US20040118133A1

US20040118133A1 - Heat pump and dehumidifying air-conditioning apparatus

Info

Publication number: US20040118133A1
Application number: US10/468,832
Authority: US
Inventors: Kensaku Maeda; Hideo Inaba; Shunro Nishikawa
Original assignee: Individual
Current assignee: Ebara Corp
Priority date: 2001-03-02
Filing date: 2002-03-01
Publication date: 2004-06-24
Also published as: EP1370809A1; EP1370809A4; WO2002070958A1; CN1503889A; JP2002257375A; JP3253021B1; CN1223804C

Abstract

A dehumidifying air-conditioning apparatus comprises a pressurizer (4) for raising a pressure of a refrigerant, a condenser (5) for condensing the refrigerant to heat a high-temperature heat source fluid, and an evaporator (1) for evaporating the refrigerant to cool process air to a temperature lower than its dew point. The dehumidifying air-conditioning apparatus further comprises a refrigerant path branched into a plurality of branched refrigerant paths (42, 43, 44) between the condenser (5) and the evaporator (1). A first heat exchanging portion (21) is disposed in the branched refrigerant path for evaporating the refrigerant under an intermediate pressure between the condensing pressure of the condenser (5) and the evaporating pressure of the evaporator (1) to cool the process air by evaporation of the refrigerant under the intermediate pressure. A second heat exchanging portion (22) is disposed in the branched refrigerant path for condensing the refrigerant under an intermediate pressure between the condensing pressure of the condenser (5) and the evaporating pressure of the evaporator (1) to heat the process air by condensation of the refrigerant under the intermediate pressure. The first heat exchanging portion (21), the evaporator (1), the second heat exchanging portion (22) are connected in the order named by paths (30, 31, 32, 33, 34).

Description

TECHNICAL FIELD

The present invention relates to a heat pump and a dehumidifying air-conditioning apparatus, and more particularly to a heat pump with a high coefficient of performance (COP) and a dehumidifying air-conditioning apparatus which has such a heat pump and a high moisture removal per energy consumption.

BACKGROUND ART

FIG. 10 is a flow diagram of a conventional air-conditioning system. As shown in FIG. 10, there has heretofore been available a dehumidifying air-conditioning apparatus having a

compressor

201 for compressing a refrigerant, a condenser 202 for condensing the compressed refrigerant with outside air OA, an evaporator 204 for depressurizing the condensed refrigerant with an expansion valve 203 and evaporating the refrigerant to cool process air from an air-conditioned space 100 to a temperature lower than its dew point, and a reheater 205 for reheating the process air, which has been cooled to a temperature lower than its dew point, at the downstream side of the condenser 202 with the refrigerant upstream of the expansion valve 203. The refrigerant is condensed in the condenser 202 and the reheater 205. With the illustrated dehumidifying air-conditioning apparatus, a heat pump HP is constituted by the compressor 201, the condenser 202, the reheater 205, the expansion valve 203, and the evaporator 204. The heat pump HP pumps heat from the process air which flows through the evaporator 204 into the outside air OA which flows through the condenser 202.

FIG. 11 is a Mollier diagram in the case where HFC134a is used as the refrigerant in the conventional dehumidifying air-conditioning apparatus. In FIG. 11, a point a represents a state of the refrigerant evaporated by the

evaporator

204, and the refrigerant is in the form of a saturated vapor. The refrigerant has a pressure of 0.34 MPa, a temperature of 5° C., and an enthalpy of 400.9 kJ/kg. A point b represents a state of the vapor drawn and compressed by the compressor 201, i.e., a state at the outlet port of the compressor 201. In the point b, the refrigerant is in the form of a superheated vapor.

The refrigerant vapor is cooled in the

condenser

202 and reaches a state represented by a point c in the Mollier diagram. In the point c, the refrigerant is in the form of a saturated vapor and has a pressure of 0.94 MPa and a temperature of 38° C. Under this pressure, the refrigerant is cooled and condensed to reach a state represented by a point d. In the point d, the refrigerant is in the form of a saturated liquid and has the same pressure and temperature as those in the point c. The saturated liquid has an enthalpy of 250.5 kJ/kg.

The refrigerant liquid is depressurized by the

expansion valve

203 to a saturation pressure of 0.34 MPa at a temperature of 5° C. and reaches a state represented by the point e. The refrigerant at the point e is delivered as a mixture of the refrigerant liquid and the vapor at a temperature of 5° C. to the evaporator 204, in which the mixture removes heat from process air and is evaporated to reach a state of the saturated vapor, which is represented by the point a in the Mollier diagram. The saturated vapor is drawn into the compressor 201 again, and the above cycle is repeated.

FIG. 12 is a psychrometric chart showing an air-conditioning cycle in the conventional dehumidifying air-conditioning apparatus. In FIG. 12, the alphabetical letters K, L, M correspond to the encircled letters in FIG. 10. As shown in FIG. 12, in the conventional dehumidifying air-conditioning apparatus, air (in a state K) from the air-conditioned

space

100 is cooled to a temperature lower than its dew point to lower the dry bulb temperature thereof and lower the absolute humidity thereof, and reaches a state L. The state L is on a saturation curve in the psychrometric chart. The air in the state L is reheated by the reheater 205 to increase the dry bulb temperature thereof and keep the absolute humidity thereof constant, and reaches a state M. Then, the air is supplied to the air-conditioned space 100. The state M is lower in both of absolute humidity and dry bulb temperature than the state K.

