GAS HEAT PUMP AIR CONDITIONING SYSTEM

Abstract

A gas heat pump air conditioning system includes: a gas engine that generates power by using gas as a fuel; a heat pump cycle including a compressor that is driven by the gas engine and at least one heat exchanger disposed in an interior space and air-conditioning the interior space by the heat exchanger; a power generator that is driven by the gas engine and generates electric power; and a local air conditioner that is disposed in the interior space in which the heat exchanger is disposed and that air-conditions the interior space by using the electric power generated by the power genera or.

Description

BACKGROUND

1. Technical Field

The present disclosure relates to gas heat pump air conditioning systems.

2. Description of the Related Art

In a typical gas heat pump air conditioning system, a compressor is driven by a gas engine. When the air conditioning load is low, however, the gas engine rotates at low speed, and the efficiency of the system decreases. In view of this, it is proposed to change the driver of the compressor from the gas engine to a motor (see Japanese Unexamined Patent Application Publication No. 2011-7356). It is also proposed to switch a driving force necessary for the compressor between the gas engine and the motor in accordance with an air conditioning load, or to use both the gas engine and the motor (see Japanese Patent No. 4958448).

FIG. 9 illustrates a configuration of a typical gas heat pump air conditioning system described in Japanese Unexamined Patent Application Publication No, 2011-7356 and Japanese Patent No. 4958448. A heat pump cycle is constituted by an indoor unit 115a, an indoor unit 115b, an expansion valve 114, a heat exchanger 113, refrigerant pipes 116, and a compressor 112. The compressor 112 is driven by a gas engine 111 through a pulley 130, a pulley 131, and a belt 132. Adjustment of a clutch 133 enables a power generator 120 to be driven by the gas engine 111 through a pulley 134, a pulley 135, and a belt 136.

In Japanese Unexamined Patent Application Publication No. 2011-7356, electric power generated by a power generator 120 is stored in a storage battery 125. When the air conditioning load is high, a large amount of heating energy or cooling energy is required for the indoor unit 115a and the indoor unit 115b. Thus, the compressor 112 needs to be operated at high rotation speed. That is, the gas engine 111 is operated at high rotation speed. Electric power generated by the power generator 120 is stored in the storage battery 125. On the other hand, when the air conditioning load is low, a small amount of heating energy or cooling energy is required for the indoor unit 115a and the indoor unit 115b. Thus, the compressor 112 needs to be operated at low rotation speed. However, operation of the gas engine 111 at low rotation speed causes a low efficiency. Thus, the control circuit 126 performs control such that the compressor 112 is driven by the power generator 120. That is, the power generator 120 is driven as a motor by using electric power of the storage battery 125, and rotates the compressor 112 through the clutch 137, the pulley 138, the pulley 139, and the belt 140.

In Japanese Parent No. 4958448, electric power for driving the power generator 120 as a motor is supplied from a commercial power supply 123 through a panel board 122 and an inverter 121. The control circuit 126 performs control so as to minimize the sum of a running cost in driving the compressor 112 by the gas engine 111 and a running cost in driving the compressor 112 by the power generator 120 (a motor).

SUMMARY

The techniques described in Japanese Unexamined Patent Application Publication No. 2011-7356 and Japanese Patent No. 4958448 are not expected to increase the efficiency with a high load.

One non-limiting and exemplary embodiment provides a technique for increasing the efficiency of a gas heat pump air conditioning system while maintaining comfort of a room.

In one general aspect, the techniques disclosed here feature a gas heat pump air conditioning system including: a gas engine that drives a compressor by using gas as a fuel; a heat pump cycle including the compressor that is driven by the gas engine and at least one heat exchanger disposed in an interior space, the heat pump cycle air-conditioning the interior space by the heat exchanger; a power generator that is driven by the gas engine and generates electric power; a local air conditioner that is disposed in the interior space in which the heat exchanger is disposed and that air-conditions the interior space by using the electric power generated by the power generator; and a control circuit that controls the power generator and the heat exchanger in accordance with an air conditioning load of the interior space.

The technique described above can increase the efficiency of the gas heat pump air conditioning system while maintaining comfort in a room.

Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a gas hear pump air conditioning system according to a first embodiment of the present disclosure;

FIG. 2 is a view of a gas heat pump air conditioning system according to a second embodiment of the present disclosure;

FIG. 3 is a graph showing efficiency characteristics of a gas heat pump cycle;

FIG. 4 is a graph showing a relationship between the clutch level and the number of revolutions of a power generator;

FIG. 5 is a graph showing a relationship between the number of revolutions of the power generator and the volume of gas consumed by a gas engine;

FIG. 6 is a graph showing a relationship between the number of revolutions of the power generator and a generation amount;

FIG. 7 is a flowchart showing control by a control circuit;

FIG. 8 is a flowchart showing control by the control circuit;

FIG. 9 is a view of a typical gas heat pump air conditioning system; and

FIG. 10 is a view for explaining problems of the typical gas heat pump air conditioning system.

DETAILED DESCRIPTION

Underlying Knowledge Forming Basis of the Present Disclosure

In a typical gas heat pump air conditioning system illustrated in FIG. 9, indoor units 115a and 115b are disposed on a ceiling. Thus, in a case where a room has both an area requiring air conditioning and an area not requiring air conditioning, it is not easy to perform air conditioning of these areas selectively. Consequently, air-conditioning energy (gas) is wasted.

A case where an air conditioning load is high and a case where an air conditioning load is low will now be described. In air conditioning an interior space, an intended temperature (a target temperature) is set for an area to be air-conditioned (an air-conditioned area). The air conditioning system is controlled such that the air-conditioned area reaches the intended temperature. An example of a high load is the time when the air conditioning system starts with a large difference between the current temperature and the intended temperature in the air-conditioned area and with the necessity of a high degree of heating energy or cooling energy for an indoor unit. Once the air conditioning system starts and continues its operation, the difference between the current temperature and the intended temperature in the air-conditioned area gradually decreases, and the degree of heating energy or cooling energy necessary for the indoor unit also decreases. That is, the air-conditioned area comes to be under a low load (a so-called steady state or part load conditions).

