Patent Publication Number: US-2023147599-A1

Title: Air Conditioning System and Method for Controlling Electrical Energy of Air Conditioning System

Description:
TECHNICAL FIELD 
     The present disclosure relates to an air conditioning system and a method for controlling electrical energy of the air conditioning system. 
     BACKGROUND ART 
     A conventionally known air conditioning system sets priority for each of a plurality of indoor units according to necessity of air conditioning. For example, WO 2013/061399 (PTL 1) discloses a heat pump system comprising a plurality of indoor units. In the heat pump system, a user sets a priority for a workspace depending on a frequency of use or a level of importance so that even when a total of the maximal cooling capacities of the indoor units exceeds a maximal cooling capacity of an outdoor unit an indoor unit for a workspace having a large air conditioning load can be operated at a rated capacity. Further, an indoor unit for a workspace highly requiring air conditioning can be operated at a rated capacity. This ensures that the workplace is comfortable. 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2013/061399 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the heat pump system disclosed in PTL 1, a plurality of indoor units are provided for one compressor. As a configuration of an air conditioning system, however, a configuration in which a plurality of indoor units are provided for a plurality of compressors is also expected. In demand control performed in response to a demand request (or an electrical energy limit request), there is a problem in how to fairly allocate limited electrical energy to one or more compressors based on a cost accompanying using each of a plurality of indoor units. For the heat pump system disclosed in PTL 1, however, no consideration is given to fair distribution of a cost accompanying using each of a plurality of indoor units. 
     The present disclosure has been made in order to solve the above-described problem, and an object of the present disclosure is to improve fairness of distribution of a cost accompanying utilization of air conditioning while achieving electrical energy limitation in an air conditioning system comprising one or more air conditioners. 
     Solution to Problem 
     An air conditioning system according to an aspect of the present disclosure comprises one or more air conditioners in which refrigerant circulates, and a first controller. When an electrical energy limit condition is satisfied, the first controller limits electrical energy consumed per unit time by the one or more air conditioners. The one or more air conditioners each include a compressor and one or more indoor units. For each of the one or more indoor units, a score corresponding to a cost of using the indoor unit is preset. The first controller calculates, for each of the one or more air conditioners, a first total value of a score of each of the one or more indoor units included in the air conditioner. The first controller calculates a second total value of the first total value of each of the one or more air conditioners. When the electrical energy limit condition is satisfied, the first controller sets for each of the one or more air conditioners a drive frequency for the compressor included in the air conditioner according to a ratio of the first total value of the air conditioner to the second total value. 
     According to another aspect of the present disclosure, when an electrical energy limit condition is satisfied, a method for controlling electrical energy of an air conditioning system limits electrical energy consumed per unit time by one or more air conditioners in which refrigerant circulates. The one or more air conditioners each include a compressor and one or more indoor units. For each of the one or more indoor units, a score corresponding to a cost of using the indoor unit is preset. A method for controlling electrical energy of an air conditioning system comprises: calculating for each of one or more air conditioners a first total value of a score of each of one or more indoor units included in the air conditioner; calculating a second total value of the first total value of each of the one or more air conditioners; and, when the electrical energy limit condition is satisfied, for each of the one or more air conditioners, setting a drive frequency for the compressor included in the air conditioner according to a ratio of the first total value of the air conditioner to the second total value. 
     Advantageous Effects of Invention 
     According to the presently disclosed air conditioning system and method for controlling electrical energy thereof, when an electrical energy limit condition is satisfied, for each of one or more air conditioners, a drive frequency for a compressor included in the air conditioner can be set according to a ratio of a first total value of the air conditioner to a second total value to improve fairness of distribution of a cost accompanying utilization of air conditioning while achieving electrical energy limitation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a functional block diagram showing a configuration of an air conditioning system according to a first embodiment. 
         FIG.  2    is a functional block diagram showing a configuration of a demand controller shown in  FIG.  1   . 
         FIG.  3    is a functional block diagram showing a configuration of an air conditioner shown in  FIG.  1   . 
         FIG.  4    is a flowchart of an electrical energy monitoring process performed by the demand controller shown in  FIG.  1   . 
         FIG.  5    is a flowchart of a specific process of demand control indicated in  FIG.  4   . 
         FIG.  6    is a diagram showing a relationship between a channel resistance of an expansion valve shown in  FIG.  3    and a degree of opening (a Cv value) of the expansion valve, and a relationship between the channel resistance of the expansion valve and an amount of heat exchanged by a heat exchanger shown in  FIG.  3   . 
         FIG.  7    is a flowchart of a process performed by a controller shown in  FIG.  3    in response to a demand control command. 
         FIG.  8    is a flowchart of a specific process for setting a degree of opening of the expansion valve as indicated in  FIG.  7   . 
         FIG.  9    is a functional block diagram showing a configuration of an air conditioning system according to a modified example of the first embodiment. 
         FIG.  10    is a flowchart of an electrical energy monitoring process performed by a demand controller shown in  FIG.  9   . 
         FIG.  11    is a flowchart of a specific process of electrical energy adjustment control indicated in  FIG.  10   . 
         FIG.  12    is a flowchart of a demand control process performed by a demand controller of an air conditioning system according to a second embodiment. 
