Patent Publication Number: US-2012031139-A1

Title: Indoor unit of air-conditioning apparatus and air-conditioning apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an indoor unit having a fan and a heat exchanger housed in a casing and an air-conditioning apparatus having the indoor unit. 
     2. Description of the Related Art 
     Conventionally, an indoor unit of an air-conditioning apparatus having a fin and tube heat exchanger (a heat exchanger having a plurality of fins arranged side by side with predetermined gaps therebetween and a plurality of heat-transfer tubes provided so as to penetrate through these fins) in a casing is known. An example of the indoor unit of the conventional air-conditioning apparatus as described above is one in which “a heat exchanger  4  is provided so as to surround the front, top, and rear top of a fan rotor  3 . The heat exchanger  4  includes a number of radiating fins attached to a heat-transfer tube which are folded back a plurality of times at both left and right ends, and is configured to allow air sucked from an upper inlet opening  10   a  and a front inlet opening  11   a  by driving the fan rotor  3  to pass toward the fan rotor  3  and cause heat exchange with respect to a refrigerant passing through the interior of the heat-transfer tube. The heat exchanger  4  is connected to a refrigerant piping from an outdoor unit via the refrigerant piping.” (see Japanese Unexamined Patent Application Publication No. 2003-254552 (Paragraph 0004, FIG. 2)) has been proposed. 
     In general, the heat exchanger is employed with most material among each units which constitute the indoor unit of the air-conditioning apparatus. As there is a current demand to save resources and energy, downsizing the heat exchanger is therefore an important issue. 
     SUMMARY OF THE INVENTION 
     In order to solve the above-described problem, it is an object of the invention to provide an indoor unit of an air-conditioning apparatus, in which a heat exchanger can be downsized, and an air-conditioning apparatus having such an indoor unit. 
     The indoor unit of the air-conditioning apparatus according to the invention includes a casing having a suction port formed on an upper portion and a blow-out port formed on a lower side of a front surface portion, an axial-flow or mixed-flow fan provided on the downstream side of the suction port in the casing, and a heat exchanger provided in the casing at a position on the downstream side of the fan and on the upstream side of the blow-out port. The heat exchanger includes a plurality of fins arranged side by side with predetermined gaps therebetween and a plurality of heat-transfer tubes penetrating through a plurality of the fins. The heat exchanger is configured in such a manner that the air-flow resistance of an area facing an outer peripheral side of the fan is larger than the air-flow resistance of an area facing a center portion of the fan. 
     The air-conditioning apparatus according to the invention includes the indoor unit described above. 
     In an axial-flow fan or a mixed-flow fan, the air volume decreases the closer it becomes to the center portion of the fan and, in contrast, increases the closer it becomes to the outer peripheral side thereof. In other words, in the heat exchanger in the area facing the axial-flow fan or a mixed-flow fan, the air volume trying to pass through decreases as it approaches the area facing the center portion of the fan and, in contrast, increases as it approaches the area facing the outer peripheral side of the fan. Therefore, the heat exchanger according to the invention is configured to have a larger air-flow resistance in the range in which the air volume trying to pass through increases (the area facing the outer peripheral side of the fan) than in the range in which the air volume trying to pass through decreases (the area facing the center portion of the fan). Therefore, the wind velocities (that is, the air volumes) in the respective ranges of the heat exchanger are uniformized, so that the heat-exchange capacity of the heat exchanger increases. Therefore, the heat exchanger is downsized in the invention, so that resource saving and energy saving of the indoor unit and the air-conditioning apparatus provided with the indoor unit are achieved. 
     In particular, in the indoor unit according to the invention, the fan is arranged on the upstream side of the heat exchanger, and generation of a swirl flow or occurrence of variations in wind velocity distribution of the air blown out from the blow-out port is restrained. In the indoor unit as described above, the height of the indoor unit increases, which may lead to a restriction on installation. Therefore, the invention which achieves a downsizing in the size of the heat exchanger is specifically effective for the indoor unit according to the invention in which the fan is arranged on the upstream side of the heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view illustrating an indoor unit according to Embodiment 1 of the invention. 
         FIG. 2  is a perspective view illustrating the indoor unit according to Embodiment 1 of the invention. 
         FIG. 3  is a perspective view of the indoor unit according to Embodiment 1 of the invention when viewed from the front right side. 
         FIG. 4  is a perspective view of the indoor unit according to Embodiment 1 of the invention when viewed from the rear right side. 
         FIG. 5  is a perspective view of the indoor unit according to Embodiment 1 of the invention when viewed from the front left side. 
         FIG. 6  is a perspective view illustrating a drain pan according to Embodiment 1 of the invention. 
         FIG. 7  is a vertical cross-sectional view illustrating a dew condensation forming position of the indoor unit according to Embodiment 1 of the invention. 
         FIG. 8  is a configuration drawing illustrating a signal processing device according to Embodiment 1 of the invention. 
         FIG. 9  is a vertical cross-sectional view illustrating another example of the indoor unit of the air-conditioning apparatus according to Embodiment 1 of the invention. 
         FIG. 10  is a vertical cross-sectional view illustrating another example of the indoor unit according to Embodiment 1 of the invention. 
         FIG. 11  is a vertical cross-sectional view illustrating still another example of the indoor unit according to Embodiment 1 of the invention. 
         FIG. 12  is a vertical cross-sectional view illustrating still another example of the indoor unit according to Embodiment 1 of the invention. 
         FIG. 13  is a vertical cross-sectional view illustrating still another example of the indoor unit according to Embodiment 1 of the invention. 
         FIG. 14  is a vertical cross-sectional view illustrating the indoor unit according to Embodiment 2 of the invention. 
         FIG. 15  is a vertical cross-sectional view illustrating the indoor unit according to Embodiment 3 of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, detailed embodiments of an air-conditioning apparatus according to the invention (more specifically, an indoor unit of the air-conditioning apparatus) will be described. In the following embodiments, the invention will be described with a wall indoor unit taken as an example. In the drawings showing respective embodiments, part of the shapes or the sizes of each units (or the components of each units) may be different. 