With the conventional dehumidifying air-conditioning apparatus described above, since it is necessary to considerably cool the air to its dew point, about half of the cooling effect of the evaporator in the heat pump is consumed to remove a sensible heat load from the air, so that the moisture removal (the dehumidifying performance) per electric power consumption is low. If a single-stage compressor is used as the compressor in the heat pump, then it produces a one-stage compression-type refrigerating cycle, resulting in a low coefficient of performance (COP) and a large amount of electric power consumed per amount of moisture removal.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a heat pump with a high coefficient of performance (COP) and a dehumidifying air-conditioning apparatus which consumes a small amount of energy per amount of moisture removal.

In order to attain the above object, according to a first aspect of the present invention, there is provided a heat pump comprising: a pressurizer for raising a pressure of a refrigerant; a condenser for condensing the refrigerant to heat a high-temperature heat source fluid; an evaporator for evaporating the refrigerant to cool a low-temperature heat source fluid; a refrigerant path branched into a plurality of branched refrigerant paths between the condenser and the evaporator; a first heat exchanging portion disposed in the branched refrigerant path between the condenser and the evaporator for evaporating the refrigerant under an intermediate pressure between the condensing pressure of the condenser and the evaporating pressure of the evaporator to cool the low-temperature heat source fluid by evaporation of the refrigerant under the intermediate pressure; a second heat exchanging portion disposed in the branched refrigerant path between the condenser and the evaporator for condensing the refrigerant under an intermediate pressure between the condensing pressure of the condenser and the evaporating pressure of the evaporator to heat the low-temperature heat source fluid by condensation of the refrigerant under the intermediate pressure; a low-temperature heat source fluid path connecting the first heat exchanging portion, the evaporator, the second heat exchanging portion in the order named.

According to a second aspect of the present invention, there is provided a dehumidifying air-conditioning apparatus comprising: a pressurizer for raising a pressure of a refrigerant; a condenser for condensing the refrigerant to heat a high-temperature heat source fluid; an evaporator for evaporating the refrigerant to cool process air to a temperature lower than its dew point; a refrigerant path branched into a plurality of branched refrigerant paths between the condenser and the evaporator; a first heat exchanging portion disposed in the branched refrigerant path between the condenser and the evaporator for evaporating the refrigerant under an intermediate pressure between the condensing pressure of the condenser and the evaporating pressure of the evaporator to cool the process air by evaporation of the refrigerant under the intermediate pressure; a second heat exchanging portion disposed in the branched refrigerant path between the condenser and the evaporator for condensing the refrigerant under an intermediate pressure between the condensing pressure of the condenser and the evaporating pressure of the evaporator to heat the process air by condensation of the refrigerant under the intermediate pressure; a process air path connecting the first heat exchanging portion, the evaporator, the second heat exchanging portion in the order named.

With the above arrangement, the low-temperature heat source fluid can be precooled in the first heat exchanging portion prior to cooling in the evaporator. The low-temperature heat source fluid can be heated in the second heat exchanging portion after cooling in the evaporator with use of the heat in precooling. When process air is used as the low-temperature heat source and is cooled to a temperature lower than its dew point by the evaporator, it is possible to provide a dehumidifying air-conditioning apparatus which consumes a small amount of energy per amount of moisture removal.

Further, with the branched refrigerant paths, the operative temperature of the refrigerant can gradually be changed to achieve a high efficiency of heat exchange. When the high-temperature fluid is cooled, i.e., the heat exchanger is used for cooling the high-temperature fluid, the efficiency φ of heat exchange is defined by

φ=(TP1−TP2)/(TP1−TC1)

where the temperature of the high-temperature fluid at the inlet of the heat exchanger is represented by TP 1, the temperature thereof at the outlet of the heat exchanger by TP2, the temperature of the low-temperature fluid at the inlet of the heat exchanger is represented by TC1, and the temperature thereof at the outlet of the heat exchanger by TC2. When the low-temperature fluid is to be heated, i.e., when the heat exchanger is used to heat the low-temperature fluid, the efficiency φ of heat exchange is defined by

φ=(TC2−TC1)/(TP1−TC1)

According to a preferred aspect of the present invention, the branched refrigerant paths extend through the interior of the evaporator in parallel, respectively, and are joined to each other at the downstream side of the evaporator. In this case, there may be provided an ejector on a branched refrigerant path for a refrigerant which exchanges heat with process air having a high temperature, for pressurizing a refrigerant which exchanges heat with process air having a low temperature by a refrigerant which has passed through the branched refrigerant path.

