Technical Field
[0001] The present invention relates to a heat pump hot water supply apparatus that includes
a refrigerant amount adjusting device.
Background Art
[0002] For a heat pump cycle including a compressor, a condenser, an expansion valve, an
evaporator, and a refrigerant amount adjusting device, a technique for changing the
storage amount of liquid refrigerant in the refrigerant amount adjusting device to
attain a predetermined capacity at optimal efficiency has been suggested (for example,
Patent Literature 1). The capacity of the heat pump cycle is controlled by changing
the amount of refrigerant in the condenser and adjusting pressure on a high-pressure
side. The amount of refrigerant in the condenser increases by temporarily decreasing
the opening degree of the expansion valve. With this increase, the storage amount
of liquid refrigerant in the refrigerant amount adjusting device at an outlet of the
evaporator decreases. As the amount of refrigerant on the high-pressure side increases,
the pressure increases and the capacity increases. In contrast, by opening the expansion
valve, the storage amount of liquid refrigerant in the refrigerant amount adjusting
device at the outlet of the evaporator increases, and the amount of refrigerant on
the high-pressure side decreases. When the pressure on the high-pressure side decreases,
the capacity decreases. As described above, operation at the optimal efficiency can
be achieved by adjusting the storage amount of liquid refrigerant in the refrigerant
amount adjusting device as a cycle.
[0003] Furthermore, for a heat pump cycle including a compressor, a condenser, an expansion
valve, an evaporator, and an internal heat exchanger, but not including a refrigerant
amount adjusting device, a technique for reducing, using the internal heat exchanger,
an increase in pressure on a high-pressure side at a time of inflow of water at high
temperature while reducing cost by not including the refrigerant amount adjusting
device, has been suggested (for example, Patent Literature 2). In the case where the
temperature of fluid sent to the condenser by a hot water circulating pump from a
bottom part of a hot water tank is high (that is, at the time of inflow of water at
high temperature), the concentration of refrigerant present in the condenser decreases,
and the pressure increases abnormally. To reduce the abnormal increase in the pressure,
refrigerant present in a region from an outlet of the condenser to an inlet of the
expansion valve is cooled down. Therefore, the concentration of refrigerant on the
high-pressure side is increased, and the abnormal increase in the pressure on the
high-pressure side is reduced. The refrigerant present in the region from the outlet
of the condenser to the inlet of the expansion valve is cooled down by refrigerant
present in a region from an outlet of the evaporator to the compressor. As described
above, by reducing the pressure on the high-pressure side by the internal heat exchanger
without using the refrigerant amount adjusting device, cost reduction can be achieved.
Citation List
Patent Literature
[0004]
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 7-18602
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2005-164103
Summary of Invention
Technical Problem
[0005] In Patent Literature 1, efficiency can be improved by adjusting, using the refrigerant
amount adjusting device, the amount of refrigerant and pressure on the high-pressure
side. However, the refrigerant amount adjusting device needs to have a large capacity
to store liquid refrigerant. Therefore, there is a problem that the size of equipment
increases and cost is thus increased. In Patent Literature 2, no refrigerant amount
adjusting device is provided. Therefore, an increase in the size of equipment can
be avoided. However, in place of the refrigerant amount adjusting device, the internal
heat exchanger is used as means for reducing an increase in the pressure on the high-pressure
side at the time of inflow of water at high temperature. In such a case, there are
problems described below. Immediately after an operation of an apparatus stops, refrigerant
flows into the evaporator with a low heat capacity and is stored in the evaporator
as liquid refrigerant. Then, when a certain period of time has passed, liquid refrigerant
is stored in the compressor with a high heat capacity. However, if the apparatus is
restarted immediately after the liquid refrigerant is stored in the evaporator, liquid
back of the refrigerant to the compressor may occur because no refrigerant amount
adjusting device is provided. If liquid compression of the liquid-back refrigerant
is performed by the compressor, malfunction may occur.
[0006] The present invention has been made to solve the above-mentioned problems, and an
object thereof is to provide a heat pump hot water supply apparatus that guarantees
the reliability of an apparatus by reducing high pressure at the time of inflow of
water at high temperature and avoiding liquid compression caused by liquid back at
the time of transition while reducing increases in the size and cost of equipment.
