U.S. patent application number 13/514617 was filed with the patent office on 2012-10-18 for air conditioner, method for controlling opening of expansion valve, and computer-readable recording medium with expansion valve opening control program recorded thereon.
Invention is credited to Michiho Yoshida.
Application Number | 20120260678 13/514617 |
Document ID | / |
Family ID | 44145507 |
Filed Date | 2012-10-18 |
United States Patent
Application |
20120260678 |
Kind Code |
A1 |
Yoshida; Michiho |
October 18, 2012 |
AIR CONDITIONER, METHOD FOR CONTROLLING OPENING OF EXPANSION VALVE,
AND COMPUTER-READABLE RECORDING MEDIUM WITH EXPANSION VALVE OPENING
CONTROL PROGRAM RECORDED THEREON
Abstract
An air conditioner includes: a compressor for compressing a
refrigerant; an expansion valve for adjusting the flow of the
refrigerant; a first temperature sensor for detecting a discharge
temperature of the compressor; and a second temperature sensor for
detecting a temperature of a condenser. A discharge temperature
difference is calculated that is a difference between the discharge
temperature detected by the first temperature sensor and the
temperature of an outdoor heat exchanger or an indoor heat
exchanger functioning as the condenser that is detected by the
second temperature sensor. The opening of the expansion valve is
set based on the calculated discharge temperature difference and a
target discharge temperature difference that is set so that a
target degree of superheat is obtained.
Inventors: |
Yoshida; Michiho;
(Osaka-shi, JP) |
Family ID: |
44145507 |
Appl. No.: |
13/514617 |
Filed: |
December 2, 2010 |
PCT Filed: |
December 2, 2010 |
PCT NO: |
PCT/JP2010/071562 |
371 Date: |
June 8, 2012 |
Current U.S.
Class: |
62/56 ;
62/222 |
Current CPC
Class: |
F25B 2600/21 20130101;
F25B 2700/21152 20130101; F25B 13/00 20130101; F25B 2600/2513
20130101; F25B 2313/0314 20130101; F25B 41/062 20130101; F24F 11/84
20180101; F25B 2313/0315 20130101; F24F 2140/20 20180101 |
Class at
Publication: |
62/56 ;
62/222 |
International
Class: |
F25B 41/04 20060101
F25B041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2009 |
JP |
2009-279390 |
Claims
1. An air conditioner comprising: a compressor for compressing a
refrigerant; an expansion valve for adjusting a flow of said
refrigerant; a first temperature sensor for detecting a discharge
temperature of said compressor; a second temperature sensor for
detecting a temperature of a condenser;and control means for
controlling an opening of said expansion valve, said control means
calculating a discharge temperature difference which is a
difference between said discharge temperature detected by said
first temperature sensor and the temperature of said condenser
detected by said second temperature sensor, and said control means
setting a basic opening which is an opening of said expansion valve
under normal control, based on said calculated discharge
temperature difference and a target discharge temperature
difference (TMP_aim) that is set so that a target degree of
superheat is obtained.
2. The air conditioner according to claim 1, wherein when said
calculated discharge temperature difference is not less than a
predetermined first threshold value (Hth), said control means
controls the opening of said expansion valve so that the opening is
larger than said basic opening under said normal control.
3. The air conditioner according to claim 2, wherein when said
calculated discharge temperature difference is not more than a
predetermined second threshold value (Lth), said control means
controls the opening of said expansion valve so that the opening is
smaller than said basic opening under said normal control, and said
second threshold value is smaller than said first threshold
value.
4. The air conditioner according to claim 1, wherein when said
calculated discharge temperature difference is not more than a
predetermined second threshold value (Lth), said control means
controls the opening of said expansion valve so that the opening is
smaller than said basic opening under said normal control.
5. The air conditioner according to claim 1, wherein said control
means calculates said target discharge temperature difference
(TMP_aim) from the number of revolutions of said compressor.
6. The air conditioner according to claim 1, further comprising: a
switch valve for switching direction of circulation of said
refrigerant between a cooling cycle operation and a heating cycle
operation; an outdoor heat exchanger for heat exchange between
outdoor air and said refrigerant; and an indoor heat exchanger for
heat exchange between indoor air and said refrigerant, wherein in
the cooling cycle operation, said condenser corresponds to said
outdoor heat exchanger and, in the heating cycle operation, said
condenser corresponds to said indoor heat exchanger.
7. A method for controlling an opening of an expansion valve of an
air conditioner, said air conditioner including: said expansion
valve for adjusting a flow of a refrigerant; a first temperature
sensor for detecting a discharge temperature of a compressor; and a
second temperature sensor for detecting a temperature of a
condenser, said method comprising the steps of: calculating a
discharge temperature difference which is a difference between said
discharge temperature detected by said first temperature sensor and
the temperature of said condenser detected by said second
temperature sensor; and setting a basic opening which is an opening
of said expansion valve under normal control, based on said
calculated discharge temperature difference and a target discharge
temperature difference (TMP_aim) that is set so that a target
degree of superheat is obtained.
