TECHNICAL FIELD
[0001] The present invention generally relates to a heat pump-type heating device, and more
particularly relates to a two-stage compression heat pump-type heating device provided
with two compressors on a heat pump cycle.
BACKGROUND ART
[0002] As a conventional heat pump-type heating device, for example, Japanese Patent Laid-Open
No.
8-210709 (PTD 1) discloses a heat pump air conditioner suitable for cold areas so as to achieve
a heating operation even when the outdoor air temperature is for example as low as
-20 °C.
[0003] In the heat pump air conditioner disclosed in PTD 1, a scroll compressor, a four-way
valve, an indoor air-heat exchanger, a receiver, an outdoor refrigerant control valve
and an outdoor air-heat exchanger are sequentially connected to one another via a
pipe. A bypass flow path equipped with a refrigerant injection control valve is provided
between the scroll compressor and the receiver for injecting liquid refrigerant into
the scroll compressor. The refrigerant injection control valve is controlled in accordance
with a difference between a temperature at the discharge side of the compressor and
a target discharge temperature thereof. The outdoor refrigerant control valve is controlled
so that the difference between temperatures obtained by temperature sensors that are
respectively provided before and after the outdoor air-heat exchanger is equal to
the degree of superheat of the refrigerant at the refrigerant outlet of the outdoor
air-heat exchanger.
[0004] Meanwhile, Japanese Patent Laying-Open No.
11-132575 (PTD 2) discloses an air conditioner designed to prevent a liquid refrigerant from
being mixed into a gas refrigerant flowing from a gas-liquid separator, which is interposed
in a liquid refrigerant pipe, back to the compressor through a gas injection bypass
pipe, and thereby prevent the reliability of the compressor from being deteriorated.
[0005] In the air conditioner disclosed in PTD 2, an outdoor heat exchanger and an indoor
heat exchanger are sequentially connected to the compressor, thereby forming a refrigerant
circulation circuit. The gas-liquid separator is interposed in the liquid refrigerant
pipe between the outdoor heat exchanger and the indoor heat exchanger. The gas injection
bypass pipe for flowing the gas refrigerant in the gas-liquid separator back to the
compressor and an on-off valve for opening or closing the flow path through the bypass
pipe are provided between the gas-liquid separator and the suction side of the compressor.
The on-off valve is closed as a difference between the discharge temperature of the
compressor and the condensing temperature of the refrigerant circulating in the refrigerant
circulation path becomes smaller than a reference temperature difference. The reference
temperature difference is set larger as the operation frequency of the compressor
becomes higher.
[0006] Moreover, Japanese Patent Laying-Open No.
2007-263440 (PTD 3) discloses an air conditioner designed to appropriately adjust an injection
amount of the refrigerant into the compressor in the compression process during the
heating operation so as to render the air conditioner to operate at a high operating
efficiency under a low load and operate at an improved heating ability under a high
load.
[0007] The air conditioner disclosed in PTD 3 is provided with an injection pipe configured
to inject a part of the refrigerant that flows out from an indoor heat exchanger to
the compressor in the compression process via an injection decompressor, a rotational
speed control means configured to control the rotational speed of compressor in response
to the magnitude of load, and an injection control means configured to control the
injection decompressor such that the degree of superheat or the discharge temperature
of gas discharged at the outlet of the compressor becomes equal to a target value.
The target value is set smaller as the rotational speed of the compressor controlled
by the rotational speed control means becomes higher, and is set larger as the rotational
speed of the compressor becomes lower.
CITATION LIST
PATENT DOCUMENT
[0008]
PTD 1: Japanese Patent Laying-Open No. 8-210709
PTD 2: Japanese Patent Laying-Open No. 11-132575
PTD 3: Japanese Patent Laying-Open No. 2007-263440
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0009] As a heat pump-type heating device such as an air conditioner or a water heater,
there has been disclosed a two-stage compression heat pump-type heating device provided
with two compressors, i.e., a low-pressure side compressor and a high-pressure side
compressor, on a heat pump cycle. However, in the two-stage compression heat pump-type
heating device, the suction temperature and the discharge temperature of the refrigerant
in the high-pressure side compressor may rise to exceed the operating range of the
compressor, disadvantageously. To solve such a problem, there has been suggested such
a method that an injection pipe is provided to connect a pipeline between the low-pressure
side compressor and the high-pressure side compressor and a pipeline between the indoor
heat exchanger (condenser) and the outdoor heat exchanger (evaporator) so that a part
of the refrigerant flowing in the pipeline between the indoor heat exchanger and the
outdoor heat exchanger is injected into the pipeline between the low-pressure side
compressor and the high-pressure side compressor through the intermediary of the injection
pipe. In this manner, the suction temperature of the refrigerant in the high-pressure
side compressor is lowered, thereby achieving an operation with maintained reliability.
[0010] In such a heat pump-type heating device employing the injection pipe, an optimal
amount of refrigerant is required to be injected into the pipeline between the low-pressure
side compressor and the high-pressure side compressor so as to improve the heating
ability. Moreover, in each of the various types of devices employing the injection
pipe as disclosed in PTD 1 to PTD 3 described above, the injection of the refrigerant
is controlled by the on-off valve or the decompressor provided on the pipeline of
the injection pipe. In this case, it is disadvantageous that the heat pump-type heating
device cannot be manufactured at low cost.
[0011] The present invention has been accomplished in view of the aforementioned problems,
and it is therefore an object of the present invention to provide a heat pump-type
heating device having a simple structure and having sufficiently improved heating
ability.
