U.S. patent application number 13/642970 was filed with the patent office on 2013-02-14 for refrigeration cycle apparatus.
This patent application is currently assigned to PANASONIC CORPORATION. The applicant listed for this patent is Takeshi Ogata, Atsuo Okaichi, Masanobu Wada. Invention is credited to Takeshi Ogata, Atsuo Okaichi, Masanobu Wada.
Application Number | 20130036757 13/642970 |
Document ID | / |
Family ID | 44861130 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130036757 |
Kind Code |
A1 |
Okaichi; Atsuo ; et
al. |
February 14, 2013 |
REFRIGERATION CYCLE APPARATUS
Abstract
A refrigeration cycle apparatus 100 is provided with a
refrigerant circuit 106, an injection flow passage 111, and a
high-pressure supply passage 130. The refrigerant circuit 106
includes a low-pressure stage compressor 105, a high-pressure stage
compressor 101, a heat radiator 102, an expander 103, a gas-liquid
separator 108, and an evaporator 104. The expander 103 and the
low-pressure stage compressor 105 are coupled by a power-recovery
shaft 107. The refrigeration cycle apparatus 100 is further
provided with a flow passage-switching mechanism that selectively
connects one of the evaporator 104 and the high-pressure supply
passage 130 to the low-pressure stage compressor 105. The flow
passage-switching mechanism, for example, is constituted by an
on-off valve 131 and a check valve 132.
Inventors: |
Okaichi; Atsuo; (Osaka,
JP) ; Ogata; Takeshi; (Kyoto, JP) ; Wada;
Masanobu; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Okaichi; Atsuo
Ogata; Takeshi
Wada; Masanobu |
Osaka
Kyoto
Osaka |
|
JP
JP
JP |
|
|
Assignee: |
PANASONIC CORPORATION
Kadoma-shi, Osaka
JP
|
Family ID: |
44861130 |
Appl. No.: |
13/642970 |
Filed: |
April 21, 2011 |
PCT Filed: |
April 21, 2011 |
PCT NO: |
PCT/JP2011/002330 |
371 Date: |
October 23, 2012 |
Current U.S.
Class: |
62/196.1 ;
62/228.1; 62/228.3; 62/510 |
Current CPC
Class: |
F25B 2400/0401 20130101;
F25B 1/10 20130101; F25B 2600/2509 20130101; F25B 2600/2519
20130101; F25B 2400/13 20130101; F25B 9/06 20130101; F25B 2400/14
20130101; F25B 2309/06 20130101 |
Class at
Publication: |
62/196.1 ;
62/510; 62/228.1; 62/228.3 |
International
Class: |
F25B 49/02 20060101
F25B049/02; F25B 41/00 20060101 F25B041/00; F25B 1/10 20060101
F25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2010 |
JP |
2010-104374 |
Apr 28, 2010 |
JP |
2010-104375 |
Claims
1. A refrigeration cycle apparatus comprising: a main refrigerant
circuit having a low-pressure stage compressor that compresses a
refrigerant, a high-pressure stage compressor that further
compresses the refrigerant that has been compressed in the
low-pressure stage compressor, a heat radiator that cools the
refrigerant that has been compressed in the high-pressure stage
compressor, an expander that recovers power from the refrigerant
that has been cooled in the heat radiator while expanding the
refrigerant, the expander being coupled to the low-pressure stage
compressor by a shaft so that the recovered power is transferred to
the low-pressure stage compressor, a gas-liquid separator that
separates the refrigerant that has been expanded in the expander
into a gas refrigerant and a liquid refrigerant, and an evaporator
that evaporates the liquid refrigerant that has been separated in
the gas-liquid separator; an injection flow passage that introduces
the gas refrigerant that has been separated in the gas-liquid
separator into a portion of the main refrigerant circuit from a
discharge port of the low-pressure stage compressor to a suction
port of the high-pressure stage compressor; a high-pressure supply
passage that communicates a portion of the main refrigerant circuit
from a discharge port of the high-pressure stage compressor to a
suction port of the expander and a portion of the main refrigerant
circuit from an outlet of the evaporator to a suction port of the
low-pressure stage compressor; a flow passage-switching mechanism
capable of selectively connecting one selected from the evaporator
and the high-pressure supply passage to the low-pressure stage
compressor so that the refrigerant is introduced from the
evaporator or the high-pressure supply passage to the low-pressure
stage compressor; and a controller that controls the flow
passage-switching mechanism before activation of the expander and
the low-pressure stage compressor so that the refrigerant is
introduced from the high-pressure supply passage to the
low-pressure stage compressor, while controlling the flow
passage-switching mechanism after the activation of the expander
and the low-pressure stage compressor so that the refrigerant is
introduced from the evaporator to the low-pressure stage
compressor, wherein a discharge pressure of the high-pressure stage
compressor is applied to the suction port of the low-pressure stage
compressor and the suction port of the expander while a suction
pressure of the high-pressure stage compressor is applied to the
discharge port of the low-pressure stage compressor and a discharge
port of the expander before activation of the expander and the
low-pressure stage compressor.
2. The refrigeration cycle apparatus according to claim 1, wherein
the high-pressure supply passage has an upstream end connected to a
portion of the main refrigerant circuit from the discharge port of
the high-pressure stage compressor to an inlet of the heat
radiator.
3. The refrigeration cycle apparatus according to claim 1, wherein
the high-pressure supply passage has a downstream end connected to
a portion of the main refrigerant circuit from the outlet of the
evaporator to the suction port of the low-pressure stage
compressor, and the flow passage-switching mechanism is constituted
by an on-off valve provided on the high-pressure supply passage and
a valve, provided in a portion of the main refrigerant circuit from
the outlet of the evaporator to the downstream end of the
high-pressure supply passage, capable of blocking flow of the
refrigerant from the high-pressure supply passage toward the
evaporator.
4. The refrigeration cycle apparatus according to claim 1, wherein
the high-pressure supply passage has a downstream end connected to
a portion of the main refrigerant circuit from the outlet of the
evaporator to the suction port of the low-pressure stage
compressor, and the flow passage-switching mechanism is constituted
by a three-way valve provided at the downstream end of the
high-pressure supply passage.
5. (canceled)
6. The refrigeration cycle apparatus according to claim 1, further
comprising: an activation detector that detects the activation of
the expander or the low-pressure stage compressor, wherein the
controller switches control of the flow passage-switching mechanism
from control before the activation to control after the activation,
according to a detection result of the activation detector.
7. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector includes a timer that measures an elapsed
time from activation of the high-pressure stage compressor, and
when the time measured by the timer exceeds a specific threshold
time, the activation of the expander or the low-pressure stage
compressor is detected.
8. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector includes a temperature detector that
detects a difference between a temperature of the refrigerant at
the suction port of the expander and a temperature of the
refrigerant at the discharge port of the expander, and when the
temperature difference detected by the temperature detector exceeds
a specific threshold, activation of the expander or the
low-pressure stage compressor is detected.
9. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector includes a pressure detector that detects a
difference between a pressure of the refrigerant at the suction
port of the expander and a pressure of the refrigerant at the
discharge port of the expander, and when the pressure difference
detected by the pressure detector exceeds a specific threshold,
activation of the expander or the low-pressure stage compressor is
detected.
10. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector includes a pressure detector that detects a
difference between a pressure of the refrigerant at the suction
port of the expander and a pressure of the refrigerant at the
discharge port of the expander, and when a value obtained by
subtracting a current pressure difference detected by the pressure
detector from a pressure difference that has been detected by the
pressure detector at a time going back for a unit time exceeds a
specific threshold, activation of the expander or the low-pressure
stage compressor is detected.
11. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector includes a temperature detector that
detects a difference between a temperature of the refrigerant at
the suction port of the expander and a temperature of the
refrigerant at the discharge port of the expander, and when a value
obtained by subtracting a current temperature difference detected
by the temperature detector from a temperature difference that has
been detected by the temperature detector at a time going back for
a unit time exceeds a specific threshold, activation of the
expander or the low-pressure stage compressor is detected.
12. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector includes a PTC heater provided in a portion
from an outlet of the heat radiator to the suction port of the
expander of the main refrigerant circuit, and when the amount of
change per unit time in an electric current flowing in the PTC
heater exceeds a specific threshold, activation of the expander or
the low-pressure stage compressor is detected.
13. The refrigeration cycle apparatus according to claim 6, wherein
the activation detector is a temperature detector that detects a
temperature of the refrigerant at the discharge port of the
low-pressure stage compressor, and when a value obtained by
subtracting a temperature that has been detected by the temperature
detector at a time going back for a unit time from a current
temperature detected by the temperature detector exceeds a specific
threshold, activation of the expander or the low-pressure stage
compressor is detected.
14. The refrigeration cycle apparatus according to claim 1, wherein
in the case where activation of the expander and the low-pressure
stage compressor has been failed, the controller stops the
high-pressure stage compressor and performs control to activate the
expander and the low-pressure stage compressor again.
15. The refrigeration cycle apparatus according to claim 1, wherein
the expander and the low-pressure stage compressor are accommodated
in a single closed casing.
16. The refrigeration cycle apparatus according to claim 1, further
comprising: a bypass flow passage that bypasses the expander; and a
bypass valve provided on the bypass flow passage, wherein the
controller opens the bypass valve to a specific degree before the
activation of the expander and the low-pressure stage compressor
and closes the bypass valve after the activation of the expander
and the low-pressure stage compressor.
17. The refrigeration cycle apparatus according to claim 1, wherein
the expander and the low-pressure stage compressor each have a
certain suction volume, and the suction volume of the low-pressure
stage compressor is larger than the suction volume of the
expander.
18-30. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration cycle
apparatus.
BACKGROUND ART
[0002] A refrigeration cycle apparatus 700 shown in FIG. 15 is
conventionally known as a refrigeration cycle apparatus provided
with an expander that recovers power by expanding a refrigerant,
and a second compressor that preliminarily increases the pressure
of the refrigerant (for example, see JP 2003-307358 A). With
reference to FIG. 15, the configuration of the conventional
refrigeration cycle apparatus 700 is described.
[0003] As shown in FIG. 15, the refrigeration cycle apparatus 700
is provided with a refrigerant circuit 6 formed of a first
compressor 1, a heat radiator 2, an expander 3, an evaporator 4, a
second compressor 5, and flow passages 10a to 10e connecting these
components in this order. The second compressor 5 is coupled to the
expander 3 by a power-recovery shaft 7, and is driven by receiving,
via the power-recovery shaft 7, mechanical energy recovered in the
expander 3.
[0004] Further, a bypass passage 8 that bypasses the second
compressor 5 and a bypass valve 9 that controls the flow of the
refrigerant in the bypass passage 8 are provided therein. The
upstream end of the bypass passage 8 is connected to the flow
passage 10d that connects the outlet of the evaporator 4 and the
suction port of the second compressor 5. The downstream end of the
bypass passage 8 is connected to the flow passage 10e that connects
the discharge port of the second compressor 5 and the suction port
of the first compressor 1.
[0005] The refrigeration cycle apparatus 700 is activated according
to the following procedures. First, the operation of the first
compressor 1 is started, and the bypass valve 9 is opened. These
allow the refrigerant in the evaporator 4 to be drawn into the
first compressor 1 through the bypass passage 8 as shown by solid
arrows in FIG. 15. The pressure of the refrigerant is increased in
the first compressor 1 and the refrigerant is discharged therefrom,
thereby causing an increase in the pressure at the suction port of
the expander 3. As a result of this, a pressure difference is
produced between before and after the expander 3, as shown in FIG.
