Danfoss Application Handbook - Automatic Controls for Industrial Refrigeration Systems Mode d'emploi

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Application Handbook
Industrial Refrigeration
Ammonia and CO
2
applications
MAKING MODERN LIVING POSSIBLE
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 1
Contents Page
Foreword.......................................................................................................... 3
1. Introduction .................................................................................................... 4
2. Compressor Controls ............................................................................................ 6
2.1 Compressor Capacity Control .............................................................................. 6
2.2 Discharge Temperature - Control with Liquid Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Crankcase Pressure Control ...............................................................................13
2.4 Reverse Flow Control .....................................................................................14
2.5 Summary.................................................................................................15
2.6 Reference Documents ....................................................................................16
3. Condenser Controls ............................................................................................17
3.1 Air Cooled Condensers....................................................................................17
3.2 Evaporative Condensers ..................................................................................22
3.3 Water Cooled Condensers.................................................................................25
3.4 Summary.................................................................................................27
3.5 Reference Documents ....................................................................................27
4. Liquid Level Control ............................................................................................28
4.1 High Pressure Liquid Level Control System (HP LLRS).......................................................28
4.2 Low Pressure Liquid Level Control System (LP LLRS)........................................................32
4.3 Summary.................................................................................................36
4.4 Reference Documents ....................................................................................36
5. Evaporator Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.1 Direct Expansion Control..................................................................................37
5.2 Pumped Liquid Circulation Control ........................................................................42
5.3 Hot Gas Defrost for DX Air Coolers.........................................................................45
5.4 Hot Gas Defrost for Pumped Liquid Circulation Air Coolers .................................................51
5.5 Multi Temperature Changeover ...........................................................................54
5.6 Media Temperature Control ...............................................................................55
5.7 Summary.................................................................................................57
5.8 Reference Documents ....................................................................................58
6. Oil Systems ....................................................................................................59
6.1 Oil cooling ...............................................................................................59
6.2 Oil Dierential Pressure Control ...........................................................................63
6.3 Oil Recovery System ......................................................................................66
6.4 Summary.................................................................................................68
6.5 Reference Documents ....................................................................................69
7. Safety systems .................................................................................................70
7.1 Pressure Relief Devices....................................................................................70
7.2 Pressure and Temperature Limiting Devices ...............................................................74
7.3 Liquid Level Devices ......................................................................................75
7.4 Refrigerant detector ......................................................................................76
7.5 Summary.................................................................................................78
7.6 Reference Documents ....................................................................................78
8. Refrigerant Pump Controls .....................................................................................79
8.1 Pump Protection with Dierential Pressure Control ........................................................79
8.2 Pump Bypass Flow Control................................................................................81
8.3 Pump Pressure Control....................................................................................82
8.4 Summary.................................................................................................83
8.5 Reference Documents ....................................................................................83
9. Others .........................................................................................................84
9.1 Filter Driers in Fluorinated Systems ........................................................................84
9.2 Water Removal for Ammonia Systems .....................................................................86
9.3 Air purging systems.......................................................................................90
9.4 Heat Recovery System ....................................................................................92
9.5 Reference Documents ....................................................................................94
10. Using CO
2
in refrigeration systems .............................................................................95
10.1 CO
2
as a refrigerant ......................................................................................96
10.2 CO
2
as a refrigerant in industrial systems..................................................................97
10.3 Design pressure .........................................................................................99
10.4 Safety ..................................................................................................101
10.5 Eciency ..............................................................................................102
10.6 Oil in CO
2
systems ......................................................................................102
10.7 Comparison of component requirements in CO
2
, ammonia and R134a systems ...........................104
10.8 Water in CO
2
Systems ...................................................................................106
10.9 Removing water........................................................................................109
10.10 How does water enter a CO
2
system? ...................................................................113
10.11 Miscellaneous features to be taken into consideration in CO
2
refrigeration systems ......................114
11. Pumped CO
2
in Industrial Refrigeration Systems...............................................................117
12. Control methods for CO
2
systems .............................................................................127
13. Design of a CO
2
sub-critical installation .......................................................................128
13.1 Electronic solution for liquid level control ...............................................................128
13.2 Hot Gas Defrost for Pumped Liquid Circulation Air Coolers ...............................................129
13.2 Hot Gas Defrost for Pumped Liquid Circulation Air Coolers ...............................................130
14. Filter Driers in CO
2
Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
15. Danfoss sub-critical CO
2
components.........................................................................132
16. Full range of stainless steel products .........................................................................134
17. Appendix ....................................................................................................136
Reference Documents - Alphabetical overview...................................................................149
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 3
Foreword
This Danfoss application guide is designed
to be used as a reference document by all
those involved in the workings of industrial
refrigeration systems.
