Patent Publication Number: US-9835368-B2

Title: Refrigerating and air-conditioning apparatus for use in a defrosting operation

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Application No. PCT/JP2011/005136 filed on Sep. 13, 2011, the disclosure of which is incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a refrigerating and air-conditioning apparatus by a vapor-compression refrigeration cycle, and in particular, to a refrigerating and air-conditioning apparatus that is capable of, even during a heating operation under air conditions leading to formation of frost, performing a defrosting operation while simultaneously continuing the heating operation. 
     BACKGROUND ART 
     As a refrigerating and air-conditioning apparatus which includes a plurality of refrigeration cycles and which is capable of performing a defrosting operation while simultaneously continuing a heating operation, for example, there has been an air-conditioning apparatus for vehicle described in Patent Literature 1. With the arrangement in which a refrigeration cycle which performs defrosting by a cooling operation and a refrigeration cycle which continues a heating operation are individually provided within the vehicle, the air-conditioning apparatus for vehicle is able to perform a defrosting operation while simultaneously continuing a heating operation. 
     Furthermore, as an air-conditioning apparatus for vehicle described in Patent Literature 2, a technique to maintain comfort by adjusting the amount of ventilation according to a vehicle occupancy, is disclosed. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2006-116981 (claim 1, FIG. 1) 
     Patent Literature 2: Japanese Patent No. 4346429 (claim 1) 
     SUMMARY OF INVENTION 
     Technical Problem 
     In Patent Literature 1, an indoor heat exchanger of the refrigeration cycle that performs a heating operation is caused to act as a condenser, while an indoor heat exchanger of the refrigeration cycle that performs a defrosting operation is caused to act as an evaporator. Then, air passing through each of the indoor heat exchangers is sucked by a shared indoor fan, is mixed within the casing of the indoor fan, and is blown out into the room as conditioned air. Therefore, there is a problem that the outlet air temperature may be lowered, causing discomfort to passengers. Because the air is sent to an outdoor heat exchanger (evaporator) by operating an outdoor fan during the defrosting operation, the condensing temperature may not rise when the outside air temperature is low, thereby causing a possibility that defrosting is not performed. 
     Furthermore, during the defrosting operation while performing the heating operation, it is preferred that the room is ventilated with an appropriate amount of ventilation. In Patent Literature 2, although ventilation during a cooling operation is considered, ventilation during a defrosting operation is not particularly considered. 
     The present invention has been made in view of the above problems. Therefore, it is an object of the present invention to provide a refrigerating and air-conditioning apparatus which is capable of, even during a heating operation under air conditions leading to formation of frost, performing a defrosting operation while simultaneously continuing a heating operation and which improves comfort through heating by securing an appropriate amount of ventilation. 
     Solution to Problem 
     A refrigerating and air-conditioning apparatus according to the present invention includes a plurality of refrigeration cycles that each include a compressor, a four-way valve, an outdoor heat exchanger, a pressure reducing device, and an indoor heat exchanger that are connected to one another, the plurality of refrigeration cycles being capable of independently performing a heating operation and a defrosting operation; an outdoor unit that includes the compressor, the four-way valve, and the outdoor heat exchanger; a plurality of indoor units that each include the ventilation port, a ventilation damper for opening and closing the ventilation port, an indoor fan for taking in outside air through the ventilation port and sending the air into a room, and the indoor heat exchanger, the plurality of indoor units being installable in a same room; and a controller that controls the ventilation damper to perform indoor ventilation during the heating operation, and that controls the ventilation damper of each of the plurality of indoor units to close the corresponding ventilation port and stop indoor ventilation during a defrosting operation. Prior to a defrosting operation, the controller performs a prior ventilation operation for securing a time-averaged required amount of ventilation including a period in which the defrosting operation is being performed by controlling the ventilation damper of the indoor unit of a refrigeration cycle that is to perform the defrosting operation to increase the amount of ventilation, and after termination of the prior ventilation operation, the controller starts the defrosting operation. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to perform a defrosting operation while simultaneously continuing a heating operation by providing a plurality of refrigeration cycles that are capable of performing the heating operation and the defrosting operation independently. In addition, since a ventilation damper is closed after a prior ventilation operation is performed before a defrosting operation to secure a sufficient amount of ventilation, a continuous heating operation is performed while securing the time-averaged required amount of ventilation, thus achieving the improvement of comfort. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a refrigerant circuit diagram of a refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 2  is a schematic cross-sectional view of an outdoor unit in  FIG. 1 . 
         FIG. 3  is a control block diagram of the refrigerating and air-conditioning apparatus in  FIG. 1 . 
         FIG. 4  is a timing chart of an operation example 1 of the refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 5  is a timing chart of an operation example 2 of the refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 6  is a timing chart of an operation example 3 of the refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 7  is a timing chart of an operation example 4 of the refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 8  is a refrigerant circuit diagram of a refrigerating and air-conditioning apparatus according to Embodiment 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of a refrigerating and air-conditioning apparatus according to the present invention will be described, with reference to the accompanying drawings. 
     Embodiment 1. 
     (Refrigerant Circuit Configuration) 
       FIG. 1  is a refrigerant circuit diagram of a refrigerating and air-conditioning apparatus according to Embodiment 1 of the present invention.  FIG. 2  is a schematic cross-sectional view of an outdoor unit in  FIG. 1 . In  FIGS. 1 and 2  and the figures described below, objects with the same reference numerals are referred to as being equal to or corresponding to one another, which is common throughout the full text of the description. 
     The refrigerating and air-conditioning apparatus according to Embodiment 1 is, for example, used as an air-conditioning apparatus for vehicle, and includes an outdoor unit  1 , and indoor units  2   a  and  2   b  which are installable in the same room. A first refrigeration cycle is configured by connecting the outdoor unit  1  and the indoor unit  2   a , and a second refrigeration cycle is configured by connecting the outdoor unit  1  and the indoor unit  2   b.    
