U.S. patent application number 12/989440 was filed with the patent office on 2011-02-17 for refrigeration apparatus.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. Invention is credited to Shuji Fujimoto, Kazuhiro Furusho, Tooru Inazuka, Hidehiko Kataoka, Mitsuharu Uchida, Takahiro Yamaguchi, Atsushi Yoshimi.
Application Number | 20110036110 12/989440 |
Document ID | / |
Family ID | 41255084 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110036110 |
Kind Code |
A1 |
Fujimoto; Shuji ; et
al. |
February 17, 2011 |
REFRIGERATION APPARATUS
Abstract
A refrigeration apparatus performs heat exchange on a water tube
system having a water inlet tube leading exterior water to a water
branching point, first and second branching water tubes extending
from the water branching point, and a water outlet tube leading to
the exterior from a convergent point of the first and second
branching water tubes. Active refrigerant is in a supercritical
state in at least part of a refrigeration cycle. The refrigeration
apparatus includes a main expansion mechanism connected to an
evaporator, first and second compression elements connected by a
first refrigerant tube, a first heat exchanger exchanging heat
between the first refrigerant tube and the first branching water
tubes, second refrigerant tubes connecting the second compression
element and the main expansion mechanism, and a second heat
exchanger in which the second refrigerant tubes exchange heat with
the second branching water tubes and does not exchange heat with
the water inlet tube.
Inventors: |
Fujimoto; Shuji; (Osaka,
JP) ; Yoshimi; Atsushi; (Osaka, JP) ;
Yamaguchi; Takahiro; (Osaka, JP) ; Inazuka;
Tooru; (Osaka, JP) ; Furusho; Kazuhiro;
(Osaka, JP) ; Uchida; Mitsuharu; (Shiga, JP)
; Kataoka; Hidehiko; (Shiga, JP) |
Correspondence
Address: |
GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Assignee: |
DAIKIN INDUSTRIES, LTD.
Osaka-shi, Osaka
JP
|
Family ID: |
41255084 |
Appl. No.: |
12/989440 |
Filed: |
April 28, 2009 |
PCT Filed: |
April 28, 2009 |
PCT NO: |
PCT/JP2009/058311 |
371 Date: |
October 25, 2010 |
Current U.S.
Class: |
62/149 ;
62/238.7 |
Current CPC
Class: |
F25B 1/10 20130101; F25B
9/008 20130101; Y02B 30/12 20130101; F25B 2700/21152 20130101; F24D
17/02 20130101; F25B 31/004 20130101; F24D 2200/24 20130101; F25B
2400/13 20130101; F25B 2309/061 20130101; F25B 2700/21171 20130101;
F25B 2700/21161 20130101; F25B 40/00 20130101; F25B 2400/0405
20130101; F24D 3/18 20130101; F25B 2339/047 20130101; F25B 2400/072
20130101 |
Class at
Publication: |
62/149 ;
62/238.7 |
International
Class: |
F25B 45/00 20060101
F25B045/00; F25B 1/10 20060101 F25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2008 |
JP |
2008-120738 |
Claims
1. A refrigeration apparatus which performs heat exchange on a
water tube system having a water inlet tube to lead water supplied
from an exterior to a water branching point, first branching water
tubes and second branching water tubes extending from the water
branching point, and a water outlet tube leading out to the
exterior from a convergent point where the first branching water
tubes and the second branching water tubes converge, active
refrigerant being in a supercritical state in at least part of a
refrigeration cycle; the refrigeration apparatus comprising: a main
expansion mechanism arranged and configured to depressurize the
refrigerant; an evaporator connected to the main expansion
mechanism, the evaporator being arranged and configured to
evaporate refrigerant; a first compression element arranged and
configured to draw refrigerant that has passed through the
evaporator, and to compress and discharge the refrigerant drawn
into the first compression element; a second compression element
arranged and configured to draw in the refrigerant discharged from
the first compression element and to compress and discharge the
refrigerant drawn into the second compression element; a first
refrigerant tube arranged and configured to draw the refrigerant
discharged from the first compression element into the second
compression element; a first heat exchanger arranged and configured
to perform heat exchange between the refrigerant passing through
the first refrigerant tube and the water flowing through the first
branching water tubes; second refrigerant tubes arranged and
configured to connect a discharge side of the second compression
element and the main expansion mechanism; and a second heat
exchanger arranged and configured to such that refrigerant passing
through the second refrigerant tubes exchanges heat with the water
flowing through the second branching water tubes, and does not
exchange heat with the water flowing through the water inlet
tube.
2. The refrigeration apparatus according to claim 1, further
comprising: a flow rate ratio adjustment mechanism arranged and
configured to adjust a ratio between a quantity of water flowing
through the first branching water tubes and a quantity of water
flowing through the second branching water tubes.
3. The refrigeration apparatus according to claim 2, further
comprising: a heating capacity detection unit arranged and
configured to detect a capacity of the refrigerant passing through
the first heat exchanger to heat the water and a capacity of the
refrigerant passing through the second heat exchanger to heat the
water; and a water distribution quantity control unit arranged and
configured to adjust the ratio between the quantity of water
flowing through the first branching water tubes and the quantity of
water flowing through the second branching water tubes by
controlling the flow rate adjustment mechanism in accordance with a
ratio between the heating capacities of the first heat exchanger
and the second heat exchanger detected by the heating capacity
detection unit.
4. The refrigeration apparatus according to claim 1, wherein the
second refrigerant tubes have a third refrigerant tube connecting
the second heat exchanger and the main expansion mechanism; and the
refrigeration apparatus further comprises: a fourth refrigerant
tube arranged and configured to connect the evaporator and an
intake side of the first compression element; a third heat
exchanger arranged and configured to perform heat exchange between
the refrigerant flowing through the third refrigerant tube and the
refrigerant flowing through the fourth refrigerant tube; a third
heat exchange bypass tube arranged and configured to connect one
end and another end of a portion of the third refrigerant tube that
passes through the third heat exchanger; and a heat exchanger
switching mechanism arranged and configured to switch between a
state in which refrigerant flows through the portion of the third
refrigerant tube that passes through the third heat exchanger, and
a state in which refrigerant flows through the third heat exchange
bypass tube.
5. The refrigeration apparatus according to claim 4, further
comprising: temperature sensory units arranged and configured to
sense a value of at least an air temperature surrounding the
evaporator or a discharged refrigerant temperature of at least the
first compression element or the second compression element; and a
heat exchange quantity control unit arranged and configured to
control the heat exchanger switching mechanism and to increase the
quantity of refrigerant flowing through the portion of the third
refrigerant tube that passes through the third heat exchanger when
the air temperature is higher than a predetermined high-temperature
air temperature when a value sensed by the temperature sensory
units is an air temperature, or the refrigerant temperature is
lower than a predetermined low-temperature refrigerant temperature
when the value sensed by the temperature sensory units is a
refrigerant temperature.
6. The refrigeration apparatus according to claim 1, wherein the
second refrigerant tubes have a third refrigerant tube connecting
the second heat exchanger and the main expansion mechanism; and the
refrigeration apparatus further comprises: a branching expansion
mechanism arranged and configured to depressurize refrigerant; a
fifth refrigerant tube which branches off from the third
refrigerant tube and extends to the branching expansion mechanism;
sixth refrigerant tubes extending from the branching expansion
mechanism to the first refrigerant tube; and a fourth heat
exchanger arranged and configured to perform heat exchange between
refrigerant flowing through the third refrigerant tube and
refrigerant flowing through the sixth refrigerant tubes.
7. The refrigeration apparatus according to claim 6, further
comprising: temperature sensory units arranged and configured to
sense a value of at least an air temperature surrounding the
evaporator or a discharged refrigerant temperature of at least the
first compression element or the second compression element; and a
branched quantity control unit arranged and configured to control
the branching expansion mechanism and to increase the quantity of
refrigerant passing therethrough when the air temperature is lower
than a predetermined low-temperature air temperature when the value
sensed by the temperature sensory units is an air temperature, or
the refrigerant temperature is higher than a predetermined
high-temperature refrigerant temperature when the value sensed by
the temperature sensory units is a refrigerant temperature.
8. The refrigeration apparatus according to claim 6, further
comprising: a water temperature sensory unit arranged and
configured to sense a temperature of water flowing through any
position in the water tube system; a first refrigerant temperature
sensory unit arranged and configured to sense a temperature of
refrigerant passing through the first refrigerant tube; and a
refrigerant distribution quantity control unit arranged and
configured to control the branching expansion mechanism and to
increase the quantity of refrigerant passing therethrough when a
difference between the temperature sensed by the water temperature
sensory unit and the temperature sensed by the first refrigerant
temperature sensory unit is less than a predetermined value.
9. The refrigeration apparatus according to claim 1, wherein the
second refrigerant tubes have a third refrigerant tube connecting
the second heat exchanger and the main expansion mechanism; and the
refrigeration apparatus further comprises: a branching expansion
mechanism arranged and configured to depressurize refrigerant;
fourth refrigerant tubes connecting the evaporator and an intake
side of the first compression element; a third heat exchanger
arranged and configured to perform heat exchange between
refrigerant flowing through the third refrigerant tube and
refrigerant flowing through the fourth refrigerant tubes; a fifth
refrigerant tube which branches off from the third refrigerant tube
and extends to the branching expansion mechanism; sixth refrigerant
tubes connecting the branching expansion mechanism and the first
refrigerant tube; and a fourth heat exchanger arranged and
configured to perform heat exchange between refrigerant flowing
through the third refrigerant tube and refrigerant flowing through
the sixth refrigerant tubes.
10. The refrigeration apparatus according to claim 9, further
comprising: temperature sensory units arranged and configured to
sense a value of at least the air temperature surrounding the
evaporator or the discharged refrigerant temperature of at least
the first compression element or the second compression element;
and a branched heat quantity control unit arranged and configured
to control the branching expansion mechanism and to increase
quantity of refrigerant passing therethrough when the air
temperature is lower than a predetermined low-temperature air
temperature when the value sensed by the temperature sensory units
is an air temperature, or the refrigerant temperature is higher
than a predetermined high-temperature refrigerant temperature when
the value sensed by the temperature sensory units is a refrigerant
temperature.
11. The refrigeration apparatus according to claim 9, further
comprising: a first heat exchange bypass tube connecting one end
and another end of a portion of the first refrigerant tube that
passes through the first heat exchanger; and a bypass switching
mechanism arranged and configured to switch between a state in
which refrigerant flows through the portion of the first
refrigerant tube that passes through the first heat exchanger, and
a state in which refrigerant flows through the first heat exchange
bypass tube.
12. The refrigeration apparatus according to claim 11, further
comprising: temperature sensory units arranged and configured to
sense a value of at least an air temperature surrounding the
evaporator or a discharged refrigerant temperature of at least the
first compression element or the second compression element; and a
bypass control unit arranged and configured to control the bypass
switching mechanism and to increase using the quantity of
refrigerant flowing through the portion of the first refrigerant
tube that passes through the first heat exchanger when the air
temperature is higher than a predetermined high-temperature air
temperature when the value sensed by the temperature sensory units
is an air temperature, or the refrigerant temperature is lower than
a predetermined low-temperature refrigerant temperature when the
value sensed by the temperature sensory units is a refrigerant
temperature.
13. The refrigeration apparatus according to claim 9, further
comprising: a water temperature sensory unit arranged and
configured to sense a temperature of water flowing through any
position in the water tube system; a first refrigerant temperature
sensory unit arranged and configured to sense a for sensing the
temperature of refrigerant passing through the first refrigerant
tube; and a water-correspondent refrigerant quantity control unit
arranged and configured to cont the branching expansion mechanism
and to increase the quantity of refrigerant passing therethrough
when a difference between the temperature sensed by the water
temperature sensory unit and the temperature sensed by the first
refrigerant temperature sensory unit is less than a predetermined
value.
14. The refrigeration apparatus according to claim 1, further
comprising: a first drive unit arranged and configured to drive the
first compression element; and a second drive unit arranged and
configured to drive the second compression element independently of
the first compression element.
15. The refrigeration apparatus according to claim 1, wherein the
first compression element and the second compression element have a
shared rotating shaft in order to perform compression work by
rotatably driving each of the first and second compression
elements.
16. The refrigeration apparatus according to claim 1, wherein the
active refrigerant is carbon dioxide.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration apparatus,
and particularly relates to a refrigeration apparatus which
performs a multi-stage compression-type refrigeration cycle using
refrigerant that operates including the process of a supercritical
state.
BACKGROUND ART
[0002] In conventional practice, one example of a refrigeration
apparatus which performs a multi-stage compression-type
refrigeration cycle using refrigerant that operates in a
supercritical range is an air-conditioning apparatus which performs
a two-stage compression-type refrigeration cycle using carbon
dioxide as a refrigerant, such as the apparatus disclosed in Patent
Literature 1 (Japanese Laid-open Patent Application No.
2007-232263).
[0003] An example of an apparatus that uses such a two-stage
compression-type refrigeration cycle as a water heater is a water
heater such as the one disclosed in Patent Literature 2 (Japanese
Laid-open Patent Application No. 2002-106988), for example. In this
water heater, a conventional technique is used for improving
compression efficiency by using an intercooler to cool refrigerant
heading from a low-stage compression element to a high-stage
compression element. Not only is water for a hot water supply
heated in a gas cooler, but some of this heated water is branched
off, part is successively led to and heated in the gas cooler while
the other part is led to and heated in an intercooler, and hot
water for a hot water supply is obtained. Thus, the intercooler can
be used as a heater of hot water and also as a cooler of
refrigerant drawn into the high-stage compression element, and
energy efficiency can be improved.
SUMMARY OF INVENTION
Technical Problem
[0004] In the water heater described above, water flowing into the
intercooler has already been heated when passing through the gas
cooler, and is warm water having a somewhat high temperature.
Therefore, there could be cases in which the temperature of the
warm water that has passed through the gas cooler and been heated
is higher than the temperature of the refrigerant passing through
the intercooler, for example. In such cases, not only is it not
possible to heat the water in the intercooler, but it is also not
possible to cool the refrigerant drawn into the high-stage
compression element, and it is therefore not possible to improve
compression efficiency.
[0005] An object of the present invention is to provide a
refrigeration apparatus which uses refrigerant that operates
including the process of a supercritical state, wherein it is
possible to more reliably improve compression efficiency and make
the heating of water for a hot water supply more efficient.
Solution to Problem
[0006] A refrigeration apparatus according to a first aspect of the
present invention is refrigeration apparatus which performs heat
exchange on a water tube system having a water inlet tube for
leading water supplied from the exterior to a water branching
point, first branching water tubes and second branching water tubes
extending from the water branching point, and a water outlet tube
leading out to the exterior from a convergent point where the first
branching water tubes and the second branching water tubes
converge, wherein the active refrigerant is in a supercritical
state in at least part of the refrigeration cycle; the
refrigeration apparatus comprising a main expansion mechanism, an
evaporator, a first compression element, a second compression
element, a first refrigerant tube, a first heat exchanger, second
refrigerant tubes, and a second heat exchanger. The main expansion
mechanism depressurizes the refrigerant. The evaporator is
connected with the main expansion mechanism and the evaporator
evaporates the refrigerant. The first compression element draws in
refrigerant that has passed through the evaporator and compresses
and discharges the refrigerant. The second compression element
draws in the refrigerant discharged from the first compression
element and further compresses and discharges the refrigerant. The
first refrigerant tube draws the refrigerant discharged from the
first compression element into the second compression element. The
first heat exchanger performs heat exchange between the refrigerant
passing through the first refrigerant tube and the water flowing
through the first branching water tubes. The second refrigerant
tubes connect the discharge side of the second compression element
and the main expansion mechanism. The second heat exchanger
subjects the refrigerant passing through the second refrigerant
tubes to heat exchange with the water flowing through the second
branching water tubes, and not to heat exchange with the water
flowing through the water inlet tube. Herein, the first compression
element and the second compression element may be either housed
within the same casing or the like and controlled together, or
disposed separately and controlled independently of each other.
[0007] Even if the intention is to warm the water passing through
the water tube system in the first heat exchanger whose refrigerant
temperature is lower than the second heat exchanger, for example,
the temperature will sometimes be higher than the temperature of
the refrigerant flowing through the first heat exchanger due to the
water already being warmed before flowing into the first heat
exchanger. In this case, there is a risk that it will not be
possible to cool the refrigerant by heat exchange in the first heat
exchanger, and that the water will be deprived of its heat by the
refrigerant.
[0008] As a countermeasure to this, in this refrigeration
apparatus, the second heat exchanger does not subject the
refrigerant passing through the second refrigerant tube to heat
exchange with the water flowing through the water inlet tube.
