GB2273763A

GB2273763A - Air conditioning apparatus having a supercooling unit provided between an outdoor unit and a plurality of indoor units

Info

Publication number: GB2273763A
Application number: GB9326493A
Authority: GB
Inventors: Hirofumi Sano; Kazuo Yamamoto
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1992-12-28
Filing date: 1993-12-29
Publication date: 1994-06-29
Anticipated expiration: 2013-12-29
Also published as: GB9326493D0; GB2273763B; JPH06201176A

Abstract

A supercooling unit (C) is provided between an outdoor unit (A) and a plurality of indoor units (B). The capacity of a compressor (1) of the outdoor unit (A) is controlled according to the requested capacity of each of the indoor units (B). When the total value of the requested capacities of the respective indoor units (B, B1) has exceeded a preset value by additionally installing an indoor unit (B1), the supercooling unit (C) is operated. By operating the supercooling unit (C), a deficient amount of operation capacity can be compensated for. The supercooling unit (A) comprises a second compressor (21) of variable capacity, a condenser (22), an expansion valve (23), and a heat exchange unit (24) for cooling refrigerant flowing between said outdoor heat exchanger (A) and the indoor heat exchanger (B). <IMAGE>

Description

"AIR CONDITIONING APPARATUS HAVING A SUPERCOOLING UNIT PROVIDED BETWEEN AN OUTDOOR UNIT AND A PLURALITY OF INDOOR UNITS" This invention relates to an air conditioning apparatus provided with a supercooling unit.

In a building having a large number of rooms or the like, a multi-type air conditioning apparatus having a plurality of indoor units connected to an outdoor unit is used. By using this type of air conditioning apparatus, a large number of rooms can be simultaneously airconditioned.

As one of air conditioning loads of the air conditioning apparatus, a cooling load for a room in which OA devices such as a computer and a printer are provided is used. The cooling load tends to become larger with a recent increase in the number of OA devices used.

As a method for coping with an increase in the cooling load, it is considered to use a large-scale air conditioning apparatus from the beginning. With installation of such a large-scale air conditioning apparatus, even if the air conditioning load of the room increases after installation of the air conditioning - apparatus, a sufficiently large cooling capacity for coping with the increased air conditioning load can be immediately attained.

As another method for coping with an increase in the cooling load, it is considered to exchange the indoor unit for an indoor unit having a larger capacity.

Alternatively, it is considered to newly provide an indoor unit in a room in which the cooling load is increased and cool the room in which the cooling load is increased by use of a plurality of indoor units.

However, if a large-scale air conditioning apparatus is used from the beginning, a problem that adaptation to the subdivided air conditioning which is the latest trend becomes difficult occurs. That is, in a case where a small space around a desk at which a person sits is cooled, it is excessively cooled if the cooling capacity is large.

Further, even if the indoor unit is exchanged for an indoor unit with a larger capacity or an indoor unit is newly installed, a sufficiently large cooling capacity for the air conditioning load cannot be attained if the compressor capacity is not changed.

That is, when the indoor unit is exchanged for an indoor unit with a larger capacity or an indoor unit is additionally installed, it becomes necessary to exchange the compressor for a compressor with a larger capacity.

At this time, large-scale pipe arrangement and wiring for the whole apparatus will become necessary.-- An object of this invention is to provide an air conditioning apparatus capable of easily attaining subdivided air conditioning and immediately coping with an increase in the air conditioning load to attain an optimum cooling capacity without effecting the large-scale pipe arrangement and wiring for the whole apparatus.

The above object can be attained by an air conditioning apparatus having a supercooling unit provided between an outdoor unit and a plurality of indoor units, comprising: a first compressor of capacity variable type provided in the outdoor unit, for drawing, compressing and discharging a refrigerant; an outdoor heat exchanger provided in the outdoor unit, for exchanging the heat of a refrigerant discharged from the compressor for the heat of external air; a plurality of indoor heat exchangers provided in the respective indoor units, for exchanging the heat of a refrigerant passing through the outdoor heat exchanger for the heat of internal air; a first refrigerating cycle constructed by connecting the first compressor, outdoor heat exchanger and indoor heat exchangers by piping;; a second compressor provided in the supercooling unit, for drawing, compressing and discharging a refrigerant; a condenser provided in the supercooling unit, for condensing a refrigerant discharged from the second compressor; a heat exchange unit provided in the supercooling unit, for cooling a refrigerant flowing between the outdoor heat exchanger and the respective indoor heat exchangers by use of the refrigerant passing through the condenser; a second refrigerating cycle constructed by connecting the second compressor, condenser and heat exchange unit by piping; first detection means for detecting the air conditioning load of the rooms in which the respective indoor units are installed; setting means for setting a requested capacity corresponding to each air conditioning load detected by the first detection means;; control means for controlling the capacity of the first compressor according to the total value of the requested capacities set by the setting means; and control means for driving the second compressor when the total value of the requested capacities set by the setting means exceeds a previously determined value.