As illustrated in FIG. 10, suppose an interior space is generally divided into an ordinary-air-conditioned area 160, a locally-air-conditioned area 161, and an air-conditioning-free area 162. The ordinary-air-conditioned area 160 is an air-conditioned area with an ordinary air conditioning load. The locally-air-conditioned area 161 is an air-conditioned area with a high air conditioning load. The air-conditioned-free area 162 is an area above the locally-air-conditioned area 161. Suppose a generally heavily clothed resident 170 works in an upright position in the air-conditioned area 160. Suppose a generally lightly clothed resident 171 works while being sitting in the locally-air-conditioned area 161. Since the resident 171 works while being sitting in the locally-air-conditioned area 161, the space above the locally-air-conditioned area 161 does not directly affect warmth or coldness felt by the resident 171. That is, the air-conditioning-free area 162 is originally a useless area for air conditioning.

In view of a comfort index predicted mean vote (PMV), the temperature necessary for obtaining comfort is determined on the basis of the state of clothes of a resident and working conditions. In the case of a heating operation, for example, the temperature required in the locally-air-conditioned area 161 is higher than that required in the ordinary-air-conditioned area 160. That is, in the example illustrated in FIG. 10, the air conditioning load of the locally-air-conditioned area 161 is higher than that of the ordinary-air-conditioned area 160. In addition, the locally-air-conditioned area 161 and the air-conditioning-free area 162 need to be air-conditioned by the indoor unit 115b. Thus, the locally-air-conditioned area 161 is generally under an extremely high load, as compared to the ordinary-air-conditioned area 160. Although the locally-air-conditioned area 161 is under a high air conditioning load, the locally-air-conditioned area 161 might be insufficiently air-conditioned because of, for example, difficulty in airflow from the indoor unit 115b. In this case, comfort satisfactory for the resident cannot be obtained. As the degree of heating energy or cooling energy supplied from the indoor unit 115b increases, unnecessary heating energy or cooling energy supplied to the air-conditioning-free area 162 increases, resulting in an increase in waste of air-conditioning energy (gas).

A gas heat pump air conditioning system according to a first aspect of the present disclosure includes: a gas engine that drives a compressor by using gas as a fuel; a heat pump cycle including the compressor that is driven by the gas engine and at least one heat exchanger disposed in an interior space, the heat pump cycle air-conditioning the interior space by the heat exchanger; a power generator that is driven by the gas engine and generates electric power; a local air conditioner that is disposed in the interior space in which the heat exchanger is disposed and that air-conditions the interior space by using the electric power generated by the power generator; and a control circuit that controls the power generator and the heat exchanger in accordance with an air conditioning load of the interior space. In other word, the control circuit includes a processor and a memory storing a program, the program, when being executed by the processor, causing the control circuit to perform operation including controlling the power generator and the heat exchanger in accordance with an air conditioning load of the interior space.

In the first aspect, the local air conditioner locally air-conditions the interior space by using electric power generated by the power generator. The power generator and the indoor unit are controlled in accordance with the air conditioning load of the interior space. The use of the local air conditioner in the air-conditioned area with a high load can reduce the load of the compressor constituting the heat pump cycle. Thus, the efficiency of the gas heat pump air conditioning system in the case of a high load can be increased.

The local air conditioner is preferably an air conditioner that does not need to be fixed to the ceiling unlike an indoor unit that is fixed to the ceiling because of restriction concerning refrigerant pipes. The local air conditioner can be disposed in an air-conditioned area with a high load. The local air conditioner can be disposed near a resident in an air-conditioned area with a high load, for example. In this case, heating energy or cooling energy is not easily supplied from the local air conditioner to an area that does not need air conditioning, and thus, waste of air-conditioning energy (gas) can be reduced. In a case where the local air conditioner is disposed near the resident, comfort of the resident is not easily impaired.

Examples of the local air conditioner include a warm-air fan heater that is operated with electricity in a heating operation. Specifically, the warm-air fan heater is disposed near the feet of the resident and is operated with electric power generated by the power generator. In this manner, even when the indoor unit stops, comfort of the resident can be maintained. In a heating operation by the indoor unit, an area that is located between the indoor unit and the resident and does not need air conditioning is inevitably heated. The local air conditioner, however, does not heat the area that does not need air conditioning, and thus, energy can be saved by use of the local air conditioner. In addition, when the indoor unit stops, a load applied to the compressor can be reduced. That is, driving of the compressor with a high load can be avoided, thereby increasing the efficiency of the heat pump cycle. From the foregoing findings, the inventors of the present disclosure arrived at the aspects below.

The first aspect of the present disclosure is superior to the techniques described in Japanese Unexamined Patent Application Publication No. 2011-7356 and Japanese Patent No. 4958448 in the following points. In Japanese Unexamined Patent Application Publication No. 2011-7356 and Japanese Patent No. 4958448, the power generator 120 is used as a motor. However, since the power generator 120 is originally provided in order to generate electric power, the power generator 120 cannot generate a sufficient degree of driving force when being used as a motor. Although the power generator 120 can be used as a motor so as to drive the compressor 112 in the case of a low load, the use of the power generator 120 alone is not sufficient for driving the compressor 112 in the case of a high load, because the compressor 112 needs to be driven at a considerably high speed. Thus, the techniques described in Japanese Unexamined Patent Application Publication No. 2011-7356 and Japanese Patent No. 4958448 cannot increase the efficiency under high loads.

On the other hand, the gas heat pump air conditioning system of the present disclosure includes the power generator driven by the gas engine and the local air conditioner that air conditions the interior space by using electric power generated by the power generator. Thus, the use of the local air conditioner in an air-conditioned area with a high load can reduce the load of the compressor constituting the heat pump cycle. As a result, the efficiency of the gas heat pump air conditioning system in the case of a high load can be increased.

In a second aspect, the control circuit of the gas heat pump air conditioning system of the first aspect, for example, may stop the power generator while air conditioning by the heat exchanger is being performed, and supply electric power from the power generator to the local air conditioner while air conditioning by the heat exchanger is stopped. In the second aspect, a load applied to the heat pump cycle can be reduced, and the efficiency of the heat pump cycle in the case of a high load can be increased.

In a third aspect, the control circuit of the gas heat pump air conditioning system of the first or second aspect, for example, may switch an operation mode between a first operation mode in which the interior space is air-conditioned by the heat exchanger and a second operation mode in which the interior space is air-conditioned by the local air conditioner, in accordance with the air conditioning load of the interior space. In the third aspect, a load applied to the heat pump cycle can be reduced, and the efficiency of the heat pump cycle in the case of a high load can be increased.

