Patent Description:
Patent Document <NUM> discloses control in which heat discharged from a freezer using a CO<NUM> refrigerant when a show case in a store is cooled using the freezer is utilized for hot water or heating. Specifically, Patent Document <NUM> discloses control in which a part of a refrigerant emitted by a compressor is supplied to a radiator unit and utilized for heating and water which has been heat-exchanged in a condenser is utilized as hot water. In addition, Patent Document <NUM> discloses an air conditioner using a CO<NUM> refrigerant with a freezing cycle in which a high pressure is in a supercritical state when a cooling operation is performed in normal environmental conditions and the high pressure is in a subcritical state in a state in which the outside air temperature is low.

There is a demand for a method for improving combined efficiency of both a load-side device (an air conditioner, a water heater, or the like), which utilizes exhaust heat from a freezer, and the freezer.

Hence, an object of this invention is to provide a control device, an exhaust heat recovery freezer system, a control method, and a program capable of resolving the problems described above.

According to an aspect of the present disclosure, a control device as defined in claim <NUM> includes an operation mode decision unit that decides, in accordance with necessity of heat recovery from a refrigerant circulating in a refrigerant circuit, which operation of a supercritical operation in which a high pressure in the refrigerant circuit is in a supercritical state and a subcritical operation in which the high pressure is in a subcritical state is to be performed; and a freezer control unit that controls the refrigerant circuit to be operated in either the supercritical operation or the subcritical operation on the basis of decision of the operation mode decision unit.

According to another aspect of the present disclosure, an exhaust heat recovery freezer system as defined in claim <NUM> includes a freezer that has a refrigerant circuit including a compressor, a gas cooler, an expansion valve, and an evaporator; an exhaust heat recovery device that recovers heat through heat exchange with a refrigerant circulating in the refrigerant circuit between the compressor and the gas cooler in the refrigerant circuit and supplies the recovered heat to a load device; and the foregoing control device.

According to another aspect of the present disclosure, a control method as defined in claim <NUM> includes a step of deciding, in accordance with necessity of heat recovery from a refrigerant circulating in a refrigerant circuit, which operation of a supercritical operation in which a high pressure in the refrigerant circuit is in a supercritical state and a subcritical operation in which the high pressure is in a subcritical state is to be performed; and a step of controlling the refrigerant circuit to be operated in either the supercritical operation or the subcritical operation on the basis of decision in the step of deciding an operation.

According to another aspect of the present disclosure, a computer program is defined in claim <NUM>.

According to the control device, the exhaust heat recovery freezer system, the control method, and the program of the present disclosure, it is possible to improve overall efficiency of both a load device, which utilizes exhaust heat of a freezer, and the freezer.

Hereinafter, an exhaust heat recovery freezer system according to an embodiment of the present disclosure will be described with reference to <FIG>.

<FIG> is a diagram illustrating an example of an exhaust heat recovery freezer system according to the embodiment.

An exhaust heat recovery freezer system <NUM> is a system in which heat discharged by a freezer <NUM> performing a cooling operation is recovered by an exhaust heat recovery device <NUM> and the recovered heat is supplied to a warming cycle of a high-temperature load device <NUM>. For example, the exhaust heat recovery freezer system <NUM> is used in supermarkets or the like, in which the freezer <NUM> refrigerates or freezes food and exhaust heat therefrom is recovered by the exhaust heat recovery device <NUM> and utilized for heating of the store or in a water heater. In the exhaust heat recovery freezer system <NUM>, CO<NUM> is used as a refrigerant. A CO<NUM> refrigerant is in a supercritical state within an ordinary temperature range at approximately <NUM>. From a viewpoint of efficiency of the exhaust heat recovery freezer system <NUM> in its entirety instead of efficiency of the freezer <NUM> alone, the exhaust heat recovery freezer system <NUM> determines necessity of heat recovery by the exhaust heat recovery device <NUM> and operates with a high pressure in the freezer <NUM> in a supercritical state or a subcritical state in accordance with the necessity thereof.

