U.S. patent application number 17/238145 was filed with the patent office on 2021-10-28 for control of refrigerant injection into a compressor in an economized refrigeration cycle.
This patent application is currently assigned to Emerson Climate Technologies GmbH. The applicant listed for this patent is Emerson Climate Technologies GmbH. Invention is credited to Paolo CHIARAMONTE, Remi DICKES, Luca MAZZORANA, Eric WINANDY.
Application Number | 20210333025 17/238145 |
Document ID | / |
Family ID | 1000005555954 |
Filed Date | 2021-10-28 |
United States Patent
Application |
20210333025 |
Kind Code |
A1 |
WINANDY; Eric ; et
al. |
October 28, 2021 |
Control Of Refrigerant Injection Into A Compressor In An Economized
Refrigeration Cycle
Abstract
A method of controlling injection into a compressor in a
refrigeration cycle is described. A refrigeration cycle may
comprise at least an economizer heat exchanger, a heat rejection
heat exchanger, a first expansion device, and a compressor. A
discharge port of the compressor is connected to the heat rejection
heat exchanger via a discharge line and an injection port of the
compressor is connected to the means for compressing. The
economizer heat exchanger comprises a first path having an input
connected to the heat rejection heat exchanger and an output
connected to the first expansion device, and a second path having
an input connected to the heat rejection heat exchanger via an
economizer valve and an output connected to the injection port of
the compressor via an injection line. The economizer valve is
regulated based on a superheat level of the refrigerant in the
economizer heat exchanger.
Inventors: |
WINANDY; Eric; (Esneux,
BE) ; DICKES; Remi; (Aachen, DE) ;
CHIARAMONTE; Paolo; (Alpago, IT) ; MAZZORANA;
Luca; (Alpago, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Emerson Climate Technologies GmbH |
Berlin |
|
DE |
|
|
Assignee: |
Emerson Climate Technologies
GmbH
Berlin
DE
|
Family ID: |
1000005555954 |
Appl. No.: |
17/238145 |
Filed: |
April 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 2700/191 20130101;
F25B 41/31 20210101; F25B 2600/2513 20130101; F25B 49/02 20130101;
F25B 2600/2501 20130101; F25B 43/02 20130101; F25B 2400/13
20130101; F25B 31/008 20130101 |
International
Class: |
F25B 31/00 20060101
F25B031/00; F25B 43/02 20060101 F25B043/02; F25B 49/02 20060101
F25B049/02; F25B 41/31 20060101 F25B041/31 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2020 |
EP |
20171292.4 |
Claims
1. A method of controlling injection into a compressor in a
refrigeration cycle, wherein the method is performed in a
refrigeration cycle, which comprises at least a flash tank
configured for receiving a refrigerant and separating liquid
refrigerant and vapour refrigerant, and a compressor configured for
compressing the refrigerant, wherein the compressor comprises a
means for compressing, a suction port and an injection port, which
is connected to the means for compressing for at least a time
instance of the refrigeration cycle, wherein the flash tank is
connected to the injection port of the compressor via an injection
valve, the method comprising: determining a pressure in the flash
tank; controlling the injection valve based on the determined
pressure in the flash tank.
2. The method according to claim 1, wherein controlling the
injection valve comprises: if the determined pressure in the flash
tank is lower than a first threshold, closing the injection
valve.
3. The method according to claim 2, wherein controlling the
injection valve comprises: if the determined pressure in the flash
tank is equal to or greater than the first threshold and lower than
a second threshold, at least partially opening the injection
valve.
4. The method according to claim 3, wherein opening the injection
valve comprises: determining, by a proportional integral
derivative, PID, controller, a value for an opening degree of the
injection valve based on the determined flash tank pressure; and
setting the opening degree of the injection valve to the determined
value.
5. The method according to claim 3, further comprising: determining
whether the compressor is operating; and wherein opening the
injection valve is only carried out, if it is determined that the
compressor is operating.
6. The method according to claim 3, wherein controlling the
injection valve comprises: if the determined pressure in the flash
tank is greater than the second threshold, closing the injection
valve.
7. The method according to claim 1, the method further comprising:
determining a pressure at the suction port of the compressor;
determining whether the pressure at the suction port is lower than
a third threshold; and if it is determined that the pressure at the
suction port is lower than the third threshold: closing the
injection valve; and turning off the compressor.
8. The method according to claim 1, the method further comprising:
controlling the compressor based on the determined pressure in the
flash tank.
9. The method according to claim 8, wherein controlling the
compressor comprises: if the determined flash tank pressure is
lower than a fourth threshold, determining, by a PID controller, an
operating speed for the compressor and setting the operating speed
to the determined operating speed.
10. The method according to claim 9, wherein controlling the
compressor comprises: if the determined flash tank pressure is
equal to or greater than the fourth threshold and lower than a
fifth threshold, unloading the compressor; and if the determined
flash tank pressure is greater than the fifth threshold, stopping
operation of the compressor.
11. The method according to claim 1, wherein the compressor
comprises a discharge port and wherein the refrigeration cycle
further comprises a heat rejection heat exchanger, which is
connected to the discharge port of the compressor, and an expansion
device disposed between the heat rejection heat exchanger and the
flash tank, wherein the method further comprises: if the determined
flash tank pressure is lower than a sixth threshold, setting an
opening degree of the expansion device to a predetermined value; if
the determined flash tank pressure is equal to or greater than the
sixth threshold and lower than a seventh, setting the opening
degree of the expansion device to a value determined by a PID
controller based on a first heat rejection heat exchanger pressure
mode; determining that the pressure in the flash tank is equal to
or greater than the seventh and lower than an eighth threshold and
setting the opening degree of the expansion device to a value
determined by the PID controller based on a second heat rejection
heat exchanger pressure mode; or determining that the pressure in
the flash tank is equal to or greater than the eighth threshold and
lower than a ninth threshold and controlling the opening degree of
the expansion device based on fuzzy regulation; or determining that
the pressure in the flash tank is equal to or greater than the
ninth threshold and lower than a tenth threshold and controlling
the opening degree of the expansion device based on a flash tank
pressure regulation mode; or determining whether the pressure in
the flash tank is equal to or greater than the tenth threshold and
closing the expansion device.
12. The method according to claim 11, wherein the first heat
rejection heat exchanger pressure mode comprises controlling the
expansion device based on the temperature of the refrigerant in the
heat rejection heat exchanger.
13. The method according to claim 11, wherein the second heat
rejection heat exchanger pressure mode (HRHE_mode2) comprises
controlling the expansion device based on the temperature of the
refrigerant in the heat rejection heat exchanger and the pressure
of the refrigerant in the flash tank.
14. The method according to claim 11, wherein the flash tank
pressure regulation mode comprises controlling the expansion device
based on the pressure if the refrigerant in the flash tank.
15. The method according to claim 1, wherein the refrigerant cycle
comprises a by-pass line connected between the flash tank and the
suction port of the compressor, wherein the by-pass line comprises
a by-pass valve, and wherein the method further comprises:
determining that the pressure of the flash tank is lower than a
eleventh threshold and closing the by-pass valve; or determining
that the pressure of the flash tank is equal to or greater than the
eleventh threshold and lower than a twelfth threshold, and
determining, by a PID controller, a value for an opening degree of
the by-pass valve based on the determined flash tank pressure; or
determining that the pressure of the flash tank is equal to or
greater than the twelfth threshold and lower than a thirteenth
threshold, and opening the by-pass valve completely; or determining
that the pressure of the flash tank is equal to or greater than the
thirteenth threshold and setting an opening degree of the by-pass
valve to a predetermined value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to European Patent
Application No. 20171292.4 filed on Apr. 24, 2020. The entire
disclosure of which is incorporated herein by reference.