16, so that the expander 3 and the second compressor 5 can be
activated rapidly. After the expander 3 and the second compressor 5
are activated, the bypass valve 9 is closed. The refrigerant that
has flowed out of the evaporator 4 is drawn into the second
compressor 5 through the flow passage 10d as shown by dashed arrows
in FIG. 15. In this way, smooth transfer to regular operation can
be achieved by providing the bypass passage 8.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: JP 2003-307358 A
SUMMARY OF INVENTION
Technical Problem
[0007] In the refrigeration cycle apparatus 700, only the expander
3 is involved in the activation of the expander 3 and the second
compressor 5, whereas the second compressor 5 does not contribute
thereto. Rather, the second compressor 5 is a load during the
activation of the expander 3. That is, friction, etc., between the
power-recovery shaft 7 and the components of the second compressor
5 cause a driving resistance to the expander 3.
[0008] Meanwhile, in the regular operation of the refrigeration
cycle apparatus 700, the second compressor 5 and the expander 3
form the refrigerant circuit 6 of a single channel, and their
rotational speeds are identical because they are coupled to each
other by the power-recovery shaft 7 that is commonly shared.
Accordingly, the volume of the second compressor 5 and the volume
of the expander 3 need to be set so that the mass of the
refrigerant to be drawn by the second compressor 5 per unit time
should be equal to the mass of the refrigerant to be drawn by the
expander 3 per unit time.
[0009] FIG. 17 is an example of the Mollier diagram when carbon
dioxide is used as the refrigerant in the conventional
refrigeration cycle apparatus 700. As shown in FIG. 17, in the
regular operation of the conventional refrigeration cycle apparatus
700, the refrigerant drawn by the second compressor 5 has a
pressure of 40 kg/cm.sup.2, and a temperature of about 10.degree.
C. (point A in FIG. 17), and the refrigerant has a density of 108.0
kg/m.sup.3. The refrigerant drawn by the expander 3 has a pressure
of 100 kg/cm.sup.2, and a temperature of 40.degree. C. (point C in
FIG. 17), and the refrigerant has a density of 628.61 kg/m.sup.3 at
this time point.
[0010] Here, the suction volume (m.sup.3) of the second compressor
5 is referred to as Vc, the suction volume (m.sup.3) of the
expander 3 is referred to as Ve, and the rotational speed
(S.sup.-1) of the power-recovery shaft 7 per second is referred to
as N. The mass (kg/s) of the refrigerant that the second compressor
5 can draw per second and the mass (kg/s) of the refrigerant that
the expander 3 can draw per second can be expressed respectively by
Formula 1 and Formula 2.
(The mass of the refrigerant that the second compressor 5 can draw
per second)=108.0.times.Vc.times.N (Formula 1)
(The mass of the refrigerant that the expander 3 can draw per
second)=628.61.times.Ve.times.N (Formula 2)
[0011] When the mass of the refrigerant that the second compressor
5 can draw per second and the mass of the refrigerant that the
expander 3 can draw per second are equal, the suction volume Vc of
the second compressor 5 can be expressed by Formula 3 from the
above-mentioned Formula 1 and Formula 2.
Vc=(628.61/108.0).times.Ve.apprxeq.5.8.times.Ve (Formula 3)
[0012] That is, in the activation of the refrigeration cycle
apparatus 700, the expander 3 is required to drive the second
compressor 5 having a suction volume that is about 5.8 times that
of the expander 3. Further, the larger the ratio between the
density of the refrigerant to be drawn by the second compressor 5
and the density of the refrigerant to be drawn by the expander 3,
the larger the ratio between the suction volume of the second
compressor 5 and the suction volume of the expander 3 also should
be. In other words, the suction volume of the expander 3 becomes
smaller with respect to the suction volume of the second compressor
5, and the driving resistance to the expander 3 in the activation
of the second compressor 5 becomes relatively larger. Accordingly,
there is a possibility that the expander 3 cannot drive the second
compressor 5 at the time of activation, depending on the
operational conditions of the refrigeration cycle apparatus 700.
Instead, it might be necessary to impose an excess pressure, as
compared to that in the regular operation, on the suction port side
of the expander 3 in order to obtain a driving force necessary to
drive the second compressor 5. As a result, the input power to the
first compressor 1 increases and the efficiency of the
refrigeration cycle apparatus 700 is reduced.
[0013] The present invention aims to solve the above-mentioned
problems, and it is an object of the present invention to provide a
refrigeration cycle apparatus that can be activated surely and
stably.
Solution to Problem
[0014] That is, the present invention provides a refrigeration
cycle apparatus including: a main refrigerant circuit having a
low-pressure stage compressor that compresses a refrigerant, a
high-pressure stage compressor that further compresses the
refrigerant that has been compressed in the low-pressure stage
compressor, a heat radiator that cools the refrigerant that has
been compressed in the high-pressure stage compressor, an expander
that recovers power from the refrigerant that has been cooled in
the heat radiator while expanding the refrigerant, the expander
being coupled to the low-pressure stage compressor by a shaft so
that the recovered power is transferred to the low-pressure stage
compressor, a gas-liquid separator that separates the refrigerant
that has been expanded in the expander into a gas refrigerant and a
liquid refrigerant, and an evaporator that evaporates the liquid
refrigerant that has been separated in the gas-liquid separator; an
injection flow passage that introduces the gas refrigerant that has
been separated in the gas-liquid separator into a portion of the
main refrigerant circuit from the discharge port of the
low-pressure stage compressor to the suction port of the
high-pressure stage compressor; a high-pressure supply passage that
communicates a portion of the main refrigerant circuit from the
discharge port of the high-pressure stage compressor to the suction
port of the expander and a portion of the main refrigerant circuit
from the outlet of the evaporator to the suction port of the
low-pressure stage compressor; and a flow passage-switching
mechanism capable of selectively connecting one selected from the
evaporator and the high-pressure supply passage to the low-pressure
stage compressor.
[0015] From another aspect, the present invention provides a
refrigeration cycle apparatus including: a main refrigerant circuit
having a low-pressure stage compressor that compresses a
refrigerant, a high-pressure stage compressor that further
compresses the refrigerant that has been compressed in the
low-pressure stage compressor, a heat radiator that cools the
refrigerant that has been compressed in the high-pressure stage
compressor, an expander that recovers power from the refrigerant
that has been cooled in the heat radiator while expanding the
refrigerant, the expander being coupled to the low-pressure stage
compressor by a shaft so that the recovered power is transferred to
the low-pressure stage compressor, a gas-liquid separator that
separates the refrigerant that has been expanded in the expander
into a gas refrigerant and a liquid refrigerant, an evaporator that
evaporates the liquid refrigerant that has been separated in the
gas-liquid separator, and an expansion valve provided on the flow
passage between the gas-liquid separator and the evaporator; an
injection flow passage that introduces the gas refrigerant that has
been separated in the gas-liquid separator into a portion of the
main refrigerant circuit from the discharge port of the
low-pressure stage compressor to the suction port of the
high-pressure stage compressor; a controller that fully closes the
expansion valve in the activation of the refrigeration cycle
apparatus so that the pressure at the suction port of the
low-pressure stage compressor is prevented from being equal to the
pressure at the discharge port of the low-pressure stage compressor
via the injection flow passage.
Advantageous Effects of Invention
[0016] According to the refrigeration cycle apparatus of the
present invention, the high-pressure stage compressor can draw the
refrigerant in the evaporator and the gas-liquid separator through
the injection flow passage. This allows the pressure on the
high-pressure side of the main refrigerant circuit to increase
rapidly.
[0017] Since a portion of the main refrigerant circuit from the
discharge port of the low-pressure stage compressor to the suction
port of the high-pressure stage compressor is connected to the
gas-liquid separator by the injection flow passage, the pressure at
the discharge port of the expander can be made equal to the
pressure at the suction port of the high-pressure stage compressor.
The pressure at the suction port of the expander is normally equal
to the pressure on the high-pressure side of the main refrigerant
circuit.
[0018] On the other hand, the pressure at the suction port of the
low-pressure stage compressor can be made equal to the pressure on
the high-pressure side of the main refrigerant circuit due to the
functions of the flow passage-switching mechanism and the
high-pressure supply passage. The pressure at the discharge port of
the low-pressure stage compressor is normally equal to the pressure
at the suction port of the high-pressure stage compressor.
[0019] In this way, according to the present invention, a pressure
difference can be produced not only before and after the expander
but also before and after the low-pressure stage compressor.
Therefore, the refrigeration cycle apparatus of the present
invention can be activated surely and stably, independent of
operational conditions.
[0020] According to another aspect of the refrigeration cycle
apparatus of the present invention, the high-pressure stage
compressor can draw the refrigerant in the gas-liquid separator
through the injection flow passage. This allows the pressure on the
high-pressure side of the main refrigerant circuit to increase
rapidly.
[0021] Since a portion of the main refrigerant circuit from the
discharge port of the low-pressure stage compressor to the suction
port of the high-pressure stage compressor is connected to the
gas-liquid separator by the injection flow passage, the pressure at
the discharge port of the expander can be made equal to the
pressure at the suction port of the high-pressure stage compressor.
The pressure at the suction port of the expander is normally equal
to the pressure on the high-pressure side of the main refrigerant
circuit.
[0022] On the other hand, the flow passages before and after the
expansion valve can be separated from each other by fully closing
the expansion valve. Accordingly, the pressure at the suction port
of the low-pressure stage compressor can be prevented from being
equal to the pressure at the discharge port of the low-pressure
stage compressor via the injection flow passage. As a result, the
pressure at the suction port of the low-pressure stage compressor
can be maintained at the pressure of the main refrigerant circuit
before the high-pressure stage compressor is driven (intermediate
pressure). The pressure at the discharge port of the low-pressure
stage compressor is normally equal to the pressure at the suction
port of the high-pressure stage compressor.
[0023] In this way, according to the present invention, a pressure
difference can be produced not only before and after the expander
but also before and after the low-pressure stage compressor.
Therefore, the refrigeration cycle apparatus of the present
invention can be activated surely and stably, independent of
operational conditions.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a configuration diagram of a refrigeration cycle
apparatus in Embodiment 1 of the present invention.
[0025] FIG. 2 is a flow chart of the activation control of the
refrigeration cycle apparatus in Embodiment 1 of the present
invention.
[0026] FIG. 3 is a configuration diagram of a refrigeration cycle
apparatus in Modification 1.
[0027] FIG. 4 is a flow chart of the activation control of the
refrigeration cycle apparatus in Modification 1.
[0028] FIG. 5 is a configuration diagram of a refrigeration cycle
apparatus in Modification 2.
[0029] FIG. 6 is a schematic view showing the state in the
activation of the refrigeration cycle apparatus in Embodiment 1,
Modification 1, and Modification 2.
[0030] FIG. 7 is a configuration diagram of a power recovery
system.
[0031] FIG. 8 is a configuration diagram of a refrigeration cycle
apparatus in Embodiment 2 of the present invention.
[0032] FIG. 9 is a flow chart of the activation control of the
refrigeration cycle apparatus in Embodiment 2 of the present
invention.
[0033] FIG. 10 is a configuration diagram of a refrigeration cycle
apparatus in Modification 3.
[0034] FIG. 11 is a flow chart of the activation control of the
refrigeration cycle apparatus in Modification 3.
[0035] FIG. 12 is a configuration diagram of a refrigeration cycle
apparatus in Modification 4.