This invention can be more fully understood from the following detailed description when taken in con-.

junction with the accompanying drawings, in which: FIG. 1 is a diagram showing the construction of a refrigerating cycle of each embodiment of this invention; FIG. 2 is a diagram showing the concrete construction of a heat exchange unit of each embodiment; FIG. 3 is a diagram showing the construction of a modification of the heat exchange unit shown in FIG. 2; FIG. 4 is a block diagram showing the construction of a control circuit of each embodiment; FIG. 5 is a flowchart for illustrating the operation of each indoor unit in the first embodiment; FIG. 6 is a flowchart for illustrating the operation of an outdoor unit in the first embodiment; FIG. 7 is a flowchart for illustrating the operation of a supercooling unit in the first embodiment; FIG. 8 is a diagram showing the condition for setting the requested capacity for each of the indoor units in each embodiment;; FIG. 9 is a diagram showing the condition for setting the driving frequency of the compressor in each embodiment; FIG. 10 is a diagram showing the condition for correcting the capacity of the supercooling unit in the first embodiment; FIG. 11 is a diagram showing the driving condition of the outdoor unit and supercooling unit in each embodiment; FIG. 12 is a flowchart for illustrating the operation of each indoor unit in the second embodiment; FIG. 13 is a flowchart for illustrating the operation of an outdoor unit in the second embodiment; FIG. 14 is a flowchart for illustrating the operation of a supercooling unit in the second embodiment; FIG. 15 is a diagram showing the condition for setting a target pseudo degree of superheat in the second embodiment; FIG. 16 is a flowchart for illustrating the operation of an outdoor unit in the third embodiment;; FIG. 17 is a flowchart for illustrating the operation of each indoor unit in the fourth embodiment; 'FIG. 18 is a flowchart for illustrating the operation of an outdoor unit in the fourth embodiment; FIG. 19 is a flowchart for illustrating the operation of a supercooling unit in the fourth embodiment; FIG. 20 is a diagram showing the capacities of the outdoor unit and each indoor unit in the fourth embodiment; FIG. 21 is a diagram showing a variation in the opening of PMV in the fourth embodiment; FIG. 22 is -a flowchart for illustrating the operation of each indoor unit in the fifth embodiment; an- - FIG. 23 is a flowchart for illustrating the operation of an outdoor-unit-in-the f-ifth embodiment.

There will now be described a first embodiment of this invention with reference to the accompanying drawings.

As shown in FIG. 1, an outdoor unit A is connected to a plurality of indoor units B, ---, B1 by piping. A supercooling unit C is connected between the outdoor unit A and the indoor units B by piping. The indoor unit B1 is an extensible indoor unit which can be additionally used when required.

The outdoor unit A includes a first compressor 1 of capacity variable type. The compressor 1 draws a refrigerant via an inlet port, compresses the refrigerant, and discharges the compressed refrigerant from a discharge port. The discharge port of the compressor 1 is connected to an outdoor heat exchanger 3 via a fourway valve 2 by piping. The heat exchanger 3 is connected to a liquid tank 6 via a parallel circuit of a check valve 4 for forming a cooling cycle and an expansion valve 5 for heating by piping.

The liquid tank 6 is connected to an indoor heat exchanger 13 via a two-way valve 11 and electrically driven flow control valve 12 by piping. The indoor heat exchanger 13 is connected to the inlet port of the compressor 1 via the four-way valve 2 and an accumulator 7. In this case, as the flow control valve 12, a pulse motor valve whose opening continuously changes according to the number of driving pulses is used. In the following description, the flow control valve is briefly expressed by PMV.

The connection and constructions of the two-way valve 11, PMV 12 and indoor heat exchanger 13 are the same in each of the indoor units B, ---, B1.

Thus, a first refrigerating cycle is created by the outdoor unit A and the indoor units B, ---, B1.

At the time of cooling operation, a refrigerant flows in a direction indicated by arrows of solid lines to create a cooling cycle. At the time of heating operation, the position of the four-way valve 2 is switched and a refrigerant flows in a direction indicated by arrows of.broken lines to create a heating cycle.

A pressure sensor 8 is mounted on a pipe on the low-pressure side between the accumulator 7 and the inlet port of the compressor 1. A temperature sensor 14 is mounted on a pipe on the refrigerant discharge side (at the time of cooling operation) of each of the indoor heat exchangers 13.