FIELD
[0002] The present patent application relates to a method for
controlling refrigerant injection into a compressor in a
refrigeration cycle, wherein the refrigeration cycle comprises an
injection compressor and an economizer.
BACKGROUND
[0003] Refrigeration systems having a refrigeration cycle are well
known in the art. In a common refrigeration cycle, a refrigerant is
circulated through a refrigeration system, in which it undergoes
changes in thermodynamic properties in different parts of the
refrigeration system. The refrigerant is a fluid, i.e. a liquid or
a vapour or a gas, respectively. Examples of refrigerants may be
artificial refrigerants like fluorocarbons. However, in recent
applications, the use of carbon dioxide, CO.sub.2, which is a
non-artificial refrigerant, has become more and more important,
because it is non-hazardous to the environment. The changes in
thermodynamic properties of the refrigerant may, for example,
include changes in temperature, pressure, volume, or enthalpy,
wherein sometimes the changes in one property may also affect at
least one other property, or wherein in some cases at least one
property may stay constant while another property is changing. The
changes in thermodynamic properties may go along with phase
transitions of at least a portion of the refrigerant, for example
from liquid to vapour and vice versa.
[0004] The refrigerant is used in a refrigeration system for
transporting heat in a refrigeration cycle. Thereby, heat is
usually transported from one point in the refrigeration cycle to
another point in the refrigeration cycle by ease of the
refrigerant. For example, these points in the refrigeration cycle
may be represented by heat exchangers. In a first heat exchanger,
the refrigerant may accept heat from a source. The source may be,
for example, the air of a room the temperature of which shall be
controlled. After being transported to a second heat exchanger, the
refrigerant may reject heat in the second heat exchanger, for
example, by transferring heat to exhaust air.
[0005] Nowadays, refrigeration systems are of particular importance
for controlling temperature or climate conditions. A particular
type of a refrigeration system is a compression refrigeration
system, which sometimes is referred to as vapour compression
refrigeration system (VCRS).
[0006] As used herein, a refrigeration cycle comprises at least a
compressor for compressing the refrigerant. Compressing the
refrigerant may drive the cycle. Further, such a refrigeration
cycle commonly comprises a heat exchanger, in which heat may be
extracted from the compressed refrigerant. The extraction of heat
from the compressed refrigerant is sometimes referred to as heat
rejection, because heat is rejected from the refrigeration system.
Accordingly, this heat exchanger often is referred to as heat
rejection heat exchanger. Further, such a refrigeration cycle
commonly comprises an expansion device, in which the pressure and
thereby the temperature of the refrigerant are reduced. The
expansion device may be, for example, a valve, in particular an
expansion valve, or a metering device. In addition, such a
refrigeration cycle commonly comprises another heat exchanger,
which may be used for accepting heat from a source. The other heat
exchanger is often referred to as heat accepting heat exchanger.
The heat accepting heat exchanger is in fluid communication with
the compressor, so that the refrigerant is guided to the compressor
in order to close the cycle.
[0007] In some refrigeration cycles, a compressor is used for
driving the refrigeration cycle. Such a compressor commonly
comprises a suction port and a discharge port, as well as a means
for compressing. The suction port is configured for receiving
refrigerant from the refrigeration cycle. For example, the
refrigerant may be received from the heat accepting heat exchanger.
The suction port is in fluid communication with the compression
chamber for at least a first time instance for providing the
refrigerant to the means for compressing. In the means for
compressing, the refrigerant will be compressed to a desired
pressure. The compression in general increases the pressure of the
refrigerant. This may go along with an increase in temperature of
the refrigerant. In case the compressor may be a scroll compressor,
the means for compressing may be formed by the scroll set of the
scroll compressor.
[0008] The means for compressing is in fluid communication with the
discharge port of the compressor for at least a second time
instance for providing the compressed refrigerant to the discharge
port. At the discharge port, the compressed refrigerant may be
discharged from the compressor at a desired discharge pressure or
desired discharge temperature.
[0009] In some refrigeration cycles, the compressor may be an
injection compressor. Additionally to the aforementioned features
of a compressor, an injection compressor comprises an injection
port. The injection port is in fluid communication with a source
for providing refrigerant. A source may be, for example, an
economizer. Further, the injection port is in fluid communication
with the means for compressing of the compressor for at least a
third time instance. In case that the injection port is in fluid
communication with the means for compressing, refrigerant is
provided from the source to the means for compressing of the
compressor. The refrigerant, which is provided from the source to
the means for compressing, may be referred to as additional
refrigerant, injected refrigerant, or fresh refrigerant. In most
applications, the injected refrigerant is in a vapour state.
However, in particular circumstances, it may be beneficial to
inject liquid refrigerant additionally to the vapour
refrigerant--for example, in a case, in which the temperature of
the refrigerant in the compressor needs to be reduced.
[0010] In general, the efficiency of the system, which is
represented by a so-called coefficient of performance (COP),
depends on the temperature or pressure difference between the
refrigerant in the heat rejection heat exchanger and the
temperature or pressure of the refrigerant in the heat accepting
heat exchanger. However, injection conditions, like pressure and
temperature, have a direct influence on the efficiency of the
system. Therefore, controlling the refrigerant system based only on
the temperature of the refrigerant in the heat rejection heat
exchanger may result in inefficient operation or in fluctuations of
the cooling, which is provided by the refrigeration system. Hence,
there is a need in the art for improving the efficiency of
refrigeration systems.
[0011] This need is overcome by the method for controlling
injection into a compressor of a refrigeration cycle according to
the presented invention.
[0012] In general, the presented invention relates to a method for
controlling injection into a compressor of a refrigeration cycle
based on the superheat level of the refrigerant in the economizer.
The method may comprise different operation modes. In some
embodiments of the current invention, one of these operation modes
may establish a default operation mode for the method according to
the current invention, while other operation modes may be used
under particular system conditions. In this case, the method
according to the current invention provides a method of switching
between suitable operation modes. Alternatively, in other
embodiments of the current invention, the method does not establish
a default mode, but may select a suitable operation mode from a
number of equitable operation modes based on determined system
parameters.
[0013] A method of controlling injection into a compressor in a
refrigeration cycle according to the invention is performed in a
refrigeration cycle, which comprises at least an economizer, a heat
rejection heat exchanger, a first expansion device, and a
compressor configured for compressing the refrigerant. The
compressor comprises a means for compressing, a suction port, a
discharge port, and an injection port. The heat rejection heat
exchanger may be disposed downstream of the discharge port of the
compressor. The connection between the discharge port and the heat
rejection heat exchanger may be referred to as discharge line. The
first expansion device may be disposed downstream of the heat
rejection heat exchanger and upstream of the suction port of the
compressor. Further, the refrigeration cycle may comprise a heat
accepting heat exchanger, which is disposed downstream of the first
expansion device and upstream of the suction port of the
compressor.
[0014] The injection port is connected to the means for compressing
for at least a particular time instance. The means for compressing
is configured for receiving a refrigerant from the suction port
and/or the injection port of the compressor. Further, the means for
compressing compresses the refrigerant. Further, the means for
compressing may be configured for providing the compressed
refrigerant to the discharge port of the compressor.