Solution to Problem
[0007] A heat pump hot water supply apparatus of an embodiment of the present invention
includes a refrigerant circuit in which a compressor, a condenser, an expansion valve,
an evaporator, and a refrigerant amount adjusting device are connected sequentially;
a hot water tank storing hot water heated by the condenser; a hot water circulating
pump circulating hot water in a region between the condenser and the hot water tank;
an inlet refrigerant temperature detection unit detecting an inlet refrigerant temperature
of the condenser; an inlet water temperature detection unit detecting an inlet water
temperature of the condenser; and a heat source unit control unit adjusting a valve
opening degree of the expansion valve such that a difference between a hot water target
temperature transmitted from a tank control unit provided at the hot water tank and
the inlet refrigerant temperature is equal to a temperature difference set in advance.
When the inlet water temperature reaches a threshold value or more, the heat source
unit control unit changes the temperature difference to adjust the valve opening degree
of the expansion valve in an opening direction.
Advantageous Effects of Invention
[0008] A heat pump hot water supply apparatus of an embodiment of the present invention
performs, in a case where the temperature of fluid sent from a hot water tank to a
condenser by a hot water circulating pump is high (that is, at the time of inflow
of water at high temperature), high-pressure suppression such that a valve opening
degree of an expansion valve is adjusted in an opening direction so that concentration
of refrigerant on a high-pressure side is reduced not to exceed a fixed pressure.
In contrast, since concentration of refrigerant on a low-pressure side increases,
and the refrigerant is thus stored in a refrigerant amount adjusting device as excess
liquid refrigerant. Even if an apparatus is restarted immediately after liquid refrigerant
is stored in an evaporator, the liquid-back refrigerant returned from the evaporator
can be stored as liquid refrigerant in the refrigerant amount adjusting device. With
this configuration, the refrigerant is stored in the refrigerant amount adjusting
device so that liquid compression can be avoided, and the reliability of the compressor
can thus be ensured. Furthermore, in the case where a suction muffler that includes
a space in which liquid refrigerant can be stored is used as the refrigerant amount
adjusting device, increases in the size and cost of equipment can also be reduced.
[0009] Furthermore, a heat pump hot water supply apparatus of an embodiment of the present
invention controls the valve opening degree of an expansion valve such that a difference
between a hot water target temperature from a tank control unit provided at a hot
water tank and a temperature detected by an inlet refrigerant detection unit of a
condenser (hereinafter, referred to as an inlet refrigerant temperature) is equal
to a temperature difference set in advance (hereinafter, referred to as a set temperature
difference). The opening degree of the expansion valve may be controlled based only
on a detection temperature obtained by a water inlet detection unit of the condenser
and a target value for the inlet refrigerant detection unit of the condenser. However,
depending on the operation environmental condition, there may be a relationship that
the hot water target temperature is higher than the target value, and water may not
boil. In contrast, according to an embodiment of the present invention, the temperature
difference is set in advance such that the relationship that a value obtained by subtracting
the hot water target temperature from the inlet refrigerant temperature is more than
0 is obtained and the opening degree of the expansion valve is adjusted to achieve
the set temperature difference. Therefore, water can be made to boil reliably irrespective
of environmental conditions.
Brief Description of Drawings
[0010]
[Fig. 1] Fig. 1 is a circuit diagram of a heat pump hot water supply apparatus according
to the present invention.
[Fig. 2] Fig. 2 is a block diagram of a heat source unit control unit and a memory
unit.
[Fig. 3] Fig. 3 is a cross-sectional view of a compressor and a refrigerant amount
adjusting device.
[Fig. 4] Fig. 4 is a flowchart illustrating boiling operation control by the heat
source unit control unit.
[Fig. 5] Fig. 5 is a schematic diagram illustrating transition of the temperature
of hot water stored in a hot water tank.
[Fig. 6] Fig. 6 is a time chart of an inlet water temperature and an inlet refrigerant
temperature of a condenser, the amount of refrigerant stored in the refrigerant amount
adjusting device, a hot water target temperature of a tank control unit, and the valve
opening degree of an expansion valve.
[Fig. 7] Fig. 7 is a circuit diagram of a heat pump hot water supply apparatus according
to the present invention that includes an internal heat exchanger.
[Fig. 8] Fig. 8 is a pressure-enthalpy chart illustrating effects in high pressure
suppression.
[Fig. 9] Fig. 9 is a pressure-enthalpy chart illustrating effects in improvement of
a coefficient of performance (hereinafter, referred to as a COP).
Description of Embodiments
Embodiment 1.