SOLUTION TO PROBLEM
[0012] The heat pump-type heating device according to the present invention is provided
with a first heat exchanger configured to perform heat exchange between a refrigerant
and a heat-receiving fluid, a second heat exchanger configured to perform heat exchange
between the refrigerant and outdoor air, a low-pressure side compressor configured
to compress the refrigerant delivered from the second heat exchanger, a high-pressure
side compressor configured to compress the refrigerant delivered from the low-pressure
side compressor and deliver the compressed refrigerant to the first heat exchanger,
a first decompressor configured to decompress the refrigerant delivered from the first
heat exchanger, a gas-liquid separator configured to separate the refrigerant delivered
from the first decompressor into a gas phase and a liquid phase, a second decompressor
connected to the liquid-phase side of the gas-liquid separator and configured to decompress
the refrigerant delivered from the gas-liquid separator and deliver the decompressed
refrigerant to the second heat exchanger, an injection pipeline connected to the gas-phase
side of the gas-liquid separator and configured to guide the refrigerant delivered
from the gas-liquid separator to a pipeline between the low-pressure side compressor
and the high-pressure side compressor, and a control unit configured to control a
decompression ratio of the refrigerant in the second decompressor so as to render
the refrigerant that flows into the high-pressure side compressor into a superheated
gas state or a saturated vapor state.
[0013] According to the heat pump-type heating device thus configured, the refrigerant flowing
in the injection pipeline is merged with the gas-phase refrigerant which is discharged
from the low-pressure side compressor and has a high temperature and a high pressure
so as to render the refrigerant that flows into the high-pressure side compressor
into a superheated gas state or a saturated vapor state. Accordingly, it is possible
to sufficiently improve the heating ability of the high-pressure side compressor.
In this case, since the second decompressor is used to decompress the refrigerant
delivered from the gas-liquid separator so as to render the refrigerant flowing into
the high-pressure side compressor into a superheated gas state or a saturated vapor
state, it is possible to simplify the structure of the heat pump-type heating device.
[0014] Preferably, the heat pump-type heating device is further provided with a first temperature
detector provided on the pipeline between the first decompressor and the gas-liquid
separator and configured to detect a temperature T1 of the refrigerant, and a second
temperature detector provided on the pipeline between the low-pressure side compressor
and the high-pressure side compressor and configured to detect a temperature T2 of
the refrigerant after having been merged with the refrigerant flowing in the injection
pipeline. The control unit controls the decompression ratio of the refrigerant in
the second decompressor based on a comparison between temperature T1 of the refrigerant
detected by the first temperature detector and temperature T2 of the refrigerant detected
by the second temperature detector.
[0015] Preferably, the control unit decreases the decompression ratio of the refrigerant
in the second decompressor when a state where temperature T2 of the refrigerant detected
by the second temperature detector is equal to temperature T1 of the refrigerant detected
by the first temperature detector has lasted for a predetermined time.
[0016] Preferably, the heat pump-type heating device is further provided with a first temperature
detector provided on the pipeline between the first decompressor and the gas-liquid
separator and configured to detect a temperature T1 of the refrigerant, and a third
temperature detector and a pressure detector both provided on the pipeline between
the high-pressure side compressor and the first heat exchanger and configured to detect
a temperature T3 and a pressure P of the refrigerant, respectively. The control unit
determines on a p-h (pressure-specific enthalpy) diagram a specific enthalpy H' as
an intersection point between an intermediate pressure line defined according to temperature
T1 of the refrigerant detected by the first temperature detector and an isentropic
line passing through a point defined according to temperature T3 of the refrigerant
detected by the third temperature detector and pressure P of the refrigerant detected
by the pressure detector, and controls the decompression ratio of the refrigerant
in the second decompressor based on a comparison between specific enthalpy H' and
a specific enthalpy H of a saturated vapor in the intermediate pressure line.
[0017] According to the heat pump-type heating device thus configured, temperature T1 detected
by the first temperature detector is considered as a temperature at which the refrigerant
is in a gas-liquid two-phase state to control the decompression ratio of the refrigerant
in the second decompressor.
[0018] Preferably, the heat pump-type heating device is further provided with a first temperature
detector provided on the pipeline between the first decompressor and the gas-liquid
separator and configured to detect a temperature T1 of the refrigerant, a second temperature
detector provided on the pipeline between the low-pressure side compressor and the
high-pressure side compressor and configured to detect a temperature T2 of the refrigerant
after having been merged with the refrigerant flowing in the injection pipeline, and
a fourth temperature detector provided on the injection pipeline and configured to
detect a temperature T4 of the refrigerant. When the relationship of T1>T4 is satisfied,
the control unit controls the decompression ratio of the refrigerant in the second
decompressor based on a comparison between temperature T1 of the refrigerant detected
by the first temperature detector and temperature T2 of the refrigerant detected by
the second temperature detector, and when the relationship of T1<T4 is satisfied,
the control unit controls the decompression ratio of the refrigerant in the second
decompressor based on a comparison between temperature T4 of the refrigerant detected
by the fourth temperature detector and temperature T2 of the refrigerant detected
by the second temperature detector.
[0019] According to the heat pump-type heating device thus configured, when the relationship
of T1>T4 is satisfied, temperature T1 of the refrigerant detected by the first temperature
detector is considered as the temperature at which the refrigerant is in a gas-liquid
two-phase state to control the decompression ratio of the refrigerant in the second
decompressor, and when the relationship of T1<T4 is satisfied, temperature T4 of the
refrigerant detected by the fourth temperature detector is considered as the temperature
at which the refrigerant is in a gas-liquid two-phase state to control the decompression
ratio of the refrigerant in the second decompressor.
[0020] Preferably, the heat pump-type heating device is further provided with a buffer unit
being provided on the pipeline which is between the low-pressure side compressor and
the high-pressure side compressor and in which the refrigerant after having been merged
with the refrigerant flowing in the injection pipeline flows and being configured
to store liquid refrigerant.
[0021] According to the heat pump-type heating device thus configured, it is possible to
render the refrigerant that flows into the high-pressure side compressor into a superheated
gas state or a saturated vapor state more certainly.
ADVANTAGEOUS EFFECTS OF INVENTION
[0022] As described in the above, according to the present invention, it is possible to
provide a heat pump-type heating device having a simple structure and having sufficiently
improved heating ability.
