U.S. patent application number 12/863249 was filed with the patent office on 2011-05-05 for refrigerant circuit and method for operating a refrigerant circuit.
Invention is credited to Roland Haussmann.
Application Number | 20110100038 12/863249 |
Document ID | / |
Family ID | 40524960 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110100038 |
Kind Code |
A1 |
Haussmann; Roland |
May 5, 2011 |
Refrigerant Circuit And Method For Operating A Refrigerant
Circuit
Abstract
There is provided a refrigerant circuit comprising a compressor
(10), a condenser or gas cooler (12), an ejector (16) with a
high-pressure connection and a suction connection, a pre-evaporator
(18), a separator (20) with a liquid phase output and a gas phase
output, a low-temperature evaporator (28) which is arranged between
the liquid phase output of the separator (20) and the suction
connection, and a superheating evaporator (24) which is arranged
between the gas phase output of the separator (20) and the suction
side of the compressor (10). A method for operating a refrigerant
circuit provides for expanding condensed or supercritical
refrigerant in an ejector (16), then pre-evaporating it, then
separating the predominantly liquid phase from the predominantly
gaseous phase, further evaporating the predominantly liquid phase
and supplying it to a suction connection of the ejector (18), and
completely evaporating the predominantly gaseous phase before
supplying it to a compressor (10).
Inventors: |
Haussmann; Roland;
(Wiesloch, DE) |
Family ID: |
40524960 |
Appl. No.: |
12/863249 |
Filed: |
January 15, 2009 |
PCT Filed: |
January 15, 2009 |
PCT NO: |
PCT/EP2009/000204 |
371 Date: |
January 14, 2011 |
Current U.S.
Class: |
62/115 ;
62/500 |
Current CPC
Class: |
F25B 40/06 20130101;
F25B 41/00 20130101; F25B 2341/0012 20130101; B60H 2001/3297
20130101; B60H 2001/3298 20130101; F25B 2341/0013 20130101; F25B
2309/06 20130101; F25B 5/04 20130101; F25B 25/005 20130101; B60H
1/3204 20130101 |
Class at
Publication: |
62/115 ;
62/500 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25B 1/06 20060101 F25B001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2008 |
DE |
DE102008005076.8 |
Claims
1. A refrigerant circuit comprising a compressor (10), a condenser
or gas cooler (12), an ejector (16) with a high-pressure connection
and a suction connection, a pre-evaporator (18), a separator (20)
with a liquid phase output and a gas phase output, a
low-temperature evaporator (28) which is arranged between the
liquid phase output of the separator (20) and the suction
connection (30) of the ejector (16), and a superheating evaporator
(24) which is arranged between the gas phase output of the
separator (20) and a suction side of the compressor (10).
2. A refrigerant circuit according to claim 1, characterised in
that the evaporators (18, 24, 28) are flowed through by a heat
transfer medium which flows through a heat exchanger (36).
3. A refrigerant circuit according to claim 2, characterised in
that the evaporators (18, 24, 28) are counterflow evaporators (18,
24, 28).
4. A refrigerant circuit according to claim 2, characterised in
that the heat transfer medium is water or a mixture of water and
glycol.
5. A refrigerant circuit according to claim 2, characterised in
that the heat exchanger (36) is part of an air conditioning
device.
6. A refrigerant circuit according to claim 2, characterised in
that the heat exchanger (36) is a cross-counterflow heat
exchanger.
7. A refrigerant circuit according to claim 1, characterised in
that the pre-evaporator (18) is arranged upstream of the separator
(20) relative to the flow direction of the refrigerant.
8. A refrigerant circuit according to claim 1, characterised in
that the low-temperature evaporator (28) and/or the superheating
evaporator (24) is/are arranged upstream of the separator (20)
relative to the flow direction of the refrigerant.
9. A refrigerant circuit according to claim 1, characterised in
that the pre-evaporator (18), the low-temperature evaporator (28)
and/or the superheating evaporator (24) form a one-piece
evaporating element (14).
10. A refrigerant circuit according to claim 9, characterised in
that the ejector (16) is integrated in the one-piece evaporating
element (14).
11. A refrigerant circuit according to claim 1, characterised in
that it has an internal heat exchanger (13), by means of which heat
can be transferred from the high-pressure side to the low-pressure
side.
12. A refrigerant circuit according to claim 11, characterised in
that the internal heat exchanger (13) is combined in an integrated
manner in the condenser or gas cooler (12).
13. A refrigerant circuit according to claim 1, characterised in
that the power of each evaporator (18, 24, 28) lies in the range
between 20 and 40% of the total power of all the evaporators.
14. A refrigerant circuit according to claim 1, characterised in
that the compressor (10) is electrically driven.
15. A refrigerant circuit according to claim 1, characterised in
that a nozzle cross section of the ejector (16) is
controllable.
