:

High pressure liquid level control system (HPLLRS)

Low pressure liquid level control system (LPLLRS)

High pressure liquid level control systems aretypically characterised by:1. Focus on the liquid level on the condensing

side of the system2. Critical refrigerant charge3. Small receiver or even no receiver4. Applies mainly to chiller units and other

systems with small refrigerant charge (forexample, small freezers)

Low pressure systems are typicallycharacterized by:1. Focus on the liquid level on the evaporating

side of the system2. Receiver is usually big

3. Large (enough) charge of refrigerant4. Mainly applied to de-centralized systems

Both principles can be achieved, usingmechanical and electronic components

4.1High Pressure Liquid LevelControl System (HP LLRS)

When designing a HP LLRS, the following pointshave to be taken into consideration:

As soon as liquid is formed in the condenser theliquid is fed to the evaporator (low pressure side).

The liquid leaving the condenser will have littleor no sub-cooling. This is important to considerwhen the liquid flows to the low pressure side.If there is pressure loss in the piping or thecomponents, flash-gas may occur and cause the

flow capacity to be reduced.

The refrigerant charge must be preciselycalculated in order to ensure that thereis adequate refrigerant in the system. Anovercharge increases the risk of flooding theevaporator or the liquid separator causingliquid carry over into the compressor (liquid

hammering). If the system is undercharged theevaporator will be starved. The size of the lowpressure vessel (liquid separator/ shell-tubeevaporator) must be carefully designed sothat it can accommodate the refrigerant in allconditions without causing liquid hammering.

Because of the above reasons, HP LLRS areespecially suitable for systems requiring smallrefrigerant charge, like chiller units, or smallfreezers. Chiller units usually do not need

receivers. Even if a receiver is necessary in orderto install pilots and provide feed refrigerant to anoil cooler, the receiver could be small.





Application example 4.1.1:Mechanical solution for HPliquid level control

Stop valve

Filter

Servo-operated main valve

Stop valve

Float valve

Stop valve

Stop valve

On large HP LLRS the SV1or SV3 float valve isused as a pilot valve for a PMFHmain valve.As illustrated above, when the liquid level in thereceiver rises above the set level, the SV1 floatvalve provides a signal to the PMFH main valveto open.

Technical data

FIASVASVA

To seperatorTo oilcooler

From condenser

EVM

PMFH

SNV

SV1

SVA

SNV

DSV

LLGReceiver

SVASVA

SFASFA

SVA

SVA

Fromdischargeline

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HP vapour refrigerantHP liquid refrigerantLP liquid refrigerant

PMFH 80 - 1 to 500

Material Low temp. spherical cast iron

Refrigerants R717, HFC, HCFC and CFC

Media temp. range [C] 60 to + 120


Max test pressure [bar] 42

Rated capacity* [kW] 139-13900

* Conditions: R717, +5/32C, T l = 28C

* Conditions: R717, +5/32C, T l = 28C

Float valve - SV 1 and SV3

Material Housing: steelCover: low temperature cast iron

Float: stainless steel


Media temp. range [C] 50 to + 65

P-band [mm] 35



Kvvalue [m3

/h] 0.06 for SV 10.14 for SV 3

Rated capacity* [kW] SV1: 25SV3: 64





Application example 4.1.2:Mechanical solution for HPliquid level control with HFI

HFI

To liquidseperator

Fromcompressor

Cooling water out

Cooling water in

Plate type condenser

Purge pipe (option 1)

Purge pipe(option 2)

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HP float valve

If the condenser is a plate heat exchanger, themechanical float valve HFIcan be used tocontrol the liquid level.

The HFI is a direct acting high pressure floatvalve; therefore no differential pressure isrequired to activate the valve

Technical data

* Conditions: R717, 10/35C


LP liquid refrigerantOil

In certain cases it may be necessary to connectthe purge pipe to the HP/LP (option 1/option 2)side, as indicated on the drawing. This solutionenables reaching the required capacity when HFIis placed remotely from the condenser.

HFI

Material Special steel approved for low temperature application

Refrigerants R717 and other non- flammable refrigerant. For the refrigerants with density greater than 700kg/m 3,please consult Danfoss.


Max. working pressure [bar] 25 bar

Max test pressure [bar] 50 bar (without float)

Rated capacity* [kW] 400 to 2400





Application example 4.1.3:Electronic solution for HP liquidlevel control

FIA SVASVA

To seperator

To oil

cooler

SNV

SVA

SNV

SFA

DSV

SFA

LLGReceiver

SVASVA

EKC 347

ICAD

ICM

SVA

SVA

AKS 41

From condenser

Fromdischargeline

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Stop valve

Filter

Motor valve

Stop valve

Controller

Level transmitter

Stop valve

Stop valve

When designing an electronic LLRS solution theliquid level signal can be given either by an AKS38 which is a level switch (ON/OFF) or an AKS 41which is a level transmitter (4-20 mA).

The electronic signal is sent to an EKC 347electronic controller which controls the injectionvalve.