     The first refrigeration cycle includes a compressor  3   a , a four-way valve  4   a , an outdoor heat exchanger  5   a , a pressure reducing device  6   a , and an indoor heat exchanger  7   a , which are sequentially connected by pipes, and is configured so that a refrigerant is able to circulate through the first refrigeration cycle. The first refrigeration cycle is configured to be capable of switching the operation mode between a cooling operation (defrosting operation) and a heating operation by the four-way valve  4   a  switching the flow path of the refrigerant discharged from the compressor  3   a . The indoor unit  2   a , in which part of the first refrigeration cycle is arranged, includes an indoor heat exchanger  7   a , an indoor fan  8   a , a ventilation port  9   a  to take in the outside air, a ventilation damper  10   a  which has an opening and closing function for opening and closing the ventilation port  9   a , and an air inlet  11   a  for indoor air. 
     The second refrigeration cycle includes a compressor  3   b , a four-way valve  4   b , an outdoor heat exchanger  5   b , a pressure reducing device  6   b , and an indoor heat exchanger  7   b , which are sequentially connected by pipes, and is configured so that a refrigerant is able to circulate through the second refrigeration cycle. The first refrigeration cycle is configured to be capable of switching the operation mode between a cooling operation (defrosting operation) and a heating operation by the four-way valve  4   b  switching the flow path of the refrigerant discharged from the compressor  3   b . The indoor unit  2   b , in which part of the second refrigeration cycle is arranged, includes an indoor heat exchanger  7   b , an indoor fan  8   b , a ventilation port  9   b  to take in the outside air, a ventilation damper  10   b  which has an opening and closing function, and an air inlet  11   b  for indoor air. 
     In addition, the outdoor unit  1  includes an outdoor fan  12  for sending the outside air into the outdoor heat exchanger  5   a  and the outdoor heat exchanger  5   b.    
     Furthermore, the refrigerating and air-conditioning apparatus includes a controller  13  for controlling the switching of the operation modes by the four-way valves  4   a  and  4   b , the opening and closing of the ventilation dampers  10   a  and  10   b , and the operation of the indoor fans  8   a  and  8   b  and the compressors  3   a  and  3   b .  FIG. 1  illustrates the configuration of the refrigerating and air-conditioning apparatus which includes two refrigeration cycles. However, the refrigerating and air-conditioning apparatus may be configured to include a further plurality of refrigeration cycles. Moreover, the number of the indoor units installable is not limited to two, and a further plurality of indoor units may be installable. 
     (Sensor Configuration) 
     The indoor unit  2   a  includes, at an air inlet for the indoor air or inside the room, an indoor temperature sensor  14   a  for detecting the indoor temperature and an indoor humidity sensor  15   a  for detecting the indoor humidity. Similarly, the indoor unit  2   b  side also includes an indoor temperature sensor  14   b  for detecting the indoor temperature and an indoor humidity sensor  15   b  for detecting the indoor humidity. 
     The outdoor unit  1  includes, at the air inlet of the outdoor fan  12  or outside the apparatus, outside air temperature sensors  16   a  and  16   b  (see  FIG. 2 ), for detecting the outside air temperature. Furthermore, the outdoor unit  1  includes a temperature sensor  17   a  for detecting the temperature of a pipe positioned between the outdoor heat exchanger  5   a  and the pressure reducing device  6   a , and a temperature sensor  17   b  for detecting the temperature of a pipe positioned between the outdoor heat exchanger  5   b  and the pressure reducing device  6   b.    
       FIG. 3  is a control block diagram of the refrigerating and air-conditioning apparatus in  FIG. 1 . 
     The controller  13  includes a CPU, a RAM for storing various data, and a ROM for storing a program for operating the refrigerating and air-conditioning apparatus (none of the CPU, the RAM, and the ROM are illustrated). With this configuration, a room occupancy detection unit  13   a , an air-conditioning capacity setting unit  13   b , an amount-of-ventilation setting unit  13   c , a defrosting start determination unit  13   d , and a defrosting end determination unit  13   e  are functionally configured in the controller  13 . 
     The room occupancy detection unit  13   a  detects the number of occupants in the room, based on information detected by a weight sensor (not illustrated), an image pickup device (not illustrated), or the like, provided in the room. 
     The air-conditioning capacity setting unit  13   b  detects the air-conditioning load based on the outside air temperature detected by the outside air temperature sensors  16   a  and  16   b , the indoor temperature detected by the indoor temperature sensors  14   a  and  14   b , and a preset indoor temperature. Based on the detected air-conditioning load, the air-conditioning capacity setting unit  13   b  sets a required air-conditioning capacity. The air-conditioning capacity setting unit  13   b  may also correct the required air-conditioning capacity on the basis of the number of occupants in the room detected by the room occupancy detection unit  13   a.    
     The amount-of-ventilation setting unit  13   c  detects ventilation load based on an output signal of an oxygen concentration sensor (not illustrated) or a carbon dioxide sensor (not illustrated), provided in the room, and sets a required amount of ventilation based on the detected ventilation load. The amount-of-ventilation setting unit  13   c  may estimate the required amount of ventilation based on the number of occupants in the room detected by the room occupancy detection unit  13   a . Setting of the amount of ventilation by the amount-of-ventilation setting unit  13   c  is performed repeatedly during the heating operation, and the required amount of ventilation is updated according to the current ventilation state, the number of occupants in the room, and the like. 
     Details of the defrosting start determination unit  13   d  and the defrosting end determination unit  13   e  will be described later. 
     The compressor  3   a , the four-way valve  4   a , the indoor fan  8   a , the ventilation damper  10   a , the indoor temperature sensor  14   a , the indoor humidity sensor  15   a , and the temperature sensor  17   a  of the first refrigeration cycle side are connected to the controller  13 . Furthermore, the compressor  3   b , the four-way valve  4   b , the indoor fan  8   b , the ventilation damper  10   b , the indoor temperature sensor  14   b , the indoor humidity sensor  15   b , and the temperature sensor  17   b  of the second refrigeration cycle side are also connected to the controller  13 . Moreover, an input unit  18  for setting the indoor temperature and inputting and changing set values of various controls is also connected to the controller  13 . 