As shown in <FIG>, the exhaust heat recovery freezer system <NUM> includes the freezer <NUM>, the exhaust heat recovery device <NUM>, the high-temperature load device <NUM>, a low-temperature load device <NUM> (for example, a refrigerating show case or a freezing show case in a supermarket), and a system controller <NUM>. The freezer <NUM> includes a two-stage compressor <NUM>, a gas cooler <NUM>, a first expansion valve 13a, a receiver <NUM>, an accumulator <NUM>, a main piping <NUM> connecting these to the low-temperature load device <NUM>, a piping <NUM> connecting a gas-phase portion of the receiver <NUM> to an emission side of a low stage-side compressor 11b of a high stage-side compressor 11a and the low stage-side compressor 11b included in the two-stage compressor <NUM>, a valve 18a controlling a flow rate of the refrigerant flowing in the piping <NUM>, a fan <NUM> provided in the gas cooler <NUM>, and temperature sensors tho <NUM> to tho3. The temperature sensor tho <NUM> is provided on the emission side of the two-stage compressor <NUM> and an entrance side of a heat exchanger <NUM>, and the temperature sensor tho2 is provided on an exit side of the heat exchanger <NUM> and the entrance side of the gas cooler <NUM>. The exit side and the entrance side are an exit side and an entrance side in a flowing direction of the refrigerant. In addition, the temperature sensor tho3 is provided at a position where an outside air temperature can be measured. The low-temperature load device <NUM> is constituted of a second expansion valve 13b and an evaporator <NUM> and is connected to a low pressure side of the freezer <NUM>.

The heat exchanger <NUM> of the exhaust heat recovery device <NUM> is connected (inserted) between the two-stage compressor <NUM> and the gas cooler <NUM>, and the CO<NUM> refrigerant of the freezer <NUM> flows in the heat exchanger <NUM>. The exhaust heat recovery device <NUM> includes the heat exchanger <NUM> for exhaust heat recovery, a pump <NUM>, and a piping <NUM> connecting these to the high-temperature load device <NUM>. For example, the high-temperature load device <NUM> is an air conditioner, a water heater, or the like in a store. In the heat exchanger <NUM>, heat exchange is performed between the CO<NUM> refrigerant of the freezer <NUM> and the refrigerant (for example, water) of the exhaust heat recovery device <NUM>. In the exhaust heat recovery device <NUM>, warm water which has been warmed through heat exchange in the heat exchanger <NUM> circulates in the piping <NUM> by driving of the pump <NUM>, and for example, exhaust heat from the freezer <NUM> is supplied to the high-temperature load device <NUM> via a heat exchanger (not shown) provided in the high-temperature load device <NUM>. Since the refrigerant does not circulate in the piping <NUM> when the pump <NUM> is at a stop, exhaust heat is not recovered by the exhaust heat recovery device <NUM>.

In the freezer <NUM>, the two-stage compressor <NUM> emits a high-pressure refrigerant compressed by the high stage-side compressor 11a and the low stage-side compressor 11b. In more detail, a suction side of the low stage-side compressor 11b is connected to the accumulator <NUM>, and the low stage-side compressor 11b suctions and compresses the refrigerant (gas) separated by the accumulator <NUM>. The low stage-side compressor 11b emits the compressed refrigerant to the suction side of the high stage-side compressor 11a. The refrigerant is supplied from the gas-phase portion of the receiver <NUM> to the suction side of the high stage-side compressor 11a through the piping <NUM> (injection circuit). The high stage-side compressor 11a suctions and compresses these refrigerants. The compressed refrigerant is supplied to the heat exchanger <NUM> for exhaust heat recovery. As described above, in the heat exchanger <NUM>, heat of the high-temperature/high-pressure CO<NUM> refrigerant is recovered by the refrigerant (water) of the exhaust heat recovery device <NUM> and is supplied to the high-temperature load device <NUM>. The CO<NUM> refrigerant which has passed through the heat exchanger <NUM> is subjected to heat dissipation through heat exchange in the gas cooler <NUM> with air sent by the fan <NUM> and is condensed and liquefied. The condensed refrigerant is subjected to pressure reduction and expansion by the first expansion valve 13a and is supplied to the receiver <NUM>. In the receiver <NUM>, a two-phase refrigerant of gas and liquid is present in a mixed manner. A part (gas-phase portion) of the refrigerant present in the receiver <NUM> branches to the piping <NUM> as described above and is supplied to the two-stage compressor <NUM>. The liquid-phase refrigerant flows out from the receiver <NUM>, is subjected to additional pressure reduction by the second expansion valve, and is then supplied to the evaporator <NUM>. The CO<NUM> refrigerant supplied to the evaporator <NUM> absorbs heat of the low-temperature load device <NUM> (for example, a show case for refrigeration or a show case for freezing in a store), is gasified, and cools the low-temperature load device <NUM>. The CO<NUM> refrigerant gasified by the evaporator <NUM> is supplied to the accumulator <NUM>. The CO<NUM> refrigerant is separated into gas and liquid by the accumulator <NUM>, and the gas refrigerant is suctioned into the low stage-side compressor 11b. The refrigerant is compressed by the low stage-side compressor 11b and the high stage-side compressor 11a and circulates through the foregoing path again.