[0036] FIG. 13 is a flow chart of the activation control of the
refrigeration cycle apparatus in Modification 4.
[0037] FIG. 14A is a schematic view showing the state in the
activation of the refrigeration cycle apparatus in Embodiment 2 and
Modification 3.
[0038] FIG. 14B is a schematic view showing the state in the
activation of the refrigeration cycle apparatus in Modification
4.
[0039] FIG. 15 is a configuration diagram of a conventional
refrigeration cycle apparatus.
[0040] FIG. 16 is a schematic view showing the state in the
activation of the refrigeration cycle apparatus shown in FIG.
15.
[0041] FIG. 17 is a Mollier diagram when carbon dioxide is used as
a refrigerant in the conventional refrigeration cycle
apparatus.
DESCRIPTION OF EMBODIMENTS
[0042] Hereinafter, embodiments of the present invention are
described with reference to drawings. It should be noted that the
present invention is not limited to the following embodiments.
Embodiment 1
[0043] <Configuration of Refrigeration Cycle Apparatus 100
[0044] FIG. 1 is a configuration diagram showing a refrigeration
cycle apparatus 100 in Embodiment 1 of the present invention. As
shown in FIG. 1, the refrigeration cycle apparatus 100 is provided
with a refrigerant circuit 106 formed by sequentially connecting a
high-pressure stage compressor 101, a heat radiator 102, an
expander 103, a gas-liquid separator 108, an evaporator 104, and a
low-pressure stage compressor 105, with flow passages 106a to 106f.
The flow passages 106a to 106f each are constituted by a
refrigerant pipe. An expansion valve 110 is provided on the flow
passage 106d between the gas-liquid separator 108 and the
evaporator 104. A check valve 132 is provided on the flow passage
106e between the evaporator 104 and the low-pressure stage
compressor 105. Hereinafter, the flow passage 106f connecting the
discharge port of the low-pressure stage compressor 105 and the
suction port of the high-pressure stage compressor 101 may be
referred to also as the "intermediate-pressure flow passage
106f".
[0045] The high-pressure stage compressor 101 is constituted by a
compression mechanism 101a and a motor 101b for driving the
compression mechanism 101a. The high-pressure stage compressor 101
compresses the refrigerant to high temperature and high pressure. A
positive displacement compressor such as a scroll compressor and a
rotary compressor can be used as the high-pressure stage compressor
101. The discharge port of the high-pressure stage compressor 101
is connected to the inlet of the heat radiator 102 via the flow
passage 106a.
[0046] The heat radiator 102 radiates heat (cools) of the
refrigerant at high temperature and high pressure that has been
compressed by the high-pressure stage compressor 101 through heat
exchange with an external heat source. The outlet of the heat
radiator 102 is connected to the suction port of the expander 103
via the flow passage 106b.
[0047] The expander 103 expands the refrigerant at intermediate
temperature and high pressure that has flowed out of the heat
radiator 102 and converts the expansion energy (power) of the
refrigerant into mechanical energy to recover it. The discharge
port of the expander 103 is connected to the inlet of the
gas-liquid separator 108 via the flow passage 106c. A positive
displacement expander such as a scroll expander and a rotary
expander can be used as the expander 103. In addition, a fluid
pressure motor expander can be also used as the expander 103. The
fluid pressure motor expander is a positive displacement fluid
machine that recovers power from a refrigerant by sequentially
performing processes of drawing the refrigerant and discharging the
drawn refrigerant without performing any substantial expansion
process in a working chamber. The detailed structure and the
operational principle of the fluid pressure motor expander are
disclosed, for example, in WO 2008/050654 A.
[0048] The gas-liquid separator 108 serves to separate the
refrigerant at low temperature and low pressure that has been
expanded in the expander 103 into a gas refrigerant and a liquid
refrigerant. The gas-liquid separator 108 can prevent the liquid
refrigerant from being drawn into the high-pressure stage
compressor 101 in a large amount in the activation of the
refrigeration cycle apparatus 100. The gas refrigerant outlet of
the gas-liquid separator 108 is connected to the flow passage 106f
via an injection flow passage 111. The liquid-refrigerant outlet of
the gas-liquid separator 108 is connected to the inlet of the
evaporator 104 via the flow passage 106d provided with the
expansion valve 110.
[0049] The expansion valve 110 serves to regulate the flow rate of
the liquid refrigerant to flow into the evaporator 104 in the
regular operation. Accordingly, a valve, which allows the degree of
opening to be varied stepwise, capable of expanding a refrigerant,
typically, an electric expansion valve is preferably used as the
expansion valve 110. In the activation of the refrigeration cycle
apparatus 100, the expansion valve 110 is fully opened or
substantially fully opened. This allows the refrigerant in the
evaporator 104 to be drawn by the high-pressure stage compressor
101 smoothly.
[0050] The evaporator 104 evaporates the liquid refrigerant at low
temperature and low pressure that has been separated in the
gas-liquid separator 108 through heat exchange with an external
heat source. The outlet of the evaporator 104 is connected to the
suction port of the low-pressure stage compressor 105 via the flow
passage 106e provided with the check valve 132.
[0051] The low-pressure stage compressor 105 draws the refrigerant
at intermediate temperature and low pressure that has flowed out of
the evaporator 104, and discharges it into the
intermediate-pressure flow passage 106f after preliminarily
increasing the pressure thereof. The discharge port of the
low-pressure stage compressor 105 is connected to the suction port
of the high-pressure stage compressor 101 via the
intermediate-pressure flow passage 106f. A positive displacement
compressor such as a scroll compressor and a rotary compressor can
be used as the low-pressure stage compressor 105. Further, a fluid
pressure motor compressor can be used as the low-pressure stage
compressor 105. The fluid pressure motor compressor is a positive
displacement fluid machine that increases the pressure of a
refrigerant by substantially sequentially performing processes of
drawing the refrigerant from the evaporator 104 and discharging the
refrigerant to the high-pressure stage compressor 101. In other
words, the fluid pressure motor compressor is a fluid machine that
allows substantially no change in the volume of the refrigerant in
a working chamber. The fluid pressure motor compressor basically
has the same structure as the fluid pressure motor expander, the
detail of which is disclosed in the above-mentioned literature.
[0052] The expander 103 is coupled to the low-pressure stage
compressor 105 by a power-recovery shaft 107. The mechanical energy
(power) recovered in the expander 103 can be transferred to the
low-pressure stage compressor 105 via the power-recovery shaft 107.
That is, the expander 103, the low-pressure stage compressor 105,
and the power-recovery shaft 107 function as a power recovery
system 109 that recovers power from the refrigerant. As shown in
FIG. 7, the expander 103 and the low-pressure stage compressor 105
are accommodated in a single closed casing 109a holding lubrication
oil, together with the power-recovery shaft 107. Therefore, no
particular sealing structure is needed.
[0053] In this embodiment, the low-pressure stage compressor 105
has a larger volume than the expander 103. In the case of using
carbon dioxide as the refrigerant, the ratio (Vc/Ve) of the volume
Vc of the low-pressure stage compressor 105 with respect to the
volume Ve of the expander 103 is set, for example, to the range of
5 to 15. In the case of using R410A as the refrigerant, the ratio
(Vc/Ve) is set, for example, to the range of 30 to 40. In the case
of using a thin refrigerant like R410A as the refrigerant to be
drawn into the compressor, the ratio (Vc/Ve) also tends to
increase. Generally, the larger the ratio (Vc/Ve), the larger the
driving force (torque) required for self-activation of the
low-pressure stage compressor 105 and the expander 103 should be.
In this regard, "the volume of the low-pressure stage compressor
105" means a confined volume, that is, the volume of the working
chamber at the time of completion of the drawing process. This
applies also to the expander 103.
[0054] The refrigeration cycle apparatus 100 is further provided
with a high-pressure supply passage 130 and an on-off valve 131.
The high-pressure supply passage 130 is connected to the main
refrigerant circuit 106 so as to communicate the flow passage 106a
and the flow passage 106e. The on-off valve 131 is provided on the
high-pressure supply passage 130 and controls the flow of the
refrigerant in the high-pressure supply passage 130.
[0055] The high-pressure supply passage 130 has an upstream end
E.sub.1 (one end) connected to the flow passage 106a and a
downstream end E.sub.2 (the other end) connected to the flow
passage 106e. That is, the high-pressure supply passage 130 is a
flow passage that can introduce the refrigerant in the flow passage
106a directly to the suction port of the low-pressure stage
compressor 105 before the rotation of the power-recovery shaft 107.
The high-pressure supply passage 130, typically, is constituted by
a refrigerant pipe.
[0056] As long as the pressure at the suction port of the
low-pressure stage compressor 105 can be increased in the
activation of the refrigeration cycle apparatus 100, the position
of the upstream end E.sub.1 is not limited to the position shown in
FIG. 1. That is, the position of the upstream end E.sub.1 is not
specifically limited, as long as a portion of the main refrigerant
circuit 106 from the discharge port of the high-pressure stage
compressor 101 to the suction port of the expander 103 and a
portion of the main refrigerant circuit 106 from the outlet of the
evaporator 104 to the suction port of the low-pressure stage
compressor 105 can be communicated. Specifically, the high-pressure
supply passage 130 may be connected to the main refrigerant circuit
106 so as to communicate the flow passage 106b and the flow passage
106e. Depending on the circumstances, the high-pressure supply
passage 130 may branch from the heat radiator 102. For example, in
the case where the heat radiator 102 is constituted by an upstream
part and a downstream part, the high-pressure supply passage 130
can easily branch from a portion between these two parts.
[0057] However, in the case where the upstream end E.sub.1 is
located on the flow passage 106a as shown in FIG. 1, the following
effects are obtained. The density of the refrigerant in the flow
passage 106a is lower than the density of the refrigerant in the
flow passage 106b. Normally, the refrigerant in the flow passage
106a is in a gas phase. It is possible to prevent the liquid
refrigerant from flowing into the high-pressure stage compressor
101 through the low-pressure stage compressor 105 by supplying the
gas refrigerant to the suction port of the low-pressure stage
compressor 105 through the high-pressure supply passage 130. This
prevents liquid compression in the high-pressure stage compressor
101, leading to an enhancement in reliability of the refrigeration
cycle apparatus 100.
[0058] The on-off valve 131 and the check valve 132 form a flow
passage-switching mechanism capable of selectively connecting one
selected from the evaporator 104 and the high-pressure supply
passage 130 to the low-pressure stage compressor 105. When one
selected from the evaporator 104 and the high-pressure supply
passage 130 is selectively connected to the low-pressure stage
compressor 105, the refrigerant is introduced from one selected
from the evaporator 104 and the high-pressure supply passage 130 to
the low-pressure stage compressor 105. The check valve 132 is
provided in a portion of the main refrigerant circuit 106 from the
outlet of the evaporator 104 to the downstream end E.sub.2 of the
high-pressure supply passage 130 (flow passage 106e).
[0059] The on-off valve 131 is closed in the regular operation, and
is opened in the activation of the refrigeration cycle apparatus
100. By opening the on-off valve 131, it is possible to supply the
refrigerant in the flow passage 106a directly to the suction port
of the low-pressure stage compressor 105 through the high-pressure
supply passage 130. At that time, the check valve 132 can block the
flow of the refrigerant from the high-pressure supply passage 130
toward the evaporator 104. On the other hand, by closing the on-off
valve 131, it is possible to supply the refrigerant from the
evaporator 104 to the low-pressure stage compressor 105 while
restricting the flow of the refrigerant from the high-pressure
supply passage 130 to the low-pressure stage compressor 105. The
check valve 132 has an advantage that there is no need for
electrical control. Of course, it is also possible to replace the
check valve 132 with a valve that can be arbitrarily opened and
closed.