     (Ventilation Operation) 
     Next, the operation of a ventilation operation in the refrigerating and air-conditioning apparatus of Embodiment 1 will be explained. The ventilation operation is able to be performed independently on indoor units  2   a  and  2   b . The operations of the indoor units  2   a  and  2   b  are both the same. Therefore, a ventilation operation will be explained hereinafter, with the operation of the indoor unit  2   a.    
     The ventilation operation is an operation for taking in the outside air through the ventilation port  9   a  by operating the indoor fan  8   a  and opening the ventilation damper  10   a  so that the air is supplied into the room. The ventilation damper  10   a  repeatedly alternates between the opening and dosing operations, and the amount of ventilation is controlled by the control of the opening and closing rate (the ratio of an opening time to one cycle of opening and closing) of the opening and closing operations by the ventilation damper  10   a . In the ventilation operation, the opening and closing rate is determined so that the amount of ventilation (the required amount of ventilation) set by the amount-of-ventilation setting unit  13   c  is secured on a time average basis, and by performing the opening and closing operations for the ventilation damper  10   a  according to the opening and closing rate, the required amount of ventilation is secured on a time average basis. The amount-of-ventilation setting unit  13   c  may store in advance the amount of ventilation per predetermined time (for example, one second) while the ventilation damper  10   a  is open, and may determine the opening and closing rate based on the amount of ventilation, the duration of one cycle of opening and closing (for example, one minute), and the required amount of ventilation. 
     However, the control of the amount of ventilation is not limited to the above method and may also be performed in accordance with the opening ratio of the ventilation port  9   a . The ventilation operation is controlled independently of a cooling operation and a heating operation, which will be described below. Accordingly, each of the first refrigeration cycle and the second refrigeration cycle may perform the ventilation operation while a cooling operation is being performed, or perform the ventilation operation while a heating operation is being performed. It should be noted that a defrosting operation and the ventilation operation are not performed at the same time. 
     (Cooling Operation) 
     Next, the operation of a refrigeration cycle for a cooling operation in the refrigerating and air-conditioning apparatus of this embodiment will be explained. A four-way valve is switched to the dotted line side in  FIG. 1  in the cooling operation. The first refrigeration cycle and the second refrigeration cycle are able to perform a cooling operation independently. The cooling operations of the first refrigeration cycle and the second refrigeration cycle are both the same. Therefore, a cooling operation will be explained hereinafter, with the cooling operation of the first refrigeration cycle. 
     In the cooling operation, the refrigerant compressed and heated in the compressor  3   a  flows into the outdoor heat exchanger  5   a  via the four-way valve  4   a . The refrigerant which has flowed into the outdoor heat exchanger  5   a  is cooled and condensed by exchanging heat with the outside air sent by the outdoor fan  12 . Then, the pressure of the refrigerant is reduced by the pressure reducing device  6   a , and the refrigerant is heated and evaporated in the indoor heat exchanger  7   a  by exchanging heat with the indoor air sent by the indoor fan  8   a , The refrigerant then flows into the compressor  3   a , and completes one cycle. The room is cooled down by repeating the above-mentioned cycle continuously. 
     In the cooling operation, the air sucked into the indoor unit  2   a  by the indoor fan  8   a  is the mixed air of the outside air flowing in through the ventilation port  9   a  and the indoor air flowing in through the air inlet  11   a , when the ventilation damper  10   a  is open. The mixed air cools down by exchanging heat with the indoor heat exchanger  7   a , and is blown out into the room. When the ventilation damper  10   a  is closed, the indoor air which flows in through the air inlet  11   a  cools down by exchanging heat with the indoor heat exchanger  7   a , and is blown out into the room. 
     (Heating Operation) 
     Next, the operation of a refrigeration cycle for a heating operation in the refrigerating and air-conditioning apparatus of Embodiment 1 will be explained. A four-way valve is switched to the solid line side in  FIG. 1  in the heating operation. The first refrigeration cycle and the second refrigeration cycle are able to perform a heating operation independently. The heating operations of the first refrigeration cycle and the second refrigeration cycle are both the same. Therefore, a heating operation will be explained hereinafter, with the heating operation of the first refrigeration cycle. 
     In the heating operation, the refrigerant compressed and heated in the compressor  3   a  flows into the indoor heat exchanger  7   a  via the four-way valve  4   a . The refrigerant which has flowed into the indoor heat exchanger  7   a  is cooled and condensed by exchanging heat with the indoor air sent by the indoor fan  8   a . Then, the pressure of the refrigerant is reduced by the pressure reducing device  6   a , and the refrigerant is heated and evaporated in the outdoor heat exchanger  5   a  by exchanging heat with the outside air sent by the outdoor fan  12 . The refrigerant then flows into the compressor  3   a , and completes one cycle. The room is heated by repeating the above-mentioned cycle continuously. 
     In the heating operation, the air sucked into the indoor unit  2   a  by the indoor fan  8   a  is the mixed air of the outside air flowing in through the ventilation port  9   a  and the indoor air flowing in through the air inlet  11   a , when the ventilation damper  10   a  is open. The mixed air cools down by exchanging heat with the indoor heat exchanger  7   a , and is blown out into the room. When the ventilation damper  10   a  is closed, the indoor air which flows in through the air inlet  11   a  is heated by exchanging heat with the indoor heat exchanger  7   a , and is blown out into the room. 
     (Defrosting Operation) 
     Next, the operation of a defrosting operation in the refrigerating and air-conditioning apparatus of Embodiment 1 will be explained. The first refrigeration cycle and the second refrigeration cycle are able to perform a defrosting operation independently. The defrosting operations of the first refrigeration cycle and the second refrigeration cycle are both the same. Therefore, a defrosting operation will be explained hereinafter, with the defrosting operation of the first refrigeration cycle. 