8. A computer-readable recording medium with an expansion valve
opening control program recorded thereon for causing a computer
provided to an air conditioner including: an expansion valve for
adjusting a flow of a refrigerant; a first temperature sensor for
detecting a discharge temperature of a compressor; and a second
temperature sensor for detecting a temperature of a condenser, to
perform the steps of: calculating a discharge temperature
difference which is a difference between said discharge temperature
detected by said first temperature sensor and the temperature of
said condenser detected by said second temperature sensor; and
setting a basic opening which is an opening of said expansion valve
under normal control, based on said calculated discharge
temperature difference and a target discharge temperature
difference that is set so that a target degree of superheat is
obtained.
9. The air conditioner according to claim 2, wherein said control
means calculates said target discharge temperature difference
(TMP_aim) from the number of revolutions of said compressor.
10. The air conditioner according to claim 3, wherein said control
means calculates said target discharge temperature difference
(TMP_aim) from the number of revolutions of said compressor.
11. The air conditioner according to claim 4, wherein said control
means calculates said target discharge temperature difference
(TMP_aim) from the number of revolutions of said compressor.
12. The air conditioner according to claim 2, further comprising: a
switch valve for switching direction of circulation of said
refrigerant between a cooling cycle operation and a heating cycle
operation; an outdoor heat exchanger for heat exchange between
outdoor air and said refrigerant; and an indoor heat exchanger for
heat exchange between indoor air and said refrigerant, wherein in
the cooling cycle operation, said condenser corresponds to said
outdoor heat exchanger and, in the heating cycle operation, said
condenser corresponds to said indoor heat exchanger.
13. The air conditioner according to claim 3, further comprising: a
switch valve for switching direction of circulation of said
refrigerant between a cooling cycle operation and a heating cycle
operation; an outdoor heat exchanger for heat exchange between
outdoor air and said refrigerant; and an indoor heat exchanger for
heat exchange between indoor air and said refrigerant, wherein in
the cooling cycle operation, said condenser corresponds to said
outdoor heat exchanger and, in the heating cycle operation, said
condenser corresponds to said indoor heat exchanger.
14. The air conditioner according to claim 4, further comprising: a
switch valve for switching direction of circulation of said
refrigerant between a cooling cycle operation and a heating cycle
operation; an outdoor heat exchanger for heat exchange between
outdoor air and said refrigerant; and an indoor heat exchanger for
heat exchange between indoor air and said refrigerant, wherein in
the cooling cycle operation, said condenser corresponds to said
outdoor heat exchanger and, in the heating cycle operation, said
condenser corresponds to said indoor heat exchanger.
Description
TECHNICAL FIELD
[0001] The present invention relates to an air conditioner as well
as a method and a program for controlling the opening of an
expansion valve, and particularly to an air conditioner adjusting
the flow of a refrigerant by controlling the opening of an
expansion valve, as well as a method and a program for controlling
the opening of an expansion valve.
BACKGROUND ART
[0002] Generally, an air conditioner includes components such as a
compressor, a four-way (switch) valve, an outdoor heat exchanger,
an expansion valve for adjusting the flow of a refrigerant when
reducing the pressure, and an indoor heat exchanger. Such an air
conditioner is capable of performing both the cooling cycle
operation and the heating cycle operation by switching the four-way
valve. When the cooling cycle operation is done, the piping
connection is made to configure a refrigerant flow path (cooling
cycle) in which the refrigerant circulates through the components
in the order of the compressor, the four-way valve, the outdoor
heat exchanger (condenser), the expansion valve, the indoor heat
exchanger (evaporator), the four-way valve, and the compressor.
Thus, the heat absorbed by the indoor heat exchanger is released
outdoors by the outdoor heat exchanger. In contrast, when the
heating cycle operation is done, the piping connection is made to
configure a refrigerant flow path (heating cycle) in which the
refrigerant circulates through the components in the order of the
compressor, the four-way valve, the indoor heat exchanger
(condenser), the expansion valve, the outdoor heat exchanger
(evaporator), the four-way valve, and the compressor. Thus, the
outdoor heat absorbed by the outdoor heat exchanger is released
into the room by the indoor heat exchanger.
[0003] When the heat exchange cycle as described above is formed,
generally the evaporator temperature and the evaporator outlet
temperature are detected to thereby calculate the degree of
superheat, and the degree of superheat is used to control the
opening of the expansion valve.
[0004] Another method for controlling the expansion valve is
disclosed in PTL 1, according to which the inlet temperature of the
expansion valve and the outlet temperature of the expansion valve
(or the inlet temperature of the evaporator) are detected to
estimate the evaporation saturation temperature. From the estimated
evaporation saturation temperature and a set degree of superheat, a
target suction temperature of the compressor is determined. The
opening of the expansion valve is controlled so that the suction
temperature of the compressor meets the target suction
temperature.