With the above arrangement, since the operative temperature of the evaporator is increased to improve the theoretical cooling effect, the theoretical work of compression is reduced to achieve a high efficiency. Further, the specific volume of the refrigerant is reduced to increase the flow rate of the refrigerant drawn by the pressurizer. Therefore, an amount of moisture removal is increased according to the improved cooling effect, and hence a high efficiency can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a whole arrangement of an air-conditioning system according to a first embodiment of the present invention; [0016]
FIG. 2 is a flow diagram of a dehumidifying air-conditioning apparatus according to the first embodiment of the present invention; [0017]
FIG. 3 is an enlarged view showing branched refrigerant paths in a heat exchanger of the dehumidifying air-conditioning apparatus shown in FIG. 2; [0018]
FIG. 4A is a perspective view showing a heat exchanger and an evaporator in the case where a refrigerant path is not branched, as viewed from a front side; [0019]
FIG. 4B is a perspective view showing a heat exchanger and an evaporator in the case where a refrigerant path is not branched, as viewed from a rear side; [0020]
FIG. 5 is a Mollier diagram of a heat pump included in the dehumidifying air-conditioning apparatus shown in FIG. 2; [0021]
FIG. 6 is a psychrometric chart showing an air-conditioning cycle in the dehumidifying air-conditioning apparatus shown in FIG. 2; [0022]
FIG. 7 is a graph showing the relationship between the number of branched refrigerant paths and the temperature efficiency in a dehumidifying air-conditioning apparatus according to the present invention; [0023]
FIG. 8 is a flow diagram of a dehumidifying air-conditioning apparatus according to a second embodiment of the present invention; [0024]
FIG. 9 is a Mollier diagram of a heat pump included in the dehumidifying air-conditioning apparatus shown in FIG. 8; [0025]
FIG. 10 is a flow diagram of a conventional dehumidifying air-conditioning apparatus; [0026]
FIG. 11 is a Mollier diagram of a heat pump included in the conventional dehumidifying air-conditioning apparatus; and [0027]
FIG. 12 is a psychrometric chart showing an air-conditioning cycle in the conventional dehumidifying air-conditioning apparatus.[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

