TECHNICAL FIELD
[0001] The present disclosure relates to a cold source unit and a refrigeration cycle apparatus.
BACKGROUND ART
[0002] In a conventional refrigerator or the like, for example, a large amount of liquid
refrigerant in the unit may return into the accumulator upon start of operation after
defrosting. At this time, a large amount of liquid refrigerant flows in an oil return
circuit located in a lower portion of the accumulator, and an excessive amount of
this liquid refrigerant may flow from the oil return circuit into the compressor,
i.e., a liquid return phenomenon (hereinafter "liquid back") may occur. The liquid
back during operation causes a pressure surge in the compressor, resulting a problem
that the operating current for the compressor becomes overcurrent.
[0003] Japanese Patent Laying-Open No. H06-034224 (PTL 1) discloses an air conditioner intended to prevent failure of a compressor
due to overcurrent, by temporarily stopping the compressor when a current value comparator
detects that the value of compressor current has been kept at a certain value or more
for a certain period of time, restarting the compressor after a certain period of
time from the stoppage of the compressor and, after this is repeated certain number
of times, completely stopping operation.
CITATION LIST
PATENT LITERATURE
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0005] If the compressor is restarted with liquid refrigerant accumulated in the compressor
due to the liquid back, increase of the load on a motor of the compressor for compressing
the liquid may cause overcurrent to cause the compressor to be stopped temporarily.
A technique disclosed in
Japanese Patent Laying-Open No. H06-034224 (PTL 1) attempts to restart the compressor when a certain period of time has elapsed
from the stoppage of the compressor. This attempt to restart the compressor is hereinafter
referred to as "start retry." The start retry under the condition that a large amount
of liquid refrigerant remains in the compressor, however, may result in stoppage of
the compressor due to overcurrent, which leads to a problem of a high possibility
of complete stoppage of operation after repeated start retry.
[0006] The present disclosure is made to solve the problem as described above, and an object
of the present disclosure is to provide a cold source unit and a refrigeration cycle
apparatus that improve the probability of success of restart of the compressor when
the compressor is stopped due to overcurrent.
SOLUTION TO PROBLEM
[0007] The present disclosure relates to a cold source unit connected to a load apparatus
and serving as a component of a refrigeration cycle apparatus. The cold source unit
includes a compressor, and a controller to control the compressor. When the controller
detects overload on the compressor, the controller performs first start retry control
of restarting the compressor after pausing the compressor for a first time period.
When the number of times of performing of the first start retry control exceeds a
first criterion value, the controller performs second start retry control of restarting
the compressor after pausing the compressor for a second time period longer than the
first time period.
ADVANTAGEOUS EFFECTS OF INVENTION
[0008] According to the present disclosure, when the compressor is not started successfully,
the compressor is restarted after an increased waiting time, and therefore, liquid
refrigerant in the compressor is discharged to improve the probability of success
of the restart.
BRIEF DESCRIPTION OF DRAWINGS
[0009]
Fig. 1 shows a refrigerant circuit of a refrigeration cycle apparatus 200 according
to the present embodiment.
Fig. 2 shows a relation between the pause time period of a compressor and the rate
of change of the liquid amount in the compressor.
Fig. 3 is a flowchart for illustrating control for performing compressor start retry.
Fig. 4 is a flowchart for illustrating energization control for a heater when liquid
discharge promotion control is started.
DESCRIPTION OF EMBODIMENTS
[0010] Embodiments of the present disclosure are hereinafter described in detail with reference
to the drawings. In the following, a plurality of embodiments are described, and it
is originally intended that characteristics described in connection with the embodiments
each are combined as appropriate. In the drawings, the same or corresponding parts
are denoted by the same reference characters, and a description thereof is not herein
repeated. In the following drawings, the relation between components in terms of the
size may be different from the actual one.
[0011] Fig. 1 shows a refrigerant circuit of a refrigeration cycle apparatus 200 according
to the present embodiment. As shown in Fig. 1, refrigeration cycle apparatus 200 includes
a cold source unit 100 and a load apparatus 110. "Cold source unit" may also be called
"heat source unit."