BRIEF DESCRIPTION OF DRAWINGS
[0023]
Fig. 1 is a circuit diagram illustrating a heat pump-type heating device according
to a first embodiment of the present invention;
Fig. 2 is a Mollier diagram illustrating a refrigeration cycle by the heat pump-type
heating device illustrated in Fig. 1;
Fig. 3 illustrates a flowchart of controlling the state of refrigerant at a suction
position of a high-pressure side compressor in the heat pump-type heating device in
Fig. 1;
Fig. 4 is a circuit diagram illustrating a modification of the heat pump-type heating
device illustrated in Fig. 1;
Fig. 5 is a graph illustrating the variation of heating ability and the variation
of COP in accordance with the ratio of an injection amount of the refrigerant relative
to the amount of the refrigerant in a gas-liquid separator before being branched;
Fig. 6 is a circuit diagram illustrating a heat pump-type heating device according
to a second embodiment of the present invention;
Fig. 7 illustrates a flowchart of controlling the state of refrigerant at a suction
position of a high-pressure side compressor in the heat pump-type heating device in
Fig. 6;
Fig. 8 is a Mollier diagram for explaining a control to be executed in the heat-pump-type
heating device in Fig. 6; and
Fig. 9 is a circuit diagram illustrating a heat pump-type heating device according
to a third embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0024] Embodiments of the present invention will be described with reference to the drawings.
In the drawings, the same or equivalent members to be referenced below will be assigned
with the same reference numbers.
(First Embodiment)
[0025] Fig. 1 is a circuit diagram illustrating a heat pump-type heating device according
to a first embodiment of the present invention. With reference to Fig. 1, the heat
pump-type heating device of the present embodiment is typically applied to a heat
pump-type water heater or a heat pump-type heating system. The heat pump-type heating
device includes a refrigeration circuit 20 and an injection circuit 50 as a circuit
configuration. A refrigerant such as R410A is enclosed in refrigeration circuit 20
and injection circuit 50.
[0026] Refrigeration circuit 20 extends annularly to form a heat pump cycle. On the path
of refrigeration circuit 20, an indoor heat exchanger (condenser) 26 and an outdoor
heat exchanger (evaporator) 27 are provided. Indoor heat exchanger 26 performs heat
exchange between the refrigerant circulating in the heat pump cycle and a heat-receiving
fluid (water or air). Outdoor heat exchanger 27 performs heat exchange between the
refrigerant circulating in the heat pump cycle and the outside air (outdoor air).
[0027] On the path of refrigeration circuit 20, a first decompressor 36, a gas-liquid separator
38 and a second decompressor 37 are further provided. First decompressor 36, gas-liquid
separator 38, and second decompressor 37 are provided between indoor heat exchanger
26 and outdoor heat exchanger 27. First decompressor 36, gas-liquid separator 38 and
second decompressor 37 are arranged in series in the flow direction of the refrigerant
in refrigeration circuit 20. On the path of refrigeration circuit 20 from indoor heat
exchanger 26 to outdoor heat exchanger 27, first decompressor 36, gas-liquid separator
38 and second decompressor 37 are arranged in the same order as described.
[0028] First decompressor 36 decompresses the refrigerant delivered from indoor heat exchanger
26. First decompressor 36 is provided as a decompression device configured to control
the supercooling of the refrigerant in indoor heat exchanger 26. Gas-liquid separator
38 separates the refrigerant delivered from first decompressor 36 into the gas-phase
refrigerant and the liquid-phase refrigerant (liquid refrigerant). Gas-liquid separator
38 has a gas-phase refrigerant space 38a for storing the gas-phase refrigerant and
a liquid-phase refrigerant space 38b for storing the liquid-phase refrigerant. Second
decompressor 37 is connected to liquid-phase refrigerant space 38b of gas-liquid separator
38 via a pipe. Second decompressor 37 decompresses the liquid refrigerant delivered
from gas-liquid separator 38. Second decompressor 37 is provided as a decompression
device configured to control the degree of superheat of the refrigerant in outdoor
heat exchanger 27 and an amount of injection refrigerant provided by injection circuit
50 which will be described later. In the present embodiment, expansion valves are
used as first decompressor 36 and second decompressor 37.
[0029] On the path of refrigeration circuit 20, a low-pressure side compressor 31 and a
high-pressure side compressor 32 are further provided. Low-pressure side compressor
31 and high-pressure side compressor 32 are provided between outdoor heat exchanger
27 and indoor heat exchanger 26. Low-pressure side compressor 31 and high-pressure
side compressor 32 are arranged in series in the flow direction of the refrigerant
in refrigeration circuit 20. On the path of refrigeration circuit 20 from outdoor
heat exchanger 27 to indoor heat exchanger 26, low-pressure side compressor 31 and
high-pressure side compressor 32 are arranged in the same order as described. Low-pressure
side compressor 31 compresses the refrigerant, which is delivered from outdoor heat
exchanger 27 and has a low pressure, to an intermediate pressure. High-pressure side
compressor 32 further compresses the refrigerant which is delivered from low-pressure
side compressor 31 and has an intermediate pressure to a high pressure.
[0030] In the present embodiment, low-pressure side compressor 31 is a displacement-variable
compressor capable of controlling the discharge displacement of the refrigerant (for
example, a compressor driven by a inverter capable of changing the rotational speed),
and high-pressure side compressor 32 is a constant speed compressor. It should be
noted that at least one of low-pressure side compressor 31 and high-pressure side
compressor 32 may be a displacement-variable compressor, or may be a combination of
a low-pressure side compressor running at constant speed and a high-pressure side
compressor having a variable displacement, or may be a combination of a low-pressure
side compressor having a variable displacement and a high-pressure side compressor
having a variable displacement. Note that in the case where the low-pressure side
compressor is a displacement-variable compressor, it provides a wider operable range
under a high load.
[0031] Injection circuit 50 is composed of an injection pipeline 51 where the refrigerant
flows. Injection pipeline 51 is provided to guide a part of the gas refrigerant separated
into gas-phase refrigerant space 38a of gas-liquid separator 38 to refrigeration circuit
20 between low-pressure side compressor 31 and high-pressure side compressor 32.
[0032] More specifically, injection pipeline 51 is provided with one end thereof connected
to gas-phase refrigerant space 38a of gas-liquid separator 38 and the other end thereof
connected to refrigeration circuit 20 between low-pressure side compressor 31 and
high-pressure side compressor 32. Injection pipeline 51 has a refrigerant inlet connected
to gas-phase refrigerant space 38a of gas-liquid separator 38, and has a refrigerant
outlet connected to refrigeration circuit 20 between low-pressure side compressor
31 and high-pressure side compressor 32.