[0005] PTL 2 discloses that the opening of the expansion valve is
controlled in accordance with a temperature difference between the
temperature of the refrigerant at the discharge of the compressor
and an optimum temperature of the refrigerant at the discharge
which is calculated based on the evaporation temperature and the
condensation temperature.
CITATION LIST
Patent Literature
[0006] PTL 1: Japanese Patent Laying-Open No. 7-98160 [0007] PTL 2:
Japanese Patent Laying-Open No. 4-93541
SUMMARY OF INVENTION
Technical Problem
[0008] In the case where the evaporator temperature and the
evaporator outlet temperature are used for calculating the degree
of superheat, temperature sensors such as thermistors have to be
provided respectively at the inlet and the outlet of the
evaporator.
[0009] Even in such a case as PTL 1 where the degree of superheat
is estimated without detecting the evaporator temperature, a
separate thermistor or the like is necessary for detecting the
suction temperature of the compressor.
[0010] According to PTL 2, the temperature of the refrigerant at
the discharge of the compressor, the evaporation temperature, and
the condensation temperature are detected to control the opening of
the expansion valve. PTL 2 thus does not disclose that the opening
of the expansion valve is controlled based on a temperature
difference between two locations.
[0011] The present invention has been made to solve the
above-described problems, and an object of the present invention is
to provide an air conditioner capable of appropriately controlling
the opening of the expansion valve without increasing the number of
temperature sensors, as well as a method and a program for
controlling the opening of the expansion valve.
Solution to Problem
[0012] An air conditioner according to an aspect of the present
invention includes: a compressor for compressing a refrigerant; an
expansion valve for adjusting a flow of the refrigerant; a first
temperature sensor for detecting a discharge temperature of the
compressor; a second temperature sensor for detecting a temperature
of a condenser; and control means for controlling an opening of the
expansion valve. The control means calculates a discharge
temperature difference which is a difference between the discharge
temperature detected by the first temperature sensor and the
temperature of the condenser detected by the second temperature
sensor, and sets a basic opening which is an opening of the
expansion valve under normal control, based on the calculated
discharge temperature difference and a target discharge temperature
difference that is set so that a target degree of superheat is
obtained.
[0013] Preferably, when the calculated discharge temperature
difference is not less than a predetermined first threshold value,
the control means controls the opening of the expansion valve so
that the opening is larger than the basic opening under the normal
control.
[0014] Preferably, when the calculated discharge temperature
difference is not more than a predetermined second threshold value,
the control means controls the opening of the expansion valve so
that the opening is smaller than the basic opening under the normal
control. The second threshold value is smaller than the first
threshold value.
[0015] Preferably, the control means calculates the target
discharge temperature difference from the number of revolutions of
the compressor.
[0016] Preferably, the air conditioner further includes: a switch
valve for switching direction of circulation of the refrigerant
between a cooling cycle operation and a heating cycle operation; an
outdoor heat exchanger for heat exchange between outdoor air and
the refrigerant; and an indoor heat exchanger for heat exchange
between indoor air and the refrigerant. In the cooling cycle
operation, the condenser corresponds to the outdoor heat exchanger.
In the heating cycle operation, the condenser corresponds to the
indoor heat exchanger.
[0017] According to another aspect of the present invention, a
method for controlling an opening of an expansion valve of an air
conditioner is provided. The air conditioner includes: the
expansion valve for adjusting a flow of a refrigerant; a first
temperature sensor for detecting a discharge temperature of a
compressor; and a second temperature sensor for detecting a
temperature of a condenser. The method includes the steps of:
calculating a discharge temperature difference which is a
difference between the discharge temperature detected by the first
temperature sensor and the temperature of the condenser detected by
the second temperature sensor; and setting a basic opening which is
an opening of the expansion valve under normal control, based on
the calculated discharge temperature difference and a target
discharge temperature difference that is set so that a target
degree of superheat is obtained.
[0018] According to still another aspect of the present invention,
a computer-readable recording medium with an expansion valve
opening control program recorded thereon is provided. The expansion
valve opening control program causes a computer, which is provided
to an air conditioner including: an expansion valve for adjusting a
flow of a refrigerant; a first temperature sensor for detecting a
discharge temperature of a compressor; and a second temperature
sensor for detecting a temperature of a condenser, to perform the
steps of: calculating a discharge temperature difference which is a
difference between the discharge temperature detected by the first
temperature sensor and the temperature of the condenser detected by
the second temperature sensor; and setting a basic opening which is
an opening of the expansion valve under normal control, based on
the calculated discharge temperature difference and a target
discharge temperature difference that is set so that a target
degree of superheat is obtained.
Advantageous Effects of Invention
[0019] In accordance with the present invention, the opening of the
expansion valve is set based on: the difference between the
compressor discharge temperature and the condenser temperature
(discharge temperature difference); and the target discharge
temperature difference that is set so that a target degree of
superheat is obtained. Accordingly, the opening of the expansion
valve can appropriately be controlled without increase of the
number of temperature sensors.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1 is a diagram schematically showing a refrigerant
circuit of an air conditioner in an embodiment of the present
invention.