[0011] Hereinafter, an outdoor unit 100 of an air-conditioning apparatus according to Embodiment
1 of the present invention will be explained with reference to drawings.
[0012] Fig. 1 is a circuit diagram of a heat pump hot water supply apparatus 100 according
to Embodiment 1 of the present invention. The heat pump hot water supply apparatus
100 includes a heat source unit 200 and a tank unit 300.
[0013] The heat source unit 200 includes a refrigerant circuit in which a compressor 1 that
compresses refrigerant and discharges the compressed refrigerant, a condenser 2 that
exchanges heat between refrigerant and water, an expansion valve 3 of an electronic
control type whose opening degree is variable to decompress high-pressure refrigerant
into low-pressure refrigerant, an evaporator 4 that exchanges heat between air and
refrigerant, and a refrigerant amount adjusting device 6 that is able to temporarily
store liquid refrigerant are connected by a refrigerant pipe 19 in a ring shape. Furthermore,
the heat source unit 200 also includes an inlet water temperature detection unit 9
that detects the temperature of water at the inlet of the condenser 2, an outlet water
temperature detection unit 10 that detects the temperature of water at the outlet
of the condenser 2, an outside air temperature detection unit 16 that detects the
outside air temperature, an inlet refrigerant temperature detection unit 17 that detects
the temperature of refrigerant at the inlet of the condenser 2, and an outlet refrigerant
temperature detection unit 18 that detects the temperature of refrigerant at the outlet
of the evaporator 4. Each of the above-mentioned detection units may include a temperature
sensor. A fan 8 that promotes heat exchange between refrigerant and air in the evaporator
4 is installed in the vicinity of the evaporator 4. The fan 8 is rotated by driving
of a fan motor 7, and air flow passing through the evaporator 4 is generated by the
rotation. Carbon dioxide (CO
2) may be used as refrigerant. An operation of the heat source unit 200 is controlled
by a heat source unit control unit 13.
[0014] The tank unit 300 includes a hot water tank 14 that stores hot water heated by the
condenser 2 and a hot water circulating pump 11 that is arranged between the condenser
2 and the hot water tank 14 and circulates hot water in a region between the condenser
2 and the hot water tank 14. The condenser 2 and the hot water tank 14 are connected
by a hot water circulating pipe 15. An operation of the tank unit 300 is controlled
by a tank control unit 12. The tank control unit 12 is able to transmit a hot water
target temperature to the heat source unit control unit of the heat source unit 200.
[0015] Fig. 2 is a block diagram of the heat source unit control unit 13. The heat source
unit control unit 13 includes a compressor rotation speed control part 21 that controls
the rotation speed of the compressor 1, a fan rotation speed control part 22 that
controls the rotation speed of the fan motor 7, a pump rotation speed control part
23 that controls the rotation speed of the hot water circulating pump 11, a detection
temperature reception part 24 that receives a detection temperature such as an inlet
refrigerant temperature of the condenser 2, an expansion valve opening degree adjustment
part 25 that adjusts the opening degree of the expansion valve 3, and a hot water
target temperature reception part 26 that receives a hot water target temperature
transmitted from the tank control unit 12. The expansion valve opening degree adjustment
part 25 adjusts the valve opening degree of the of the expansion valve 3 such that
a difference between the hot water target temperature and the inlet refrigerant temperature
becomes equal to a set temperature difference. When the inlet water temperature reaches
a predetermined threshold value or more, the expansion valve opening degree adjustment
part 25 changes the set temperature difference and adjusts the valve opening degree
of the expansion valve 3 in an opening direction. The set temperature difference is
stored in advance in a memory unit 30 in the heat source unit 200. The heat source
unit control unit 13 includes, for example, a microchip. The memory unit 30 includes,
for example, a semiconductor memory.