In a fourth aspect, the control circuit of the gas heat pump air conditioning system of the first or second aspect may control the power generator and the heat exchanger such that the interior space is air-conditioned by the local air conditioner in a case where a gas flow rate necessary for the gas engine in air-conditioning the interior space by the heat exchanger is higher than a gas flow rate necessary for the gas engine in air-conditioning the interior space by the local air conditioner, and the interior space is air-conditioned by the heat exchanger in a case where a gas flow rate necessary for the gas engine in air-conditioning the interior space by the heat exchanger is lower than or equal to the gas flow rate necessary for the gas engine in air-conditioning the interior space by the local air conditioner. In the fourth aspect, it is possible to ensure saving of gas while maintaining comfort.

In a fifth aspect, the control circuit of the gas heat pump air conditioning system of the first aspect, for example, may cause the power generator to supply electric power to the local air conditioner and starts air conditioning performed by the local air conditioner when a temperature change amount per unit time in the interior space that has been air-conditioned by the heat exchanger is less than or equal to a predetermined value.

In a sixth aspect, the control circuit of the gas heat pump air conditioning system of the fifth aspect, for example, may select a first operation mode in which the interior space is air-conditioned by the heat exchanger in a case where the temperature change amount per unit time in the interior space that has been air-conditioned by the heat exchanger exceeds the predetermined value, and selects a second operation mode in which the interior space is air-conditioned by the local air conditioner in a case where the temperature change amount per unit time in the interior space that has been air-conditioned by the heat exchanger is less than or equal to the predetermined value.

In a seventh aspect, the heat exchanger included in the gas heat pump air conditioning system of one of the first to sixth aspects, for example, may include a plurality of heat exchangers, and the control circuit may cause the local air conditioner to air-condition the interior space, instead of at least one of the plurality of heat exchangers. In the seventh aspect, on/off of the heat pump cycle can be avoided as much as possible. This also contributes to an increase in the efficiency of the air conditioning system.

In an eighth aspect, the gas heat pump air conditioning system of one of the first to seventh aspects, for example, may further include a clutch that transmits power from the gas engine to the power generator, and the control circuit may control the number of revolutions of the power generator by controlling the clutch. In the eighth aspect, a sufficient amount of electric power can be generated by the power generator, and thus, energy (gas) is not easily wasted.

In a ninth aspect, the heat exchanger included in the heat pump cycle of the gas heat pump air conditioning system of one of the first to eighth aspects, for example, may include a plurality of heat exchangers, the plurality of heat exchangers may include a first heat exchanger and a second heat exchanger, the air-conditioned area included in the interior space may include a plurality of air-conditioned areas, and the plurality of air-conditioned areas may include an ordinary-air-conditioned area that is air-conditioned by the first heat exchanger and a locally-air-conditioned area that is air-conditioned by one of the second heat exchanger and the local air conditioner. When air conditioning is performed in manners appropriate for the individual air-conditioned areas, the efficiency of the air conditioning system can be easily increased.

A gas heat pump air conditioning system according to a tenth aspect includes: a gas engine that drives a compressor by using gas as a fuel; a heat pump cycle including the compressor and a heat exchanger disposed in an interior space and air-conditioning the interior space by the heat exchanger; a power generator that is driven by the gas engine and generates electric power; and a local air conditioner that air-conditions the interior space by using the electric power generated by the power generator, in which an air-conditioned area with a high degree of the air conditioning load is air-conditioned by the local air conditioner, and the other air-conditioned areas are air-conditioned by the heat exchanger.

In the tenth aspect, the same advantages as those of the first aspect can be obtained. In addition, in the tenth aspect, the number of indoor units can be reduced, and no complicated control is required. Thus, an initial investment cost can be reduced.

In an eleventh aspect, the heat pump cycle of the gas heat pump air conditioning system of the tenth aspect, for example, may perform a heating operation on the interior space by the heat exchanger, the local air conditioner may perform a heating operation on the interior space, the heat exchanger may be disposed on a ceiling of the interior space, and the local air conditioner may be disposed on a floor of the interior space.

In a twelfth aspect, the local air conditioner of the heat pump cycle of the gas heat pump air conditioning system of one of the first to tenth aspects may be a portable electric warm-air fan heater. If the heat pump cycle is portable, the local air conditioner can be easily disposed near a resident.

Embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the embodiments below. In this description, the term “air conditioning” includes both cooling and heating.

First Embodiment

As illustrated in FIG. 1, a gas heat pump air conditioning system 100 according to a first embodiment includes an outdoor unit 10, a first indoor unit 15a disposed in an interior space and serving as a heat exchanger, a second indoor unit 15b disposed in the interior space and serving as a heat exchanger, a control circuit 50, and a local air conditioner 80. The outdoor unit 10 includes a compressor 12, a heat exchanger 13, and an expansion valve 14. The compressor 12, the heat exchanger 13, the expansion valve 14, the first indoor unit 15a, and the second indoor unit 15b are connected to form a loop by refrigerant pipes 16, thereby forming a heat pump cycle 17.

The outdoor unit 10 further includes a gas engine 11, a power transmission mechanism 40, a clutch 33, a power transmission mechanism 41, a power generator 20, and an inverter 21. The power transmission mechanism 40 includes a pulley 30, a pulley 31, and a belt 32. The power transmission mechanism 41 includes a pulley 34, a pulley 35, and a belt 36. The power transmission mechanisms 40 and 41 are not limited to belt transmission mechanisms, and may be other transmission mechanisms such as chain transmission mechanisms and gear transmission mechanisms. The compressor 12 is driven by the gas engine 11 through the power transmission mechanism 40. The clutch 33 transmits power from the gas engine 11 to the power generator 20. The power generator 20 is driven by the gas engine 11 through the clutch 33 and the power transmission mechanism 41. A torque that is transmitted from the gas engine 11 to the power generator 20 can be adjusted by controlling the clutch 33.

The power generator 20 is connected to the local air conditioner 80 through the inverter 21 and the panel board 22. The local air conditioner 80 is operated by electric power generated by the power generator 20.