     During a heating operation, when the outside air temperature is low and the evaporating temperature of the outdoor heat exchanger  5   a  is at or below 0 degrees Celsius, moisture contained in the outside air is frozen on the outdoor heat exchanger  5   a , and frost is generated (formation of frost). When frost is formed on the outdoor heat exchanger  5   a , the air flow decreases due to clogging of the fins, and furthermore, since the heat transmission is impeded by the frost layer, the amount of heat gained from the outside air decreases and the heating capacity is thus reduced. Therefore, a defrosting operation to melt the frost on the outdoor heat exchanger  5   a  is performed on a regular basis. 
     The defrosting start determination unit  13   d  determines whether or not defrosting of the outdoor heat exchanger  5   a  in the refrigeration cycle needs to start in the heating operation. Regarding the determination as to whether or not defrosting needs to be performed, for example, it is determined that defrosting needs to start when the saturation temperature, that is, the evaporating temperature, of the refrigerant in the outdoor heat exchanger  5   a  is at or below 0 degrees Celsius and the difference between the outside air temperature and the evaporating temperature is equal to or greater than a predetermined temperature difference (for example, 15 degrees Celsius). Furthermore, if the amount of frost formation can be estimated in advance, the heating operation time may be measured, and the determination as to start of defrosting may be made using a timer. The determination by the defrosting start determination unit  13   d  as to whether or not defrosting needs to start is not limited to the methods described above. In addition, for example, a reduction in the amount of cooing or the amount of frost formation of the outdoor heat exchanger  5   a  may be detected and the determination may be made based on the result of the detection. 
     The defrosting end determination unit  13   e  determines whether a defrosting operation is to be terminated. Regarding the determination as to whether a defrosting operation is to be terminated, for example, when the temperature detected by the temperature sensor  17   a  has reached a predetermined temperature (for example, 10 degrees Celsius), it is determined that frost on the outdoor heat exchanger  5   a  has melted and that defrosting is to be terminated. Furthermore, if the amount of defrosting can be estimated in advance, the defrosting operation time may be measured and the determination as to termination of defrosting may be made using a timer. The determination by the defrosting end determination unit  13   e  as to termination of defrosting is not limited to the methods described above. In addition, for example, recovery of the amount of cooling or the amount of frost formed on the outdoor heat exchanger  5   a  may be detected, and the determination may be made based on the result of the detection. 
     In performing a defrosting operation, there is no heating capacity in the refrigeration cycle that performs the defrosting operation. Therefore, if one of the two refrigeration cycles enters a defrosting operation, the other refrigeration cycle performs a heating operation, so that indoor heating continues to be performed. Furthermore, during the defrosting operation, in order to prevent a drop in the room temperature caused by introduction of outside air, the operation is performed when the ventilation dampers  10   a  and  10   b  of the indoor units  2   a  and  2   b  are closed. That is, a ventilation operation is stopped during a defrosting operation. 
     A defrosting operation includes off-cycle defrosting and reverse defrosting. The operations of the off-cycle defrosting and the reverse defrosting will be described below. Here, the first refrigeration cycle will be explained by way of example. 
     (Off-cycle Defrosting) 
     The off-cycle defrosting is an operation for defrosting using heat of the outside air by stopping the compressor  3   a , operating the outdoor fan  12 , and sending the outside air to the outdoor heat exchanger  5   a  when the outside air temperature is above a predetermined temperature. When the outside air is at or above 0 degrees Celsius, frost melts. Therefore, the predetermined temperature may be set to about 5 degrees Celsius to secure melting. The off-cycle defrosting is excellent in energy saving since the compressor  3   a  is stopped. Furthermore, since the indoor heat exchanger  7   a  does not act as an evaporator unlike reverse defrosting, which will be described later, the room temperature can be prevented from dropping. That is, when the outside air temperature is at or above 5 degrees Celsius, off-cycle defrosting is effective in terms of energy saving. 
     (Reverse Defrosting) 
     When the outside air temperature is at 5 or below degrees Celsius, defrosting cannot be performed with off-cycle defrosting. Therefore, a reverse defrosting operation using the heat of refrigerant is performed. When explanation of reverse defrosting will be given with the first refrigeration cycle as an example, the reverse defrosting is an operation for defrosting using the condensing heat of refrigerant by switching the four-way valve  4   a  from a heating circuit to a cooling circuit, so that the refrigerant that has been compressed by the compressor  3   a  into a high-temperature and high-pressure state is caused to flow into the outdoor heat exchanger  5   a.    
     In addition, although in the reverse defrosting a defrosting operation is generally performed by stopping the indoor fan  8   a  and the outdoor fan  12  (fan operation control  1 ), the indoor fan  8   a  and the outdoor fan  12  may be operated. For example, the indoor fan  8   a  may be operated when the heating load is smaller than or equal to a predetermined value and the indoor fan  8   a  may be stopped when the heating load is greater than the predetermined value (fan operation control  2 ). In the case where the indoor fan  8   a  is operated in the reverse defrosting, defrosting of the outdoor heat exchanger  5   a  can be achieved using the heat of the indoor air. Therefore, the defrosting time can further be shortened. Since cold air is blown when the indoor fan  8   a  operates, the indoor fan  8   a  should be operated only when the heating load is smaller than or equal to the predetermined value. 
     Furthermore, the outdoor fan  12  may be operated when the outside air temperature detected by the outside air temperature sensor  16   a  is at or above a predetermined value and the outdoor fan  12  may be stopped when the outside air temperature detected by the outside air temperature sensor  16   a  is below the predetermined value (fan operation control  3 ). In the case where the outdoor fan  12  is operated in the reverse defrosting, since a larger amount of heat can be acquired from the outside air with the other heating operation cycle, the heating capacity can be increased. Since the outside air at a low temperature impedes defrosting when the outdoor fan  12  operates, the outdoor fan  12  should be operated only when the outside air temperature is at or above the predetermined value. 