On the other hand, the supercooling unit A includes a second compressor 21 of capacity variable type. The compressor 21 draws a refrigerant via the inlet port, compresses the refrigerant, and discharges the compressed refrigerant from the discharge port. The discharge port of the compressor 21 is connected to a condenser 22 by piping. The condenser 22 condenses the refrigerant discharged from the compressor 21. The condenser 22 is connected to a heat exchange unit 24 via an expansion valve 23 by piping. The heat exchange unit 24 is connected to the inlet port of the compressor 21 via an accumulator 25.

Thus, a second refrigerating cycle is constructed in the supercooling unit A.

The heat exchange unit 24 is arranged in a pipe (pipe on the liquid side) between the liquid tank 6 of the first refrigerating cycle and each of the two-way valves 11 for heat exchange and cools the refrigerant flowing in a pipe between the liquid tank 6 and each of the two-way valves by use of the liquid refrigerant introduced from the expansion valve 23.

A concrete example of the heat exchange unit 23 is shown in FIG. 2. That is, the heat exchange unit 24 is of capacity variable type constructed by a plurality of, for example, four supercooling heat exchanges 31 and the capacity thereof can be varied by selectively using the supercooling heat exchanges 31. Each of the supercooling heat exchanges 31 includes a first coil 31a connected to the pipe of the first refrigerating cycle and a second coil 31b connected to the pipe of the second refrigerating cycle. The circulation of the refrigerant for the first coils 31a of three of the supercooling heat exchanges 31 is controlled by three flow control valves 32 and the circulation of the refrigerant for the second coils 31a of the same three supercooling heat exchanges 31 are controlled by three flow control valves 33.By this control operation, the supercooling heat exchanges 31 can be selectively used.

Another example of the heat exchange unit 24 is shown in FIG. 3. That is, the heat exchange unit 24 is of capacity variable type constructed by one supercooling heat exchanger 34 having a plurality of circulation paths and the capacity thereof can be varied by selectively using the refrigerant circulation paths of the supercooling heat exchanges 34. The supercooling heat exchanges 34 includes a first coil 34a connected to the pipe of the first refrigerating cycle and a second coil 34b connected to the pipe of the second refrigerating cycle. A plurality of circulation ports are formed in the second coil 34b and the circulation of the refrigerant for each of the circulation ports is controlled by three flow control valves 35. By this control operation, the refrigerant circulation paths of the supercooling heat exchanges 34 can be selectively used.

In the pipe of the first refrigerating cycle in which the heat exchange unit 24 is provided, temperature sensors 26, 27 are arranged on both sides of the heat exchange unit 24.

In the pipe of the second refrigerating cycle, a temperature sensor 28 and a pressure sensor 29 are disposed in position between the heat exchange unit 24 and the accumulator 25.

FIG. 4 shows the control circuit.

The outdoor unit A includes a controller 40. The controller 40 is connected to controllers 50 for the respective indoor units B, ---, B1 and a controller 60 for the supercooling unit C.

The controller 40 includes a microcomputer and a peripheral circuit thereof. The outdoor controller 40 is connected to the four-way valve 2, pressure sensor 8 and inverter 41.

The inverter 41 rectifies a voltage of a commercial A.C. power source 42, converts the voltage into a voltage with a preset frequency by switching the voltage according to an instruction of the controller 40, and outputs the same. The output is used as a driving power of a compressor motor 1M.

Each of the controllers 50 includes a microcomputer and a peripheral circuit thereof. Each of the controllers 50 is connected to the two-way valve 11, PMV 12, temperature sensor 14, remote control type operating unit 51, and indoor temperature sensor 52.

The controller 60 includes a microcomputer and a peripheral circuit thereof. The controller 60 is connected to the heat exchange unit 24, temperature sensors 26, 27, 28, pressure sensor 29 and inverter 61.

The inverter 61 rectifies a voltage of a commercial A.C. power source 62, converts the voltage into a voltage with a preset frequency by switching the voltage according to an instruction of the controller 60, and outputs the same. The output is used as a driving power of a compressor motor 21M.

The controller 50 of the indoor units B, ---, B1 mainly includes the following functioning means.

[1] Means for outputting the operating condition (operating mode, set temperature Ts, operation starting instruction, operation interrupting instruction, and the like) set by the operating unit 51 to the outdoor unit A.

cm Means for opening the two-way valve 11 when the operation start is specified by the operating unit 51 and closing the two-way valve 11 when the interruption of operation is specified.

t3] Means for detecting a difference At between the detection temperature Ta of the indoor temperature sensor 52 and a target value (which is hereinafter referred to as a set temperature) Ts of the indoor temperature set by the operating unit 51 as an air conditioning load.

t4] Means for setting a requested capacity f(x) (= operating frequency) corresponding to the detected air conditioning load At and outputting information of the same to the outdoor unit A.