The control circuit 50 includes a load detector 51, a switching determiner 52, a constant setting unit 53, a clutch controller 54, and an indoor unit controller 55. The load detector 51 detects intended temperatures that have been individually set for air-conditioned areas in the interior space, and calculates air conditioning loads of the air-conditioned areas. The constant setting unit 53 stores a constant indicating characteristics of the heat pump cycle 17 and a constant that affects the air conditioning loads of the air-conditioned areas. These constants are used for calculating the air conditioning loads. Based on the calculation results of the air conditioning loads of the air-conditioned areas, the switching determiner 52 determines whether local air conditioning using the local air conditioner 80 is necessary or not. The indoor unit controller 55 transmits an ON signal or an OFF signal to the indoor unit 15b in response to the determination of the switching determiner 52. In response to the determination of the switching determiner 52, the clutch controller 54 calculates a necessary number of revolutions of the power generator 20, and transmits a control signal to the clutch 33.

The control circuit 50 only needs to have a control function and includes a processing unit (nor shown) and a memory unit (not shown) storing a control program. Examples of the processing unit include an MPU and a CPU. Examples of the memory unit include a memory. The control circuit may be a single control circuit that performs centralized control or may be constituted by a plurality of control circuits that perform decentralized control in cooperation (the same holds for control circuits of other embodiments and variations thereof). The memory unit stores a program for appropriately operating the air conditioning system 100. Functions of the load detector 51, the switching determiner 52, the constant setting unit 53, the clutch controller 54, and the indoor unit controller 55 can be achieved by software executed on a hardware. The control circuit 50 may be disposed in the outdoor unit 10. In a manner similar to a building energy management system (BEMS), the control circuit 50 may be provided in a central monitoring unit that enables control of units of the air conditioning system 100 through networks.

As illustrated in FIG. 1, suppose a plurality of air-conditioned areas 60, 61, and 62 are present in the same room. In this embodiment, the air-conditioned areas 60, 61, and 62 include an ordinary-air-conditioned area 60, a locally-air-conditioned area 61, and an air-conditioning-free area 62. The ordinary-air-conditioned area 60 is an air-conditioned area with an ordinary load. The locally-air-conditioned area 61 is an air-conditioned area with a high air conditioning load. The air-conditioning-free area 62 is an area where no residents are present and air conditioning is not required. A first indoor unit 15a is disposed above the ordinary-air-conditioned area 60, and a second indoor unit 15b is disposed above the locally-air-conditioned area 61. A local air conditioner 80 is also disposed in the locally-air-conditioned area 61. The ordinary-air-conditioned area 60 is air-conditioned by the first indoor unit 15a. The locally-air-conditioned area 61 is air-conditioned by one of the second indoor unit 15a and the local air conditioner 80. Air conditioning suitable for each of the air-conditioned areas facilitates an increase in the efficiency of the air conditioning system 100.

Suppose a generally heavily clothed resident 70 usually works in the air-conditioned area 60. Suppose a generally lightly clothed resident 71 usually works in the locally-air-conditioned area 61. In the case of heating, the locally-air-conditioned area 61 is an air-conditioned area with a high load in view of a comfort index PMV. Heating energy necessary for the ordinary-air-conditioned area 60 is supplied from the first indoor unit 15a, and heating energy necessary for the locally-air-conditioned area 61 is supplied from the second indoor unit 15b.

The local air conditioner 80 is disposed in the locally-air-conditioned area 61. The local air conditioner 80 is supplied with electric power generated by the power generator 20 through a power line 24. In this manner, the locally-air-conditioned area 61 is locally supplied with heating energy or cooling energy. The locally-air-conditioned area 61 can be supplied with heating energy or cooling energy from each of the heat pump cycle 17 and the local air conditioner 80. Examples of the local air conditioner 80 include an electric warm-air fan heater and a fan cooler. The local air conditioner 80 is preferably equipment that is portable with human power. If the local air conditioner 80 is portable, the local air conditioner 80 can be easily disposed near the resident.

The control circuit 50 obtains an intended temperature TL (a target temperature) of the first indoor unit 15a, an intended temperature TH (a target temperature) of the second indoor unit 15b, and an outdoor air temperature To. Based on the intended temperature TL, the intended temperature TH, and the outdoor air temperature To, the control circuit 50 determines whether the local air conditioner 80 effectively air-conditions the locally-air-conditioned area 61. In other words, the control circuit 50 determines whether the local air conditioner 80 should perform local air conditioning or not. The control circuit 50 issues an instruction of turning the second indoor unit 15b on or off, to the second indoor unit 15b. The control circuit 50 outputs a clutch level U to the clutch 33. The control circuit 50 adjusts the amount of power generation Pg of the power generator 20.

Operation of the air conditioning system 100 will now be described.

The load detector 51 of the control circuit 50 calculates a load of the air-conditioned area that is air-conditioned by the first indoor unit 15a and a load of the air-conditioned area that is air-conditioned by the second indoor unit 15b, and transmits calculation results to the switching determiner 52. One of techniques for calculating loads is a technique of calculating loads Q (W) from an intended temperature T (K) of an indoor unit and the outdoor air temperature To. A intended temperature T can be input by the resident to a remote controller of the indoor unit. The control circuit 50, for example, directly obtains an intended temperature T of the indoor unit through wireless communication from the remote controller of the indoor unit. The outdoor air temperature To can be obtained from, for example, an outdoor air temperature sensor (not shown). The load Q can be calculated from Expression (1):

Q=(T−To)·k·A   (1)

where A (m²) is a space surface area of a space to be air-conditioned and k (W/(m²·K)) is an overall heat transmission coefficient with respect to the space surface area.

The load detector 51 calculates an air conditioning load QL from Expression (2-1):

QL=(TL−To)·kL·AL   (2-1)

where QL is an air conditioning load of the ordinary-air-conditioned area 60, TL is an intended temperature, AL is a space surface area, and kL is an overall heat transmission coefficient. Similarly, the load detector 51 calculates an air conditioning load QH from Expression (2-2):

QH=(TH−To)·kH·AH   (2-2)

where QH is an air conditioning load of the locally-air-conditioned area 61, TH is an intended temperature, AH is a space surface area, and kH is an overall heat transmission coefficient.