A dehumidifying air-conditioning apparatus according to a first embodiment of the present invention will be described below with reference to FIGS. 1 through 6. FIG. 1 is a schematic view showing a whole arrangement of an air-conditioning system according to the first embodiment of the present invention, and FIG. 2 is a flow diagram of a dehumidifying air-conditioning apparatus according to the first embodiment of the present invention. The dehumidifying air-conditioning apparatus in the first embodiment serves to cool process air to a temperature lower than its dew point for dehumidifying the air. The dehumidifying air-conditioning apparatus includes a heat pump HP[0029] 1 therein. The dehumidifying air-conditioning apparatus lowers the humidity of the process air to maintain a comfortable environment in an air-conditioned space 100 supplied with the process air.
As shown in FIG. 1, the dehumidifying air-conditioning apparatus mainly comprises an [0030] indoor unit 10 and an outdoor unit 20 installed outside of the air-conditioned space 100 (outdoor). The indoor unit 10 in the dehumidifying air-conditioning apparatus comprises a refrigerant evaporator 1 for evaporating a refrigerant, a heat exchanger 2 for exchanging heat between the refrigerant and the process air, and an air blower 3 for circulating the process air. The heat exchanger 2 performs a heat exchange between process air flowing into the evaporator 1 and process air flowing out of the evaporator 1, indirectly with the refrigerant. The heat exchanger 2 has a first heat exchanging portion 21 for evaporating the refrigerant to cool the process air, and a second heat exchanging portion 22 for condensing the refrigerant to heat the process air. The outdoor unit 20 in the dehumidifying air-conditioning apparatus comprises a pressurizer (compressor) 4 for raising a pressure of the refrigerant, a refrigerant condenser 5 for cooling and condensing the refrigerant, and an air blower 6 for circulating the cooling air.
Process air paths, which are paths for circulating process air, include a [0031] path 30 connecting the air-conditioned space 100 and the first heat exchanging portion 21 in the heat exchanger 2, a path 31 connecting the first heat exchanging portion 21 and the evaporator 1, a path 32 connecting the evaporator 1 and the second heat exchanging portion 22 in the heat exchanger 2, a path 33 connecting the second heat exchanging portion 22 and the air blower 3, and a path 34 connecting the air blower 3 and the air-conditioned space 100. Thus, the first heat exchanging portion 21 in the heat exchanger 2, the evaporator 1, and the second heat exchanging portion 22 in the heat exchanger 2 are connected in the order named by the process air paths.
Refrigerant paths include a [0032] path 40 connecting the evaporator 1 and the compressor 4, a path 41 connecting the compressor 4 and the condenser 5, and a path connecting the condenser 5 and the evaporator 1. The path connecting the condenser 5 and the evaporator 1 is branched into a plurality of branched refrigerant paths at the downstream side of the condenser 5. In FIG. 2, three branched refrigerant paths 42, 43, 44 are formed at the downstream side of the condenser 5. The branched refrigerant paths 42, 43, 44 are joined to one path 45 at the upstream side of the evaporator 1.
Outside air OA is introduced as cooling air through the [0033] path 46 into the condenser 5. The outside air OA removes heat from the refrigerant which is condensed, and the heated outside air OA is drawn through the path 47 into the air blower 6, from which the air is discharged through the path 48 as exhaust air EX.
The branched [0034] refrigerant paths 42, 43, 44 penetrate the first heat exchanging portion 21 and the second heat exchanging portion 22 in the heat exchanger 2, respectively. An evaporating section 51 for evaporating the refrigerant to cool the process air which flows through the first heat exchanging portion 21 is provided in the first heat exchanging portion 21 of the heat exchanger 2. A condensing section 52 for condensing the refrigerant to heat (reheat) the process air which flows through the second heat exchanging portion 22 is provided in the second heat exchanging portion 22 of the heat exchanger 2. Restrictions 11, 12, 13 are disposed on the respective branched refrigerant paths 42, 43, 44 at the upstream side of the first heat exchanging portion 21. Restrictions 14, 15, 16 are disposed on the respective branched refrigerant paths 42, 43, 44 at the downstream side of the second heat exchanging portion 22. The restrictions 11-16 may comprise orifices, capillary tubes, expansion valves, or the like.
FIG. 3 is an enlarged view showing the branched [0035] refrigerant paths 42, 43, 44 in the heat exchanger 2 of the dehumidifying air-conditioning apparatus shown in FIG. 2. The refrigerant paths including the evaporating section 51 and the condensing section 52 penetrate the first heat exchanging portion 21 and the second heat exchanging portion 22 in the heat exchanger 2, alternately and repeatedly. Specifically, as shown in FIG. 3, the refrigerant path 42 has an evaporating section 61 a, a condensing section 62 a, a condensing section 62 b, an evaporating section 61 b, an evaporating section 61 c, and a condensing section 62 c. The refrigerant path 43 has an evaporating section 63 a, a condensing section 64 a, a condensing section 64 b, an evaporating section 63 b, an evaporating section 63 c, and a condensing section 64 c. The refrigerant path 44 has an evaporating section 65 a, a condensing section 66 a, a condensing section 66 b, an evaporating section 65 b, an evaporating section 65 c, and a condensing section 66 c.
The [0036] heat exchanger 2 has the first heat exchanging portion 21 for allowing the process air before flowing through the evaporator 1 to pass therethrough, and the second heat exchanging portion 22 for allowing the process air after flowing through the evaporator 1 to pass therethrough. The first heat exchanging portion 21 and the second heat exchanging portion 22 form respective separate spaces, each in the form of a rectangular parallelepiped. The evaporator 1 is disposed between the first heat exchanging portion 21 and the second heat exchanging portion 22. FIGS. 4A and 4B show the arrangement of a heat exchanger and an evaporator in the case where a refrigerant path is not branched, for reference. FIG. 4A is a perspective view as viewed from the front side, and FIG. 4B is a perspective view as viewed from the rear side.
The first [0037] heat exchanging portion 21 and the second heat exchanging portion 22 have a plurality of substantially parallel heat exchange tubes as refrigerant passages in each of a plurality of planes which lie perpendicularly to the flow of the process air. Tubes 67 are provided across the evaporator 1 between the corresponding sections, for example, the evaporating section 61 a and the condensing section 62 a, the evaporating section 61 b and the condensing section 62 b, and the evaporating section 61 c and the condensing section 62 c (see FIG. 4B). Thus, the corresponding evaporating and condensing sections are connected to each other. The ends of the evaporating sections 61 b, 61 c, the ends of the evaporating sections 63 b, 63 c, and the ends of the evaporating sections 65 b, 65 c are connected to each other by a U tube 68. Similarly, the ends of the condensing sections 62 a, 62 b, the ends of the condensing sections 64 a, 64 b, and the ends of the condensing sections 66 a, 66 b are connected to each other by a U tube 69 (see FIG. 4A).
With the above arrangement, for example, in the [0038] refrigerant path 42, the refrigerant flowing in one direction from the evaporating section 61 a to the evaporating section 62 a is introduced into the condensing section 62 b by the U tube 69. The refrigerant introduced into the condensing section 62 b then flows into the evaporating section 61 b, from which the refrigerant flows into the evaporating section 61 c via the U tube 68 and further flows into the condensing section 62 c. In this manner, the refrigerant passages are provided as a group of meandering thin pipes. A group of meandering thin pipes pass through the first heat exchanging portion 21 and the second heat exchanging portion 22, and are held in alternate contact with the process air which has a higher temperature and the process air which has a lower temperature.