[0060] The refrigeration cycle apparatus 100 is further provided
with the injection flow passage 111 and an injection
flow-regulating valve 112. The injection flow passage 111 serves to
introduce the gas refrigerant separated from the liquid refrigerant
in the gas-liquid separator 108, to a portion of the main
refrigerant circuit 106 from the discharge port of the low-pressure
stage compressor 105 to the suction port of the high-pressure stage
compressor 101 (intermediate-pressure flow passage 106f).
Specifically, the injection flow passage 111 is connected to the
main refrigerant circuit 106 so as to communicate the gas
refrigerant outlet of the gas-liquid separator 108 and the
intermediate-pressure flow passage 106f. The injection
flow-regulating valve 112 is provided on the injection flow passage
111 and controls the flow of the refrigerant in the injection flow
passage 111. The injection flow passage 111, typically, is
constituted by a refrigerant pipe. As the injection flow-regulating
valve 112, a valve, which allows the degree of opening to be varied
stepwise, capable of expanding a refrigerant, typically, an
electric expansion valve is preferably used.
[0061] The injection flow-regulating valve 112 serves to regulate
the flow rate of the gas refrigerant to be injected into the
intermediate-pressure flow passage 106f in the regular operation.
On the other hand, the injection flow-regulating valve 112 is fully
opened or substantially fully opened in the activation of the
refrigeration cycle apparatus 100. When the injection
flow-regulating valve 112 is opened in the activation, the
high-pressure stage compressor 101 can draw the refrigerant present
in the flow passage 106c, the gas-liquid separator 108, the flow
passage 106d, and the evaporator 104. This enables the pressure on
the high-pressure side of the main refrigerant circuit 106 to
increase rapidly. Particularly, since the gas-liquid separator 108
is provided in this embodiment, it is possible to store a
sufficient amount of refrigerant between the discharge port of the
expander 103 and the check valve 132 during stoppage.
[0062] In order to improve the coefficient of performance of the
refrigeration cycle apparatus 100, the gas refrigerant can be
supplied from the gas-liquid separator 108 to the
intermediate-pressure flow passage 106f through the injection flow
passage 111 after the activation of the refrigeration cycle
apparatus 100. By appropriately adjusting the degree of opening of
each of the expansion valve 110 and the injection flow-regulating
valve 112, it is possible to prevent the liquid refrigerant from
flowing from the gas-liquid separator 108 into the
intermediate-pressure flow passage 106f as well as preventing the
backflow of the refrigerant from the intermediate-pressure flow
passage 106f to the gas-liquid separator 108.
[0063] The refrigeration cycle apparatus 100 is further provided
with a controller 117. The expansion valve 110, the injection
flow-regulating valve 112, and the on-off valve 131 are controlled
by the controller 117. The controller 117, typically, is
constituted by a microcomputer. When a command to start the
operation of the refrigeration cycle apparatus 100 is given to the
controller 117 through an input device (not shown), a predetermined
control program stored in an internal memory of the controller 117
is executed. Specifically, the controller 117 executes the
predetermined activation control described below with reference to
FIG. 2. Further, the controller 117 controls the action of the
motor 101b that drives the high-pressure stage compressor 101.
[0064] The refrigeration cycle apparatus 100 is further provided
with an activation detector 119 that detects the activation of the
expander 103 or the low-pressure stage compressor 105. The
controller 117 switches the control of the on-off valve 131 (flow
passage-switching mechanism) from the control before the activation
to the control after the activation, according to a detection
result of the activation detector 119. Specifically, the on-off
valve 131 is opened before the activation of the expander 103 and
the low-pressure stage compressor 105 so that the refrigerant is
introduced from the high-pressure supply passage 130 to the
low-pressure stage compressor 105. After the activation of the
expander 103 and the low-pressure stage compressor 105, the on-off
valve 131 is closed so that the refrigerant is introduced from the
evaporator 104 to the low-pressure stage compressor 105. For
example, upon the reception of signals that indicate the activation
of the low-pressure stage compressor 105 from the activation
detector 119, the controller 117 closes the on-off valve 131. In
this way, smooth transfer to the control in the regular operation
can be achieved.
[0065] A temperature detector, a pressure detector, or the like can
be used as the activation detector 119. The activation detector 119
as a temperature detector, for example, includes a temperature
detecting element such as a thermocouple and a thermistor, and
detects the difference .DELTA.T between the temperature of the
refrigerant at the suction port of the expander 103 and the
temperature of the refrigerant at the discharge port of the
expander 103. The activation detector 119 as a pressure detector,
for example, includes a piezoelectric element, and detects the
difference .DELTA.P between the pressure of the refrigerant at the
suction port of the expander 103 and the pressure of the
refrigerant at the discharge port of the expander 103. Further, the
activation detector 119 may include a timer that measures an
elapsed time from the activation of the high-pressure stage
compressor 101. Such a timer can be provided also as a function of
the controller 117. In this case, the controller 117 itself can
function as the activation detector 119. Furthermore, a contact or
noncontact displacement sensor that detects the driving of the
power-recovery shaft 107, such as an encoder, may be provided as
the activation detector 119.
[0066] Depending on the type of the activation detector 119, the
method for detecting the activation of the power recovery system
109 differs as follows. According to the following methods, it is
possible to detect the activation of the power recovery system 109
easily.
[0067] In the case of using a pressure detector as the activation
detector 119, a threshold P.sub.th that has been determined
experimentally or theoretically, for example, is preset in the
controller 117. When the value obtained by subtracting the current
pressure difference .DELTA.P.sub.n+1 detected by the pressure
detector from the pressure difference .DELTA.P.sub.n (n: natural
number) that has been detected by the pressure detector at a time
going back for a unit time exceeds the specific threshold P.sub.th,
the activation of the expander 103 or the low-pressure stage
compressor 105 is detected. In the controller 117, a single
threshold P.sub.th may be set, or a plurality of thresholds
P.sub.th associated with the outdoor temperature or the like may be
set. In the latter case, the controller 117 selects an optimal
threshold P.sub.th on the basis of the outdoor temperature or the
like. This applies also to other thresholds described below.
[0068] The difference .DELTA.P between the pressure of the
refrigerant at the suction port of the expander 103 and the
pressure of the refrigerant at the discharge port of the expander
103 generally monotonically increases during the period after the
activation of the high-pressure stage compressor 101 and before the
activation of the expander 103. When the expander 103 starts to
operate, the pressure difference .DELTA.P turns to decrease
temporarily, and becomes smaller than that immediately before the
activation of the expander 103. It is possible to detect the
activation of the expander 103 or the low-pressure stage compressor
105 by capturing this change in the pressure difference .DELTA.P.
Specifically, the pressure difference .DELTA.P is detected at every
unit time and stored in the memory of the controller 117. Then, the
last pressure difference .DELTA.P.sub.n previously stored in the
memory and the current pressure difference .DELTA.P.sub.n+1 are
compared. When the current pressure difference .DELTA.P.sub.+1
significantly falls below the last past pressure difference
.DELTA.P.sub.n, the expander 103 or the low-pressure stage
compressor 105 can be determined to have been activated. In other
words, when (.DELTA.P.sub.n-.DELTA.P.sub.n+1)>P.sub.th is
satisfied, the expander 103 or the low-pressure stage compressor
105 can be determined to have been activated. It should be noted
that the "unit time" can be set arbitrarily to a sufficient time to
capture a sudden decrease in the pressure difference .DELTA.P, for
example, in the range of 1 to 5 seconds.
[0069] Instead of the pressure difference .DELTA.P, it is also
possible to use the temperature difference .DELTA.T. That is, when
a value obtained by subtracting the current temperature difference
.DELTA.T.sub.n+1 detected by the temperature detector from the
temperature difference .DELTA.T.sub.n (n: natural number) that has
been detected by the temperature detector at a time going back for
a unit time exceeds a specific threshold T.sub.th, the activation
of the expander 103 or the low-pressure stage compressor 105 is
detected.
[0070] Further, there is also a possibility that the activation of
the power recovery system 109 can be detected on the basis of the
discharge temperature from the expander 103 or the discharge
pressure from the expander 103. When the power recovery system 109
is activated, the expander 103 is also rotated. The expander 103
draws the refrigerant, then expands the drawn refrigerant, and
discharges it. Therefore, the temperature and pressure of the
refrigerant after being discharged from the expander 103 are lower
than those before being drawn. The power recovery system 109 can be
determined to have been activated by capturing a sudden change in
the temperature (or pressure) at the discharge port of the expander
103 while monitoring the temperature (or pressure) in chronological
order.
[0071] Meanwhile, on the presumption that the power recovery system
109 is activated without fail, the activation of the expander 103
or the low-pressure stage compressor 105 may be detected by the
method described below. The below-described method is rather a
method of determining whether the power recovery system 109 is in a
state that allows continuous operation, than a method of capturing
the activation of the expander 103 or the low-pressure stage
compressor 105. After the activation of the expander 103 or the
low-pressure stage compressor 105 is detected by the
below-described method, the control of the on-off valve 131 (flow
passage-switching mechanism) can be switched from the control
before the activation to the control after the activation according
to the detected results. In this way, the power recovery system 109
continues to operate stably even after the on-off valve 131 is
closed.
[0072] Specifically, in the case of using a temperature detector as
the activation detector 119, a threshold T.sub.1 that has been
determined experimentally or theoretically, for example, is preset
in the controller 117. When the temperature difference .DELTA.T
detected by the temperature detector exceeds the threshold T.sub.1,
the activation of the expander 103 or the low-pressure stage
compressor 105 is detected.
[0073] In the case of using a pressure detector as the activation
detector 119, a threshold P.sub.1 that has been determined
experimentally or theoretically, for example, is preset in the
controller 117. When the pressure difference .DELTA.P detected by
the pressure detector exceeds the specific threshold P.sub.1, the
activation of the expander 103 or the low-pressure stage compressor
105 is detected.
[0074] The reason why the activation of the expander 103 or the
low-pressure stage compressor 105 can be detected by comparison
between the temperature difference .DELTA.T and the threshold
T.sub.1, or comparison between the pressure difference .DELTA.P and
the threshold P.sub.1 is as follows. When the high-pressure stage
compressor 101 is activated, the refrigerant discharged from the
high-pressure stage compressor 101 is supplied to the suction port
of the low-pressure stage compressor 105 through the high-pressure
supply passage 130. This activates the power recovery system 109.
At this time, since the low-pressure stage compressor 105 serves as
a driving source, the power recovery system 109 starts to rotate
before the temperature difference between the suction temperature
of the high-pressure stage compressor 101 and the discharge
temperature of the high-pressure stage compressor 101 becomes
significant. When the power recovery system 109 starts to rotate,
the pressure difference in the cycle has not been sufficiently
increased, and the power to rotate the power recovery system 109 is
low. Therefore, the rotational speed of the power recovery system
109 is also low. When the rotational speed of the power recovery
system 109 is low, the rotational speed of the expander 103 is also
low. This state corresponds to a "narrowed state" that is a
description for expansion valves. Accordingly, the discharge
temperature and discharge pressure of the high-pressure stage
compressor 101 gradually increase as well.