The exhaust heat recovery freezer system <NUM> shown in <FIG> is a schematic basic constitution and may further include other constituent elements. In <FIG>, the exhaust heat recovery device <NUM> has only one heat exchanger <NUM>, but the exhaust heat recovery device <NUM> may include two or more heat exchangers <NUM>. In this case, all or some of the plurality of heat exchangers <NUM> may be connected to (inserted into) a refrigerant circuit of the freezer <NUM>. In addition, a plurality of exhaust heat recovery devices <NUM> may be present, and the heat exchanger <NUM> provided in each exhaust heat recovery device <NUM> may be connected to the refrigerant circuit of the freezer <NUM>.

The system controller <NUM> controls the freezer <NUM> and the exhaust heat recovery device <NUM>. The system controller <NUM> includes a signal acquisition unit <NUM>, a setting reception unit <NUM>, an exhaust heat recovery device control unit <NUM>, an operation mode decision unit <NUM>, a freezer control unit <NUM>, and a storage unit <NUM>. In addition, the system controller <NUM> has a timer, which can recognize the current date and time.

The signal acquisition unit <NUM> acquires the temperature detected by the temperature sensors tho1 to tho3, a signal indicating a working state of the exhaust heat recovery device <NUM>, and a signal indicating an operation state (a working state or a load state) of the high-temperature load device <NUM>. The signal acquisition unit <NUM> records various kinds of acquired signals in the storage unit <NUM>.

The setting reception unit <NUM> receives an input of various kinds of settings made by a user. For example, the setting reception unit <NUM> receives a setting for working (ON) or stopping (OFF) of the exhaust heat recovery device <NUM> and outputs the setting to the exhaust heat recovery device control unit <NUM>. In addition, regarding the operation of the freezer <NUM>, the setting reception unit <NUM> receives a setting of conditions for switching between an operation in which the high pressure is in the supercritical state (which may hereinafter be referred to as a supercritical operation) and an operation in which the high pressure is in the subcritical state (which may hereinafter be referred to as a subcritical operation) and records the received setting of the conditions for switching in the storage unit <NUM>.

The exhaust heat recovery device control unit <NUM> controls working (ON) and stopping (OFF) of the exhaust heat recovery device <NUM>. For example, when a user performs setting for causing the exhaust heat recovery device <NUM> to work, the exhaust heat recovery device control unit <NUM> acquires the setting through the setting reception unit <NUM> and causes the exhaust heat recovery device <NUM> to work by starting the pump <NUM>, or the like. When a user performs setting for causing the exhaust heat recovery device <NUM> to stop, the exhaust heat recovery device control unit <NUM> acquires the setting through the setting reception unit <NUM> and causes the exhaust heat recovery device <NUM> to stop by stopping the pump <NUM>, or the like. When the exhaust heat recovery device <NUM> is caused to work or stop, the exhaust heat recovery device control unit <NUM> records the time at which the control is performed and the executed operation of either working or stopping in the storage unit <NUM> as a working log.