[0015] In a preferred embodiment, the compressor may be a scroll
compressor and the means for compressing may be formed by a scroll
set of the scroll compressor.
[0016] The economizer comprises an economizer heat exchanger, which
comprises a first path and a second path, for exchanging heat
between refrigerant in the first path and refrigerant in the second
path. The first path has an input, which is connected to the heat
rejection heat exchanger, and an output, which is connected to the
first expansion device. The second path has an input, which is
connected to the heat rejection heat exchanger via an economizer
valve, and an output, which is connected to the injection port of
the compressor via an injection line. Preferably, the first path
and the second path of the economizer have counterwise flow
directions. However, it may also be possible that the first path
and the second path have other flow relative flow directions. For
example, it may be possible that the first path and the second path
are oriented in co-current flow directions or in cross-flow
directions, where the orientation of the flow in the first path is
perpendicular to the orientation of the flow in the second path.
Furthermore, any combination of the mentioned flow types is
possible. Since the present invention deals with the control of the
refrigerant in the refrigerant cycle of the refrigerant system, the
term connected is used throughout the application to describe a
connection, which enables a fluid communication via this
connection. In other words, the connection enables the exchange of
refrigerant between the connected entities.
SUMMARY
[0017] According to the present invention, the method comprises
regulating the economizer valve by using a first operation mode,
which is based on a superheat level of the refrigerant in the
economizer heat exchanger. The method may also comprise determining
the superheat level of the refrigerant in the economizer heat
exchanger. The superheat level may, for example, be determined at
the output of the second path of the heat rejection heat
exchanger.
[0018] The regulating may comprise calculating an opening degree of
the economizer valve based on the superheat level of the
refrigerant in the economizer heat exchanger and setting the
opening degree to the calculated value. Throughout this
application, anytime it is mentioned that an opening degree is
calculated, this may also include setting the opening degree to the
calculated value.
[0019] The first operation mode may be referred to as superheat
control mode. This operation mode is based on the finding that a
maximum of the refrigeration cycle efficiency is reached with a
minimum superheat at the economizer. Superheat may be measured in
temperature increase compared to the boiling point. For example, a
superheat value of 5 Kelvin would refer to a temperature increase
of 5 Kelvin compared to the saturation point. The saturation point
may also be referred to as boiling point. The desired superheat
value depends on the refrigerant, which is used. In typical CO2
refrigeration cycles, a value of 5 Kelvin is the target for the
superheat in the economizer, since lower values may cause
instabilities or may cause the injection of droplets into the
compressor, which would decrease the cycle efficiency. Other
preferred refrigerants, which have the same target superheat value
of 5 Kelvin are R717 (ammonia), R290 (propane), and R32.
[0020] The superheat level (SH) may be calculated based on the
temperature measured at the output of the second path of the
economizer and the saturation temperature measured downstream of
the economizer valve. Said saturation temperature, which may also
be referred to as boiling temperature, may be measured directly or
indirectly. An example of a direct temperature measurement is to
measure the temperature between the economizer valve and the inlet
port of the second path of the economizer. An example of an
indirect temperature measurement is to measure the pressure at said
location and determine the temperature from the pressure. Using
said temperature values, the superheat level may be calculated by
SH=T.sub.out-T.sub.sat, with T.sub.out being the temperature
measured at the outlet port of the second path of the economizer
and T.sub.sat being the saturation temperature.
[0021] The first operation mode may be referred to as superheat
control mode and may comprise setting an opening degree of the
economizer valve to a value calculated by using the first operation
mode in order to keep the superheat level of the refrigerant at the
output of the second path of the economizer heat exchanger at a
first predetermined setpoint. The predetermined setpoint may be set
by a manufacturer or an operator of the respective refrigeration
system. In some embodiments, the calculated value for the opening
degree may be a pre-calculated value. Further, this pre-calculated
value may be updated by a feedback controller, for example a PID
controller.
[0022] In a preferred embodiment, different operation modes may be
used for controlling the economizer valve. For example, the first
operation mode, which may be referred to as superheat control mode,
may be a default operation mode of the control of the injection
control. At least two additional operation modes may be provided.
Among these two additional operation modes may be a second
operation mode, which may be referred to as discharge line
temperature (DLT) control mode, and a third operation mode, which
may be referred to as economizer heat exchanger pressure (EHXP)
control mode or injection pressure control mode.
[0023] According to at least some embodiments of the present
invention, it may be possible to determine system parameters and to
switch from the first operation mode to either one of the second
operation mode and the third operation mode based on the determined
system parameters. The person skilled in the art will appreciate
that it is also possible to switch from any of the second operation
mode and the third operation back to the first operation mode based
on the determined system parameters. Also, it may be possible to
switch from the second operation mode directly to the third
operation mode and vice versa. Accordingly, the determination of
the system parameters may allow any switching between the operation
modes. The system parameters may include any temperature or
pressure of the refrigerant in the refrigeration cycle, as well as
the superheat level. Preferably, the superheat level of the
refrigerant at the output of the second path of the economizer heat
exchanger, the pressure of the refrigerant in the injection line,
and the temperature of the refrigerant, which is discharged from
the compressor, are used. In most applications, the pressure of the
refrigerant in the second path of the economizer and the pressure
of the refrigerant in the injection line are essentially the same.
For the purpose of this application, these system parameters may be
used interchangeably.
[0024] The second operation mode may be referred to as discharge
line temperature control mode. The aim of the second operation mode
is to prevent the temperature of the refrigerant in the compressor
from exceeding a threshold, which would be harmful for the
refrigeration system. This may be performed by injecting liquid
refrigerant additionally to the vapour refrigerant. Since liquid
injection may cause dysfunction of the compressor, it is desired to
keep liquid injection as low as possible.
[0025] In a preferred embodiment, the method may further comprise
the steps of determining a pressure of the refrigerant in the
injection line and determining a temperature of the refrigerant in
the discharge line. The pressure of the refrigerant in the
injection line and the temperature of the refrigerant in the
discharge line may be examples of system parameters, the
determination of which may enable a switching between operation
modes.
[0026] Based on the determined pressure and the determined
temperature, it may be determined whether to proceed with
regulating the economizer valve by using the first operation mode
or whether to perform one of regulating the economizer valve by
using the second operation mode or regulating the economizer by
using the third operation mode. Thereby, the regulating the
economizer valve by using the second operation mode is based on the
temperature of the refrigerant in the discharge line and the
regulating the economizer valve by using the third operation mode
is based on the pressure of the refrigerant in the injection
line.
[0027] The second operation mode, which may be referred to as DLT
control mode, may comprise regulating the economizer valve in order
to keep the temperature of the refrigerant in the discharge line
below a second predetermined setpoint. The second predetermined
setpoint may be set by a manufacturer or an operator of the
respective refrigeration system. Such a predetermined setpoint may
be updated by a feedback controller, for example a PID
controller.
[0028] The third operation mode may be referred to as injection
pressure control mode. This mode can be used in case that the
discharge temperature of the refrigerant at the compressor is under
control, but the pressure inside the compressor is rising.
Accordingly, the economizer valve needs to be closed to a higher
degree than would be desired reaching a superheat target. This is
necessary to restrict the injection of refrigerant into the
compressor and thereby reduce the pressure inside the
compressor.