     Embodiment 1 
     &lt;Basic Configuration&gt; 
       FIG. 1  is a vertical cross-sectional view illustrating an indoor unit (referred to as “indoor unit  100 ”) of an air-conditioning apparatus according to Embodiment 1 of the invention.  FIG. 2  is a perspective view illustrating the indoor unit shown in  FIG. 1 . In the description of Embodiment 1 and other embodiments described later, the left side in  FIG. 1  is defined as the front side of the indoor unit  100 . Referring now to  FIG. 1  and  FIG. 2 , a configuration of the indoor unit  100  will be described. 
     (General Configuration) 
     The indoor unit  100  supplies air-conditioned air to an area to be air-conditioned such as an indoor space by utilizing a refrigerating cycle circulating a refrigerant. The indoor unit  100  mainly includes a casing  1  formed with suction ports  2  for taking in indoor air and a blow-out port  3  for supplying air-conditioned air to the area to be air-conditioned, fans  20  housed in the casing  1  and configured to take in the indoor air from the suction ports  2  and blow out the air-conditioned air from the blow-out port  3 , and heat exchangers  50  disposed in air paths from the fans  20  to the blow-out port  3  and configured to generate the air-conditioned air by heat exchange between the refrigerant and the indoor air. In these components, each of the air paths (an arrow Z in  FIG. 1 ) communicates with the interior of the casing  1 . The suction ports  2  are formed so as to open at an upper portion of the casing  1 . The blow-out port  3  is formed so as to open at a lower portion of the casing  1  (more specifically, on the lower side of a front surface portion of the casing  1 ). The fans  20  are each disposed on the downstream side of the suction ports  2  and the upstream side of the heat exchangers  50 , and, for example, axial-flow fans or mixed-flow fans are employed. 
     Since the fans  20  are provided on the upstream side of the heat exchangers  50  in the indoor unit  100  as configured above, generation of a swirl flow of air blown out from the blow-out port  3  and occurrence of variation in wind velocity distribution can be restrained in comparison with the indoor unit of the conventional air-conditioning apparatus having the fan  20  at the blow-out port  3 . Therefore, blowing of comfortable air to the area to be air-conditioned is achieved. Since no complex structure such as a fan is provided at the blow-out port  3 , measures against dew condensation formed at a boundary between warm air and cool air at the time of a cooling operation can easily be implemented. In addition, since a fan motor  30  is not exposed to air-conditioned air, namely, cool air or warm air, a long operational life can be provided. 
     (Fan) 
     In general, the indoor unit of the air-conditioning apparatus has limitations in terms of installation space, so the fan cannot be increased in size in many cases. Therefore, in order to obtain a desired air volume, a plurality of fans of moderate sizes are arranged in parallel. In the indoor unit  100  according to Embodiment 1, three fans  20  are arranged in parallel along the longitudinal direction of the casing  1  (that is, along the longitudinal direction of the blow-out port  3 ) as shown in  FIG. 2 . In order to obtain a desired heat-exchange capacity with the indoor unit of the air-conditioning apparatus having typical dimensions, three to four fans  20  are preferably provided. In the indoor unit according to Embodiment 1, substantially equivalent air volumes can be obtained from all of the fans  20  by configuring all of the fans  20  to have an identical shape and so as to operate all with the same rotation speed. 
     In this configuration, by combining the number, the shape, and the size of the fans  20  according to the required air volume and the air-flow resistance in the interior of the indoor unit  100 , an optimal fan design for the indoor units  100  having various specifications is achieved. 
     (Bell Mouth) 
     In the indoor unit  100  according to Embodiment 1, a duct-like bell mouth  5  is arranged around each of the fans  20 . The bell mouth  5  is intended to guide intake air into and exhaust air out of the fans smoothly. As shown in  FIG. 2 , for example, the bell mouth  5  according to Embodiment 1 has a substantially circular shape in plan view. In the vertical cross section, the bell mouth  5  according to Embodiment 1 has the following shape. An end portion of an upper portion  5   a  has a substantially circular arc shape extending outward and upward. A center portion  5   b  is a straight portion of the bell mouth  5 , having a constant diameter. An end portion of a lower portion  5   c  has a substantially circular arc shape extending outward and downward. An end portion (a circular arc portion on the suction side) of the upper portion  5   a  of the bell mouth  5  forms the suction port  2 . 
     The bell mouth  5  may be formed integrally with, for example, the casing  1  in order to reduce the number of components and improve the strength. It is also possible, for example, to improve maintainability by modularizing the bell mouth  5 , the fan  20 , and the fan motor  30  so as to be detachably attachable to the casing  1 . 
     In Embodiment 1, the end portion (the circular arc portion on the suction side) of the upper portion  5   a  of the bell mouth  5  is formed so as to have a uniform shape in terms of the circumferential direction of an opening surface of the bell mouth  5 . In other words, the bell mouth  5  does not have structures such as a notch or a rib in the direction of rotation about an axis of rotation  20   a  of the fan  20 , and has a uniform shape in terms of axial symmetry. 
     With the configuration of the bell mouth  5  as described above, the end portion (the circular arc portion on the suction side) of the upper portion  5   a  of the bell mouth  5  has a uniform shape with respect to the rotation of the fan  20 , and hence a uniform flow of the suction flow of the fan  20  is also realized. Therefore, the noise generated by a drift of the suction flow of the fan  20  can be decreased. 
     (Partitioning Panel) 
     As shown in  FIG. 2 , the indoor unit  100  according to Embodiment 1 is provided with partitioning panels  90  between the adjacent fans  20 . These partitioning panels  90  are installed between the heat exchangers  50  and the fans  20 . In other words, the air paths between the heat exchangers  50  and the fans  20  are divided into a plurality of air paths (three in Embodiment 1). The partitioning panels  90  are arranged between the heat exchangers  50  and the fans  20 , so each end portion that is in contact with the heat exchanger  50  has a shape conforming to the shape of the heat exchanger  50 . More specifically, as shown in  FIG. 1 , the heat exchanger  50  is arranged so as to form a substantially A-shape in a vertical cross section from the front side to the back side of the indoor unit  100  (that is, the vertical cross section when viewing the indoor unit  100  from the right side, referred to as “right vertical cross-section”, hereinafter). Therefore, an end portion of each of the partitioning panels  90  on the side of the heat exchanger  50  also has a substantially A-shape. 