This guide aims to provide answers to the various
questions relating to industrial refrigeration
system control: - Why a type of control method
is necessary for the refrigeration system? Why
should it be designed in this way? What type of
components can be used? How to select control
methods for dierent refrigeration systems? In
answering these questions, the principles of the
dierent control methods are introduce followed
by same control examples, comprising Danfoss
Industrial Refrigeration products.
The main technical data of the components is
also provided. Finally, comparisons between
dierent solutions for each control method are
made, so that the reader should know how to
select a solution.
In this application guide, the pilot-operated servo
valve ICS is recommended as a pressure and
temperature regulator. Please note that the well
established PM valve could also be applied where
ICS is used.
The application guide is designed to be used
as a reference document. The guide aims to
provide answers to the various questions relating
to industrial refrigeration system control and
in answering these questions, the principles of
the dierent control methods are introduced
followed by some control examples, comprising
Danfoss Industrial Refrigeration products. It
is non capacity and performance related and
operating parameters of each application should
be considered accordingly before adopting any
particular layout.
Not all valves are shown and the application
drawings are not to be used for construction
purposes.
For the nal design of the installation it is
necessary to use other tools, such as the
manufacturers catalogues and calculation
software (e.g. Danfoss Industrial Refrigeration
catalogue and DIRcalc software).
DIRcalc is the software for calculation and
selection of Danfoss Industrial Refrigeration
valves. DIRcalc is delivered free of charge.
Please contact your local Danfoss sales company.
Please do not hesitate to contact Danfoss, if
you have questions about control methods,
application and controls described in this
application guide.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
4 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
1. Introduction
Refrigeration System with Pump Circulation
Danfoss
Tapp_0015_02
10-2012
À
Compressor Control
Why?
Primary: to control the suction pressure;
Secondary: reliable compressor operation
(start/stop, etc.)
How?
Control the compressor capacity according
to the refrigeration load by means of
bypassing hot gas from the HP side back into
the LP side, compressor ON/OFF step control or
controling the rotating speed of the
compressor;
Install check valve on the discharge line in
order to prevent reverse ow of the refrigerant
to the compressor;
Keep pressures and temperatures on the inlet
and outlet of the compressor within the
working range.
Á
Oil control
Why?
Keep optimal oil temperature and pressure
in order to guarantee reliable compressor
operation.
How?
Pressure: maintain and control the pressure
dierential across the compressor for oil
circulation, maintain the crankcase pressure
(only for piston compressors);
Temperature: bypass some oil around the oil
cooler; control the cooling air or water to the
oil cooler;
Level: return the oil in ammonia systems and
low temperature uorinated systems.
Oil
separator
Oil cooler
Condenser
Receiver
Liquid separator
Expansion
valve 1
Refrigerant pump
Evaporator
LP vapour refrigerant
LP liquid refrigerant
Oil
HP vapour refrigerant
HP liquid refrigerant
Liquid/vapour mixture of refrigerant
Compressor
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 5
1. Introduction
(continued)
Â
Condenser Control
Why?
Maintain the condensing pressure above the
minimum acceptable value in order to
guarantee sucient ow through the
expansion devices;
Ensure the right distribution of the refrigerant
in the system.
How?
On/o operation or control the speed of the
condenser fans, control the ow of the cooling
water, ood the condensers with liquid
refrigerant.
Ã
Liquid Level Control
Why?
Provide the correct ow of liquid refrigerant
from the high pressure side to the low pressure
side according to the actual demand;
Ensure safe and reliable operation of the
expansion devices.
How?
Control the opening degree of the expansion
device according to the change of the liquid
level.