The operation mode decision unit <NUM> determines necessity of exhaust heat recovery and decides the operation mode of the freezer <NUM> on the basis of the outside air temperature acquired by the signal acquisition unit <NUM>, the working state of the exhaust heat recovery device <NUM>, the load state of the high-temperature load device <NUM>, and the setting of the conditions for switching recorded in the storage unit <NUM> by the setting reception unit <NUM>. The operation mode is either the supercritical operation or the subcritical operation. For example, when the efficiency of the exhaust heat recovery freezer system <NUM> in its entirety is improved by intensifying exhaust heat recovery, the operation mode decision unit <NUM> determines that necessity of exhaust heat recovery is high. If not, it is determined that necessity of exhaust heat recovery is low. When necessity of exhaust heat recovery is high, the operation mode decision unit <NUM> decides that the supercritical operation is performed, and when necessity of exhaust heat recovery is not high, it is decided that the subcritical operation is performed.

The freezer control unit <NUM> causes the freezer <NUM> to operate in the operation mode decided by the operation mode decision unit <NUM>. For example, the two-stage compressor <NUM> is constituted to operate with a rotation frequency in which the pressure on the high-pressure side is in the supercritical state when instructed to perform the supercritical operation and to operate with a rotation frequency in which the pressure on the high-pressure side is in the subcritical state when instructed to perform the subcritical operation. When the operation mode decision unit <NUM> decides that the supercritical operation is performed, the freezer control unit <NUM> instructs the two-stage compressor <NUM> to perform the supercritical operation. When the operation mode decision unit <NUM> decides that the subcritical operation is performed, the freezer control unit <NUM> instructs the two-stage compressor <NUM> to perform the subcritical operation. Above this, the freezer control unit <NUM> performs various kinds of control related to the freezer <NUM>, but description related to functions other than switching of the operation mode will be omitted. The storage unit <NUM> stores signals acquired by the signal acquisition unit <NUM> and the setting of the conditions for switching received by the setting reception unit <NUM>.

<FIG> shows characteristics of the supercritical operation and the subcritical operation according to the embodiment. The applicant has found the characteristics shown in <FIG> after performing verification and desk calculation using the exhaust heat recovery freezer system <NUM> shown in <FIG> as an example. That is, when the freezer <NUM> is in the supercritical operation, the efficiency of the freezer <NUM> alone deteriorates, but the overall efficiency of the freezer <NUM> and the high-temperature load device <NUM> in their entirety rises. In contrast, when the freezer <NUM> is in the subcritical operation, the operation efficiency of the freezer <NUM> alone can be improved, but the overall efficiency of the exhaust heat recovery freezer system <NUM> (the freezer <NUM> and the high-temperature load device <NUM> in their entirety) deteriorates. Here, for example, efficiency indicates consumption energy consumed by the exhaust heat recovery freezer system <NUM>. Through trial calculation, it has been confirmed that the total annual energy consumption of the freezer <NUM> and the high-temperature load device <NUM> can be reduced by several percent by performing the operation of the freezer <NUM> while switching between the supercritical operation and the subcritical operation under predetermined conditions.

The operation mode decision unit <NUM> may determine that necessity of heat recovery is high when at least one of the outside air temperature, the load state of the high-temperature load device <NUM> (whether the load is large or small), and the period or the timeslot satisfies the predetermined conditions. <FIG> shows an example of criteria for such determination. <FIG> is a diagram illustrating an example of conditions for switching between the supercritical operation and the subcritical operation according to the embodiment. In the table of <FIG>, "-" denotes that the corresponding condition is not taken into consideration. In addition, the following (<NUM>) to (<NUM>) respectively correspond to the item numbers <NUM> to <NUM> in <FIG>.

The conditions for switching between the supercritical operation and the subcritical operation in the item numbers <NUM> to <NUM> described above are examples and are not limited thereto. For example, on condition that the outside air temperature is lower than X1°C (or is X2°C or lower), the exhaust heat recovery device <NUM> is working, the high-temperature load device <NUM> is working with a high load, and it is a predetermined period and a predetermined timeslot, the conditions for switching may be set such that it is decided to set the operation mode to the supercritical operation. Alternatively, the conditions for switching the operation mode to the supercritical operation when the outside air temperature is lower than X1°C (or is X2°C or lower) and it is a predetermined period and a predetermined timeslot, or the conditions for switching the operation mode to the supercritical operation when the outside air temperature is simply lower than X1°C (or is X2°C or lower) may be set.