The liquid injection can be controled in severaldifferent ways:

With a modulating motor valve type ICM with

an ICAD actuator.

With a pulse-width-modulating expansionvalve type AKVA. The AKVA valve should beused only where the pulsation from the valveis acceptable.

Technical data

HP vapour refrigerantHP liquid refrigerantLP liquid refrigerant

* Conditions: R717, Te= 10C, p = 8.0 bar, Tsub= 4K;

With a regulating valve REG acting as anexpansion valve and an EVRA solenoid valveto implement ON/OFF control.

The system illustrated is an AKS 41leveltransmitter which sends a level signal to anEKC 347liquid level controller. The ICMmotor valve acts as an expansion valve.

Motor valve - ICM





DN [mm] 20 to 80

Nominal capacity* [kW] 224 to 14000

Level transmitter - AKS 41

Material Thread and pipe: stainless steel

Top part: cast aluminium

Refrigerants R717, R22, R404a, R134a, R718, R744



Measuring range [mm] 207 to 2927





4.2Low Pressure LiquidLevel Control System (LPLLRS)

When designing a LP LLRS, the following pointshave to be taken into consideration:

The liquid level in the low pressure vessel (liquidseparator/ shell-tube evaporator) is maintained at

a constant level. This is safe to the system, sincea too high liquid level in the liquid separatormay cause liquid hammering to the compressor,and a too low level may lead to cavitation of therefrigerant pumps in a pump circulation system.

The receiver must be big enough to accumulatethe liquid refrigerant coming from theevaporators when the content of refrigerant insome evaporators vary with the cooling load,some evaporators are shut off for service, or partof the evaporators are drained for defrosting.

As a result of the above, LP LLRS are especiallysuitable for de-centralised systems in whichthere are many evaporators, and the refrigerantcharge is large, like cold stores. With LP LLRS,these systems could run safely even though the

refrigerant charge is impossible to be preciselycalculated.

In conclusion, HP LLRS are suitable for compactsystems like chillers; the advantage is the reducedcost (small receiver or no receiver). While LP LLRSare very suitable for de-centralised systems withmany evaporators and long piping, like a largecold storage; the advantage being the highersafety and reliability.

Application example 4.2.1:Mechanical solution for LP

liquid level control

FIASVA

Fromreceiver

AKS 38

AKS 38

SNV

SVASNV

DSV

LiquidSeparator

Tocompressorsuction line

From evaporator

To evaporator

LLG

SVA

SVA

SVA

EVM

ICS1

SVA

SFASFASVA

SVA

SVA

SV4

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Stop valve

Filter

Solenoid valve

LP float valve

Stop valve

Stop valve

SV float valves monitor the liquid level in lowpressure vessels. If the capacity is small the SV valves can directly act as an expansion valve inthe low pressure vessel as shown.

Technical data

HP liquid refrigerantLiquid/vapour mixtureof refrigerantLP vapour refrigerantLP liquid refrigerant

SV 4-6

Material Housing: steelCover: low temperature cast iron(spherical)

Float: stainless steel



P-band [mm] 35



Kvvalue [m3/h] 0.23 for SV 4

0.31 for SV 5

0.43 for SV 6

Rated capacity* [kW] SV4: 102

SV5: 138

SV6: 186

* Conditions: R717, +5/32C, Tsub= 4K.





Application example 4.2.2:Mechanical solution for LPliquid level control

AKS 38

AKS 38

SNV

SV4

SVASNV

DSV

LiquidSeparatorLLG

SVA

SVA

SVA

SVA

SFASFA

SVA

SVA

FIAPMFL

EVM

SVA

SVA


SVA

Fromreceiver

Fromevaporator

To evaporatorQDV

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Stop valve

Filter

Servo-operated main valve

Stop valve

LP float valve

Stop valve

Stop valve

If the capacity is large, the float valve SVisused as a pilot valve for the PMFL main valve.As illustrated above, when the liquid level in thereceiver falls below the set level, the float valveSVprovides a signal to the PMFL value to open.

Technical data



PMFL 80 - 1 to 500

Material Low temp. spherical cast iron




Max test pressure [bar] 42Rated capacity* [kW] 139-13,900

Application example 4.2.3:Electronic solution for LP liquidlevel control

AKS 38

SNV

SVA

DSV

LiquidSeparator

From evaporator

LLG

SFASFA

ICSFIA

EVM

EKC 347AKS 41

SVA

SVA

SVA SVA

SVA

SVA

SVA

SNV

ICAD

ICM

Fromreceiver


To evaporator QDVDanfoss

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Stop valve

Filter

Solenoid valve

Motor valve

Stop valve

Controller

Level transmitter

Level switch

The level transmitter AKS 41, monitors the

liquid level in the separator and sends a levelsignal to the liquid level controller EKC 347,which sends a modulating signal to the actuatorof the motor valve ICM. The ICM motor valveacts as an expansion valve.