     The position of an end portion of each of the partitioning panels  90  on the side of the fan  20  may be determined as follows, for example. When the adjacent fans  20  are positioned sufficiently away from each other to avoid influencing each other on the suction side, the end portion of each of the partitioning panels  90  on the side of the fan  20  may need only be extend to an exit surface of the fan  20 . However, in a case where the adjacent fans  20  are as near to each other to influence each other on the suction side and, in addition, in a case where the shape of the end portion (the circular arc portion on the suction side) of the upper portion  5   a  of the bell mouth  5  can be formed sufficiently large, the end portion of each of the partitioning panels  90  on the side of the fan  20  may extend up to the upstream side of the fan  20  (the suction side) so that the adjacent air paths do not influence each other (the adjacent fans  20  do not influence each other on the suction side). 
     The partitioning panels  90  may be formed of various materials. For example, the partitioning panels  90  may be formed of a metal such as steel or aluminum. Also, for example, the partitioning panels  90  may be formed of a resin. When the partitioning panels  90  are formed of a material with a low melting point such as a resin, however, since the heat exchangers  50  are heated to high temperatures at the time of a heating operation, formation of slight spaces between the partitioning panels  90  and the heat exchangers  50  is recommended. When the partitioning panels  90  are formed of a material with a high melting point such as aluminum or steel, the partitioning panels  90  may be arranged so as to be in contact with the respective heat exchangers  50 . If the heat exchangers  50  are, for example, fin and tube heat exchangers, the partitioning panels  90  may be inserted between the fins of the heat exchangers  50 . 
     As described above, the air path between the heat exchangers  50  and the fans  20  is divided into a plurality of air paths (three in Embodiment 1). It is also possible to reduce the noise generated in the ducts by providing sound-absorbing materials in these air paths, that is, on the partitioning panels  90  or in the casing  1 . 
     The divided air paths are each formed into a substantially square shape of L 1 ×L 2 . In other words, the widths of the divided air paths are L 1  and L 2 . Therefore, the air volume generated by the fan  20  installed in the interior of the substantially square shape of L 1 ×L 2 , for example, reliably passes through the heat exchanger  50  surrounded by an area defined by L 1  and L 2  on the downstream side of the fan  20 . 
     By dividing the air path in the casing  1  into the plurality of air paths as described above, even when the flow field which is generated by the fan  20  on the downstream side has a swirling component, air blown out from each of the fans  20  is prevented from moving freely in the longitudinal direction of the indoor unit  100  (the direction orthogonal to the plane of the paper of  FIG. 1 ). Therefore, the air blown out from the fan  20  can be made to pass through the heat exchanger  50  in the area defined by L 1  and L 2  on the downstream side of the fan  20 . Consequently, variations in air volume distribution of the air flowing into all the heat exchangers  50  in the longitudinal direction of the indoor unit  100  (the direction orthogonal to the plane of the paper of  FIG. 1 ) is restrained, so that a high heat exchanging capacity can be provided. Furthermore, by partitioning the interior of the casing  1  by using the partitioning panels  90 , the mutual interference of the swirl flows generated by the adjacent fans  20  can be prevented between the fans  20  adjacent to each other. Therefore, an energy loss of fluid due to the mutual interference of the swirl flows can be prevented, and hence reduction of a pressure loss in the indoor unit  100  is possible in addition to the improvement in the wind velocity distribution. Each of the partitioning panels  90  does not necessarily have to be formed of a single plate, and may be made up of a plurality of plates. For example, the partitioning panel  90  may be divided into two parts on the side of a front side heat exchanger  51  and on the side of a back side heat exchanger  55 . Needless to say, it is preferable that no gap be formed at a joint portion between the respective plates which constitute the partitioning panel  90 . By dividing the partitioning panel  90  into a plurality of plates, assemblability of the partitioning panels  90  is improved. 
     (Fan Motor) 
     The fan  20  is driven and rotated by the fan motor  30 . The fan motor  30  to be used may be either of an inner-rotor type or an outer-rotor type. In the case of the fan motor  30  of the outer-rotor type, a motor having a structure in which a rotor is integrated with a boss  21  of the fan  20  (the rotor is held by the boss  21 ) is also employed. By setting the dimensions of the fan motor  30  to be smaller than the dimensions of the boss  21  of the fan  20 , loss of airflow generated by the fan  20  can be prevented. In addition, by disposing the motor in the interior of the boss  21 , an axial dimension can also be reduced. With the easily detachable and attachable structure of the fan motor  30  and the fan  20 , cleanability is also improved. 
     By using a Brushless DC motor which is relatively high in cost as the fan motor  30 , improvement in efficiency, elongation of service life, and improvement in controllability are achieved. Needless to say, however, a primary function of an air-conditioning apparatus is achieved even when motors of other types are employed. 
     A circuit for driving the fan motor  30  may be integrated with the fan motor  30 , or may be provided externally for dust-proofing measures and fire prevention measures. 
     The fan motor  30  is attached to the casing  1  using a motor stay  16 . In addition, by configuring the fan motor  30  to be of a box-type fan motor (in which the fan  20 , a housing, and the fan motor  30  are integrally modularized) used for cooling a CPU and configuring the fan motor  30  so as to be detachably attached to the motor stay  16 , maintainability can be improved, and accuracy of tip clearance of the fan  20  can also be improved. 
     A drive circuit of the fan motor  30  may be provided either in the interior of or on the exterior of the fan motor  30 . 
     (Motor Stay) 
     The motor stay  16  is provided with a fixing member  17  and supporting members  18 . The fixing member  17  is a member to which the fan motor  30  is attached. The supporting members  18  are members configured to fix the fixing member  17  to the casing  1 . The supporting members  18  are, for example, rod-shaped members, and extend, for example, radially from an outer peripheral portion of the fixing member  17 . As shown in  FIG. 1 , the supporting members  18  according to Embodiment 1 are extend approximately horizontally. 