[0012] Load apparatus 110 includes an expansion valve 3 and a first heat exchanger (hereinafter
referred to as evaporator 4). Cold source unit 100 is connected to load apparatus
110 and serves as a part of refrigeration cycle apparatus 200. Cold source unit 100
includes a compressor 1, a second heat exchanger (hereinafter referred to as condenser
2), a heater 40, and a controller 30 to control compressor 1 and heater 40.
[0013] Controller 30 includes a CPU (Central Processing Unit) 31, a memory 32 (ROM (Read
Only Memory) and RAM (Random Access Memory)), and an input/output device (not shown)
for allowing various signals to be input, for example. CPU 31 deploys a program stored
in the ROM on the RAM for example and executes the program. The program stored in
the ROM is a program in which a process procedure for controller 30 is specified.
In accordance with the program, controller 30 controls each component of cold source
unit 100. This control is not limited to processing by software, but may be processing
by dedicated hardware (electronic circuit).
[0014] Compressor 1 is equipped with a thermistor 5 that detects the suction temperature,
a thermistor 6 that detects the temperature of a lower portion of a housing shell
of compressor 1 or the temperature of refrigeration oil remaining in the housing of
compressor 1 (hereinafter referred to as "shell-bottom temperature"), and a current
sensor 7 that detects overcurrent.
[0015] In refrigeration cycle apparatus 200, compressor 1 compresses refrigerant gas into
high-pressure gas, and the high-pressure gas refrigerant flows into condenser 2.
[0016] In condenser 2, heat is released from the refrigerant and the high-pressure gas refrigerant
is condensed into high-pressure liquid refrigerant. The high-pressure liquid refrigerant
flows into expansion valve 3. In expansion valve 3, the pressure of the high-pressure
liquid refrigerant is reduced and the resultant low-pressure liquid refrigerant flows
into evaporator 4. In evaporator 4, the liquid refrigerant is evaporated to absorb
heat from the environment, i.e., cooling is done. The evaporated gas refrigerant returns
into compressor 1. Thus, a refrigerant circuit is completed.
[0017] According to the present embodiment, compressor 1 is paused when overload is detected,
and a sufficient pause time period is ensured to reduce the amount of liquid in compressor
1 and thereby suppress unsuccessful start when the start retry is made. For example,
when overcurrent is detected by current sensor 7, controller 30 detects that load
on compressor 1 is overload.
[0018] Specifically, when controller 30 detects overload on compressor 1, controller 30
performs first start retry control, i.e., restarts compressor 1 after pausing compressor
1 for a first time period. When the number of times the first start retry control
is performed exceeds a criterion value, controller 30 performs second start retry
control, i.e., restarts compressor 1 after pausing compressor 1 for a second time
period longer than the first time period. The first time period can be 3 minutes and
the second time period can be 30 minutes. The pause time period, however, is not limited
to the above-specified ones.
[0019] Fig. 2 shows a relation between the pause time period of the compressor and the rate
of change of the liquid amount in the compressor. In consideration of the relation
shown in Fig. 2 and increase of the internal temperature of a refrigerator compartment
resultant from pause of the compressor, the compressor pause time period per liquid
discharge promotion control is determined.
[0020] If the compressor is paused with the inside of the refrigerator compartment cooled
by normal operation, the time for which increase of the internal temperature of the
refrigerator compartment is permissible is approximately 60 minutes. If, however,
the liquid amount has been reduced enough, before 60 minutes elapse, to cause no overcurrent
when compressor 1 is started, the pause time period should be as short as possible.
According to the present embodiment, therefore, the liquid discharge promotion control
is performed up to twice, and the compressor pause time period per liquid discharge
promotion control is set to 30 minutes.
[0021] Fig. 3 is a flowchart for illustrating control for performing compressor start retry.
Based on this flowchart, improvement to avoid unsuccessful start due to overcurrent
abnormality is described.
[0022] In step S1, initially controller 30 determines whether or not the start retry control
in response to overcurrent has been performed five times.
[0023] When the start retry control has been performed five times in total (YES in S1),
controller proceeds to step S10 to give a notification of stoppage due to abnormality,
so as not to perform the start retry control any more. For example, a light-emitting
diode is lit to enable users to identify stoppage due to abnormality.