[0021] FIG. 2 is an external view of an indoor unit of an air
conditioner in an embodiment of the present invention.
[0022] FIG. 3 is a cross-sectional view schematically showing an
internal configuration of the indoor unit shown in FIG. 2.
[0023] FIG. 4 is an external view of an outdoor unit of an air
conditioner in an embodiment of the present invention.
[0024] FIG. 5 is a diagram schematically showing an internal
configuration of the outdoor unit shown in FIG. 4.
[0025] FIG. 6 is a functional block diagram showing a functional
configuration of an air conditioner in an embodiment of the present
invention.
[0026] FIG. 7 is a diagram showing an example of a Mollier diagram
(P-h diagram).
[0027] FIG. 8 is a diagram showing a relation between a target
discharge temperature difference and each threshold value, and the
number of revolutions of a compressor in an embodiment of the
present invention.
[0028] FIG. 9 is a flowchart showing a process of calculating a
target opening in an embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0029] An embodiment of the present invention will be described in
detail with reference to the drawings. In the drawings, the same or
corresponding components are denoted by the same reference
characters, and a description thereof will not be repeated.
[0030] <As to Refrigerant Circuit>
[0031] First, an example of a refrigerant circuit of an air
conditioner in the present embodiment will be described.
[0032] FIG. 1 is a diagram schematically showing the refrigerant
circuit of the air conditioner in the embodiment of the present
invention.
[0033] Referring to FIG. 1, the air conditioner includes a heat
exchanger 1 for an outdoor unit (hereinafter referred to as
"outdoor heat exchanger"), an expansion valve 2, a heat exchanger 3
for an indoor unit (hereinafter referred to as "indoor heat
exchanger"), a four-way valve 4, and a compressor 5. They are
connected in order in the form of a closed loop. Compressor 5
compresses a refrigerant. Outdoor heat exchanger 1 transfers heat
between the outdoor air and the refrigerant. Expansion valve 2 is
controlled for adjusting the flow of the refrigerant. Indoor heat
exchanger 3 transfers heat between the indoor air and the
refrigerant. Four-way valve 4 switches the direction in which the
refrigerant circulates, depending on whether the operation is the
cooling cycle operation or the heating cycle operation.
[0034] The air conditioner further includes a temperature sensor 6
for measuring the temperature of outdoor heat exchanger 1, a
temperature sensor 7 for measuring the discharge temperature of
compressor 5, and a temperature sensor 8 for measuring the
temperature of indoor heat exchanger 3. These temperature sensors
6, 7, 8 are, for example, thermistors.
[0035] As indicated by an arrow in FIG. 1, when the cooling cycle
operation is performed, the refrigerant circulates through
compressor 5, four-way valve 4, outdoor heat exchanger 1, expansion
valve 2, indoor heat exchanger 3, four-way valve 4, and compressor
5 in this order. In this case, outdoor heat exchanger 1 functions
as a condenser for condensing and liquefying the compressed
refrigerant of a high temperature, and indoor heat exchanger 3
functions as an evaporator for evaporating the liquefied
refrigerant to thereby convert the refrigerant into a
low-temperature gas. When the heating operation is performed, the
refrigerant circulates through compressor 5, four-way valve 4,
indoor heat exchanger 3, expansion valve 2, outdoor heat exchanger
1, four-way valve 4, and compressor 5 in this order. In this case,
outdoor heat exchanger 1 functions as an evaporator and indoor heat
exchanger 3 functions as a condenser.
[0036] While the present embodiment will be described in which the
heating cycle operation and the cooling cycle operation can be
switched to each other, the air conditioner may be capable of only
one of the heating cycle operation and the cooling cycle operation.
In this case, outdoor heat exchanger 1 and indoor heat exchanger 3
each function solely as a condenser or an evaporator.
[0037] <External Appearance and Configuration>
[0038] As to indoor unit:
[0039] FIG. 2 is an external view of an indoor unit 100 of the air
conditioner in the embodiment of the present invention. FIG. 3 is a
cross-sectional view schematically showing an internal
configuration of indoor unit 100 in FIG. 2. In FIG. 3, a cross
section of indoor unit 100 as seen in the direction of the Y axis
in FIG. 2 is shown.
[0040] Referring to FIG. 3, indoor unit 100 further includes, in
addition to indoor heat exchanger 3 and temperature sensor 8 shown
in FIG. 1, a temperature sensor 11 for measuring the room
temperature, an indoor fan 14, a louver 15, and a louver motor 16.
Louver 15 is a wind direction guide member provided in an air
outlet of indoor unit 100. Louver motor 16 drives louver 15 so that
louver 15 turns. A plurality of louvers 15 are driven so that they
are identically oriented.
[0041] As to outdoor unit:
[0042] FIG. 4 is an external view of an outdoor unit 200 of the air
conditioner in the embodiment of the present invention. FIG. 5 is a
diagram schematically showing an internal configuration of outdoor
unit 200 in FIG. 4.