Therefore, the water can be made to flow in during a state of low
temperature in which not only is the water flowing into the second
heat exchanger not yet heated by heat exchange with the
refrigerant, but neither is the water flowing into the first heat
exchanger.
[0009] Thereby, the refrigerant heading from the first compression
element toward the second compression element is cooled to reliably
improve compression efficiency, heat exchanging which can raise the
water temperature can be reliably performed by both the first heat
exchanger and the second heat exchanger, and the coefficient of
performance of the refrigeration apparatus can be improved.
[0010] A refrigeration apparatus according to a second aspect of
the present invention is the refrigeration apparatus according to
the first aspect of the present invention, further comprising a
flow rate ratio adjustment mechanism capable of adjusting the ratio
between a quantity of water flowing through the first branching
water tubes and a quantity of water flowing through the second
branching water tubes.
[0011] According to this refrigeration apparatus, since it is
possible to adjust the flow rate ratio between the quantity of
water flowing through the first heat exchanger and the quantity of
water flowing through the second heat exchanger, it is possible for
the water to be heated efficiently.
[0012] A refrigeration apparatus according to a third aspect of the
present invention is the refrigeration apparatus according to the
second aspect of the present invention, further comprising a
heating capacity detection unit and a water distribution quantity
control unit. The heating capacity detection unit is capable of
detecting the capacity of the refrigerant passing through the first
heat exchanger to heat the water and the capacity of the
refrigerant passing through the second heat exchanger to heat the
water. The water distribution quantity control unit adjusts the
ratio between the quantity of water flowing through the first
branching water tubes and the quantity of water flowing through the
second branching water tubes by controlling the flow rate
adjustment mechanism in accordance with the ratio between the
heating capacities of the first heat exchanger and the second heat
exchanger detected by the heating capacity detection unit. The
control by this water distribution quantity control unit may
involve, for example, adjusting the ratio between the quantity of
water flowing through the first branching water tubes and the
quantity of water flowing through the second branching water tubes,
either so as to achieve equality with the ratio between a first
specific enthalpy obtained by subtracting the specific enthalpy of
the refrigerant discharged from the first compression element from
the specific enthalpy of the refrigerant drawn into the second
compression element, and a second specific enthalpy obtained by
subtracting the specific enthalpy of the refrigerant drawn into the
second compression element from the specific enthalpy of the
refrigerant discharged from the second compression element, or so
as to approach this ratio. The control by this water distribution
quantity control unit may otherwise involve, for example, adjusting
the ratio between the quantity of water flowing through the first
branching water tubes and the quantity of water flowing through the
second branching water tubes, so that the water temperature in the
outlet of the first heat exchanger in the first branching water
tubes and the water temperature in the outlet of the second heat
exchanger in the second branching water tubes are substantially
equal.
[0013] In this refrigeration apparatus, heat exchange for cooling
the refrigerant and heating the water can be performed by both the
first heat exchanger and the second heat exchanger, and flow rate
control for improving the coefficient of performance of the
refrigeration apparatus can be performed automatically.
[0014] A refrigeration apparatus according to a fourth aspect of
the present invention is the refrigeration apparatus according to
any of the first through third aspects of the present invention,
wherein the second refrigerant tubes have a third refrigerant tube
for connecting the second heat exchanger and the main expansion
mechanism. The refrigeration apparatus further comprises a fourth
refrigerant tube for connecting the evaporator and an intake side
of the first compression element, a third heat exchanger for
performing heat exchange between the refrigerant flowing through
the third refrigerant tube and the refrigerant flowing through the
fourth refrigerant tube, a third heat exchange bypass tube for
connecting one end and another end of a portion of the third
refrigerant tube that passes through the third heat exchanger, and
a heat exchanger switching mechanism capable of switching between a
state in which refrigerant flows through the portion of the third
refrigerant tube that passes through the third heat exchanger, and
a state in which refrigerant flows through the third heat exchange
bypass tube.
[0015] In this refrigeration apparatus, through heat exchange in
the third heat exchanger, the coefficient of performance can be
improved by raising the degree of supercooling of the refrigerant
headed to the main expansion mechanism. Furthermore, through heat
exchange in the third heat exchanger, the refrigerant drawn into
the first compression element can be subjected to an appropriate
amount of superheating, liquid compression in the first compression
element can be suppressed, and the discharge temperature can be
increased to keep the resulting water temperature high.
[0016] A refrigeration apparatus according to a fifth aspect of the
present invention is the refrigeration apparatus according to the
fourth aspect of the present invention, further comprising
temperature sensory units and a heat exchange quantity control
unit. The temperature sensory units sense at least the air
temperature surrounding the evaporator or the discharged
refrigerant temperature of at least the first compression element
or the second compression element. The heat exchange quantity
control unit controls the heat exchanger switching mechanism and
increases the quantity of refrigerant flowing through the portion
of the third refrigerant tube that passes through the third heat
exchanger when the following condition is fulfilled: the air
temperature is higher than a predetermined high-temperature air
temperature when the value sensed by the temperature sensory units
is an air temperature, or the refrigerant temperature is lower than
a predetermined low-temperature refrigerant temperature when the
value sensed by the temperature sensory units is a refrigerant
temperature.
[0017] In this refrigeration apparatus, the quantity of refrigerant
flowing through the portion of the third refrigerant tube that
passes through the third heat exchanger can be increased even in
cases in which it appears that the air temperature surrounding the
evaporator could increase or that the temperature of the
refrigerant discharged from the compression element could
decrease.
[0018] It is thereby possible to increase the degree of
supercooling of the refrigerant headed to the main expansion
mechanism, and to improve the coefficient of performance.
[0019] Since the refrigerant drawn into the first compression
element can be subjected to the appropriate degree of superheating,
it is possible to impede liquid compression from occurring in the
first compression element.
[0020] Furthermore, since the degree of superheating of the
refrigerant drawn into the first compression element can be
increased, it is possible to conform to cases in which the
temperature required in the radiator is high.
[0021] A refrigeration apparatus according to a sixth aspect of the
present invention is the refrigeration apparatus according to any
of the first through third aspects of the present invention,
wherein the second refrigerant tubes have a third refrigerant tube
connecting the second heat exchanger and the main expansion
mechanism. The refrigeration apparatus further comprises a
branching expansion mechanism, a fifth refrigerant tube, sixth
refrigerant tubes, and a fourth heat exchanger. The branching
expansion mechanism depressurizes refrigerant. The fifth
refrigerant tube branches off from the third refrigerant tube and
extends to the branching expansion mechanism. The sixth refrigerant
tubes extend from the branching expansion mechanism to the first
refrigerant tube. The fourth heat exchanger performs heat exchange
between refrigerant flowing through the third refrigerant tube and
refrigerant flowing through the sixth refrigerant tubes.
[0022] With this refrigeration apparatus, it is possible to improve
the coefficient of performance by raising the degree of
supercooling of the refrigerant heading to the branching expansion
mechanism.
[0023] When the temperature of the refrigerant being mixed in from
the sixth refrigerant tubes is lower than the temperature of the
refrigerant flowing through the first refrigerant tube, it is also
possible to suppress excessive increases in the discharged
refrigerant temperature of the second compression element.
[0024] Furthermore, the quantity of refrigerant passing through the
second heat exchanger can be increased.
[0025] A refrigeration apparatus according to a seventh aspect of
the present invention is the refrigeration apparatus according to
the sixth aspect of the present invention, further comprising
temperature sensory units and a branched quantity control unit. The
temperature sensory units sense at least the air temperature
surrounding the evaporator or the discharged refrigerant
temperature of at least the first compression element or the second
compression element. The branched quantity control unit controls
the branching expansion mechanism and increases the quantity of
refrigerant passing through when the following condition is
fulfilled: the air temperature is lower than a predetermined
low-temperature air temperature when the value sensed by the
temperature sensory units is an air temperature, or the refrigerant
temperature is higher than a predetermined high-temperature
refrigerant temperature when the value sensed by the temperature
sensory units is a refrigerant temperature. The control by the
branched quantity control unit for increasing the quantity of
refrigerant passing through the branching expansion mechanism
herein includes control for creating a flow from conditions of a
flow rate of zero (no flow), for example.
[0026] With this refrigeration apparatus, even in cases in which
the temperature of the refrigerant discharged from the first
compression element or the second compression element will
presumably increase or cases in which the air temperature
surrounding the evaporator decreases, excessive increases in the
discharged refrigerant temperature of the second compression
element can be suppressed by increasing the quantity of refrigerant
passing through the branching expansion mechanism, and it is
possible to improve the reliability of the first compression
element or the second compression element.
[0027] A refrigeration apparatus according to an eighth aspect of
the present invention is the refrigeration apparatus according to
the sixth or seventh aspect of the present invention, further
comprising a water temperature sensory unit, a first refrigerant
temperature sensory unit, and a refrigerant distribution quantity
control unit. The water temperature sensory unit senses the
temperature of water flowing through any position in the water tube
system. The first refrigerant temperature sensory unit senses the
temperature of refrigerant passing through the first refrigerant
tube. The refrigerant distribution quantity control unit controls
the branching expansion mechanism and increases the quantity of
refrigerant passing through when the difference between the
temperature sensed by the water temperature sensory unit and the
temperature sensed by the first refrigerant temperature sensory
unit is less than a predetermined value.
[0028] With this refrigeration apparatus, even when the water's
effect of cooling the refrigerant flowing through the first
refrigerant tube is insufficient, it is possible to improve the
coefficient of performance of the refrigeration cycle by causing
the sixth refrigerant tubes to converge and thereby lowering the
temperature of the refrigerant passing through the first
refrigerant tube.
[0029] A refrigeration apparatus according to a ninth aspect of the
present invention is the refrigeration apparatus according to any
of the first through third aspects of the present invention,
wherein the second refrigerant tubes have a third refrigerant tube
connecting the second heat exchanger and the main expansion
mechanism. The refrigeration apparatus further comprises a
branching expansion mechanism, a fourth refrigerant tube, a third
heat exchanger, a fifth refrigerant tube, sixth refrigerant tubes,
and a fourth heat exchanger. The branching expansion mechanism
depressurizes refrigerant. The fourth refrigerant tubes connect the
evaporator and an intake side of the first compression element. The
third heat exchanger performs heat exchange between refrigerant
flowing through the third refrigerant tube and refrigerant flowing
through the fourth refrigerant tubes. The fifth refrigerant tube
branches off from the third refrigerant tube and extends to the
branching expansion mechanism. The sixth refrigerant tubes connect
the branching expansion mechanism and the first refrigerant tube.
The fourth heat exchanger performs heat exchange between
refrigerant flowing through the third refrigerant tube and
refrigerant flowing through the sixth refrigerant tubes.
[0030] With this refrigeration apparatus, it is possible to raise
the degree of supercooling of the refrigerant heading to the
branching expansion mechanism and improve the coefficient of
performance, and to apply the appropriate amount of heating to the
refrigerant drawn into the first compression element and prevent
liquid compression in the first compression element and/or cool the
refrigerant flowing through the third refrigerant tube.
[0031] A refrigeration apparatus according to a tenth aspect of the
present invention is the refrigeration apparatus according to the
ninth aspect of the present invention, further comprising
temperature sensory units and a branched heat quantity control
unit. The temperature sensory units sense at least the air
temperature surrounding the evaporator or the discharged
refrigerant temperature of at least the first compression element
or the second compression element. The branched heat quantity
control unit controls the branching expansion mechanism and
increases the quantity of refrigerant passing through when the
following condition is fulfilled: the air temperature is lower than
a predetermined low-temperature air temperature when the value
sensed by the temperature sensory units is an air temperature, or
the refrigerant temperature is higher than a predetermined
high-temperature refrigerant temperature when the value sensed by
the temperature sensory units is a refrigerant temperature. The
control by the branched quantity control unit for increasing the
quantity of refrigerant passing through the branching expansion
mechanism herein includes control for creating a flow from
conditions of a flow rate of zero (no flow), for example.
[0032] With this refrigeration apparatus, even in cases in which
the temperature of the refrigerant discharged from the compression
element will presumably increase or cases in which the air
temperature surrounding the evaporator decreases, excessive
increases in the discharged refrigerant temperature of the second
compression element can be suppressed by increasing the quantity of
refrigerant passing through the branching expansion mechanism, and
it is possible to improve the reliability of the second compression
element.
[0033] A refrigeration apparatus according to an eleventh aspect of
the present invention is the refrigeration apparatus according to
the ninth or tenth aspect of the present invention, further
comprising a first heat exchange bypass tube and a bypass switching
mechanism. The first heat exchange bypass tube connects one end and
another end of the portion of the first refrigerant tube that
passes through the first heat exchanger. The bypass switching
mechanism is capable of switching between a state in which
refrigerant flows through the portion of the first refrigerant tube
that passes through the first heat exchanger, and a state in which
refrigerant flows through the first heat exchange bypass tube.
[0034] With this refrigeration apparatus, in the first heat
exchanger, the switching of the bypass switching mechanism makes it
possible to switch between a state of allowing and a state of not
allowing the passage of refrigerant in the heat exchange bypass
tube, and also to adjust the usage condition of the first heat
exchanger.
[0035] A refrigeration apparatus according to a twelfth aspect of
the present invention is the refrigeration apparatus according to
the eleventh aspect of the present invention, further comprising
temperature sensory units and a bypass control unit. The
temperature sensory units sense at least the air temperature
surrounding the evaporator or the discharged refrigerant
temperature of at least the first compression element or the second
compression element. The bypass control unit controls the bypass
switching mechanism and increases the quantity of refrigerant
flowing through the portion of the first refrigerant tube that
passes through the first heat exchanger when the following
condition is fulfilled: the air temperature is higher than a
predetermined high-temperature air temperature when the value
sensed by the temperature sensory units is an air temperature, or
the refrigerant temperature is lower than a predetermined
low-temperature refrigerant temperature when the value sensed by
the temperature sensory units is a refrigerant temperature. The
control by the bypass control unit for increasing the quantity of
refrigerant passing through the portion of the first refrigerant
tube herein includes control for creating a flow from conditions of
a flow rate of zero (no flow), for example.
[0036] With this refrigeration apparatus, even in cases in which
the temperature of the refrigerant discharged from the compression
element will presumably be low or cases in which the air
temperature surrounding the evaporator has increased, the degree of
superheating of the refrigerant drawn into the second compression
element can be raised by reducing the quantity of refrigerant
flowing through the portion of the first refrigerant tube that
passes through the first heat exchanger, and it is possible to
comply with a high temperature requirement in the radiator.
[0037] A refrigeration apparatus according to a thirteenth aspect
of the present invention is the refrigeration apparatus according
to any of the ninth through twelfth aspects of the present
invention, further comprising a water temperature sensory unit, a
first refrigerant temperature sensory unit, and a
water-correspondent refrigerant quantity control unit. The water
temperature sensory unit senses the temperature of water flowing
through any position in the water tube system. The first
refrigerant temperature sensory unit senses the temperature of
refrigerant passing through the first refrigerant tube. The
water-correspondent refrigerant quantity control unit controls the
branching expansion mechanism and increases the quantity of
refrigerant passing through when the difference between the
temperature sensed by the water temperature sensory unit and the
temperature sensed by the first refrigerant temperature sensory
unit is less than a predetermined value.
[0038] With this refrigeration apparatus, even when the water's
effect of cooling the refrigerant flowing through the first
refrigerant tube is insufficient, it is possible to improve the
coefficient of performance of the refrigeration cycle by causing
the refrigerant passing through the sixth refrigerant tubes to mix,
thereby lowering the temperature of the refrigerant flowing through
the first refrigerant tube.
[0039] A refrigeration apparatus according to a fourteenth aspect
of the present invention is the refrigeration apparatus according
to any of the first through thirteenth aspects of the present
invention, further comprising a first drive unit for driving the
first compression element, and a second drive unit for driving the
second compression element independently of the first compression
element.
[0040] With this refrigeration apparatus, since the capacity of the
first compression element and the capacity of the second
compression element can be adjusted so as to be different, during
control for mixing the water flowing through the first branching
water tube and the water flowing through the second branching water
tube and attempting to bring the temperature of the water flowing
through the output water tube to a target temperature, the
coefficient of performance can be made satisfactory and the effect
of minimizing the compression work can be further improved by
separately adjusting the capacity of the first compression element
and the capacity of the second compression element.
[0041] A refrigeration apparatus according to a fifteenth aspect of
the present invention is the refrigeration apparatus according to
any of the first through thirteenth aspects of the present
invention, wherein the first compression element and the second
compression element have a shared rotating shaft for performing
compression work by rotatably driving each of the compression
elements.
[0042] With this refrigeration apparatus, vibrations and/or
fluctuations in torque load can be suppressed by driving the
compression elements while causing their centrifugal forces to
cancel each other out.