16. A method for operating a refrigerant circuit, in which
condensed or supercritical refrigerant is expanded in an ejector
(16), then is partially evaporated, then the predominantly liquid
phase is separated from the predominantly gaseous phase, the
predominantly liquid phase is evaporated in a low-temperature
evaporator (28) and is supplied to a suction connection of the
ejector (16), and the predominantly gaseous phase is completely
evaporated before being supplied to a compressor (10).
17. A method according to claim 16, characterised in that the
predominantly gaseous phase is superheated.
18. A method according to claim 16, characterised in that the mass
flow of the heat transfer medium is controlled in such a way that
the temperature difference .DELTA.T.sub.WT of the heat transfer
medium between the output and the input of a heat exchanger (36) is
equal to x times the temperature difference .DELTA.T.sub.L of the
air between the input and the output of the heat exchanger (36),
wherein x is between 0.7 and 1.3.
19. A method according to claim 18, characterised in that x is
between 0.9 and 1.1.
Description
[0001] The invention relates to a refrigerant circuit as used as
part of an air conditioning unit, in particular for a motor
vehicle.
[0002] In general, there is the desire in such refrigerant circuits
to increase the efficiency in order to reduce the amount of energy
required in order to operate the refrigerant circuit and thus
ultimately to reduce the fuel consumption of the motor vehicle.
[0003] The object of the invention is to provide a refrigerant
circuit which is characterised by a high degree of efficiency.
[0004] In order to achieve this object, there is provided according
to the invention a refrigerant circuit comprising a compressor, a
condenser or gas cooler, an ejector with a high-pressure connection
and a suction connection, a pre-evaporator, a separator with a
liquid phase output and a gas phase output, a low-temperature
evaporator which is arranged between the liquid phase output of the
separator and the suction connection, and a superheating evaporator
which is arranged between the gas phase output of the separator and
the suction side of the compressor. In order to achieve the object,
there is also provided according to the invention a method for
operating a refrigerant circuit, in which condensed refrigerant or
supercritical gas is expanded in an ejector, then is partially
evaporated, then the predominantly liquid phase is separated from
the predominantly gaseous phase, the predominantly liquid phase is
evaporated in a low-temperature evaporator and is supplied to a
suction connection of the ejector, and the predominantly gaseous
phase is completely evaporated before being supplied to a
compressor. The invention is based on the main concept of
evaporating the refrigerant after expansion in three steps. In a
first step, approximately one-third of the liquid refrigerant is
evaporated to the pressure level at the output of the ejector. Then
the separation between the predominantly gaseous phase and the
predominantly liquid phase takes place in the separator. The
predominantly liquid phase, which once again is approximately
one-third of the refrigerant, is evaporated via the low-temperature
evaporator and is fed back to the pre-evaporator via the suction
connection of the ejector. The predominantly gaseous phase is
passed through the superheating evaporator, which is connected to
the suction connection of the compressor. In this way, it is
ensured that only gaseous refrigerant is supplied to the
compressor. Furthermore, since each of the evaporators has a
specific task to perform, it can be specially designed for this.
This ensures a high degree of efficiency.
[0005] Compared to other systems known from the prior art, the
solution according to the invention has the advantage that it is
cost-effective, since there is no need for electronic control.
Furthermore, a system is provided which is characterised by a good
ejector effect with a high throughput over the entire operating
range. There is no need for a second expansion device, and the
throughput through the suction connection of the ejector is not
excessively high. There is no need for a pre-throttle.
[0006] According to one preferred embodiment of the invention, it
is provided that the evaporators are not flowed through directly by
the conditioning air that is to be cooled, but rather by a heat
transfer medium which flows through a heat exchanger. This
embodiment provides an indirect cooling system which, if well
designed, has the same degree of efficiency as or even a higher
degree of efficiency than a conventional direct cooling system,
i.e. a system in which the air to be cooled is passed directly
through the evaporators instead of through the separate heat
exchanger provided in an indirect system.
[0007] A particularly high degree of efficiency can be achieved if
the evaporators are counterflow evaporators. In this way, the
optimal temperature difference between the heat transfer medium and
the refrigerant can be used for each of the different evaporation
steps.
[0008] Water and/or glycol may be used as the heat transfer
medium.
[0009] Preferably, the evaporators are designed in such a way that
the power of each evaporator lies in the range between 20 and 40%
of the total power of all the evaporators. In particular, the
evaporating power can be distributed equally, so that each
evaporator provides approximately one-third of the evaporating
power.
[0010] According to one preferred embodiment of the invention, it
is provided that the compressor is electrically driven. In this
way, the compressor power is independent of the rotational speed of
the combustion engine which is otherwise usually used for driving
purposes, so that the refrigerant circuit can be better controlled.