[0043] Referring to FIG. 5, outdoor unit 200 includes, in addition
to outdoor heat exchanger 1, four-way valve 4, compressor 5, and
temperature sensor 6 shown in FIG. 1, a temperature sensor 21 for
measuring the outdoor air temperature, and an outdoor fan 24.
[0044] As to functional configuration of air conditioner:
[0045] FIG. 6 is a functional block diagram showing a functional
configuration of the air conditioner in the embodiment of the
present invention.
[0046] Referring to FIG. 6, the air conditioner further includes,
in addition to the components shown in FIGS. 1, 3, and 5, a stepper
motor 12 driven for adjusting the opening of expansion valve 2, a
control unit 30 for controlling the whole air conditioner, and an
operation unit 36 for receiving instructions from a user. In the
present embodiment, the opening of expansion valve 2 is calculated
as corresponding to the number of excitation steps for the phases
of stepper motor 12. It is noted that expansion valve 2 is not
limited to the expansion valve whose opening is adjusted by stepper
motor 12, and may be a thermostatic expansion valve, for example.
Specifically, a feeler bulb in which the refrigerant is enclosed
and the expansion valve are connected by a capillary tube, and the
inside of the expansion valve is partitioned by a diaphragm. The
opening of the expansion valve may also be controlled by means of
the pressure that is applied to the diaphragm depending on the
temperature of the feeler bulb.
[0047] Control unit 30 is contained in indoor unit 100 and includes
a processor 32 for performing various operations, and a memory 34
for storing various programs and data. Processor 32 is configured
for example by a CPU (Central Processing Unit). Processor 32
executes a program stored in memory 34 to thereby control the
opening of expansion valve 2 as described later herein. Memory 34
may for example be a nonvolatile memory such as flash memory.
[0048] Operation unit 36 includes, for example, a power switch, a
temperature adjustment key, an air volume adjustment key, and a
timer set key.
[0049] The air conditioner may further include an interface unit 38
for reading/writing data/program from/in a computer-readable
non-transitory recording medium 38a. Processor 32 stores in memory
34 the program read by interface unit 38 from recording medium 38a
(or updates an existing program) to thereby perform control of the
opening of expansion valve 2 as described later herein (a process
of calculating the opening). Recording medium 38a includes, for
example, an optical medium such as CD-ROM (Compact Disc-ROM) and a
magnetic recording medium such as memory card.
[0050] As to control of expansion valve:
[0051] A description will be given of control (control of the
opening) of expansion valve 2 performed by control unit 30
(processor 32) in the present embodiment.
[0052] Generally, in order to efficiently perform heat exchange in
each cycle, the opening of the expansion valve is often controlled
by means of the degree of superheat which is calculated from the
outlet temperature of the evaporator. Actually, the evaporator
temperature and the evaporator outlet temperature are detected and
control is performed so that the temperature difference between the
evaporator temperature and the evaporator outlet temperature is a
target degree of superheat. "Degree of superheat" represents a
temperature difference between a superheated vapor temperature and
a dry saturated vapor temperature at a certain pressure.
[0053] In the present embodiment as well, the degree of superheat
is used to control expansion valve 2. The target degree of
superheat, however, is estimated in the present embodiment from a
temperature difference (TMP_diff) between a discharge temperature
(TMP_to) and a condenser temperature (TMP_con).
[0054] As described above, conventionally the degree of superheat
is usually calculated from the evaporator temperature and the
evaporator outlet temperature. However, since a compression line on
a Mollier diagram is determined by the compression pressure
(corresponding to the number of revolutions) of compressor 5,
control can also be performed by means of a difference between the
discharge temperature and the condenser temperature (the difference
will hereinafter be referred to as "discharge temperature
difference") similarly to the control using the difference between
the evaporator temperature and the evaporator outlet temperature.
This will be described in more detail with reference to FIG. 7.
[0055] FIG. 7 is a diagram showing an example of the Mollier
diagram (P-h diagram). In the Mollier diagram, a relation between
the pressure (kg/dm2) and the enthalpy (kcal/kg) is shown.
[0056] In FIG. 7, the closed loop drawn by lines L1 to L4
represents a heat pump cycle. Line L1 is ideally parallel with an
isentrope 74 and called compression line. Line L2 is called
condensation line, line L3 is called expansion line, and line L4 is
called evaporation line. Condensation line L2 and evaporation line
L4 are determined respectively by a temperature detected by a
thermistor provided at the condenser and a temperature detected by
a thermistor provided at the evaporator.
[0057] Isothermal lines 71 located in the region on the left side
of a saturated liquid line 76 (on the side where the enthalpy is
smaller) represent isothermal lines of supercooled liquid.
Isothermal lines 72 located in the region surrounded by saturated
liquid line 76 and a saturated vapor line 77 represent isothermal
lines of wet vapor. Isothermal lines 73 located in the region on
the right side of saturated vapor line 77 (on the side where the
enthalpy is larger) represent isothermal lines of superheated
vapor. Saturated liquid line 76 and saturated vapor line 77 meet at
a critical point 75.