         FIG.  13    is a flowchart of a specific process for setting an upper limit value for a drive frequency for a compressor as indicated in  FIG.  12   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the figures, identical or corresponding components are identically denoted and will not be described redundantly in principle. 
     First Embodiment 
       FIG.  1    is a functional block diagram showing a configuration of an air conditioning system  1000  according to a first embodiment. As shown in  FIG.  1   , air conditioning system  1000  comprises a demand controller  1  (a first controller) and a plurality of air conditioners  100 . The plurality of air conditioners  100  each include a heat source unit  10  and one or more indoor units  20 . Refrigerant circulates through each of the plurality of air conditioners  100 . For each of one or more indoor units  20 , a priority score corresponding to a cost of using indoor unit  20  is preset. The cost of using indoor unit  20  includes, for example, a rent for a space in which indoor unit  20  is installed, and an electricity fee determined by a contract. Air conditioning system  1000  may comprise one air conditioner  100 . 
     Demand controller  1  performs an electrical energy monitoring process for the plurality of air conditioners  100  for every sampling time. Specifically, when demand controller  1  receives a demand request DR (an electrical energy limit request) in the electrical energy monitoring process, demand controller  1  performs demand control to reduce electrical energy consumed by the plurality of air conditioners  100  per unit time. Demand request DR is issued, for example, from an electrical energy management system that integrally manages electrical energy of a plurality of systems including air conditioning system  1000  when a possibility of insufficient electrical energy is increased due to shortage of electrical energy. 
       FIG.  2    is a functional block diagram showing a configuration of demand controller  1  shown in  FIG.  1   . As shown in  FIG.  2   , demand controller  1  includes circuitry  91 , a memory  92 , a communication unit  93 , and an input/output unit  94 . Circuitry  91 , memory  92 , communication unit  93 , and input/output unit  94  are interconnected via a bus  95 . 
     Circuitry  91  may be dedicated hardware or a central processing unit (CPU) configured to execute a program stored in memory  92 . When circuitry  91  is dedicated hardware, circuitry  91  corresponds for example to a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an application specific integrated circuit (ASIC), a field programmable gate Array (FPGA), or a combination thereof. When circuitry  91  is a CPU, demand controller  1  has functionality implemented by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in memory  92 . Circuitry  91  reads and executes a program stored in memory  92 . The CPU is also referred to as a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, or a digital signal processor (DSP). Memory  92  includes a non-volatile or volatile semiconductor memory (e.g., random access memory (RAM), read only memory (ROM), flash memory, erasable programmable read only memory (EPROM), or electrically erasable programmable read only memory (EEPROM)), and a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a digital versatile disc (DVD). 
     Communication unit  93  communicates with each of the plurality of air conditioners  100  via a network NW. Network NW includes, for example, a local area network (LAN), a wide area network (WAN), or the Internet. 
     Input/output unit  94  receives an operation from a user and outputs a processing result to the user. Input/output unit  94  includes, for example, a mouse, a keyboard, a touch panel, a display, and a speaker. 
       FIG.  3    is a functional block diagram showing a configuration of air conditioner  100  shown in  FIG.  1   . As shown in  FIG.  3   , heat source unit  10  includes a compressor  11 , a heat exchanger  12 , a four-way valve  13 , and a controller  14  (a second controller). One or more indoor units  20  each include an expansion valve  21 , a heat exchanger  22 , and a controller  24  (the second controller). Air conditioner  100  selectively performs a cooling operation and a heating operation, and receives a demand control command from demand controller  1  to perform a demand operation. 
     Controller  14  controls a drive frequency for compressor  11  to control an amount of refrigerant discharged from compressor  11  per unit time. Controller  14  controls a degree of opening of expansion valve  21  via controller  24 . Controller  14  controls four-way valve  13  to switch between the cooling operation and the heating operation a direction in which the refrigerant circulates. Controllers  14  and  24  can each have a configuration similar to that of demand controller  1  shown in  FIG.  2   . Controllers  14  and  24  may be integrally formed. 
     In the cooling operation, the refrigerant circulates through compressor  11 , four-way valve  13 , heat exchanger  12 , expansion valve  21 , heat exchanger  22 , and four-way valve  13  in this order. In the cooling operation, controller  14  controls the degree of opening of expansion valve  21  so that the degree of superheating of refrigerant flowing between heat exchanger  22  and compressor  11  approaches a target degree of superheating. In the heating operation, the refrigerant circulates through compressor  11 , four-way valve  13 , heat exchanger  22 , expansion valve  21 , and heat exchanger  12  in this order. In the heating operation, controller  14  controls the degree of opening of expansion valve  21  so that the degree of supercooling of the refrigerant flowing between heat exchanger  22  and expansion valve  21  approaches a target degree of supercooling. 
       FIG.  4    is a flowchart of an electrical energy monitoring process performed by demand controller  1  shown in  FIG.  1   . The electrical energy monitoring process is invoked by a main routine (not shown) that controls demand controller  1  integrally. Hereinafter, a step is simply referred to as S. A priority score of a j-th indoor unit  20  of an i-th air conditioner  100  is denoted as P i,j . Indices i and j are each a natural number. 
     As shown in  FIG.  4   , demand controller  1  in S 110  calculates for each of the plurality of air conditioners  100  a total value Q i  (a first total value) of a priority score of each of one or more indoor units  20  included in air conditioner  100 , as indicated by the following expression (1), and proceeds to S 120 . In the expression (1), a natural number M i  is the number of one or more indoor units  20  included in the i-th air conditioner  100 . 
     [Expression 1] 
       Expression 1 
         Q   i =Σ j=1   j=M     i     P   i,j   (1)
 