5) Means for controlling the opening of the PMV 12according to the air conditioning load At.

The controller 40 of the outdoor unit A mainly includes the following functioning means.

1) Means for determining the operation mode by totally taking information of the operation modes given by the indoor units B, ---, B1 into consideration.

12] Means for switching the position of the fourway valve 2 when the operation mode is set in the heating operation mode.

t3] Means for deriving information of the total value 2f(x) of requested capacities f(x) given from the indoor units B, ---, B1 and controlling the operation frequency F1 (output frequency of the inverter 41) of the compressor 1 according to the total value.

[4] Means for outputting an instruction of operation start to the supercooling unit C when the total value 2f(x) of the requested capacities f(x) has exceeded a predetermined set value fs (for example, 100 % of the rated capacity of the outdoor unit A) at the time of cooling operation, setting a requested value fc corresponding to an amount fup (= 2f(x) - fs) by which the total value 2f(x) has exceeded the set value fs, and outputting information of the amount to the supercooling unit C.

t5] Means for outputting an instruction of the interruption of operation to the supercooling unit C when the total value 2f(x) of the requested capacities f(x) becomes smaller than a value (for example, 90 % of the rated capacity of the outdoor unit A) which is smaller than the set value fs.

The controller 60 of the supercooling unit C mainly includes the following functioning means.

[1) Means for starting the operation of the compressor 21 in response to the operation starting instruction from the outdoor unit A and controlling the operation frequency F2 (output frequency of the inverter 61) of the compressor 21 according to information of the requested capacity fc given from the outdoor unit A.

cm Means for adjusting the capacity of the heat exchange unit 24 according to a variation in the operation frequency F2 of the compressor 21.

[3] Means for setting a capacity correction value Afc which is used to set the detection temperature (refrigerant temperature) T of the temperature sensor 28 and the detection pressure (refrigerant pressure) P of the pressure sensor 29 into respective preset stable regions and correcting at least one of the operation frequency F2 of the compressor 21 and the capacity of the heat exchange unit 24 according to the-capacity correction value Afc.

4) Means for interrupting the operation of the compressor 21 in response to the operation interrupting instruction from the outdoor unit A.

Next, the operation of the apparatus with--the above construction is explained with reference to FIGS. 5, 6 and 7. FIG. 5 illustrates the operation of the indoor units B, ---, B1, FIG. 6 illustrates the operation of the outdoor unit A, and FIG. 7 illustrates the operation of the supercooling unit C.

When the operating condition (such as the operation mode, set temperature Ts, operation starting instruction, operation interrupting instruction) in the operating unit 51 of each of the indoor units B, ---, B1 is set, information of the operating condition is given to the outdoor unit A (step 101). In the outdoor unit A, the cooling mode or heating mode is set by taking the given information of the operating condition into consideration (step 201).

In the case of the cooling mode, a refrigerant discharged from the compressor 1 passes through the four-way valve 2 and flows into the-outdoor heat exchanger 3. In the outdoor heat -exchanger 3, the refrigerant is subjected to the heat exchange with the external air and condensed. The refrigerant passing through the outdoor heat exchanger 3 passes through the heat exchange unit 24 and flows into the indoor heat exchanger 13 of at least one of the indoor units B, ---, B1 which outputs the operation starting instruction via the two-way valve (which is opened according to the operating starting instruction) 11 and the PMV 12 of the corresponding indoor unit. In the corresponding indoor heat exchangers 13, the refrigerant is subjected to the heat exchange with the internal air and evaporates. By this heat exchange, a space in the room can be cooled.

The refrigerant passing through each of the indoor heat exchangers 13 is drawn into the compressor 1 via the four-way valve 2.

In the case of the heating operation, the position of the four-way valve 2 is switched and a refrigerant discharged from the compressor 1 flows into the indoor heat exchangers 13 in those of the indoor units B, ---, B1 which output the operation starting instruction via the four-way valve 2. In each of the indoor heat exchangers 13, the refrigerant is subjected to the heat exchange with the external air and condensed. By this heat exchange, the space in the room can be heated. The refrigerant passing through the indoor heat exchangers 13 passes through the respective PMVs 12 and the two-way valves (which are opened according to the operating-starting instruction) 11 and flows into the outdoor heat exchanger 3 via the heat exchange unit 24. In the outdoor heat exchanger 3, the refrigerant is subjected to the heat exchange with the external air and evaporates.

The refrigerant passing through the outdoor heat exchanger 3 is drawn into the compressor 1 via the fourway valve 2.