As shown in FIGS. 1 and 2, a [0039] drain pan 7 is provided in the indoor unit 10 of the dehumidifying air-conditioning apparatus. The drain pan 7 is preferably located below not only the evaporator 1, but also the heat exchanger 2. Particularly, the drain pan 7 is preferably disposed below the first heat exchanging portion 21 because the process air is mainly precooled in the first heat exchanging portion 21 and some moisture may possibly be condensed in the first heat exchanging portion 21.
The flow of the refrigerant in the devices will be described below with reference to FIGS. 2 and 3. [0040]
A refrigerant vapor pressurized by the [0041] compressor 4 is introduced into the condenser 5 via the refrigerant pipe 41 connected to the discharge port of the compressor 4. The refrigerant vapor compressed by the compressor 4 is cooled and condensed by the outside air OA as cooling air. The refrigerant liquid flowing out of the condenser 5 is branched into the branched refrigerant paths 42, 43, 44. The refrigerants similarly flow through the respective refrigerant paths 42, 43, 44. Therefore, the refrigerant flowing through the refrigerant path 42 will mainly be described below, and the refrigerants flowing through the other refrigerant paths 43, 44 will not be described in detail below.
The refrigerant flowing through the [0042] refrigerant path 42 is depressurized by the restriction 11 and expanded so as to be partly evaporated (flashed). The refrigerant which is a mixture of the liquid and the vapor reaches the evaporating section 61 a, where the refrigerant liquid flows so as to wet the inner wall surface of the tube in the evaporating section 61 a. The refrigerant flows into the evaporating section 61 a in the liquid phase. The refrigerant may be a refrigerant liquid which has been partly evaporated to slightly contain a vapor phase. While the refrigerant liquid is flowing through the evaporating section 61 a, it is evaporated to cool (precool) the process air before flowing into the evaporator 1. The refrigerant itself is heated while increasing the vapor phase thereof.
As described above, the evaporating [0043] section 61 a and the condensing section 62 a are constructed as a continuous tube. Specifically, since the evaporating section 61 a and the condensing section 62 a are provided as an integral passage, the refrigerant vapor evaporated in the evaporating section 61 a (and the refrigerant liquid which has not been evaporated) flows into the condensing section 62 a, and heats (reheats) the process air, which has been cooled and dehumidified in the evaporator 1 and has a temperature lower than the process air in the evaporating section 61 a. At this time, heat is removed from the evaporated refrigerant vapor itself, and while the evaporated refrigerant vapor in the vapor phase is condensed, the refrigerant flows into the next condensing section 62 b. While the refrigerant is flowing through the condensing section 62 b, heat is further removed from the refrigerant by the process air having a lower temperature, and the refrigerant in the vapor phase is further condensed.
The condensed refrigerant liquid flows into the next evaporating [0044] section 61 b and the subsequent evaporating section 61 c to cool (precool) the process air before flowing into the evaporator 1 in the same manner as described above. Thereafter, the refrigerant vapor flows into the condensing section 62 c to heat (reheat) the process air. In this manner, the refrigerant flows through the branched refrigerant path while changing in phase between the vapor phase and the liquid phase. Thus, heat is exchanged between the process air before being cooled by the evaporator 1 and the process air which has been cooled by the evaporator 1 to lower its absolute humidity.
The refrigerant liquid condensed in the condensing [0045] section 62 c is depressurized and expanded by the restriction 14 provided at the downstream side of the second heat exchanging portion 22, for thereby lowering its pressure. Then, the refrigerant liquid is joined to the refrigerants which have flowed through the other branched refrigerant liquid paths 43, 44. The joined refrigerant liquid enters the evaporator 1 to be evaporated to cool the process air with heat of evaporation. The refrigerant which has been evaporated into a vapor in the evaporator 1 is introduced into the suction side of the compressor 4 through the path 40, and thus the above cycle is repeated.
Next, operation of the heat pump HP[0046] 1 included in the dehumidifying air-conditioning apparatus according to the first embodiment of the present invention will be described below with reference to FIG. 5. FIG. 5 is a Mollier diagram of the heat pump HP1 included in the dehumidifying air-conditioning apparatus shown in FIG. 2. The diagram shown in FIG. 5 is a Mollier diagram in the case where HFC134a is used as the refrigerant. In the Mollier diagram, the horizontal axis represents the enthalpy, and the vertical axis represents the pressure. In addition to the above refrigerant, HFC407C and HFC410A are suitable refrigerants for the heat pump and the dehumidifying air-conditioning apparatus according to the present invention. These refrigerants have an operating pressure region shifted toward a higher pressure side than HFC134a.
In FIG. 5, a point a represents a state of the refrigerant which has been evaporated by the [0047] evaporator 1 shown in FIG. 2, and the refrigerant is in the form of a saturated vapor. The refrigerant has a pressure of 0.234 MPa, a temperature of 5° C., and an enthalpy of 395.1 kJ/kg. A point b represents a state of the vapor drawn and compressed by the compressor 4, i.e., a state at the outlet port of the compressor 4. In the point b, the refrigerant has a pressure of 0.706 MPa and is in the form of a superheated vapor.
The refrigerant vapor at the point b is cooled in the [0048] condenser 5 and reaches a state represented by a point c in the Mollier diagram. In the point c, the refrigerant is in the form of a saturated vapor and has a pressure of 0.706 MPa and a temperature of 38° C. Under this pressure, the refrigerant is cooled and condensed to reach a state represented by a point d. In the point d, the refrigerant is in the form of a saturated liquid and has the same pressure and temperature as those in the point c. The saturated liquid has an enthalpy of 237.4 kJ/kg.
The refrigerant liquid is branched into the branched [0049] refrigerant liquid paths 42, 43, 44, and the branched refrigerant liquids flow into the heat exchanger 2. First, the refrigerant flowing through the refrigerant path 43 will be described below. The refrigerant liquid is depressurized by the restriction 12 and flows into the evaporating section 63 a in the first heat exchanging portion 21. This state is indicated at a point e on the Mollier diagram. The refrigerant liquid is a mixture of the liquid and the vapor because a part of the liquid is evaporated. The pressure of the refrigerant liquid is an intermediate pressure between the condensing pressure in the condenser 5 and the evaporating pressure in the evaporator 1, i.e., is of an intermediate value between 0.234 MPa and 0.706 MPa in the present embodiment.
In the evaporating [0050] section 63 a, the refrigerant liquid is evaporated under the intermediate pressure, and reaches a state represented by a point f1, which is located intermediately between the saturated liquid curve and the saturated vapor curve, under the intermediate pressure. In the point f1, while a part of the liquid is evaporated, the refrigerant liquid remains in a considerable amount. The refrigerant in the state represented by the point f1 flows into the condensing sections 64 a, 64 b. In the condensing sections 64 a, 64 b, heat is removed from the refrigerant by the process air which has a low temperature and flows through the second heat exchanging portion 22, and the refrigerant reaches a state represented by a point g1.