Ä
Refrigerant Pump Control
Why?
Maintain the pump running in trouble free
mode by maintaining the ow through the
pump within the permissible operating range;
Maintain a constant dierential pressure across
the pump in some systems.
How?
Design a bypass loop so that the ow can be
maintained above the minimum permissible
ow;
Shut o the pump if it fails to build up enough
dierential pressure.
Install a pressure regulating valve.
Å
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 evaporators
enters the suction line of the compressor.
How?
Change the ow rate of the refrigerant into
evaporators according to the demand;
Defrost evaporators.
Æ
Safety Systems
Why?
Avoid unintended pressure of the vessels;
Protect the compressor from being damaged
by liquid hammering, overloading, oil shortage
and high temperature, etc;
Protect the pump from being damaged by
cavitation.
How?
Install safety relief valve on vessels and other
necessary places;
Shut o the compressor and pump if the
inlet/outlet pressure or dierential is out of
permissible range;
Shut o the system of part of the system when
the level in the liquid separator or the receiver
exceeds the permissible level.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
6 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
2. Compressor Controls
The compressor is the “heart of the refrigeration
system. It has two basic functions:
1. Maintain the pressure in the evaporator so
that the liquid refrigerant can evaporate at the
required temperature;
2. Compress the refrigerant so that it can be
condensed at a normal temperature.
The basic function of compressor control,
therefore, is to adjust the capacity of the
compressor to the actual demand of the
refrigeration system so that the required
evaporating temperature can be maintained.
If the compressor capacity is bigger than
the demand, the evaporating pressure and
temperature will be lower than that required, and
vice versa.
Additionally, the compressor should not be
allowed to operate outside of the acceptable
temperature and pressure range, in order to
optimise its running conditions.
2.1
Compressor Capacity Control
The compressor in a refrigeration system is
normally selected to be able to satisfy the highest
possible cooling load. However, the cooling load
during normal operation is usually lower than the
design cooling load. This means that it is always
necessary to control the compressor capacity so
that it matches the actual heat load. There are
several common ways to control the compressor
capacity:
1. Step control.
This means to unload cylinders in a multi-cylinder
compressor, to open and close the suction ports
of a screw compressor, or to start and stop some
compressors in a multi-compressor system. This
system is simple and convenient. Furthermore,
eciency decreases very little during part-load.
It is especially applicable to systems with several
multi-cylinder reciprocating compressors.
2. Slide valve control.
The most common device used to control the
capacity of a screw compressor is the slide valve.
The action of the oil-driven slide valve allows
part of the suction gas to avoid from being
compressed. The slide valve permits a smooth
and continuous modulation of capacity from
100% down to 10%, but the eciency drops at
part load.
3. Variable speed control.
Variable speed regulation. This solution is
applicable to all kinds of compressors, and
is ecient. A two-speed electric motor or a
frequency converter can be used to vary the
speed of the compressor. The two-speed electric
motor regulates the compressor capacity by
running at the high speed when the heat load is
high (e.g. cooling down period) and at the low
speed when the heat load is low (e.g. storage
period). The frequency converter can vary the
rotation speed continuously to satisfy the actual
demand. The frequency converter observes
limits for min. and max. speed, temperature and
pressure control, protection of compressor motor
as well as current and torque limits. Frequency
converters oer a low start up current.
4. Hot gas bypass.
This solution is applicable to compressors with
xed capacities and more typical for commercial
refrigeration. In order to control the refrigeration
capacity, part of the hot gas ow on the
discharge line is bypassed into the low pressure
circuit. This helps to decrease the refrigeration
capacity in two ways: by diminishing the supply
of liquid refrigerant and releasing some heat into
the low pressure circuit.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 7
Application example 2.1.1:
Step control of compressor
capacity
À
Step Controller
Á
Pressure Transmitter
Danfoss
Tapp_0016
10-2012
HP vapour refrigerant
LP vapour refrigerant
Oil
Step control solution for compressor capacity can
be achieved by using a step controller EKC 331 À.