     (Heat Exchanger) 
     The heat exchangers  50  of the indoor unit  100  according to Embodiment  1  are arranged on the downstream sides of the fans  20 . Fin and tube heat exchangers are preferably used as the heat exchangers  50 . The heat exchangers  50  are each divided by a line of symmetry  50   a  in the right vertical cross section as shown in  FIG. 1 . The line of symmetry  50   a  divides the area substantially in the center in the horizontal direction of which the heat exchanger  50  is installed in this cross section. In other words, the front side heat exchanger  51  is arranged on the front side (the left side in the plane of the paper in  FIG. 1 ) with respect to the line of symmetry  50   a  and the back side heat exchanger  55  is arranged on the back side (the right side in the plane of the paper in  FIG. 1 ) with respect to the line of symmetry  50   a,  respectively. The front side heat exchanger  51  and the back side heat exchanger  55  are arranged in the casing  1  so that the distance between the front side heat exchanger  51  and the back side heat exchanger  55  increases in the direction of an air current, that is, so that the cross-sectional shape of the heat exchanger  50  forms a substantially inverted V-shape in the right vertical cross section. In other words, the front side heat exchanger  51  and the back side heat exchanger  55  are arranged so as to be inclined with respect to the direction of the air current supplied from the fan  20 . 
     In addition, the heat exchanger  50  is characterized in that the air path area of the back side heat exchanger  55  is larger than the air path area of the front side heat exchanger  51 . In other words, the heat exchanger  50  is arranged so that the air volume of the back side heat exchanger  55  is larger than the air volume of the front side heat exchanger  51 . In Embodiment 1, the length of the back side heat exchanger  55  in the longitudinal direction is larger than the length of the front side heat exchanger  51  in the longitudinal direction in the right vertical cross section. Accordingly, the air path area of the back side heat exchanger  55  is larger than the air path area of the front side heat exchanger  51 . The rest of the configuration (such as the lengths in the depth direction in  FIG. 1 ) of the front side heat exchanger  51  and that of the back side heat exchanger  55  are the same. In other words, the heat conduction area of the back side heat exchanger  55  is larger than the heat conduction area of the front side heat exchanger  51 . Also, the axis of rotation  20   a  of the fan  20  is arranged above the line of symmetry  50   a.    
     With the configuration of the heat exchanger  50  as described above, the generation of the swirl flow of the air blown out from the blow-out port  3  and the occurrence of a variation in wind velocity distribution can be restrained in comparison with the indoor unit of the conventional air-conditioning apparatus having the fan at the blow-out port. Also, with the configuration of the heat exchanger  50  as described above, the air volume of the back side heat exchanger  55  is larger than the air volume of the front side heat exchanger  51 . Because of this difference in air volume, when air currents having passed through the front side heat exchanger  51  and the back side heat exchanger  55  merge, the merged air current is curved toward the front side (the side of the blow-out port  3 ). Therefore, necessity to curve the airflow steeply in the vicinity of the blow-out port  3  is eliminated, and hence the pressure loss in the vicinity of the blow-out port  3  can be reduced. 
     In the indoor unit  100  according to Embodiment 1, the air current flowing out from the back side heat exchanger  55  flows in the direction from the back side to the front side. Therefore, in the indoor unit  100  according to Embodiment 1, the air current after having passed the heat exchanger  50  can be curved more easily than in the case where the heat exchanger  50  is arranged in a substantially V-shape in the right vertical cross section. 
     The indoor unit  100  includes the plurality of fans  20 , which often results in an increase in weight. When the weight of the indoor unit  100  increases, a wall surface strong enough for installing the indoor unit  100  is required, which leads to a restriction of installation. Therefore, reduction of weight of the heat exchanger  50  is preferred. In addition, in the indoor unit  100 , since the fans  20  are arranged on the upstream sides of the heat exchangers  50 , the height of the indoor unit  100  is increased, which often leads to a restriction of installation. Therefore, downsizing of the heat exchanger  50  is preferred. 
     Accordingly, in Embodiment 1, the fin and tube heat exchanger is employed as the heat exchanger  50  (the front side heat exchanger  51  and the back side heat exchanger  55 ) to achieve downsize of the heat exchanger  50 . More specifically, the heat exchanger  50  according to Embodiment 1 includes a plurality of fins  56  arranged side by side with predetermined gaps therebetween and a plurality of heat-transfer tubes  57  penetrating through the fins  56 . In Embodiment 1, the fins  56  are arranged side by side in the horizontal direction of the casing  1  (the direction orthogonal to the plane of the paper of  FIG. 1 ). In other words, the heat-transfer tubes  57  penetrate through the fins  56  along the horizontal direction of the casing  1  (the direction orthogonal to the plane of the paper of  FIG. 1 ). In Embodiment 1, in order to improve heat-transfer efficiency of the heat exchanger  50 , two rows of the heat-transfer tubes  57  are arranged in the direction of air flow of the heat exchanger  50  (the width direction of the fins  56 ). The heat-transfer tubes  57  are arranged in a substantially zigzag shape in right vertical cross section. 
     Downsizing of the heat exchanger  50  is achieved by configuring the heat-transfer tubes  57  with circular tubes having a small diameter (on the order of diameters ranging from 3 mm to 7 mm), and employing R32 as the refrigerant flowing through the heat-transfer tubes  57  (the refrigerant used in the indoor unit  100  and in the air-conditioning apparatus having the indoor unit  100 ). In other words, the heat exchanger  50  exchanges heat between the refrigerant flowing in the interiors of the heat-transfer tubes  57  and the indoor air via the fins  56 . Therefore, when the diameter of the heat-transfer tubes  57  is reduced, with the same amount of circulation of the refrigerant, the pressure loss of the refrigerant is larger than that of the heat exchanger provided with heat-transfer tubes having a large diameter. However, the latent heat of evaporation of R32 is higher than that of R410A at the same temperature, and hence the same capacity can be obtained with a smaller amount of circulation of the refrigerant. Therefore, by using R32, reduction of the amount of a refrigerant to be used is made possible, and the pressure loss in the heat exchanger  50  can be reduced. Therefore, by employing thin circular tubes as the heat-transfer tubes  57 , and using R32 as the refrigerant, downsizing of the heat exchanger  50  is achieved. 
     Furthermore, in the heat exchanger  50  according to Embodiment 1, a reduction in the weight of the heat exchanger  50  is achieved by forming the fins  56  and the heat-transfer tubes  57  with aluminum or aluminum alloy. And if the weight of the heat exchanger  50  does not cause a restriction of installation, the heat-transfer tubes  57  may be formed of copper as a matter of course. 
     Although a decrease in the size and weight is attempted in the heat exchanger  50  having the substantially inverted V-shape in right vertical cross section in Embodiment 1, the shape of the heat exchanger  50  is not limited thereto. The heat exchanger  50  made up of the fins  56  and the heat-transfer tubes  57  may be formed as shown below for example. 