The refrigerant in the state represented by the point g1 flows into the evaporating [0051] sections 63 b, 63 c, where heat is removed from the refrigerant. The refrigerant increases its liquid phase and reaches a state represented by a point f2. Then, the refrigerant flows into the condensing section 64 c, where the refrigerant increases its liquid phase and reaches a state represented by a point g2. On the Mollier diagram, the point g2 is on the saturated liquid curve. In this point, the refrigerant has a temperature of 18° C. and an enthalpy of 209.5 kJ/kg.
The refrigerant liquid at the point g2 is depressurized to 0.234 MPa, which is a saturated pressure at a temperature of 5° C., by the [0052] restriction 15, and reaches a state represented by a point h. The refrigerant at the point h flows as a mixture of the refrigerant liquid and the vapor at a temperature of 5° C. into the evaporator 1, where the refrigerant removes heat from the process air to thus be evaporated into a saturated vapor at the state indicated by the point a on the Mollier diagram. The evaporated vapor is drawn again by the compressor 4, and thus the above cycle is repeated.
In the same manner as described above, the refrigerant flowing into the [0053] refrigerant path 42 passes through the restriction 11, the evaporating sections, the condensing sections, and the restriction 14. The refrigerant goes through states represented by points j, i1, k1, i2, and k2 and reaches the a state represented by a point l. The refrigerant flowing into the refrigerant path 44 passes through the restriction 13, the evaporating sections, the condensing sections, and the restriction 16. The refrigerant goes through states represented by points m, n1, o1, n2, and o2 and reaches a state represented by a point P.
In the [0054] heat exchanger 2, as described above, the refrigerant goes through changes of the evaporated state from the point e to the point f1 or from the point g1 to the point f2 in the evaporating section 51, and goes through changes of the condensed state from the point f1 to the point g1 or from the point f2 to the point g2 in the condensing section 52. Since the refrigerant transfers heat by way of evaporation and condensation, the rate of heat transfer is very high and the efficiency of heat exchanger is high.
In the vapor compression type heat pump HP[0055] 1 including the compressor 4, the condenser 5, the restrictions 11-16, and the evaporator 1, when the heat exchanger 2 is not provided, the refrigerant at the state represented by the point d in the condenser 5 is returned to the evaporator 1 through the restrictions. Therefore, the enthalpy difference that can be used by the evaporator 1 is only 395.1−237.4=157.7 kJ/kg. With the heat pump HP1 according to the present embodiment which has the heat exchanger 2, however, the enthalpy difference that can be used by the evaporator 1 is 395.1−209.5=185.6 kJ/kg. Thus, the amount of refrigerant that is circulated to the compressor under the same cooling load and the required power can be reduced by 15% (=1−157.7/185.6). Consequently, the heat pump HP1 according to the present embodiment can perform the same operation as with a well-known subcooled cycle.
FIG. 6 is a psychrometric chart showing an air-conditioning cycle in the dehumidifying air-conditioning apparatus shown in FIG. 2. In FIG. 6, the alphabetical letters K, X, L, M correspond to the encircled letters in FIG. 2. [0056]
In FIG. 6, the process air (in a state K) from the air-conditioned [0057] space 100 flows through the path 30 into the first heat exchanging portion 21 in the heat exchanger 2, where the process air is cooled to a certain extent by the refrigerant that is evaporated in the evaporating section 51. This process can be referred to as precooling because the process air is preliminarily cooled before being cooled to a temperature lower than its dew point by the evaporator 1. While the process air is being precooled in the evaporating section 51, a certain amount of moisture is removed from the air to lower the absolute humidity of the air, and then air reaches a point X on the saturation curve. Alternatively, the air may be precooled to an intermediate point between the point K and the point X. Further, the air may be precooled to a point that is shifted beyond the point X slightly toward a lower humidity on the saturation curve.
The process air precooled by the first [0058] heat exchanging portion 21 is introduced through the path 31 into the evaporator 1, where the air is cooled to a temperature lower than its dew point by the refrigerant which has been depressurized by the restrictions 14-16 and is evaporated at a low temperature. Moisture is removed from the air to lower the absolute humidity and the dry bulb temperature of the air, and the air reaches a point L. Although the thick line representing a change from the point X to the point L is plotted as being remote from the saturation curve for illustrative purpose in FIG. 6, it is actually aligned with the saturation curve.
The process air in the state represented by the point L flows through the [0059] path 32 into the second heat exchanging portion 22 in the heat exchanger 2, where the process air is heated, with the constant absolute humidity, by the refrigerant condensed in the condensing section 52, and reaches a point M. The process air in the point M has a sufficiently lower absolute humidity than the process air in the point K, a dry bulb temperature which is not excessively lower than the process air in the point K, and a suitable relative humidity. The process air in the point M is then drawn by the air blower 3 and returned to the air-conditioned space 100 through the path 34.
In the air cycle on the psychrometric chart shown in FIG. 6, the amount of heat which has precooled the process air in the first [0060] heat exchanging portion 21, i.e., the amount AH of heat which has reheated the process air in the second heat exchanging portion 22, represents the amount of heat recovered, and the amount of heat which has cooled the process air in the evaporator 1 is represented by ΔQ. The cooling effect for cooling the air-conditioned space 100 is represented by Δi.
As described above, in the [0061] heat exchanger 2, the process air is precooled by evaporation of the refrigerant in the evaporating section 51, and the process air is reheated by condensation of the refrigerant in the condensing section 52. The refrigerant evaporated in the evaporating section 51 is condensed in the condensing section 52. The same refrigerant is thus evaporated and condensed to perform a heat exchange indirectly between the process air before being cooled in the evaporator 1 and the process air after being cooled in the evaporator 1.
In the embodiment described above, the same refrigerant is used as a heat transfer medium in the evaporator for cooling the process air to a temperature lower than its dew point, the precooler for precooling the process air, and the reheater for reheating the process air. Therefore, the refrigerant system is simplified. The refrigerant is positively circulated because the pressure difference between the evaporator and the condenser can be utilized. Since a boiling phenomenon with a phase change is applied to heat exchanges for precooling and reheating the process air, a high heat transfer efficiency can be achieved. [0062]
In the embodiment described above, the refrigerant path is branched into the three branched refrigerant paths. However, the present invention is not limited to three branched refrigerant paths. The refrigerant path may be branched into any number of branched refrigerant paths. FIG. 7 is a graph showing the relationship between the number of branched refrigerant paths and the temperature efficiency in a dehumidifying air-conditioning apparatus according to the present invention. It is inferred from FIG. 7 that the temperature efficiency can be improved when the number of branched refrigerant paths is larger. Thus, when a plurality of branched refrigerant paths are provided, the operative temperature of the refrigerant can gradually be changed to achieve a high efficiency of heat exchange. [0063]