Next, with reference to <FIG>, switching control of the operation mode of the freezer <NUM> will be described.

<FIG> is a flowchart illustrating an example of switching control according to the embodiment.

First, a user sets conditions for switching between the supercritical operation and the subcritical operation. For example, a user sets conditions for the item numbers <NUM>, <NUM>, <NUM>, and <NUM> in <FIG>. The setting reception unit <NUM> receives a setting of the conditions for switching and records the set conditions for switching in the storage unit <NUM> (Step S1).

The operation mode decision unit <NUM> acquires the outside air temperature (Step S2). For example, the signal acquisition unit <NUM> acquires the outside air temperature detected by the temperature sensor tho3 from hour to hour and records the acquired outside air temperature together with the time in the storage unit <NUM>. The operation mode decision unit <NUM> acquires the outside air temperature recorded in the storage unit <NUM>.

Next, the operation mode decision unit <NUM> acquires the working state of the exhaust heat recovery device <NUM> (Step S3). For example, the signal acquisition unit <NUM> acquires a signal indicating the working state of the exhaust heat recovery device <NUM> from hour to hour, such as a measurement value including the rotation frequency of the pump <NUM>, the temperature of water flowing in the piping <NUM>, or the like, and records these together with the time in the storage unit <NUM>. The operation mode decision unit <NUM> acquires a signal indicating the working state of the exhaust heat recovery device <NUM> recorded in the storage unit <NUM>. Alternatively, the operation mode decision unit <NUM> acquires the latest record of the working log recorded in the storage unit <NUM>.

Next, the operation mode decision unit <NUM> acquires the working state or the load state of the high-temperature load device <NUM> (Step S4). For example, the signal acquisition unit <NUM> acquires a signal indicating the working state of the high-temperature load device <NUM> from hour to hour, such as the rotation frequency of the compressor or the water level of the water storage tank in the high-temperature load device <NUM> or a signal which can be used for estimation of the load state and records these together with the time in the storage unit <NUM>. Alternatively, in the storage unit <NUM>, a prediction value of the load on the high-temperature load device <NUM> predicted by means of a predetermined predictive model in advance (for example, a load prediction value for each daily timeslot during a predetermined period of time) may be recorded. The operation mode decision unit <NUM> acquires a signal indicating the working state or the load state of the high-temperature load device <NUM> recorded in the storage unit <NUM> and the prediction value of the load. The order of processing of Steps S2 to S4 can be arbitrarily changed, and Steps S2 to S4 may be simultaneously performed in parallel.

Next, the operation mode decision unit <NUM> decides the operation mode (Step S5). The operation mode decision unit <NUM> determines necessity of heat recovery and decides the operation mode on the basis of the signals acquired in Steps S2 to <NUM> and the conditions for switching set in Step S <NUM>. For example, when the outside air temperature is X1°C or higher, the operation mode decision unit <NUM> decides that the operation mode is set to the supercritical operation (the conditions for switching of the item number <NUM>). For example, when a signal indicating that the outside air temperature is lower than X1°C and the exhaust heat recovery device <NUM> is at a stop is acquired, the operation mode decision unit <NUM> decides that the operation mode is set to the subcritical operation (the conditions for switching of the item number <NUM>). For example, when either conditions whether a signal indicating that the outside air temperature is lower than X1°C, the exhaust heat recovery device <NUM> is working, and the high-temperature load device <NUM> is working with a high load has been acquired (the conditions for switching of the item number <NUM>), or whether a signal indicating that the outside air temperature is X2°C or lower, the exhaust heat recovery device <NUM> and the high-temperature load device <NUM> are working has been acquired (the conditions for switching of the item number <NUM>) are satisfied, the operation mode decision unit <NUM> determines that necessity of heat recovery is high and decides that the operation mode is set to the supercritical operation. When none of the conditions for switching of the item number <NUM> and the item number <NUM> is satisfied, the operation mode decision unit <NUM> determines that necessity of heat recovery is low and decides that the operation mode is set to the subcritical operation.