[0058] Since compression line L1 is specific to compressor 5,
compression line L1 is determined according to the operating state
of compressor 5. From the condenser's thermistor detecting the
temperature of the condenser (the temperature corresponds to the
condensation pressure) and the evaporator's thermistor detecting
the temperature of the evaporator (the temperature corresponds to
the evaporation pressure), a pressure difference between the inlet
and the outlet of the expansion valve is known. Here, essentially
the degree of superheat which is used for the conventional control
cannot be determined without the evaporator inlet temperature and
the evaporator outlet temperature. However, in the case where
expansion valve 2 with a certain opening is stable, the pressure
difference between the inlet and the outlet of the expansion valve
is determined by the compression pressure (the number of
revolutions) of compressor 5. Therefore, the degree of superheat
(corresponding to .DELTA.h1) which is conventionally detected from
the evaporator temperature and the evaporator outlet temperature
can be calculated from the degree of superheat (corresponding to
.DELTA.h2) which is determined by means of a thermistor for the
discharge temperature (corresponding to temperature sensor 7 in the
present embodiment) and a condenser's thermistor (corresponding to
temperature sensor 6 or 8 in the present embodiment). For the
reason above, in the present embodiment, a target discharge
temperature difference (TMP_aim) that provides a target degree of
superheat is calculated from the number of revolutions (F) of
compressor 5 corresponding to the compression pressure of
compressor 5.
TMP_aim=f(F)
[0059] The number of revolutions of compressor 5 may be determined
based on a known algorithm. For example, the number of revolutions
is determined based on a difference between a room temperature set
by operation unit 36 and a current room temperature (temperature
sensor 11). Namely, the larger the difference between the set
temperature and the room temperature, the greater the number of
revolutions of compressor 5.
[0060] Essentially, the degree of superheat can be calculated more
reliably by detecting both the temperature of the evaporator inlet
and the temperature of the evaporator outlet. The present
embodiment, however, chiefly aims to perform control for escaping
from an unsafe state (hereinafter referred to as "safety control")
as described later herein, rather than accurate calculation of the
degree of superheat. Therefore, an experimentally determined
pressure difference between the inlet and the outlet of the
expansion valve generated by the opening of expansion valve 2 is
used to perform control by means of only the temperature difference
between the discharge temperature and the condenser temperature
(discharge temperature difference).
[0061] Here, while the target discharge temperature difference is
determined by calculation, it may also be determined by means of a
data table stored in advance in memory 34. Specifically,
thermistors (temperature sensors) are provided in advance
respectively at the evaporator and the evaporator outlet. Then, the
discharge temperature and the condenser temperature when the degree
of superheat determined from respective values detected by these
thermistors is equal to the target degree of superheat are
measured. The difference between the measured discharge temperature
and the measured condenser temperature may be used as a target
discharge temperature difference corresponding to the number of
revolutions of the compressor when they are measured.
[0062] Regarding control of expansion valve 2, for the sake of
cycle stabilization immediately after compressor 5 is driven,
usually an initial opening of expansion valve 2 is set and the
control of the opening based on the discharge temperature
difference is not performed for a certain period of time (this
period is referred to as mask time). In general, different values
of the initial opening may be set respectively for the cooling
cycle and the heating cycle as well as the case where the outdoor
air temperature is high and the case where the outdoor air
temperature is low, to thereby shorten the time taken for
stabilizing the cycle.
[0063] After the mask time has elapsed that is a predetermined
period of time in which the opening of the expansion valve is set
to the initial opening, the opening of expansion valve 2 is
controlled so that the opening is equal to the opening determined
from the number of revolutions of compressor 5. After this, based
on the degree of superheat determined for each number of
revolutions of compressor 5, the opening of expansion valve 2 is
subjected to PID control (Proportional control, Integral control,
Derivative control), so that the discharge temperature difference
meets the target discharge temperature difference which is defined
for each number of revolutions of compressor 5.
[0064] The PID control is mentioned above as control for making the
actual temperature difference closer to a target temperature
difference. Here, only the proportional control or only the
integral control may be performed. However, it is desirable that
control is performed so that the overshoot is reduced as much as
possible to thereby make the temperature difference closer to the
target temperature difference. It should be noted that the
influence of the opening of expansion valve 2 is reflected at a
considerably later time on a change of the discharge temperature.
Therefore, the opening may be controlled according to a method of
the feed-forward control. Specifically, a stable discharge
temperature may be predicted from the gradient of the temperature
change at the time when the discharge temperature changes due to
change of the opening of expansion valve 2. Alternatively, the
opening may be controlled by a method according to which a mask
time is provided between the time when the opening is changed once
and the time when the opening is changed next time. It is desirable
that the control method eventually prevents overshoot of the
discharge temperature and quickly makes the discharge temperature
stable.
[0065] As to safety control:
[0066] The air conditioner in the present embodiment performs
safety control in the following manner.