       FIGS. 10 to 13  are vertical cross-sectional views showing another example of the indoor unit according to Embodiment 1 of the invention. 
     In right vertical cross section, for example, the heat exchanger  50  made up of the fins  56  and the heat-transfer tubes  57  may be formed into a substantially N-shape ( FIG. 10 ), a substantially W-shape ( FIG. 11 ), a substantially inverted N-shape ( FIG. 12 ), or a substantially M-shape ( FIG. 13 ). In these cases, a heat exchanger  51   a  and the heat exchanger  51   b  arranged on the front side with respect to the line of symmetry  50   a  corresponds to the front side heat exchanger  51 . A heat exchanger  55   a  and a heat exchanger  55   b  arranged on the back side with respect to the line of symmetry  50   a  corresponds to the back side heat exchanger  55 . With the configuration of the heat exchanger  50  as in  FIGS. 10 to 13 , the air volume passing through the heat exchanger  50  increases and the heat-exchange capacity of the heat exchanger  50  is further improved. Therefore, the heat exchanger  50  can further be downsized. 
     (Finger Guard and Filter) 
     The indoor unit  100  according to Embodiment 1, a finger guard  15  and a filter  10  are provided at the suction port  2 . The finger guard  15  is installed for the purpose of preventing the rotating fan  20  from being touched. Therefore, the shape of the finger guard  15  is arbitrary as long as the fan  20  is prevented from being touched. For example, the shape of the finger guard  15  may be a lattice shape, or may be a circular shape made up of a number of rings having different sizes. Alternatively, the finger guard  15  may be formed either of materials such as resin or metallic materials. However, when strength is required, it is preferably formed of metal. The finger guard  15  is preferably formed of materials and shapes as strong and thin as possible in terms of reduction of air-flow resistance and retention of strength. The filter  10  is provided for the purpose of preventing dust from flowing into the interior of the indoor unit  100 . The filter  10  is provided in the casing  1  so as be detachable and attachable. The indoor unit  100  according to Embodiment 1 includes an automatic cleaning mechanism which cleans the filter  10  automatically. 
     (Wind Direction Control Vane) 
     The indoor unit  100  according to Embodiment 1 includes a vertical wind direction control vane  70  (see  FIG. 2 ) and a horizontal wind-direction control vane (not shown), as a mechanism which controls the blowing direction of the airflow at the blow-out port  3 . 
     (Drain Pan) 
       FIG. 3  is a perspective view of the indoor unit according to Embodiment 1 of the invention when viewed from the front right side.  FIG. 4  is a perspective view of the same indoor unit when viewed from the back right side.  FIG. 5  is a perspective view of the same indoor unit when viewed from the front left side.  FIG. 6  is a perspective view illustrating a drain pan according to Embodiment 1 of the invention. In order to facilitate understanding of the shape of the drain pan, the right side of the indoor unit  100  is shown in cross section in  FIG. 3  and  FIG. 4 , and the left side of the indoor unit  100  is shown in cross section in  FIG. 5 . 
     Provided below a lower end portion of the front side heat exchanger  51  (a front side end portion of the front side heat exchanger  51 ) is a front side drain pan  110 . Provided below a lower end portion of the back side heat exchanger  55  (a back side end portion of the back side heat exchanger  55 ) is a back side drain pan  115 . In Embodiment 1, the back side drain pan  115  and a back side portion  1   b  of the casing  1  are integrally formed. In the back side drain pan  115 , connecting ports  116  to which a drain hose  117  is connected are provided on both a left side end portion and a right side end portion. It is not necessary to connect the drain hose  117  to both of the connecting ports  116 , and the drain hose  117  may be connected to one of the connecting ports  116 . For example, when drawing of the drain hose  117  to the right side of the indoor unit  100  is desired at the time of installation of the indoor unit  100 , the drain hose  117  is connected to the connecting port  116  provided on the right side end portion of the back side drain pan  115 , and the connecting port  116  provided on the left side end portion of the back side drain pan  115  may be closed with a rubber cap or the like. 
     The front side drain pan  110  is arranged at a position higher than the back side drain pan  115 . Provided between the front side drain pan  110  and the back side drain pan  115  on both of the left side end portion and the right side end portion are drain channels  111  which correspond to drain flow channels. The drain channels  111  are each connected at an end portion on the front side thereof to the front side drain pan  110 , and are provided so as to incline downward from the front side drain pan  110  toward the back side drain pan  115 . Also, formed at end portions of the drain channels  111  on the back side are tongue portions  111   a.  The end portions of the drain channels  111  on the back side are arranged so as to extend over an upper surface of the back side drain pan  115 . 
     When the indoor air is cooled by the heat exchangers  50  at the time of cooling operation, dew condensation forms on the heat exchangers  50 . Then, dew on the front side heat exchanger  51  drops from the lower end portion of the front side heat exchanger  51 , and is collected by the front side drain pan  110 . Dew on the back side heat exchanger  55  drops from the lower end portion of the back side heat exchanger  55 , and is collected by the back side drain pan  115 . 
     Since the front side drain pan  110  is provided at a position higher than the back side drain pan  115  in Embodiment 1, the drain water collected by the front side drain pan  110  flows through the drain channel  111  toward the back side drain pan  115 . Then, the drain water drops down from the tongue portion  111   a  of the drain channel  111  to the back side drain pan  115 , and is collected by the back side drain pan  115 . The drain water collected by the back side drain pan  115  passes through the drain hose  117 , and is drained to the outside of the casing  1  (the indoor unit  100 ). 
     As in Embodiment 1, by providing the front side drain pan  110  at a position higher than the back side drain pan  115 , the drain water collected by both of the drain pans can be gathered in the back side drain pan  115  (the drain pan arranged on the backmost side of the casing  1 ). Therefore, by providing the connecting port  116  of the drain hose  117  in the back side drain pan  115 , the drain water collected in the front side drain pan  110  and the back side drain pan  115  can be drained to the outside of the casing  1 . When performing maintenance (cleaning of the heat exchangers  50  and the like) of the indoor unit  100  by opening the front side portion or the like of the casing  1 , there is, therefore, no need to detach and attach the drain pan having the drain hose  117  connected thereto, thus workability such as maintenance is improved. 