[0033] In the present embodiment, no on-off valve configured to allow or block the flowing
of the refrigerant or no flow-regulating valve capable of adjusting the flow rate
of the refrigerant is provided on injection pipeline 51.
[0034] A buffer unit 41 and a buffer unit 42 are further provided on the path of refrigeration
circuit 20. Each of buffer unit 41 and buffer unit 42 is constituted by an accumulator
capable of accumulating therein liquid refrigerant. Buffer 41 is provided on the path
of refrigeration circuit 20 between outdoor heat exchanger 27 and low-pressure side
compressor 31. Buffer unit 42 is provided on the path of refrigeration circuit 20
between low-pressure side compressor 31 and high-pressure side compressor 32. In the
case where injection pipeline 51 is connected to refrigeration circuit 20 at a connection
portion 53, buffer unit 42 is provided between connection portion 53 and high-pressure
side compressor 32. Buffer unit 41 and buffer unit 42 are provided to prevent the
reliability of the compressors from being deteriorated due to the introduction of
liquid refrigerant into low-pressure side compressor 31 and high-pressure side compressor
32.
[0035] Fig. 2 is a Mollier diagram illustrating a refrigeration cycle by the heat pump-type
heating device illustrated in Fig. 1.
[0036] The Mollier diagram is also referred to as a P-h diagram with the vertical axis representing
the pressure [MPa] and the horizontal axis representing the specific enthalpy [kJ/kg].
The Mollier diagram depicts refrigerant-specific properties such as pressure, specific
enthalpy, temperature, phase state, enthalpy and specific volume of the refrigerant
used in the refrigeration cycle. The refrigerant states denoted by A to H in Fig.
2 correspond to the refrigerant states denoted by A to H in Fig. 1, respectively.
[0037] With reference to Figs. 1 and 2, firstly, the gas refrigerant (state A) discharged
from high-pressure side compressor 32 flows into indoor heat exchanger (condenser)
26 and is condensed into a high-temperature liquid refrigerant (state B). After the
high-temperature liquid refrigerant passes through first decompressor 36, the pressure
and the temperature of the liquid refrigerant are decreased (state C). If a device
such as an internal heat exchanger is not provided, the refrigerant is generally in
a gas-liquid two-phase state.
[0038] Next, the refrigerant flows into gas-liquid separator 38 and is separated into the
gas phase and the liquid phase. After the separated liquid refrigerant (state D) passes
through second decompressor 37, the pressure and the temperature of the refrigerant
are further decreased (state E). Thereafter, when the refrigerant passes through outdoor
heat exchanger 27, the refrigerant absorbs heat from the outside air to evaporate
(state F). The refrigerant in state F flows into low-pressure side compressor 31 and
is compressed to have an intermediate pressure (state G).
[0039] Meanwhile, the gas-phase refrigerant (injection refrigerant) separated into gas-phase
refrigerant space 38a of gas-liquid separator 38 passes through injection pipeline
51, and is then merged with the refrigerant discharged from low-pressure side compressor
31. Since the temperature of the injection refrigerant is lower than the temperature
of the refrigerant discharged from low-pressure side compressor 31, the temperature
of the refrigerant after having been merged with the injection refrigerant is decreased
(state H).
[0040] Although during the heating operation, when the outside air temperature becomes low,
the evaporation pressure is decreased, and thereby the compression ratio is increased,
by adding the injection refrigerant into the refrigerant having an intermediate pressure
at a stage posterior to the compression process performed by low-pressure side compressor
31 and prior to the compression process performed by high-pressure side compressor
32 so as to increase the flow rate of the refrigerant, it is possible to secure the
heating (room-warming) ability without causing the discharge temperature to rise abnormally.
Thus, with the effect provided by the injection refrigerant, even when the outside
air temperature is for example as low as about - 20 °C, it is possible to obtain sufficient
heating ability.
[0041] The heat pump-type heating device further includes a control unit 46, a temperature
detector 61 serving as a first temperature detector, and a temperature detector 62
serving as a second temperature detector.
[0042] Temperature detector 61 is provided between first decompressor 36 and gas-liquid
separator 38, and specifically, temperature detector 61 is provided at a discharge
position of first decompressor 36. Temperature detector 61 detects a temperature T1
of the refrigerant which is discharged from first decompressor 36 and flows into gas-liquid
separator 38. Temperature detector 62 is provided between low-pressure side compressor
31 and high-pressure side compressor 32, and specifically, temperature detector 62
is provided at a position between connection portion 53 and high-pressure side compressor
32, and more specifically, temperature detector 62 is provided at a position between
connection portion 53 and buffer unit 42. Temperature detector 62 detects a temperature
T2 of the refrigerant which is discharged from low-pressure side compressor 31 and
merged with the refrigerant flowing in injection pipeline 51. Temperature detector
62 detects temperature T2 of the refrigerant at a suction position of high-pressure
side compressor 32.
[0043] Control unit 46 controls the decompression ratio of the refrigerant in second decompressor
37 based on a comparison between temperature T1 of the refrigerant detected by temperature
detector 61 and temperature T2 of the refrigerant detected by temperature detector
62. Specifically, control unit 46 controls the decompression ratio of the refrigerant
in second decompressor 37 based on a difference between temperature T1 of the refrigerant
detected by temperature detector 61 and temperature T2 of the refrigerant detected
by temperature detector 62.
[0044] The heat-pump-type heating device according to the present embodiment, based on temperature
T1 of the refrigerant detected by temperature detector 61 and temperature T2 of the
refrigerant detected by temperature detector 62, controls the opening degree of second
decompressor 37 so as to render the refrigerant at the suction position of high-pressure
side compressor 32 into a state between the superheated gas state containing the gas
phase only and the saturated vapor state. Thereby, the refrigerant to be sucked into
high-pressure side compressor 32 can be maintained at a desired state regardless of
the magnitude of the heating load or the rotational speed of the compressor so as
to improve the heating ability of the heat pump-type heating device or to maintain
high the COP (Coefficient Of Performance).