[0075] When the discharge temperature and discharge pressure of the
high-pressure stage compressor 101 increase, the power to rotate
the expander 103 and the low-pressure stage compressor 105 also
increases, and the rotational speed of the power recovery system
109 increases. Then, when a high rotational speed is achieved, the
power recovery system 109 stably rotates under the influence of the
inertial force. The on-off valve 131 is desirably maintained open
until such a stable rotation state is reached.
[0076] On the other hand, the suction temperature of the expander
103 gradually increases from the temperature during stoppage, which
is substantially the same as the outdoor temperature. Depending on
the suction temperature (or suction pressure) of the expander 103,
the discharge temperature (or discharge pressure) of the expander
103 is determined. The suction temperature, the discharge
temperature, the suction pressure, and the discharge pressure of
the expander 103 each in the activation of the power recovery
system 109 and in the regular operation of the power recovery
system 109, for example, with the outdoor temperature being
10.degree. C., are shown below as an example. It should be noted
that the following values are calculated with the expansion
ratio=2.0. The refrigerant is carbon dioxide.
[0077] <In Activation>
[0078] Suction temperature: 10.degree. C.
[0079] Suction pressure: 5.0 MPa
[0080] Discharge temperature: -3.0.degree. C.
[0081] Discharge pressure: 3.2 MPa
[0082] Difference between suction temperature and discharge
temperature: 13.degree. C.
[0083] Difference between suction pressure and discharge pressure:
1.8 MPa
[0084] <In Regular Operation>
[0085] Suction temperature: 40.degree. C.
[0086] Suction pressure: 10.0 MPa
[0087] Discharge temperature: 13.4.degree. C.
[0088] Discharge pressure: 4.9 MPa
[0089] Difference between suction temperature and discharge
temperature: 26.6.degree. C. Difference between suction pressure
and discharge pressure: 5.1 MPa
[0090] When the power recovery system 109 is activated with the
discharge temperature and discharge pressure of the high-pressure
stage compressor 101 being low, the suction temperature of the
expander 103 and the discharge temperature of the expander 103 each
gradually increase as mentioned above. The difference between the
suction temperature and the discharge temperature gradually
increase as well. This applies also to the pressure. Therefore, the
activation of the power recovery system 109 can be detected by
setting appropriate values as the threshold T.sub.1 and the
threshold P.sub.1, e.g., respective values that are slightly larger
than the temperature difference and the pressure difference to be
reached when the activation of the power recovery system 109 can be
estimated.
[0091] In the case of using a timer as the activation detector 119,
a threshold time t.sub.1 that has been determined experimentally or
theoretically, for example, is preset in the controller 117. When
the time t measured by the timer exceeds the threshold time
t.sub.1, the activation of the expander 103 or the low-pressure
stage compressor 105 is detected.
[0092] The "threshold time t.sub.1" is written in the activation
control program to be executed by the controller 117. For example,
the time from the activation of the high-pressure stage compressor
101 to the activation of the low-pressure stage compressor 105 is
actually measured under various operational conditions (such as
outdoor temperatures). Then, a time at which the activation of the
low-pressure stage compressor 105 can be surely determined under
all the operational conditions can be set as the "threshold time
t.sub.1". Theoretically, a model of the refrigeration cycle
apparatus 100 is constructed, and a pressure difference that is
necessary and sufficient to activate the power recovery system 109
is estimated by computer simulation. Thereafter, using parameters
such as the volume of the high-pressure stage compressor 101 and
the filling amount of the refrigerant in the main refrigerant
circuit 106, the initial activation time necessary to produce the
estimated pressure difference is calculated. The calculated initial
activation time can be set as the "threshold time t.sub.1".
[0093] The method for detecting the activation of the expander 103
or the low-pressure stage compressor 105 is not limited to one, and
a plurality of methods can be performed in combination. For
example, the activation of the expander 103 or the low-pressure
stage compressor 105 is accurately captured by a method of
monitoring the pressure difference .DELTA.P and/or the temperature
difference .DELTA.T between the suction port and the discharge port
of the expander 103. Thereafter, whether the power recovery system
109 is in a state that allows continuous operation is determined by
a method of comparing the temperature difference .DELTA.T with the
threshold T.sub.1, a method of comparing the pressure difference
.DELTA.P with the threshold P.sub.1, or a method of comparing the
elapsed time t with the threshold time t.sub.1. When these
plurality of conditions are satisfied, the expander 103 or the
low-pressure stage compressor 105 is determined to be activated,
and the on-off valve 131 is closed.
[0094] <Operation of Refrigeration Cycle Apparatus 100>
[0095] FIG. 2 is a flow chart showing the activation control of the
refrigeration cycle apparatus 100. The refrigeration cycle
apparatus 100 starts the regular operation after performing the
activation control shown in FIG. 2. In an operation standby state,
the high-pressure stage compressor 101 is stopped, the expansion
valve 110 is opened, and the pressure of the refrigerant in the
main refrigerant circuit 106 is substantially uniform.
[0096] When an activation command is input in step S11, the
controller 117 transmits control signals to the actuators of the
expansion valve 110 and the injection flow-regulating valve 112 so
that these valves 110 and 112 are fully opened (step S12). Further,
it transmits control signals to the actuator of the on-off valve
131 so that the on-off valve 131 is opened (step S13). This allows
the high-pressure supply passage 130 to be open.
[0097] Next, the controller 117 starts to supply power to the motor
101b in order to activate the high-pressure stage compressor 101
(step S14). This activates the high-pressure stage compressor 101
and causes the refrigerant present in the intermediate-pressure
flow passage 106f, the injection flow passage 111, the flow passage
106c, the gas-liquid separator 108, the flow passage 106d, the
evaporator 104, and a part of the flow passage 106e (portion
between the evaporator 104 and the check valve 132) to be drawn
into the high-pressure stage compressor 101.
[0098] Instead of opening the on-off valve 131 before the
activation of the high-pressure stage compressor 101, it is also
possible to open the on-off valve 131 upon the activation of the
high-pressure stage compressor 101.
[0099] Upon the activation of the high-pressure stage compressor
101, a fan or pump that causes a fluid (air or water) for heat
exchange with the refrigerant to flow into the heat radiator 102 is
activated. This can prevent an excessive increase in the high
pressure of the cycle. Likewise, a fan or pump of the evaporator
104 is activated upon the activation of the high-pressure stage
compressor 101. This allows efficient production of the gas
refrigerant to be drawn into the high-pressure stage compressor
101.
[0100] Once the drawing of the refrigerant into the high-pressure
stage compressor 101 is started, the internal pressure of the
intermediate-pressure flow passage 106f, etc., decreases. On the
other hand, since the refrigerant compressed in the high-pressure
stage compressor 101 is discharged, the pressure in flow passages
from the discharge port of the high-pressure stage compressor 101
to the suction port of the expander 103 (the flow passage 106a, the
heat radiator 102, and the flow passage 106b), the high-pressure
supply passage 130, and a part of the flow passage 106e (portion
between the check valve 132 and the suction port of the
low-pressure stage compressor 105) increases.
[0101] As a result, as shown in FIG. 6, the pressure at the suction
port of each of the expander 103 and the low-pressure stage
compressor 105 is rendered relatively high, and the pressure at the
discharge port of each of the expander 103 and the low-pressure
stage compressor 105 is rendered relatively low. That is, a
pressure difference can be produced not only between the suction
port and the discharge port of the expander 103, but also between
the suction port and the discharge port of the low-pressure stage
compressor 105. The pressure difference of the refrigerant acts on
each of the expander 103 and the low-pressure stage compressor 105,
and thus self-activation of the power recovery system 109 can be
achieved easily. The high-pressure stage compressor 101 can draw a
sufficient amount of the refrigerant to produce a large pressure
difference because the injection flow passage 111 and the
gas-liquid separator 108 are provided.
[0102] Upon detecting the activation of the low-pressure stage
compressor 105 through the activation detector 119 (step S15), the
controller 117 transmits control signals to the actuator of the
on-off valve 131 so that the on-off valve 131 is closed (step S16).
This allows the backpressure acting on the check valve 132 to be
released, and the refrigerant is supplied from the evaporator 104
to the low-pressure stage compressor 105 through the flow passage
106e. Meanwhile, the gas-liquid two-phase refrigerant whose
pressure has been reduced in the expander 103 is supplied to the
gas-liquid separator 108. The opening degree of each of the
expansion valve 110 and the injection flow-regulating valve 112 is
adjusted so that excess supply of the liquid refrigerant to the
high-pressure stage compressor 101 through the injection flow
passage 111 and the flow passage 106f is prevented (step S17).
After the completion of the activation control shown in FIG. 2,
transfer to the regular operation where the refrigerant is
circulated in the main refrigerant circuit 106 is performed in the
refrigeration cycle apparatus 100.
[0103] When the operation of the refrigeration cycle apparatus 100
is intended to be stopped, the rotational speed of the
high-pressure stage compressor 101, for example, is progressively
reduced. After the high-pressure stage compressor 101 has been
stopped, the refrigerant moves through the high-pressure stage
compressor 101, the expander 103, and the low-pressure stage
compressor 105, taking sufficient time. Therefore, the pressure
difference in the main refrigerant circuit 106 is naturally
released, and the pressure in the main refrigerant circuit 106
becomes substantially uniform to be stabilized. This causes the
expander 103 and the low-pressure stage compressor 105 to be
stopped naturally.
[0104] <Effects of Refrigeration Cycle Apparatus 100>
[0105] According to this embodiment, the high-pressure stage
compressor 101 can draw and compress the refrigerant in the
evaporator 104 and the gas-liquid separator 108 in the activation
of the refrigeration cycle apparatus 100. Therefore, the pressure
in flow passages from the discharge port of the high-pressure stage
compressor 101 to the suction port of the expander 103 can be
rapidly increased. Since a large pressure difference is produced
between the suction port and the discharge port of the expander
103, the power recovery system 109 is self-activated smoothly.
[0106] Further, the compressed refrigerant is introduced into a
part of the flow passage 106e from the check valve 132 to the
suction port of the low-pressure stage compressor 105 through the
high-pressure supply passage 130. This produces a large pressure
difference also between the suction port and the discharge port of
the low-pressure stage compressor 105. This fact contributes to a
smoother self-activation of the power recovery system 109. In this
embodiment, the low-pressure stage compressor 105 and the expander
103 each have a certain suction volume. Particularly, when the
suction volume of the low-pressure stage compressor 105 is larger
than the suction volume of the expander 103, the power recovery
system 109 is activated more smoothly by producing a pressure
difference between the suction port and the discharge port of the
low-pressure stage compressor 105.
[0107] In the case where a certain period of time has elapsed
without detecting the activation of the expander 103 or the
low-pressure stage compressor 105 after the activation of the
high-pressure stage compressor 101, it can be determined that the
activation of the power recovery system 109 has been failed. In the
case where the activation of the power recovery system 109 has been
failed, the controller 117 stops the high-pressure stage compressor
101 and performs the control to activate the power recovery system
109 again. In this way, it is possible to prevent an excessive
increase in the pressure in flow passages from the discharge port
of the high-pressure stage compressor 101 to the suction port of
the expander 103. It is also possible to prevent damages to the
components of the expander 103 from occurring due to an excessive
pressure difference between before and after the expander 103.
Thus, the reliability of the refrigeration cycle apparatus 100 can
be improved.
