U.S. patent application number 12/888733 was filed with the patent office on 2012-03-29 for control of a transcritical vapor compression system.
This patent application is currently assigned to THERMO KING CORPORATION. Invention is credited to Michal Hegar, Michal Kolda, Marketa Kopecka, Vaclav Rajtmajer.
Application Number | 20120073316 12/888733 |
Document ID | / |
Family ID | 44532687 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120073316 |
Kind Code |
A1 |
Hegar; Michal ; et
al. |
March 29, 2012 |
CONTROL OF A TRANSCRITICAL VAPOR COMPRESSION SYSTEM
Abstract
A transcritical vapor compression system includes a compressor
for compressing a refrigerant, a first heat exchanger for cooling
the refrigerant, an expansion device for decreasing the pressure of
the refrigerant, a second heat exchanger for absorbing heat into
the refrigerant, and a controller programmed to calculate a first
energy difference across the second heat exchanger and a second
energy difference across the compressor, to calculate an energy
ratio by dividing the first energy difference by the second energy
difference, to compare the energy ratio to a previously calculated
energy ratio, and to adjust operating parameters of the system
based on the comparison of the energy ratio with respect to the
previously calculated energy ratio.
Inventors: |
Hegar; Michal; (Prague,
CZ) ; Kolda; Michal; (Prague, CZ) ; Kopecka;
Marketa; (Vsetin, CZ) ; Rajtmajer; Vaclav;
(Beroun, CZ) |
Assignee: |
THERMO KING CORPORATION
Minneapolis
MN
|
Family ID: |
44532687 |
Appl. No.: |
12/888733 |
Filed: |
September 23, 2010 |
Current U.S.
Class: |
62/115 ;
62/228.1; 62/498; 62/513 |
Current CPC
Class: |
F25B 2600/17 20130101;
F25B 2700/1933 20130101; F25B 2700/2102 20130101; F25B 2500/19
20130101; F25B 2700/21152 20130101; F25B 2700/21174 20130101; F25B
2700/1931 20130101; F25B 2309/061 20130101; F25B 2700/197 20130101;
F25B 9/008 20130101; F25B 2700/21151 20130101 |
Class at
Publication: |
62/115 ; 62/498;
62/513; 62/228.1 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25B 49/02 20060101 F25B049/02; F25B 41/00 20060101
F25B041/00 |
Claims
1. A transcritical vapor compression system, comprising: a
compressor for compressing a refrigerant; a first heat exchanger
for cooling the refrigerant; an expansion device for decreasing the
pressure of the refrigerant; a second heat exchanger for absorbing
heat into the refrigerant; and a controller programmed to calculate
a first energy difference across the second heat exchanger and a
second energy difference across the compressor, to calculate an
energy ratio by dividing the first energy difference by the second
energy difference, to compare the energy ratio to a previously
calculated energy ratio, and to adjust operating parameters of the
system based on the comparison of the energy ratio with respect to
the previously calculated energy ratio.
2. The transcritical vapor compression system of claim 1, further
comprising: a first blower for directing a first fluid over the
first heat exchanger; and a second blower for directing a second
fluid over the second heat exchanger; wherein the controller is
programmed to adjust at least one of speed of the first blower,
speed of the second blower, speed of the compressor and opening of
the expansion device based on the comparison of the energy ratio
with respect to the previously calculated energy ratio.
3. The transcritical vapor compression system of claim 1, further
comprising: a first temperature sensor and a first pressure sensor
positioned proximate an inlet to the compressor for measuring
temperature and pressure, respectively; a second temperature sensor
and a second pressure sensor positioned proximate an outlet of the
compressor for measuring temperature and pressure, respectively; a
third temperature sensor positioned proximate an inlet to the
second heat exchanger for measuring temperature; a fourth
temperature sensor positioned proximate an outlet of the second
heat exchanger for measuring temperature; and a third pressure
sensor positioned proximate one of the inlet and the outlet to the
second heat exchanger for measuring pressure.