[0045] Furthermore, in the heat pump type heating device according to the present embodiment,
second decompressor 37 provided at the upstream side of outdoor heat exchanger 27
in the flow direction of the refrigerant during the heating operation is used instead
of providing, on injection pipeline 51, a device configured to control the state of
the refrigerant at the suction position of high-pressure side compressor 32. Accordingly,
it is possible to obtain an effect comparable to that in the case where a decompressor
is provided on the injection pipeline to directly control the flow rate of the injection
refrigerant. In addition, since no on-off valve or decompressor needs to be disposed
on the injection pipeline, the device can be constructed at low cost.
[0046] The following specifically describes the above-described method of controlling the
state of the refrigerant at the suction position of high-pressure side compressor
32. First, since the rotational speed of a compressor is a manipulated variable which
can be used to adjust the heating ability most directly, the rotational speed of low-pressure
side compressor 31 having a variable displacement is controlled in accordance with
a load. For example, the rotational speed of low-pressure side compressor 31 is increased
or decreased in accordance with a deviation between a target heating temperature set
by a user or a target heating temperature set in advance in the device and a measured
heating temperature.
[0047] Fig. 3 illustrates a flowchart of control over the state of the refrigerant at the
suction position of the high-pressure side compressor in the heat pump-type heating
device illustrated in Fig. 1. The control flow illustrated in the figure is performed
by control unit 46.
[0048] With reference to Figs. 1 and 3, prior to the control over the state of the refrigerant
at the suction position of high-pressure side compressor 32, at the start of operation,
the following controls are performed: the control over the rotational speed of low-pressure
side compressor 31; the control over the supercooling at the outlet of indoor heat
exchanger 26 through the adjustment of the opening degree of first decompressor 36;
and the control over the degree of superheating at the outlet of outdoor heat exchanger
27 through the adjustment of the opening degree of second decompressor 37. The enclosed
refrigerant is configured in such a manner that the injection refrigerant is brought
into the gas phase state when the series of controls are completed.
[0049] In the control over the state of the refrigerant at the suction position of high-pressure
side compressor 32, firstly, temperature T1 of the refrigerant between first decompressor
36 and gas-liquid separator 38 is detected by temperature detector 61, temperature
T2 of the refrigerant at the suction position of high-pressure side compressor 32
is detected by temperature detector 62, and the detected temperatures T1 and T2 are
stored in control unit 46 (S101).
[0050] Next, a target refrigerant temperature T2
SP at the suction position of high-pressure side compressor 32 is determined (S102).
[0051] The refrigerant in refrigeration circuit 20 between first decompressor 36 and gas-liquid
separator 38 where temperature detector 61 is provided is in the gas-liquid two-phase
state. Since no decompressor is present between the position where temperature detector
61 is provided and the position where temperature detector 62 is provided, the refrigerant
pressures at both positions are identical to each other. In addition, when the refrigerant
is in an intermediate state between the saturated vapor state and the gas-liquid two-phase
state, the degree of dryness of the refrigerant will change in accordance with the
ratio between the gas-phase refrigerant and the liquid-phase refrigerant, but the
temperature of the refrigerant remains constant. Thus, in the case of rendering the
refrigerant at the suction position of the high-pressure side compressor 32 into the
saturated vapor state, target refrigerant temperature T2
SP may be set equal to T1.
[0052] In the present embodiment, in order to render the refrigerant at the suction position
of high-pressure side compressor 32 into a superheated gas state which is close to
the saturated vapor state, target refrigerant temperature T2
SP is set so that T2
SP= T1+α (α is any predetermined value) (S102). By way of example, α is set to 5 °C.
Preferably, α is set greater than 0 °C and equal to or less than 10 °C, and more preferably,
α is set greater than 0 °C and equal to or less than 5 °C.
[0053] Thereafter, temperature T2 is compared with target refrigerant temperature T2
SP (S103). When the relationship of T2>T2
SP (T2-T1>α) is satisfied, it can be considered that the refrigerant at the suction
position of high-pressure side compressor 32 has been shifted to the side of the superheating
state further than the target state, the opening degree of second decompressor 37
is decreased (i.e., increase the compression ratio of the refrigerant in second decompressor
37) (S104). The amount of the liquid refrigerant in gas-liquid separator 38 is increased,
and consequently the liquid refrigerant overflows from gas-liquid separator 38 into
injection pipeline 51. Accordingly, the refrigerant in injection pipeline 51 changes
from the gas phase state into the gas-liquid two-phase state, and thus, the flow density
of the refrigerant flowing from injection pipeline 51 into the pipeline between low-pressure
side compressor 31 and high-pressure side compressor 32 increases. On the other hand,
when the relationship of T2≤T2
SP (T2-T1≤α) is satisfied, it can be considered that the refrigerant at the suction
position of high-pressure side compressor 32 has been shifted to the side of the saturated
vapor state further than the target state, the opening degree of second decompressor
37 is increased (i.e., decrease the decompression ratio of the refrigerant in second
decompressor 37) (S105).
[0054] The heat pump-type heating device remains idle for t seconds after the operation
of second decompressor 37 (S106). Thereafter, the step of detecting temperature T1
and temperature T2 (S101), the step of S102 and the subsequent steps are repeated
so as to maintain the refrigerant at the suction position of high-pressure side compressor
32 to the desired state.
[0055] In the step of S 102 as described above, in order to render the refrigerant at the
suction position of high-pressure side compressor 32 into the saturated vapor state,
in the case where target refrigerant temperature T2
SP is set so that T2
SP= T1, decreasing the opening degree of second decompressor 37 will increase the ratio
of the liquid refrigerant in injection pipeline 51. However, since the temperature
of the refrigerant will not change even if the refrigerant is rendered from the saturated
vapor state into the gas-liquid two-phase state, the temperature of the refrigerant
at the suction position of high-pressure side compressor 32 will not change despite
the introduction of the liquid refrigerant from injection pipeline 51. In such a case,
as a method of setting the lower limit of the opening degree of second decompressor
37, when the state of T2
SP(T1)= T2 has lasted for a predetermined time of β seconds, it is determined that the
refrigerant has been transferred across the saturated vapor state into the gas-liquid
two-phase state. According to the method, after the state of T2
SP(T1)= T2 has lasted for β seconds, increasing the opening degree of second decompressor
37 will transfer the refrigerant at the suction position of high-pressure side compressor
32 back into the superheating state. By way of example, β is set to 10 seconds.