[0108] According to this embodiment, the heat radiator 102 is
connected to the suction port of the expander 103, the evaporator
104 is connected to the suction port of the low-pressure stage
compressor 105, and the gas-liquid separator 108 is connected to
the discharge port of the expander 103. The gas-liquid separator
108 is connected also to the discharge port of the low-pressure
stage compressor 105 via the injection flow passage 111. Since the
volumes of the heat radiator 102, the evaporator 104, and the
gas-liquid separator 108 are comparatively large, these components
can function as a buffer space for the refrigerant in the
activation of the refrigeration cycle apparatus 100. Thus, an
effect of suppressing the pressure pulsation in the activation can
be obtained.
[0109] The type of refrigerant (working fluid) that can be used in
this embodiment is not specifically limited. For example, fluorine
refrigerant such as R410A, natural refrigerant such as carbon
dioxide, and low GWP (Global Warming Potential) refrigerant such as
R1234yf can be used. Whichever the refrigerant is used, the
above-mentioned effects can be obtained.
Modification 1
[0110] <Configuration of Refrigeration Cycle Apparatus
200>
[0111] FIG. 3 is a configuration diagram of a refrigeration cycle
apparatus 200 in Modification 1. As shown in FIG. 3, the flow
passage-switching mechanism is constituted by a three-way valve 133
in the refrigeration cycle apparatus 200. As the activation
detector 119, a PTC (Positive Temperature Coefficient) heater 140
and a current detector 141 are used. Further, a bypass flow passage
201 and a bypass valve 202 are provided. Other configurations are
the same as those in Embodiment 1. In this modification, the same
components as those in Embodiment 1 are denoted by the same
reference numerals, and the detailed descriptions thereof are
omitted.
[0112] The three-way valve 133 as a flow passage-switching
mechanism is provided at the downstream end E.sub.2 of the
high-pressure supply passage 130 so as to be capable of switching
between a first state in which the refrigerant is introduced from
the evaporator 104 into the low-pressure stage compressor 105 and a
second state in which the refrigerant is introduced from the
high-pressure supply passage 130 into the low-pressure stage
compressor 105. In the first state, the flow of the refrigerant
from the high-pressure supply passage 130 to the low-pressure stage
compressor 105 is blocked. In the second state, the flow of the
refrigerant from the evaporator 104 to the low-pressure stage
compressor 105 is blocked. In this way, the on-off valve 131 and
the check valve 132 in Embodiment 1 can be replaced with the
three-way valve 133. The three-way valve 133 can suppress an
increase in the number of components.
[0113] The bypass flow passage 201 is connected to the main
refrigerant circuit 106 so as to bypass the expander 103. The
upstream end E.sub.3 of the bypass flow passage 201 is located on
the flow passage 106b, and the downstream end E.sub.4 thereof is
located on the flow passage 106c. The bypass valve 202 is provided
on the bypass flow passage 201. The bypass flow passage 201,
typically, is constituted by a refrigerant pipe. As the bypass
valve 202, a valve, which allows the degree of opening to be varied
stepwise, capable of expanding a refrigerant, typically, an
electric expansion valve is preferably used.
[0114] The current detector 141 detects the magnitude of the
current flowing in the PTC heater 140. The PTC heater 140 is
provided in a portion of the main refrigerant circuit 106 from the
outlet of the heat radiator 102 to the suction port of the expander
103, that is, on the flow passage 106b. Specifically, the PTC
heater 140 is located on the expander 103 side as seen from the
upstream end E.sub.3 of the bypass flow passage 201. When the PTC
heater 140 is provided at such a position, the PTC heater 140 is
less likely to be affected by the flow of the refrigerant toward
the bypass flow passage 201. Therefore, it is possible to detect
the flow of the refrigerant into the expander 103 accurately.
[0115] In the case of using the PTC heater 140 and the current
detector 141 as the activation detector 119, a threshold
.DELTA.I.sub.1 that has been determined experimentally or
theoretically, for example, is preset in the controller 117. When
the power recovery system 109 is activated, the refrigerant starts
to flow also at the suction port of the expander 103. Then, the
magnitude of the current also suddenly changes due to the
temperature change (temperature reduction) of the PTC heater 140.
In order to capture such a change, the amount of change per unit
time in the current flowing in the PTC heater 140 can be preset as
the threshold .DELTA.I.sub.1. The "unit time", for example, can be
set arbitrarily in the range of 1 to 5 seconds. The amount of
change per unit time in the current flowing in the PTC heater 140
is calculated by the current detector 141, and when the calculated
amount of change exceeds the threshold .DELTA.I.sub.1, the
activation of the expander 103 or the low-pressure stage compressor
105 is detected. The PTC heater 140 and the current detector 141
can be used also in other embodiments and modifications.
[0116] <Operation of Refrigeration Cycle Apparatus 200>
[0117] FIG. 4 is a flow chart showing the activation control of the
refrigeration cycle apparatus 200. When an activation command is
input in step S21, the controller 117 transmits control signals to
the actuators of the expansion valve 110, the injection
flow-regulating valve 112, and the bypass valve 202 so that the
expansion valve 110 and the injection flow-regulating valve 112 are
fully opened as well as the bypass valve 202 is opened to a
specific degree (step S22). Here, the phrase "the bypass valve 202
is opened to a specific degree" means to be set within a range of
the degree of opening that allows the pressure difference between
the suction port and the discharge port of the expander 103 to be
maintained to the level that is required for the activation of the
expander 103. This "specific degree of opening" can be determined
experimentally or theoretically. In short, the bypass valve 202 is
slightly opened so as to prevent excessive reduction in the
pressure difference between before and after the expander 103.
[0118] Next, the low-pressure stage compressor 105 and the
high-pressure supply passage 130 are connected by controlling the
three-way valve 133 (step S23).
[0119] Next, the controller 117 starts to supply power to the motor
101b in order to activate the high-pressure stage compressor 101
(step S24). This activates the high-pressure stage compressor 101
and causes the refrigerant present in the intermediate-pressure
flow passage 106f, the injection flow passage 111, the flow passage
106c, the gas-liquid separator 108, the flow passage 106d, the
evaporator 104, and a part of the flow passage 106e (portion
between the evaporator 104 and the three-way valve 133) to be drawn
into the high-pressure stage compressor 101.
[0120] When the drawing of the refrigerant into the high-pressure
stage compressor 101 is started, as has been described in
Embodiment 1 with reference to FIG. 6, the pressure at the suction
port of each of the expander 103 and the low-pressure stage
compressor 105 is rendered relatively high, and the pressure at the
discharge port of each of the expander 103 and the low-pressure
stage compressor 105 is rendered relatively low. As a result, the
power recovery system 109 is self-activated smoothly.
[0121] Upon detecting the activation of the low-pressure stage
compressor 105 through the activation detector 119 (step S25), the
controller 117 controls the three-way valve 133 so that the
low-pressure stage compressor 105 and the evaporator 104 are
connected (step S26). This allows the refrigerant to be supplied
from the evaporator 104 to the low-pressure stage compressor 105
through the flow passage 106e. The opening degree of each of the
expansion valve 110 and the injection flow-regulating valve 112 is
adjusted because of the same reason as in Embodiment 1 (step S27).
Further, the bypass valve 202 is closed. Thereafter, transfer to
the regular operation is performed.
[0122] <Effects of the Refrigeration Cycle Apparatus 200>
[0123] According to this modification, the following effects can be
obtained in addition to the effects described in Embodiment 1.
According to this modification, the controller 117 opens the bypass
valve 202, before the activation of the expander 103 and the
low-pressure stage compressor 105, to a degree within the range
that allows a pressure difference required for the activation of
the expander 103 to be produced between the suction port and the
discharge port of the expander 103. That is, the activation of the
power recovery system 109 is attempted while the bypass valve 202
is slightly opened. The controller 117 closes the bypass valve 202
after the activation of the expander 103 and the low-pressure stage
compressor 105. Thus, a sudden reduction in the pressure difference
between before and after the expander 103 can be prevented from
occurring immediately after the activation of the power recovery
system 109. Accordingly, smooth transfer to the regular operation
can be achieved while a driving force to continue the operation of
the power recovery system 109 is sufficiently ensured.
Modification 2
[0124] FIG. 5 is a configuration diagram of a refrigeration cycle
apparatus 300 in Modification 2. As shown in FIG. 5, the
refrigeration cycle apparatus 300 differs from Embodiment 1 in that
a temperature detector that detects the temperature of the
refrigerant at the discharge port of the low-pressure stage
compressor 105 is used as the activation detector 119. In this
modification, the same components as those in Embodiment 1 are
denoted by the same reference numerals, and the detailed
descriptions thereof are omitted.
[0125] In the case of using a temperature detector as the
activation detector 119, a threshold T.sub.2 that has been
determined experimentally or theoretically, for example, is preset
in the controller 117. When a value obtained by subtracting a
temperature that has been detected by the temperature detector at a
time going back for a unit time from the current temperature
detected by the temperature detector exceeds the specific threshold
T.sub.2, the activation of the expander 103 or the low-pressure
stage compressor 105 is detected.
[0126] The temperature of the refrigerant at the discharge port of
the low-pressure stage compressor 105 is low during the period
after the activation of the high-pressure stage compressor 101 and
before the activation of the expander 103. When the low-pressure
stage compressor 105 starts to operate, the temperature of the
refrigerant at the discharge port of the low-pressure stage
compressor 105 suddenly increases. The change in the temperature of
the refrigerant at the discharge port of the low-pressure stage
compressor 105, for example, is about 10.degree. C., though it
depends also on the intended use, operational conditions, etc., of
the refrigeration cycle apparatus 100. By capturing this
temperature change, the activation of the expander 103 or the
low-pressure stage compressor 105 can be detected. Specifically,
the temperature T of the refrigerant at the discharge port of the
low-pressure stage compressor 105 is detected per unit time and
stored in the memory of the controller 117. Then, the last
temperature T.sub.n (n: natural number) previously stored in the
memory and the current temperature T.sub.n+1 are compared. When the
current temperature T.sub.n+1 significantly exceeds the last past
temperature T.sub.n, in other words, when
(T.sub.n+1-T.sub.n)>T.sub.2 is satisfied, the expander 103 or
the low-pressure stage compressor 105 can be determined to have
been activated. It should be noted that the "unit time" can be set
to a sufficient time to capture the sudden reduction in the
temperature T, for example, can be arbitrarily set in the range of
1 to 5 seconds.
[0127] Upon the activation of the low-pressure stage compressor
105, the refrigerant at high pressure and high temperature is drawn
into the low-pressure stage compressor 105 from the high-pressure
supply passage 130. Since the pressure in the flow passage 106f is
low, the low-pressure stage compressor 105 temporarily functions as
an expander. The refrigerant that has been expanded in the
low-pressure stage compressor 105 is discharged into the flow
passage 106f. The refrigerant that has been compressed in the
high-pressure stage compressor 101 and that has been expanded again
in the low-pressure stage compressor 105 obtains an enthalpy
corresponding to the loss occurring in each of the high-pressure
stage compressor 101 and the low-pressure stage compressor 105.
That is, the refrigerant present in the flow passage 106f flows
through the high-pressure stage compressor 101 and the low-pressure
stage compressor 105, and when it returns to the flow passage 106f
again, the temperature of the refrigerant increases by the
increment in the enthalpy of the refrigerant. The temperature
detector detects the activation of the low-pressure stage
compressor 105 by comparing the temperature increase with the
threshold T.sub.2.