[0043] A refrigeration apparatus according to a sixteenth aspect of
the present invention is the refrigeration apparatus according to
any of the first through fifteenth aspects of the present
invention, wherein the active refrigerant is carbon dioxide.
[0044] In this refrigeration apparatus, with carbon dioxide in a
supercritical state near a critical point, the density of the
refrigerant can be changed dramatically merely by slightly changing
the refrigerant pressure. Therefore, the efficiency of the
refrigeration apparatus can be improved by a small amount of
compression work.
ADVANTAGEOUS EFFECTS OF INVENTION
[0045] As stated in the above descriptions, the following effects
are achieved according to the present invention.
[0046] In the first aspect, the refrigerant heading from the first
compression element toward the second compression element is cooled
to reliably improve compression efficiency, heat exchanging which
can raise the water temperature can be reliably performed by both
the first heat exchanger and the second heat exchanger, and the
coefficient of performance of the refrigeration apparatus can be
improved.
[0047] In the second aspect, it is possible for the water to be
heated efficiently.
[0048] In the third aspect, flow rate control for improving the
coefficient of performance of the refrigeration apparatus can be
performed automatically.
[0049] In the fourth aspect, it is possible to improve the
coefficient of performance, to suppress liquid compression in the
first compression element, and to increase the discharge
temperature to keep the resulting water temperature high.
[0050] In the fifth aspect, it is possible to increase the degree
of supercooling of the refrigerant headed to the main expansion
mechanism, and to improve the coefficient of performance.
[0051] In the sixth aspect, it is possible to improve the
coefficient of performance by raising the degree of supercooling of
the refrigerant heading to the branching expansion mechanism.
[0052] In the seventh aspect, it is possible to improve the
reliability of the first compression element or the second
compression element.
[0053] In the eighth aspect, even when the water's effect of
cooling the refrigerant flowing through the first refrigerant tube
is insufficient, it is possible to improve the coefficient of
performance of the refrigeration cycle.
[0054] In the ninth aspect, it is possible to improve the
coefficient of performance, and to prevent liquid compression in
the first compression element and/or cool the refrigerant flowing
through the third refrigerant tube.
[0055] In the tenth aspect, even in cases in which the temperature
of the refrigerant discharged from the compression element will
presumably increase or cases in which the air temperature
surrounding the evaporator decreases, it is possible to improve the
reliability of the second compression element.
[0056] In the eleventh aspect, it is possible to switch between a
state of allowing and a state of not allowing the passage of
refrigerant in the heat exchange bypass tube, and also to adjust
the usage condition.
[0057] In the twelfth aspect, even in cases in which the
temperature of the refrigerant discharged from the compression
element will presumably be low or cases in which the air
temperature surrounding the evaporator has increased, it is
possible to comply with a high temperature requirement in the
radiator.
[0058] In the thirteenth aspect, even when the water's effect of
cooling the refrigerant flowing through the first refrigerant tube
is insufficient, it is possible to improve the coefficient of
performance of the refrigeration cycle.
[0059] In the fourteenth aspect, the coefficient of performance can
be made satisfactory and the effect of minimizing the compression
work can be further improved.
[0060] In the fifteenth aspect, the occurrence of vibrations and/or
fluctuations in torque load can be suppressed by driving the
compression elements while causing their centrifugal forces to
cancel each other out.
[0061] In the sixteenth aspect, the efficiency of the refrigeration
apparatus can be improved by a small amount of compression
work.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1 is a schematic structural diagram of an
air-conditioning apparatus as an embodiment of the refrigeration
apparatus according to the first embodiment of the present
invention.
[0063] FIG. 2 is a pressure-enthalpy graph representing the
refrigeration cycle of the air-conditioning apparatus according to
the first embodiment.
[0064] FIG. 3 is a temperature-entropy graph representing the
refrigeration cycle of the air-conditioning apparatus according to
the first embodiment.
[0065] FIG. 4 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1 of the first
embodiment.
[0066] FIG. 5 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 2 of the first
embodiment.
[0067] FIG. 6 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 3 of the first
embodiment.
[0068] FIG. 7 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 7 of the first
embodiment.
[0069] FIG. 8 is a schematic structural diagram of an
air-conditioning apparatus as an embodiment of the refrigeration
apparatus according to the second embodiment of the present
invention.
[0070] FIG. 9 is a pressure-enthalpy graph representing the
refrigeration cycle of the air-conditioning apparatus according to
the second embodiment.
[0071] FIG. 10 is a temperature-entropy graph representing the
refrigeration cycle of the air-conditioning apparatus according to
the second embodiment.
[0072] FIG. 11 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1 of the
second embodiment.
[0073] FIG. 12 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 5 of the
second embodiment.
[0074] FIG. 13 is a schematic structural diagram of an
air-conditioning apparatus as an embodiment of a refrigeration
apparatus according to the third embodiment of the present
invention.
[0075] FIG. 14 is a pressure-enthalpy graph representing the
refrigeration cycle of an air-conditioning apparatus according to
the third embodiment.
[0076] FIG. 15 is a temperature-entropy graph representing the
refrigeration cycle of an air-conditioning apparatus according to
the third embodiment.
[0077] FIG. 16 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1 of the third
embodiment.
[0078] FIG. 17 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 4 of the third
embodiment.
[0079] FIG. 18 is a schematic structural diagram of an
air-conditioning apparatus as an embodiment of a refrigeration
apparatus according to the fourth embodiment of the present
invention.
[0080] FIG. 19 is a pressure-enthalpy graph representing the
refrigeration cycle of an air-conditioning apparatus according to
the fourth embodiment.
[0081] FIG. 20 is a temperature-entropy graph representing the
refrigeration cycle of an air-conditioning apparatus according to
the fourth embodiment.
[0082] FIG. 21 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1 of the
fourth embodiment.
[0083] FIG. 22 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 2 of the
fourth embodiment.
[0084] FIG. 23 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 3 of the
fourth embodiment.
[0085] FIG. 24 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 4 of the
fourth embodiment.
[0086] FIG. 25 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 8 of the
fourth embodiment.
DESCRIPTION OF EMBODIMENTS
<1> First Embodiment
<1-1> Configuration of Air-Conditioning Apparatus
[0087] FIG. 1 is a schematic structural diagram of a water heater 1
as an embodiment of the refrigeration apparatus according to the
present invention. The water heater 1 is an apparatus for producing
heated water by using refrigerant that operates in a supercritical
range (carbon dioxide in this case) to perform a two-stage
compression-type refrigeration cycle.
[0088] The water heater 1 has a water circuit 910 and a refrigerant
circuit 10.
[0089] (Water Circuit)
[0090] The water circuit 910 has a water inlet tube 901 for leading
water supplied from the exterior to a water branching point W, heat
source water tubes 902, 903 and intermediate water tubes 904, 905
extending from the branching point W, and a water outlet tube 906
leading out to the exterior from a convergent point Z where the
heat source water tubes 902, 903 and the intermediate water tubes
904, 905 converge, as shown in FIG. 1.
[0091] A pump 921 capable of adjusting the quantity of water
passing through is provided to the water inlet tube 901. This pump
921 is provided with a motor 921m, the rotational speed is adjusted
by a control unit 99, and the flow rate of the pump is adjusted.
The water circuit 910 is also provided with a water temperature
sensor 910T for detecting the temperature of the water passing
through the water inlet tube 901. Through the water temperature
sensor 910T, the control unit 99 can perceive the temperature of
the supplied water, the control unit 99 perceives the difference
from the output water temperature requested by the user, and a
refrigeration cycle of the refrigerant circuit 10 is adjusted.
[0092] The heat source water tube 902 extends from the branching
point W to a heat source-side heat exchanger 4 of the refrigerant
circuit 10, described hereinafter. The heat source water tube 903
extends so as to lead water flowing out of the heat source-side
heat exchanger 4 to the convergent point Z. Thus, the water flowing
through the heat source water tubes 902, 903 is warmed in the heat
source-side heat exchanger 4 by heat exchange with the refrigerant
flowing through the refrigerant circuit 10, and heated water is
produced. A tube configuration is created so that the refrigerant
and water flow opposite each other in an intercooler 7, and the
heat exchange efficiency is improved.
[0093] The intermediate water tube 904 extends from the branching
point W to the intercooler 7 of the refrigerant circuit 10,
described hereinafter. The intermediate water tube 905 extends so
as to lead the water flowing out of the intercooler 7 to the
convergent point Z. Thus, the water flowing through the
intermediate water tubes 904, 905 is warmed in the intercooler 7 by
heat exchange with the refrigerant flowing through the refrigerant
circuit 10, and heated water is produced. A tube configuration is
created so that the refrigerant and water flow opposite each other
in the heat source-side heat exchanger 4, and the heat exchange
efficiency is improved. Since the refrigerant temperature in the
intermediate water tubes 904, 905, which is the target of heat
exchange, is lower than the refrigerant temperature in the heat
source-side heat exchanger 4, the intermediate water tubes 904, 905
are designed to be smaller in diameter than the heat source water
tubes 902, 903 in order to ensure that the water heating will take
place primarily in the heat source-side heat exchanger 4.
[0094] Hot water which has been warmed in the heat source water
tubes 902, 903 and in the intermediate water tubes 904, 905 and
mixed at the convergent point Z is then supplied to the user
through the water outlet tube 906.
[0095] (Refrigerant Circuit)
[0096] The refrigerant circuit 10 has primarily a low-stage
compression element 2c, a high-stage compression element 2d, the
heat source-side heat exchanger 4, an expansion mechanism 5, a
usage-side heat exchanger 6, an intermediate refrigerant tube 22,
an intercooler 7, connection tubes 71, 72, 76 or the like
connecting these components, and a usage-side temperature sensor
6T.
[0097] In the present embodiment, the low-stage compression element
2c and the high-stage compression element 2d compress the
refrigerant sequentially in two stages.
[0098] The low-stage compression element 2c has a hermetically
sealed structure in which a compressor drive motor 21b and a drive
shaft 21c are housed within a casing 21a. The compressor drive
motor 21b is linked to the drive shaft 21c. This drive shaft 21c is
linked to the compression element 2c. The compression element 2c is
a rotary-type, scroll-type, or another type of positive
displacement compression element in the present embodiment. The
low-stage compression element 2c draws refrigerant in from an
intake tube 2a, compresses the drawn-in refrigerant, and discharges
the refrigerant toward the intermediate refrigerant tube 22. The
intermediate refrigerant tube 22 connects the discharge side of the
low-stage compression element 2c and the intake side of the
high-stage compression element 2d via the intercooler 7. A
discharge tube 2b is a refrigerant tube for feeding the refrigerant
discharged from the low-stage compression element 2c to the
high-stage compression element 2d via the intercooler 7, and the
discharge tube 2b is provided with a non-return mechanism 42c and a
mechanism for separating the refrigerant from refrigeration oil
which accompanies the refrigerant discharged from the low-stage
compression element 2c and returning the refrigeration oil to the
intake side of the low-stage compression element 2c. The mechanism
for returning the refrigeration oil has primarily an oil separator
41a for separating the refrigerant from the refrigeration oil
accompanying the refrigerant discharged from the low-stage
compression element 2c, and an oil return tube 41b which is
connected to the oil separator 41a and which returns the
refrigeration oil separated from the refrigerant to the intake tube
2a of the low-stage compression element 2c. The oil return tube 41b
is provided with a depressurization mechanism 41c for
depressurizing the refrigeration oil flowing through the oil return
tube 41b. A capillary tube is used as the depressurization
mechanism 41c in the present embodiment. The non-return mechanism
42c is a mechanism for allowing the flow of refrigerant from the
discharge side of the low-stage compression element 2c to the
intercooler 7 and blocking the flow of refrigerant from the
intercooler 7 to the discharge side of the low-stage compression
element 2c, and a non-return valve is used in the present
embodiment.
[0099] The high-stage compression element 2d is similar to the
low-stage compression element 2c, and has a hermetically sealed
structure in which a compressor drive motor 21e and a drive shaft
21f are housed within a casing 21d. The compressor drive motor 21e
is linked to the drive shaft 21f. This drive shaft 21f is linked to
the compression element 2d. The compression element 2d is a
rotary-type, scroll-type, or another type of positive displacement
compression element in the present embodiment. The high-stage
compression element 2d draws refrigerant in from the intermediate
refrigerant tube 22, compresses the drawn-in refrigerant, and
discharges the refrigerant toward a discharge tube 2e. The
discharge tube 2e connects the discharge side of the high-stage
compression element 2d and the heat source-side heat exchanger 4.
The discharge tube 2e is provided with a non-return mechanism 42d
and a mechanism for separating the refrigerant from refrigeration
oil which accompanies the refrigerant discharged from the
high-stage compression element 2d and returning the refrigeration
oil to the intake side of the high-stage compression element 2d.
The mechanism for returning the refrigeration oil has primarily an
oil separator 41d for separating the refrigerant from the
refrigeration oil accompanying the refrigerant discharged from the
high-stage compression element 2d, and an oil return tube 41e which
is connected to the oil separator 41d and which returns the
refrigeration oil separated from the refrigerant to the
intermediate refrigerant tube 22, which is on the intake side of
the high-stage compression element 2d. The oil return tube 41e is
provided with a depressurization mechanism 41f for depressurizing
the refrigeration oil flowing through the oil return tube 41e. A
capillary tube is used as the depressurization mechanism 41f in the
present embodiment. The non-return mechanism 42d is a mechanism for
allowing the flow of refrigerant from the discharge side of the
high-stage compression element 2d to the heat source-side heat
exchanger 4 and blocking the flow of refrigerant from the heat
source-side heat exchanger 4 to the discharge side of the
high-stage compression element 2d, and a non-return valve is used
in the present embodiment.
[0100] That is, the two compression elements 2c, 2d are connected
to each other in series and are linked to their respective
individual drive shafts 21c, 21f, and the two compression elements
2c, 2d have two-stage compression structures in which they are
rotatably driven individually by respective compressor drive motors
21b, 21e.
[0101] The intercooler 7 warms the water flowing through the
intermediate water tubes 904, 905 by the heat of the refrigerant
flowing through the intermediate refrigerant tube 22, and cools the
refrigerant flowing through the intermediate refrigerant tube 22 by
the water flowing through the intermediate water tubes 904, 905.
The degree of superheating of the refrigerant drawn into the
high-stage compression element 2d can thereby be reduced, and the
temperature of the refrigerant discharged from the high-stage
compression element 2d is prevented from increasing excessively.
The refrigeration capacity can also be improved because the density
of the refrigerant drawn into the high-stage compression element 2d
is increased by lowering the temperature of the refrigerant flowing
through the intermediate refrigerant tube 22 in this manner.
[0102] The heat source-side heat exchanger 4 is a heat exchanger
which has air as a heat source and functions as a radiator of
refrigerant. The heat source-side heat exchanger 4 is connected at
one end to the discharge side of the high-stage compression element
2d via the connection tube 71 and the non-return mechanism 42, and
is connected at the other end to the expansion mechanism 5 via the
connection tube 72. In this heat source-side heat exchanger 4, the
water flowing through the heat source water tubes 902, 903 is
heated by the refrigerant heading from the connection tube 71 to
the connection tube 72, and the refrigerant heading from the
connection tube 71 to the connection tube 72 is cooled by the water
flowing through the heat source water tubes 902, 903.
[0103] The expansion mechanism 5 is connected at one end to the
connection tube 72, and is connected at the other end to the
usage-side heat exchanger 6 via the connection tube 76. The
expansion mechanism 5 is a mechanism for depressurizing the
refrigerant, and an electric expansion valve is used in the present
embodiment. In the present embodiment, the expansion mechanism 5
depressurizes the high-pressure refrigerant cooled in the heat
source-side heat exchanger 4 nearly to the saturation pressure of
the refrigerant before feeding the refrigerant to the usage-side
heat exchanger 6.
[0104] The usage-side heat exchanger 6 is a heat exchanger which
functions as an evaporator of refrigerant. The usage-side heat
exchanger 6 is connected at one end to the expansion mechanism 5
via the connection tube 76, and is connected at the other end to
the intake side of the low-stage compression element 2c via the
intake tube 2a. Though not shown in the diagram, the usage-side
heat exchanger 6 is supplied with water and/or air as a heating
source for performing heat exchange with the refrigerant flowing
through the usage-side heat exchanger 6.
[0105] The usage-side temperature sensor 6T detects the temperature
of the water and/or air supplied as a heating source in order to
perform heat exchange with the refrigerant flowing through the
usage-side heat exchanger 6 described above.
[0106] As described above, the water heater 1 is provided with a
control unit 99 which perceives the temperature sensed by the
usage-side temperature sensor 6T, and which controls the actions of
the low-stage compression element 2c, the high-stage compression
element 2d, the expansion mechanism 5, the pump 921, and other
components constituting the water heater 1.