Furthermore, the electronic control of the compressor makes it
possible to use an ejector of simple design with a constant nozzle
cross section, since the refrigerant throughput can be suitably
controlled.
[0011] According to one alternative embodiment, it is provided that
the nozzle cross section of the ejector is controllable. This makes
it possible to adapt the ejector to very different refrigerant mass
flows.
[0012] According to one preferred embodiment of the invention, it
is provided that the mass flow of the heat transfer medium is
controlled in such a way that the temperature difference
.DELTA.T.sub.WT of the heat transfer medium between the output and
the input of the heat exchanger is equal to x times the temperature
difference .DELTA.T.sub.L of the air between the input and the
output of the heat exchanger, wherein x is between 0.7 and 1.3, in
particular between 0.9 and 1.1. The indirect cooling system makes
it possible, by controlling the mass throughput of the heat
transfer medium, to adjust the temperature difference at the heat
exchanger so that an optimal efficiency is obtained. In particular,
the temperature difference for the air flowing through the heat
exchanger and the heat transfer medium flowing through the heat
exchanger is set to approximately the same value.
[0013] The invention will be described below with reference to a
preferred embodiment which is shown in the appended drawings. In
the drawings:
[0014] FIG. 1 schematically shows a refrigerant circuit according
to the invention;
[0015] FIG. 2 shows the evaporator region of FIG. 1 on an enlarged
scale;
[0016] FIG. 3 shows a temperature diagram for the evaporator
region; and
[0017] FIG. 4 shows an enthalpy diagram for the refrigerant
circuit.
[0018] FIG. 1 shows a refrigerant circuit 5 which comprises an
electrically driven compressor 10, a condenser or gas cooler 12 and
an evaporator region 14. The condenser or gas cooler 12 is combined
with an internal heat exchanger 13, by means of which heat from the
refrigerant on the high-pressure side can be transferred to the
low-pressure side. The term "condenser" is used here as an
encompassing term for "condenser or gas cooler".
[0019] The evaporator region 14 has an ejector 16, by means of
which the refrigerant circulating in the refrigerant circuit can be
expanded. On the low-pressure side, the ejector 16 is adjoined by a
pre-evaporator 18, the output of which is connected to a separator
20. The separator has a gas phase output 22 which is connected to a
superheating evaporator 24. The output of the superheating
evaporator 24 leads via the internal heat exchanger 13 to the
suction side of the compressor 10. The separator 20 is also
provided with a liquid phase output 26, to which a low-temperature
evaporator 28 is connected. The output of the low-temperature
evaporator 28 is connected to a suction connection 30 of the
ejector 16. The separator 20 is also provided with an oil return
32.
[0020] Each of the evaporators 18, 24, 28 is connected to a heat
exchange circuit 34 which comprises a heat exchanger 36 and a pump
38. As the heat exchange medium in the heat exchange circuit 34,
use may be made for example of water and/or glycol. The heat
exchanger 36 is preferably designed as a cross-counterflow heat
exchanger and is part of an air conditioning unit. The heat
exchange medium is passed from the heat exchanger 36 firstly
through the superheating evaporator 24, then through the
pre-evaporator 18 and then through the low-temperature evaporator
28, before it returns to the heat exchanger 36. All the evaporators
are designed here as counterflow evaporators.
[0021] During operation of the refrigerant circuit, the refrigerant
compressed by the compressor 10 and in the liquid or supercritical
state at the output of the condenser or gas cooler 12 is passed
through the ejector 16, in which it expands. It then flows through
the pre-evaporator 18, in which approximately one-third of the
refrigerant mass flow is evaporated. The mixture of liquid and
gaseous coolant is then separated in the separator 20 into an
essentially gaseous fraction and an essentially liquid fraction.
The essentially liquid fraction flows via a throttle to the
low-temperature evaporator 28, in which it is (largely) evaporated.
The refrigerant is then aspirated by the suction connection 30 of
the ejector 16 and is fed back to the pre-evaporator 18. The
essentially gaseous fraction of the refrigerant passes from the
separator 20 into the superheating evaporator 24, in which the
remaining liquid components are evaporated. The refrigerant in
vapour form is also superheated. It then passes via the internal
heat exchanger 13 to the suction side of the compressor 10.
[0022] The quantity of heat required in order to evaporate the
refrigerant is supplied via the heat exchange circuit 34. The heat
exchange medium, which is at a high temperature level after flowing
through the heat exchanger 36, first flows through the superheating
evaporator 24. After flowing through the superheating evaporator
24, the heat exchange medium is at a medium temperature level and
flows through the pre-evaporator 18. After leaving the
pre-evaporator 18, the heat exchange medium is at a low temperature
level and is passed through the low-temperature evaporator 28. From
there, it passes to the heat exchanger 36, where it draws heat from
the air that is to be cooled.