4. The transcritical vapor compression system of claim 3, wherein
the controller is programmed to calculate the internal energy of
the refrigerant proximate the inlet to the compressor, the outlet
of the compressor, the inlet of the second heat exchanger and the
outlet of the second heat exchanger based on the measurements of
temperature and pressure.
5. The transcritical vapor compression system of claim 4, wherein
the controller is programmed to calculate the first energy
difference by subtracting the internal energy of refrigerant
proximate the inlet to the second heat exchanger from the internal
energy of refrigerant proximate the outlet of the second heat
exchanger, and wherein the controller is programmed to calculate
the second energy difference by subtracting the internal energy of
refrigerant proximate the inlet to the compressor from the internal
energy of the refrigerant proximate the outlet of the
compressor.
6. (canceled)
7. A method of controlling a transcritical vapor compression
system, the method comprising: providing a compressor for
compressing a refrigerant; providing a first heat exchanger for
cooling the refrigerant; providing an expansion device for
decreasing the pressure of the refrigerant; providing a second heat
exchanger for absorbing heat into the refrigerant; calculating a
first energy difference across the second heat exchanger;
calculating a second energy difference across the compressor;
calculating an energy ratio by dividing the first energy difference
by the second energy difference; comparing the energy ratio to a
previously calculated energy ratio; and adjusting operating
parameters of the system based on the comparison of the energy
ratio with respect to the previously calculated energy ratio.
8. The method of claim 7, further comprising: providing a first
blower for directing a first fluid over the first heat exchanger;
providing a second blower for directing a second fluid over the
second heat exchanger; adjusting at least one of speed of the first
blower, speed of the second blower, speed of the compressor and
opening of the expansion device based on the comparison of the
energy ratio with respect to the previously calculated energy
ratio.
9. The method of claim 7, further comprising: measuring temperature
and pressure proximate an inlet to the compressor; measuring
temperature and pressure proximate an outlet of the compressor;
measuring temperature proximate an inlet to the second heat
exchanger; measuring temperature proximate an outlet of the second
heat exchanger; and measuring pressure proximate one of the inlet
and the outlet to the second heat exchanger.
10. The method of claim 9, further comprising calculating the
internal energy of the refrigerant proximate the inlet to the
compressor, the outlet of the compressor, the inlet of the second
heat exchanger and the outlet of the second heat exchanger based on
the measurements of temperature and pressure.
11. The method of claim 10, further comprising calculating the
first energy difference by subtracting the internal energy of
refrigerant proximate the inlet to the evaporator from the internal
energy of refrigerant proximate the outlet of the evaporator, and
calculating the second energy difference by subtracting the
internal energy of refrigerant proximate the inlet to the
compressor from the internal energy of the refrigerant proximate
the outlet of the compressor.
12. (canceled)
13. A transcritical vapor compression system, comprising: a
compressor for compressing a refrigerant; a first heat exchanger
for cooling the refrigerant; an expansion device for decreasing the
pressure of the refrigerant; a second heat exchanger for absorbing
heat into the refrigerant; a first blower for directing a first
fluid over the first heat exchanger; a second blower for directing
a second fluid over the second heat exchanger; a first temperature
sensor and a first pressure sensor positioned proximate an inlet to
the compressor for measuring temperature and pressure,
respectively; a second temperature sensor and a second pressure
sensor positioned proximate an outlet of the compressor for
measuring temperature and pressure, respectively; a third
temperature sensor positioned proximate an inlet to the second heat
exchanger for measuring temperature; a fourth temperature sensor
positioned proximate an outlet of the second heat exchanger for
measuring temperature; a third pressure sensor positioned proximate
one of the inlet and the outlet to the second heat exchanger for
measuring pressure; and a controller programmed to calculate the
internal energy of the refrigerant proximate the inlet to the
compressor, the outlet of the compressor, the inlet of the second
heat exchanger and the outlet of the second heat exchanger based on
the measurements of temperature and pressure, to calculate a first
energy difference by subtracting the internal energy of refrigerant
proximate the inlet to the second heat exchanger from the internal
energy of refrigerant proximate the outlet of the second heat
exchanger, to calculate a second energy difference by subtracting
the internal energy of refrigerant proximate the inlet to the
compressor from the internal energy of the refrigerant proximate
the outlet of the compressor, to calculate an energy ratio by
dividing the first energy difference by the second energy
difference, to compare the energy ratio to a previously calculated
energy ratio, and to adjust at least one of speed of the first
blower, speed of the second blower, speed of the compressor and
opening of the expansion device based on the comparison of the
energy ratio with respect to the previously calculated energy
ratio.