<1-2> Action of Air-Conditioning Apparatus
[0107] Next, the action of the water heater 1 of the present
embodiment will be described using FIGS. 1, 2 and 3.
[0108] Herein, FIG. 2 is a pressure-enthalpy graph representing the
refrigeration cycle, and FIG. 3 is a temperature-entropy graph
representing the refrigeration cycle.
[0109] The states of the refrigerant at the points indicated by A,
B, C, D, K, and M in the refrigerant circuit 10 of FIG. 1
correspond to the same points in the pressure-enthalpy graph shown
in FIG. 2 and the temperature-entropy graph shown in FIG. 3.
[0110] In this refrigeration cycle, the refrigerant flowing through
the intermediate refrigerant tube 22 is cooled by the refrigerant
flowing through the intermediate water tubes 904, 905 of the water
circuit 910 when passing through the intercooler 7 (refer to point
B point C in FIGS. 2 and 3).
[0111] (Target Capacity Output Control)
[0112] In this type of refrigeration cycle, the control unit 99
performs target capacity output control as follows.
[0113] First, the control unit 99 receives an input value of output
water temperature and an input value of a required output water
quantity from the user via a controller or the like (not shown).
The control unit 99 controls the flow rate of water by controlling
the rotational speed of the motor 921m of the pump 921 on the basis
of the input value of the required output water quantity.
[0114] The control unit 99 then perceives the water temperature
detected by the water temperature sensor 910T and the flow rate
controlled by the motor 921m of the pump 921, and calculates
emitted heat quantity required for the refrigerant supplied to the
heat source-side heat exchanger 4. Based on this required emitted
heat quantity, the control unit 99 then calculates the target
discharge pressure for the pressure of the refrigerant discharged
from the high-stage compression element 2d.
[0115] A case of a target discharge pressure being the target value
in the target capacity output control is herein described as an
example, but instead of the target discharge pressure, target
values of the discharged refrigerant pressure and the discharged
refrigerant temperature may be established so that the value
obtained by multiplying the discharged refrigerant temperature by
the discharged refrigerant pressure is within a predetermined
range. This is because in cases in which the load has changed, the
density of the discharged refrigerant decreases when the degree of
superheating of the drawn-in refrigerant is high; therefore, even
if it is possible to maintain the temperature of the refrigerant
discharged from the high-stage compression element 2d, it becomes
impossible to guarantee the emitted heat quantity required in the
heat source-side heat exchanger 4.
[0116] Next, based on the temperature sensed by the usage-side
temperature sensor 6T, the control unit 99 establishes a target
evaporation temperature and a target evaporation pressure (a
pressure equal to or less than the critical pressure). This setting
of the target evaporation pressure is performed every time the
temperature sensed by the usage-side temperature sensor 6T
changes.
[0117] Based on this target evaporation temperature value, the
control unit 99 performs superheat degree control so that the
degree of superheating of the refrigerant drawn in by the low-stage
compression element 2c is a target value x (degree of superheating
target value) of 5.degree. C. or less.
[0118] The control unit 99 then controls the low-stage compression
element 2c so as to raise the refrigerant pressure and refrigerant
temperature while causing isentropic change for maintaining the
entropy value at the degree of superheating established in this
manner, and refrigerant is discharged to the intermediate
refrigerant tube 22. In the intercooler 7 provided to the
intermediate refrigerant tube 22, heat exchange is performed while
the water and refrigerant flow against each other, the refrigerant
is cooled by the water flowing through the intermediate water tubes
904, 905, and the water flowing through the intermediate water
tubes 904, 905 is heated. Thus, the refrigerant flowing through the
intermediate refrigerant tube 22 is cooled in the intercooler 7 and
drawn into the high-stage compression element 2d. In the high-stage
compression element 2d, refrigerant is discharged at a pressure
exceeding the critical pressure due to the operating capacity being
controlled by controlling the rotational speed. Having been
increased in temperature by being further compressed by the
high-stage compression element 2d in this manner, the refrigerant
is fed to the heat source-side heat exchanger 4. In the heat
source-side heat exchanger 4, heat exchange is performed while the
high-temperature, high-pressure refrigerant in a supercritical
state and the water flow against each other, and water having the
target output water temperature is obtained.
[0119] In this heat radiation process in the heat source-side heat
exchanger 4, since the refrigerant is in a supercritical state, the
refrigerant temperature continuously decreases while the pressure
is being changed such that the refrigerant is maintained at the
target discharge pressure as an isobaric change. The refrigerant
flowing through the heat source-side heat exchanger 4 has a
temperature equal to or greater than the temperature of the water
supplied as a heating target through the heat source water tubes
902, 903, and the refrigerant is cooled to a value y near the water
supplied as a heating target. The value of y changes due to the
supplied quantity being controlled by the motor 921m of the pump
921.
[0120] The refrigerant cooled in the heat source-side heat
exchanger 4 in this manner is depressurized to the target
evaporation pressure (a pressure equal to or less than the critical
pressure) by the expansion mechanism 5, and the refrigerant flows
into the usage-side heat exchanger 6.
[0121] The refrigerant flowing through the usage-side heat
exchanger 6 absorbs heat from the water and/or air supplied as a
heating source, whereby the dryness of the refrigerant is
progressively improved while isobaric-isothermal change is
conducted such that the target evaporation temperature and the
target evaporation pressure are maintained. The control unit 99
then controls the quantity supplied by a heating source supply
device (not shown) (a pump in the case of water, and a fan or the
like in the case of air) so that the degree of superheating reaches
the degree of superheating target value.
[0122] When performing control in this manner, the control unit 99
calculates the value of x and the value of y so that the
coefficient of performance (COP) in the refrigeration cycle will be
as high as possible, and performs the target capacity output
control described above. When calculating the value of x and the
value of y which yield the best coefficient of performance, the
control unit 99 performs the calculation on the basis of the
properties (a Mollier diagram or the like) of carbon dioxide as the
active refrigerant. A condition may be established at which the
coefficient of performance can be satisfactorily maintained to a
certain extent, and if this condition is met, the value of x and
the value of y may be determined such that the compression work
will be a smaller value. Another option is to use a precondition
that the compression work is suppressed to a predetermined value or
lower, and to determine the value of x and the value of y which
yield the best coefficient of performance while this precondition
is being met.
[0123] The relationship between heat radiation quantity control
guaranteed in the heat source-side heat exchanger 4 and/or the
intermediate refrigerant tube 22 of the refrigerant circuit 10 and
flow rate control of the pump 921, which are performed by the
control unit 99, includes a large adjustment of the flow rate of
the pump 921 of the water circuit 910 or another action when the
refrigerant circuit 10 is controlled so that the heat radiation
quantity in the heat source-side heat exchanger 4 and/or the
intermediate refrigerant tube 22 increases, for example. This
relationship between heat radiation quantity control and flow rate
control also includes control for minimizing the flow rate of the
pump 921 of the water circuit 910 when, conversely, a large heat
radiation quantity cannot be achieved in the heat source-side heat
exchanger 4 and/or the intermediate refrigerant tube 22. The
control unit 99 gives less priority to controlling the output water
quantity than to the output water temperature while achieving the
output water temperature requested by the user.
[0124] (Characteristics of First Embodiment)
[0125] The water that has branched off in the branching point W and
that flows through the intermediate water tubes 904, 905 is water
that has not been heated in the heat source-side heat exchanger 4,
and this water has the same temperature as the temperature of the
refrigerant flowing through the water inlet tube 901. During
control performed by the control unit 99, in the refrigerant
circuit 10 which uses carbon dioxide as the active refrigerant,
degree of superheating control is performed so that the degree of
superheating reaches a target value x of 5.degree. C. or less, and
the compression ratio in the low-stage compression element 2c and
the compression ratio in the high-stage compression element 2d are
adjusted so as to be equal. Therefore, according to the properties
of carbon dioxide in a Mollier diagram, the temperature of the
refrigerant flowing through the heat source-side heat exchanger 4
is inevitably higher than the temperature of the refrigerant
flowing through the intercooler 7. Thus, in a refrigeration cycle
in which the temperature of the refrigerant flowing through the
intercooler 7 and the temperature of the refrigerant flowing
through the heat source-side heat exchanger 4 are different and the
temperature of the refrigerant flowing through the intercooler 7 is
the lower of the two, in order to achieve the refrigeration cycle
effect by way of the intercooler 7, i.e., effect of cooling the
refrigerant drawn into the high-stage compression element 2d, the
refrigeration cycle is limited to cases in which the temperature of
the water flowing through the intermediate water tubes 904, 905 is
lower than the temperature of the refrigerant flowing through the
intermediate refrigerant tube 22. Therefore, if the water flowing
into the intercooler 7 has already been heated to a certain extent
in the heat source-side heat exchanger 4 before flowing into the
intercooler 7, not only is this effect of cooling the refrigerant
drawn into the high-stage compression element 2d lessened, but the
reverse effect will sometimes occur when the temperature of the
water flowing through the intermediate water tubes 904, 905 is
higher than the temperature of the refrigerant flowing through the
intermediate refrigerant tube 22. As a countermeasure to this, in
the water heater 1 of the present embodiment, the water flowing
into the intercooler 7 can be made to flow into the intercooler 7
via the intermediate water tube 904 without taking heat from the
exterior after the water has branched off at the branching point W.
Therefore, the effect of cooling the refrigerant drawn into the
high-stage compression element 2d can be achieved merely due to the
temperature of the water flowing through the water inlet tube 901
at least being lower than the temperature of the refrigerant
flowing through the intermediate refrigerant tube 22, and it is
possible to prevent this effect from lessening or to prevent the
reverse effect from occurring due to the water flowing through the
intermediate water tubes 904, 905 being heated before flowing into
the intercooler 7.
<1-3> Modification 1
[0126] As one example of control by the control unit 99 in the
embodiment described above, the following type of control can be
performed, for example.
[0127] In this example, the design pressure resistance of the
low-stage compression element 2c and the high-stage compression
element 2d is 12 MPa, and the discharged refrigerant pressure must
be maintained at or below this design pressure resistance.
[0128] In cases in which the control unit 99 establishes the
discharged refrigerant temperature on the basis of the input value
of the output water temperature from the user, the target discharge
pressure and target discharge temperature are established so as to
achieve a refrigerant pressure and refrigerant temperature which
are equal to or less than the design pressure described above and
which can guarantee a heat radiation quantity of the refrigerant
supplied to the heat source-side heat exchanger 4. The target state
of the discharged refrigerant thereby converges at one point in a
Mollier diagram of the refrigeration cycle which uses carbon
dioxide as the active refrigerant.
[0129] On the other hand, the target evaporation pressure of the
refrigeration cycle is established according to the temperature
sensed by the usage-side temperature sensor 6T.
[0130] In cases in which a control is performed so that the
compression ratio in the low-stage compression element 2c and the
compression ratio in the high-stage compression element 2d are
equal, the target intermediate pressure flowing through the
intermediate refrigerant tube 22 is established according to the
above-described relationship between the target discharge pressure
and the evaporation pressure.
[0131] When the degree of superheating of the refrigerant drawn
into the low-stage compression element 2c is set at 5.degree. C.,
the discharged refrigerant temperature and pressure are established
by causing isentropic change in the low-stage compression element
2c. Furthermore, if isentropic change takes place in the high-stage
compression element 2d so that the target discharge pressure and
target discharge temperature can be achieved, the temperature of
the refrigerant drawn into the high-stage compression element 2d is
established.
[0132] The quantity of cold energy needed to cool the refrigerant
discharged from the low-stage compression element 2c until it is
drawn into the high-stage compression element 2d is thereby
established, and the control unit 99 may control the flow rate of
the pump 921 on the basis of the value detected by the water
temperature sensor 910T so that this cold energy quantity can be
supplied.
[0133] The degree of superheating is not limited to 5.degree. C.,
and can be selected within a range of 0 to 5.degree. C. The
temperature of the refrigerant flowing into the expansion mechanism
5 is also adjustable, and the value of x and the value of y may be
established so as to yield the best coefficient of performance of
the refrigeration cycle while these values are being adjusted.
<1-4> Modification 2
[0134] As shown in FIG. 4, for example, a refrigerant circuit 10A
may be used which has a discharged refrigerant temperature sensor
2T for sensing the temperature of the refrigerant discharged from
the high-stage compression element 2d.
[0135] If the temperature detected by this discharged refrigerant
temperature sensor 2T is too high, it will not be possible to
maintain the reliability of the high-stage compression element 2d,
and the control unit 99 may therefore perform control for reducing
the flow rate of the pump 921 while reducing the discharged
refrigerant temperature.
[0136] It is thereby possible to achieve the output water
temperature requested by the user while guaranteeing the
reliability of the high-stage compression element 2d.
<1-5> Modification 3
[0137] In the embodiment described above, an example was described
in which the diameters of the intermediate water tubes 904, 905 are
designed to be smaller than the diameters of the heat source water
tubes 902, 903.
[0138] However, the present invention is not limited to this
example, and another option is to use a refrigerant circuit 10B
provided with a flow rate ratio adjustment mechanism 911 capable of
adjusting the ratio between the quantity of water flowing through
the intermediate water tubes 904, 905 and the quantity of water
flowing through the heat source water tubes 902, 903, as shown in
FIG. 5, for example.
[0139] For example, the flow rate ratio adjustment mechanism 911
can be provided at an intermediate point in the intermediate water
tubes 904, 905. The flow rate ratio can thereby be adjusted even if
the diameters of the intermediate water tubes 904, 905 and the
diameters of the heat source water tubes 902, 903 are the same.
[0140] When the flow rate ratio between the quantity of water
flowing through the heat source water tubes 902, 903 and the
quantity of water flowing through the intermediate water tubes 904,
905 is adjusted, the control unit 99 may control the flow rate
ratio so as to achieve equality between the ratio of the heating
amount in the heat source-side heat exchanger 4 and the heating
amount in the intercooler 7 as obtained from the Mollier diagram,
and the ratio of the quantity of water flowing through the heat
source water tubes 902, 903 and the quantity of water flowing
through the intermediate water tubes 904, 905, for example. The
heating amount in the intercooler 7 in this case can be perceived
according to an intermediate specific enthalpy (point
B.fwdarw.point C in the Mollier diagram) obtained by subtracting
the specific enthalpy of the refrigerant discharged from the
low-stage compression element 2c from the specific enthalpy of the
refrigerant drawn into the high-stage compression element 2d. The
heating amount in the heat source-side heat exchanger 4 can be
perceived according to a heat source specific enthalpy (point
D.fwdarw.point K in the Mollier diagram) obtained by subtracting
the specific enthalpy of the refrigerant discharged from the
high-stage compression element 2d from the specific enthalpy of the
refrigerant in the outlet of the heat source-side heat exchanger 4.
Thus, the control unit 99 performs a control so that the ratio of
the quantity of water flowing through the heat source water tubes
902, 903 and the quantity of water flowing through the intermediate
water tubes 904, 905 is equal to the ratio of the heat source
specific enthalpy and the intermediate specific enthalpy. When the
value of the heat source specific enthalpy and/or the intermediate
specific enthalpy changes during adjustment of the flow rate ratio
by control, the control unit 99 may perform feedback control in
accordance with predetermined time intervals (or a predetermined
degree of ratio deviation) so as to adapt to the ratio between the
heat source specific enthalpy and the intermediate specific
enthalpy at the point in time of the change.
[0141] Instead of merely performing control using the values of the
heat source specific enthalpy and/or the intermediate specific
enthalpy in this manner, the control unit 99 may control the ratio
between the quantity of water flowing through the heat source water
tubes 902, 903 and the quantity of water flowing through the
intermediate water tubes 904, 905 so that the outlet temperature of
the heat source-side heat exchanger 4 in the heat source water tube
903 and the outlet temperature of the intercooler 7 in the
intermediate water tube 905 are substantially equal, for example.
The control unit 99 may cause the outlet temperatures to coincide
through a predetermined feedback control in this case as well.
[0142] In cases in which the intention is to increase only the
quantity of water in the heat source water tubes 902, 903, for
example, it is possible for the control unit 99 to also make
adjustments for increasing the quantity of water flowing through
the heat source water tubes 902, 903 while maintaining a constant
quantity of water flowing through the intermediate water tubes 904,
905, by increasing the rotational speed of the motor of the pump
921 to increase the flow rate and by narrowing the opening degree
of the flow rate ratio adjustment mechanism 911.
[0143] The control unit 99 can thereby perform control for bringing
the coefficient of performance of the refrigeration cycle to a
satisfactory value in an operation for achieving not only the
user's desired output water temperature but the user's desired
output water quantity as well.