[0016] Fig. 3 is a cross-sectional view of the compressor 1 and the refrigerant amount adjusting
device 6. In the case where refrigerant in a two-phase gas-liquid state flows from
the evaporator 4 through a suction pipe 31 into the refrigerant amount adjusting device
6, gas refrigerant flows through a relay pipe 32 into the compressor 1, and liquid
refrigerant is stored as excess refrigerant in a liquid refrigerant storage part 33
of the refrigerant amount adjusting device 6. The compressor 1 compresses the gas
refrigerant, causes the compressed gas refrigerant to be discharged through a discharge
pipe 34, and sends the discharged gas refrigerant to the condenser 2. The liquid refrigerant
storage part 33 is an internal space provided at a bottom part of the refrigerant
amount adjusting device 6, which is a tube shape. A so-called suction muffler achieving
a muffling effect may be used as the refrigerant amount adjusting device 6. In this
case, the suction muffler serves as both muffling means and excess refrigerant storing
means. Refrigerating machine oil, along with refrigerant, flows through the suction
pipe 31 into the refrigerant amount adjusting device 6. An oil return hole 35 through
which refrigerating machine oil stored at the bottom of the liquid refrigerant storage
part 33 returns to the compressor 1 is provided at the relay pipe 32. Refrigerant
and refrigerating machine oil may be temporarily stored in a mixed or separate state
at the bottom of the liquid refrigerant storage part 33.
[0017] Fig. 4 is a flowchart of boiling operation control by the heat source unit control
unit 13. Boiling operation control for the heat pump hot water supply apparatus 100
will be explained below with reference to Fig. 4.
[0018] First, when receiving a boiling operation instruction from the tank control unit
12 provided in the tank unit 300, the heat source unit control unit 13 provided in
the heat source unit 200 starts a boiling operation (step S11). The heat source unit
control unit 13 receives a hot water target temperature, along with the boiling operation
instruction. Next, the heat source unit control unit 13 receives an inlet water temperature
of the condenser 2 (step S12). In the case where the inlet water temperature is equal
to or higher than a predetermined temperature, the heat source unit control unit 13
ends the operation control, without performing the boiling operation (step S13). In
the case where the inlet water temperature is lower than the predetermined temperature,
the heat source unit control unit 13 controls the rotation frequency of the compressor
1 in accordance with the inlet water temperature detected by the outside air temperature
detection unit 16 and the inlet water temperature detection unit 9 (step S14).
[0019] Next, the heat source unit control unit 13 determines whether or not the inlet water
temperature detected by the inlet water temperature detection unit 9 of the condenser
2 is equal to or more than a predetermined threshold value (step S15). In the case
where the inlet water temperature is less than the predetermined threshold value,
the heat source unit control unit 13 reads a first temperature difference stored in
the memory unit 30, and defines the read first temperature difference as a set temperature
difference (step S16). In the case where the inlet water temperature is equal to or
more than the predetermined threshold value, the heat source unit control unit 13
reads a second temperature difference stored in the memory unit 30, and defines the
read second temperature difference as a set temperature difference (step S17). The
second temperature difference is smaller than the first temperature difference.
[0020] After setting a temperature difference, the heat source unit control unit 13 performs
processing described below. First, the heat source unit control unit 13 receives an
inlet refrigerant temperature detected by the inlet refrigerant detection unit 17
of the condenser 2 (step S18). Next, the heat source unit control unit 13 calculates
a difference between the hot water target temperature and the inlet refrigerant temperature
(step S19). Hereinafter, this difference will be referred to as a calculated temperature
difference. Next, the heat source unit control unit 13 adjusts the opening degree
of the expansion valve 3 such that the calculated temperature difference becomes equal
to the set temperature difference (step S20). When the inlet water temperature of
the condenser 2 reaches the predetermined threshold value or more, the valve opening
degree is adjusted based on the second temperature difference, which is smaller than
the first temperature difference. Accordingly, the valve opening degree is adjusted
in an opening direction.
[0021] The first temperature difference may be set such that an optimal COP can be obtained
under environmental conditions such as, for example, certain outside air temperature
conditions and inlet water temperature conditions (winter standard heating conditions,
mid-term standard heating conditions, or other conditions defined by JIS). The second
temperature difference is set to a value smaller than the first temperature difference
such that pressure on the high-pressure side at the time of inflow of water at high
temperature does not exceed the designed upper limit. These temperature differences
are fixed values under certain fixed conditions such as the above-mentioned outside
air temperature or inlet water temperature. These temperature differences may be set
to fixed values, for example, within a range from 15 degrees C to 30 degrees C. The
opening degree of the expansion valve 3 may be controlled based only on the outside
air temperature, the inlet water temperature detected by the inlet water temperature
detection unit 9 of the condenser 2, a target value for the inlet refrigerant temperature
detected by the inlet refrigerant detection unit 17 of the condenser 2, and the hot
water target temperature from the tank control unit 12. However, depending on the
environmental condition, there may be a relationship that the hot water target temperature
is higher than the target value for the inlet refrigerant temperature, and water may
not boil. For example, in the case where, at the time of inflow of water at high temperature,
to suppress the pressure on the high-pressure side, processing for uniformly decreasing
the target value for the inlet refrigerant temperature is performed, regardless of
the hot water target temperature, the relationship that the hot water target temperature
is higher than the target value for the inlet refrigerant temperature may be obtained.