[0029] The third operation mode, which may be referred to as EHXP
operation mode, may comprise regulating the economizer valve in
order to keep the pressure of the refrigerant in the injection line
under a third predetermined setpoint. The third predetermined
setpoint may be set by a manufacturer or an operator of the
respective refrigeration system. Such a predetermined setpoint may
be updated by a feedback controller, for example a PID
controller.
[0030] In some preferred embodiments, the above-mentioned
regulating may be performed based on a combination of two or more
of the first, second, and third operation modes.
[0031] In a preferred embodiment, the regulating may comprise
closing the economizer valve, if the pressure of the refrigerant in
the injection line is determined to be below a first threshold. The
first threshold may be referred to as a minimum injection pressure
at the economizer for injection into the compressor. The minimum
injection pressure may depend on the operating conditions of the
compressor. Also, the minimum injection pressure may correspond to
setpoint, which is predetermined by a manufacturer or an operator
of the refrigeration system.
[0032] If the pressure of the refrigerant in the injection line is
below the minimum injection pressure, it is necessary to close the
economizer valve and thereby prevent refrigerant from being
injected into the compressor. Otherwise, the pressure in the
injection line may be lower than the pressure in the means for
compression at the point, where the refrigerant should be injected
into the means for compressing. Accordingly, this may lead to
undesired reverse flow of refrigerant form the compressor through
the injection line.
[0033] Further, the regulating may comprise, if the pressure of the
refrigerant in the injection line is determined to be above the
first threshold and below a second threshold, setting an opening
degree of the economizer valve to a value calculated by using the
first operation mode, the second operation mode, or a combination
of both. The second threshold may be referred to as a maximum
injection pressure at the economizer for the first operation mode
and the second operation mode.
[0034] Further, the regulating may comprise, if the pressure of the
refrigerant in the injection line is determined to be above the
second threshold and below a third threshold, setting the opening
degree of the economizer valve to a value calculated by using a
combination of at least the first operation mode and the third
operation mode.
[0035] Further, the regulating may comprise, if the pressure of the
refrigerant in the injection line is determined to be above the
third threshold and below a fourth threshold, setting the opening
degree of the economizer valve to a value calculated by using the
third operation mode and if the pressure of the refrigerant in the
injection line is determined to be above the fourth threshold,
closing the economizer valve and stopping the operation of the
compressor. The fourth threshold may be referred to as a maximum
injection pressure. Since too high injection pressures may harm the
operation of the compressor or the compressor itself, the fourth
threshold may correspond to a safety condition, which prevents the
pressure inside the compressor from rising beyond the fourth
threshold.
[0036] In a further preferred embodiment, if the determined
pressure of the refrigerant in the discharge line is above the
first threshold but below the second threshold, the setting the
economizer valve to a value calculated by using the first operation
mode or the second operation mode may comprise, if the temperature
of the refrigerant in the discharge line is below a fifth
threshold, setting the opening degree of the economizer valve to a
value calculated from the superheat level of the refrigerant in the
economizer heat exchanger. The fifth threshold may be referred to
as discharge temperature threshold for enabling superheat and
temperature control. Below the fifth threshold, only the superheat
value of the refrigerant is used for calculating the opening degree
of the economizer valve in case that the pressure of the
refrigerant in the injection line is below the second threshold.
The aim of this operation is to optimize the superheat value by
reaching the superheat target value.
[0037] Further, the setting the opening degree of the economizer
valve may comprise, if the temperature of the refrigerant in the
discharge line is above the fifth threshold and below a sixth
threshold, setting the opening degree of the economizer valve to a
value calculated from the superheat level of the refrigerant in the
economizer heat exchanger and the determined temperature of the
refrigerant, which is discharged from the compressor. The sixth
threshold may be referred to alarm discharge line temperature
threshold. The fifth threshold and the sixth threshold define a
transition area, in which a combination of the first operation mode
and the second operation mode is performed.
[0038] Further, the setting the opening degree of the economizer
valve may comprise, if the temperature of the refrigerant in the
discharge line is above the sixth threshold and below a seventh
threshold, setting the opening degree of the economizer valve to a
value calculated from the determined temperature of the
refrigerant, which is discharged from the compressor. Also, the
setting the opening degree of the economizer valve may comprise, if
the temperature of the refrigerant in the discharge line is
determined to be above the seventh threshold, closing the
economizer valve and stopping the operation of the compressor. The
seventh threshold may be referred to as maximum discharge line
temperature threshold. This threshold may define a temperature
point above which refrigerant injection into the compressor would
be harmful for the compressor. Hence, if the discharge line
temperature exceeds the seventh threshold, the economizer valve is
closed and the injection is stopped. Preferably, the operation of
the compressor is also stopped.
[0039] In a further preferred embodiment, if the determined
pressure of the refrigerant in the discharge line is above the
second threshold but below the third threshold, the setting the
opening degree of the economizer valve to a value calculated by
using the third operation may comprise, if the determined
temperature of the refrigerant in the discharge line is below a
eighth threshold, setting the opening degree of the economizer
valve to a value calculated from the determined pressure of the
refrigerant in the injection line and the superheat value. Thereby,
a combination of the first and the third operation modes is
performed.
[0040] Further, the setting the opening degree of the economizer
valve may comprise, if the determined temperature of the
refrigerant in the discharge line is above the eighth threshold and
below a ninth threshold, setting the opening degree of the
economizer valve to a value calculated from the determined pressure
of the refrigerant in the injection line, the determined
temperature of the refrigerant, which is discharged from the
compressor, and the superheat value. Thereby, a combination of all
three operation modes may be performed.
[0041] Further, the setting the opening degree of the economizer
valve may comprise, if the determined temperature of the
refrigerant in the discharge line is above the ninth threshold,
closing the economizer valve and stopping the operation of the
compressor.
[0042] In at least some embodiments, the eighth threshold may be
equal to the fifth threshold. Also, the ninth threshold may be
equal to the seventh threshold.
[0043] In another preferred embodiment, if the determined pressure
of the refrigerant in the discharge line is above the third
threshold but below the fourth threshold, the setting the opening
degree of the economizer to a value calculated by using calculated
by using at least the third operation mode may comprise, if the
determined temperature of the refrigerant in the discharge line is
below a tenth threshold, setting the opening degree of the
economizer valve to a value calculated from the determined pressure
of the refrigerant at economizer heat exchanger.
[0044] Further, the setting the opening degree of the economizer
valve may comprise, if the determined temperature of the
refrigerant in the discharge line is above the tenth threshold and
below an eleventh threshold, setting the opening degree of the
economizer valve to a value calculated from the determined pressure
of the refrigerant at economizer heat exchanger, the determined
temperature of the refrigerant in the discharge line, and the
superheat value.
[0045] Also, the setting the opening degree of the economizer valve
may comprise, if the determined temperature of the refrigerant in
the discharge line is above the eleventh threshold, closing the
economizer valve and stopping operation of the compressor.
[0046] In at least some embodiments, the tenth threshold may be
equal to the fifth threshold. Also, the eleventh threshold may be
equal to the seventh threshold.
[0047] In an alternative embodiment of the present invention, the
method for controlling injection into a compressor may not use a
default operation mode, but may instead determine system parameters
and determine a suitable control operation mode based on the
determined system parameters.