[0067] (1) Safety Control for Preventing Dew Condensation
[0068] Particularly in the cooling cycle operation, the air
conditioner in the present embodiment performs control for avoiding
the state of dew condensation in the evaporator, namely indoor heat
exchanger 3. If the condenser temperature is different by an
excessive degree from the discharge temperature, the opening of
expansion valve 2 is too small, which causes the state of a small
flow of the refrigerant (the state where the refrigerant is likely
to be vaporized). Accordingly, the refrigerant quickly becomes dry
in indoor heat exchanger 3 (the ratio of the refrigerant that is
converted into the gas phase in indoor heat exchanger 3 is high),
and thus the refrigerant is separated in indoor heat exchanger 3
into a portion whose heat is exchanged and a portion whose heat is
not exchanged. Therefore, a mixture of cold air and warm air is
generated which causes the state where dew is likely to be formed
in indoor heat exchanger 3.
[0069] In view of the above, the opening of expansion valve 2 is
controlled so that the opening is made larger than the opening
under normal control (hereinafter referred to as "basic opening")
when the discharge temperature difference becomes not less than a
threshold value Hth, to thereby prevent dew condensation in indoor
heat exchanger 3. Specifically, the opening of expansion valve 2 is
controlled so that it is larger by "Shigh" steps than the basic
opening under normal control.
[0070] Threshold value Hth will be described with reference to FIG.
8. FIG. 8 is a diagram showing a relation between a target
discharge temperature difference and each threshold value, and the
number of revolutions of the compressor. In FIG. 8, the vertical
axis represents the discharge temperature difference (difference:
discharge temperature-(minus) condenser temperature), and the
horizontal axis represents the number of revolutions of compressor
5.
[0071] Referring to FIG. 8, threshold value Hth is set for example
higher by a certain temperature than a target discharge temperature
difference line ("TMP_aim" in FIG. 8) which is defined for each
number of revolutions of compressor 5. For example, a discharge
temperature difference in the state where dew is likely to be
formed in the heat exchanger (indoor heat exchanger 3) which is
used as an evaporator in the cooling cycle may experimentally be
measured in advance. Then, a margin may be provided with respect to
the measured discharge temperature difference to determine the
temperature difference line of threshold value Hth.
[0072] The number of steps "Shigh" may be determined experimentally
or calculated by multiplying the opening of expansion valve 2 that
is determined for each frequency (number of revolutions) of
compressor 5 by 1/X. It should be noted that even when the same
change of the opening is made, a greater number of revolutions of
compressor 5 causes a larger change of the temperature, and
therefore, it is desirable that the number of correction steps
Shigh is larger for a larger number of revolutions of compressor
5.
Shigh (low rev of compressor)<Shigh (high rev of compressor)
[0073] (2) Safety Control for Preventing Liquid Back
[0074] The air conditioner in the present embodiment further
performs control for avoiding the state where the refrigerant still
in the liquid phase returns to compressor 5 regardless of whether
the cycle is the cooling cycle or heating cycle.
[0075] When the discharge temperature difference becomes not more
than a threshold value Lth, the opening of expansion valve 2 is
controlled so that the opening is smaller than the opening under
normal control. Regarding both the cooling cycle and the heating
cycle, if the difference between the discharge temperature and the
condenser temperature is excessively small, a state is likely to
occur where the refrigerant which is still in the liquid phase
returns from the heat exchanger used as the evaporator back to
compressor 5 (the state of high humidity), which is likely to cause
the liquid to return to compressor 5. In such a case, the opening
of expansion valve 2 is controlled so that the opening is reduced
to a large extent to thereby increase the gas phase of the two
phases, namely the gas phase and the liquid phase, after the
refrigerant is decompressed. Specifically, the opening of expansion
valve 2 is controlled so that the opening is reduced by "Slow"
steps relative to the basic opening under normal control. In this
way, the lifetime of compressor 5 can be prevented from shortening
and compressor 5 can be made less likely to fail.
[0076] Threshold value Lth will be described with reference again
to FIG. 8. Referring to FIG. 8, threshold value Lth is set, for
example, lower by a certain temperature than the target discharge
temperature difference line ("TMP_aim" in FIG. 8) which is defined
for each number of revolutions of compressor 5. For example, a
discharge temperature difference in the state where the liquid back
is likely to occur may experimentally be measured in advance. Then,
a margin may be provided with respect to the measured discharge
temperature difference to determine the temperature difference line
of threshold value Hth.
[0077] The number of steps "Slow" here may be determined
experimentally or calculated by multiplying the opening of
expansion valve 2 which is determined for each frequency (number of
revolutions) of compressor 5 by 1/Y. It should be noted that even
when the same change of the opening is made, a greater number of
revolutions of compressor 5 causes a larger change of the
temperature, and therefore, it is desirable that the number of
correction steps Slow is larger for a larger number of revolutions
of compressor 5.
Slow (low rev of compressor)<Slow (high rev of compressor)
[0078] <Process of Calculating Target Opening of Expansion Valve
2>
[0079] Next, a description will be given of a process of
calculating a target opening that is executed by processor 32 for
controlling the opening of expansion valve 2 in the present
embodiment.