<1-6> Modification 4
[0144] Another possibility, for example, is to use a refrigerant
circuit 10C which is provided with a heat source refrigerant
temperature sensor 4T for detecting the temperature of the
refrigerant passing through the heat source-side heat exchanger 4,
a heat source refrigerant pressure sensor 4P for detecting the
pressure of the refrigerant passing through the heat source-side
heat exchanger 4, an intermediate refrigerant temperature sensor
22T for detecting the temperature of the refrigerant passing
through the intermediate refrigerant tube 22, an intermediate
refrigerant pressure sensor 22P for detecting the pressure of the
refrigerant passing through the intermediate refrigerant tube 22,
and the flow rate ratio adjustment mechanism 911 shown in
Modification 3.
[0145] The radiated heat quantity that can be supplied to the water
from the refrigerant in the heat source-side heat exchanger 4 can
be perceived according to the values sensed by the heat source
refrigerant temperature sensor 4T for detecting the temperature of
the refrigerant passing through the heat source-side heat exchanger
4 and the heat source refrigerant pressure sensor 4P for detecting
the pressure of the refrigerant passing through the heat
source-side heat exchanger 4, and the heat radiation quantity that
can be supplied to the water from the refrigerant in the
intercooler 7 can be perceived according to the values sensed by
intermediate refrigerant temperature sensor 22T for detecting the
temperature of the refrigerant passing through the intermediate
refrigerant tube 22 and the intermediate refrigerant pressure
sensor 22P for detecting the pressure of the refrigerant passing
through the intermediate refrigerant tube 22. Therefore, the
control unit 99 can adjust the opening degree of the flow rate
ratio adjustment mechanism 911 so as to adapt to the radiated heat
quantity that can be supplied to the water from the refrigerant in
the heat source-side heat exchanger 4 and the heat radiation
quantity that can be supplied to the water from the refrigerant in
the intercooler 7, and the control unit 99 can perform control so
as to achieve an efficient flow rate ratio for obtaining the
required output water temperature.
<1-7> Modification 5
[0146] In Modification 4 described above, a water circuit 910
provided with a flow rate ratio adjustment mechanism 911 was
described as an example.
[0147] However, the present invention is not limited to this
example, and a water circuit may be used in which an on/off valve
is provided to the heat source water tubes 902, 903 and an on/off
valve is also provided to the intermediate water tubes 904, 905,
instead of the flow rate ratio adjustment mechanism 911, for
example.
<1-8> Modification 6
[0148] In the embodiment described above, an example of a
refrigerant circuit was described in which only one two-stage
compression mechanism was provided, wherein compression took place
in two stages in the low-stage compression element 2c and the
high-stage compression element 2d.
[0149] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit
wherein the aforementioned two-stage compression mechanisms which
perform compression in two stages are provided in parallel to each
other, for example.
[0150] In the refrigerant circuit, a plurality of usage-side heat
exchangers 6 may be disposed in parallel to each other. In this
case, a refrigerant circuit may be used in which expansion
mechanisms are disposed immediately ahead of the respective
usage-side heat exchangers so that the quantity of refrigerant
supplied to the usage-side heat exchangers 6 can be controlled, and
the expansion mechanisms are also disposed in parallel to each
other.
<1-9> Modification 7
[0151] In the embodiment described above, an example was described
in which the low-stage compression element 2c and the high-stage
compression element 2d were provided with separate drive shafts
21c, 21f and compressor drive motors 21b, 21e.
[0152] However, the present invention is not limited to this
example; another possibility is a refrigerant circuit 10D which
uses a compression mechanism 2 having a shared drive shaft 121c
which is a drive shaft shared by the low-stage compression element
2c and the high-stage compression element 2d, wherein one shared
compressor drive motor 121b is used to transmit drive force to the
shared drive shaft 121c, as shown in FIG. 7, for example.
[0153] This compression mechanism 2 has a hermetically sealed
structure in which the compressor drive motor 121b, the shared
drive shaft 121c, and the compression elements 2c, 2d are housed
within a casing 21a. The shared compressor drive motor 121b is
linked to the shared drive shaft 121c. This shared drive shaft 121c
is linked to the two compression elements 2c, 2d. That is, the
compression mechanism has a so-called single-shaft two-stage
compression structure in which the two compression elements 2c, 2d
are linked to a single shared drive shaft 121c, and the two
compression elements 2c, 2d are both rotatably driven by the shared
compressor drive motor 121b. The compression elements 2c, 2d are
rotary-type, scroll-type, or another type of positive displacement
compression elements. The low-stage compression element 2c draws
refrigerant in from an intake tube 2a, compresses the drawn-in
refrigerant, and discharges the refrigerant toward the intermediate
refrigerant tube 22. The intermediate refrigerant tube 22 connects
the discharge side of the low-stage compression element 2c and the
intake side of the high-stage compression element 2d via the
intercooler 7. The high-stage compression element 2d further
compresses the refrigerant drawn in via the intermediate
refrigerant tube 22 and then discharges the refrigerant to the
discharge tube 2b. In FIG. 7, the discharge tube 2b is a
refrigerant tube for feeding the refrigerant discharged from the
compression mechanism 2 to the heat source-side heat exchanger 4,
and the discharge tube 2b is provided with an oil separation
mechanism 41 and a non-return mechanism 42. The oil separation
mechanism 41 is a mechanism for separating the refrigerant from
refrigeration oil which accompanies the refrigerant discharged from
the compression mechanism 2 and returning the refrigeration oil to
the intake side of the compression mechanism 2, and the oil
separation mechanism 41 has primarily an oil separator 41a for
separating the refrigerant from the refrigeration oil accompanying
the refrigerant discharged from the compression mechanism 2, and an
oil return tube 41b which is connected to the oil separator 41a and
which returns the refrigeration oil separated from the refrigerant
to the intake tube 2a of the compression mechanism 2. The oil
return tube 41b is provided with a depressurization mechanism 41c
for depressurizing the refrigeration oil flowing through the oil
return tube 41b. A capillary tube is used as the depressurization
mechanism 41c. The non-return mechanism 42 is a mechanism for
allowing the flow of refrigerant from the discharge side of the
compression mechanism 2 to the heat source-side heat exchanger 4
and blocking the flow of refrigerant from the heat source-side heat
exchanger 4 to the discharge side of the compression mechanism 2,
and a non-return valve is used.
[0154] Thus, the compression mechanism 2 has two compression
elements 2c, 2d, and the compression mechanism 2 is configured so
that refrigerant discharged from the first-stage compression
element of these compression elements 2c, 2d is sequentially
compressed by the second-stage compression element.
[0155] Since a single-shaft two-stage compression mechanism is used
herein, the control unit 99 drives the low-stage compression
element 2c and the high-stage compression element 2d while causing
their centrifugal forces to cancel each other out to suppress
vibrations and/or fluctuations in torque load, and the control unit
99 can perform control so that the operating capacity of the
low-stage compression element 2c and the operating capacity of the
high-stage compression element 2d are balanced, and the compression
ratios are equal in the low-stage and high-stage elements.
<2> Second Embodiment
<2-1> Configuration of Air-Conditioning Apparatus
[0156] FIG. 8 is a schematic structural diagram of a water heater
201 as a refrigeration apparatus according to the second embodiment
of the present invention.
[0157] Components in the second embodiment having the same
specifics as those of the first embodiment are not described
hereinbelow.
[0158] (Water Circuit)
[0159] The water circuit 910 is the water circuit of the embodiment
described above, but further having the flow rate ratio adjustment
mechanism 911 disposed at an intermediate point in the intermediate
water tubes 904, 905. The opening degree of this flow rate ratio
adjustment mechanism 911 is controlled by the control unit 99, and
the ratio between the quantity of water flowing through the heat
source water tubes 902, 903 and the quantity of water flowing
through the intermediate water tubes 904, 905 can be adjusted.
[0160] (Refrigerant Circuit)
[0161] The refrigerant circuit 210 is the refrigerant circuit of
the embodiment described above, but further having a liquid-gas
heat exchanger 8, a liquid-gas three-way valve 8C, a liquid-gas
bypass tube 8B, and connecting tubes 71, 72, 73, 74, 75, 76, 77,
and the like connecting these components together.
[0162] The liquid-gas heat exchanger 8 has a liquid-side liquid-gas
heat exchanger 8L through which passes the refrigerant flowing from
the connecting tube 73 to the connecting tube 74, and a gas-side
liquid-gas heat exchanger 8G through which passes the refrigerant
flowing from the connecting tube 77 to the intake tube 2a. The
liquid-gas heat exchanger 8 performs heat exchange between the
refrigerant flowing through the liquid-side liquid-gas heat
exchanger 8L and the refrigerant flowing through the gas-side
liquid-gas heat exchanger 8G. Although the description uses wording
such as "liquid"-side "liquid"-gas heat exchanger 8, the
refrigerant passing through the liquid-side liquid-gas heat
exchanger 8L is not limited to a liquid state, and may be
refrigerant in a supercritical state, for example. Nor is the
refrigerant flowing through the gas-side liquid-gas heat exchanger
8G limited to refrigerant in a gas state, and refrigerant as
moisture may flow through, for example.
[0163] The liquid-gas bypass tube 8B connects one switching port of
the liquid-gas three-way valve 8C connected to the connecting tube
73, which is on the upstream side of the liquid-side liquid-gas
heat exchanger 8L, and an end of the connecting tube 74 extending
downstream of the liquid-side liquid-gas heat exchanger 8L.
[0164] The liquid-gas three-way valve 8C can switch between a
liquid-gas usage connection state in which the connection tube 72
extending from the heat source-side heat exchanger 4 is connected
to the connecting tube 73 extending from the liquid-side liquid-gas
heat exchanger 8L, and a liquid-gas non-usage connection state in
which the connection tube 72 extending from the heat source-side
heat exchanger 4 is not connected to the connecting tube 73
extending from the liquid-side liquid-gas heat exchanger 8L but is
connected to the liquid-gas bypass tube 8B.
<2-2> Action of Air-Conditioning Apparatus
[0165] Next, the action of the water heater 201 of the second
embodiment is described using FIGS. 8, 9, and 10.
[0166] FIG. 9 is a pressure-enthalpy graph representing the
refrigeration cycle, and FIG. 10 is a temperature-entropy graph
representing the refrigeration cycle.
[0167] (Liquid-Gas Usage Connection State)
[0168] In the liquid-gas usage connection state, the connection
state of the liquid-gas three-way valve 8C is switchably controlled
by the control unit 99 so that heat exchange is performed in the
liquid-gas heat exchanger 8 between the refrigerant passing through
the liquid-side liquid-gas heat exchanger 8L and the refrigerant
passing through the gas-side liquid-gas heat exchanger 8G.
[0169] Herein, the refrigerant drawn in from the intake tube 2a of
the low-stage compression element 2c (refer to point A in FIGS. 9
and 10) is compressed by the low-stage compression element 2c
(refer to point B in FIGS. 9 and 10), and the refrigerant flowing
through the intermediate refrigerant tube 22 is cooled in the
intercooler 7 by the water flowing through the intermediate water
tubes 904, 905 (refer to point C in FIGS. 9 and 10).
[0170] Having been compressed to a pressure exceeding the critical
pressure by the high-stage compression element 2d (refer to point D
in FIGS. 9 and 10), the refrigerant is fed to the heat source-side
heat exchanger 4. In the heat source-side heat exchanger 4, the
water flowing through the heat source water tubes 902, 903 is then
heated, whereby the heat within the refrigerant itself is radiated.
Since carbon dioxide is used here as the active refrigerant and the
refrigerant flows into the heat source-side heat exchanger 4 in a
supercritical state, heat is radiated to the exterior by the change
in sensible heat while the refrigerant pressure remains constant in
the heat radiation step, and the temperature of the refrigerant
itself continuously decreases (refer to point K in FIGS. 9 and 10).
Having exited the heat source-side heat exchanger 4, the
refrigerant flows into the liquid-side liquid-gas heat exchanger
8L, where heat is further radiated due to heat exchange with the
low-temperature, low-pressure gas refrigerant flowing through the
gas-side liquid-gas heat exchanger 8G, and the temperature of the
refrigerant itself continuously decreases further (refer to point L
in FIGS. 9 and 10). Having exited the liquid-side liquid-gas heat
exchanger 8L, the refrigerant is depressurized by the expansion
mechanism 5 (refer to point M in FIGS. 9 and 10), and the
refrigerant flows into the usage-side heat exchanger 6. In the
usage-side heat exchanger 6, due to heat exchange with external air
and/or water while the pressure remains constant, the refrigerant
evaporates while the heat taken from the exterior is consumed in a
change of latent heat, whereby the dryness of the refrigerant
increases (refer to point P in FIGS. 9 and 10). Having exited the
usage-side heat exchanger 6, the refrigerant evaporates further
while undergoing a change in latent heat in the gas-side liquid-gas
heat exchanger 8G due this time to the heat taken by heat exchange
with the high-temperature, high-pressure refrigerant passing
through the liquid-side liquid-gas heat exchanger 8L while the
pressure remains constant, and the refrigerant reaches a
superheated state above the dry saturated vapor curve at this
pressure. This refrigerant in a superheated state is then drawn
into the low-stage compression element 2c through the intake tube
2a (point A in FIGS. 9 and 10). This refrigerant circulation is
repeated in the liquid-gas usage connection state.
[0171] (Liquid-Gas Non-Usage Connection State)
[0172] In the liquid-gas non-usage connection state, the control
unit 99 controls the connection state of the liquid-gas three-way
valve 8C and creates a state in which the connection tube 72 and
the liquid-gas bypass tube 8B are connected, so that heat exchange
is not performed in the liquid-gas heat exchanger 8.
[0173] The points A, B, C, D, and K of FIGS. 9 and 10 in the
liquid-gas non-usage connection state are the same as in the
liquid-gas usage connection state and are therefore not
described.
[0174] The refrigerant that has exited the heat source-side heat
exchanger 4 herein flows through the liquid-gas bypass tube 8B to
be depressurized in the expansion mechanism 5 without flowing into
the liquid-side liquid-gas heat exchanger 8L (refer to point L' in
FIGS. 9 and 10). The refrigerant is then depressurized in the
expansion mechanism 5, and the refrigerant flows into the
usage-side heat exchanger 6 (refer to point M' in FIGS. 9 and 10).
In the usage-side heat exchanger 6, through heat exchange with
external air and/or water while the pressure remains constant, the
refrigerant evaporates while the heat taken from the exterior is
consumed in a latent heat change, whereby the refrigerant reaches a
superheated state above the dry saturated vapor curve at this
pressure. This refrigerant in a superheated state is then drawn
into the low-stage compression element 2c through the intake tube
2a (refer to point P' in FIGS. 9 and 10). This refrigerant
circulation is repeated in the liquid-gas non-usage connection
state.
[0175] (Liquid-Gas Heat Exchanger Switching Control)
[0176] The control unit 99 performs the same control as the target
capacity output control described in Embodiment 1 above, and also
performs liquid-gas heat exchanger switching control for switching
between the above-described liquid-gas usage connection state and
liquid-gas non-usage connection state.
[0177] In this liquid-gas heat exchanger switching control, the
control unit 99 switches the connection state of the liquid-gas
three-way valve 8C in accordance with the temperature sensed by the
usage-side temperature sensor 6T.
[0178] In the target capacity output control described above, the
target evaporation temperature is established based on the
temperature sensed by the usage-side temperature sensor 6T, but
when the temperature sensed by the usage-side temperature sensor 6T
decreases and the target evaporation temperature is set to be even
lower, the discharged refrigerant temperature increases under the
control condition that the target discharge pressure of the
high-stage compression element 2d does not change (under the
condition that the required radiated heat quantity must be
guaranteed in the heat source-side heat exchanger 4). The
reliability of the high-stage compression element 2d is compromised
when the discharged refrigerant temperature increases too much in
this manner. Therefore, the control unit 99 herein performs a
control for bringing the connection state of the liquid-gas
three-way valve 8C to the liquid-gas non-usage connection state.
Thereby, even if the temperature sensed by the usage-side
temperature sensor 6T decreases and the target evaporation
temperature is set to be even lower, the extent of the increase in
the degree of superheating of the refrigerant drawn in by the
high-stage compression element 2d can be minimized to minimize the
increase in the discharged refrigerant temperature, and the
required heat radiation quantity can be maintained.