[0056] Fig. 4 is a circuit diagram illustrating a modification of the heat pump-type heating
device in Fig. 1. With reference to Fig. 4, in the heat pump-type heating device according
to the present modification, on the path of refrigeration circuit 20, an internal
heat exchanger 43 is further provided. Internal heat exchanger 43 is provided between
indoor heat exchanger 26 and first decompressor 36. Injection pipeline 51 is provided
so as to pass through internal heat exchanger 43. Internal heat exchanger 43 performs
heat exchange between the refrigerant flowing out from indoor heat exchanger 26 and
the refrigerant flowing in injection pipeline 51.
[0057] According to the abovementioned configuration, when the refrigerant in liquid phase
flows into injection pipeline 51, the liquid-phase refrigerant is heated by internal
heat exchanger 43 to vaporize, and as a result, the flow rate of the injection refrigerant
is increased, making it possible to improve the heating ability.
[0058] Hereinafter, the description will be carried on explaining why the improvement in
the heating ability can be achieved in the heat pump-type heating device according
to the present embodiment.
[0059] The supply of the injection refrigerant can increase the heating ability by increasing
the flow rate of the refrigerant at the heating side and increase the limit of the
operating pressure ratio of high-pressure side compressor 32 by decreasing the discharge
temperature of high-pressure side compressor 32. For the purpose of increasing the
flow rate of the refrigerant at the heating side, the injection refrigerant in the
gas-liquid two-phase state is more effective than the injection refrigerant in the
gas phase state. However, when the injection refrigerant in the gas-liquid two-phase
state is supplied too much, the COP may be deteriorated and the reliability of the
compressor may be decreased due to liquid compression. Hence, it is preferable to
perform injection to such an extent that the liquid phase in the injection refrigerant
is phase-changed into a saturated vapor state by the high-temperature gas refrigerant
discharged from low-pressure side compressor 31 and the refrigerant sucked into high-pressure
side compressor 32 is at the saturated vapor state.
[0060] Therefore, in the present embodiment, the opening degree of second decompressor 37
is adjusted on the basis of temperature T1 of the refrigerant between first decompressor
36 and gas-liquid separator 38 and temperature T2 of the refrigerant at the suction
position of high-pressure side compressor 32 to keep the refrigerant at the suction
position of high-pressure side compressor 32 at the saturated vapor state to a superheated
gas state close to the saturated vapor state so as to maintain the cycle involving
the increased refrigerant flow rate at the heating side. When the condensation temperature,
the evaporating temperature, and the rotational speed of the compressor are in the
same conditions, it can be said that the major factor that determines the ability
of the cycle is the suction pressure of high-pressure side compressor 32 (state H
in Fig. 2). As the flow rate of the injection refrigerant increases, the pressure
of the sucked refrigerant becomes higher, and the density thereof becomes greater,
and thereby, the flow rate of the refrigerant in indoor heat exchanger 26 is increased.
In the present embodiment, by setting the suction pressure at a value comparable to
the conventional value, increasing the flow rate of the refrigerant at the heating
side can achieve the heating ability as good as or better than the conventional heating
ability.
[0061] In order to render the refrigerant at the suction position of high-pressure side
compressor 32 into the saturated vapor state, the temperature of the refrigerant at
the suction position of high-pressure side compressor 32 should be set to the saturated
vapor temperature relative to the pressure at the same position. Thus, it is required
to set the refrigerant at the suction position of high-pressure side compressor 32
to the saturated vapor temperature, and according to the present embodiment, it is
easy to set the refrigerant at the suction position of high-pressure side compressor
32 to the saturated vapor temperature by using temperature T1 of the refrigerant between
first decompressor 36 and gas-liquid separator 38.
[0062] If the liquid-phase refrigerant is supplied just before the suction position of high-pressure
side compressor 32, it is possible to approach the starting point of the compression
process by high-pressure side compressor 32 to the saturated vapor state. Therefore,
in the present embodiment, the refrigerant discharged from low-pressure side compressor
31 is merged with the injection refrigerant to reliably decrease the refrigerant temperature,
and thereby, the temperature of the refrigerant discharged from high-pressure side
compressor 32 is kept low. Accordingly, the limit of the operating pressure ratio
in the compressor can be increased.
[0063] Hereinafter, the description will be carried out on explaining why the improvement
in controllability can be achieved in the heat pump-type heating device according
to the present embodiment.
[0064] The control method in the present embodiment includes the control over the rotational
speed of the compressor in accordance with the heating load, the control over the
injection in accordance with the temperature of the refrigerant discharged from low-pressure
side compressor 31, and the control means configured to control the decompressor subsequent
to indoor heat exchanger 26 in the flow direction of the refrigerant. The cycle can
be controlled by using the two decompressors. Accordingly, the number of the decompressors
and control means, which are control factors, can be suppressed to the minimum, and
consequently, the controllability can be improved.
[0065] Under a low load, for example, when the outside air temperature is high, a large
amount of the injection refrigerant may disadvantageously cause the COP to decrease
excessively. Such a problem can be solved by providing an on-off valve in injection
pipeline 51 and opening or closing it based on the outside air temperature or the
like.
[0066] Fig. 5 is a graph illustrating the variation of heating ability and the variation
of COP in accordance with the ratio of an injection amount of the refrigerant relative
to the amount of the refrigerant in a gas-liquid separator before being branched.
In Fig. 5, the horizontal axis represents the ratio of the injection amount whereas
the vertical axis represents experimental values of the heating ability and the COP.
[0067] With reference to Fig. 5, when increasing the flow rate of the injection refrigerant
by decreasing the opening degree of second decompressor 37, the heating ability is
improved. Furthermore, when the injection state is brought into the gas-liquid two-phase
state, the flow rate of the injection refrigerant is increased further, and thereby
the heating ability becomes higher. However, as a large amount of the liquid refrigerant
flows into injection pipeline 51, the heating ability decreases. On the other hand,
the COP decreases gradually as the injection amount increases.