[0024] When the start retry control has not been performed five times in total (NO in S1),
controller 30 proceeds to step S2 to determine whether or not the start retry control
has been performed three times in total.
[0025] When the start retry control has not been performed three times in total (NO in S2),
controller 30 proceeds to step S11 to perform normal start retry control for the compressor.
In this case, for example, compressor restart is attempted by energizing compressor
1 after keeping the compressor paused for three minutes. The period of three minutes
is a time period determined for preventing repeated start and pause of compressor
1 in which the amount of liquid refrigerant is small.
[0026] In contrast, when the start retry control has been performed three times in total
(YES in S2), controller 30 proceeds to step S3.
[0027] As a rule, when the answer is YES in step S2, control is performed from step S5 in
which start of compressor 1 is delayed more than before. It should be noted that,
in order to prevent malfunction due to failure to cool resultant from long-time pause
of compressor 1, or in order to perform another control of higher priority, start
of compressor 1 may be repeated up to five times as before, without performing the
process from step S5, in some cases. This situation may occur in the following cases,
for example.
- Priority has to be given to cooling, because the internal temperature of the refrigerator
compartment is a certain threshold or more due to defrosting, or because the refrigeration
capacity of the cold source unit is insufficient, for example.
- No liquid back occurs.
- Oil-return control is started due to shortage of refrigeration oil in compressor 1.
- The pressure at the discharge side and the pressure at the suction side of compressor
1 may be reversed to each other.
- Malfunction occurs due to open- or short-circuit detected by a low-pressure sensor.
[0028] For each of all these cases, a determination may be made as to whether or not such
a condition occurs. According to the present embodiment, however, the determination
in each of steps S3 and S4 is made before proceeding to step S5.
[0029] In step S3, controller 30 determines whether or not any one of the superheat of the
sucked refrigerant (suction SH), the shell-bottom temperature, and the superheat of
refrigeration oil remaining in the shell of compressor 1 (hereinafter "shell-bottom
SH"), measured by thermistor 5 and thermistor 6, is kept lower than a reference value
associated to each for a certain period of time (three minutes, for example). In this
way, controller 30 determines whether or not the liquid back occurs.
[0030] The superheat (SH) is a temperature difference between the actually measured refrigerant
temperature and the saturated gas temperature at a measured pressure.
[0031] When the suction SH is kept lower by 10 K than a target value for three minutes,
for example, controller 30 detects occurrence of the liquid back.
[0032] When all the suction SH, the shell-bottom temperature, and the shell-bottom SH are
not kept lower than the reference value for a certain period of time (NO in S3), controller
30 performs the normal start retry control for the compressor in step S12. In this
case, for example, compressor restart is attempted by energizing compressor 1 after
keeping the compressor paused for three minutes.
[0033] In contrast, when any of the suction SH, the shell-bottom temperature, and the shell-bottom
SH is kept lower than the reference value for a certain period of time (YES in S3),
controller 30 proceeds to step S4.
[0034] In step S4, controller 30 determines whether or not an evaporation temperature ET
is lower than a target evaporation temperature ETm+10K (kelvin). When the difference
between evaporation temperature ET and target evaporation temperature ETm is less
than or equal to 10K, it is determined that the inside of the refrigerator compartment
can be kept cooled even when the compressor is paused for some time. While evaporation
temperature ET may be measured with a temperature sensor provided for evaporator 4,
the temperature detected by thermistor 5 which detects the suction temperature may
be used instead.
[0035] When ET < ETm+10K is not satisfied (NO in S4), controller 30 performs the normal
start retry control for the compressor in step S13. In this case, for example, compressor
restart is attempted by energizing compressor 1 after keeping the compressor paused
for three minutes. This is for the following reason. If the internal temperature of
the refrigerator compartment after defrosting is high, or if the internal temperature
of the refrigerator compartment is high due to insufficient refrigeration capacity
of the cold source unit to which a plurality of load units are connected, the pause
time period of 30 minutes is too long.