The space surface areas AL and AH and the overall heat transmission coefficients kL and kH are individually designed values of the air conditioning system 100. Thus, these values are previously stored in the constant setting unit 53, obtained from the constant setting unit 53 by the load detector 51 when necessary, and used for the calculations of Expressions (2-1) and (2-2).

Next, the switching determiner 52 of the control circuit 50 obtains a load Q from the load detector 51 and calculates a gas volume Vhp (m³/min) necessary for driving the compressor 12 of the heat pump cycle 17. The gas volume Vhp can be calculated by using a coefficient of performance (COP) ((min·W)/m³) indicating the efficiency of the heat pump cycle 17, from Expression (3):

Vhp=Q/COP   (3)

Referring to FIG. 3, efficiency characteristics of the gas heat pump cycle will be described. FIG. 3 shows a relationship between the efficiency (COP) of the heat pump cycle and the load Q. For example, the efficiency with respect to the air conditioning load QL in the ordinary-air-conditioned area 60 is COP_L. This relationship is determined on the basis of performance of equipment such as the compressor 12 and the configuration of the heat pump cycle 17. In general, in the gas heat pump cycle, the efficiency is at maximum with a load called an intermediate load. The efficiency is low with a rated load higher than the intermediate load and a higher load. The efficiency is also low in a region of a low load or a load called a partial load. Although Japanese Unexamined Patent Application Publication No. 2011-7356 and Japanese Patent No. 4958448 described above show techniques of increasing the efficiency under a low load or a partial bad, but fail to disclose techniques of increasing the efficiency under a high bad.

In consideration of the relationship between the efficiency COP and the bad Q, a gas volume Vhp_ALL necessary for air conditioning by the first indoor unit 15a and the second indoor unit 15b is calculated. The area that is air-conditioned by the first indoor unit 15a is the ordinary-air-conditioned area 60, and the air conditioning load thereof is QL. The area that is air-conditioned by the second indoor unit 15b is the locally-air-conditioned area 61 and the air-conditioned-free area 62. The air-conditioning-free area 62 does not directly affect warmth or coldness felt by the resident 71. However, since the second indoor unit 15b is disposed on the ceiling, air-conditioning is inevitably needed. Suppose the bad of the air-conditioning-free area 62 is QLoss, the air conditioning bad of the second indoor unit 15b is QH+QLoss. The sum of the air conditioning loads of the first indoor unit 15a and the second indoor unit 15b is QL+QH+QLoss. As shown in FIG. 3, if the efficiency with respect to QL+QH+QLoss is COP_ALL, gas volume Vhp_ALL can be calculated, by using Expressions (2-1), (2-2), and (3), from Expression (4):

$\begin{array}{cc}\mathrm{Vhp\_ALL}=\left(\mathrm{QL}+\mathrm{QH}+\mathrm{QLoss}\right)\text{/}\mathrm{COP\_ALL}=\left(\left(\mathrm{TL}-\mathrm{To}\right)·\mathrm{kL}·\mathrm{AL}+\left(\mathrm{TH}-\mathrm{To}\right)·\mathrm{kH}·\mathrm{AH}+\mathrm{QLoss}\right)\text{/}\mathrm{COP\_ALL}& \left(4\right)\end{array}$

In this manner, the gas volume Vhp_ALL necessary for covering all the air conditioning loads by the first indoor unit 15a and the second indoor unit 15b can be calculated from the loads QL and QH calculated by the load detector 51. In other words, the gas volume Vhp_ALL necessary for covering the air conditioning loads only by the heat pump cycle 17 without using the local air conditioner 80 can be calculated.

Then, a gas volume Vg necessary for the gas engine 11 in a case where the local air conditioner 80 is operated with electric power Pg(W) generated by the power generator 20 is calculated.

FIG. 4 is a graph showing a relationship between a clutch level in the clutch 33 and the number of revolutions of the power generator 20. Suppose the clutch level that is an input of the clutch 33 is U (dimensionless) and the number of revolutions of the power generator is N (rpm), the relationship expressed by Expression (5) below is established:

N=α1·U   (5)

where α1 (rpm) is a constant. The clutch level U is an input signal to the clutch 33. As the clutch level U is increased, a driving force transmitted from the gas engine 11 to the power generator 20 increases, and the number of revolutions N of the power generator 20 increases. The number of revolutions Nmax is the number of revolutions of the gas engine 11 obtained when the clutch 33 operates to cause power of the gas engine 11 to be transmitted to the power generator 20, and varies in accordance with the number of revolutions necessary for the compressor 12.

FIG. 5 is a graph showing a relationship between the number of revolutions of the power generator 20 and the gas volume consumed by the gas engine 11. Suppose the gas volume consumed by the gas engine 11 is Vg and the number of revolutions of the power generator is N, the relationship of Expression (6) is established:

Vg=α2·N   (6)

where α2 (m³/(min·rpm)) is a constant.

FIG. 6 is a graph showing a relationship between the number of revolutions and the amount of power generation of the power generator 20. Suppose the amount of power generated by the power generator 20 is Pg and the number of revolutions of the power generator 20 is N, the relationship of Expression (7) is established:

Pg=α3·N   (7)

where α3 (W/rpm) is a constant.

From Expressions (5) to (7), the relationship between the amount of power generation Pg of the power generator 20 and the necessary gas volume Vg is expressed as Expression (8):

Vg=(α2/α3)·Pg   (8)

In a case where the load Q is covered by operating the local air conditioner 80, the relationship between the necessary electric power and the load Q is expressed as Expression (9):

Q=β·(Pg+Pin)   (9)

where Pin is the amount of power purchased from the commercial power supply 23, Pg is the amount of power generated by the power generator 20, and β (dimensionless) is the efficiency of the local air conditioner 80.