[0068] In summary, the above-described heat pump type heating device according to the first
embodiment of the present invention includes: indoor heat exchanger 26 serving as
a first heat exchanger performing heat exchange between refrigerant and heat-receiving
fluid; outdoor heat exchanger 27 serving as a second heat exchanger performing heat
exchange between the refrigerant and outdoor air; low-pressure side compressor 31
compressing the refrigerant delivered from outdoor heat exchanger 27; high-pressure
side compressor 32 compressing the refrigerant delivered from low-pressure side compressor
31; first decompressor 36 decompressing the refrigerant delivered from indoor heat
exchanger 26; gas-liquid separator 38 separating the refrigerant delivered from first
decompressor 36 into a gas phase and a liquid phase; second decompressor 37 connected
to a liquid phase side of gas-liquid separator 38 and decompressing the refrigerant
delivered from gas-liquid separator 38; injection pipeline 51 connected to a gas phase
side of gas-liquid separator 38 and guiding the refrigerant delivered from gas-liquid
separator 38 to a pipeline between low-pressure side compressor 31 and high-pressure
side compressor 32; and control unit 46 controlling a decompression ratio of the refrigerant
in second decompressor 37 such that the refrigerant flowing in injection pipeline
51 is brought into a gas-liquid two-phase state.
[0069] According to the heat pump-type heating device thus configured in the first embodiment
of the present invention, it is possible to make the heat pump-type heating device
excellent in controllability while having the heating ability improved sufficiently.
[0070] In the present embodiment, in order to prevent liquid refrigerant from flowing into
high-pressure side compressor 32 more certainly, buffer unit 42 is provided at the
suction position of high-pressure side compressor 32. In such a configuration, second
decompressor 37 may be controlled by control unit 46 such that the refrigerant at
the suction position of high-pressure side compressor 32 is brought into the state
just after it is transferred from the gas phase state to the gas-liquid two-phase
state. In this case, even though the refrigerant at the suction position of high-pressure
side compressor 32 contains some liquid refrigerant, the liquid refrigerant is captured
by buffer unit 42, and thereby the refrigerant to be sucked into high-pressure side
compressor 32 is kept at the saturated vapor state or the superheated gas state.
[0071] Alternatively, buffer unit 42 may not be provided at the suction position of high-pressure
side compressor 32. In this case, preferably, α in the equation of target refrigerant
temperature T2
SP= T1+α is set so as to shift the state of the refrigerant at the suction position
of high-pressure side compressor 32 slightly to the superheated gas side. Thereby,
it is possible to prevent liquid refrigerant from flowing into high-pressure side
compressor 32 more certainly.
(Second Embodiment)
[0072] Fig. 6 is a circuit diagram illustrating a heat pump-type heating device according
to a second embodiment of the present invention. The heat pump-type heating device
in the present embodiment has basically the same structures as those in the heat pump-type
heating device in the first embodiment. In the description below, the same structures
as those in the heat pump-type heating device in the first embodiment will not be
described repeatedly.
[0073] With reference to Fig. 6, the heat pump-type heating device according to the present
embodiment, in addition to temperature detector 61, further includes a temperature
detector 66 serving as a third temperature detector and a pressure detector 67.
[0074] Temperature detector 66 is provided between high-pressure side compressor 32 and
indoor heat exchanger 26, and specifically, temperature detector 66 is provided at
a discharge position of high-pressure side compressor 32. Temperature detector 66
detects a temperature T3 of the refrigerant that is discharged from high-pressure
side compressor 32 and then flows into indoor heat exchanger 26. Pressure detector
67 is provided between high-pressure side compressor 32 and indoor heat exchanger
26, and specifically, pressure detector 67 is provided at a discharge position of
high-pressure side compressor 32. Pressure detector 67 detects a pressure P of the
refrigerant that is discharged from high-pressure side compressor 32 and then flows
into indoor heat exchanger 26.
[0075] Fig. 7 illustrates a flowchart of controlling the state of the refrigerant at a suction
position of a high-pressure side compressor in the heat pump-type heating device of
Fig. 6. Fig. 8 is a Mollier diagram for explaining a control to be executed in the
heat-pump-type heating device of Fig. 6.
[0076] With reference to Figs. 6 to 8, in the present embodiment, firstly, temperature T1
of the refrigerant between first decompressor 36 and gas-liquid separator 38 is detected
by temperature detector 61, and temperature T3 and pressure P of the refrigerant at
the discharge side of high-pressure side compressor 32 are detected by temperature
detector 66 and pressure detector 67, respectively. The detected temperature T1, temperature
T3 and pressure P are stored in control unit 46 (S201).
[0077] Next, temperature T1 of the refrigerant between first decompressor 36 and gas-liquid
separator 38 is considered as the temperature at which the refrigerant is in the gas-liquid
two-phase state, and based on temperature T1, an intermediate pressure line 301 (D→C→H→G)
is defined on the p-h diagram by using the physical properties of the refrigerant.
Moreover, an isentropic line X' passing through a point A' defined according to temperature
T3 and pressure P is defined on the p-h diagram. An intersection point between intermediate
pressure line 301 and isentropic line X' represents a specific enthalpy H' at the
suction position of high-pressure side compressor 32 in the current cycle, and an
intersection point between intermediate pressure line 301 and saturated vapor curve
302 of the refrigerant represents a specific enthalpy H of the refrigerant in the
saturated vapor state (S202).
[0078] In the present embodiment, in the case where isentropic line X' defined on the p-h
diagram overlaps with isentropic line X passing through specific enthalpy H of the
refrigerant in the saturated vapor state and thus the relationship of H'= H is satisfied,
the refrigerant at the suction position of high-pressure side compressor 32 is in
the saturated vapor state. In the case where isentropic line X' (isentropic line X'1
in Fig. 8) defined on the p-h diagram shifts to the outer side of saturated vapor
curve 302 than isentropic line X and thus the relationship of H'>H is satisfied, the
refrigerant at the suction position of high-pressure side compressor 32 is in the
superheated gas state. In the case where isentropic line X' (isentropic line X'2 in
Fig. 8) defined on the p-h diagram shifts to the inner side of saturated vapor curve
302 than isentropic line X and thus the relationship of H'<H is satisfied, the refrigerant
at the suction position of high-pressure side compressor 32 is in the gas-liquid two-phase
state at which the liquid phase is dominant.