     Since the drain channels  111  are provided on both the left side end portion and the right side end portion, even when the indoor unit  100  is installed in an inclined state, the drain water collected in the front side drain pan  110  can be guided reliably to the back side drain pan  115 . Since the connecting ports to which the drain hoses  117  are to be connected are provided on both the left side end portion and the right side end portion, the drawing direction of the hose can be selected according to the conditions of the indoor unit  100  in installation, so that workability when installing the indoor unit  100  is improved. Also, since the drain channels  111  are provided so as to extend over the back side drain pan  115  (that is, since a connecting mechanism is not necessary between the drain channel  111  and the back side drain pan  115 ), attachment and detachment of the front side drain pan  110  is facilitated, and hence maintainability is further improved. 
     It is also possible to connect the back side end of the drain channels  111  to the back side drain pan  115  and arrange the drain channels  111  so that the front side drain pan  110  extends over the drain channels  111 . In this configuration as well, the same effects as the configuration in which the drain channels  111  are arranged so as to extend over the back side drain pan  115  are achieved. The front side drain pan  110  does not necessarily have to be provided at a higher position than the back side drain pan  115 , and the drain water collected in both drain pans can be drained from the drain hose connected to the back side drain pan  115  even when the front side drain pan  110  and the back side drain pan  115  are provided at the same level. 
     (Nozzle) 
     The indoor unit  100  according to Embodiment 1 is configured in such a manner that an opening length dl of a nozzle  6  on the suction side (a throttle length dl between the drain pans defined by a portion between the front side drain pan  110  and the back side drain pan  115 ) is defined to be larger than an opening length d 2  (the length of the blow-out port  3 ) of the nozzle  6  on the blow-out side. In other words, the nozzle  6  of the indoor unit  100  has opening lengths which satisfy d 1 &gt;d 2 . 
     The reason why the nozzle  6  is configured to have opening lengths of d 1 &gt;d 2  is as follows. Since the value d 2  affects the distribution distance of the airflow, which is one of basic functions of the indoor unit, the opening length d 2  of the indoor unit  100  according to Embodiment 1 is assumed to be a comparable length with the blow-out port of the conventional indoor unit in the description given below. 
     By setting the dimensions of the nozzle  6  in the vertical cross section to be d 1 &gt;d 2 , the air path is widened, and an angle A of the heat exchanger  50  arranged on the upstream side (the angle formed between the front side heat exchanger  51  an the back side heat exchanger  55  on the downstream side of the heat exchanger  50 ) can be widened. Therefore, the wind velocity distribution generated in the heat exchanger  50  is reduced, and the air path of the downstream side of the heat exchanger  50  can be widened, whereby reduction of pressure loss in the entire indoor unit  100  can be achieved. In addition, the deviation of the wind velocity distribution generated in the vicinity of the inlet portion of the nozzle  6  can be unified and guided to the blow-out port by the effect of flow contraction. 
     For example, when d 1 =d 2 , the deviation of the wind velocity distribution generated in the vicinity of the inlet portion of the nozzle  6  (for example, a flow deviated toward the back side) is reflected directly in the deviation of the wind velocity distribution at the blow-out port  3 . In other words, when d 1 =d 2 , air is blown out from the blow-out port  3  still having the deviation in the wind velocity distribution. When d 1 &lt;d 2  is satisfied, for example, the contraction flow loss is increased when airflows passed through the front side heat exchanger  51  and the back side heat exchanger  55  merge in the vicinity of the inlet portion of the nozzle  6 . Therefore, when d 1 &lt;d 2  is satisfied, a loss corresponding to the contraction flow loss is generated unless otherwise a diffusion effect at the blow-out port  3  cannot be obtained. 
     (ANC) 
     In the indoor unit  100  according to Embodiment 1, an active silencing mechanism is provided as shown in  FIG. 1 . 
     More specifically, the silencing mechanism of the indoor unit  100  according to Embodiment 1 includes a noise detection microphone  161 , a control speaker  181 , a silencing effect detection microphone  191 , and a signal processing device  201 . The noise detection microphone  161  is a noise detection device configured to detect an operation sound (noise) of the indoor unit  100  including a blast sound of the fan  20 . The noise detection microphone  161  is arranged between the fan  20  and the heat exchanger  50 . In Embodiment 1, the noise detection microphone  161  is provided on the front surface portion in the casing  1 . The control speaker  181  is a control sound output device configured to output a control sound with respect to the noise. The control speaker  181  is arranged below the noise detection microphone  161  and above the heat exchanger  50 . In Embodiment 1, the control speaker  181  is provided on the front surface portion in the casing  1  so as to face the center of the air path. The silencing effect detection microphone  191  is a silencing effect detection device configured to detect the silencing effect using the control sound. The silencing effect detection microphone  191 , being intended to detect a noise coming from the blow-out port  3 , is provided in the vicinity of the blow-out port  3 . The silencing effect detection microphone  191  is attached at a position avoiding the airflow so as not to be exposed to the air coming out from the blow-out port  3 . The signal processing device  201  is a control sound generating device configured to cause the control speaker  181  to output the control sound on the basis of the results of detection by the noise detection microphone  161  and the silencing effect detection microphone  191 . 
       FIG. 8  is a configuration drawing illustrating a signal processing device according to Embodiment 1 of the invention. Electric signals supplied from the noise detection microphone  161  and the silencing effect detection microphone  191  are amplified by a microphone amplifier  151 , and are converted from analogue signals to digital signals by an A/D converter  152 . The converted digital signals are input to an FIR filter  158  and an LMS algorithm  159 . In the FIR filter  158 , a control signal, which is corrected to cause a noise with the same amplitude as and an opposite phase from the detected noise by the noise detection microphone  161  when the noise reaches a position where the silencing effect detection microphone  191  is installed, and is converted from a digital signal to an analogue signal by an D/A converter  154 , then is amplified by an amplifier  155 , and then is emitted as the control sound from the control speaker  181 . 
