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Automatic Controls
for Industrial Refrigeration Systems
Application HandbookREFRIGERATION &
AIR CONDITIONING DIVISION
MAKING MODERN LIVING POSSIBLE
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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
3.5 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
4.4 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
5.8 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
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
6.5 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
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
7.5 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
8.5 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
9.6 Reference Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
10. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8810.1 Typical Refrigeration Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
10.2 ON/OFF and modulating controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Reference Literature - Alphabetical overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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.
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
Tap
p_
0015_
02
04-2006
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.
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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.
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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.
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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
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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
Tapp_
0017_
02
04-2006
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
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
Danfoss A/S (RA Marketing/MWA), 12 - 200 6 DKRCI.PA.000.C1.02 / 520H1623 9
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_
0139_
02
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
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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
HP vapour refrigerantHP liquid refrigerantLP vapour refrigerantLP liquid refrigerantOil
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
Refrigerants R717 and fluorinated refrigerants
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
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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Application example 2.2.2:Liquid injection with motorvalve
Stop valve
Solenoid valve
Motor valve
Stop valve
Controller
Temperature sensor
HP vapour refrigerantHP liquid refrigerantLP vapour refrigerantLP liquid refrigerantOil
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
From liquidseparator/evaporator
SVA
FIA
Danfoss
Tapp_0019_02
04-2006
Motor valve - ICM
Material Body: Low temperature steel
Refrigerants All common refrigerants including R717 and R744
Media temp. range [C] 60 to 120
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
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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 liquidseparator/evaporator
From oilcooler
EKC 361
AKS 21
FIA
ICFS
ICF
ICFM
ICFF
ICM ICFE ICFS
DanfossTapp_0020_02
04-2006
ICF control solution
Material Body: Low temperature steel
Refrigerants All common refrigerants including R717 and R744
Media temp. range [C] 60 to 120Max. working pressure [bar] 52 bar
DN [mm] 20 to 40
M
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
HP vapour refrigerantLP vapour refrigerantOil
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
Media temp. range [C] 60 to +120
Max. working pressure [bar] 52
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
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
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Application example 2.3.2:Crankcase pressure control withICS and CVP - (P > 17 bar)
Pilot-operated servo valve
Hand regulating valve
Hand regulating valve
Constant pressurepilot valve
Stop valve
HP vapour refrigerantLP vapour refrigerantOil
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
Refrigerants All common refrigerants
Media temp. range [C] 50 to 120
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
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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
HP vapour refrigerantLP vapour refrigerantOil
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.
Media temp. range [C] 60 to 150
Opening differential pressure [bar] 0.04
Max. working pressure [bar] 40
DN [mm] 15 to 125
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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
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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
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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.
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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
Refrigerants All refrigerant including R717
Operating range [bar] 1 up to 34 1 up to 34
Max. working pressure [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
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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
HP vapour refrigerantHP liquid refrigerant
Frequency converter control offer the followingadvantages:
Energy savings
Improved control and product quality
Noise reduction
Longer lifetime
Simplified installation
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
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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
Refrigerants All common refrigerants
Media temp. range [C] 50 to 120
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
Media temp. range [C] 50 to 150
Max. working pressure [bar] 40
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.
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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 vapour refrigerant
HP liquid refrigerantOil
HP pressure control - RT 5A
Refrigerants R717 and fluorinated refrigerants
Enclosure IP 66/54
Ambient temp. [C] 50 to 70
Regulating range [bar] RT 5A: 4 to 17
Max. working pressure [bar] 22
Max. test pressure [bar] 25
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
Pressure transmitter
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 vapour refrigerant
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
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
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
Media temp. range [C] 25 to 90
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
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
Pressure transmitter
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%
Media temp. range [C] 2 to 150
Max. working pressure [bar] 25
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%
Media temp. range [C] 2 to 200
Max. working pressure [bar] 16/25/40
DN [mm] 15 to 250
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
Simplified installation
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
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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.
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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
Danfoss
Tapp_
0044_
02
04-2006
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. working pressure [bar] 28
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
Refrigerants R717, HFC, HCFC and CFC
Media temp. range [C] 50 to + 65
P-band [mm] 35
Max. working pressure [bar] 28
Max test pressure [bar] 36
Kvvalue [m3
/h] 0.06 for SV 10.14 for SV 3
Rated capacity* [kW] SV1: 25SV3: 64
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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)
Danfoss
Tapp_0045_02
08-2006
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
HP vapour refrigerantHP liquid refrigerant
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.