[0048] According to the current invention, an alternative method of
controlling injection into a compressor in a refrigeration cycle
according to the invention is performed in a refrigeration cycle,
which comprises at least an economizer, a heat rejection heat
exchanger, a first expansion device, and a compressor configured
for compressing the refrigerant. The compressor comprises a means
for compressing, a suction port, a discharge port, and an injection
port. The heat rejection heat exchanger may be disposed downstream
of the discharge port of the compressor. The connection between the
discharge port and the heat rejection heat exchanger may be
referred to as discharge line. The first expansion device may be
disposed downstream of the heat rejection heat exchanger and
upstream of the suction port of the compressor. Further, the
refrigeration cycle may comprise a heat accepting heat exchanger,
which is disposed downstream of the first expansion device and
upstream of the suction port of the compressor.
[0049] The injection port is connected to the means for compressing
for at least a particular time instance. The means for compressing
is configured for receiving a refrigerant from the suction port
and/or the injection port of the compressor. Further, the means for
compressing compresses the refrigerant. Further, the means for
compressing may be configured for providing the compressed
refrigerant to the discharge port of the compressor.
[0050] In a preferred embodiment, the compressor may be a scroll
compressor and the means for compressing may be formed by a scroll
set of the scroll compressor.
[0051] The economizer comprises an economizer heat exchanger, which
comprises a first path and a second path, for exchanging heat
between refrigerant in the first path and refrigerant in the second
path. The first path has an input, which is connected to the heat
rejection heat exchanger, and an output, which is connected to the
first expansion device. The second path has an input, which is
connected to the heat rejection heat exchanger via an economizer
valve, and an output, which is connected to the injection port of
the compressor via an injection line. Since the present invention
deals with the control of the refrigerant in the refrigerant cycle
of the refrigerant system, the term connected is used throughout
the application to describe a connection, which enables a fluid
communication via this connection. In other words, the connection
enables the exchange of refrigerant between the connected
entities.
[0052] According to the present invention, the method comprises
determining a pressure of the refrigerant in the injection line and
determining a temperature of the refrigerant discharged from the
discharge port of the compressor. The determining may be performed
by one or more sensors.
[0053] Further, the method comprises selecting, based on the
determined pressure and the determined temperature, one of a first
operation mode for regulating the economizer valve based on a
superheat level of the refrigerant in the economizer heat
exchanger, a second operation mode for regulating the economizer
valve based on the temperature of the refrigerant in the discharge
line, and a third operation mode for calculating the economizer
valve based on the pressure of the refrigerant in the injection
line. Also, the method comprises regulating the economizer valve by
using the selected operation mode.
[0054] The thresholds, which are described throughout this
application, may be independent from the operating conditions of
the refrigeration system in at least some embodiments. However, in
other embodiments, at least one of the thresholds may be dependent
on the operating conditions of the refrigeration system. For
example, the third threshold may depend on at least one of the
pressure of the refrigerant in the heat rejection heat exchanger,
the pressure of the refrigerant in the heat accepting heat
exchanger, or the ambient temperature. In this case, the
controller, which performs the method according to the invention
may comprise a logic for adaptively adjusting the third threshold
based on the operating conditions of the refrigeration system.
Since the third threshold may be the maximum injection pressure, a
dependency of the third threshold on the operating conditions of
the refrigeration system may improve the flexibility of the
control, may result in a higher COP and increased reliability of
the compressor, and may also protect the compressor from
failure.
[0055] The following description and the annexed drawings set forth
in detail certain illustrative aspects of the systems described
above. These aspects are indicative, however, of but a few of the
various ways in which the principles of various embodiments can be
employed and the described embodiments are intended to include all
such aspects and their equivalent.
DRAWINGS
[0056] In the drawings, like reference characters generally refer
to the same parts throughout the different drawings. The drawings
are not necessarily to scale, emphasis instead generally being
placed upon illustrating the principles of the invention.
[0057] In the following description, various embodiments of the
invention are described with reference to the following drawings,
in which:
[0058] FIG. 1 shows a schematic of an exemplary refrigeration
system control of refrigerant injection into a compressor in an
economized refrigeration cycle;
[0059] FIG. 2 shows a diagram of the influence of refrigerant
injection on the optimum heat rejection heat exchanger
pressure;
[0060] FIG. 3 shows a discharge temperature over injection pressure
diagram for exemplary embodiments of the current invention;
[0061] FIG. 4a, 4b show block diagrams of the inputs and outputs of
controllers as may be used in connection with the current
invention;
[0062] FIG. 5 shows a flow diagram of a method of controlling the
injection into a compressor according to an embodiment of the
current invention;
[0063] FIG. 6 shows a flow diagram of an alternative method of
controlling the injection into a compressor according to another
embodiment of the current invention;
[0064] FIG. 7 shows a decision diagram of a preferred embodiment of
a method of controlling the injection into a compressor, wherein
the decision diagram relates to regulating the amount of injection
into the compressor;
[0065] FIG. 8 shows a decision diagram, which further specifies
step 310 of FIG. 7;
[0066] FIG. 9 shows a decision diagram, which further specifies
step 314 of FIG. 7; and
[0067] FIG. 10 shows a decision diagram, which further specifies
step 318 of FIG. 7.
DETAILED DESCRIPTION
[0068] The following detailed description refers to the
accompanying drawings that show, by way of illustration, specific
details and embodiments in which the invention may be
practiced.
[0069] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration". Any embodiment or design
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other embodiments or designs.
[0070] FIG. 1 shows a schematic of a refrigeration system 1 for
economizer-based control of refrigerant injection into a compressor
2 of the refrigeration system 1. The refrigeration system 1
comprises a compressor 2, which comprises a suction port 2a, a
discharge port 2b, and an injection port 2c, a heat rejection heat
exchanger 3 downstream of the compressor 2, a first expansion
device 4 downstream of the heat rejection heat exchanger 3, and a
heat accepting heat exchanger 7 downstream of the first expansion
device 4 and upstream of the compressor 2.
[0071] Further, the refrigeration system 1 comprises a second
expansion device 6 and a flash tank 5. The flash tank 5 and the
second expansion device 6 are disposed between the first expansion
device 4 and the heat accepting heat exchanger 7. In detail, the
flash tank 5 is disposed downstream of the first expansion device 4
and upstream of the second expansion device 6, which is disposed
upstream of the heat accepting heat exchanger 7. Thereby, the
pressure and the temperature of the refrigerant could be
reduced.
[0072] In the refrigeration system 1 depicted in FIG. 1, the flash
tank 5 comprises two separation chambers 5a, 5b. However, it would
also be possible that the flash tank separates the liquid
refrigerant and the vapour refrigerant in the same volume.
[0073] The two separation chambers 5a, 5b include a chamber 5a used
for collecting vapour or flash gas and a chamber 5b for collecting
liquid. Liquid collecting chamber 5b comprises at least one outlet.
The connection between the flash tank 5 and the second expansion
device 6 is established via at least one of the at least one
outlets of the liquid collecting chamber 5b of the flash tank
5.
[0074] The vapour collecting chamber 5a of the flash tank 5
comprises at least one outlet. The at least one outlet of the
vapour collecting chamber 5a is connected to the suction port of
the compressor 2 via a by-pass path 8 and a by-pass valve 9.
[0075] Although a flash tank 5 and a by-pass line 8 are depicted in
FIG. 1, the person skilled in the art will appreciate that the
flash tank 5 is not necessary for the refrigeration system. In at
least some embodiments, no flash tank is used or a flash tank 5 is
used without a by-pass line.