     Furthermore, reverse defrosting can be performed even when the outside air temperature is at or above 5 degrees Celsius. Since the compressor  3   a  is operated, the defrosting time can be shortened compared to off cycle defrosting. Furthermore, in the case where the indoor fan  8   a  is operated with the reverse defrosting, since defrosting of the outdoor heat exchanger  5   a  can be achieved using the heat of the indoor air, the defrosting time can further be shortened. 
     (Defrosting Operation Control Operation) 
     Next, a defrosting operation control operation with ventilation load and heating load will be explained. Although repetitive explanation will be given, in the case where a defrosting operation is performed, since there is no heating capacity in the refrigeration cycle on the defrosting operation side, one of two refrigeration cycles performs defrosting and the other refrigeration cycle performs a heating operation. At this time, the operations are performed when the ventilation dampers  10   a  and  10   b  in the indoor units  2   a  and  2   b  are closed. With the operations described above, the refrigerating and air-conditioning apparatus is capable of reducing the heating load by blocking the introduction of the outside air during the defrosting operation and is capable of performing the defrosting operation while securing the heating capacity by defrosting alternately between the first refrigeration cycle and the second refrigeration cycle. 
     Here, the overview of a defrosting operation control operation during a heating operation will be explained. Since a ventilation operation is stopped during a defrosting operation, there is a possibility of a shortage of ventilation during the defrosting operation unless any measures are taken. Therefore, before starting a defrosting operation, a prior ventilation operation for securing the time-averaged required amount of ventilation including the period during which the defrosting operation is being performed is performed. After that, the defrosting operation is entered. In the prior ventilation operation, an operation for controlling the opening and closing operation ratio of the ventilation dampers  10   a  and  10   b  to increase the amount of ventilation to be greater than the amount of ventilation in a normal ventilation operation which is performed during a heating operation. In the prior ventilation operation, the heating operation continues to be performed. 
     (Air-conditioning Control Operation during Heating in Refrigerating and Air-conditioning Apparatus) 
     Hereinafter, specific operation examples of an air-conditioning control operation during heating in a refrigerating and air-conditioning apparatus will be explained by way of multiple examples. As a heating operation performed by each refrigeration cycle, a ventilation operation is performed while performing a heating operation or only a heating operation is performed without performing a ventilation operation. In the explanation given below and  FIGS. 4 to 7 , a distinction is made between the former as heating (execution of ventilation) and the latter as heating (non-execution of ventilation). 
     (Operation Example 1) 
       FIG. 4  is a timing chart for explaining an operation example 1 of an air-conditioning control operation during heating in the refrigerating and air-conditioning apparatus. The operation example 1 is an example of the case in which both the refrigeration cycles are performing a heating operation. 
     When both the refrigeration cycles are performing a heating operation, in the case where the defrosting start determination unit  13   d  determines that defrosting of the outdoor heat exchanger of one refrigeration cycle needs to start, the refrigeration cycle for which it is determined that defrosting needs to start performs the above-described prior ventilation operation before starting the defrosting operation. That is, by controlling the ventilation damper of the one refrigeration cycle side to increase the amount of ventilation, the time-averaged required amount of ventilation including the period during which the defrosting operation is being performed is secured. After the prior ventilation operation is terminated, the defrosting operation is started. During the defrosting operation, the ventilation dampers  10   a  and  10   b  are closed so that ventilation is not performed, as described above. Then, after terminating the defrosting operation, the one refrigeration cycle returns to heating (execution of ventilation). 
     Furthermore, when the one refrigeration cycle starts the defrosting operation, the other refrigeration cycle closes the ventilation damper  10   b  and performs heating (non-execution of ventilation). After the defrosting operation by the one refrigeration cycle is terminated, the other refrigeration cycle returns to heating (execution of ventilation). 
     With the operations described above, comfort is maintained without a shortage of ventilation during the defrosting operation. Although the example in which two refrigeration cycles are provided is illustrated as the operation example 1, the number of refrigeration cycles is three or more, as described above. In this case, when two or more of all the refrigeration cycles are performing a heating operation, if it is determined that any of the refrigeration cycles needs to start defrosting, the refrigeration cycle that has been determined to need to start defrosting may perform the operation of the one refrigeration cycle in  FIG. 4 , and the other refrigeration cycle that is performing a heating operation may perform the other refrigeration cycle in  FIG. 4 . 
     (Operation Example 2) 
       FIG. 5  is a timing chart for explaining an operation example 2 of the air-conditioning control operation during heating in the air-conditioning apparatus. The operation example 2 is an example applied to the case in which when heating load is large and one refrigeration cycle enters a defrosting operation, the heating capacity of only a heating operation of the other refrigeration cycle is not sufficient and the time-averaged required heating capacity cannot be secured. 
     In the operation example 2 illustrated in  FIG. 5 , during the period in which prior ventilation is performed in the operation example 1 illustrated in  FIG. 4 , prior heating is performed at the same time as the prior ventilation. The prior heating is an operation for securing the time-averaged required heating capacity including the period during which the defrosting operation is being performed. With the operations described above, even in the case where a defrosting operation is performed when the heating load is large, a defrosting operation can be achieved while securing the heating capacity. Therefore, a drop in the room temperature and a shortage of ventilation can be suppressed, thus enabling a high degree of comfort to be maintained. 
     Although the example in which two refrigeration cycles are provided has been explained as the operation example 2, the number of refrigeration cycles may be three or more, as described above. The operation of the operation example 2 in this case corresponds to an operation in the case where during the period while two or more of all the refrigeration cycles are performing a heating operation, when it is determined that any one of the refrigeration cycles needs to start defrosting, if the refrigeration cycle that has been determined to need to start defrosting enters a defrosting operation, the heating capacity of only the refrigeration cycle that is currently performing a heating operation is not sufficient. Therefore, the refrigeration cycle that has been determined to need to start defrosting may be caused to perform one refrigeration cycle in  FIG. 5 , and the other refrigeration cycle that is performing a heating operation may be caused to perform the other refrigeration cycle in  FIG. 5 . 