During the operation, in the indoor units B, ---, B1, the room temperature Ta is detected (step 102) and a difference At (= Ta - Ts) between the room temperature Ta and the set temperature Ts is detected as an air conditioning load (step 103). The requested capacity f(x) of each of the indoor units B, ---, B1 is set based on the air conditioning load At and the requested capacity setting condition shown in FIG. 8 (step 104).

Information of the requested capacities f(x) is output to the outdoor unit A (step 105). Further, the opening of the PMV is controlled according to each of the requested capacities f(x) (step 106). By the control of the opening, a refrigerant of an amount corresponding to each of the requested capacities f(x) is caused to flow into a corresponding one of the indoor heat exchangers 13.

In the outdoor unit A, the total value Ef(x) of the requested capacities f(x) is derived (step 202) and the operation frequency F1 of the compressor 1 is controlled based on the total value Ef(x) and the operation frequency setting condition shown in FIG. 9 (step 203).

In the case of the cooling operation ("YES" in the step 204), the total value Ef(x) and the set value fs (= 100 % of the rated capacity of the outdoor unit A) are compared with each other (step 205). When the total value 2f(x) exceeds the set value fs ("YES" in the step 205), an operation starting instruction is supplied to the supercooling unit C based on the fact that FLAG is.

set at "0" (steps 206,...207), FLAG is-used to store the operation state of the supercooling unit C, and is set to "1" in the operating state and set to "O in the interrupted state.

In the supercooling unit C, the compressor 21 is started according to the operation starting instruction from the outdoor unit A (steps 301, 302).

A refrigerant discharged from the compressor 21 flows into the condenser 22. In the condenser 22, the refrigerant is subjected to the heat exchange with the external air and condensed. The refrigerant passing through the condenser 22 passes through the expansion valve 23 and flows into the heat exchange unit 24. The refrigerant flowing into the heat exchange unit 24 is subjected to the heat exchange with the refrigerant flowing in the liquid side pipe of the first refrigerating cycle and evaporates. By the heat exchange, the refrigerant flowing in the liquid side pipe of the first refrigerating cycle is cooled. The refrigerant passing through the heat exchange unit 24 is drawn into the compressor 1.

In the outdoor unit A, an excessive amount fup (= 2f(x) - fs) of the total value Ef(x) with respect to the set value fs is detected at the time of operation of the supercooling unit C (step 208) and a requested capacity fc corresponding to the excessive amount fup is set (step 209). Then, information of the requested capacity fc is output to the supercooling unit C (step 210) and FLAG is set to "1" (step 211).

In the supercooling unit C, the operation frequency F2 of the compressor 21 is controlled according to information of the requested capacity fc given from the outdoor unit A (step 303). That is, a deficient amount of cooling capacity caused when only the outdoor unit A is operated can be compensated for by the compressor 21 and a necessary and sufficient amount of cooling capacity can be attained in the respective indoor units B, ---, B1. In order to attain the safety operation of the second refrigerating cycle, the capacity of the heat exchange unit 24 is controlled according to a variation in the operation frequency F2 (step 304).

Further, during the operation of the supercooling unit C, a capacity correction value Afc is set so as to set the detection temperature T of the temperature sensor 28 and the detection pressure P of the pressure sensor 29 into respective preset stable regions (step 305).

At least one of the operation frequency F2 of the compressor 21 and the capacity of the heat exchange unit 24 is corrected according to the capacity correction value Afc (step 306). The temperature T and pressure P of the refrigerant flowing out of the heat exchange unit 24 substantially correspond to the degree of superheat of the refrigerant in the-heat exchange unit 24. The degree of superheat of the refrigerant in the heat exchange unit 24 can be kept at an optimum value by setting the temperature T and pressure P into the stable regions, thereby making it possible to efficiently effect the heat exchange in the heat exchange unit 24.

FIG. 10 shows an example of a method for correcting the operation frequency F2 and the capacity of the heat exchange unit 24. E1 indicates a stable region which is the target value of T and P, zones E2, E4 indicate regions for lowering the operation frequency F2, zones E3, E5 indicate regions for raising the operation frequency F2, and zones E6, E7, Eg, Eg indicate regions for correcting the operation frequency F2 and the capacity of the heat exchange unit 24.

In the outdoor unit A, the total value 2f(x) of the requested capacities f(x) and a value equal to 90 % of the set value fs are compared with each other (step 212). When the cooling load decreases and the total value 2f(x) of the requested capacities f(x) becomes equal to or smaller than 90 % of the set value fs ("YES"in the step 212), the operation interrupting instruction is supplied to the supercooling unit C (step 213).

In the supercooling unit C which has received the operation interrupting instruction, the operation of the compressor 21 is interrupted (steps 307, 308).