[0076] The refrigeration system 1 comprises an economizer heat
exchanger 11. The economizer heat exchanger comprises two path--a
first path 11a, which is connected to the heat rejection heat
exchanger 3 and the first expansion device 4, and a second path
11b, which is connected to the heat rejection heat exchanger 3 via
an economizer valve 13 and is connected to the injection port 2c of
the compressor 2 via an injection line 12. In the example depicted
in FIG. 1, the first path and the second path of the economizer
have counter-wise flow directions.
[0077] In the economizer heat exchanger 11 depicted in FIG. 1, the
first path 11a and the second path 11b are in near proximity to
each other, such that heat exchange is possible between both paths.
Because the refrigerant in the second path 11b is expanded by the
economizer valve 13, the refrigerant in the second path 11b has a
lower temperature than the refrigerant in the first path 11a.
Therefore, heat is exchanged from the refrigerant of the first path
11a to the refrigerant of the second path 11b. This process is a
subcooling process, which decreases the amount of heat of the
refrigerant in the first path 11a and may thereby also reduce the
temperature of the refrigerant in the first path 11a.
[0078] Further, the refrigeration system 1 comprises a controller
10, which is used for regulating at least the economizer valve 13.
Additionally, the controller 10 may also be used to control any of
the first expansion device 4, the flash tank 5, the second
expansion device 6, the by-pass valve 9, and the compressor 2. The
operation of the controller 10 is based on the superheat level of
the refrigerant in the economizer heat exchanger 11. Additionally,
the controller 10 may also use system parameters like the pressure
of the refrigerant in the injection line 12 or the temperature of
the refrigerant, which is discharged from the compressor 2.
[0079] FIG. 1 indicates the connection for exchanging control
signals by ease of dashed lines. Although FIG. 1 shows dashed lines
between the controller 10 and the economizer valve 13, the first
expansion device 4, the second expansion device 6, the compressor
2, and the flash tank 5, the person skilled in the art will
appreciate that these dashed lines are shown for illustration
purposes only. The controller 10 may be connected to any subset of
the aforementioned components of the refrigeration cycle. With
respect to the connection between the controller 10 and the flash
tank 5, it is to be noted that the controller 10 may be connected
to a sensor within the flash tank 5, wherein the sensor may be a
pressure sensor. Furthermore, in some examples, multiple
controllers may be employed in the refrigeration system. Each of
these multiple controllers may control any subset of the expansion
devices, the compressor, and the flash tank as is described before
with respect to controller 10.
[0080] FIG. 2 shows a diagram of the influence of refrigerant
injection on the optimum heat rejection heat exchanger pressure. In
detail, FIG. 2 depicts the coefficient of performance (COP)
depending on the pressure of the refrigerant in the heat rejection
heat exchanger (p.sub.c). Thereby, solid line 50 represents the
curve of the COP for a refrigeration system with closed injection
valve, i.e. without injection of refrigerant into the means for
compressing of the compressor.
[0081] The dashed line 55 represents an exemplary curve of the COP
for the same refrigeration system with an at least partially opened
injection valve, i.e. with injection of refrigerant into the means
for compressing of the compressor. The difference between the
curves is shown for illustrative purpose.
[0082] In a refrigeration system, the operating conditions are
controlled in order to achieve a higher COP. Without refrigerant
injection, the COP depends on the temperature of the refrigerant in
the heat rejection heat exchanger. However, refrigerant injection
has a direct influence on the efficiency of the system. This
influence depends on the injection conditions, like pressure of the
injected refrigerant or temperature of the injected refrigerant. As
can be seen, injection does not only improve the overall COP.
Injection also shifts the maximum of the COP to a lower pressure of
the refrigerant in the heat rejection heat exchanger. The maximum
of the respective curve represents the optimum heat rejection heat
exchanger pressure. This optimum pressure is lower when injection
of refrigerant into the compressor is used.
[0083] FIG. 3 shows a discharge temperature over injection pressure
diagram for exemplary embodiments of the current invention. The
pressure p corresponds to the pressure at which the refrigerant is
injected into the injection port of the compressor. This pressure
may be measured in the second path of the economizer or in the
injection line and may be referred to as injection pressure. The
temperature T corresponds to the temperature of the refrigerant,
which is discharged from the discharge port of the compressor. This
temperature may be measured at the discharge port or in the
connection line between the discharge port and the heat rejection
heat exchanger and may be referred to as discharge line
temperature, DLT.
[0084] In the temperature-pressure-diagram, different areas 70, 71,
72, 73, 74, 75 are depicted. These areas are based on particular
pressure and temperature thresholds and indicate the pressure and
temperature ranges for each of the three operation modes or
combinations thereof.
[0085] Below an injection pressure of p.sub.0, no injection into
the compressor is performed. In this case, the injection pressure
would be too low for an efficient injection. Instead, the pressure
may be so low that the refrigerant from the injection line would
not be injected into the compressor, but that undesired reverse
flow from the compressor through the discharge line may occur.
P.sub.0 may be referred to as minimum pressure for injection.
[0086] Also, there will be no injection performed for a pressure
higher than p.sub.max. If the pressure would exceed p.sub.max, the
refrigerant would be injected at such a high pressure that the
compressor may be damaged or the efficiency of the refrigeration
cycle would be reduced. Similarly, no injection will be performed
for temperatures exceeding a maximum temperature value of
T.sub.max.
[0087] Between the pressure stages p.sub.0 and p.sub.max, injection
is performed based on the three operation modes or combinations
thereof. Thereby, the first operation mode is denoted as superheat
control mode. The first operation mode is performed for pressure
ranges from p.sub.0 up to p.sub.1 and temperature ranges below
T.sub.1. The corresponding area in the temperature-pressure-diagram
is area 70.
[0088] The second operation mode is denoted as discharge line
temperature control mode and is performed for pressure ranges from
p.sub.0 up to p.sub.1 and temperature ranges between T.sub.2 and
T.sub.max. The corresponding area in the
temperature-pressure-diagram is area 72.
[0089] At 71, for p.sub.0 to p.sub.1 and T.sub.1 to T.sub.2, a
combination of the superheat control mode and the discharge line
temperature control mode is performed.
[0090] The third operation mode is denoted as injection pressure
control mode and is performed for pressure ranges from p.sub.2 up
to p.sub.max and temperature ranges below T.sub.1. The
corresponding area in the temperature-pressure-diagram is area
74.
[0091] At 73, for p.sub.1 to p.sub.2 and discharge line
temperatures below T.sub.1, a combination of the superheat control
mode and injection pressure control mode is performed.
[0092] Further, for discharge line temperatures higher than T.sub.1
and injection pressures between p.sub.1 and p.sub.max, a
combination of all three operation modes is performed in area
75.
[0093] The person skilled in the art will appreciate that the
pressure stages p.sub.i and the temperature stages T.sub.i are for
illustrative purposes. The particular values of these stages depend
on the system to which the control operation is applied.
[0094] FIGS. 4a, 4b show block diagrams of the inputs and the
outputs of controllers as may be used in connection with the
current invention.
[0095] In FIG. 4a, the controller, which is represented by block
"CTRL" receives the superheat value of the refrigerant in the
second path of the economizer as input and controls at least the
economizer valve, which is denoted as economizer heat exchanger
valve "EHXV". Additionally, the controller may also control the
operation of the compressor CMP. In FIG. 4a, the output arrow of
the compressor CMP is shown as dashed line in order to illustrate
that the controller may perform economizer valve control, or both,
the economizer valve control and the compressor control.