     In S 120 , demand controller  1  calculates a total value R (a second total value) of total value Q i  of each of the plurality of air conditioners  100 , as indicated by the following expression (2), and proceeds to S 130 . In the expression (2), a natural number N is the number of the plurality of air conditioners  100 . 
     [Expression 2] 
       Expression 2 
         R=Σ   i=1   i=N   Q   i   (2)
 
     In S 130 , demand controller  1  determines whether the condition that demand request DR is received (i.e., an electrical energy limit condition) is satisfied. When demand request DR is not received (NO in S 130 ), demand controller  1  returns the process back to the main routine. When demand request DR is received (YES in S 130 ), demand controller  1  performs demand control in S 140 . The electrical energy limit condition is not limited to the condition that demand request DR is received. The electrical energy limit condition may include the condition that demand controller  1  directly measures electrical energy per unit time of the plurality of air conditioners  100  and the electrical energy exceeds reference electrical energy. 
       FIG.  5    is a flowchart of a specific process of the demand control (S 140 ) indicated in  FIG.  4   . As indicated in  FIG.  5   , demand controller  1  in S 141  calculates for the plurality of air conditioners  100  a reference frequency W i  (an index value) as a product of a drive frequency H i  for the compressor of the i-th air conditioner, a stroke volume (a suction volume) V i  of the compressor, and an inverse of a reference stroke volume V r  (i.e., a first product), as indicated by the following expression (3), and proceeds to S 142 . Drive frequency H i  is a drive frequency when demand controller  1  receives demand request DR. Reference frequency W i  is an index value of electrical energy consumed per unit time by the air conditioner, that has drive frequency H i  and in addition thereto stroke volume V i  also reflected therein. Reference stroke volume V r  is a reference value for normalizing stroke volume V i , and may for example be 1 cc. 
     
       
         
           
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     In S 142 , demand controller  1  calculates a total reference frequency G (a total index value) of reference frequency W i , as indicated by the following expression (4), and proceeds to S 143 . 
     [Expression 4] 
       Expression 4 
         G=Σ   i=1   i=N   W   i   (4)
 
     In S 143 , demand controller  1  calculates an upper limit total reference frequency U as a product of an electrical energy limit rate D and total reference frequency G, as indicated by the following expression (5), and proceeds to S 144 . 
     [Expression 5] 
       Expression 5 
         U=D×G   (5)
 
     In S 144 , demand controller  1  calculates an upper limit reference frequency E i  as a product of upper limit total reference frequency U and a ratio of total value Q i  to total value R, as indicated by the following expression (6), and proceeds to S 145 . 
     