     (Operation Example 3) 
       FIG. 6  is a timing chart for explaining an operation example 3 of the air-conditioning control operation during heating in the refrigerating and air-conditioning apparatus. The operation example 3 is an example of the case in which heating load is small, only one of the refrigeration cycles is performing a heating operation, and the other refrigeration cycle is stopped. 
     In the case where it is determined by the defrosting start determination unit  13   d  that defrosting of the outdoor heat exchanger of the one refrigeration cycle that is performing a heating operation needs to start, the one refrigeration cycle that has been determined to need to start defrosting performs a prior ventilation operation, and then closes the ventilation dampers  10   a  and  10   b  to start the defrosting operation, as described above. 
     Here, since the other refrigeration cycle is stopped, if the other refrigeration cycle is stopped during the period in which the one refrigeration cycle is performing the prior ventilation operation and the defrosting operation, heating operations in both the refrigeration cycles are stopped, and indoor heating is thus not performed. Therefore, when it is determined that the one refrigeration cycle that is performing a heating operation needs to start defrosting, the stopped other refrigeration cycle is driven to perform a heating operation. Then, after the one refrigeration cycle terminates the defrosting operation, the other refrigeration cycle continues the heating operation. After terminating the defrosting operation, the one refrigeration cycle stops. 
     With the operations described above, a defrosting operation can be achieved without a drop in the indoor temperature during the defrosting operation, thus enabling comfort to be maintained. Furthermore, since the one refrigeration cycle for which defrosting needs to be performed performs a defrosting operation and then stops and the other refrigeration cycle that has been stopped is caused to perform a heating operation instead of the one refrigeration cycle for which defrosting needs to be performed, the operation times of the refrigeration cycles can be equalized, thus achieving an effect of improving the reliability of the compressors. 
     Although the example in which two refrigeration cycles are provided has been illustrated here, the number of refrigeration cycles may be three or more, as described above. In this case, when only one refrigeration cycle is performing a heating operation and all the other refrigeration cycles are stopped, if it is determined that the refrigeration cycle that is performing the heating operation needs to start defrosting, the refrigeration cycle that has been determined to start defrosting may perform the operation of the one refrigeration cycle in  FIG. 6  and any one of the stopped refrigeration cycles may perform the operation of the other refrigeration cycle in  FIG. 6 . Also at this time, the stopped refrigeration cycle is operated so that the operation times of the compressors can be equalized. 
     In the operation example 3, when the refrigeration cycle that is performing a heating operation starts a defrosting operation, in order to avoid an operation state in which indoor heating is not performed, the stopped refrigeration cycle is activated to perform a heating operation. However, the operation example 3 is not limited to this. For example, in an operation state in which there are five refrigeration cycles in total, three of the refrigeration cycles are performing a heating operation, and the remaining two refrigeration cycles are stopped (in other words, there are refrigeration cycles that are performing a heating operation and refrigeration cycles that are stopped), in the case where it is determined that any one of the three refrigeration cycles that are performing a heating operation needs to start defrosting, either one of the two stopped refrigeration cycles may be activated to perform a heating operation. 
     (Operation Example 4) 
       FIG. 7  is a timing chart for explaining an operation example 4 of the air-conditioning control operation during heating in the refrigerating and air-conditioning apparatus. The operation example 4 is an example of the case in which both the refrigeration cycles are performing a heating operation and a decrease in the heating load is detected by an air-conditioning load detection unit. 
     In the case where the heating load decreases and the heating capacity of one refrigeration cycle is sufficient, one refrigeration cycle is stopped. At this time, after causing the refrigeration cycle that is to be stopped to perform a defrosting operation, the refrigeration cycle is stopped. Accordingly, for the next operation of the stopped refrigeration cycle, a heating operation can be started in the state in which no frost is formed on the outdoor heat exchanger of the refrigeration cycle. Therefore, the heating operation time can be extended, and thus enabling comfort to be maintained for a long time. Also in this time, the refrigeration cycle that is to perform a defrosting operation first performs a prior ventilation operation and then performs the defrosting operation, as described in  FIG. 7 . After the defrosting operation, the refrigeration cycle stops. 
     Furthermore, the function in which during the period in which one refrigeration cycle performs a defrosting operation, the other refrigeration cycle performs a heating (non-execution of ventilation) operation and then returns to a heating (execution of ventilation) operation after the one refrigeration cycle terminates the defrosting operation, is as described above. The refrigeration cycle whose integrated operation time of the compressor is longer of the two refrigeration cycles may be selected as a refrigeration cycle to be stopped. Accordingly, the compressor operation times are equalized, and the reliability of the compressors can be improved. Although the example in which two refrigeration cycles are provided has been illustrated in the operation example 4, the number of refrigeration cycles may be three or more, as described above. In this case, when two or more refrigeration cycles are performing a heating operation, if it is determined that any one of the refrigeration cycles needs to start defrosting, the refrigeration cycle that has been determined to need to start defrosting may perform the operation of one refrigeration cycle in  FIG. 7 , and the other refrigeration cycle that is performing a heating operation may perform the operation of the other refrigeration cycle in  FIG. 7 . 
     Next, control for causing a defrosting operation to be alternately performed between two refrigeration cycles in the refrigerating and air-conditioning apparatus of this example will be explained. 
     In order to cause defrosting to be alternately performed between two refrigeration cycles, a condition for starting a heating operation and starting the first defrosting operation may be set different between the refrigeration cycles. More specifically, a predetermined temperature difference between the outside air temperature and the evaporating temperature, which is used for a start determination in the defrosting start determination unit  13   d , may be set different between the refrigeration cycles. In the above description, as the start determination condition for a defrosting operation, the temperature difference between the outside air temperature and the evaporating temperature is set at or above 15 degrees Celsius. This value is used for one refrigeration cycle, and for the other refrigeration cycle, for example, the temperature difference between the outside air temperature and the evaporating temperature is set to at or above 13 degrees Celsius. With this setting, the timing at which defrosting starts differs between the refrigeration cycles. Subsequently, defrosting operations will be started alternately. 