The amount of power generation Pg of the power generator 20 is generally sufficient for providing the load Q. In this case, since the amount of power purchase Pin from the commercial power supply 23 is zero, the relationship between the amount of power generation Pg and the load Q is expressed as Expression (10):

Q=β·Pg   (10)

In a case where the load QH is covered by the local air conditioner 80, instead of the second indoor unit 15b, by air-conditioning the locally-air-conditioned area 61, a gas volume Vg_H necessary for the gas engine 11 can be calculated, by using Expressions (8) and (10), from Expression (11):

$\begin{array}{cc}\mathrm{Vg\_H}=\left(\mathrm{\alpha 2}\text{/}\mathrm{\alpha 3}\right)·\mathrm{Pg}=\left(\mathrm{\alpha 2}\text{/}\mathrm{\alpha 3}\right)·\left(\mathrm{QH}\text{/}\beta \right)=\left(\mathrm{\alpha 2}\text{/}\mathrm{\alpha 3}\right)·\left(\left(\mathrm{TH}-\mathrm{To}\right)·\mathrm{kH}·\mathrm{AH}\text{/}\beta \right)& \left(11\right)\end{array}$

In a case where the locally-air-conditioned area 61 is air-conditioned by the local air conditioner 80, the second indoor unit 15b is stopped. On the other hand, the ordinary-air-conditioned area 60 is air-conditioned by the first indoor unit 15a. As described with reference to FIG. 3, the efficiency with respect to the load QL is correlated with the COP_L. Thus, the gas volume Vhp_L necessary for covering the load QL with the first indoor unit 15a can be calculated, by using Expressions (3) and (4), from Expression (12):

$\begin{array}{cc}\mathrm{Vhp\_L}=\mathrm{QL}\text{/}\mathrm{COP\_L}=\left(\mathrm{TL}-\mathrm{To}\right)·\mathrm{kL}·\mathrm{AL}\text{/}\mathrm{COP\_L}& \left(12\right)\end{array}$

The gas volume necessary in a case where the local air conditioner 80 is not used and air conditioning is performed only by the first indoor unit 15a and the second indoor unit 15b is Vhp_ALL. The gas volume necessary in a case where the locally-air-conditioned area 61 is air-conditioned by the local air conditioner 80 and the ordinary-air-conditioned area 60 is air-conditioned by the first indoor unit 15a is (Vg_H+Vhp_L).

The use of the local air conditioner 80 is effective for saving energy in a case where the gas volume (Vg_H+Vhp_L.) is smaller than the gas volume Vhp_ALL. Thus, if Expression (13):

Vg _— H+Vhp _— L<Vhp _— ALL   (13)

is established, the locally-air-conditioned area 61 is air-conditioned by the local air conditioner 80. On the other hand, if Expression (13) is not established, the locally-air-conditioned area 61 is air-conditioned by the second indoor unit 15b.

The switching determiner 52 of the control circuit 50 determines whether Expression (13) is established or not. If Expression (13) is established, a signal is transmitted from the switching determiner 52 to the indoor unit controller 55, and a stop signal is transmitted as an indoor unit instruction from the indoor unit controller 55 to the second indoor unit 15b. At the same time, a signal is transmitted from the switching determiner 52 to the clutch controller 54, and a clutch level U is transmitted from the clutch controller 54 to the clutch 33. The clutch level U_H necessary for the power generator 20 to generate an electric power Pg necessary for the local air conditioner 80 can be calculated, by using Expressions (2), (5), (6), and (11), from Expression (14):

$\begin{array}{cc}\mathrm{U\_H}=\mathrm{N\_H}\text{/}\text{α1}=\mathrm{Vg\_H}\text{/}\left(\mathrm{\alpha 1}·\mathrm{\alpha 2}\right)=\left(1\text{/}\left(\mathrm{\alpha 1}·\mathrm{\alpha 3}·\beta \right)\right)·\mathrm{QH}=\left(1\text{/}\left(\mathrm{\alpha 1}·\mathrm{\alpha 3}·\beta \right)\right)·\left(\mathrm{TH}-\mathrm{To}\right)·\mathrm{kH}·\mathrm{AH}& \left(14\right)\end{array}$

where N_H is the number of revolutions necessary for the power generator 20 to generate electric power Pg.

The clutch controller 54 transmits to the clutch 33 the clutch level U_H calculated from Expression (14). The clutch 33 can transmit power of the gas engine 11 to the power generator 20 through the power transmission mechanism 41. As a result, minimum electric power necessary for the local air conditioner 80 to cover the load Q_H of the locally-air-conditioned area 61 can be generated by the power generator 20.

If Expression (13) is not established, it is determined that the use of the local air conditioner 80 is not effective. Thus, no signal is transmitted to the indoor unit controller 55, and the second indoor unit 15b does not stop and continues to operate. No signal is transmitted from the switching determiner 52 to the clutch controller 54, either, and the clutch level U is not transmitted to the clutch 33. The power generator 20 does not generate power for the local air conditioner 80.

In this manner, the control circuit 50 controls the number of revolutions of the power generator 20 and on/off operation of the second indoor unit 15b such that when the indoor unit 15b operates, the power generator 20 stops, and when the second indoor unit 15b stops, the power generator 20 operates and supplies electric power to the local air conditioner 80. In other words, the control circuit 50 switches, in accordance with the degree of the air conditioning load of the interior space, between the operation mode in which the interior space (the locally-air-conditioned area 61) is air-conditioned by the second indoor unit 15b and the operation mode in which the interior space (the locally-air-conditioned area 61) is air-conditioned by the local air conditioner 80. In this manner, the load applied to the heat pump cycle 17 can be reduced, thereby increasing the efficiency under a high load on the heat pump cycle 17.

More specifically, the control circuit 50 controls the power generator 20 and the second indoor unit 15b such that the locally-air-conditioned area 61 is air-conditioned by the local air conditioner 80 in a case where the gas flow rate necessary for the gas engine 11 in air-conditioning the locally-air-conditioned area 61 by the second indoor unit 15b is higher than the gas flow rate necessary for the gas engine 11 in air-conditioning the locally-air-conditioned area 61 by the local air conditioner 80. The control circuit 50 also controls the power generator 20 and the second indoor unit 15b such that the locally-air-conditioned area 61 is air-conditioned by the second indoor unit 15b in a case where the gas flow rate necessary for the gas engine 11 in air-conditioning the locally-air-conditioned area 61 by the second indoor unit 15b is lower than or equal to the gas flow rate necessary for the gas engine 11 in air-conditioning the locally-air-conditioned area 61 by the local air conditioner 80. Then, it is possible to ensure saving of gas while maintaining comfort.