EKC 331 is a four-step controller with up to four
relay outputs. It controls the loading/unloading
of the compressors/pistons or the electric motor
of the compressor according to the suction
pressure signal from the pressure transmitter AKS
33 Á or AKS 32R. Based on a neutral zone control,
EKC 331 can control a pack system with up to four
equally sized compressor steps or alternatively
two capacity controlled compressors (each
having one unload valve).
EKC 331T version can accept a signal from a
PT 1000 temperature sensor, which may be
necessary for secondary systems.
Neutral Zone Control
A 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 away
from 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 it
were in the hatched area.
For more details, please refer to the manual of
EKC 331(T) from Danfoss.
Technical data
Pressure transmitter-AKS 33 Pressure transmitter-AKS 32R
Refrigerants All refrigerants including R717 All refrigerants including R717
Operating range [bar] –1 to 34 –1 to 34
Max. working pressure PB [bar] 55 (depending on operating range) 60 (depending on operating range)
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
Pressure transmitter - AKS 3000 Pressure transmitter - AKS 32
Refrigerants All refrigerants including R717 All refrigerants including R717
Operating range [bar] 0 to 60 (depending on range) –1 to 39 (depending on range)
Max. working pressure PB [bar] 100 (depending on operating range) 60 (depending on operating range)
Operating temp. range [°C] –40 to 80 –40 to 85
Compensated temp. range [°C] LP: –30 to +40 / HP: 0 to +80 LP: –30 to +40 / HP: 0 to +80
Rated output signal 4 to 20 mA 1 to 5V or 0 to 10V
From liquid
separator
evaporator
Piston compressor
To
condenser
Oil
separator
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
8 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
Application example 2.1.2:
Compressor capacity control
by hot gas bypass
À
Stop valve
Á
Capacity regulator
Â
Stop valve
Danfoss
Tapp_0017
10-2012
HP vapour refrigerant
HP liquid refrigerant
LP vapour refrigerant
LP liquid refrigerant
Oil
Hot gas bypass can be used to control the
refrigeration capacity for compressors with xed
capacity. The pilot-operated servo valve ICS
Á with a CVC pilot valve is used to control the
hot gas bypass ow according to the pressure
on the suction line. The CVC is a back pressure
controlled pilot valve, which opens the ICS and
increases the ow of hot gas when the suction
pressure is below the set value. In this way, the
suction pressure ahead of the compressor is kept
constant, therefore the refrigeration capacity
satises the actual cooling load.
Technical data
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 150
Pilot valve - CVC (LP)
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
K
v
value [m
3
/h] 0.2
Pilot valve - CVC (XP)
Refrigerants All common refrigerants
Media temp. range [°C] –50 to 120
Max. working pressure [bar] High pressure side: 52
Low pressure side: 28
Pressure range [bar] 4 to 28
K
v
value [m
3
/h] 0.2
Compressor
To
condenser
From receiver
Evaporator
Oil
separator
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 9
Application example 2.1.3:
Compressor variable speed
capacity control
Danfoss
Tapp_0139
10-2012
À
Frequency converter
Á
Controller
Â
Pressure transducer
HP vapour refrigerant
LP vapour refrigerant
Frequency converter control oer the following
advantages:
Energy savings
Improved control and product quality
Noise reduction
Longer lifetime
Simplied installation
Easy to use complete control of the system
Technical data
Frequency converter AKD 102
Frequency converter
VLT FC 102 / FC 302
kW rating 1.1 kW to 45 kW 1.1 kW to 250 kW Up to 1200 kW
Voltage 200-240 V 380-480 V 200-690 V
To oil separator
To oil separator
To oil separator
From liquid
separator
evaporator
From liquid
separator
evaporator
From liquid
separator
evaporator
PLC/OEM
controller
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
10 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
2.2
Discharge Temperature
Control with Liquid Injection
Compressor manufacturers generally
recommend limiting the discharge temperature
below a certain value to prevent overheating of
values, prolonging their life and preventing the
breakdown of oil at high temperatures.
From the log p-h diagram, it can be seen that the
discharge temperature may be high when:
the compressor runs with high pressure
dierential.
the compressor receives highly superheated
suction vapour.
the compressor runs with capacity control by
hot gas bypass.