[0096] In FIG. 4b, the controller receives the superheat value as
input and controls the economizer valve and optionally the
compressor. Further, the controller receives the pressure of the
refrigerant in the injection line (denoted as economizer heat
exchanger pressure "EHXP") and the temperature of the refrigerant
in the discharge line (denoted as discharge line temperature "DLT")
as additional inputs.
[0097] FIG. 5 shows a flow diagram of a method 100 of controlling
the injection into a compressor according to an embodiment of the
invention. The method 100 may be performed by a controller in a
refrigeration cycle, for example controller 10 as depicted in FIG.
1. Throughout the flow diagram, solid lines indicate steps, which
are essential to the current invention, whereas dashed lines
indicate steps, which are performed in preferred embodiments of the
current invention.
[0098] The method 100 comprises the step of determining 102 a
pressure of the refrigerant in the injection line 12. Determining a
pressure of the refrigerant in the injection line may comprise
determining a pressure in any part of the injection line 12, the
second path of the economizer heat exchanger 11b, or at the outlet
of the second path of the economizer heat exchanger 11b.
[0099] Further, the method 100 comprises the step of determining
104 a temperature of the refrigerant in the discharge line 14.
Because of the similar temperature of the refrigerant at the
discharge port 2b and the discharge line 14, determining the
temperature of the refrigerant at the discharge port 2b of the
compressor 2 also may be performed by measuring the temperature of
the refrigerant in the discharge line 14.
[0100] Also, the method comprises regulating 106 the economizer
valve 13 by using a first operation mode. The first operation mode
may correspond to the superheat control mode. Regulating 106 the
economizer valve 13 may comprise determining 108 whether to proceed
with regulating the economizer valve by using the first operation
mode or whether to perform one of a second and a third operation
mode. Thereby, the first operation mode may establish a default
operation of the controller. The second operation mode may
correspond to the discharge line temperature control mode and the
third operation mode may correspond to the injection pressure
control mode.
[0101] Based on the determining 108, the method 100 may comprise
proceeding 110 with regulating 106 the economizer valve by using
the first operation mode, or regulating 112 the economizer valve by
using the second operation mode, or regulating 114 the economizer
valve by using the third operation mode.
[0102] FIG. 6 shows a flow diagram of the method 200 of controlling
the injection into a compressor according to an alternative
embodiment of the invention. The method 200 may be performed by a
controller in a refrigeration cycle, for example controller 10 as
depicted in FIG. 1.
[0103] The method 200 comprises the step of determining 202 a
pressure of the refrigerant in the injection line 12. Determining a
pressure of the refrigerant in the injection line may comprise
determining a pressure in any part of the injection line 12, the
second path of the economizer heat exchanger 11b, or at the outlet
of the second path of the economizer heat exchanger 11b.
[0104] Further, the method 200 comprises the step of determining
204 a temperature of the refrigerant in the discharge line 14.
Because of the similar temperature of the refrigerant at the
discharge port 2b and in the discharge line 14, determining the
temperature of the refrigerant at the discharge port of the
compressor 2 also may be performed by measuring the temperature of
the refrigerant in the discharge line 14.
[0105] Also, the method 200 comprises the step of selecting 206 one
of a first operation mode, a second operation mode, and a third
operation mode. Thereby, the first operation mode may correspond to
the superheat control mode, the second operation mode may
correspond to the discharge line temperature control mode, and the
third operation mode may correspond to the injection pressure
control mode.
[0106] Further, the method 200 comprises regulating 208 the
economizer valve 13 by using the selected operation mode.
[0107] FIG. 7 shows a decision diagram 300 of a preferred
embodiment of a method of controlling the injection into a
compressor, wherein the decision diagram relates to regulating the
amount of injection into the compressor. The amount of injection
into the compressor is controlled by regulating the so-called
economizer valve or economizer heat exchanger valve, which is
referred to as EHXV (cf. reference sign 13 in FIG. 1). The decision
may be carried out by a controller, for example controller 10.
[0108] The method starts at step 302 where the determined pressure
of the refrigerant in the injection line is received. In FIG. 7,
the pressure of the refrigerant in the injection line is referred
to as p.
[0109] At step 304, it is determined whether the injection pressure
p is below a first threshold. In case that the pressure is lower
than the first threshold, the method continues at step 306 where
the economizer valve EHXV is closed. Otherwise, the method
continues at step 308.
[0110] At step 308, it is determined whether the injection pressure
p is greater than or equal to the first threshold and lower than a
second threshold. In case that the injection pressure is greater
than or equal to the first threshold and lower than the second
threshold, the method continues at step 310 where the economizer
valve EHXV is opened. There, the opening degree of the economizer
valve EHXV is calculated as a function of at least one of the
superheat value, SH, of the refrigerant in the economizer heat
exchanger or the temperature of the refrigerant in the discharge
line, DLT. As will be described in more detail with respect to FIG.
8, the opening degree may be calculated based on the superheat
value, the discharge line temperature, or a combination of both,
depending on value of the discharge line temperature. In case that
the injection pressure is not greater than or equal to the first
threshold and lower than the second threshold, the method continues
at step 312.
[0111] At step 312, it is determined whether the injection pressure
p is greater than or equal to the second threshold and lower than a
third threshold. In case that the injection pressure is greater
than or equal to the second threshold and lower than the third
threshold, the method continues at step 314 where the economizer
valve EHXV is opened. There, the opening degree of the economizer
valve EHXV is calculated as a function of at least the superheat
value, SH, the injection pressure, p. As will be described in more
detail with respect to FIG. 9, the opening degree may be calculated
based on the injection pressure, the discharge line temperature, or
a combination of both, depending on value of the discharge line
temperature. Additionally, considering the superheat value for the
calculation may also be possible. In case that the injection
pressure is not greater than or equal to the second threshold and
lower than the third threshold, the method continues at step
316.
[0112] At step 316, it is determined whether the injection pressure
p is greater than or equal to the third threshold and lower than a
fourth threshold. In case that the injection pressure is greater
than or equal to the third threshold and lower than the fourth
threshold, the method continues at step 318 where the economizer
valve EHXV is opened. There, the opening degree of the economizer
valve EHXV is calculated as a function of at least the injection
pressure, p. As will be described in more detail with respect to
FIG. 10, the discharge line temperature or the superheat value may
also be considered for the calculation of the opening degree,
depending on value of the discharge line temperature. In case that
the injection pressure is not greater than or equal to the third
threshold and lower than the fourth threshold, the method continues
at step 320 where the economizer valve EHXV is closed and the
compressor is turned off.
[0113] In case the method reaches either one of steps 306, 310,
314, 318, or 320, the method may again continue at step 302 by
determining or receiving an injection pressure p. In this case, the
method may determine or receive an updated value for the injection
pressure p.
[0114] FIG. 8 shows a decision diagram, which describes a method
400 for determining the opening degree of the economizer valve EHXV
based on step 310 of the decision diagram of FIG. 7 in more
detail.
[0115] Following step 310, method 400 receives a determined value
for the temperature of the refrigerant in the discharge line at
step 402.