     In the refrigerating and air-conditioning apparatus, when defrosting operations by the refrigeration cycles are alternately started at equal intervals, a variation in the room temperature is reduced to minimum, thus improving comfort. However, since the interval between starts of defrosting operations varies according to the state of the outside air or the operation ratio of each refrigeration cycle, it may be difficult to cause defrosting operations to be performed alternately between the refrigeration cycles at equal intervals. In this case, during a period in which one refrigeration cycle is performing a defrosting operation or during a predetermined time T 1  after returning from the defrosting operation to a heating operation, the other refrigeration cycle does not perform a defrosting operation even if it is determined by the defrosting start determination unit  13   d  that defrosting needs start. 
     Namely, after the predetermined time T 1  after one refrigeration cycle terminates defrosting and returns to a heating operation, the other refrigeration cycle performs a defrosting operation. Therefore, the defrosting operations of the refrigeration cycles are not simultaneously performed but are alternately performed, and a heating operation can continue to be performed. Also in this case, a function in which a prior ventilation operation is performed before a defrosting operation in order to secure the amount of ventilation, is as described above. 
     Therefore, on the control, the longer one of the predetermined time T 1  from returning to a heating operation after one refrigeration cycle terminates a defrosting operation and the execution time of a prior ventilation operation (defrosting start delay time) T 2  may be selected. That is, in the case where the predetermined time T 1  is shorter than the defrosting start delay time T 2 , by performing a prior ventilation operation, the function in that a defrosting operation is not performed during the predetermined time T 1  can be attained at the same time, and alternate defrosting operations between the refrigeration cycles can be achieved. In contrast, in the case where the predetermined time T 1  is longer than the defrosting start delay time T 2 , after a prior ventilation operation is performed and start of a defrosting operation is further delayed by a difference time between the predetermined time T 1  and the defrosting start delay time T 2 , the defrosting operation may be started. 
     Although the example in which two refrigeration cycles are provided has been described here, the number of refrigeration cycles may be three or more, as described above. In this case, during the time in which at least one of a plurality of refrigeration cycles is performing a defrosting operation or during the predetermined time T 1  after returning from the defrosting operation to a heating operation, all the other refrigeration cycles may not perform a defrosting operation, 
     As described above, according to Embodiment 1, by providing a plurality of refrigeration cycles that are independent from each other, a defrosting operation can be achieved while simultaneously continuing a heating operation. Furthermore, in a defrosting operation, since all the ventilation ports  9   a  and  9   b  are closed so that the outside air is not introduced, a drop in the room temperature during the defrosting operation can be suppressed. Furthermore, a heating operation can be achieved while reducing the heating load during a defrosting operation. Moreover, before starting the defrosting operation, a prior ventilation operation is performed in advance, in order to secure the time-averaged required amount of ventilation including the period in which the defrosting operation is being performed, so that shortage of ventilation does not occur during a defrosting operation. Accordingly, even in a heating operation under air conditions leading to formation of frost, an appropriate amount of ventilation can be secured, and the comfort through heating can be improved. 
     Furthermore, since the indoor heat exchangers  7   a  and  7   b  and the indoor fans  8   a  and  8   b  of the plurality of refrigeration cycles are separately arranged in the indoor units  2   a  and  2   b  and the indoor fan of the indoor unit that is performing a defrosting operation is stopped, conventional discomfort caused by a drop in the air outlet temperature in the case where air passing through the indoor heat exchanger of a defrosting operation side and air passing through the indoor heat exchanger of a heating operation side are mixed together in indoor units and the air is blown into the room, can be prevented. 
     In a defrosting operation, in terms of preventing a drop in the room temperature caused by the introduction of the outside air, it is preferable that all the ventilation ports  9   a  and  9   b  are closed. However, the present invention is not necessarily limited to that in which all the ventilation ports are dosed. A ventilation port may be opened as long as the opening of the ventilation port does not affect a drop in the room temperature. 
     Furthermore, in the case where a prior heating operation for securing the time-averaged required heating capacity including the period in which a defrosting operation is being performed is performed along with a prior ventilation operation before performing the defrosting operation and the defrosting operation is performed after termination of the prior heating operation and the ventilation operation, the defrosting operation can be achieved while securing the heating capacity. Therefore, a drop in the room temperature and a shortage of ventilation can be suppressed, thus enabling a high degree of comfort to be maintained. 
     Furthermore, in the case where there is a stopped refrigeration cycle among a plurality of refrigeration cycles, if it is determined that any one of the refrigeration cycles that is performing a heating operation needs to perform a defrosting operation, during the period in which the refrigeration cycle that is to perform a defrosting operation performs a prior ventilation operation and a defrosting operation, the stopped refrigeration cycle is activated to perform a heating operation. Accordingly, heating can be achieved even during the defrosting operation, and the room temperature can be maintained. Furthermore, the required amount of ventilation can be maintained, thus enabling a high degree of comfort to be maintained, 
     Furthermore, when two or more refrigeration cycles of a plurality of refrigeration cycles are performing a heating operation and the heating operation of one refrigeration cycle to stop for a certain reason, for example, a decrease in the heating load, the refrigeration cycle that is to be stopped performs a defrosting operation and is then stopped. Accordingly, for the next operation of the stopped refrigeration cycle, a heating operation can be started in the state in which no frost is formed on the outdoor heat exchanger. Therefore, the heating operation time can be extended, thus enabling comfort to be maintained for a long time. 
     Embodiment 2. (Injection Circuit) 
     A refrigerating and air-conditioning apparatus according to Embodiment 2 is different from Embodiment 1 in the configuration of a refrigerant circuit. 
       FIG. 8  is a diagram illustrating a refrigerant circuit of the refrigerating and air-conditioning apparatus according to Embodiment 2 of the present invention. The configuration and control of portions other than the refrigerant circuit are basically similar to those of the refrigerating and air-conditioning apparatus of Embodiment 1. Hereinafter, functions of Embodiment 2 that are different from Embodiment 1 will be mainly explained. A modification applied with respect to the configuration and control similar to those in Embodiment 1 is also applied to Embodiment 2 in a similar manner. 