Description
BACKGROUND
[0001] The present invention relates to control of a transcritical
vapor compression system.
[0002] Typically, a transcritical vapor compression system is
controlled to optimize the coefficient of performance (COP). Known
control methods include measuring various parameters and comparing
the measured parameter to a stored value representative of an
efficient system. For example, if the measured parameter is
significantly higher than the stored value, then the system is
operating inefficiently and operating parameters are adjusted
accordingly.
SUMMARY
[0003] In one aspect, the invention provides a transcritical vapor
compression system. The transcritical vapor compression system
includes a compressor for compressing a refrigerant, a first heat
exchanger for cooling the refrigerant, an expansion device for
decreasing the pressure of the refrigerant, a second heat exchanger
for absorbing heat into the refrigerant, and a controller
programmed to calculate a first energy difference across the second
heat exchanger and a second energy difference across the
compressor, to calculate an energy ratio by dividing the first
energy difference by the second energy difference, to compare the
energy ratio to a previously calculated energy ratio, and to adjust
operating parameters of the system based on the comparison of the
energy ratio with respect to the previously calculated energy
ratio.
[0004] In another aspect, the invention provides a method of
controlling a transcritical vapor compression system. The method
includes providing a compressor for compressing a refrigerant,
providing a first heat exchanger for cooling the refrigerant,
providing an expansion device for decreasing the pressure of the
refrigerant, providing a second heat exchanger for absorbing heat
into the refrigerant, calculating a first energy difference across
the second heat exchanger, calculating a second energy difference
across the compressor, calculating an energy ratio by dividing the
first energy difference by the second energy difference, comparing
the energy ratio to a previously calculated energy ratio, and
adjusting operating parameters of the system based on the
comparison of the energy ratio with respect to the previously
calculated energy ratio.
[0005] In another aspect, the invention provides a transcritical
vapor compression system. The transcritical vapor compression
system includes a compressor for compressing a refrigerant, a first
heat exchanger for cooling the refrigerant, an expansion device for
decreasing the pressure of the refrigerant, a second heat exchanger
for absorbing heat into the refrigerant, a first blower for
directing a first fluid over the first heat exchanger, a second
blower for directing a second fluid over the second heat exchanger,
a first temperature sensor and a first pressure sensor positioned
proximate an inlet to the compressor for measuring temperature and
pressure, respectively, a second temperature sensor and a second
pressure sensor positioned proximate an outlet of the compressor
for measuring temperature and pressure, respectively, a third
temperature sensor positioned proximate an inlet to the second heat
exchanger for measuring temperature, a fourth temperature sensor
positioned proximate an outlet of the second heat exchanger for
measuring temperature, a third pressure sensor positioned proximate
one of the inlet and the outlet to the second heat exchanger for
measuring pressure, and a controller. The controller is programmed
to calculate the internal energy of the refrigerant proximate the
inlet to the compressor, the outlet of the compressor, the inlet of
the second heat exchanger and the outlet of the second heat
exchanger based on the measurements of temperature and pressure, to
calculate a first energy difference by subtracting the internal
energy of refrigerant proximate the inlet to the second heat
exchanger from the internal energy of refrigerant proximate the
outlet of the second heat exchanger, to calculate a second energy
difference by subtracting the internal energy of refrigerant
proximate the inlet to the compressor from the internal energy of
the refrigerant proximate the outlet of the compressor, to
calculate an energy ratio by dividing the first energy difference
by the second energy difference, to compare the energy ratio to a
previously calculated energy ratio, and to adjust at least one of
speed of the first blower, speed of the second blower, speed of the
compressor and opening of the expansion device based on the
comparison of the energy ratio with respect to the previously
calculated energy ratio.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic diagram of a transcritical vapor
compression system in accordance with the invention.