In this case, the supercooling unit C is prevented from frequently and repeatedly effecting the operation start and the operation interruption by driving the supercooling unit C when the total value 2f(x) of the requested capacities f(x) exceeds the set value fs and interrupting the operation of the supercooling unit C when the total value 2f(x) of the requested capacities f(x) is equal to or smaller than 90 z of the set value fs.

FIG. 11 shows the relation between the capacity of the outdoor unit A and the capacity of the supercooling unit C.

When the cooling capacity attained only by the rated capacity of the indoor unit A becomes insufficient, a sufficiently large capacity can be attained in all of the indoor units B, ---, B1 by driving the supercooling unit C to compensate for a deficient amount of the cooling capacity even if the indoor unit B1 is additionally installed later to cope with an increase in the cooling load.

Particularly, since the supercooling unit C is operated to compensate for a deficient cooling capacity only when it is required, it can be easily applied to the subdivided air conditioning for cooling small spaces. In addition, it is only necessary to additionally install the indoor unit B1 later for an increase in the cooling capacity and it is not necessary to effect the large-scale piping work and wiring for the whole apparatus.

Next, the second embodiment of this invention is explained.

In the first embodiment, the capacity of the supercooling unit C was corrected according to the temperature T and pressure P of the refrigerant in the supercooling unit C. On the other hand, in the second embodiment, the capacity of the supercooling unit C is corrected according to the pseudo degree of superheat of the refrigerant in each of the indoor heat exchangers 13.

The constructions of the refrigerating cycle and control circuit are the same as those of the first embodiment.

As shown in FIG. 12, each of the indoor units B, ---, B1 has a function of new steps 107 to 110 in' addition to the function of the first embodiment. As shown in FIG. 13, the indoor unit A has steps 221 to 225 instead of the step 210 of the first embodiment. As shown in FIG. 14, the supercooling unit C has a function in which the steps 305-,- 306 in the first embodiment are omitted.

That is, in the indoor units B, ---, B1, one of the zones of the pseudo degree-of-superheat setting condition shown in FIG. 15 in which the air conditioning load At (=Ta - Ts) lies is determined at the time of cooling operation ("YES" in the step 107) and a target pseudo degree of superheat SHt for each indoor heat exchanger 13 is set according to the result of determination (step 108). The temperature (evaporation temperature) Te of the refrigerant supplied from the indoor heat exchanger 13 is detected by the temperature sensor 14 (step 109) and information of the detection temperature Te is output to the outdoor unit A together with the target pseudo degree of superheat SHt (step 110).

In the outdoor unit A, a difference between the detection temperature Te given from each of the indoor units B, ---, B1 and the pressure (low-pressure side pressure) Ps of the refrigerant detected by the pressure sensor 8 is detected as the pseudo degree of superheat SH of the refrigerant in each of the indoor heat exchangers 13 (step 221). A difference ASH (= SH - SHt) between each of the pseudo degrees of superheat SH and the target pseudo degree of superheat SHt given from each of the indoor units B, ---, B1 is detected (step 222) and capacity correction values Afc respectively corresponding to the differences -ASH are set (step 223).

The requested capacity fc already set in the step 209 is corrected by an amount of the total value of the capacity correction values Afc (step 224). Information of the requested capacity fc after correction is output to the supercooling unit C (step 225).

In the supercooling unit C, the operation frequency F2 of the compressor 21 is controlled according to information of the requested capacity fc given from the outdoor unit A (step 303). That isX a deficient amount of cooling capacity caused when only the outdoor unit A is operated can be compensated for by the compressor 21 and a necessary and sufficient amount of cooling capacity can be attained in the respective indoor units B, ---, B1.

Next, the third embodiment of this invention is explained.

In the second embodiment, the capacity of the supercooling unit C was corrected according to the pseudo degree of superheat SH of the refrigerant in each of the indoor heat exchangers 13. On the other hand, in the third embodiment, the capacity of the outdoor unit A -is corrected according to the pseudo degree of superheat SH of the refrigerant in each of the indoor heat exchangers 13.

The constructions of the refrigerating cycle and the control circuit are the same as those of the first and second embodiments.

Each of the indoor units B, ---, B1 has the same function as that in the second embodiment. As shown in FIG. 16, the outdoor unit A has a function in which the step 203 of the second embodiment is omitted and new steps 231 to 233 are used instead of the steps 222 to 225 of the second embodiment. The supercooling unit C has the same function as that in the second embodiment.