     The refrigerant circuit of the refrigerating and air-conditioning apparatus of Embodiment 2 includes a bypass pipe  19   a  that branches off between the indoor heat exchanger  7   a  and the pressure reducing device  6   a  and that reaches a compression chamber of the compressor  3   a  through a flow control unit  20   a , an internal heat exchanger  21   a , and a solenoid valve  22   a , as well as the refrigerant circuit of the first refrigeration cycle of Embodiment 1. The internal heat exchanger  21   a  performs heat exchange between a pipe positioned between the flow control unit  20   a  and the solenoid valve  22   a  in the bypass pipe  19   a  and a pipe positioned between the indoor heat exchanger  7   a  and the pressure reducing device  6   a.    
     Similar to the refrigerant circuit of the first refrigeration cycle, the refrigerant circuit of the second refrigeration cycle includes a bypass pipe  19   b  that branches off between the indoor heat exchanger  7   b  and the pressure reducing device  6   b  and that reaches a compression chamber of the compressor  3   b  through the flow control unit  20   b , the internal heat exchanger  21   b , and the solenoid valve  22   b , as well as the refrigerant circuit of the second refrigeration cycle of Embodiment 1. The internal heat exchanger  21   b  performs heat exchange between a pipe positioned between the flow control unit  20   b  and the solenoid valve  22   b  in the bypass pipe  19   b  and a pipe between the indoor heat exchanger  7   b  and the pressure reducing device  6   b.    
     (Cooling Operation) 
     Next, the operation of a cooling operation in the refrigerating and air-conditioning apparatus of Embodiment 2 will be explained. A cooling operation is performed when the solenoid valves  22   a  and  22   b  are closed. Accordingly, an operation as in Embodiment 1 is performed. The other operations are similar to those in Embodiment 1. 
     (Heating Operation) 
     Next, the operation of a heating operation in the refrigerating and air-conditioning apparatus of Embodiment 2 will be explained. In a heating operation, the solenoid valves  22   a  and  22   b  are opened to perform an injection operation. The injection operation allows the refrigerant flow rate of the compressors  3   a  and  3   b  to increase, and allows the compressor input, that is, the heating capacity, to increase. Furthermore, in the case where the outside air temperature is low, since the evaporating temperature drops and the compression ratio increases, the discharge temperature rises. However, an injection operation suppresses the discharge temperature, thus increasing the reliability of the compressors. Moreover, if the capacity of a compressor is variable, the capacity can be increased while suppressing the discharge temperature, thus significantly increasing the heating capacity. 
     As described above, in the refrigerating and air-conditioning apparatus of Embodiment 2, by performing an injection operation during a heating operation, the heating capacity can be increased. Therefore, for example, in the case where the first refrigeration cycle performs a defrosting operation and the second refrigeration cycle performs a heating operation, the advantages described below can be achieved. That is, by performing an injection operation in the second refrigeration cycle, the heating capacity during a defrosting operation can be secured without the prior heating explained in Embodiment 1 being performed in the first refrigeration cycle. 
     (Defrosting Operation) 
     The operation of a defrosting operation in the refrigerating and air-conditioning apparatus of Embodiment 2 will now be explained. A defrosting operation is performed when the solenoid valves  22   a  and  22   b  are closed. Accordingly, an operation as in Embodiment 1 is performed. The other operations are similar to those in Embodiment 1. 
     According to Embodiment 2, advantages similar to those in Embodiment 1 are attained. In addition, in starting a defrosting operation in any one of refrigeration cycles in the refrigerating and air-conditioning apparatus, by performing an injection operation on a heating operation side, the required heating capacity can be secured without performing a prior heating operation to secure the time-averaged required heating capacity on the defrosting operation side. 
     Furthermore, in a situation in which one refrigeration cycle performs a heating operation while the other refrigeration cycle is performing a defrosting operation, for example, the outdoor fan  12  may be caused to be stopped, for example, when the outside air temperature is low. At this time, by performing an injection operation in the refrigeration cycle on the heating operation side, as described above, even if the evaporating temperature drops due to the stoppage of the outdoor fan  12 , the heating capacity can be increased. Even in this case, the required heating capacity can be secured without performing prior heating on the defrosting operation side. Therefore, when the outside air temperature is low, a defrosting operation which secures the heating capacity can be achieved while suppressing a rise in the discharge temperature by injection, thus securing a high reliability. 
     Although the example in which two refrigeration cycles are provided is illustrated in  FIG. 8 , the number of refrigeration cycles may be three or more. Also in this case, similar operation effects can be achieved. 
     REFERENCE SIGNS LIST 
       1 : outdoor unit,  2   a : indoor unit,  2   b : indoor unit,  3   a : compressor,  3   b : compressor,  4   a : four-way valve,  4   b : four-way valve,  5   a : outdoor heat exchanger,  5   b : outdoor heat exchanger,  6   a : pressure reducing device,  6   b : pressure reducing device,  7   a : indoor heat exchanger,  7   b : indoor heat exchanger,  8   a : indoor fan,  8   b : indoor fan,  9   a : ventilation port,  9   b : ventilation port,  10   a : ventilation damper,  10   b : ventilation damper,  11   a : air inlet,  11   b : air inlet,  12 : outdoor fan,  13 : controller,  14   a : indoor temperature sensor,  14   b : indoor temperature sensor,  15   a : indoor humidity sensor,  15   b : indoor humidity sensor,  16   a : outside air temperature sensor,  16   b : outside air temperature sensor,  17   a : temperature sensor,  17   b : temperature sensor,  18 : input unit,  19   a : bypass pipe,  19   b : bypass pipe,  20   a : flow control unit,  20   b : flow control unit,  21   a : internal heat exchanger,  21   b : internal heat exchanger,  22   a : solenoid valve,  22   b : solenoid valve