[0008] FIG. 2 is a diagram of internal energy and pressure of the
transcritical vapor compression system shown in FIG. 1.
DETAILED DESCRIPTION
[0009] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways.
[0010] FIG. 1 illustrates a transcritical vapor compression system
10. The transcritical vapor compression system 10 is a closed
circuit single stage vapor compression cycle preferably utilizing
carbon dioxide (CO.sub.2) as a refrigerant, although other
refrigerants suitable for a transcritical vapor compressor system
may be employed, as are known in the art. The system 10 includes a
compressor 14, a gas cooler 18, an expansion valve 22, an
evaporator 26 and an accumulator tank 30 connected in series.
Temperature sensors 42a-42e and pressure sensors 46a-46e are
located at the compressor inlet 1, the compressor outlet 2, the gas
cooler outlet 3, the evaporator inlet 4 and the evaporator outlet
5, respectively.
[0011] In the illustrated construction, CO.sub.2 refrigerant exits
the evaporator coil 26 as a heated gas and is drawn into a suction
port of the compressor 14, such as a variable speed compressor. The
temperature and pressure of the CO.sub.2 refrigerant are measured
at the compressor inlet 1 by the temperature and pressure sensors
42a, 46a, respectively. The compressor 14 pressurizes and
discharges heated CO.sub.2 refrigerant gas into the gas cooler 18.
The temperature and pressure of the heated CO.sub.2 refrigerant are
measured at the compressor outlet 2 by the temperature and pressure
sensors 42b, 46b, respectively. In the gas cooler 18, or heat
exchanger, the heated CO.sub.2 refrigerant is cooled to a lower
temperature gas as a result of a forced flow of air 34 flowing over
the gas cooler 18 and generated by blowers 36, such as variable
speed blowers. The gas cooler 18 can include one or more heat
exchanger coils having any suitable construction, as is known in
the art. The temperature and pressure of the cooled CO.sub.2
refrigerant are measured at the gas cooler outlet 3 by the
temperature and pressure sensors 42c, 46c, respectively. Then, the
cooled CO.sub.2 is throttled through the expansion valve 22, such
as an electronic expansion valve, and directed toward the
evaporator coil 26 at a decreased pressure as a liquid-vapor
mixture. The temperature and pressure of the cooled CO.sub.2
refrigerant are measured at the evaporator inlet 4 by the
temperature and pressure sensors 42d, 46d, respectively. In the
evaporator coil 26, or heat exchanger, the cooled CO.sub.2
refrigerant is heated to a higher temperature gas as a result of a
forced flow of air 38 generated by blowers 40, such as variable
speed blowers. In other words, the CO.sub.2 passing through the
evaporator coil 26 absorbs the heat from the flow of air 38 such
that the flow of air 38 is cooled. The evaporator coil 26 can
include one or more heat exchanger coils having any suitable
construction, as is known in the art. The temperature of the heated
CO.sub.2 refrigerant is measured at the evaporator outlet 5 by the
temperature sensor 42e and, optionally, the pressure is measured by
the pressure sensor 46e. As the pressures at the inlet 4 and outlet
5 of the evaporator 26 are substantially the same, only one of the
pressure sensors 46d, 46e are necessary.