[0116] At step 404, it is determined whether the discharge line
temperature DLT is below a fifth threshold. In case that the
temperature is lower than the fifth threshold, the method continues
at step 406 where the opening degree of the economizer valve EHXV
is calculated as a function of the superheat level of the
refrigerant in the economizer. This refers to the first operation
mode, also called superheat control mode. With reference to FIG. 3,
step 406 may refer to the operation performed for pressure and
temperature being located in area 70. Otherwise, the method
continues at step 408.
[0117] At step 408, it is determined whether the discharge line
temperature DLT is greater than or equal to the fifth threshold and
lower than a sixth threshold. In case that the temperature is
greater than or equal to the fifth threshold and lower than the
sixth threshold, the method continues at step 410 where the opening
degree of the economizer valve is calculated as a function of the
superheat level of the refrigerant in the economizer and the
temperature of the refrigerant in the discharge line, DLT. Thereby,
a combination of the superheat control and the discharge line
control mode may be performed. With reference to FIG. 3, step 410
may refer to the operation performed for pressure and temperature
being located in area 71. In case that the discharge line
temperature is not greater than or equal to the fifth threshold and
lower than the sixth threshold, the method continues at step
412.
[0118] At step 412, it is determined whether the discharge line
temperature DLT is greater than or equal to the sixth threshold and
lower than a seventh threshold. In case that the temperature is
greater than or equal to the sixth threshold and lower than the
seventh threshold, the method continues at step 414 where the
opening degree of the economizer valve EHXV is calculated as a
function of the temperature of the refrigerant in the discharge
line, DLT. Thereby, the operation is performed based on the
discharge line control mode. With reference to FIG. 3, step 414 may
refer to the operation performed for pressure and temperature being
located in area 72. In case that the discharge line temperature is
not greater than or equal to the sixth threshold and lower than
seventh threshold, the method continues at step 416 where the
economizer valve EHXV is closed and the compressor is turned
off.
[0119] In case the method reaches either one of steps 406, 410,
414, or 416, the method may again continue at step 402 by
determining or receiving the discharge line temperature. In this
case, the method may determine or receive an updated value for the
discharge line temperature.
[0120] FIG. 9 shows a decision diagram, which describes a method
500 for determining the opening degree of the economizer valve EHXV
based on step 314 of the decision diagram of FIG. 7 in more
detail.
[0121] Following step 314, method 500 receives a determined value
for the temperature of the refrigerant in the discharge line at
step 502.
[0122] At step 504, it is determined whether the discharge line
temperature DLT is below an eighth threshold. In case that the
temperature is lower than the eighth threshold, the method
continues at step 506 where the opening degree of the economizer
valve EHXV is calculated as a function of the pressure of the
refrigerant in the injection line and the superheat value. Thereby,
a combination of the superheat control mode and the injection
pressure control mode is performed. With reference to FIG. 3, step
506 may refer to the operation performed for pressure and
temperature being located in area 73. Otherwise, the method
continues at step 508.
[0123] At step 508, it is determined whether the discharge line
temperature DLT is greater than or equal to the eighth threshold
and lower than a ninth threshold. In case that the temperature is
greater than or equal to the eighth threshold and lower than the
ninth threshold, the method continues at step 510 where the opening
degree of the economizer valve is calculated as a function of the
superheat value, the pressure of the refrigerant in the injection
line, and the temperature of the refrigerant in the discharge line,
DLT. Thereby, a combination of all three operation modes is
performed. With reference to FIG. 3, step 510 may refer to the
operation performed for pressure and temperature being located in
area 75. In case that the discharge line temperature is not greater
than or equal to the eighth threshold and lower than the ninth
threshold, the method continues at step 512, where the economizer
valve EHXV is closed and the compressor is turned off.
[0124] In some embodiments, the eighth threshold is equal to the
fifth threshold and the ninth threshold is equal to the seventh
threshold.
[0125] In case the method reaches either one of steps 506, 510, or
512, the method may again continue at step 502 by determining or
receiving the discharge line temperature. In this case, the method
may determine or receive an updated value for the discharge line
temperature.
[0126] FIG. 10 shows a decision diagram, which describes a method
600 for determining the opening degree of the economizer valve EHXV
based on step 318 of the decision diagram of FIG. 7 in more
detail.
[0127] Following step 318, method 600 receives a determined value
for the temperature of the refrigerant in the discharge line at
step 602.
[0128] At step 604, it is determined whether the discharge line
temperature DLT is below a tenth threshold. In case that the
temperature is lower than the tenth threshold, the method continues
at step 606 where the opening degree of the economizer valve EHXV
is calculated as a function of the pressure of the refrigerant in
the injection line. Thereby, injection pressure control mode is
performed. With reference to FIG. 3, step 606 may refer to the
operation performed for pressure and temperature being located in
area 74. Otherwise, the method continues at step 608.
[0129] At step 608, it is determined whether the discharge line
temperature DLT is greater than or equal to the tenth threshold and
lower than an eleventh threshold. In case that the temperature is
greater than or equal to the tenth threshold and lower than the
eleventh threshold, the method continues at step 610 where the
opening degree of the economizer valve is calculated as a function
of the superheat value, the pressure of the refrigerant in the
injection line, and the temperature of the refrigerant in the
discharge line, DLT. Thereby, a combination of all three operation
modes is performed. With reference to FIG. 3, step 610 may refer to
the operation performed for pressure and temperature being located
in area 75. In case that the discharge line temperature is not
greater than or equal to the tenth threshold and lower than the
eleventh threshold, the method continues at step 612, where the
economizer valve EHXV is closed and the compressor is turned
off.
[0130] In some embodiments, the tenth threshold is equal to the
fifth threshold and the eleventh threshold is equal to the seventh
threshold.
[0131] In case the method reaches either one of steps 606, 610, or
612, the method may again continue at step 602 by determining or
receiving the discharge line temperature. In this case, the method
may determine or receive an updated value for the discharge line
temperature.
[0132] In some embodiments, the operation of the control operation
is performed on the basis of the interrelated methods described
with respect to FIGS. 7 to 10. If, in such a case, the eighth
threshold is equal to the fifth threshold and the ninth threshold
is equal to the seventh threshold and the tenth threshold is equal
to the fifth threshold and the eleventh threshold is equal to the
seventh threshold, one arrives at the areas 70 to 75 described with
respect to FIG. 2, wherein the first threshold corresponds to
p.sub.0, the second threshold corresponds to p.sub.1, the third
threshold corresponds to p.sub.2, the fourth threshold corresponds
to p.sub.max, the fifth threshold corresponds to T.sub.1, the sixth
threshold corresponds to T.sub.2, and the seventh threshold
corresponds to T.sub.max. Accordingly, the first operation mode,
which is the superheat control mode, is performed in area 70, the
second operation mode, which is the discharge line temperature
control mode, is performed in area 72, and the third operation
mode, which is the injection pressure control mode, is performed in
area 74, whereas a combination of the first and second control
modes is performed in area 71, a combination of the first and the
third operation modes is performed in area 73, and a combination of
all three operation modes is performed in area 75, and the
economizer expansion valve is closed, while the compressor is
turned off outside of areas 70 to 75.
[0133] What has been described above includes examples of one or
more embodiments. It is, of course, not possible to describe every
conceivable combination of components or methodologies for purposes
of describing the aforementioned embodiments, but one of ordinary
skill in the art may recognize that many further combinations and
permutations of various embodiments are possible. Accordingly, the
described embodiments are intended to embrace all such alterations,
modifications and variations that fall within the scope of the
appended claims.
* * * * *