       
         
           
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     In S 145 , demand controller  1  calculates an upper limit drive frequency Z i  as a product of upper limit reference frequency E i , reference stroke volume V r , and an inverse of stroke volume V i  (i.e., a second product), as indicated by the following expression (7), and returns the process back to the main routine. The i-th air conditioner continues an air conditioning operation with upper limit drive frequency Z i  set as an upper limit value for the drive frequency for the compressor included in the air conditioner. 
     
       
         
           
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     Demand controller  1  sets a drive frequency for compressor  11  depending on the ratio of total value Q i  to total value R, as indicated in the expression (6). Demand controller  1 , in the demand control, suppresses decrease of the drive frequency for compressor  11  included in air conditioner  100  having a relatively high priority score among the plurality of air conditioners  100 . The drive frequency for compressor  11  correlates with the electrical energy consumed by compressor  11  per unit time. The electrical energy of compressor  11  occupies a large proportion of the electrical energy consumed by air conditioner  100  per unit time. Therefore, by setting a drive frequency for compressor  11  in accordance with the ratio of total value Q i  of air conditioner  100  to total value R, electrical energy is allocated preferentially to air conditioner  100  having a relatively high cost of using one or more indoor units  20 . Air conditioning system  1000  can thus improve fairness of distribution of a cost accompanying utilization of air conditioning while achieving electrical energy limitation. 
     The electrical energy of the compressor can vary with the size of the compressor even if the compressor has the same drive frequency. Air conditioning system  1000 , in distributing electrical energy in the demand control, allows a stroke volume correlated with the size of the compressor to be also considered in addition to the drive frequency for the compressor, and can thus further improve fairness of distribution of the cost accompanying utilization of air conditioning. 
     In the above description, fair distribution of electrical energy based on a cost of using one or more indoor units  20  among a plurality of air conditioners  100  has been described. Hereinafter, reference will be made to  FIGS.  6 ,  7  and  8    to describe fair distribution in amount of refrigerant among one or more indoor units  20  in air conditioner  100 , based on a cost of using one or more indoor units  20 . 
       FIG.  6    is a diagram showing a relationship between a channel resistance of expansion valve  21  shown in  FIG.  3    and a degree of opening (a Cv value) of expansion valve  21 , and a relationship between the channel resistance of expansion valve  21  and an amount of heat exchanged by heat exchanger  22  shown in  FIG.  3   . As shown in FIG.  6 , the larger the degree of opening of expansion valve  21  is, the smaller the channel resistance of expansion valve  21  is. Further, the smaller the channel resistance of expansion valve  21  is, the larger the amount of heat exchanged by heat exchanger  22  is. The larger the amount of heat exchanged by heat exchanger  22  is, the larger an effect of air conditioning by indoor unit  20  is. That is, the larger the degree of opening of expansion valve  21  is, the larger the effect of air conditioning by indoor unit  20  is. 
     Accordingly, in air conditioner  100 , for each of one or more indoor units  20 , a degree of opening of expansion valve  21  included in indoor unit  20  is set in accordance with a ratio of a priority score P i,j  of indoor unit  20  to total value Q i  of air conditioner  100 . 
       FIG.  7    is a flowchart of a process performed by controller  14  shown in  FIG.  3    in response to a demand control command. The process shown in  FIG.  7    is invoked by a main routine (not shown) that integrally controls air conditioner  100 . 
     As shown in  FIG.  7   , in S 161 , controller  14  calculates an average value P ave  of priority score P i,j  of each of one or more indoor units  20  from total value Q i  of air conditioner  100  and number M i  of one or more indoor units  20 , as indicated by the following expression (8), and proceeds to S 162 . 
     