There are several ways to reduce the discharge
temperature. One way is to install water cooled
heads in reciprocating compressors, another
method is liquid injection, by which liquid
refrigerant from the outlet of the condenser
or receiver is injected into the suction line, the
intermediate cooler, or the side port of the screw
compressor.
Application example 2.2.1:
Liquid injection with
thermostatic injection valve
À
Stop valve
Á Solenoid valve
 Thermostatic injection valve
à Stop valve
Ä Thermostat
HP vapour refrigerant
HP liquid refrigerant
LP vapour refrigerant
LP liquid refrigerant
Oil
Danfoss
Tapp_0018
10-2012
When the discharge temperature rises above
the set value of the thermostat RT 107 Ä, RT 107
will energise the solenoid valve EVRA Á which
will start liquid injection into the side port of the
screw compressor.
The thermostatic injection valve TEAT Â
controls the injected liquid ow according to
the discharge temperature, which prevents the
discharge temperature from rising further.
Technical data
Thermostat - RT
Refrigerants R717 and uorinated refrigerants
Enclosure IP 66/54
Max. bulb temp. [°C] 65 to 300
Ambient temp. [°C] –50 to 70
Regulating range [°C] –60 to 150
Dierential Δt [°C] 1.0 to 25.0
Thermostatic injection valve - TEAT
Refrigerants R717 and uorinated refrigerants
Regulating range [°C] Max. bulb temp.: 150°C
P band: 20°C
Max. working pressure [bar] 20
Rated Capacity* [kW] 3.3 to 274
* Conditions: T
e
= +5°C, p = 8 bar, T
sub
= 4°C
Compressor
To oil
separator
From
receiver
Oil injection
From liquid
separator
evaporator
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 11
Application example 2.2.2:
Liquid injection with motor
valve
À
Stop valve
Á Solenoid valve
 Motor valve
à Stop valve
Ä Controller
Å Temperature sensor
HP vapour refrigerant
HP liquid refrigerant
LP vapour refrigerant
LP liquid refrigerant
Oil
An electronic solution for liquid injection control
can be achieved with the motorised valve
ICM Â. An AKS 21 PT 1000 temperature sensor Å
will register the discharge temperature and
transmit the signal to the temperature controller
EKC 361 Ä. The EKC 361 controls the ICAD actuator
which adjusts to opening degree of the ICM motor
valve in order to limit and maintain the required
discharge temperature.
Technical data
Danfoss
Tapp_0019
10-2012
ICM for expansion
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 80
Nominal Capacity* [kW] 72 to 22,700
* Conditions: T
e
= –10°C, p = 8.0 bar, T
sub
= 4K
Actuator - ICAD
Media temp. range [°C] –30 to 50 (ambient)
Control input signal 0/4-10mA, or 0/2-10
Open-close time with
maximum selected speed
3 to 45 seconds depending on valve size
From liquid
separator
evaporator
Oil injection
From
receiver
To oil
separator
Compressor
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
12 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
Application example 2.2.3:
A compact solution for liquid
injection with ICF
À
Valve station with:
Stop valve
Filter
Solenoid valve
Manual opener
Motor valve
Stop valve
Á Controller
 Temperature sensor
HP vapour refrigerant
HP liquid refrigerant
LP vapour refrigerant
LP liquid refrigerant
Oil
For liquid injection, Danfoss can supply a very
compact control solution ICF À. Up to six
dierent modules can be assembled into the
same housing. This solution works in the same
way as example 2.2.2, and is very compact and
easy to install.
Technical data
Danfoss
Tapp_0020
10-2012
ICF control solution
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 40
M
From liquid
separator
evaporator
Oil injection
From
receiver
To oil
separator
Compressor
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 13
2.3
Crankcase Pressure Control
During start-up or after defrost, the suction
pressure has to be controled, otherwise it can
be too high, and the compressor motor will be
overloaded.
The electric motor for the compressor may be
damaged 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 to
start compressor at part load, e.g. unload
part of the pistons for multi-piston
reciprocating compressors, or bypass some
suction gas for screw compressors with slide
valves, etc.