     In a case where the air-conditioning apparatus is in cooling operation, for example, as shown in  FIG. 7 , the temperature in an area B between the heat exchanger  50  and the blow-out port  3  is lowered due to cool air, thereby causing dew condensation to appear as water droplets from water vapor in the air. Therefore, in the indoor unit  100 , a water trap or the like (not shown) is attached in the vicinity of the blow-out port  3  for preventing the water droplets from coming out from the blow-out port  3 . The area where the noise detection microphone  161  and the control speaker  181  are arranged, which is on the upstream side of the heat exchanger  50  is not subjected to dew condensation, because it is located on the upstream side of the area to be cooled by cool air. 
     Subsequently, a method of restraining an operating sound of the indoor unit  100  will be described. The operating sound (noise) including the blast sound of the fan  20  in the indoor unit  100  that is detected by the noise detection microphone  161  attached between the fan  20  and the heat exchanger  50  is converted into a digital signal via the microphone amplifier  151  and the ND converter  152 , and is supplied to the FIR filter  158  and the LMS algorithm  159 . 
     A tap coefficient of the FIR filter  158  is updated sequentially by the LMS algorithm  159 . The tap coefficient is updated by the LMS algorithm  159  according to an expression 1 (h (n+1)=h(n)+2 μe(n)×(n)), and is updated to an optimal tap coefficient so as to cause an error signal e to approach zero. 
     In the expression shown above, h is a tap coefficient of the filter, e is the error signal, x is a filter input signal, and μ is a step size parameter, and the step size parameter μ is used for controlling the update amount of the filter coefficient at every sampling. 
     In this manner, the digital signal passed through the FIR filter  158  whose tap coefficient is updated by the LMS algorithm  159  is converted into an analogue signal by the D/A converter  154 , is amplified by the amplifier  155 , and is released into the air path in the indoor unit  100  as the control sound from the control speaker  181  attached between the fan  20  and the heat exchanger  50 . 
     And the silencing effect detection microphone  191 , attached to a lower end of the indoor unit  100  on the outer wall of the blow-out port  3  so as to avoid wind blown out from the blow-out port  3 , detects a sound which has been propagated from the fan  20  to the air path coming out from the blow-out port, the sound after having been interfered by the control sound released from the control speaker  181 . 
     Since the sound detected by the silencing effect detection microphone  191  is input to the error signal of the LMS algorithm  159  described above, the tap coefficient of the FIR filter  158  is updated so as to cause the sound after the interference to approach zero. Consequently, the noise in the vicinity of the blow-out port  3  can be restrained by the control sound having passed through the FIR filter  158 . 
     In this manner, in the indoor unit  100  to which an active silencing method is applied, the noise detection microphone  161  and the control speaker  181  are arranged between the fan  20  and the heat exchanger  50 , and the silencing effect detection microphone  191  is attached to a position avoiding the airflow from the blow-out port  3 . Therefore, since it is not necessary to attach members required for active silencing to area B which is subjected to dew condensation, water droplets dropping on the control speaker  181 , the noise detection microphone  161 , and the silencing effect detection microphone  191  is prevented, and hence deterioration of silencing capabilities or defects of the speaker or the microphone can be prevented. 
     The positions where the noise detection microphone  161 , the control speaker  181 , and the silencing effect detection microphone  191  are attached shown in Embodiment 1 are only examples. For example, as shown in  FIG. 9 , the silencing effect detection microphone  191  may be arranged between the fan  20  and the heat exchanger  50  together with the noise detection microphone  161  and the control speaker  181 . Although the microphone is exemplified as detecting means for detecting the noise or the silencing effect after having cancelled the noise using the control sound, it may be an acceleration sensor or the like for sensing vibrations of the casing. Alternatively, it is also possible to understand the sound as turbulence of air current, and detect the noise or the silencing effect after having cancelled the noise by the control sound as turbulence of the air current. In other words, a flow velocity sensor which detects the air current or a hot-wire probe may be used as the detecting means for detecting the noise or the silencing effect after having cancelled the noise using the control sound. It is also possible to detect the air current by increasing a gain of the microphone. 
     Although the FIR filter  158  and the LMS algorithm  159  are employed in the signal processing device  201  in Embodiment 1, any adaptive signal processing circuit may be employed as long as it causes the sound detected by the silencing effect detection microphone  191  to approach zero, and also may be one in which a filtered-X algorithm generally used in the active silencing method is applicable. In addition, the signal processing device  201  may be configured to generate the control signal using a fixed tap coefficient instead of employing adaptive signal processing. And further, the signal processing device  201  may be an analogue signal processing circuit instead of the digital signal processing circuit. 
     In addition, in Embodiment 1, the heat exchanger  50  disposed to cool air which forms due condensation has been described, but the invention can be applied also to a case where the heat exchanger  50  of a level which does not cause dew condensation is arranged, and has effects to prevent deterioration of performances of the noise detection microphone  161 , the control speaker  181 , the silencing effect detection microphone  191 , and the like without considering the presence or absence of occurrence of due condensation due to the heat exchanger  50 . 
     Embodiment 2 
     (Flat Tube) 
     In Embodiment 1, the heat-transfer tubes  57  are each formed of a circular tube. The invention is not limited thereto, and the heat-transfer tubes  57  can be formed of a flat tube as a matter of course. In Embodiment 2, points which are different from Embodiment 1 described above will be described principally, and the same components as Embodiment 1 are assigned with the same numbers. 
       FIG. 14  is a vertical cross-sectional view illustrating the indoor unit according to Embodiment 2 of the invention. 
     The heat exchanger  50  according to Embodiment 2 includes heat-transfer tubes  57  formed of a flat tube. The rest of the configuration are the same as the heat exchanger  50  shown in Embodiment 1. In Embodiment 2, R32 is employed as a refrigerant flowing through the heat-transfer tubes  57  (the refrigerant used in the indoor unit  100  and the air-conditioning apparatus having the indoor unit  100 ) as in Embodiment 1. 
     The heat exchanger  50  in which the flat tube-shaped heat-transfer tubes  57  are employed has a narrower flow channel for the refrigerant in comparison with the heat exchanger in which the circular heat-transfer tubes are employed. Therefore, the heat exchanger  50  in which the flat tube-shaped heat-transfer tubes  57  are employed is subjected to a larger pressure loss of the refrigerant in comparison with the heat exchanger in which the circular heat-transfer tubes are employed in the same amount of circulation of the refrigerant. However, the latent heat of evaporation of R32 is higher than that of R410A at the same temperature, and hence the same capacity can be achieved with a smaller amount of circulation of the refrigerant. Therefore, by using R32, reduction of the amount of a refrigerant to be used is made possible, so that the pressure loss in the heat exchanger  50  can be reduced. Therefore, by employing the flat tubes as the heat-transfer tubes  57 , and using R32 as the refrigerant, downsizing of the heat exchanger  50  is achieved. 