That is, in the outdoor unit A, a difference between the detection temperature Te- given from each of the indoor units B, ---, B1 and the pressure (low-pressure side pressure) Ps detected by the pressure sensor 8 is detected as the pseudo degree of superheat SH of the refrigerant in each of the indoor heat exchangers 13 (step 221). Capacity correction values Afa corresponding to the respective pseudo degrees of superheat SH are set (step 231).

The total value zf(x) already derived in the step 202 is corrected by an amount of the total value of the capacity correction values Afa (step 232). The operation frequency F1 of the compressor 1 is controlled according to the total value Ef(x) after correction (step 233).

Next, the fourth embodiment of this invention is explained.

Assume that when some of the indoor units B, B1 are already set in the operative state, the operations of some indoor units B1 are newly started and the operation of the supercooling unit C is started.

In this case, the degree of superheat of the refrigerant in the liquid side pipe (pipe in which the heat source unit 24 is provided) of the first refrigerating cycle increases and therefore an amount of the liquid refrigerant increases. The liquid refrigerant of an increased amount tends to flow into the indoor unit B side already set in the operative state and is difficult to flow into the indoor units B1 whose operations arenewly started.

Therefore, in the fourth embodiment, the degree of supercool SC of a refrigerant in the liquid side pipe of the first refrigerating cycle is detected, and when the degree of supercool SC becomes equal to or larger than a preset value SC, the PMV 12 in the indoor unit B which is already set in the operative state is closed by a preset amount.

As shown in FIG. 17, each of the indoor units B, ---, B1 has a function of the steps 121 to 123 in addition to the function of the first embodiment. As shown in FIG. 18, the outdoor unit A additionally has a function of the steps 241 to 244 between the steps 210 and 211 of the first embodiment. As shown in FIG. 19, the supercooling unit C additionally has a function of the steps 311, 312 between the steps 306 and 307 in the first embodiment.

That is, in the supercooling unit C, the temperature Tcl of a refrigerant passing in the liquid side pipe of the first refrigerating cycle and flowing into the heat source unit 24 is detected by the temperature sensor 26. The temperature Tc2 of a refrigerant passing in the liquid side pipe of the first refrigerating cycle and flowing out of the heat source unit 24 is detected by the temperature sensor 27 (step 311).

Information of the detected temperatures Tcl, Tc2 is output to the outdoor unit A (step 312).

In the outdoor unit A, a difference between the detected temperatures Tcl, Tc2 is detected as the degree of supercool SC of a refrigerant in the liquid side pipe of the first refrigerating cycle (step 241). The degree of supercool SC is compared with the preset value SC (step 242). When the degree of supercool SC becomes equal to or larger than the preset value SC ("YES" in the step 242), the opening reducing value is set according to the degree of supercool SC (step 243).

Information of the opening reducing value is output to the indoor units B, ---, B1 (step 244).

In each of the indoor units B, ---, B1, if it is not the operation starting time ("NO" in the step 121) and data of the opening reducing value from the outdoor unit A is received ("YES" in the step 122), the opening of the PMV 12 is reduced by an amount corresponding to the opening reducing value (step 123).

When the opening of the PMV 12 in the indoor unit B set in the operative state is reduced, a liquid refrigerant of an amount increased by the operation of the supercooling unit C does not flow into each of the indoor units B which are now set in the operative state and flows into the indoor unit B1 which is newly operated. Therefore, a necessary and sufficient cooling capacity can be attained also in the newly operated indoor unit B1.

The capacity of each of the units attained at this time is shown in FIG. 20. In FIG. 20, broken lines indicate the capacity attained when the opening of the PMV 12 is not reduced and the solid lines indicate the capacity attained when the opening of the PMV 12 is reduced. Further, the mutual relation between the operation of the supercooling unit C, a variation in the degree of supercool and a variation in the opening of the PMV 12 is shown in FIG. 21.

Next, the fifth embodiment of this invention is explained.

In the fourth embodiment, the opening of the PMV 12 was reduced by an amount corresponding to the degree of supercool SC. On the other hand, in the fifth embodiment, the opening of the PMV 12 is reduced by a previously determined amount in synchronism with the operation starting timing of the supercooling unit C.

The constructions of the refrigerating cycle and the control circuit are the same as those of the first, second, third and fourth embodiments.

As shown in FIG. 22, each of the indoor units B, ---, B1 has a function of new steps 131, 132 instead of the steps 122, 123 of the fourth embodiment. As shown in FIG. 23, the outdoor unit A has a function of the new step 251 instead of the steps 241 to 244 of the fourth embodiment. The supercooling unit C has the same function as that of the first embodiment.

That is, in the indoor unit A, the operation starting instruction is given to the supercooling unit C (step 207), and at the same time, the opening reducing instruction is output to each of the indoor units B, ---, B1 (step 251).