[0179] On the other hand, in the target capacity output control
described above, the target evaporation temperature is established
based on the temperature sensed by the usage-side temperature
sensor 6T, but when the temperature sensed by the usage-side
temperature sensor 6T increases and the target evaporation
temperature is set to be even higher, the discharged refrigerant
temperature decreases under the control condition that the target
discharge pressure of the high-stage compression element 2d does
not change (under the condition that the required radiated heat
quantity must be guaranteed in the heat source-side heat exchanger
4). In this case, it will sometimes not be possible to supply the
heat source-side heat exchanger 4 with refrigerant having the
required heat radiation quantity. In such cases, the control unit
99 is capable of switching the connection state of the liquid-gas
three-way valve 8C to the liquid-gas usage connection state,
raising the degree of superheating of the refrigerant drawn into
the high-stage compression element 2d, and guaranteeing the heat
radiation quantity required in the heat source-side heat exchanger
4. There are also cases in which it is possible to improve the
coefficient of performance even when the required heat radiation
quantity can be supplied in this manner. In such cases, the control
unit 99 is capable of guaranteeing the required heat radiation
quantity and improving the coefficient of performance by switching
the connection state of the liquid-gas three-way valve 8C to the
liquid-gas usage connection state, lowering the specific enthalpy
of the refrigerant drawn into the expansion mechanism 5, and
improving the refrigerating capacity of the refrigeration cycle.
Since the refrigerant drawn into the low-stage compression element
2c can be guaranteed to have the appropriate degree of
superheating, it is possible to prevent the risk of liquid
compression occurring in the low-stage compression element 2c.
<2-3> Modification 1
[0180] In the embodiment described above, an example was described
in which the control unit 99 switches the connection state of the
liquid-gas three-way valve 8C on the basis of the temperature
sensed by the usage-side temperature sensor 6T (on the basis of the
established target evaporation temperature).
[0181] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit 210A
having a discharged refrigerant temperature sensor 2T for sensing
the temperature of the refrigerant discharged from the high-stage
compression element 2d, instead of the usage-side temperature
sensor 6T, as shown in FIG. 11, for example.
[0182] With this discharged refrigerant temperature sensor 2T, an
increase in the temperature sensed by the usage-side temperature
sensor 6T described above corresponds to a decrease in the
temperature sensed by the discharged refrigerant temperature sensor
2T, and a decrease in the temperature sensed by the usage-side
temperature sensor 6T described above corresponds to an increase in
the temperature sensed by the discharged refrigerant temperature
sensor 2T. That is, if the temperature sensed by the discharged
refrigerant temperature sensor 2T is too high, it will not be
possible to maintain the reliability of the high-stage compression
element 2d, and the control unit 99 will therefore bring the
connection state of the liquid-gas three-way valve 8C to the
liquid-gas non-usage connection state, preventing the degree of
superheating of the refrigerant drawn into the low-stage
compression element 2c from increasing. If the temperature sensed
by the discharged refrigerant temperature sensor 2T decreases, it
will not be possible to supply the heat radiation quantity required
in the heat source-side heat exchanger 4, and the control unit 99
therefore will bring the connection state of the liquid-gas
three-way valve 8C to the liquid-gas usage connection state and
increase the degree of superheating of the refrigerant drawn into
the low-stage compression element 2c, guaranteeing a capacity. In
conditions in which the refrigerant drawn into the low-stage
compression element 2c has a low temperature and the temperature of
the refrigerant discharged by the high-stage compression element 2d
does not increase excessively even if the degree of superheating
has been raised, the control unit 99 brings the connection state of
the liquid-gas three-way valve 8C to the liquid-gas usage
connection state and lowers the specific enthalpy of the
refrigerant fed to the expansion mechanism 5 to improve the
refrigerating capacity of the refrigeration cycle, thereby raising
the coefficient of performance.
<2-4> Modification 2
[0183] In the embodiment described above, an example was described
in which the connection state of the liquid-gas three-way valve 8C
is switched to switch between the liquid-gas usage connection state
and the liquid-gas non-usage connection state.
[0184] However, the present invention is not limited to this
example; another possibility is to cause refrigerant to flow to
both the liquid-gas bypass tube 8B and the liquid-gas heat
exchanger 8L and control the refrigerant flow rate ratio of both
refrigerant passages by adjusting the switched state of the
liquid-gas three-way valve 8C, for example.
<2-5> Modification 3
[0185] In the embodiment described above, an example was described
of a refrigerant circuit provided with the liquid-gas three-way
valve 8C.
[0186] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit which
has an on/off valve provided to the connecting tube 73 and an
on/off valve also provided to the liquid-gas bypass tube 8B,
instead of the liquid-gas three-way valve 8C, for example.
<2-6> Modification 4
[0187] In the embodiment described above, an example was described
of a refrigerant circuit provided with only one two-stage
compression mechanism, wherein refrigerant is compressed in two
stages in the low-stage compression element 2c and the high-stage
compression element 2d.
[0188] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit
wherein the aforementioned two-stage compression mechanisms which
perform compression in two stages are provided in parallel to each
other, for example.
[0189] In the refrigerant circuit, a plurality of usage-side heat
exchangers 6 may be disposed in parallel to each other. In this
case, a refrigerant circuit may be used in which expansion
mechanisms are disposed immediately ahead of the respective
usage-side heat exchangers and the expansion mechanisms are also
disposed in parallel to each other so that the quantity of
refrigerant supplied to the usage-side heat exchangers 6 can be
controlled.
<2-7> Modification 5
[0190] In the embodiment described above, an example was described
in which the low-stage compression element 2c and the high-stage
compression element 2d were provided with separate drive shafts
21c, 21f and compressor drive motors 21b, 21e.
[0191] However, the present invention is not limited to this
example; another possibility is a refrigerant circuit 210B which
uses a compression mechanism 2 having a shared drive shaft 121c
which is a drive shaft shared by the low-stage compression element
2c and the high-stage compression element 2d, wherein one shared
compressor drive motor 121b is used to transmit drive force to the
shared drive shaft 121c, as shown in FIG. 12, for example.
[0192] This compression mechanism 2 has a hermetically sealed
structure in which the compressor drive motor 121b, the shared
drive shaft 121c, and the compression elements 2c, 2d are housed
within a casing 21a. The shared compressor drive motor 121b is
linked to the shared drive shaft 121c. This shared drive shaft 121c
is linked to the two compression elements 2c, 2d. That is, the
compression mechanism has a so-called single-shaft two-stage
compression structure in which the two compression elements 2c, 2d
are linked to a single shared drive shaft 121c, and the two
compression elements 2c, 2d are both rotatably driven by the shared
compressor drive motor 121b. The compression elements 2c, 2d are
rotary-type, scroll-type, or another type of positive displacement
compression elements. The low-stage compression element 2c draws
refrigerant in from an intake tube 2a, compresses the drawn-in
refrigerant, and discharges the refrigerant toward the intermediate
refrigerant tube 22. The intermediate refrigerant tube 22 connects
the discharge side of the low-stage compression element 2c and the
intake side of the high-stage compression element 2d via the
intercooler 7. The high-stage compression element 2d further
compresses the refrigerant drawn in via the intermediate
refrigerant tube 22 and then discharges the refrigerant to the
discharge tube 2b. In FIG. 12, the discharge tube 2b is a
refrigerant tube for feeding the refrigerant discharged from the
compression mechanism 2 to the heat source-side heat exchanger 4,
and the discharge tube 2b is provided with an oil separation
mechanism 41 and a non-return mechanism 42. The oil separation
mechanism 41 is a mechanism for separating the refrigerant from
refrigeration oil which accompanies the refrigerant discharged from
the compression mechanism 2 and returning the refrigeration oil to
the intake side of the compression mechanism 2, and the oil
separation mechanism 41 has primarily an oil separator 41a for
separating the refrigerant from the refrigeration oil accompanying
the refrigerant discharged from the compression mechanism 2, and an
oil return tube 41b which is connected to the oil separator 41a and
which returns the refrigeration oil separated from the refrigerant
to the intake tube 2a of the compression mechanism 2. The oil
return tube 41b is provided with a depressurization mechanism 41c
for depressurizing the refrigeration oil flowing through the oil
return tube 41b. A capillary tube is used as the depressurization
mechanism 41c. The non-return mechanism 42 is a mechanism for
allowing the flow of refrigerant from the discharge side of the
compression mechanism 2 to the heat source-side heat exchanger 4
and blocking the flow of refrigerant from the heat source-side heat
exchanger 4 to the discharge side of the compression mechanism 2,
and a non-return valve is used.
[0193] Thus, the compression mechanism 2 has two compression
elements 2c, 2d, and the compression mechanism 2 is configured so
that refrigerant discharged from the first-stage compression
element of these compression elements 2c, 2d is sequentially
compressed by the second-stage compression element.
[0194] Since a single-shaft two-stage compression mechanism is used
herein, the control unit 99 drives the low-stage compression
element 2c and the high-stage compression element 2d while causing
their centrifugal forces to cancel each other out to suppress
vibrations and/or fluctuations in torque load, and the control unit
99 can perform control so that the operating capacity of the
low-stage compression element 2c and the operating capacity of the
high-stage compression element 2d are balanced, and the compression
ratios are equal in the low-stage and high-stage elements.
<3> Third Embodiment
<3-1> Configuration of Air-Conditioning Apparatus
[0195] FIG. 13 is a schematic structural diagram of a water heater
301, which is a refrigeration apparatus according to the third
embodiment of the present invention.
[0196] Components in the third embodiment that have the same
specifications as those of the first embodiment are not described
hereinbelow.
[0197] (Water Circuit)
[0198] The water circuit 910 is the water circuit of the embodiment
described above, but further having the flow rate ratio adjustment
mechanism 911 disposed at an intermediate point in the intermediate
water tubes 904, 905. The opening degree of this flow rate ratio
adjustment mechanism 911 is controlled by the control unit 99, and
the ratio between the quantity of water flowing through the heat
source water tubes 902, 903 and the quantity of water flowing
through the intermediate water tubes 904, 905 can be adjusted.
[0199] (Refrigerant Circuit)
[0200] The refrigerant circuit 310 is the refrigerant circuit of
the embodiment described above, but further having an economizer
circuit 9, and connecting tubes 73c, 74c, etc. connecting the other
components.
[0201] The economizer circuit 9 has a branching upstream tube 9a
branching off from a branching point X between the connection tube
72 and the connecting tube 73c, an economizer expansion mechanism
9e for depressurizing refrigerant, a branching midstream tube 9b
for leading the refrigerant depressurized in the economizer
expansion mechanism 9e to the economizer heat exchanger 20, and a
branching downstream tube 9c for leading the refrigerant that has
flowed out of the economizer heat exchanger 20 to a convergent
point Y in the intermediate refrigerant tube 22.
[0202] The connecting tube 73c leads refrigerant through the
economizer heat exchanger 20 to a connecting tube 75c. This
connecting tube 75c is connected to the expansion mechanism 5.
[0203] The configuration is otherwise the same as that of the water
heater 1 of the first embodiment described above.
<3-2> Action of Air-Conditioning Apparatus
[0204] Next, the action of the water heater 301 of the third
embodiment will be described using FIGS. 13, 14, and 15.
[0205] FIG. 14 is a pressure-enthalpy graph representing the
refrigeration cycle, and FIG. 15 is a temperature-entropy graph
representing the refrigeration cycle.
[0206] (Economizer Usage State)
[0207] In an economizer usage state, refrigerant is caused to flow
to the economizer circuit 9 by adjusting the opening degree of the
economizer expansion mechanism 9e.
[0208] In the economizer circuit 9, refrigerant that has branched
off from the branching point X and flowed into the branching
upstream tube 9a is depressurized in the economizer expansion
mechanism 9e (refer to point R in FIGS. 13, 14, and 15), and the
refrigerant flows into the economizer heat exchanger 20 via the
branching midstream tube 9b.
[0209] In the economizer heat exchanger 20, heat exchange takes
place between the refrigerant flowing through the connecting tube
73c and the connecting tube 75c (refer to point X.fwdarw.point Q in
FIGS. 13, 14, and 15), and the refrigerant flowing into the
economizer heat exchanger 20 via the branching midstream tube 9b
(refer to point R.fwdarw.point Y in FIGS. 13, 14, and 15).
[0210] At this time, the refrigerant flowing through the connecting
tube 73c and the connecting tube 75c is cooled by the refrigerant
flowing through the branching midstream tube 9b, which is being
depressurized and reduced in temperature in the economizer heat
exchanger 20, and the specific enthalpy decreases (refer to point X
point Q in FIGS. 13, 14, and 15). Thus, the degree of supercooling
of the refrigerant fed to the expansion mechanism 5 increases,
whereby the refrigeration capacity of the refrigeration cycle
increases and the coefficient of performance improves. The
refrigerant whose specific enthalpy has decreased is depressurized
by passing through the expansion mechanism 5, and the refrigerant
flows into the usage-side heat exchanger 6 (refer to point Q point
M in FIGS. 13, 14, and 15). The refrigerant evaporates in the
usage-side heat exchanger 6, and the refrigerant is drawn into the
low-stage compression element 2c (refer to point M point A in FIGS.
13, 14, and 15). The refrigerant drawn into the low-stage
compression element 2c is compressed and increased in temperature,
creating a state in which refrigerant increased in pressure to an
intermediate pressure flows through the intermediate refrigerant
tube 22.
[0211] When the refrigerant flowing through the intermediate
refrigerant tube 22 passes through the intercooler 7, the
refrigerant radiates heat upon heating the water flowing through
the intermediate water tubes 904, 905, and the refrigerant
temperature decreases (refer to point B.fwdarw.point S in FIGS. 13,
14, and 15).
[0212] The refrigerant flowing into the economizer heat exchanger
20 via the branching midstream tube 9b is heated by the refrigerant
flowing through the connecting tube 73c and the connecting tube
75c, whereby the dryness of the refrigerant improves (refer to
point R.fwdarw.point Y in FIGS. 13, 14, and 15).
[0213] Thus, refrigerant that has passed through the economizer
circuit 9 (refer to point Y in FIGS. 13, 14, an 15) mixes with
refrigerant that has been cooled in the intercooler 7 while flowing
through the intermediate refrigerant tube 22 (refer to point S in
FIGS. 13, 14, and 15) at the convergent point Y in the intermediate
refrigerant tube 22 described above, the refrigerant temperature
decreases while the intermediate pressure is maintained, the degree
of superheating of the refrigerant discharged from the low-stage
compression element 2c is reduced, and the refrigerant is drawn
into the high-stage compression element 2d (refer to points Y, S,
and C in FIGS. 13, 14, and 15). The temperature of the refrigerant
drawn into the high-stage compression element 2d thereby decreases,
and it is therefore possible to prevent the temperature of the
refrigerant discharged from the high-stage compression element 2d
from increasing excessively. The refrigerant density also increases
due to the temperature of the refrigerant drawn into the high-stage
compression element 2d decreasing, and the quantity of refrigerant
circulating through the heat source-side heat exchanger 4 is
increased by the refrigerant injected via the economizer circuit 9;
therefore, the capacity to supply refrigerant to the heat
source-side heat exchanger 4 can be greatly improved.
[0214] In the economizer usage state, this manner of refrigerant
circulation is repeated.
[0215] (Economizer Non-Usage State)
[0216] In the economizer non-usage state, the economizer expansion
mechanism 9e in the economizer circuit 9 is brought to a fully
closed state. A state thereby arises in which the flow of
refrigerant in the branching midstream tube 9b ceases and the
economizer heat exchanger 20 does not function (refer to points Q',
M', and D' in FIGS. 13, 14, and 15).
[0217] The cooling effects of the refrigerant flowing through the
intermediate refrigerant tube 22 thereby ceases, the temperature of
the refrigerant discharged from the high-stage compression element
2d therefore increases, and it is possible to comply with a high
output water temperature requested by the user.
[0218] (Economizer Switching Control)
[0219] The control unit 99 performs the same control as the target
capacity output control described in Embodiment 1 described above,
and performs economizer switching control for switching between the
economizer usage state and the economizer non-usage state described
above.
[0220] In this economizer switching control, the control unit 99
controls the opening degree of the economizer expansion mechanism
9e in accordance with the temperature sensed by the usage-side
temperature sensor 6T.
[0221] In the target capacity output control described above, the
target evaporation temperature is established based on the
temperature sensed by the usage-side temperature sensor 6T, but
when the temperature sensed by the usage-side temperature sensor 6T
decreases and the target evaporation temperature is set to be even
lower, the discharged refrigerant temperature increases under the
control condition that the target discharge pressure of the
high-stage compression element 2d does not change (under the
condition that the required radiated heat quantity must be
guaranteed in the heat source-side heat exchanger 4). The
reliability of the high-stage compression element 2d is compromised
when the discharged refrigerant temperature increases too much in
this manner. Therefore, the control unit 99 herein performs a
control for creating the economizer usage state, wherein the
economizer heat exchanger 20 is made to function by opening the
economizer expansion mechanism 9e and causing refrigerant to flow
to the economizer circuit 9. Thereby, even if the temperature
sensed by the usage-side temperature sensor 6T decreases and the
target evaporation temperature is set to be even lower, the extent
of the increase in the temperature of the refrigerant drawn in by
the high-stage compression element 2d can be minimized to minimize
the increase in the discharged refrigerant temperature, and the
required heat radiation quantity can be maintained.