A dehumidifying air-conditioning apparatus according to a second embodiment of the present invention will be described below with reference to FIGS. 8 and 9. FIG. 8 is a flow diagram of a dehumidifying air-conditioning apparatus according to the second embodiment of the present invention, and FIG. 9 is a Mollier diagram of a heat pump HP[0064] 2 included in the dehumidifying air-conditioning apparatus shown in FIG. 8. In FIGS. 8 and 9, like parts and components are denoted by the same reference numerals and characters as those of the first embodiment and will not be described below.
In the present embodiment, a refrigerant path is branched into a plurality of refrigerant paths at the downstream side of the [0065] condenser 5 to form branched refrigerant paths 142, 143, 144. The present embodiment differs from the first embodiment in that these branched refrigerant paths 142, 143, 144 extend to the interior of an evaporator 101, respectively, and joined to each other at the downstream side of the evaporator 101. Among these branched refrigerant paths 142, 143, 144, the refrigerant path for the refrigerant which exchanges heat with the process air having a high temperature, i.e., the branched refrigerant path 142, has an ejector 8 provided thereon for pressurizing the refrigerant which exchanges heat with the process air having a low temperature, i.e., the refrigerant that has passed through the refrigerant path 144.
In FIG. 9, a point a represents a state of the refrigerant which has been evaporated by the [0066] evaporator 101 shown in FIG. 8, and the refrigerant is in the form of a saturated vapor. The refrigerant has a pressure of 0.262 MPa, a temperature of 8° C., and an enthalpy of 396.8 kJ/kg. A point b represents a state of the vapor drawn and compressed by the compressor 4, i.e., a state at the outlet port of the compressor 4. In the point b, the refrigerant has a pressure of 0.706 MPa and is in the form of a superheated vapor.
The refrigerant vapor is cooled in the [0067] condenser 5 and reaches a state represented by a point c in the Mollier diagram. In the point c, the refrigerant is in the form of a saturated vapor and has a pressure of 0.706 MPa and a temperature of 38° C. Under this pressure, the refrigerant is cooled and condensed to reach a state represented by a point d. In the point d, the refrigerant is in the form of a saturated liquid and has the same pressure and temperature as those in the point c. The saturated liquid has an enthalpy of 237.4 kJ/kg.
The refrigerant liquid is depressurized by the [0068] restriction 12 and reaches a state represented by a point e on the Mollier diagram. The pressure of the refrigerant liquid is an intermediate pressure between the condensing pressure in the condenser 5 and the evaporating pressure in the evaporator 101, i.e., is of an intermediate value between 0.262 MPa and 0.706 MPa in the present embodiment. Then, the refrigerant flows alternately through the evaporating sections in the first heat exchanging portion 21 and the condensing sections in the second heat exchanging portion 22 and goes through states represented by points f1, g1, f2, and g2. Thereafter, the refrigerant is depressurized by the restriction 15 to a saturation pressure of 0.262 MPa at a temperature of 8° C. and reaches a state represented by the point h. The refrigerant at the point h is delivered as a mixture of the refrigerant liquid and the vapor at a temperature of 8° C. to the evaporator 101, in which the mixture removes heat from the process air and is evaporated to reach a state of the saturated vapor, which is represented by the point a in the Mollier diagram. The saturated vapor is drawn into the compressor 4 again, and the above cycle is repeated.
The refrigerant flowing into the [0069] refrigerant path 142 passes through the restriction 11, the evaporating sections, the condensing sections, and the restriction 14. The refrigerant goes through states represented by points j, i1, k1, i2, and k2 and reaches the a state represented by a point 1. The refrigerant in the state represented by the point 1 flows into the evaporator 101, where the refrigerant removes heat from the process air to be evaporated and reaches a state indicated by the point q on the Mollier diagram. The refrigerant flowing into the refrigerant path 144 passes through the restriction 13, the evaporating sections, the condensing sections, and the restriction 16. The refrigerant goes through states represented by points m, n1, o1, n2, and o2 and reaches a state represented by a point P.
The refrigerant in the state represented by the point p flows into the [0070] evaporator 101, where the refrigerant removes heat from the process air to be evaporated and reaches a state indicated by the point r on the Mollier diagram. The refrigerant in the state represented by the point r is pressurized by the ejector 8 provided on the refrigerant path 142. Specifically, in the ejector 8, the refrigerant at a low pressure in the state represented by the point r is pressurized by the refrigerant at a high pressure in the state represented by the point q. As a result, the refrigerant in the state represented by the point r and the refrigerant in the state represented by the point q reach a state of the saturated vapor, which is represented by the point a in the Mollier diagram. In this manner, with the ejector 8, since the operative temperature of the evaporator is increased to improve the theoretical cooling effect, the theoretical work of compression is reduced to achieve a high efficiency. Further, the specific volume of the refrigerant is reduced to increase the flow rate of the refrigerant drawn by the compressor. Therefore, an amount of moisture removal is increased according to the improved cooling effect, and hence a high efficiency can be achieved.
In the vapor compression type heat pump HP[0071] 2 including the compressor 4, the condenser 5, the restrictions 11-16, and the evaporator 101, when the heat exchanger 2 is not provided, the refrigerant at the state represented by the point d in the condenser 5 is returned to the evaporator 101 through the restrictions. Therefore, the enthalpy difference that can be used by the evaporator 101 is only 396.8−237.4=159.4 kJ/kg. With the heat pump HP2 according to the present embodiment which has the heat exchanger 2, however, the enthalpy difference that can be used by the refrigerant evaporator 101 is 396.8-209.5=187.3 kJ/kg. Thus, the amount of refrigerant that is circulated to the compressor under the same cooling load and the required power can be reduced by 15% (=1−159.4/187.3). Consequently, the heat pump HP2 according to the present embodiment can perform the same operation as with a well-known subcooled cycle.
While the present invention has been described in detail with reference to the preferred embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit and scope of the present invention. For example, the number of the evaporating sections on the respective branched refrigerant paths in the first heat exchanging portion and the number of the condensing sections on the respective branched refrigerant paths in the second heat exchanging portion are not limited to the illustrated examples. With respect to the order of the refrigerant paths in the heat exchanger, the refrigerant may be introduced into the heat exchanger from the second heat exchanging portion in place of the first heat exchanging portion. In this case, the second heat exchanging portion, the first heat exchanging portion, and the second heat exchanging portion are arranged in the order named, so that the number of paths can be increased. Further, the dehumidifying air-conditioning apparatus according to the above embodiments has been described as the dehumidifying air-conditioning apparatus for air-conditioning a space. However, the dehumidifying air-conditioning apparatus according to the present invention is applicable not only to the air-conditioned space, but also to other spaces that need to be dehumidified. [0072]