In each of the indoor units B, ---, B1, if it is not the operation starting time ("NO" in the step 121) and the opening reducing instruction is received from the outdoor unit A ("YES" in the step 131), the opening of the PMV 12 is reduced by a previously determined amount (step 123).

Claims

Claims:

1. An air conditioning apparatus having a supercooling unit provided between an outdoor unit and a plurality of indoor units, comprising: a first compressor of capacity variable type provided in said outdoor unit, for drawing, compressing and discharging a refrigerant; an outdoor heat exchanger provided in said outdoor unit, for exchanging the heat of a refrigerant discharged from said compressor for the heat of external air; a plurality of indoor heat exchangers provided in said respective indoor units, for exchanging the heat of a refrigerant passing through said outdoor heat exchanger for the heat of internal air; a first refrigerating cycle constructed by connecting said first compressor, outdoor exchanger and indoor exchangers by piping; a second compressor provided in said supercooling unit, for drawing, compressing and discharging a refrigerant;; a condenser provided in said supercooling unit, for condensing a refrigerant discharged from said second compressor; a heat exchange unit provided in said supercooling unit, for cooling a refrigerant flowing between said outdoor heat exchanger and said respective indoor heat exchangers by use of the refrigerant passing through said condenser; a second refrigerating cycle constructed by connecting said second compressor, condenser and heat exchanger unit by piping; first detection means for detecting the air conditioning load of the rooms in which said indoor units are installed; setting means for setting a requested capacity corresponding to each air conditioning load detected by said first detection means; control means for controlling the capacity of said first compressor according to the total value of the requested capacities set by said setting means; and control means for driving said second compressor when the total value of the requested capacities set by said setting means exceeds a previously determined value.

2. An apparatus according to claim 1, wherein said second compressor is of capacity variable type and said heat exchange unit is of capacity variable type.

3. An apparatus according to claim 2, wherein said heat exchange unit includes a plurality of heat exchangers for supercooling, the capacity of said heat exchange unit being varied by selectively using said plurality of heat exchangers for supercooling.

4. An apparatus according to claim 2, wherein said heat exchange unit includes a single heat exchanger for supercooling having a plurality of refrigerant circulation paths, the capacity of said heat exchange unit being varied by selectively using said plurality of refrigerant circulation paths of said heat exchanger for supercooling.

5. An apparatus according to claim 2, further comprising: detection means for detecting the temperature and pressure of a refrigerant which is part of the refrigerant flowing in said second refrigerating cycle and flows out of said heat exchange unit; and control means for controlling at least one of the capacity of said second compressor and the capacity of said heat exchange unit according to the result of detection by said detection means at the time of operation of said second-compressor.

6. An apparatus according to claim 2, further comprising: second detection means for detecting the degree of super-heat of the refrigerant in each of said indoor heat exchangers; and control means for controlling at least one of the capacity of said second compressor and the capacity of said heat exchange unit according to each degree of superheat detected by said detection means at the time of operation of said second compressor.

7. An apparatus according to claim 6, wherein said second detection means detects a difference between the temperature of the refrigerant flowing out of each of said indoor heat exchangers and the pressure of the refrigerant flowing on the low-pressure side of said first refrigerating cycle as the degree of superheat.

8. An apparatus according to claim 1, further comprising: second detection means for detecting the degree of superheat of the refrigerant in each of said indoor heat exchangers; and control means for correcting the capacity of said first compressor according to each degree of superheat detected by said detection means at the time of operation of said second compressor.

9. An apparatus according to claim 8, wherein said second detection means detects a difference between the temperature of the refrigerant flowing out of each of said indoor heat exchangers and the pressure of the refrigerant flowing on the low-pressure side of said first refrigerating cycle as the degree of superheat.

10. An apparatus according to claim 1, further comprising: flow control valves for controlling the amount of the refrigerant flowing into each of said indoor heat exchangers; second detection means for detecting a supercool degree of the refrigerant which is part of the refrigerant flowing in said first refrigerating cycle and has passed through said heat exchange unit; and control means for closing the openings of the flow control valves corresponding to those of said indoor heat exchangers in which the refrigerant already flows by a preset amount when the supercool degree detected by said second detection means becomes equal to for larger than a previously determined value at the time of operation of said second compressor.

11. An apparatus according to claim 1, further comprising: flow control valves for controlling the amount of the refrigerant flowing into each of said indoor heat exchangers; and control means for closing the openings of the flow control valves corresponding to those of said indoor heat exchangers in which the refrigerant already flows by a preset amount when the operation of said second compressor is started.

12. An air conditioning apparatus having a supercooling unit provided between an outdoor unit and a plurality of indoor units, substantially as hereinbefore described with reference to the accompanying drawings.