[0222] On the other hand, in the target capacity output control
described above, the target evaporation temperature is established
based on the temperature sensed by the usage-side temperature
sensor 6T, but when the temperature sensed by the usage-side
temperature sensor 6T increases and the target evaporation
temperature is set to be even higher, the discharged refrigerant
temperature decreases under the control condition that the target
discharge pressure of the high-stage compression element 2d does
not change (under the condition that the required radiated heat
quantity must be guaranteed in the heat source-side heat exchanger
4). In this case, it will sometimes not be possible to supply the
heat source-side heat exchanger 4 with refrigerant having the
required heat radiation quantity. In such cases, the control unit
99 is capable of creating the economizer non-usage state in which
the economizer expansion mechanism 9e is fully closed, ensuring
that the degree of superheating of the refrigerant drawn in by the
high-stage compression element 2d does not decrease, and
guaranteeing the heat radiation quantity required in the heat
source-side heat exchanger 4. There are also cases in which it is
possible to improve the coefficient of performance even when the
required heat radiation quantity can be supplied in this manner. In
such cases, the control unit 99 is capable of guaranteeing the
required heat radiation quantity and improving the coefficient of
performance by opening the economizer expansion mechanism 9e to
create the economizer usage state, lowering the specific enthalpy
of the refrigerant drawn into the expansion mechanism 5, and
improving the refrigerating capacity of the refrigeration
cycle.
<3-3> Modification 1
[0223] In the embodiment described above, an example was described
in which the control unit 99 switches the opening degree of the
economizer expansion mechanism 9e on the basis of the temperature
sensed by the usage-side temperature sensor 6T (on the basis of the
established target evaporation temperature).
[0224] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit 310A
having a discharged refrigerant temperature sensor 2T for sensing
the temperature of the refrigerant discharged from the high-stage
compression element 2d, instead of the usage-side temperature
sensor 6T, as shown in FIG. 16, for example.
[0225] With this discharged refrigerant temperature sensor 2T, an
increase in the temperature sensed by the usage-side temperature
sensor 6T described above corresponds to a decrease in the
temperature sensed by the discharged refrigerant temperature sensor
2T, and a decrease in the temperature sensed by the usage-side
temperature sensor 6T described above corresponds to an increase in
the temperature sensed by the discharged refrigerant temperature
sensor 2T. That is, if the temperature sensed by the discharged
refrigerant temperature sensor 2T is too high, it will not be
possible to maintain the reliability of, the high-stage compression
element 2d, and the control unit 99 will therefore increase the
opening degree of the economizer expansion mechanism 9e to bring
about the economizer usage state, preventing the discharged
refrigerant temperature of the high-stage compression element 2d
from increasing excessively by reducing the degree of superheating
of the refrigerant drawn into the low-stage compression element 2c.
If the temperature sensed by the discharged refrigerant temperature
sensor 2T decreases, it will not be possible to supply the heat
radiation quantity required in the heat source-side heat exchanger
4, and the control unit 99 therefore will fully close the
economizer expansion mechanism 9e to bring about the economizer
non-usage state and guarantee a capacity without reducing the
degree of superheating of the refrigerant drawn into the high-stage
compression element 2d. In conditions in which the refrigerant
drawn into the high-stage compression element 2d has a low
temperature and the temperature of the refrigerant discharged by
the high-stage compression element 2d does not increase excessively
even if the degree of superheating has been raised, the control
unit 99 increases the opening degree of the economizer expansion
mechanism 9e to bring about the economizer usage state and lowers
the specific enthalpy of the refrigerant fed to the expansion
mechanism 5 to improve the refrigerating capacity of the
refrigeration cycle, thereby raising the coefficient of
performance.
<3-4> Modification 2
[0226] In the embodiment described above, an example was described
in which the opening degree of the economizer expansion mechanism
9e is adjusted to switch between the economizer usage state and the
economizer non-usage state.
[0227] However, the present invention is not limited to this
example; another possibility is to control the flow rate ratio of
the refrigerants flowing to the economizer circuit 9 and the
connecting tubes 73c, 75c by adjusting the valve opening degree of
the economizer expansion mechanism 9e, for example.
<3-5> Modification 3
[0228] In the embodiment described above, an example was described
of a refrigerant circuit provided with only one two-stage
compression mechanism, wherein refrigerant is compressed in two
stages in the low-stage compression element 2c and the high-stage
compression element 2d.
[0229] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit
wherein the aforementioned two-stage compression mechanisms which
perform compression in two stages are provided in parallel to each
other, for example.
[0230] In the refrigerant circuit, a plurality of usage-side heat
exchangers 6 may be disposed in parallel to each other. In this
case, a refrigerant circuit may be used in which expansion
mechanisms are disposed immediately ahead of the respective
usage-side heat exchangers and the expansion mechanisms are also
disposed in parallel to each other so that the quantity of
refrigerant supplied to the usage-side heat exchangers 6 can be
controlled.
<3-6> Modification 4
[0231] In the embodiment described above, an example was described
in which the low-stage compression element 2c and the high-stage
compression element 2d were provided with the separate drive shafts
21c, 21f and the compressor drive motors 21b, 21e.
[0232] However, the present invention is not limited to this
example; another possibility is a refrigerant circuit 310B which
uses a compression mechanism 2 having a shared drive shaft 121c
which is a drive shaft shared by the low-stage compression element
2c and the high-stage compression element 2d, wherein one shared
compressor drive motor 121b is used to transmit drive force to the
shared drive shaft 121c, as shown in FIG. 17, for example.
[0233] This compression mechanism 2 has a hermetically sealed
structure in which the compressor drive motor 121b, the shared
drive shaft 121c, and the compression elements 2c, 2d are housed
within a casing 21a. The shared compressor drive motor 121b is
linked to the shared drive shaft 121c. This shared drive shaft 121c
is linked to the two compression elements 2c, 2d. That is, the
compression mechanism has a so-called single-shaft two-stage
compression structure in which the two compression elements 2c, 2d
are linked to a single shared drive shaft 121c, and the two
compression elements 2c, 2d are both rotatably driven by the shared
compressor drive motor 121b. The compression elements 2c, 2d are
rotary-type, scroll-type, or another type of positive displacement
compression elements. The low-stage compression element 2c draws
refrigerant in from an intake tube 2a, compresses the drawn-in
refrigerant, and discharges the refrigerant toward the intermediate
refrigerant tube 22. The intermediate refrigerant tube 22 connects
the discharge side of the low-stage compression element 2c and the
intake side of the high-stage compression element 2d via the
intercooler 7. The high-stage compression element 2d further
compresses the refrigerant drawn in via the intermediate
refrigerant tube 22 and then discharges the refrigerant to the
discharge tube 2b. In FIG. 17, the discharge tube 2b is a
refrigerant tube for feeding the refrigerant discharged from the
compression mechanism 2 to the heat source-side heat exchanger 4,
and the discharge tube 2b is provided with an oil separation
mechanism 41 and a non-return mechanism 42. The oil separation
mechanism 41 is a mechanism for separating the refrigerant from
refrigeration oil which accompanies the refrigerant discharged from
the compression mechanism 2 and returning the refrigeration oil to
the intake side of the compression mechanism 2, and the oil
separation mechanism 41 has primarily an oil separator 41a for
separating the refrigerant from the refrigeration oil accompanying
the refrigerant discharged from the compression mechanism 2, and an
oil return tube 41b which is connected to the oil separator 41a and
which returns the refrigeration oil separated from the refrigerant
to the intake tube 2a of the compression mechanism 2. The oil
return tube 41b is provided with a depressurization mechanism 41c
for depressurizing the refrigeration oil flowing through the oil
return tube 41b. A capillary tube is used as the depressurization
mechanism 41c. The non-return mechanism 42 is a mechanism for
allowing the flow of refrigerant from the discharge side of the
compression mechanism 2 to the heat source-side heat exchanger 4
and blocking the flow of refrigerant from the heat source-side heat
exchanger 4 to the discharge side of the compression mechanism 2,
and a non-return valve is used.
[0234] Thus, the compression mechanism 2 has the two compression
elements 2c, 2d, and the compression mechanism 2 is configured so
that refrigerant discharged from the first-stage compression
element of these compression elements 2c, 2d is sequentially
compressed by the second-stage compression element.
[0235] Since a single-shaft two-stage compression mechanism is used
herein, the control unit 99 drives the low-stage compression
element 2c and the high-stage compression element 2d while causing
their centrifugal forces to cancel each other out to suppress
vibrations and/or fluctuations in torque load, and the control unit
99 can perform control so that the operating capacity of the
low-stage compression element 2c and the operating capacity of the
high-stage compression element 2d are balanced, and the compression
ratios are equal in the low-stage and high-stage elements.
<4> Fourth Embodiment
<4-1> Configuration of Air-Conditioning Apparatus
[0236] FIG. 18 is a schematic structural diagram of a water heater
401, which is a refrigeration apparatus according to the fourth
embodiment of the present invention.
[0237] Components in the fourth embodiment that have the same
specifics as those of the first embodiment are not described
herein.
[0238] (Water Circuit)
[0239] The water circuit 910 is the water circuit of the embodiment
described above, but further having the flow rate ratio adjustment
mechanism 911 disposed at an intermediate point in the intermediate
water tubes 904, 905. The opening degree of this flow rate ratio
adjustment mechanism 911 is controlled by the control unit 99, and
the ratio between the quantity of water flowing through the heat
source water tubes 902, 903 and the quantity of water flowing
through the intermediate water tubes 904, 905 can be adjusted.
[0240] (Refrigerant Circuit)
[0241] The refrigerant circuit 410 is the refrigerant circuit of
the embodiment described above, but further having the liquid-gas
heat exchanger 8, a switching three-way valve 28C, the liquid-gas
bypass tube 8B, the economizer circuit 9, and connecting tubes 74g,
75g, etc. connecting these components.
[0242] The liquid-gas heat exchanger 8 has a liquid-side liquid-gas
heat exchanger 8L through which passes the refrigerant flowing from
the connecting tube 73 to the connecting tube 74, and a gas-side
liquid-gas heat exchanger 8G through which passes the refrigerant
flowing from the connecting tube 77 to the intake tube 2a. The
liquid-gas heat exchanger 8 performs heat exchange between the
refrigerant flowing through the liquid-side liquid-gas heat
exchanger 8L and the refrigerant flowing through the gas-side
liquid-gas heat exchanger 8G. Although the description uses wording
such as "liquid"-side "liquid"-gas heat exchanger 8, the
refrigerant passing through the liquid-side liquid-gas heat
exchanger 8L is not limited to a liquid state, and may be
refrigerant in a supercritical state, for example. Nor is the
refrigerant flowing through the gas-side liquid-gas heat exchanger
8G limited to refrigerant in a gas state, and refrigerant as
moisture may flow through, for example. An expansion mechanism 95e
is provided at an intermediate point in the connecting tube 74.
[0243] The liquid-gas bypass tube 8B connects one switching port of
the switching three-way valve 28C connected to the connecting tube
73, which is on the upstream side of the liquid-side liquid-gas
heat exchanger 8L, and an end of the connecting tube 74 extending
downstream of the liquid-side liquid-gas heat exchanger 8L.
[0244] The switching three-way valve 28C can switch between a
liquid-gas state in which the connection tube 72 extending from the
heat source-side heat exchanger 4 is connected to the connecting
tube 73 extending from the liquid-side liquid-gas heat exchanger
8L, and an economizer state in which the connection tube 72
extending from the heat source-side heat exchanger 4 is not
connected to the connecting tube 73 extending from the liquid-side
liquid-gas heat exchanger 8L but is connected to the liquid-gas
bypass tube 8B. By fully closing the economizer expansion mechanism
9e in the economizer state, a dual-function non-usage state can be
brought about in which neither the economizer circuit 9 nor the
liquid-gas heat exchanger 8 are used.
[0245] The economizer circuit 9 has a branching upstream tube 9a
branching off from a branching point X between the liquid-gas
bypass tube 8B and the connecting tube 74g, an economizer expansion
mechanism 9e for depressurizing refrigerant, a branching midstream
tube 9b for leading the refrigerant depressurized in the economizer
expansion mechanism 9e to the economizer heat exchanger 20, and a
branching downstream tube 9c for leading the refrigerant that has
flowed out of the economizer heat exchanger 20 to a convergent
point Y in the intermediate refrigerant tube 22.
[0246] The connecting tube 74g leads refrigerant through the
economizer heat exchanger 20 to a connecting tube 75g. This
connecting tube 75g is connected to the expansion mechanism 5.
[0247] The refrigerant that has passed through the liquid-side
liquid-gas heat exchanger 8L and the refrigerant that has passed
through the economizer heat exchanger 20 mix together at a
convergent point L and flow into the usage-side heat exchanger 6
via the connection tube 76.
[0248] The control unit 99 can switch between the economizer state,
the liquid-gas state, and the dual-function non-usage stage by
adjusting the connection state of the switching three-way valve 28C
and the opening degree of the economizer expansion mechanism
9e.
[0249] The configuration otherwise has the same specifics as those
described in the above-described water heater 1 of the first
embodiment, the water heater 201 of the second embodiment, and/or
the water heater 301 of the third embodiment.
<4-2> Action of the Air-Conditioning Apparatus
[0250] Next, the action of the water heater 401 of the fourth
embodiment will be described using FIGS. 18, 19, and 20.
[0251] FIG. 19 is a pressure-enthalpy graph representing the
refrigeration cycle, and FIG. 20 is a temperature-entropy graph
representing the refrigeration cycle.
[0252] Between the specific enthalpy at point Q in the economizer
state and the specific enthalpy at point T in the liquid-gas state,
whichever has the greater value changes depending on the opening
degree of the expansion mechanism 5 and/or the expansion mechanism
95e, and these specific enthalpies are therefore not limited to the
examples shown in FIGS. 19 and 20.
[0253] (Economizer State)
[0254] In the economizer state, the control unit 99 switches the
connection state of the switching three-way valve 28C so that
refrigerant does not flow to the connecting tube 73 but refrigerant
does flow to the liquid-gas bypass tube 8B, increases the opening
degree of the economizer expansion mechanism 9e, and performs the
refrigeration cycle so that the refrigerant flows to the economizer
circuit 9. The same refrigeration cycle as in the economizer usage
state in Embodiment 3 described above is performed here, as shown
by points A, B, C, D, K, X, R, Y, Q, L, and P in FIGS. 18, 19, and
20.
[0255] The specific enthalpy of the refrigerant flowing through the
connecting tube 75g into the expansion mechanism 5 herein can be
lowered by heat exchange in the economizer heat exchanger 20, and
the refrigerating capacity of the refrigeration cycle can be
improved to bring the coefficient of performance to a satisfactory
value. Furthermore, the degree of superheating of the refrigerant
drawn into the high-stage compression element 2d can be further
reduced by the refrigerant passing through the economizer circuit 9
and mixing at the convergent point Y of the intermediate
refrigerant tube 22, rather than by the intercooler 7 alone, the
density of the refrigerant drawn into the compression element 2d
can be raised to improve compression efficiency, and abnormal
increases in the discharged refrigerant temperature can be
prevented. At this time, injection into the intermediate
refrigerant tube 22 via the economizer circuit 9 makes it possible
to increase the quantity of refrigerant supplied to the heat
source-side heat exchanger 4 and to increase the quantity of heat
supplied as well.
[0256] (Liquid-Gas State)
[0257] In the liquid-gas state, the control unit 99 switches the
connection state of the switching three-way valve 28C so that
refrigerant does not flow to the liquid-gas bypass tube 8B but does
flow to the connecting tube 73, and performs a refrigeration cycle
that makes the liquid-gas heat exchanger 8 function. The same
refrigeration cycle as in the liquid-gas usage connection state in
Embodiment 2 described above is performed here, as shown by points
A, B, C', D, K, T, L', and P' in FIGS. 18, 19, and 20.
[0258] The specific enthalpy of the refrigerant flowing into the
expansion mechanism 95e here can be lowered; therefore, the
refrigerating capacity in the refrigeration cycle can be improved
to bring the coefficient of performance to a satisfactory value, a
degree of superheating can be guaranteed in the refrigerant drawn
into the low-stage compression element 2c to prevent liquid
compression, and the discharge temperature can be increased to
guarantee the heat quantity required in the heat source-side heat
exchanger 4.
[0259] (Dual-Function Non-Usage State)
[0260] In the dual-function non-usage state, the control unit 99
switches the connection state of the switching three-way valve 28C
so that refrigerant does not flow to the connecting tube 73 but
does flow to the liquid-gas bypass tube 8B, fully closes the
economizer expansion mechanism 9e, and performs the refrigeration
cycle so that neither the economizer circuit 9 nor the liquid-gas
heat exchanger 8 are used. A simple refrigeration cycle is
performed here, as shown by points A, B, C, D'', K, X, Q'', L'',
and P in FIGS. 18, 19, and 20.