[0079] Next, control unit 46 compares H' and H+α (α is any predetermined value) (S203).
When the relationship of H+α≤H' is satisfied, it is considered that the refrigerant
at the suction position of high-pressure side compressor 32 has been shifted to the
side of the superheating state further than the target state, the opening degree of
second decompressor 37 is decreased (S205). When the relationship of H+α>H' is satisfied,
control unit 46 compares H and H' (S204). When the relationship of H-H'≥0 (H≥H'),
it is considered that the refrigerant at the suction position of high-pressure side
compressor 32 has been shifted to the side of the saturated vapor state further than
the target state, the opening degree of second decompressor 37 is increased (S206).
[0080] When the relationship of H-H'<0 (H<H') is satisfied, the heat pump-type heating device
remains idle for t seconds after the operation of second decompressor 37 (S207). In
other words, after the step of S205 or S206, the heat pump-type heating device remains
idle for t seconds after operation of second decompressor 37 (S207). Thereafter, the
step of detecting temperatures T1, T3 and pressure P1 (S201), the step of S202 and
the subsequent steps are repeated so as to maintain the refrigerant at the suction
position of high-pressure side compressor 32 to the desired state.
[0081] Thus, in the present embodiment, the opening degree of second decompressor 37 is
controlled on the basis of temperature T1 of the refrigerant detected by temperature
detector 61, temperature T3 detected by temperature detector 63 and pressure P detected
by the pressure detector so as to maintain the refrigerant at the suction position
of high-pressure side compressor 32 in an intermediate state between the superheated
gas state and the saturated vapor state.
[0082] According to the heat pump-type heating device thus configured in the second embodiment
of the present invention, it is possible to obtain the same effects as those described
in first embodiment.
[0083] Moreover, in the present embodiment, the refrigerant is supplied just after it is
transferred from the gas phase state to the gas-liquid two-phase state so as to increase
the injection flow rate in the circuit configuration where buffer unit 42 is provided
at the suction position of high-pressure side compressor 32 , which is the same as
that in the first embodiment. Especially in the present embodiment, since the ratio
of the liquid-phase refrigerant relative to the refrigerant in the gas-liquid two-phase
state can be determined according to the specific enthalpy, it is possible to supply
the injection refrigerant having a larger percentage of liquid phase in accordance
with the capacity of buffer unit 42.
(Third Embodiment)
[0084] Fig. 9 is a circuit diagram illustrating a heat pump-type heating device according
to a third embodiment of the present invention. The heat pump-type heating device
in the present embodiment has basically the same structures as those in the heat pump-type
heating device in the first embodiment. In the description below, the same structures
as those in the heat pump-type heating device in the first embodiment will not be
described repeatedly.
[0085] With reference to Fig. 9, the heat pump-type heating device according to the present
embodiment, in addition to temperature detector 61 and temperature detector 62, further
includes a temperature detector 71 as a fourth temperature detector. Temperature detector
71 is provided on injection pipeline 51. Temperature detector 71 detects a temperature
T4 of the refrigerant flowing in injection pipeline 51.
[0086] The method of controlling the opening degree of second decompressor 37 is basically
identical to that shown in the flowchart in Fig. 3. However, since the pipeline may
be cooled when the outside air temperature is low, as the refrigerant discharged from
first decompressor 36 performs heat exchange with the injection refrigerant in the
cycle including an internal heat exchanger (see Fig. 4), it may be transferred into
a supercooled state and thereby becomes the liquid refrigerant. In this case, the
refrigerant temperature detected by temperature detector 61 cannot be considered as
the refrigerant temperature at the suction position of high-pressure side compressor
32. According to the present embodiment, even in such a situation, by providing temperature
detector 71 to detect the temperature of the refrigerant flowing in injection pipeline
51 and comparing temperature T4 of the refrigerant flowing in injection pipeline 51
and temperature T1 of the refrigerant at the discharge side of first decompressor
36, it is possible to determine the temperature of the refrigerant in the gas-liquid
two-phase state.
[0087] Specifically, in the case where the relationship of T4=T1 is satisfied, the refrigerant
at either detection position is in the gas-liquid two-phase state, and thereby, either
T1 or T4 may be used in step S102 of Fig. 3. In the case where the relationship of
T1>T4 is satisfied, the refrigerant flowing in injection pipeline 51 is likely in
the overcooled state, T1 is used in step S102 of in Fig. 3. In the case where the
relationship of T1<T4 is satisfied, due to the influence of the outside air temperature
and the internal heat exchanger, the refrigerant after first decompressor 36 is likely
to be overcooled into the liquid refrigerant, T4 is used in step S102 of in Fig. 3.
[0088] According to the heat pump-type heating device thus configured in the third embodiment
of the present invention, it is possible to obtain the same effects as those described
in first embodiment.
[0089] It is acceptable to combine the heat-pump-type heating device according to each of
the first to third embodiments as described above to achieve a new heat pump-type
heating device.
[0090] It should be understood that the embodiments disclosed herein have been presented
for the purpose of illustration and description but not limited in all aspects. It
is intended that the scope of the present invention is not limited to the description
above but defined by the scope of the claims and encompasses all modifications equivalent
in meaning and scope to the claims.
INDUSTRIAL APPLICABILITY
[0091] The present invention, for example, is applied to a heat pump-type hot water supplier
or a heat pump-type heating system.
REFERENCE SIGNS LIST
[0092]
20: refrigeration circuit; 26: indoor heat exchanger; 27: outdoor heat exchanger;
31: low-pressure side compressor; 32: high-pressure side compressor; 36: first decompressor;
37: second decompressor; 38: gas-liquid separator; 38a: gas-phase refrigerant space;
38b: liquid-phase refrigerant space; 41, 42: buffer unit; 43: internal heat exchanger;
46: control unit; 50: injection circuit; 51: injection pipeline; 53: connection portion;
61, 62, 63, 66, 71: temperature detector; 67: pressure detector; 301: intermediate
pressure line; 302: saturated vapor curve