[0128] <Effects of Refrigeration Cycle Apparatus 300>
[0129] According to this modification, the following effects can be
obtained in addition to the effects described in Embodiment 1. In
this modification, the activation is detected on the basis of the
temperature of the refrigerant at the discharge port of the
low-pressure stage compressor 105. This can ensure the capture of
the activation of the power recovery system 109, thereby enabling
rapid transfer to the regular operation.
Embodiment 2
[0130] <Configuration of Refrigeration Cycle Apparatus
400>
[0131] FIG. 8 is a configuration diagram of a refrigeration cycle
apparatus 400 in Embodiment 2. As shown in FIG. 8, the
refrigeration cycle apparatus 400 differs from Embodiment 1 in that
the high-pressure supply passage 130, the on-off valve 131, and the
check valve 132 are omitted. In this embodiment, the same
components as those in Embodiment 1 are denoted by the same
reference numerals, and the detailed descriptions thereof are
omitted.
[0132] In this embodiment, activation control that is different
from that in Embodiment 1 is performed. That is, the expansion
valve 110 is fully closed in the activation of the refrigeration
cycle apparatus 400. This allows the pressure at the suction port
of the low-pressure stage compressor 105 to be maintained at the
pressure in a standby state (before the activation of the
high-pressure stage compressor 101). Upon the activation of the
high-pressure stage compressor 101, a pressure difference occurs
between the suction port and the discharge port of the expander
103. Likewise, a pressure difference occurs between the suction
port and the discharge port of the low-pressure stage compressor
105. As a result, the power recovery system 109 is activated.
[0133] In the activation of the refrigeration cycle apparatus 400,
the injection flow-regulating valve 112 is fully opened or
substantially fully opened. When the injection flow-regulating
valve 112 is opened in the activation, the high-pressure stage
compressor 101 can draw the refrigerant present in the flow passage
106c, the gas-liquid separator 108, and a part of the flow passage
106d. This enables the pressure on the high-pressure side of the
main refrigerant circuit 106 to increase rapidly. Particularly,
since the gas-liquid separator 108 is provided in this embodiment,
it is possible to store a sufficient amount of refrigerant between
the discharge port of the expander 103 and the expansion valve 110
during stoppage.
[0134] In this embodiment, the controller 117 controls the
expansion valve 110 according to a detection result of the
activation detector 119. Specifically, it fully closes the
expansion valve 110 in the activation of the refrigeration cycle
apparatus 400. This can prevent the pressure at the suction port of
the low-pressure stage compressor 105 from being equal to the
pressure at the discharge port of the low-pressure stage compressor
105 via the injection flow passage 111. On the other hand, the
controller 117 opens the expansion valve 110 after the activation
of the expander 103 and the low-pressure stage compressor 105. For
example, upon the reception of signals that indicate the activation
of the low-pressure stage compressor 105 from the activation
detector 119, the controller 117 fully opens the expansion valve
110.
[0135] Also in this embodiment, the activation of the power
recovery system 109 can be detected by the method described in
Embodiment 1. The control of the expansion valve 110 can be
switched from the control before the activation to the control
after the activation, according to the detection result. In this
way, after the expansion valve 110 is opened, the power recovery
system 109 continues to operate stably.
[0136] In this embodiment, a temperature detector that detects the
temperature of the refrigerant in a portion of the main refrigerant
circuit 106 from the expansion valve 110 to the suction port of the
low-pressure stage compressor 105 (a part of the flow passage 106d,
the evaporator 104, and the flow passage 106e) can be further used
as the activation detector 119. In this case, when the difference
between a temperature in a standby state (before the activation of
the high-pressure stage compressor 101) detected by the temperature
detector and the current temperature detected by the temperature
detector exceeds a specific threshold T.sub.0, the activation of
the expander 103 or the low-pressure stage compressor 105 is
detected. Typically, a temperature detector that detects the
evaporation temperature of the refrigerant in the evaporator 104
can be used as the activation detector 119.
[0137] Likewise, a pressure detector that detects the pressure of
the refrigerant in a portion of the main refrigerant circuit 106
from the expansion valve 110 to the suction port of the
low-pressure stage compressor 105 can be used as the activation
detector 119. When the difference between a pressure in a standby
state detected by the pressure detector and the current pressure
detected by the pressure detector exceeds a specific threshold
P.sub.0, the activation of the expander 103 or the low-pressure
stage compressor 105 is detected.
[0138] When the power recovery system 109 is activated, the
low-pressure stage compressor 105 draws the refrigerant present in
the evaporator 104. This causes a reduction in the temperature and
the pressure in the evaporator 104. An optimal threshold T.sub.0 or
threshold P.sub.0 determined by an experimental or theoretical
technique is preset in the controller 117. The activation of the
power recovery system 109 can be detected by comparing the
temperature change in flow passages from the expansion valve 110 to
the suction port of the low-pressure stage compressor 105 (flow
passages on the low-pressure side) with the threshold T.sub.0.
Likewise, the activation of the power recovery system 109 can be
detected by comparing the pressure change in flow passages on the
low-pressure side with the threshold P.sub.0.
[0139] Also in this embodiment, the method for detecting the
activation of the expander 103 or the low-pressure stage compressor
105 is not limited to one, and a plurality of methods can be
performed in combination. For example, the activation of the
expander 103 or the low-pressure stage compressor 105 is accurately
captured by a method of monitoring the temperature or pressure of
the refrigerant in a portion of the main refrigerant circuit 106
from the expansion valve 110 to the suction port of the
low-pressure stage compressor 105. Thereafter, whether the power
recovery system 109 is in a state that allows continuous operation
is determined by a method of comparing the temperature difference
.DELTA.T with the threshold T.sub.1, a method of comparing the
pressure difference .DELTA.P with the threshold P.sub.1, or a
method of comparing the elapsed time t with the threshold time
t.sub.1. When these plurality of conditions are satisfied, the
expander 103 or the low-pressure stage compressor 105 is determined
to have been activated, and the expansion valve 110 is opened.
[0140] <Operation of Refrigeration Cycle Apparatus 400>
[0141] FIG. 9 is a flow chart showing the activation control of the
refrigeration cycle apparatus 400. The refrigeration cycle
apparatus 400 starts the regular operation after performing the
activation control shown in FIG. 9. In an operation standby state,
the high-pressure stage compressor 101 is stopped, the expansion
valve 110 and the injection valve 112 are opened, and the pressure
of the refrigerant in the main refrigerant circuit 106 is
substantially uniform.
[0142] When an activation command is input in step ST11, the
controller 117 transmits control signals to the actuator of the
expansion valve 110 so that the expansion valve 110 is closed
(fully closed) (step ST12).
[0143] Next, the controller 117 starts to supply power to the motor
101b in order to activate the high-pressure stage compressor 101
(step ST13). This activates the high-pressure stage compressor 101
and causes the refrigerant present in the intermediate-pressure
flow passage 106f, the injection flow passage 111, the flow passage
106c, the gas-liquid separator 108, and a part of the flow passage
106d (portion between the gas-liquid separator 108 and the
expansion valve 110) to be drawn into the high-pressure stage
compressor 101. Instead of closing the expansion valve 110 before
the activation of the high-pressure stage compressor 101, it is
also possible to close the expansion valve 110 corresponding to the
activation of the high-pressure stage compressor 101.
[0144] A fan or pump that causes a fluid (air or water) for heat
exchange with the refrigerant to flow into the heat radiator 102 is
activated, corresponding to the activation of the high-pressure
stage compressor 101. This can prevent an excessive increase in the
high pressure of the cycle. The fan or pump of the evaporator 104
may be activated corresponding to the activation of the
high-pressure stage compressor 101, or may be activated after the
expansion valve 110 is opened. In order to maintain the pressure at
the suction port of the low-pressure stage compressor 105 to the
pressure in a standby state, the latter operation is
recommended.
[0145] Once the drawing of the refrigerant into the high-pressure
stage compressor 101 is started, the internal pressure of the
intermediate-pressure flow passage 106f, etc., decreases. On the
other hand, since the refrigerant compressed in the high-pressure
stage compressor 101 is discharged, the pressure in flow passages
from the discharge port of the high-pressure stage compressor 101
to the suction port of the expander 103 (the flow passage 106a, the
heat radiator 102, and the flow passage 106b) increases. Meanwhile,
the pressure of the refrigerant in flow passages from the expansion
valve 110 to the suction port of the low-pressure stage compressor
105 (a part of the flow passage 106d, the evaporator 104, and the
flow passage 106e) is maintained to the pressure in the refrigerant
circuit 106 during stoppage of the refrigeration cycle apparatus
400.
[0146] As a result, as shown in FIG. 14A, a pressure difference can
be produced not only between the suction port and the discharge
port of the expander 103, but also between the suction port and the
discharge port of the low-pressure stage compressor 105. The
pressure difference of the refrigerant acts on each of the expander
103 and the low-pressure stage compressor 105, and thus
self-activation of the power recovery system 109 can be achieved
easily. The high-pressure stage compressor 101 can draw a
sufficient amount of the refrigerant to produce a large pressure
difference because the injection flow passage 111 and the
gas-liquid separator 108 are provided.
[0147] Upon detecting the activation of the low-pressure stage
compressor 105 through the activation detector 119 (step ST14), the
controller 117 transmits control signals to the actuator of the
expansion valve 110 so that the expansion valve 110 is fully opened
(or substantially fully opened) (step ST15). This causes the
gas-liquid two-phase refrigerant whose pressure has been reduced in
the expander 103 to be supplied to the gas-liquid separator 108.
After the completion of the activation control shown in FIG. 9,
transfer to the regular operation where the refrigerant is
circulated in the main refrigerant circuit 106 is performed in the
refrigeration cycle apparatus 400. In the regular operation, the
opening degree of each of the expansion valve 110 and the injection
flow-regulating valve 112 is adjusted so that excess supply of the
liquid refrigerant to the high-pressure stage compressor 101
through the injection flow passage 111 and the flow passage 106f is
prevented.
[0148] Also in this embodiment, the operation of the refrigeration
cycle apparatus 400 can be stopped according to the method
described in Embodiment 1.
[0149] <Effects of Refrigeration Cycle Apparatus 400>
[0150] According to this embodiment, the high-pressure stage
compressor 101 can draw and compress the refrigerant in the
gas-liquid separator 108 in the activation of the refrigeration
cycle apparatus 400. Therefore, the pressure in flow passages from
the discharge port of the high-pressure stage compressor 101 to the
suction port of the expander 103 can be increased rapidly. Since a
large pressure difference is produced between the suction port and
the discharge port of the expander 103, the power recovery system
109 is self-activated smoothly.
[0151] Further, it is possible to maintain the pressure of the
refrigerant in flow passages from the expansion valve 110 to the
suction port of the low-pressure stage compressor 105 to the
pressure in the refrigerant circuit 106 during stoppage of the
refrigeration cycle apparatus 400 by closing the expansion valve
110. Therefore, a pressure difference occurs also between the
suction port and the discharge port of the low-pressure stage
compressor 105. This fact contributes to a smoother self-activation
of the power recovery system 109. In this embodiment, the
low-pressure stage compressor 105 and the expander 103 each have a
certain suction volume. Particularly, when the suction volume of
the low-pressure stage compressor 105 is larger than the suction
volume of the expander 103, the power recovery system 109 is
activated more smoothly by producing a pressure difference between
the suction port and the discharge port of the low-pressure stage
compressor 105.