2. Control the crankcase pressure for
reciprocating compressors. By installing a
back pressure controlled regulating valve in
the suction line, which will not open until
the pressure in the suction line drops below
the set value, suction pressure can be kept
under a certain level.
Application example 2.3.1:
Crankcase pressure control with
ICS and CVC
À
Crankcase pressure regulator
Á Stop valve
HP vapour refrigerant
LP vapour refrigerant
Oil
In order to control the crankcase pressure during
start-up, after defrost, or in others cases when
the suction pressure may run too high, the
pilot-operated servo valve ICS À with the back
pressure controlled pilot valve CVC is installed
in the suction line. The ICS will not open until
the downstream suction pressure falls below
the set value of the pilot valve CVC. In this way,
the high pressure vapour in the suction line
can be released into the crankcase gradually,
which ensures a manageable capacity for the
compressor.
Technical data
Danfoss
Tapp_0021
10-2012
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 150
Capacity* [kW] 11 to 2440
* Conditions: T
e
= –10°C, T
l
= 30°C, p = 0.2 bar, T
sub
= 8K
Pilot valve - CVC (LP)
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
K
v
value [m
3
/h] 0.2
Pilot valve - CVC (XP)
Refrigerants All common refrigerants
Media temp. range [°C] –50 to 120
Max. working pressure [bar] High pressure side: 52
Low pressure side: 28
Pressure range [bar] 4-28
K
v
value [m
3
/h] 0.2
Compressor
Oil
separator
To condenser
From
evaporator
Not all valves are shown.
Not to be used for construction
purposes.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
14 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
2.4
Reverse Flow Control
Reverse ow and condensation of refrigerant
from the condenser to the oil separator and
the compressor should be avoided at all time.
For piston compressors, reverse ow can result
in liquid hammering. For screw compressors,
reverse ow can cause reversed rotation
and damage to the compressor bearings.
Furthermore, migration of refrigeration into the
oil separator and further into the compressor at
standstill should be avoided. To avoid this reverse
ow, it is necessary to install a check valve on the
outlet of the oil separator.
Application example 2.4.1:
Reverse ow control
À
Stop check valve
HP vapour refrigerant
LP vapour refrigerant
Oil
The stop check valve SCA À can function as a
check valve when the system is running, and
can also shut o the discharge line for service
as a stop valve. This combined stop/check valve
solution is easier to install and has lower ow
resistance compared to a normal stop valve plus
check valve installation.
When selecting a stop check valve, it is important
to note:
1. Select a valve according to the capacity and
not the pipe size.
2. Consider both the nominal and part load
working conditions. The velocity in the
nominal condition should be near to the
recommended value, at the same time
the velocity in the part load condition should
be higher than the minimum recommended
velocity.
For details on how to select valves, please refer to
the product catalogue.
Technical data
Danfoss
Tapp_0023_02
10-2012
Stop check valve - SCA
Material Housing: special cold resistant steel approved for low temperature operation.
Spindle: polished stainless steel
Refrigerants All common non-ammable refrigerants, incl. R717.
Media temp. range [°C] –60 to 150
Opening dierential pressure [bar] 0.04 (0.3 bar spring availble as spare part)
Max. working pressure [bar] 40
DN [mm] 15 to 125
Not all valves are shown.
Not to be used for construction
purposes.
Compressor
To condenser
From
evaporator
Oil
separator
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 15
Solution Application Benets Limitations
Compressor Capacity Control
Step control of compressor
capacity with EKC 331 and
AKS 32/33
Applicable to multi-
cylinder compressor, screw
compressor with multiple
suction ports, and systems
with several compressors
running in parallel.
Simple.
Almost as ecient 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 control
with hot gas bypass using
ICS and CVC
Applicable to compressors
with xed capacities.
Eective to control the
capacity continuously
according to the actual
heat load.The hot gas can
help the oil return from the
evaporator.
Not ecient at part load.
Energy consuming.
Compressor variable speed
capacity control
Applicable to all
compressors with the ability
to run at reduced speed.
Low start up current
Energy savings
Lower noise
Longer lifetime
Simplied installation
Compressor must be suited
for reduced speed operation.
Discharge Temperature Control with Liquid Injection
Mechanical solution for
liquid injection with TEAT,
EVRA(T) and RT
Applicable to systems where
the discharge temperatures
may run too high.