       
         
           
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     In S 162 , controller  14  sets for each of one or more indoor units  20  a degree of opening of expansion valve  21  included in indoor unit  20  according to a ratio of priority score P i,j  of indoor unit  20  to total value Q i , and returns the process back to the main routine. 
       FIG.  8    is a flowchart of a specific process for step S 162  of setting a degree of opening of expansion valve  21  as indicated in  FIG.  7   . As shown in  FIG.  8   , in S 1621 , controller  14  determines whether the condition that priority score P i,j  of indoor unit  20  is smaller than average value P ave  is satisfied. When priority score P i,j  is smaller than average value P ave  (YES in S 1621 ), then, in S 1622 , controller  14  decreases the degree of opening of expansion valve  21  included in indoor unit  20  to be smaller than that when whether the condition is satisfied is determined in S 1621 , and controller  14  returns the process back to the main routine. When priority score P i,j  is equal to or larger than average value P ave  (NO in S 1621 ), then in S 1623 , controller  14  increases the degree of opening of expansion valve  21  included in indoor unit  20  to be larger than that when whether the condition is satisfied is determined in S 1621 , and controller  14  returns the process back to the main routine. 
     In the cooling operation, the degree of opening of expansion valve  21  may be decreased by increasing the target degree of superheating in S 1622 , and the degree of opening of expansion valve  21  may be increased by decreasing the target degree of superheating in S 1623 . In the heating operation, the degree of opening of expansion valve  21  may be decreased by increasing the target degree of supercooling in S 1622 , and the degree of opening of expansion valve  21  may be increased by decreasing the target degree of supercooling in S 1623 . 
     The condition in S 1621  that priority score P i,j  is smaller than average value P ave  is the same, from the expression (8), as the condition that the following expression (9) is satisfied. The condition that the expression (9) is satisfied is the condition that a ratio of priority score P i,j  to total value Q i  is smaller than an inverse of number M i  of one or more indoor units  20 . 
     
       
         