[0152] In the case where a specific condition is satisfied without
detecting the activation of the expander 103 or the low-pressure
stage compressor 105 after the activation of the high-pressure
stage compressor 101, it can be determined that the activation of
the power recovery system 109 has been failed. When the activation
of the power recovery system 109 has been failed, the controller
117 stops the high-pressure stage compressor 101 and performs the
control to activate the power recovery system 109 again. That is,
when a failure of the activation is detected, the expansion valve
110 is once fully opened. Thereafter, the activation control
described with reference to FIG. 9 is performed. In this way, it is
possible to prevent an excessive increase in the pressure in flow
passages from the discharge port of the high-pressure stage
compressor 101 to the suction port of the expander 103. It is also
possible to prevent damages to the components of the expander 103
from occurring due to an excessive pressure difference between
before and after the expander 103. Thus, the reliability of the
refrigeration cycle apparatus 400 can be improved.
[0153] The method for detecting a failure in the activation of the
power recovery system 109 is not specifically limited. For example,
after the activation of the high-pressure stage compressor 101, the
current temperature (or pressure) of the refrigerant in flow
passages from the expansion valve 110 to the suction port of the
low-pressure stage compressor 105 (flow passages on the
low-pressure side), e.g., in the evaporator 104 is detected. When
the difference between the detected temperature (or pressure) and a
reference temperature (or reference pressure) does not reach a
specific threshold within a certain period of time, the power
recovery system 109 can be determined to have failed to be
activated. As the threshold, the aforementioned threshold T.sub.0
or threshold P.sub.0 can be used. As the reference temperature (or
reference pressure), the temperature (or pressure) of the
refrigerant in the evaporator 104 before the activation of the
high-pressure stage compressor 101 can be used. In the case where a
certain period of time has elapsed without detecting the activation
of the power recovery system 109 after the activation of the
high-pressure stage compressor 101, it can be determined that the
activation of the power recovery system 109 has been failed. It is
also possible to determine whether or not the activation of the
power recovery system 109 has been failed by detecting the
temperature or pressure in flow passages from the discharge port of
the high-pressure stage compressor 101 to the suction port of the
expander 103 (flow passages on the high-pressure side), on the
basis of the difference between the detected temperature or
pressure and the temperature or pressure in the flow passages on
the high-pressure side before the activation of the high-pressure
stage compressor 101.
Modification 3
[0154] <Configuration of Refrigeration Cycle Apparatus
500>
[0155] FIG. 10 is a configuration diagram of a refrigeration cycle
apparatus 500 in Modification 3. As shown in FIG. 10, the
refrigeration cycle apparatus 500 is provided with the bypass flow
passage 201 and the bypass valve 202. Other configurations are the
same as those in Embodiment 2. In this modification, the same
components as those in Embodiment 2 are denoted by the same
reference numerals, and the detailed descriptions thereof are
omitted.
[0156] The bypass flow passage 201 is connected to the main
refrigerant circuit 106 so as to bypass the expander 103. The
upstream end E.sub.3 of the bypass flow passage 201 is located on
the flow passage 106b, and the downstream end E.sub.4 thereof is
located on the flow passage 106c. The bypass valve 202 is provided
on the bypass flow passage 201. The bypass flow passage 201,
typically, is constituted by a refrigerant pipe. As the bypass
valve 202, a valve, which allows the degree of opening to be varied
stepwise, capable of expanding a refrigerant, typically, an
electric expansion valve is preferably used.
[0157] The element portion of the activation detector 119 is
provided on the flow passage 106b. The element portion of the
activation detector 119 may be located on the heat radiator 102
side, or may be located on the expander 103 side, as seen from the
upstream end E.sub.3 of the bypass flow passage 201.
[0158] <Operation of Refrigeration Cycle Apparatus 500>
[0159] FIG. 11 is a flow chart showing the activation control of
the refrigeration cycle apparatus 500. When an activation command
is input in step ST21, the controller 117 transmits control signals
to the actuators of the expansion valve 110 and the bypass valve
202 so that the expansion valve 110 is fully closed, and the bypass
valve 202 is opened to a specific degree (step ST22). Here, the
phrase "the bypass valve 202 is opened to a specific degree" means
to be set within a range of the degree of opening that allows the
pressure difference between the suction port and the discharge port
of the expander 103 to be maintained to the level that is required
for the activation of the expander 103. This "specific degree of
opening" can be determined experimentally or theoretically. In
short, the bypass valve 202 is slightly opened so as to prevent
excessive reduction in the pressure difference between before and
after the expander 103.
[0160] Next, the controller 117 starts to supply power to the motor
101b in order to activate the high-pressure stage compressor 101
(step ST23). This activates the high-pressure stage compressor 101
and causes the refrigerant present in the intermediate-pressure
flow passage 106f, the injection flow passage 111, the flow passage
106c, the gas-liquid separator 108, and a part of the flow passage
106d to be drawn into the high-pressure stage compressor 101.
[0161] When the drawing of the refrigerant into the high-pressure
stage compressor 101 is started, as has been described in
Embodiment 2 with reference to FIG. 14A, a pressure difference can
be produced not only between the suction port and the discharge
port of the expander 103, but also between the suction port and the
discharge port of the low-pressure stage compressor 105. The
pressure difference of the refrigerant acts on each of the expander
103 and the low-pressure stage compressor 105, and thus
self-activation of the power recovery system 109 can be achieved
easily.
[0162] Upon detecting the activation of the low-pressure stage
compressor 105 through the activation detector 119 (step ST24), the
controller 117 transmits control signals to the actuator of the
expansion valve 110 so that the expansion valve 110 is fully opened
(or substantially fully opened) (step ST25). Further, it transmits
control signals to the actuator of the bypass valve 202 so that the
bypass valve 202 is fully closed.
[0163] <Effects of Refrigeration Cycle Apparatus 500>
[0164] According to this modification, the following effects can be
obtained in addition to the effects described in Embodiment 2.
According to this modification, the controller 117 opens the bypass
valve 202, before the activation of the expander 103 and the
low-pressure stage compressor 105, to a degree within the range
that allows a pressure difference required for the activation of
the expander 103 to be produced between the suction port and the
discharge port of the expander 103. That is, the activation of the
power recovery system 109 is attempted while the bypass valve 202
is slightly opened. The controller 117 closes the bypass valve 202
after the activation of the expander 103 and the low-pressure stage
compressor 105. Thus, a sudden reduction in the pressure difference
between before and after the expander 103 can be prevented from
occurring immediately after the activation of the power recovery
system 109. Accordingly, smooth transfer to the regular operation
can be achieved while a driving force to continue the operation of
the power recovery system 109 is sufficiently ensured.
Modification 4
[0165] <Configuration of Refrigeration Cycle Apparatus
600>
[0166] FIG. 12 is a configuration diagram of a refrigeration cycle
apparatus 600 in Modification 4. As shown in FIG. 12, the
refrigeration cycle apparatus 600 is further provided with a bypass
flow passage 301 and a bypass valve 302. Other configurations are
the same as in Embodiment 2. In this modification, the same
components as those in Embodiment 2 are denoted by the same
reference numerals, and the detailed descriptions thereof are
omitted.
[0167] The bypass flow passage 301 is connected to the main
refrigerant circuit 106 so as to communicate the flow passage 106b
and the flow passage 106d. The bypass valve 302 is provided on the
bypass flow passage 301 and controls the flow of the refrigerant in
the bypass flow passage 301. The bypass flow passage 301,
typically, is constituted by a refrigerant pipe. As the bypass
valve 302, an on-off valve can be used.
[0168] Specifically, the bypass flow passage 301 has an upstream
end E.sub.5 located at a portion of the main refrigerant circuit
106 from the outlet of the heat radiator 102 to the suction port of
the expander 103 (the flow passage 106b), and a downstream end
E.sub.6 located at a portion of the main refrigerant circuit 106
from the expansion valve 110 to the inlet of the evaporator 104 (a
part of the flow passage 106d). The bypass flow passage 301 allows
the refrigerant at high pressure in the flow passage 106b to be
introduced directly to the suction port of the low-pressure stage
compressor 105.
[0169] As long as the pressure at the suction port of the
low-pressure stage compressor 105 can be increased, the positions
of the upstream end E.sub.5 and the downstream end E.sub.6 are not
limited to the positions shown in FIG. 12. That is, as long as the
portion of the main refrigerant circuit 106 from the discharge port
of the high-pressure stage compressor 101 to the suction port of
the expander 103 and a portion of the main refrigerant circuit 106
from the expander 110 to the suction port of the low-pressure stage
compressor 105 can be communicated, the position of the upstream
end E.sub.5 is not specifically limited. Specifically, the bypass
flow passage 301 may be connected to the main refrigerant circuit
106 so as to communicate the flow passage 106a and the flow passage
106e. Depending on the circumstances, the bypass flow passage 301
may branch from the heat radiator 102. For example, in the case
where the heat radiator 102 is constituted by an upstream part and
a downstream part, the bypass flow passage 301 can easily branch
from a portion between these two parts.
[0170] <Operation of Refrigeration Cycle Apparatus 600>
[0171] FIG. 13 is a flow chart showing the activation control of
the refrigeration cycle apparatus 600. When an activation command
is input in step ST31, the controller 117 transmits control signals
to the actuators of the expansion valve 110 and the bypass valve
302 so that the expansion valve 110 is fully closed, and the bypass
valve 302 is fully opened (step ST32).
[0172] Next, the controller 117 starts to supply power to the motor
101b in order to activate the high-pressure stage compressor 101
(step ST33). This activates the high-pressure stage compressor 101
and causes the refrigerant present in the intermediate-pressure
flow passage 106f, the injection flow passage 111, the flow passage
106c, the gas-liquid separator 108, and a part of the flow passage
106d to be drawn into the high-pressure stage compressor 101.
[0173] When the drawing of the refrigerant into the high-pressure
stage compressor 101 is started, as shown in FIG. 14B, a large
pressure difference can be produced not only between the suction
port and the discharge port of the expander 103, but also between
the suction port and the discharge port of the low-pressure stage
compressor 105. The pressure difference of the refrigerant acts on
each of the expander 103 and the low-pressure stage compressor 105,
and thus self-activation of the power recovery system 109 can be
achieved easily. Particularly, according to this modification, the
pressure at the suction port of the low-pressure stage compressor
105 can be increased due to the functions of the bypass flow
passage 301 and the bypass valve 302.
[0174] Upon detecting the activation of the low-pressure stage
compressor 105 through the activation detector 119 (step ST34), the
controller 117 transmits control signals to the actuator of the
expansion valve 110 so that the expansion valve 110 is fully opened
(or substantially fully opened) (step ST35). Further, it transmits
control signals to the actuator of the bypass valve 302 so that the
bypass valve 302 is fully closed.
[0175] <Effects of Refrigeration Cycle Apparatus 600>
[0176] According to this modification, the following effects can be
obtained in addition to the effects described in Embodiment 2.
According to this modification, the pressure at the suction port of
the low-pressure stage compressor 105 can be also increased through
the bypass flow passage 301. Accordingly, the drive torque to be
imparted to the low-pressure stage compressor 105 increases, and a
smoother activation of the power recovery system 109 is
enabled.
[0177] Various constituents described in the respective embodiments
and modifications can be applied to other embodiments and
modifications without restriction as long as no technical
contradiction occurs. For example, the three-way valve 133 (see
FIG. 3) described in Modification 2 can be applied to Embodiment 1
and Modification 2.
INDUSTRIAL APPLICABILITY
[0178] The refrigeration cycle apparatus of the present invention
is useful for devices such as water heaters, air conditioners, and
dryers.
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