[0012] In the illustrated construction, CO.sub.2 refrigerant does
not change phase to a liquid in the transcritical CO.sub.2
refrigeration cycle. In other words, the CO.sub.2 refrigerant
behaves as a single-phase refrigerant in a transcritical CO.sub.2
refrigeration cycle, as opposed to the two-phase behavior of
refrigerant in a reverse-Rankine refrigeration cycle. To obtain
desirable refrigeration characteristics from the CO.sub.2
refrigerant, or other refrigerant used, the transcritical
refrigeration cycle requires higher operating pressures compared to
a reverse-Rankine refrigeration cycle. The pressure of the
refrigerant in the gas cooler 18 is in the supercritical region of
the refrigerant, i.e., at or above the critical temperature and
critical pressure of the refrigerant. For example, the critical
point of CO.sub.2 occurs at approximately 7.38 MPa (1070 psia) and
approximately 31.1 degrees Ceslius (88 degrees Fahrenheit). In the
illustrated construction, the pressure of refrigerant in the gas
cooler 18 is approximately 8.5 MPa (1233 psia). The pressure of
refrigerant in the evaporator 26 is also higher than pressures seen
in a reverse-Rankine refrigeration cycle. In the illustrated
construction, the pressure of refrigerant in the evaporator 26 is
approximately 2.7 MPa (392 psia). As a result, the gas cooler 18
and evaporator coil 26 employ a heavy-duty construction to
withstand the higher pressures. In the illustrated construction,
the gas cooler 18 is built to withstand pressures of at least 7.38
MPa (1070 pisa) and the evaporator 26 is built to withstand
pressures of at least 2.7 MPa (392 psia).
[0013] As shown schematically in FIG. 1, the transcritical vapor
compression system 10 is controlled by a controller 50. The
controller 50 controls the opening of the expansion valve 22, the
speed of the blowers 36, 40 and the speed of the compressor 14, and
receives input signals from the temperature sensors 42a-42e and the
pressure sensors 46a-46e, as will be described in greater detail
below.
[0014] FIG. 2 is a diagram illustrating the saturated liquid line
54 for CO.sub.2, the saturated vapor line 58 for CO.sub.2, and the
relationship between internal energy and pressure of the CO.sub.2
refrigerant throughout the cycle of the transcritical vapor
compression system 10. The controller 50 is programmed to calculate
the internal energy of the refrigerant at each of the compressor
inlet 1, the compressor outlet 2, the gas cooler outlet 3, the
evaporator inlet 4 and the evaporator outlet 5 from the respective
temperature and pressure measurements from the respective
temperature and pressure sensors 42a-42e, 46a-46e, in a manner well
understood in the art. Further, the controller 50 is programmed to
calculate the change in energy (.DELTA.E.sub.evaporator) across the
evaporator 26 and the change in energy (.DELTA.E.sub.compressor)
across the compressor 14, as shown in FIG. 2. The change in energy
(.DELTA.E.sub.evaporator) across the evaporator 26 is calculated as
the difference between the internal energy calculated at the
evaporator outlet 5 and the internal energy calculated at the
evaporator inlet 4. The change in energy (.DELTA.E.sub.compressor)
across the compressor 14 is calculated as the difference between
the internal energy calculated at the compressor outlet 2 and the
internal energy calculated at the compressor inlet 1. Further, the
controller 50 is programmed to calculate an energy ratio across the
evaporator 26 and compressor 14 by dividing the energy change
across the evaporator (.DELTA.E.sub.evaporator) by the energy
change across the compressor (.DELTA.E.sub.compressor).
[0015] Further, the controller 50 is programmed to compare the
energy ratio to a previous energy ratio, more specifically, to the
immediately previous energy ratio calculated. Then, the controller
is programmed to adjust operating parameters, such as the opening
of the expansion valve 22, the compressor speed of the compressor
14 and the blower speed of the blowers 36, 40, based on the energy
ratio and, more specifically, based on the comparison between the
current and previous energy ratios. Specifically, the controller 50
is programmed to adjust the operating parameters to optimize the
energy balance, i.e., reach a desired efficiency of the
transcritical vapor compression system 10. The controller 50 is
programmed to repeat the above steps to continuously adjust the
operating parameters based on the difference between the current
and previous energy ratios, as described above, in order to
maintain the efficiency of the system 10.
[0016] Thus, the invention provides, among other things, a
transcritical vapor compression system and a controller therefor
programmed to adjust the operating parameters of the system based
on the energy ratio across the evaporator and compressor. Various
features and advantages of the invention are set forth in the
following claims.
* * * * *