[0023] With reference to FIGS. 2 to 4, the heat transfers in the
evaporator region 14 and in the heat exchanger 36 will be described
below.
[0024] The refrigerant has at the point E at the output of the
ejector a temperature of approximately 0.degree. C. This
temperature remains constant through the pre-evaporator 18. At the
point I at the input of the low-temperature evaporator 28, the
predominantly liquid phase of the refrigerant has a temperature of
-5.degree. C., which it also has at the point J at the output of
the low-temperature evaporator 28. The predominantly gaseous phase
of the refrigerant has at the point H at the input of the
superheating evaporator 24 a temperature of 0.degree. C., while it
has a temperature of 10.degree. C. at the point K at the output of
the superheating evaporator 24. Said values are examples of a
preferred operating state of the refrigerant circuit.
[0025] FIG. 3 shows the course of the temperature of the
refrigerant in the refrigerant circuit 5, of the heat exchange
medium in the heat exchange circuit 34, and of the air L which
flows through the heat exchanger 36. It can be seen that the
temperature of the heat exchange medium circulating in the heat
exchange circuit 34 drops as it flows through the three evaporators
24, 18 and 28. This drop corresponds to the different, rising
temperature levels of the refrigerant in the three evaporators 28,
18 and 24. It can be seen that at least a temperature difference of
4 K exists between the temperature of the heat exchange medium and
the temperature of the refrigerant. This ensures a good heat
transfer. The evaporators 28, 18 and 24 are designed here as
counterflow evaporators, so that the temperature difference is
maintained across the entire evaporator in each case. For the sake
of completeness, it is also possible to see the course of the
temperature of the air L which flows through the heat exchanger 36.
The latter is designed as a cross-counterflow heat exchanger, so
that the temperature difference between the air and the heat
exchange medium is kept approximately constant, here at a value of
10 K, while the air is cooled from 25.degree. C. to 5.degree. C.
and the heat exchange medium is heated from -3.degree. C. to
+16.degree. C.
[0026] The described refrigerant circuit can preferably be used in
electric vehicles, hybrid vehicles or vehicles which are operated
by fuel cells, since these usually comprise an electric compressor
and also a battery of sufficient capacity. The refrigerant circuit
can therefore also be used for the air conditioning of the vehicle
at a standstill or for the air pre-conditioning of a parked
vehicle.
[0027] The system can be operated with an optimised refrigerant
mass throughput in almost all operating states, so that the suction
effect at the suction connection of the ejector is great enough to
ensure a sufficient refrigerant throughput through the
low-temperature evaporator 28.
[0028] The refrigerant circuit can be operated with all
refrigerants which allow operation according to the Carnot
principle, for example R134a or R744.
[0029] One particular advantage of the described refrigerant
circuit consists in that, on account of the use of the
pre-evaporator 18, only a relatively small quantity of refrigerant
has to be evaporated in the low-temperature evaporator 28. Due to
the lower mass throughput through this evaporator, the pressure
ratio of the ejector between the suction pressure at the suction
connection of the compressor 10 and the suction connection on the
ejector 16 is increased so that, for the same required suction
pressure at the low-temperature evaporator 28, the pressure on the
suction side of the compressor 10 is higher, which leads to a
better coefficient of performance of the refrigerant circuit and
thus to a lower fuel consumption.
[0030] Due to the advantageous splitting of the evaporator work
between three separate evaporators which are in each case flowed
through in countercurrent by the heat exchange medium, a sufficient
temperature difference between the refrigerant and the heat
transfer medium is ensured at any point of the evaporator. The
evaporators can therefore be designed to be relatively small. Due
to the low temperature level of the low-temperature evaporator 28,
the temperature of the heat exchange circuit 34 can be reduced
below the saturation temperature of the refrigerant at the suction
connection of the compressor 10. In this way, it is ensured that
the present indirect system, in which the evaporators do not cool
the air directly but rather are flowed through by a heat exchange
medium, achieves the necessary temperature drop and thus a high
degree of efficiency.
[0031] The heat exchanger 36 is designed with regard to an optimal
ratio between the pressure drop and heat transfer coefficient for a
mass throughput of heat exchange medium of between 70 l/h and at
most 300 l/h, preferably between 120 l/h and 250 l/h. The average
of all local temperature differences in the heat exchanger 36 is
maximal, so that the best heat exchanger performance can be
achieved by the same heat exchanger surface area and the same heat
exchanger design. The total specific heat capacity in the heat
exchange circuit 34 should be in the range between 5 kJ/K and 15
kJ/K.
[0032] The minimum rotational speed of the compressor can be
increased to such a value that the suction effect of the ejector is
satisfactory. Furthermore, the compressor can be operated in a
cyclical manner if the required refrigerating power falls below a
certain value. The heat capacity of the heat exchange circuit 34
then acts as a cold store during the operating phases in which the
compressor is switched off.
* * * * *