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a heat pump with a high coefficient of performance (COP) and a dehumidifying air-conditioning apparatus which has such a heat pump and a high moisture removal per energy consumption. [0073]

Claims

1. A heat pump comprising:

a pressurizer for raising a pressure of a refrigerant;

a condenser for condensing said refrigerant to heat a high-temperature heat source fluid;

an evaporator for evaporating said refrigerant to cool a low-temperature heat source fluid;

a refrigerant path branched into a plurality of branched refrigerant paths between said condenser and said evaporator;

a first heat exchanging portion disposed in said branched refrigerant path between said condenser and said evaporator for evaporating said refrigerant under an intermediate pressure between the condensing pressure of said condenser and the evaporating pressure of said evaporator to cool said low-temperature heat source fluid by evaporation of said refrigerant under said intermediate pressure;

a second heat exchanging portion disposed in said branched refrigerant path between said condenser and said evaporator for condensing said refrigerant under an intermediate pressure between the condensing pressure of said condenser and the evaporating pressure of said evaporator to heat said low-temperature heat source fluid by condensation of said refrigerant under said intermediate pressure;

a low-temperature heat source fluid path connecting said first heat exchanging portion, said evaporator, said second heat exchanging portion in the order named.

2. A dehumidifying air-conditioning apparatus comprising:

a pressurizer for raising a pressure of a refrigerant;

an evaporator for evaporating said refrigerant to cool process air to a temperature lower than its dew point;

a first heat exchanging portion disposed in said branched refrigerant path between said condenser and said evaporator for evaporating said refrigerant under an intermediate pressure between the condensing pressure of said condenser and the evaporating pressure of said evaporator to cool said process air by evaporation of said refrigerant under said intermediate pressure;

a second heat exchanging portion disposed in said branched refrigerant path between said condenser and said evaporator for condensing said refrigerant under an intermediate pressure between the condensing pressure of said condenser and the evaporating pressure of said evaporator to heat said process air by condensation of said refrigerant under said intermediate pressure;

a process air path connecting said first heat exchanging portion, said evaporator, said second heat exchanging portion in the order named.

3. A dehumidifying air-conditioning apparatus according to claim 2, wherein said branched refrigerant paths extend through the interior of said evaporator in parallel, respectively, and are joined to each other at the downstream side of said evaporator.

4. A dehumidifying air-conditioning apparatus according to claim 3, further comprising an ejector provided on a branched refrigerant path for a refrigerant which exchanges heat with process air having a high temperature, for pressurizing a refrigerant which exchanges heat with process air having a low temperature by a refrigerant which has passed through said branched refrigerant path.