In this embodiment, the interior space (the locally-air-conditioned area 61) is air-conditioned by the local air conditioner 80 instead of at least one indoor unit 15b selected from the indoor units 15a and 15b. The other indoor unit 15a is operated to air-condition the interior space (the ordinary-air-conditioned area 60) independently of on/off of the local air conditioner 80. In this manner, on/off of the heat pump cycle 17 can be avoided as much as possible. This also contributes to an increase in efficiency of the air conditioning system 100.

In air-conditioning the locally-air-conditioned area 61 by the local air conditioner 80, the control circuit 50 outputs an appropriate clutch level U. Then, an appropriate torque is transmitted to the power generator 20. That is, the control circuit 50 controls the number of revolutions of the power generator 20 by controlling the clutch 33. Accordingly, a sufficient amount of electric power is generated by the power generator 20, and thus, energy (gas) is less likely to be wasted.

The load QLoss of the air-conditioning-free area 62, the efficiency COP_ALL corresponding to the air conditioning load (QL+QH+QLoss), and the efficiency COP_L with respect to the air conditioning load QL are design values in the air conditioning system 100. Thus, these values are stored in the constant setting unit 53, obtained from the constant setting unit 53 by the switching determiner 52 when necessary, and used for calculations in Expressions (4) and (14). The constant α1 indicating characteristics of the clutch 33, the constant α2 indicating the relationship between the power generator 20 and the gas engine 11, the constant α3 indicating characteristics of the power generator 20, and the efficiency β of the local air conditioner 80 are also design values in the air conditioning system 100. Thus, these values are stored in the constant setting unit 53 and used by the switching determiner 52 and the clutch controller 54 when necessary.

In this embodiment, the locally-air-conditioned area 61 with a high load is air-conditioned by the local air conditioner 80 with electric power generated by the power generator 20. Thus, a load applied to the heat pump cycle 17 can be reduced, and the efficiency of the heat pump cycle 17 in a case of a high load can be increased. In addition, in a period in which the air-conditioning-free area 62 is not air-conditioned, energy is not wasted. As a result, energy (gas) consumption can be saved in total. Thus, it is possible to provide the gas heat pump air conditioning system 100 having high efficiency under a high load as well as a low load.

The control circuit 50 determines whether the local air conditioner 80 should perform air conditioning while determining the loads of the air-conditioned areas (the ordinary-air-conditioned area 60 and the locally-air-conditioned area 61). If the efficiency of the heat pump cycle 17 is high, the main unit of air conditioning is not switched from the second indoor unit 15b to the local air conditioner 80, and all the area can be air-conditioned by the heat pump cycle 17 (the indoor units 15a and 15b).

Since the local air conditioner 80 can be operated with electric power generated by the power generator 20, the degree of freedom in installation is high. For example, since the local air conditioner 80 can be disposed near the resident 71, comfort of the resident can be maintained.

Second Embodiment

As illustrated in FIG. 2, in a gas heat pump air conditioning system 200 according to a second embodiment, the second indoor unit 15b is omitted. That is, the air conditioning system 200 is configured such that an air-conditioned area (a locally-air-conditioned area 61) with a high air conditioning load is air-conditioned by a local air conditioner 80, and the other air-conditioned area (an ordinary-air-conditioned area) is air-conditioned by the indoor unit 15a.

This embodiment is based on a premise that inequality of Expression (13) described in the first embodiment is always established. When Expressions (4), (11), and (12) are substituted into Expression (13), the following Expression (15) is derived:

(α2/α3)·((TH−To)·kH·AH/β)+(TL−To)·kL·AL/COP_—L<((TL−To)·kL·AL+(TH−To)·kH·AH+QLoss)/COP_ALL   (15)

In Expression (15), if the load QLoss of an air-conditioning-free area 62 is significantly high, inequality of Expression (15) is always established irrespective of an intended temperature TL, an intended temperature TH, and an outdoor air temperature To. As shown in FIG. 3, inequality of Expression (15) is also always established in a case where the efficiency with a high load is very low, that is, the COP_ALL is much smaller than the COP_L.

In this case, it is effective that the locally-air-conditioned area 61 is always air-conditioned by the local air conditioner 80. Thus, the second indoor unit 15b can be omitted. A clutch 33 always transmits the maximum driving force of a gas engine 11 to a power generator 20. All the electric power generated by the power generator 20 is supplied to the local air conditioner 80 through a power line 24. Thus, the control circuit 50 of the first embodiment can also be omitted. In this embodiment, the second indoor unit 15b and the control circuit 50 can be omitted. In other words, the number of indoor units can be reduced, and complicated control is not required. Thus, an initial investment cost can be reduced.

In a case where only electric power generated by the power generator 20 is insufficient as electric power required for the local air conditioner 80, electric power can be supplied from the commercial power supply 23 through the panel board 22. On the contrary, in a case where electric power generated by the power generator 20 is in excess, the excess electric power can be supplied to, and used in, other indoor electrical appliance (not shown) through the power line 24. This holds for the first embodiment.

Other Embodiments

The number of air-conditioned areas is not limited to two (e.g., the ordinary-air-conditioned area 60 and the locally-air-conditioned area 61). Even in a case where a larger number of air-conditioned areas are present, the number of indoor units and the number of local air conditioners 80 can be increased. The control circuit 50 may detect (obtain) comfort indexes PMV in the air-conditioned areas, instead of or in addition to the intended temperature TL, the intended temperature TH, and the outdoor air temperatures To.

The control circuit 50 may start air conditioning by the local air conditioner 80 by causing the power generator 20 to supply electric power to the local air conditioner 80 when a temperature change amount Ta per unit time in an interior space that is air-conditioned by a heat exchanger is less than or equal to a predetermined value C1.

Specifically, as illustrated in FIG. 7, the control circuit 50 may control the power generator 20 and the local air conditioner 80, for example. First, the control circuit 50 obtains the temperature change amount Ta per unit time in an interior space (step S1). The control circuit 50 obtains a temperature detected by a temperature sensor disposed in the interior space and obtains the temperature change amount Ta based on the temperature. For example, the control circuit 50 can obtain a temperature change amount Ta by obtaining from the temperature sensor a room temperature T1 at a predetermined time and a room temperature T2 when a predetermined time Δt has elapsed from the predetermined time and calculating |T1−T2|/Δt. Then, the control circuit 50 determines whether the temperature change amount Ta per unit time in the interior space is less than or equal to a predetermined value C1 (step S2). If the temperature change amount Ta per unit time in the interior space is less than or equal to the predetermined value C1, (Yes step S2), the control circuit 50 causes the power generator 20 to supply electric power to the local air conditioner 80 and starts air conditioning by the local air conditioner 80 (step S3). On the other hand, if the temperature change amount Ta per unit time in the interior space is larger than the predetermined value C1 (No in step S2), the control circuit 50 performs step S1 again.