HP liquid refrigerantLiquid/vapour mixtureof refrigerantLP vapour refrigerant

LP liquid refrigerant

The liquid level controller EKC 347also

provides relay outputs for upper and lower limitsand for alarm level. However, it is recommendedthat a level switch AKS 38is fitted as a highlevel cut out.






AKS 38

SNV

SVA

DSV

LiquidSeparatorLLG

SFASFA

AKVAICS1

FIA

EVM

EKC 347

AKS 41

SVA

SVA

SVA

SVA

SVA

SVA

SVA

SNV


Fromreceiver

To evaporator

From evaporator

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Stop valve

Filter

Solenoid valve

Electronically operatedexpansion valve

Stop valve

Controller

Level transmitter

This solution is similar to solution 4.2.3. However,with this example the motor valve ICM isreplaced by a pulse width electronically operatedexpansion valve AKVA. The servo valve ICS isbeing used as an additional solenoid valve toensure 100% closure during off cycles.

Technical data

HP liquid refrigerant

Liquid/vapour mixtureof refrigerantLP vapour refrigerantLP liquid refrigerant



AKS 38

SNV

SVA

DSV

LiquidSeparatorLLG

SFASFA

AKS 41

SVA

SVA

SVA

SVA

SVA

SNV


To evaporator

From evaporator

EKC 347

ICFS

ICM

ICF

ICFM

ICFE

ICFF

ICFS

From receiver

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ICF valve station including:

Stop valve

Filter Solenoid valve Manual opener Motor valve Stop valve

Controller

Level transmitterDanfoss can supply a very compact valve

solution ICF. Up to six different modules can beassembled into the same housing, which is easyto install.


The module ICM acts as an expansion valve and

the module ICFE is a solenoid valve.This solution works in an identical manner toexample 4.2.3. ICF solution similar to example4.2.4 is also available. Please refer to ICF literaturefor further information.

The liquid level controller EKC 347alsoprovides relay outputs for upper and lower limitsand for alarm level. However, it is recommendedthat a level switch AKS 38 is fitted as a high levelcut out.

AKVA

Material AKVA 10: stainless steelAKVA 15: cast iron

AKVA 20: cast iron

Refrigerants R717

Media temp. range [C] AKVA 10: 50 to +60

AKVA 15/20: 40 to +60

Max. working pressure [bar] 42DN [mm] 10 to 50

Nominal capacity* [kW] 4 to 3150

M






AKS 38

SNV

SVA

DSV

LiquidSeparator

LLG

SFASFA

SVA

SVA

SVA

SVA

SVA

SNV


To evaporator

From evaporator

Fromreceiver

REG

SVA SVA

EVRA+FA

AKS 38

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AKS 38

Stop valve

Solenoid valve


Stop valve

Level switch

This solution controls the liquid injection usingon/off control. The level switch AKS 38 , controlsthe switching of the solenoid valve EVRA , inaccordance with liquid level in the separator.

The hand regulating valve REGacts as theexpansion valve.

Technical data


AKS 38

Material Housing: zinc chromate cast iron

Refrigerants All common non-flammable refrigerants, including R717.


Max. working pressure [bar] 28Measuring range [mm] 12.5 to 50

REG

Material Special cold resistant steel approved for low temperature operation

Refrigerants All common non-flammable refrigerants, including R717.



Test pressure [bar] Strength test: 80Leakage test: 40

Kvvalue [m3/h] 0.17 to 81.4 for fully open valves

EVRA

Refrigerants R717, R22, R134a, R404a, R410a, R744, R502



Rated capacity* [kW] 21.8 to 2368

Kvvalue [m3/h] 0.23 to 25.0

* Conditions: R717, 10/+25C, p = 0.15 bar





Solution Application Benefits LimitationsHigh pressure mechanical

solution:SV1/3 + PMFH

Receiver

Applicable to systems with

small refrigerant charges,like chillers.

Pure mechanical.

Wide capacity range.

Unable to control remotely,

the distance between SVand PMFH is limited to

several meters.

A little bit slow in response.

High pressure mechanical

solution:

HFI Plate typecondenser

Applicable to systems

with small refrigerant

charges and with plate type

condensers only.

Pure mechanical.

Simple solution.

Especially suitable for plate

heat exchanger

Unable to provide

thermosyphon oil cooling.

High pressure electronic

solution:

AKS 41+EKC 347 + ICM Receiver

M

LC

LT Applicable to systems with

small refrigerant charges,

like chillers.

Flexible and compact.

Possible to monitor and

control remotely.

Covers a wide range of

capacity.

Not allowed for flammable

refrigerant.

Low pressure mechanical

solution:

SV4-6Liquid separator

Applicable to small systems. Pure mechanical.

Simple, low cost solution.

Limited capacity.

Low pressure mechanical

solution:

SV 4-6 + PMFLLiquid separator

Particularly applicable to

de-central systems, like cold

stores.

Pure mechanical.

Wide c

Automatic Controls for Industrial Refrigeration Systems-DANFOSS

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