In contrast, in the heat pump hot water supply apparatus 100 according to Embodiment
1, temperature differences satisfying the relationship that a value obtained by subtracting
the hot water target temperature from the inlet refrigerant temperature is more than
0 are stored in advance as first and second temperature differences in the memory
unit 30. Then, the opening degree of the expansion valve 3 is adjusted such that the
calculated temperature difference becomes equal to a set temperature difference by
defining the first temperature difference as the set temperature difference in the
case where the inlet water temperature is less than the predetermined threshold value
and defining the second temperature difference, which is smaller than the first temperature
difference, as the set temperature difference in the case where the inlet water temperature
reaches the predetermined threshold value or more. With the above processing, a failure
in which water does not boil can be avoided while performing adjustment such that
the pressure on the high-pressure side does not exceed the designed upper limit pressure
at the time of inflow of water at high temperature.
[0022] Fig. 5 is a schematic diagram illustrating transition of the temperature of hot water
stored in the hot water tank 14. During a period of a boiling operation from the start
of boiling, the temperature of water supplied to the heat source unit 200 is low (for
example, 5 degrees C). However, the inlet water temperature of the condenser 2 increases
before boiling is completed (for example, 5 to 60 degrees C). For example, in the
case where the city water minimum temperature is 5 degrees C and the hot water tapping
maximum temperature is 90 degrees C, the temperature of water in the hot water tank
14 before the boiling operation is about 5 degrees C, the temperature of hot water
in an upper part of the hot water tank 14 during the boiling operation is 90 degrees
C, and the temperature of hot water in a lower part of the hot water tank 14 during
the boiling operation is 5 degrees C. The temperature of hot water in the upper part
of the hot water tank 14 before boiling is completed is 90 degrees C, and the temperature
of hot water in the lower part of the hot water tank 14 before boiling is completed
is 60 degrees C, which is medium temperature water.
[0023] When the inlet water temperature increases, concentration of refrigerant present
in the condenser 2 decreases. At this time, if the first temperature difference set
in advance to achieve the optimal COP under certain environmental conditions is maintained,
the pressure abnormally increases. Thus, under certain environmental conditions that
may cause the pressure on the high-pressure side to exceed a designed pressure (for
example, under conditions where, at a low outside air temperature, the maximum boiling
temperature and the maximum heating capacity are required, the inlet refrigerant temperature
of the condenser 2 is high, and the rotation speed of the compressor 1 reaches the
maximum), the second temperature difference, which is smaller than the first temperature
difference, is defined as the set temperature difference. The second temperature difference
is smaller than the first temperature difference. Therefore, when the inlet water
temperature reaches the predetermined temperature or more, the set temperature difference
decreases. Then, the opening degree of the expansion valve 3 is set such that the
difference between the hot water target temperature from the tank control unit 12
and the detection temperature obtained by the inlet refrigerant detection unit 17
of the condenser 2 becomes equal to the changed set temperature difference. With such
control, high-pressure suppression can be performed such that the concentration of
refrigerant on the high-pressure side can be reduced and the pressure on the high-pressure
side does not exceed the designed pressure.
[0024] Fig. 6 is a time chart illustrating an inlet water temperature 41 of the condenser
2, an inlet refrigerant temperature 42 of the condenser 2, a hot water target temperature
43 of the tank control unit 12, a stored refrigerant amount 44 in the refrigerant
amount adjusting device 6, and the valve opening degree of the expansion valve. The
pressure on the high-pressure side is reduced by adjustment of the opening degree
of the expansion valve 3 mentioned above, whereas the concentration of refrigerant
on the low-pressure side increases. During a period up to a time point T1 at which
the inlet water temperature 41 detected by the inlet water temperature detection unit
9 of the condenser 2 reaches a predetermined threshold value 41 (for example, 50 degrees
C), refrigerant is used up under the designed pressure or below, and there is no excess
liquid refrigerant. Therefore, no liquid refrigerant is stored in the refrigerant
amount adjusting device 6. During this period, the inlet refrigerant temperature 42
and the hot water target temperature 43 are constant. After the inlet water temperature
41 detected by the inlet water temperature detection unit 9 of the condenser 2 exceeds
the predetermined threshold value 41a, to achieve an operation at the designed pressure
or below, liquid storage of excess liquid refrigerant into the refrigerant amount
adjusting device 6 is performed, and high-pressure suppression is thus performed.