           
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     Since controller  14  sets a degree of opening of expansion valve  21  using whether the condition that the expression (9) is satisfied is satisfied, controller  14  sets the degree of opening of expansion valve  21  included in indoor unit  20  according to a ratio of priority score of indoor unit  20  to total value Q i . Controller  14 , in the demand control, increases a degree of opening of an expansion valve included in one or more indoor units  20  having a relatively high cost of using one or more indoor units  20 . Since expansion valve  21  serves as a flow rate adjusting valve configured to adjust refrigerant passing through indoor unit  20 , the larger the degree of opening of expansion valve  21  is, the larger the amount of the refrigerant passing through indoor unit  20  is. Air conditioning system  1000  allows refrigerant to be allocated preferentially to indoor unit  20  having a relatively high cost of using it, and can thus improve fairness of distribution, even among one or more indoor units  20 , of a cost accompanying using air conditioning by air conditioning system  1000 . 
     Modification of First Embodiment 
     In a modified example of the first embodiment, a configuration in which demand control is followed by electrical energy adjustment control to suppress excessive deviation from a targeted electrical energy will be described. 
       FIG.  9    is a functional block diagram showing a configuration of an air conditioning system  1100  according to the modified example of the first embodiment. Air conditioning system  1100  is configured such that demand controller  1  shown in  FIG.  1    is replaced with a demand controller  1 A and an electrical energy sensor Ps configured to measure electrical energy consumed by air conditioner  100  is added to each of a plurality of air conditioners  100 . The remainder is the same, and accordingly, will not be described repeatedly. 
       FIG.  10    is a flowchart of an electrical energy monitoring process performed by demand controller  1 A shown in  FIG.  9   . The electrical energy monitoring process is invoked by a main routine (not shown) that integrally controls demand controller  1 A. The flowchart shown in  FIG.  9    is a flowchart in which demand control S 140  indicated in  FIG.  4    is followed by electrical energy adjustment control S 200 . The remainder is the same, and accordingly, will not be described repeatedly. 
     As shown in  FIG.  10   , demand controller  1 A performs S 110 , S 120 , S 130 , and S 140  as done in the first embodiment and subsequently performs electrical energy adjustment control in S 200 , and thereafter returns the process back to the main routine. 
       FIG.  11    is a flowchart of a specific process of electrical energy adjustment control S 200  indicated in  FIG.  10   . As shown in  FIG.  11   , in S 201 , demand controller  1 A determines whether an absolute value of a value obtained by subtracting targeted electrical energy from consumed electrical energy is larger than a reference value δ (a second reference value). When the absolute value is less than or equal to reference value δ (NO in S 201 ), demand controller  1 A returns the process back to the main routine. When the absolute value is larger than reference value δ (YES in S 201 ), demand controller  1 A proceeds to S 202 . Reference value δ can be determined appropriately through an actual experiment or a simulation. 
     In S 202 , demand controller  1 A determines whether the consumed electrical energy is larger than the targeted electrical energy. When the consumed electrical energy is larger than the targeted electrical energy (YES in S 202 ), demand controller  1 A proceeds to S 203  to decrease the drive frequency for compressor  11  included in each of the plurality of air conditioners  100  to be lower than that when whether the condition is satisfied is determined in S 202 , and demand controller  1 A proceeds to S 205 . When the consumed electrical energy is equal to or less than the targeted electrical energy (NO in S 202 ), demand controller  1 A proceeds to S 204  to increase the drive frequency for compressor  11  included in each of the plurality of air conditioners  100  to be higher than that when whether the condition is satisfied is determined in S 202 , and demand controller  1 A proceeds to S 205 . After waiting for a fixed period of time in S 205 , demand controller  1 A returns the process back to S 201 . 
     Air conditioning system  1100  can suppress deviation between consumed electrical energy and targeted electrical energy after the demand control to reference value δ or less, and even under electrical energy limitation, permitted electrical energy can sufficiently be used. 
     Thus, the air conditioning system and method for controlling electrical energy thereof according to the first embodiment and a modified example thereof can improve fairness of distribution of a cost accompanying utilization of air conditioning while achieving electrical energy limitation. 
     Second Embodiment 
     In the first embodiment, a configuration in which electrical energy is allocated preferentially to an air conditioner having a relatively high priority score has been described. According to the first embodiment, a cost of using an indoor unit under electrical energy limitation can vary with a relative relationship in magnitude of a priority score of the indoor unit, rather than the priority score per se. In a second embodiment, a configuration in which electrical energy allocated is limited based on a priority score per se so that a cost of using an indoor unit corresponds to the priority score will be described. 
       FIG.  12    is a flowchart of a demand control process performed by a demand controller of an air conditioning system according to the second embodiment. The process indicated in  FIG.  12    is a process with the  FIG.  5    S 145  replaced with S 245 . The remainder is the same, and accordingly, will not be described repeatedly. 
     As shown in  FIG.  12   , after performing S 141  to S 144  in the same manner as in the first embodiment, the demand controller proceeds to S 245  to set an upper limit value for the drive frequency for the compressor included in each of one or more air conditioners, and the demand controller returns the process back to the main routine. 
       FIG.  13    is a flowchart of a specific process for setting an upper limit value for the drive frequency for the compressor, as indicated in  FIG.  12    (S 245 ). The demand controller performs the  FIG.  13    process for each of one or more air conditioners.  FIG.  13    shows the process for an i-th air conditioner. 
     As shown in  FIG.  13   , in step S 2451 , the demand controller determines whether total value Q i  is smaller than a reference value σ (a first reference value). When total value Q i  is equal to or larger than reference value σ (the first reference value) (NO in S 2451 ), the demand controller proceeds to S 2452  to set product Z i  that is calculated according to the expression (7) as an upper limit value for the drive frequency for the compressor included in the i-th air conditioner, and the demand controller returns the process back to the main routine. When total value Q i  is smaller than reference value σ (the first reference value) (YES in S 2451 ), the demand controller proceeds to S 2453  to set a value F i  smaller than product Z i  as the upper limit value for the drive frequency for the compressor included in the i-th air conditioner, and the demand controller returns the process back to the main routine. Value F i  is calculated, for example, by multiplying product Z i  by a predetermined coefficient smaller than one or a coefficient corresponding to total value Q i . Reference value σ can be determined appropriately through an actual experiment or a simulation. 
     Thus, the air conditioning system and method for controlling electrical energy thereof according to the second embodiment can further improve fairness of distribution of a cost accompanying utilization of air conditioning while achieving electrical energy limitation than the first embodiment. 
     The embodiments disclosed herein are also intended to be combined within a consistent scope as appropriate and thus implemented. It should be understood that the embodiments disclosed herein have been described for the purpose of illustration only and in a non-restrictive manner in any respect. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       1 , 1 A demand controller,  10  heat source unit,  11  compressor,  12 ,  22  heat exchanger,  13  four-way valve  14 ,  24  controller,  20  indoor unit,  21  expansion valve,  91  circuitry,  92  memory,  93  communication unit,  94  input/output unit,  95  bus,  100  air conditioner,  1000 ,  1100  air conditioning system, NW network, Ps electrical energy sensor.