Media temp. range [C] 50 to 80
Max. working pressure [bar] 25 bar
Max test pressure [bar] 50 bar (without float)
Rated capacity* [kW] 400 to 2400
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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
Danfoss
Tapp_
0046_
02
04-2006
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
Material Body: Low temperature steel
Refrigerants All common refrigerants including R717 and R744
Media temp. range [C] 60 to 120
Max. working pressure [bar] 52
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
Media temp. range [C] 60 to 100
Max. working pressure [bar] 60
Measuring range [mm] 207 to 2927
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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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
QDVDanfoss
Tapp_0047_02
04-2006
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
Refrigerants R717, HFC, HCFC and CFC
Media temp. range [C] 50 to +120
P-band [mm] 35
Max. working pressure [bar] 28
Max test pressure [bar] 42
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.
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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
Tocompressorsuction line
SVA
Fromreceiver
Fromevaporator
To evaporatorQDV
Danfoss
Tapp_0048_02
04-2006
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
HP liquid refrigerantLiquid/vapour mixtureof refrigerantLP vapour refrigerantLP liquid refrigerant
* Conditions: R717, +5/32C, Tsub= 4K.
PMFL 80 - 1 to 500
Material Low temp. spherical cast iron
Refrigerants R717, HFC, HCFC and CFC
Media temp. range [C] 60 to +120
Max. working pressure [bar] 28
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
Tocompressorsuction line
To evaporator QDVDanfoss
Tapp_0049_02
04-2006
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.
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Application Handbook Automatic Controls for Industrial Refrigeration Systems
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Application example 4.2.4:Electronic solution for LP liquidlevel control
AKS 38
SNV
SVA
DSV
LiquidSeparatorLLG
SFASFA
AKVAICS1
FIA
EVM
EKC 347
AKS 41
SVA
SVA
SVA
SVA
SVA
SVA
SVA
SNV
Tocompressorsuction line
Fromreceiver
To evaporator
From evaporator
QDVDanfoss
Tapp_0050_02
04-2006
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
* Conditions: R717, +5/32C, Tsub= 4K.
Application example 4.2.5:Electronic solution for LP liquidlevel control
AKS 38
SNV
SVA
DSV
LiquidSeparatorLLG
SFASFA
AKS 41
SVA
SVA
SVA
SVA
SVA
SNV
Tocompressorsuction line
To evaporator
From evaporator
EKC 347
ICFS
ICM
ICF
ICFM
ICFE
ICFF
ICFS
From receiver
QDVDanfoss
Tapp_0051_02
04-2006
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.
HP liquid refrigerantLiquid/vapour mixtureof refrigerantLP vapour refrigerantLP liquid refrigerant
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
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Application example 4.2.6:Electronic solution for LP liquidlevel control
AKS 38
SNV
SVA
DSV
LiquidSeparator
LLG
SFASFA
SVA
SVA
SVA
SVA
SVA
SNV
Tocompressorsuction line
To evaporator
From evaporator
Fromreceiver
REG
SVA SVA
EVRA+FA
AKS 38
QDVDanfoss
Tapp_0052_0204-2006
AKS 38
Stop valve
Solenoid valve
Hand regulating 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
HP liquid refrigerantLiquid/vapour mixtureof refrigerantLP vapour refrigerantLP liquid refrigerant
AKS 38
Material Housing: zinc chromate cast iron
Refrigerants All common non-flammable refrigerants, including R717.
Media temp. range [C] 50 to +65
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.
Media temp. range [C] 50 to +150
Max. working pressure [bar] 40
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
Media temp. range [C] 40 to +105
Max. working pressure [bar] 42
Rated capacity* [kW] 21.8 to 2368
Kvvalue [m3/h] 0.23 to 25.0
* Conditions: R717, 10/+25C, p = 0.15 bar
5/21/2018 Automatic Controls for Industrial Refrigeration Systems-DANFOSS - slidepdf...
http:///reader/full/automatic-controls-for-industrial-refrigeration-systems-
Application Handbook Automatic Controls for Industrial Refrigeration Systems
Danfoss A/S (RA Marketing/MWA), 12 - 200 6 DKRCI.PA.000.C1.02 / 520H1623 35
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
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