[0080] FIG. 9 is a flowchart showing the process of calculating a
target opening in the embodiment of the present invention. This
flowchart shows a function by which a target opening of expansion
valve 2 is calculated. The process of the flowchart in FIG. 9 is
performed periodically for example until an ending event occurs
such as an instruction to stop operation. Further, the process
shown in the flowchart of FIG. 9 is stored in advance in memory 34
in the form of a program, and processor 32 reads and executes this
program to thereby perform the capability of the process of
calculating the target opening.
[0081] Referring to FIG. 9, respective values of discharge
temperature "TMP_to" and condenser temperature "TMP_con" are first
updated (step S1). In the case of the cooling cycle operation,
respective temperatures are detected by temperature sensor 7
provided at the outlet of compressor 5 and temperature sensor 6
provided at outdoor heat exchanger 1. In the case of the heating
cycle operation, respective temperatures are detected by
temperature sensor 7 provided at the outlet of compressor 5 and
temperature sensor 8 provided at indoor heat exchanger 3.
[0082] Next, from the temperatures updated in step S1, discharge
temperature difference "TMP_diff" is calculated. Specifically, the
discharge temperature difference (TMP_diff) is calculated by
subtracting the condenser temperature (TMP_con) from the discharge
temperature (TMP_to).
[0083] The discharge temperature difference (TMP_diff) is thus
calculated, and then the opening (basic opening) of expansion valve
2 under normal control is calculated as an opening implementation
value "S" so that the temperature difference (TMP_diff) is
identical to the target temperature difference "TMP_aim" (step S3).
The target temperature difference (TMP_aim) is set in advance for
each frequency of compressor 5 so that a target degree of superheat
is met. The formula for calculating the basic opening under normal
control may be determined based on the results of experiment
performed in advance. Further, such a basic opening (number of
steps) may be determined from a data table stored in memory 34,
rather than by means of the calculation formula.
[0084] Subsequently, it is determined whether the discharge
temperature difference (TMP_diff) is smaller than the set threshold
value Hth (step S4). When the discharge temperature difference
(TMP_diff) is equal to or larger than threshold value Hth ("FALSE"
in step S4), a new opening implementation value S is set to a value
determined by adding "S_high" to the basic opening under normal
control (opening implementation value S in step S3) so that the
opening is further increased (step S5). In this way, the opening
implementation value is changed. Processor 32 drives stepper motor
12 using the changed opening implementation value. Consequently,
the opening of expansion valve 2 is controlled so that the flow is
larger than that under normal control.
[0085] When the discharge temperature difference (TMP_diff) is
smaller than threshold value Hth ("TRUE" in step S4), the process
proceeds to step S6.
[0086] In step S6, it is determined whether the discharge
temperature difference (TMP_diff) is larger than the set threshold
value Lth. When the discharge temperature difference (TMP_diff) is
equal to or smaller than threshold value Lth ("FALSE" in step S6),
a new opening implementation value S is set to a value determined
by subtracting "S_low" from the basic opening under normal control
(opening implementation value S in step S3) so that the opening is
further reduced (step S7). Thus, the opening implementation value
is changed. Processor 32 drives stepper motor 12 using the changed
opening implementation value. Consequently, the opening of
expansion valve 2 is controlled so that the flow is smaller than
that under normal control.
[0087] When the discharge temperature difference (TMP_diff) is
larger than threshold value Lth ("TRUE" in step S6), the opening
implementation value is not changed, and the opening implementation
value used for control is set to the basic opening under normal
control.
[0088] As seen from the foregoing, according to the present
embodiment, only the discharge temperature thermistor (temperature
sensor 7) and the thermistor (temperature sensors 6, 8) for the
heat exchanger serving as the condenser are used to estimate the
degree of superheat. Therefore, the opening of the expansion valve
can be controlled without increase of the number of temperature
sensors to be used for calculating the degree of superheat.
Consequently, the production cost of the air conditioner can be
reduced.
[0089] Even in the case where the refrigerant becomes an unstable
state, the opening of the expansion valve is immediately controlled
so that a safe state is regained, and thus failures of the
compressor can be reduced. Consequently, the comfortable and safe
air conditioner can be provided.
[0090] It should be construed that embodiments disclosed herein are
by way of illustration in all respects, not by way of limitation.
It is intended that the scope of the present invention is defined
by claims, not by the description above, and encompasses all
modifications and variations equivalent in meaning and scope to the
claims.
REFERENCE SIGNS LIST
[0091] 1 outdoor heat exchanger; 2 expansion valve; 3 indoor heat
exchanger; 4 four-way valve; 5 compressor; 6, 7, 8, 11, 21
temperature sensor; 12 stepper motor; 14 indoor fan; 15 louver; 16
louver motor; 24 outdoor fan; 30 control unit; 32 processor; 34
memory; 36 operation unit; 38 interface unit; 38a recording medium;
100 indoor unit; 200 outdoor unit
* * * * *