[0261] Since the temperature of the refrigerant discharged from the
high-stage compression element 2d can be increased here, it is
possible to supply the required heat quantity even in cases in
which the radiated heat quantity required in the heat source-side
heat exchanger 4 has increased.
[0262] (Switching Control of Economizer State, Liquid-Gas State,
and Dual-Function Non-Usage State)
[0263] The control unit 99 performs a control for switching the
above-described states such that the first priority is that the
discharged refrigerant temperature be within a range of not
increasing abnormally and the discharged refrigerant pressure be a
pressure equal to or less than the pressure capacity of the
low-stage compression element 2c and the high-stage compression
element 2d, the second priority is that the output water
temperature and output water quantity requested by the user be
achieved, and the third priority is that the operating efficiency
be satisfactory (that an appropriate balance can be established
between improving the coefficient of performance and increasing
compression efficiency).
[0264] That is, in cases in which the radiated heat quantity of the
refrigerant in the heat source-side heat exchanger 4 is
insufficient, control is performed such that the liquid-gas state
goes into effect if the discharge temperature is within a range of
not increasing abnormally, and the dual-function non-usage state
goes into effect if an abnormal increase in the discharge
temperature is avoided. In cases in which the heat radiation
quantity in the heat source-side heat exchanger 4 is sufficient,
the economizer state goes into effect, the opening degree of the
economizer expansion mechanism 9e is controlled, the valve opening
degree is increased within a margin whereby the heat radiation
quantity required in the heat source-side heat exchanger 4 can be
supplied, the coefficient of performance is brought to a
satisfactory value by improving the refrigerating capacity of the
refrigeration cycle, and control is performed for increasing the
supplied heat quantity by increasing the quantity of refrigerant
that can be supplied to the heat source-side heat exchanger 4.
[0265] The heat radiation quantity herein is determined by the
control unit 99 on the basis of the temperature sensed by the water
temperature sensor 910T, as well as the output water temperature
and the output water quantity required by the user. Whether or not
the discharge temperature has increased abnormally is determined by
the control unit 99 on the basis of (the evaporation temperature
established corresponding to) the temperature sensed by the
usage-side temperature sensor 6T.
<4-3> Modification 1
[0266] In the embodiment described above, an example was described
of a case in which the control unit 99 performs a control for
switching between the economizer state, the liquid-gas state, and
the dual-function non-usage state.
[0267] However, the present invention is not limited to this
example; another possibility is to allow the use of a dual-usage
state in which the economizer circuit 9 is used while the
liquid-gas heat exchanger 8 is used as well, for example.
[0268] On the preconditions that the discharged refrigerant
temperature of the high-stage compression element 2d be within a
range of not increasing abnormally, the discharged refrigerant
pressure be one equal to or less than the pressure capacity of the
low-stage compression element 2c and the high-stage compression
element 2d, and it be possible to supply the output water
temperature and output water quantity requested by the user, for
example, the control unit 99 herein may control the ratio between
the flow rate of refrigerant flowing through the economizer circuit
9 and the flow rate of the liquid-gas heat exchanger 8L while
refrigerant is flowing simultaneously to both the economizer
circuit 9 and the liquid-gas heat exchanger 8L, rather than simply
alternately switching the connection state of the switching
three-way valve 28C, so that the operating efficiency can be made
satisfactory (an appropriate balance can be established between
improving the coefficient of performance and increasing compression
efficiency). The configuration which can adjust the ratio herein is
not limited to the switching three-way valve 28C, and an expansion
mechanism may be provided immediately ahead of the liquid-gas heat
exchanger 8L to perform flow rate ratio control, for example.
[0269] For the ratio between the flow rate in the economizer
circuit 9 and the flow rate in the liquid-gas heat exchanger 8, the
control unit 99 herein ensures that the discharged refrigerant
temperature of the high-stage compression element 2d is within a
range of not increasing abnormally (under conditions such as the
temperature of the refrigerant discharged from the high-stage
compression element 2d being equal to or less than a predetermined
temperature) when the target evaporation temperature is established
based on the temperature sensed by the usage-side temperature
sensor 6T, and also that the discharged refrigerant pressure is
equal to or less than the pressure capacity of the low-stage
compression element 2c and the high-stage compression element 2d;
and the control unit 99 calculates a heat quantity sufficient to
guarantee the output water temperature and output water quantity
requested by the user.
[0270] Assuming that the flow rate of the economizer circuit 9 is
zero, for example, the control unit 99 then calculates a flow rate
of the liquid-gas heat exchanger 8L needed in order to guarantee a
radiated heat quantity, whereby abnormal increases in the
discharged refrigerant temperature at the target evaporation
temperature can be prevented, and the discharge pressure is equal
to or less than a predetermined pressure corresponding to the
pressure capacity of the low-stage compression element 2c and the
high-stage compression element 2d. Next, while reducing this
calculated flow rate in the liquid-gas heat exchanger 8L and
assuming that refrigerant equivalent to the reduced flow rate has
flowed to the economizer circuit 9, the control unit 99 controls
the flow rate ratio so that the respective compression ratios of
the low-stage compression element 2c and the high-stage compression
element 2d are within a predetermined range and the coefficient of
performance is within a predetermined range, while taking into
account the decrease in the refrigerating capacity resulting from
the increase in specific enthalpy accompanying the decrease in the
flow rate of the liquid-gas heat exchanger 8, the increase in the
refrigerating capacity resulting from the decrease in specific
enthalpy accompanying the increase in the flow rate of the
economizer circuit 9, the increase in the compression ratio of the
compression mechanism resulting from the high pressure increasing
in order to guarantee the heat radiation quantity by increasing the
flow rate of the economizer circuit 9, and the increase in the
supplied heat amount accompanying the increase in the refrigerant
density supplied to the heat source-side heat exchanger 4 resulting
from the increase in the flow rate of the economizer circuit 9.
[0271] For example, in this flow rate control by the control unit
99, an intermediate pressure at which the compression ratio of the
low-stage compression element 2c and the compression ratio of the
high-stage compression element 2d are equal may be calculated as
the intermediate pressure for minimizing the compression work, and
the economizer expansion mechanism 9e may be controlled so that the
extent of depressurization in the economizer expansion mechanism 9e
yields this intermediate pressure (and pressures within a
predetermined range from this intermediate pressure), whereupon the
flow rate ratio in the switching three-way valve 28C may be
adjusted so that the coefficient of performance is
satisfactory.
<4-4> Modification 2
[0272] In the embodiment described above, an example was described
in which the control unit 99 switches the opening degree of the
switching three-way valve 28C and/or the economizer expansion
mechanism 9e on the basis of the temperature sensed by the
usage-side temperature sensor 6T (on the basis of the established
target evaporation temperature).
[0273] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit 410A
having a discharged refrigerant temperature sensor 2T for sensing
the temperature of the refrigerant discharged from the high-stage
compression element 2d, instead of the usage-side temperature
sensor 6T, as shown in FIG. 21, for example.
[0274] With this discharged refrigerant temperature sensor 2T, an
increase in the temperature sensed by the usage-side temperature
sensor 6T described above corresponds to a decrease in the
temperature sensed by the discharged refrigerant temperature sensor
2T, and a decrease in the temperature sensed by the usage-side
temperature sensor 6T described above corresponds to an increase in
the temperature sensed by the discharged refrigerant temperature
sensor 2T.
<4-5> Modification 3
[0275] In the embodiment described above, an example was described
of a case in which the connection state of the switching three-way
valve 28C is switched to switch between the liquid-gas state, the
economizer state, and the dual-function non-usage state.
[0276] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit which
has an on/off valve provided to the connecting tube 73g and an
on/off valve also provided to the connecting tube 73, instead of
the switching three-way valve 28C, for example.
<4-6> Modification 4
[0277] In the embodiment described above, an example was described
of a refrigerant circuit 410 provided with both an expansion
mechanism 5 and an expansion mechanism 95e.
[0278] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit 410B
having a dual-use expansion mechanism 405B which can be used both
in control during the economizer state and control during the
liquid-gas state, as shown in FIG. 22, for example. This dual-use
expansion mechanism 405B is provided at an intermediate point in a
connecting tube 76g extending from the convergent point L to the
usage-side heat exchanger 6.
[0279] In this case, the number of expansion mechanisms can be
reduced to fewer than that of the refrigerant circuit 410 in the
fourth embodiment described above.
<4-7> Modification 5
[0280] In the embodiment described above, an example was described
of a refrigerant circuit 410 in which the branching point X which
branches in the economizer circuit 9 is bypassed by the liquid-gas
heat exchanger 8.
[0281] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit 410C
in which the branching point X which branches in the economizer
circuit 9 is provided between a dual-use expansion mechanism 405C
and a convergent point V between the connecting tube 74 and the
liquid-gas bypass tube 8B which extends from the liquid-gas
three-way valve 8C for switching between the liquid-gas state and
the economizer state, as shown in FIG. 23, for example.
<4-8> Modification 6
[0282] Furthermore, another possibility is to use a refrigerant
circuit 410D in which the branching point X which branches in the
economizer circuit 9 is provided between the liquid-gas three-way
valve 8C and the heat source-side heat exchanger 4, as shown in
FIG. 24.
[0283] In this refrigerant circuit 410D, the connection in the
liquid-gas three-way valve 8C is switched between leading to the
connecting tube 73 and leading to the liquid-gas bypass tube 8B.
The refrigerant that has passed through the liquid-gas heat
exchanger 8L then passes through the connecting tube 74 and mixes
at the convergent point L with the liquid-gas bypass tube 8B. The
connecting tube 76g and a dual-use expansion mechanism 405D are
provided between this convergent point L and the usage-side heat
exchanger 6.
<4-9> Modification 7
[0284] In the embodiment described above, an example was described
of a refrigerant circuit provided with only one two-stage
compression mechanism, wherein refrigerant is compressed in two
stages in the low-stage compression element 2c and the high-stage
compression element 2d.
[0285] However, the present invention is not limited to this
example; another possibility is to use a refrigerant circuit
wherein the above-described two-stage compression mechanisms which
perform compression in two stages are provided in parallel to each
other, for example.
[0286] In the refrigerant circuit, a plurality of usage-side heat
exchangers 6 may be disposed in parallel to each other. In this
case, a refrigerant circuit may be used in which expansion
mechanisms are disposed immediately ahead of the respective
usage-side heat exchangers and the expansion mechanisms are also
disposed in parallel to each other so that the quantity of
refrigerant supplied to the usage-side heat exchangers 6 can be
controlled.
<4-10> Modification 8
[0287] In the embodiment described above, an example was described
in which the low-stage compression element 2c and the high-stage
compression element 2d were provided with the separate drive shafts
21c, 21f and the compressor drive motors 21b, 21e.
[0288] However, the present invention is not limited to this
example; another possibility is a refrigerant circuit 410E which
uses a compression mechanism 2 having a shared drive shaft 121c
which is a drive shaft shared by the low-stage compression element
2c and the high-stage compression element 2d, wherein one shared
compressor drive motor 121b is used to transmit drive force to the
shared drive shaft 121c, as shown in FIG. 25, for example.
[0289] This compression mechanism 2 has a hermetically sealed
structure in which the compressor drive motor 121b, the shared
drive shaft 121c, and the compression elements 2c, 2d are housed
within a casing 21a. The shared compressor drive motor 121b is
linked to the shared drive shaft 121c. This shared drive shaft 121c
is linked to the two compression elements 2c, 2d. That is, the
compression mechanism has a so-called single-shaft two-stage
compression structure in which the two compression elements 2c, 2d
are linked to a single shared drive shaft 121c, and the two
compression elements 2c, 2d are both rotatably driven by the shared
compressor drive motor 121b. The compression elements 2c, 2d are
rotary-type, scroll-type, or another type of positive displacement
compression elements. The low-stage compression element 2c draws
refrigerant in from an intake tube 2a, compresses the drawn-in
refrigerant, and discharges the refrigerant toward the intermediate
refrigerant tube 22. The intermediate refrigerant tube 22 connects
the discharge side of the low-stage compression element 2c and the
intake side of the high-stage compression element 2d via the
intercooler 7. The high-stage compression element 2d further
compresses the refrigerant drawn in via the intermediate
refrigerant tube 22 and then discharges the refrigerant to the
discharge tube 2b. In FIG. 25, the discharge tube 2b is a
refrigerant tube for feeding the refrigerant discharged from the
compression mechanism 2 to the heat source-side heat exchanger 4,
and the discharge tube 2b is provided with an oil separation
mechanism 41 and a non-return mechanism 42. The oil separation
mechanism 41 is a mechanism for separating the refrigerant from
refrigeration oil which accompanies the refrigerant discharged from
the compression mechanism 2 and returning the refrigeration oil to
the intake side of the compression mechanism 2, and the oil
separation mechanism 41 has primarily an oil separator 41a for
separating the refrigerant from the refrigeration oil accompanying
the refrigerant discharged from the compression mechanism 2, and an
oil return tube 41b which is connected to the oil separator 41a and
which returns the refrigeration oil separated from the refrigerant
to the intake tube 2a of the compression mechanism 2. The oil
return tube 41b is provided with a depressurization mechanism 41c
for depressurizing the refrigeration oil flowing through the oil
return tube 41b. A capillary tube is used as the depressurization
mechanism 41c. The non-return mechanism 42 is a mechanism for
allowing the flow of refrigerant from the discharge side of the
compression mechanism 2 to the heat source-side heat exchanger 4
and blocking the flow of refrigerant from the heat source-side heat
exchanger 4 to the discharge side of the compression mechanism 2,
and a non-return valve is used.
[0290] Thus, the compression mechanism 2 has two compression
elements 2c, 2d, and the compression mechanism 2 is configured so
that refrigerant discharged from the first-stage compression
element of these compression elements 2c, 2d is sequentially
compressed by the second-stage compression element.
[0291] Since a single-shaft two-stage compression mechanism is used
herein, the control unit 99 drives the low-stage compression
element 2c and the high-stage compression element 2d while causing
their centrifugal forces to cancel each other out to suppress
vibrations and/or fluctuations in torque load, and the control unit
99 can perform control so that the operating capacity of the
low-stage compression element 2c and the operating capacity of the
high-stage compression element 2d are balanced, and the compression
ratios are equal in the low-stage and high-stage elements.
<5> Other Embodiments
[0292] Embodiments of the present invention and modifications
thereof were described above based on the drawings, but the
specific configuration is not limited to these embodiments and
their modifications; other changes can be made within a range that
does not deviate from the scope of the invention.
[0293] For example, in the embodiments and their modifications
described above, the present invention may be applied to a
so-called chiller-type air-conditioning apparatus in which water
and/or brine is used as the heating source or cooling source for
performing heat exchange with the refrigerant flowing through the
usage-side heat exchanger 6, and a secondary heat exchanger is
provided for performing heat exchange between indoor air and the
water and/or brine that has undergone heat exchange in the
usage-side heat exchanger 6.
[0294] The present invention can also be applied even to a
refrigeration apparatus of a type different from the aforementioned
chiller-type air-conditioning apparatus, such as a cooling-only
air-conditioning apparatus or the like.
[0295] The refrigerant that operates in a supercritical range is
not limited to carbon dioxide; ethylene, ethane, nitric oxide, and
the like may also be used.
INDUSTRIAL APPLICABILITY
[0296] In the refrigeration apparatus of the present invention,
since compression efficiency can be more reliably improved in the
refrigeration apparatus and the heating of the water for the hot
water supply can be made more efficient, the refrigeration
apparatus is particularly useful in cases in which the present
invention is applied to a refrigeration apparatus which has
multi-stage compression-type compression elements and which uses
refrigerant that operates including the supercritical state process
as the active refrigerant.
REFERENCE SIGNS LIST
[0297] 1 Air-conditioning apparatus (refrigeration apparatus)
[0298] 2 Compression mechanism [0299] 4 Heat source-side heat
exchanger [0300] 5 Expansion mechanism [0301] 6 Usage-side heat
exchanger [0302] 7 Intercooler [0303] 8 Liquid-gas heat exchanger
[0304] 10 Refrigerant circuit [0305] 20 Economizer heat exchanger
[0306] 22 Intermediate refrigerant tube [0307] 99 Control unit
[0308] 902, 903 Heat source water tubes [0309] 904, 905
Intermediate water tubes [0310] 910 Water circuit [0311] 911 Flow
rate ratio adjustment mechanism
CITATION LIST
Patent Literature
<Patent Literature 1>
[0312] Japanese Laid-open Patent Application No. 2007-232263
<Patent Literature 2>
[0313] Japanese Laid-open Patent Application No. 2002-106988
* * * * *