Simple and eective. Injection of liquid refrigerant
may be dangerous to the
compressor. Not as ecient
as intermediate cooler.
Electronic solution for liquid
injection control with EKC
361 and ICM
Applicable to systems where
the discharge temperatures
may run too high.
Flexible and compact.
Possible to monitor and
control remotely.
Not applicable to ammable
refrigerants. Injection of
liquid refrigerant may
be dangerous to the
compressor. Not as ecient
as intermediate cooler.
Electronic solution for liquid
injection control with EKC
361 and ICF
Crankcase Pressure Control
Crankcase pressure control
with ICS and CVC
Applicable to reciprocating
compressors, normally
used for small and medium
systems.
Simple and reliable. Eective
in protecting reciprocating
compressors at start-up or
after hot gas defrost.
Gives constant pressure
drop in the suction line.
Crankcase pressure control
with ICS and CVP
Reverse Flow Control
Reverse ow control with
SCA
Applicable to all
refrigeration plants.
Simple.
Easy to install.
Low ow resistance.
Gives constant pressure
drop in the discharge line.
2.5
Summary
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
16 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
2.6
Reference Documents
For an alphabetical overview of
all reference documents please
go to page 149
To download the latest version of the literature please visit the Danfoss internet site
http://www.danfoss.com/Products/Literature/RA_Documentation.htm
Type Literature no.
AKD 102 PD.R1.B
AKS 21 RK.0Y.G
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) PD.BM0.B
Type Literature no.
ICF PD.FT0.A
ICM PD.HT0.B
ICS PD.HS0.A
REG PD.KM1.A
SCA PD.FL1.A
SVA PD.KD1.A
TEAT RD.1F.A
Technical Leaet / Manual
Type Literature no.
AKD 102 MG.11.L
AKS 21 RI.14.D
AKS 32R PI.SB0.A
AKS 33 PI.SB0.A
CVC RI.4X.L
CVP PI.HN0.C
EKC 331 RI.8B.E
EKC 361 RI.8B.F
EVRA(T) RI.3D.A
Type Literature no.
ICF PI.FT0.A
ICM 20-65 PI.HT0.A
ICM 100-150 PI.HT0.B
ICS 25-65 PI.HS0.A
ICS 100-150 PI.HS0.B
REG PI.KM1.A
SCA PI.FL1.A
SVA PI.KD1.A
TEAT PI.AU0.A
Product instruction
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
© Danfoss A/S (AC-SMC/MWA), 2013-02 DKRCI.PA.000.C4.02 / 520H1623 17
3. Condenser Controls
In areas where there are large variations in
ambient air temperatures and/or load conditions,
it is necessary to control the condensing
pressure to avoid it from falling too low. Too
low condensing pressures results in there being
insucient pressure dierential across the
expansion device and the evaporator is supplied
with insucient refrigerant. It means that
condenser capacity control is mainly used in the
temperate climate zones and to a lesser degree in
subtropical and tropical zones.
The basic idea of control is to control the
condenser capacity when the ambient
temperature is low, so that the condensing
pressure is maintained above the minimum
acceptable level.
This condensing capacity control is achieved
either by regulating the ow of circulating air or
water through the condenser, or by reducing the
eective heat exchange surface area.
Dierent solutions can be designed for dierent
types of condensers:
3.1 Air cooled condensers
3.2 Evaporative condensers
3.3 Water cooled condensers
3.1
Air Cooled Condensers
An air-cooled condenser consists of tubes mounted
within a n block. The condenser can be horizontal,
vertical or V-shaped. The ambient air is drawn across
the heat exchanger surface with axial or centrifugal
fans.
Air-cooled condensers are used on industrial
refrigeration systems where the relative air humidity
is high. Controlling the condensing pressure for air-
cooled condensers can be achieved in the following
ways:
3.1.1 - Step Control of Air Cooled Condensers
The rst method was using the required number
of pressure controls in the form the Danfoss RT-5
and adjusting them to dierent set cut-in and
cut-out pressures.