The control circuit 50 may select an operation mode based on the relationship between the temperature change amount Ta per unit time in the interior space that is air-conditioned by a heat exchanger and a predetermined value C2. For example, when the temperature change amount Ta per unit time in the interior space that is air-conditioned by the heat exchanger exceeds the predetermined value C2, the control circuit 50 selects a first operation mode in which the interior space is air-conditioned by the heat exchanger. On the other hand, the control circuit 50 selects a second operation mode in which the interior space is air-conditioned by the local air conditioner 80 when the temperature change amount Ta per unit time in the interior space that is air-conditioned by the heat exchanger is less than or equal to the predetermined value C2.

Specifically, as illustrated in FIG. 8, the control circuit 50 may control the power generator 20, the local air conditioner 80, and the heat exchanger. First, the control circuit 50 obtains a temperature change amount Ta per unit time in an interior space (step S11), and determines whether the temperature change amount Ta per unit time in the interior space exceeds the predetermined value C2 or not (step S12). If the temperature change amount Ta per unit time in the interior space exceeds the predetermined value C2 (Yes in step S12), the control circuit 50 selects the first operation mode in which the interior space is air-conditioned by the heat exchanger (step S13). On the other hand, if the temperature change amount Ta per unit time in the interior space does not exceed the predetermined value C2 (No in step S12), the control circuit 50 selects the second operation mode in which the interior space is air-conditioned by the local air conditioner 80 (step S14).

The technique described in this disclosure can provide an air conditioning system that can achieve both comfort of a resident and a high efficiency.

Claims

1. A gas heat pump air conditioning system comprising: a gas engine;a heat pump cycle that includes a compressor and at least one heat exchanger, the compressor being driven by the gas engine, the at least one heat exchanger being disposed in an interior space and air-conditioning the interior space;a power generator that is driven by the gas engine and that generates electric power;a local air conditioner that is disposed in the interior space and that air-conditions the interior space by using the electric power generated by the power generator; anda control circuit that controls the power generator and the heat exchanger in accordance with an air conditioning load of the interior space.

2. The gas heat pump air conditioning system of claim 1, wherein the control circuit stops the power generator while air conditioning by the heat exchanger is being performed, andsupplies electric power from the power generator to the local air conditioner while air conditioning by the heat exchanger is stopped.

3. The gas heat pump air conditioning system of claim 1, wherein the control circuit switches an operation mode between a first operation mode in which the interior space is air-conditioned by the heat exchanger and a second operation mode in which the interior space is air-conditioned by the local air conditioner, in accordance with the air conditioning load of the interior space.

4. The gas heat pump air conditioning system of claim 1, wherein in a case where a gas flow rate necessary for the gas engine in air-conditioning the interior space by the heat exchanger is higher than a gas flow rate necessary for the gas engine in air-conditioning the interior space by the local air conditioner, the control circuit controls the power generator and the heat exchanger, thereby causing the interior space to be air-conditioned by the local air conditioner, andin a case where a gas flow rate necessary for the gas engine in air-conditioning the interior space by the heat exchanger is lower than or equal to the gas flow rate necessary for the gas engine in air-conditioning the interior space by the local air conditioner, the control circuit controls the power generator and the heat exchanger, thereby causing the interior space to be air-conditioned by the heat exchanger.

5. The gas heat pump air conditioning system of claim 1, wherein the control circuit causes the power generator to supply electric power to the local air conditioner and starts air conditioning performed by the local air conditioner when a temperature change amount per unit time in the interior space that has been air-conditioned by the heat exchanger is less than or equal to a predetermined value.

6. The gas heat pump air conditioning system of claim 5, wherein the control circuit selects a first operation mode in which the interior space is air-conditioned by the heat exchanger in a case where the temperature change amount per unit time in the interior space that has been air-conditioned by the heat exchanger exceeds the predetermined value, andselects a second operation mode in which the interior space is air-conditioned by the local air conditioner in a case where the temperature change amount per unit time in the interior space that has been air-conditioned by the heat exchanger is less than or equal to the predetermined value.

7. The gas heat pump air conditioning system of claim 1, wherein the heat exchanger included in the heat pump cycle includes a plurality of heat exchangers, andthe control circuit causes the local air conditioner to air-condition the interior space, instead of at least one of the plurality of heat exchangers.

8. The gas heat pump air conditioning system of claim 1, further comprising a clutch that transmits power from the gas engine to the power generator, wherein the control circuit controls the number of revolutions of the power generator by controlling the clutch.

9. The gas heat pump air conditioning system of claim 1, wherein the heat exchanger included in the heat pump cycle includes a plurality of heat exchangers,the plurality of heat exchangers include a first heat exchanger and a second heat exchanger,the air-conditioned area included in the interior space includes a plurality of air-conditioned areas, andthe plurality of air-conditioned areas include an ordinary-air-conditioned area that is air-conditioned by the first heat exchanger and a locally-air-conditioned area that is air-conditioned by one of the second heat exchanger and the local air conditioner.

10. A gas heat pump aft conditioning system comprising: a gas engine;a heat pump cycle that includes a compressor and a heat exchanger, the heat exchanger being disposed in an interior space and air-conditioning the interior space;a power generator that is driven by the gas engine and that generates electric power; anda local air conditioner that air-conditions the interior space by using the electric power generated by the power generator, whereinan air-conditioned area with a high degree of the air conditioning load is air-conditioned by the local air conditioner, and the other air-conditioned areas are air-conditioned by the heat exchanger.

11. The gas heat pump air conditioning system of claim 10, wherein the heat pump cycle performs a heating operation on the interior space by the heat exchanger disposed on a ceiling of the interior space, andthe local air conditioner is disposed on a floor of the interior space and performs a heating operation on the interior space.

12. The gas heat pump air conditioning system of claim 1, wherein the local air conditioner is a portable electric warm-air fan heater.