Regarding judgment whether or not the high-temperature load device <NUM> in the item number <NUM> is working with a high load, for example, if it is a timeslot in which the prediction value of the load predicted by the predictive model is high, the operation mode decision unit <NUM> may judge that the high-temperature load device <NUM> is working with a high load, and if the compressor in the high-temperature load device <NUM> is in operation with a rotation frequency equal to or higher than a predetermined value, it may be judged that the high-temperature load device <NUM> is working with a high load. When it can be estimated that the exhaust heat recovery device <NUM> is working, the outside air temperature is lower than X1°C, and the high-temperature load device <NUM> is working with a high load, the operation mode decision unit <NUM> determines that necessity of heat exchange is high. In addition, regarding the item number <NUM>, when the exhaust heat recovery device <NUM> and the high-temperature load device <NUM> are working and the outside air temperature is X2°C or lower, the operation mode decision unit <NUM> determines that necessity of heat exchange is high. In addition, regarding the item number <NUM>, if the exhaust heat recovery device <NUM> is working, the outside air temperature is lower than X1°C, and it is a predetermined period and/or timeslot, the operation mode decision unit <NUM> determines that necessity of heat exchange is high.

The operation mode decision unit <NUM> outputs the decided operation mode to the freezer control unit <NUM>. The freezer control unit <NUM> causes the freezer <NUM> to operate in accordance with the decision of the operation mode decision unit <NUM>. When the operation mode decision unit <NUM> decides that the operation mode is set to the supercritical operation, the freezer control unit <NUM> instructs the two-stage compressor <NUM> to perform the supercritical operation. Accordingly, the high-pressure supercritical operation in which a refrigerant is in the supercritical state on the high-pressure side of the refrigerant circuit is executed (Step S6). When the operation mode decision unit <NUM> decides that the operation mode is set to the subcritical operation, the freezer control unit <NUM> instructs the two-stage compressor <NUM> to perform the subcritical operation. Accordingly, the high-pressure subcritical operation in which a refrigerant is in the subcritical state on the high-pressure side of the refrigerant circuit is executed (Step S7).

As described above, according to the present embodiment, the operation of the freezer <NUM> is controlled to be either the supercritical operation or the subcritical operation on the basis of a setting of the conditions for switching set such that the overall efficiency of the freezer <NUM> and the high-temperature load device <NUM> is improved (<FIG>). The efficiency of the exhaust heat recovery freezer system <NUM> can be improved by switching between the high-pressure supercritical operation and the high-pressure subcritical operation of the freezer in accordance with the efficiency of the exhaust heat recovery freezer system <NUM> in its entirety.

<FIG> is a diagram illustrating an example of a hardware constitution of a system controller according to the embodiment. A computer <NUM> includes a CPU <NUM>, a main storage device <NUM>, an auxiliary storage device <NUM>, an input/output interface <NUM>, and a communication interface <NUM>. The system controller <NUM> is mounted in the computer <NUM>. Further, each of the functions described above is stored in the auxiliary storage device <NUM> in a form of a program. The CPU <NUM> reads the program from the auxiliary storage device <NUM> and develops it in the main storage device <NUM>, and the foregoing processing is executed in accordance with the program. In addition, the CPU <NUM> secures a storage domain in the main storage device <NUM> in accordance with the program. In addition, the CPU <NUM> secures the storage domain for storing data being processed in the auxiliary storage device <NUM> in accordance with the program.

Claim 1:
A control device (<NUM>) comprising:
an operation mode decision unit (<NUM>) that is configured to decide, in accordance with necessity of heat recovery from a refrigerant circulating in a refrigerant circuit, which operation of a supercritical operation in which a high pressure in the refrigerant circuit is in a supercritical state and a subcritical operation in which the high pressure is in a subcritical state is to be performed; and
a freezer control unit (<NUM>) that is configured to control the refrigerant circuit to be operated in either the supercritical operation or the subcritical operation on the basis of decision of the operation mode decision unit (<NUM>),
characterized in that
the operation mode decision unit (<NUM>) is configured to judge whether or not an exhaust heat recovery device (<NUM>), which recovers the heat through heat exchange with the refrigerant circulating in the refrigerant circuit between a compressor (<NUM>) and a gas cooler (<NUM>) in the refrigerant circuit, is working, and to decide to perform the subcritical operation when the exhaust heat recovery device (<NUM>) is stopped.