[0036] When ET < ETm+10K is satisfied (YES in S4), controller 30 starts, in step S5, the
liquid discharge promotion control for delaying start of compressor 1. Then, measurement
of the time from stoppage of compressor 1 is started. Such a measured time from the
stoppage of compressor 1 to restart thereof is herein referred to as "delay time."
In order to sufficiently reduce liquid refrigerant in compressor 1, controller 30
keeps stopping compressor 1 until the delay time reaches a second time period (30
minutes, for example). The second time period is set longer than the first time period
(3 minutes, for example) that is the pause time period in steps S11, S12, and S13.
At this time, the situation in which the liquid discharge promotion control is performed
is determined by a user, and therefore, it is preferable to show "Lout" or the like
on a liquid crystal display of a control panel mounted on the refrigeration apparatus.
[0037] In step S6, initially it is determined whether or not the delay time has reached
the set time (30 minutes, for example). When the delay time has reached the set time
(YES in S6), start retry for compressor 1 is performed in step S14.
[0038] In contrast, when the delay time has not reached the set time (NO in S6), the process
proceeds to step S7. In step S7, it is determined whether or not a request to start
oil return control is made. The oil return control is requested when shortage of the
refrigeration oil in compressor 1 occurs, in order to prevent burning of compressor
1.
[0039] When a request to start the oil return control is made (YES in S7), start retry for
compressor 1 is performed in step S15.
[0040] In contrast, when the request to start the oil return control is not made (NO in
S7), the process proceeds to step S8. In step S8, it is determined whether or not
a request to start high-low pressure reverse prevention control is made. The high-low
pressure reverse prevention control is requested when it is detected that the pressure
at the suction port side of compressor 1 is higher than the pressure at the discharge
port side.
[0041] When the request to start the high-low pressure reverse prevention control is made
(YES in S8), start retry for compressor 1 is performed in step S16.
[0042] In contrast, when the request to start the high-low pressure reverse prevention control
is not made (NO in S8), the process proceeds to step S9. In step S9, it is determined
whether or not evaporation temperature ET is kept higher than or equal to target evaporation
temperature ETm+10K (kelvin) for three minutes.
[0043] When the relation: Et ≥ ETm+10K is kept satisfied for three minutes (YES in S9),
start retry for compressor 1 is performed in step S17, since increase of the internal
temperature of the refrigerator compartment is not permissible. Because evaporation
temperature Et may momentarily exceed the threshold, the fact that the above relation
is kept satisfied for three minutes is used as a condition for stopping delay of start.
[0044] When Et ≥ target evaporation temperature ETm+10K (kelvin) is kept satisfied for less
than three minutes (NO in S9), the process returns to step S6 and measurement of the
delay time to the start of the compressor start retry is continued.
[0045] When the start retry for compressor 1 is performed in any of steps S1 to S17, controller
30 determines in step S18 whether or not the start of compressor 1 has normally been
completed.
[0046] For example, when overcurrent is detected again, it is determined that the start
of compressor 1 is not in success (NO in S18), energization of the motor of compressor
1 is stopped, and compressor 1 is thus stopped. In this case, in step S19, controller
30 increments, by one, the number of times the start retry is performed, and performs
the process again from step S1.
[0047] When the start retry fails to start the compressor after the liquid refrigerant discharge
promotion control is performed twice, operation is stopped in step S10. At this time,
it is determined that the cause of detection of overcurrent abnormality is not liquid
back.
[0048] When overcurrent is not detected, it is determined that compressor 1 is started successfully
(YES in S18), and the count of the start retry is initialized in step S20, and the
process returns to the control routine for the normal operating state of normal compressor
1 in step S21.
[0049] When the liquid discharge promotion control is started in step S5, heater 40 may
additionally be used for heating. When the outside air temperature is high, however,
heater 40 may be stopped for saving energy.
[0050] Fig. 4 is a flowchart for illustrating energization control for the heater when the
liquid discharge promotion control is started. Referring to Fig. 4, controller 30
obtains an outside air temperature Ta from an outside air temperature sensor 8 and
determines whether or not outside air temperature Ta is lower than a first threshold
temperature Tth in step S51.