That is, at the time point T1 at which the inlet water temperature exceeds the predetermined
threshold value 41, adjustment of the valve opening degree in steps S17 to S20 starts.
At this time, a valve opening degree 45 is adjusted such that the difference between
the inlet refrigerant temperature 42 and the hot water target temperature 43 becomes
equal to a fixed set temperature difference (second temperature difference). The valve
opening degree 45 starts increasing at the time point T1. Accordingly, the actual
temperature difference decreases. For example, the temperature difference between
the inlet refrigerant temperature 42 and the hot water target temperature 43 during
the period up to the time point T1 at which the inlet water temperature 41 reaches
the predetermined threshold value 41a is 30 degrees C, and the temperature difference
at or later than the time point T1 at which the inlet water temperature 41 reaches
the predetermined threshold value 41a is 25 degrees C. At a time point T2 at which
the inlet water temperature 41 reaches a predetermined temperature 41b, the boiling
operation ends (step S13). The amount of refrigerant filled in the entire refrigeration
circuit may be, for example, about 1000 grams. A target value 44a for the stored refrigerant
amount 44 in the refrigerant amount adjusting device 6 may be, for example, about
30 grams. In the case where a suction muffler is used as the refrigerant amount adjusting
device 6, excess liquid refrigerant is stored at the bottom part of the suction muffler.
[0025] Soon after the boiling operation stops, the heat source unit control unit 13 may
start a boiling operation. After the operation stops, the expansion valve 3 is fully
opened, and the pressure on the high-pressure side and the pressure on the low-pressure
side are balanced. At this time, by being affected by the outside air temperature,
refrigerant flows into the evaporator 4 that has a low heat capacity (easily transfers
heat), and is stored as liquid refrigerant. When a fixed time has passed, liquid refrigerant
is stored in the compressor 1, which has a high heat capacity. If restarting is performed
immediately after the entire liquid refrigerant is stored in the evaporator 4, the
liquid refrigerant stored in the evaporator 4 flows into the compressor 1 at one time.
In the case where the refrigerant amount adjusting device 6 is not provided unlike
Embodiment 1, liquid back of liquid refrigerant to the compressor 1 may occur, resulting
in liquid compression by the compressor 1. In contrast, in the heat pump hot water
supply apparatus 100 according to Embodiment 1, liquid refrigerant from the evaporator
4 at the time of start of the apparatus is temporarily stored in the refrigerant amount
adjusting device 6. Therefore, liquid compression of refrigerant by the compressor
1 can be avoided, and the reliability of the compressor 1 can thus be ensured.
[0026] As described above, in the heat pump hot water supply apparatus 100 according to
Embodiment 1, in the case where the temperature of fluid sent from the bottom part
of the hot water tank 14 to the condenser 2 by the hot water circulating pump 11 is
high (that is, at the time of inflow of water at high temperature), concentration
of refrigerant on the high-pressure side is reduced by adjusting the valve opening
degree of the expansion valve 3 in the opening direction, and high-pressure suppression
is thus performed such that a certain fixed pressure is not exceeded. In contrast,
the concentration of refrigerant on the low-pressure side increases, and liquid storage
of excess liquid refrigerant into the refrigerant amount adjusting device 6 is thus
performed. Due to storage of excess liquid refrigerant in the refrigerant amount adjusting
device 6, there is no need to provide an internal heat exchanger that allows heat
exchange between high-pressure-side refrigerant and low-pressure-side refrigerant.
Thus, cost can be reduced. After the operation stops, refrigerant flows into the evaporator
4 with a low heat capacity and is stored as liquid refrigerant in the evaporator 4.
After that, when the fixed time has passed, liquid refrigerant is stored in the compressor
1 with a high heat capacity. In the case where the apparatus is restarted immediately
after liquid refrigerant is stored in the evaporator 4, if no refrigerant amount adjusting
device 6 is provided, liquid back to the compressor 1 may cause liquid compression.