The second method of controlling the fans was
by using a neutral zone pressure controller in the
form of the Danfoss type RT-L. Initially it was used
together with a step controller with the required
number of contacts for the number of fans.
3.1.2 - Fan speed control of air cooled condensers
This method of condenser fan control is mainly
used whenever a reduction in noise level is
desired due to environmental concerns.
For this type of installation Danfoss frequency
converter AKD can be used.
3.1.3 - Area control of air cooled condensers
For area or capacity control of air cooled
condensers a receiver is required. This receiver
must have sucient volume to be able to
accommodate the variations in the amount of
refrigerant in the condenser.
Two ways this condenser area control can be
done:
1. Main valve ICS or PM combined with the
constant pressure pilot CVP(HP) mounted in
the hot gas line on the inlet side to the
condenser and ICV combined with a
dierential pressure pilot CVPP(HP) mounted
in the pipe between the hot gas line and the
receiver. In the pipe between the condenser
and the receiver a check valve NRVA is
mounted to prevent liquid migration from the
receiver to the condenser.
However this system reacted too fast and timers
were used for delaying the cut-in and cut-out of
the fans.
The Third method is todays step controller the
Danfoss EKC-331.
2. Main valve ICS combined with the constant
pressure pilot CVP(HP) mounted in the pipe
between the condenser and the receiver and
a ICS combined with a dierential pressure
pilot CVPP(HP) mounted in the pipe between
the hot gas line and the receiver. This method
is mainly used in commercial refrigeration.
Application Handbook Industrial Refrigeration ammonia and CO
2
applications
18 DKRCI.PA.000.C4.02 / 520H1623 © Danfoss A/S (AC-SMC/MWA), 2013-02
Application example 3.1.1:
Step control of fans with step
controller EKC 331
À Step controller
Á Pressure transmitter
 Stop valve
à Stop valve
Ä Stop valve
HP vapour refrigerant
HP liquid refrigerant
EKC 331 À is a four-step controller with up to
four relay outputs. It controls the switching of the
fans according to the condensing pressure signal
from a pressure transmitter AKS 33 Á or AKS 32R.
Based on neutral zone control, EKC 331 À
can control the condensing capacity so that the
condensing pressure is maintained above the
required minimum level.
For more information on neutral zone control,
please refer to section 2.1.
The bypass pipe where SVA Ä is installed is
an equalizing pipe, which helps balance the
pressure in the receiver with the inlet pressure of
the condenser so that the liquid refrigerant in the
condenser can be drained into the receiver.
In some installations, EKC 331T is used. In this
case the input signal could be from a PT 1000
temperature sensor, e.g. AKS 21. The temperature
sensor is usually installed in the outlet of the
condenser.
Note! The EKC 331T + PT1000 temperature
sensor solution is not as accurate as the EKC
331 + pressure transmitter solution because
the condenser outlet temperature may not
entirely reect the actual condensing pressure
due to the liquid subcooling or the presence of
incondensable gasses in the refrigeration system.
If the subcooling is too low, ash gas may occur
when the fans start.
Technical data
Danfoss
Tapp_0031_02
10-2012
Pressure transmitter-AKS 33 Pressure transmitter-AKS 32R
Refrigerants All refrigerants including R717 All refrigerants including R717
Operating range [bar] –1 to 34 –1 to 34
Max. working pressure PB [bar] 55 (depending on operating range) 60 (depending on operating range)
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
Pressure transmitter - AKS 3000 Pressure transmitter - AKS 32
Refrigerants All refrigerants including R717 All refrigerants including R717
Operating range [bar] 0 to 60 (depending on range) –1 to 39 (depending on range)
Max. working pressure PB [bar] 100 (depending on operating range) 60 (depending on operating range)
Operating temp. range [°C] –40 to 80 –40 to 85
Compensated temp. range [°C] LP: –30 to +40 / HP: 0 to +80 LP: –30 to +40 / HP: 0 to +80
Rated output signal 4 to 20 mA 1 to 5V or 0 to 10V
Not all valves are shown.
Not to be used for construction
purposes.
From
discharge line
To expansion
device
Condenser
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Danfoss Application Handbook - Automatic Controls for Industrial Refrigeration Systems Mode d'emploi

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