[0051] When Ta < Tth is satisfied (YES in S51), controller 30 causes heater 40 to be energized
to heat the liquid refrigerant in compressor 1 by heater 40 for a delay time of 30
minutes. In contrast, when Ta <Tth is not satisfied (NO in S51), controller 30 does
not cause heater 40 to be energized, and waits until the liquid refrigerant in compressor
1 is warmed up by the outside air temperature while the heater is off in the delay
time of 30 minutes.
[0052] In this way, whether to perform heating by the heater is determined depending on
the outside air temperature so as not to heat the refrigerant more than necessary,
and accordingly the power consumption can be reduced.
[0053] As seen from the foregoing, the refrigeration cycle apparatus according to the present
embodiment sets the pause time period of compressor 1 for the fourth and subsequent
start retries longer than the pause time period for the first start retry. Thus, even
when the liquid amount in compressor 1 is increased due to the liquid back, the liquid
refrigerant in compressor 1 can be heated by heater 40 or by the outside air temperature,
and discharged sufficiently from compressor 1. In this way, the liquid amount in compressor
1 can be reduced to suppress unsuccessful start due to overcurrent abnormality at
the time of the start retry.
[0054] Finally, the present embodiment is summarized with reference again to the drawings.
[0055] Referring to Fig. 1, the present embodiment relates to cold source unit 100 connected
to load apparatus 110 and serving as a component of refrigeration cycle apparatus
200. Cold source unit 100 includes compressor 1 and controller 30 to control compressor
1. When controller 30 detects overload on compressor 1, controller 30 performs first
start retry control of restarting compressor 1 after pausing compressor 1 for a first
time period. When the number of times the first start retry control is performed exceeds
a first criterion value, controller 30 performs second start retry control of restarting
compressor 1 after pausing compressor 1 for a second time period longer than the first
time period.
[0056] Preferably, the second time period is a time period required for the amount of liquid
in compressor 1 to be reduced enough to enable compressor 1 to be restarted.
[0057] Accordingly, when the second start retry control is performed, the amount of liquid
refrigerant in compressor 1 is expected to be smaller than that when the first start
retry control is performed, and therefore, overload on compressor 1 is removed to
increase the possibility of success of restart of compressor 1.
[0058] Preferably, cold source unit 100 further includes heater 40 to heat liquid refrigerant
in compressor 1. When controller 30 performs the second start retry control, controller
30 causes the liquid refrigerant to be heated by heater 40.
[0059] Thus, when the second retry control is performed, the amount of liquid in compressor
1 is expected to be reduced by further promotion of evaporation of the liquid refrigerant
in compressor 1 by heater 40, and therefore, the overload on compressor 1 when started
is removed to further increase the possibility of success of restart of compressor
1.
[0060] More preferably, as shown in Fig. 4, when outside air temperature Ta is less than
or equal to first threshold temperature Tth, controller 30 performs the second start
retry control while causing the liquid refrigerant to be heated by heater 40. When
outside air temperature Ta is more than first threshold temperature Tth, controller
30 performs the second start retry control while stopping heating of the liquid refrigerant
by heater 40.
[0061] Thus, when outside air temperature Ta is high and accordingly the amount of liquid
refrigerant in compressor 1 is reduced within the waiting time corresponding to the
second time period, without requiring heating by heater 40, heater 40 is not energized
and the power consumption can therefore be reduced.
[0062] Preferably, as shown in step S4 in Fig. 3, when a difference between refrigerant
evaporation temperature ET and target refrigerant evaporation temperature ETm is less
than a second threshold temperature (10 K for example), controller 30 performs the
first start retry control.
[0063] Thus, when the internal temperature of the refrigerator compartment is high after
defrosting or the refrigeration capacity of the cold source unit is insufficient to
cause evaporation temperature ET to be higher than target evaporation temperature
ETm to some extent, further increase of the internal temperature of the refrigerator
compartment resultant from the start time delay can be avoided.
[0064] Preferably, as shown in step S3 in Fig. 3, when liquid refrigerant is not sucked
into compressor 1, controller 30 still performs the first start retry control regardless
of that the number of times the first start retry control is performed exceeds the
first criterion value (three, for example). Controller 30 determines whether or not
the liquid refrigerant is sucked into compressor 1, based on at least one of superheat
of refrigerant sucked into compressor 1, shell-bottom temperature of compressor 1,
and superheat of refrigerant in compressor 1.