Thus, the refrigerant amount adjusting device 6 is provided in the heat pump hot water
supply apparatus 100 according to Embodiment 1, and liquid refrigerant is stored in
the refrigerant amount adjusting device 6. Therefore, liquid compression by the compressor
1 can be avoided, and the reliability of the compressor 1 can thus be ensured. A suction
muffler may be used as the refrigerant amount adjusting device 6. The suction muffler
serves as both muffling means and the refrigerant amount adjusting device 6. Therefore,
there is no need to provide a separate refrigerant amount adjusting device. Thus,
effects such as reduction of cost and reduction of the increase of capacity of an
outdoor unit can be achieved.
Embodiment 2.
[0027] Hereinafter, an outdoor unit 100 of an air-conditioning apparatus according to Embodiment
2 of the present invention will be explained with reference to drawings.
[0028] Fig. 7 is a circuit diagram of the heat pump hot water supply apparatus 100 that
includes an internal heat exchanger 5. For example, due to constraints on structure,
the refrigerant amount adjusting device 6 with a certain size or more cannot be installed.
In such a case, if a designed pressure on a high-pressure side may be exceeded, the
internal heat exchanger 5, which allows heat exchange between refrigerant in a region
from the outlet of a condenser 2 to the inlet of an expansion valve 3 and refrigerant
in a region from the outlet of an evaporator 4 to the inlet of a compressor 1, may
be provided, as illustrated in Fig. 7. In this case, the expansion valve 3 is provided
at a refrigerant flow passage between the evaporator 4 and the internal heat exchanger
5.
[0029] Fig. 8 is a pressure-enthalpy chart illustrating effects in high-pressure suppression.
Fig. 9 is a pressure-enthalpy chart illustrating effects in COP improvement. The internal
heat exchanger 5 has two roles. One of the roles is, as illustrated in Fig. 8, to
increase the concentration of refrigerant in the evaporator 4 and store the refrigerant
in the evaporator when the inlet water temperature of the condenser 2 increases by
heat exchange by the internal heat exchanger 5. In accordance with this, the concentration
of refrigerant on the high-pressure side can be reduced, and high pressure can thus
be suppressed. Signs 51 and 52 represent an enthalpy range on the low-pressure side
and an enthalpy range on the high-pressure side, respectively, varied by heat exchange
by the internal heat exchanger 5. The other role is, as illustrated in Fig. 9, to
be able to provide superheat at the outlet of the evaporator 4 and thus improve the
COP. A sign 54 in Fig. 9 represents an enthalpy range increased when superheat is
provided at the outlet of the evaporator 4 by the internal heat exchanger 5. A sign
55 represents transition of state of refrigerant in the case where the internal heat
exchanger 5 is provided. A sign 56 represents transition of state of refrigerant in
the case where the internal heat exchanger 5 is not provided.
[0030] In the case where both the internal heat exchanger 5 and the refrigerant amount
adjusting device 6 are used as in Embodiment 2, effects of high-pressure suppression
and COP improvement mentioned above can be achieved. If the amount of liquid storage
in the refrigerant amount adjusting device 6 can be increased to an extent not causing
overflow, the internal heat exchanger 5 can be made compact, which leads to reduction
in cost. Furthermore, by performing control such that the entire amount of excess
liquid refrigerant can be stored only in the refrigerant amount adjusting device 6,
the internal heat exchanger 5 can be removed as in Embodiment 1. Therefore, a further
reduction in cost can be achieved.
Reference Signs List
[0031] 1 compressor, 2 condenser, 3 expansion valve, 4 evaporator, 5 internal heat exchanger,
6 refrigerant amount adjusting device, 7 fan motor, 8 fan, 9 inlet water temperature
detection unit, 10 outlet water temperature detection unit, 11 hot water circulating
pump, 12 tank control unit, 13 heat source unit control unit, 14 hot water tank, 15
hot water circulating pipe, 16 outside air temperature detection unit, 17 inlet refrigerant
temperature detection unit, 18 outlet refrigerant temperature detection unit, 19 refrigerant
pipe, 21 compressor rotation speed control part, 22 fan rotation speed control part,
23 pump rotation speed control part, 24 detection temperature reception part, 25 expansion
valve opening degree adjustment part, 26 temperature reception part, 30 memory unit,
31 suction pipe, 32 relay pipe, 33 liquid refrigerant storage part, 34 discharge pipe,
35 oil return hole, 100 heat pump hot water supply apparatus, 200 heat source unit,
300 tank unit