[0065] When no liquid back occurs, overload is not removed even when start of compressor
1 is delayed, and therefore, increase of the internal temperature of the refrigerator
compartment due to delay of start of compressor 1 can thus be avoided.
[0066] Preferably, when controller 30 is unsuccessful in starting compressor 1 by the second
start retry control, controller 30 repeats the second start retry control. When the
number of times the second start retry control is performed exceeds a second criterion
value, controller 30 sets compressor 1 in a paused state. The first criterion value
is 60% to a sum of the first criterion value and the second criterion value.
[0067] Specifically, according to the flowchart in Fig. 3, the first retry control is performed
three times, and then the retry control is performed twice. When start of compressor
1 is still unsuccessful regardless of this, controller 30 sets compressor 1 in the
paused state. As seen from this, the first criterion value is 3, the second criterion
value is 2, and the first criterion value is 60% to the sum of the first criterion
value and the second criterion value. The maximum effect of liquid discharge is expected
to be derived from a pause of 60 minutes (30 min × 2 times) in total, and therefore,
liquid discharge is done when the start retry is done more than three times out of
five times.
[0068] It should be construed that the embodiments disclosed herein are given 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 above description of the
embodiments, and encompasses all modifications and variations equivalent in meaning
and scope to the claims.
REFERENCE SIGNS LIST
[0069] 1 compressor; 2 condenser; 3 expansion valve; 4 evaporator; 5, 6 thermistor; 7 current
sensor; 8 outside air temperature sensor; 30 controller; 31 CPU; 32 memory; 40 heater;
100 cold source unit; 110 load apparatus; 200 refrigeration cycle apparatus
1. A cold source unit connected to a load apparatus and serving as a component of a refrigeration
cycle apparatus, the cold source unit comprising:
a compressor; and
a controller to control the compressor, wherein
when the controller detects overload on the compressor, the controller performs first
start retry control of restarting the compressor after pausing the compressor for
a first time period, and
when the number of times of performing of the first start retry control exceeds a
first criterion value, the controller performs second start retry control of restarting
the compressor after pausing the compressor for a second time period longer than the
first time period.
2. The cold source unit according to claim 1, further comprising a heating apparatus
to heat liquid refrigerant in the compressor, wherein
when the controller performs the second start retry control, the controller causes
the liquid refrigerant to be heated by the heating apparatus.
3. The cold source unit according to claim 2, wherein
when an outside air temperature is less than or equal to a first threshold temperature,
the controller performs the second start retry control while causing the liquid refrigerant
to be heated by the heating apparatus, and
when the outside air temperature is more than the first threshold temperature, the
controller performs the second start retry control while stopping heating of the liquid
refrigerant by the heating apparatus.
4. The cold source unit according to any one of claims 1 to 3, wherein when a difference
between a refrigerant evaporation temperature and a target refrigerant evaporation
temperature is less than a second threshold temperature, the controller performs the
first start retry control.
5. The cold source unit according to claim 1, wherein
when liquid refrigerant is not sucked into the compressor, the controller still performs
the first start retry control even if the number of times of performing of the first
start retry control exceeds the first criterion value, and
the controller determines whether or not the liquid refrigerant is sucked into the
compressor, based on at least one of superheat of refrigerant sucked into the compressor,
shell-bottom temperature of the compressor, and superheat of refrigerant in the compressor.
6. The cold source unit according to any one of claims 1 to 5, wherein the second time
period is a time period required for a liquid amount in the compressor to be reduced
enough to enable the compressor to be restarted.
7. The cold source unit according to any one of claims 1 to 5, wherein
when the controller is unsuccessful in starting the compressor by the second start
retry control, the controller repeats the second start retry control,
when the number of times of performing of the second start retry control exceeds a
second criterion value, the controller sets the compressor in a paused state, and
the first criterion value is 60% to a sum of the first criterion value and the second
criterion value.
8. A refrigeration cycle apparatus comprising the cold source unit according to any one
of claims 1 to 7, and the load apparatus.