     The heat exchanger  50  in Embodiment 2 is arranged so that the long sides of the heat-transfer tubes  57  agree with the direction of the air flow. More specifically, the air-flow directions of the heat exchanger  50  (the direction of air flowing in the heat exchanger  50 ) when the fan  20  is driven are as indicated by hollow arrows in  FIG. 14 . The heat exchanger  50  in Embodiment 2 is arranged so that the long sides of the heat-transfer tubes  57  agree with the directions of air flow. Accordingly, the air-flow resistance of the heat exchanger  50  is reduced, and hence a power of the fan  20  can be held down, thereby reducing the power consumption of the fan  20 . In addition, since the air-flow resistance of the heat exchanger  50  is lowered, the distances between the adjacent heat-transfer tubes  57  can be reduced (narrowed). Therefore, the heat exchanger  50  can further be downsized. 
     In the heat exchanger  50  according to Embodiment 2, the fin  56  and the heat-transfer tubes  57  may be also formed of aluminum or aluminum alloy. Accordingly, weight reduction of the heat exchanger  50  is achieved. 
     Embodiment 3 
     (Density of Heat-Transfer Tubes) 
     The heat exchanger  50  may also be downsized with the configuration of the heat exchanger  50  as described below. In Embodiment 3, points which are different from Embodiment 1 and Embodiment 2 described above will be described principally, and the same components as in Embodiment 1 and Embodiment 2 are assigned with the same numbers. 
       FIG. 15  is a vertical cross-sectional view illustrating the indoor unit according to Embodiment 3 of the invention. 
     In the fan  20 , which is an axial-flow fan or a mixed-flow fan, the air volume decreases the closer it becomes to the center portion of the fan and, in contrast, increases the closer it becomes to the outer peripheral side thereof. In other words, in the heat exchanger  50  in the area facing the fan  20 , the air volume trying to pass through decreases as it approaches an area facing the center portion of the fan  20  and, in contrast, increases as it approaches an area facing the outer peripheral side of the fan  20 . Therefore, the heat exchanger  50  according to Embodiment 3 is configured to have a larger air-flow resistance in the range in which the air volume trying to pass through is large (the area facing the outer peripheral side of the fan  20 ) than in the range in which the air volume trying to pass through is small (the area facing the center portion of the fan  20 ). 
     More specifically, in the heat exchanger  50  according to Embodiment 3 having a right vertical cross section in a substantially inverted V-shape, the air-flow resistance increases gradually from a back side end portion of the front side heat exchanger  51  to a front side end portion of the front side heat exchanger  51 . Also, the air-flow resistance increases gradually from the front side end portion of the back side heat exchanger  55  to the back side end portion of the back side heat exchanger  55 . In Embodiment 3, the air-flow resistance is adjusted by adjusting the distance between the adjacent heat-transfer tubes  57 . In other words, in the heat exchanger  50  according to Embodiment 3 having the right vertical cross section in the substantially inverted V-shape, the distance between the adjacent heat-transfer tubes  57  decreases gradually from the back side end portion of the front side heat exchanger  51  to the front side end portion of the front side heat exchanger  51 . Also, the distance between the adjacent heat-transfer tubes  57  decreases gradually from the front side end portion of the back side heat exchanger  55  to the back side end portion of the back side heat exchanger  55 . 
     With the configuration of the heat exchanger  50  as described above, the wind velocities (that is, the air volumes) in the respective ranges of the heat exchanger  50  is uniformized, so that the heat-exchange capacity of the heat exchanger  50  increases. Therefore, the heat exchanger  50  can be downsized. 
     In Embodiment 3, the air-flow resistance is adjusted by adjusting the distance between the adjacent heat-transfer tubes  57 . However, the air-flow resistance may be adjusted by changing the diameter of the heat-transfer tubes  57 . In other words, in the heat exchanger  50  according to Embodiment 3 having the right vertical cross section in the substantially inverted V-shape, the diameter of the heat-transfer tubes  57  may be increased gradually from the back side end portion of the front side heat exchanger  51  to the front side end portion of the front side heat exchanger  51 . Also, the diameter of the heat-transfer tubes  57  may be increased gradually from the front side end portion of the back side heat exchanger  55  to the back side end portion of the back side heat exchanger  55 . 
     It is not necessary to gradually increase the air-flow resistance of the heat exchanger  50  from the area facing the center portion of the fan  20  to the area facing the outer peripheral side of the fan  20 . For example, the air-flow resistance of the heat exchanger  50  may be increased step by step from the area facing the center portion of the fan  20  to the area facing the outer peripheral side of the fan  20 . In other words, what is essential is that the air-flow resistance of the area facing the outer peripheral side of the fan  20  is larger than the air-flow resistance of the area facing the center portion of the fan  20 . 
     The heat-transfer tubes  57  of the heat exchanger  50  according to Embodiment 3 may be formed of a circular tube having a small diameter (diameters on the order from 3 mm to 7 mm) as shown in Embodiment 1 or may be formed of a flat tube as shown in Embodiment 2. In this case, by employing R32 as the refrigerant, further downsizing of the heat exchanger  50  is achieved. In a case of forming the heat-transfer tubes  57  with the flat tube, further downsizing of the heat exchanger  50  is achieved by arranging the heat exchanger  50  so that the long sides of the flat tubes agree with the directions of air flow. 
     In the heat exchanger  50  according to Embodiment 3, the fin  56  and the heat-transfer tubes  57  may also be formed of aluminum or aluminum alloy. Accordingly, weight reduction of the heat exchanger  50  is achieved. 
     REFERENCE SIGNS LIST 
     
         
         casing,  1   b  back side portion,  2  suction port,  3  blow-out port,  5  bell mouth,  5   a  upper portion,  5   b  center portion,  5   c  lower portion,  6  nozzle, filter,  15  finger guard,  16  motor stay,  17  fixed member,  18  supporting member,  20  fan,  20   a  axis of rotation,  21  boss,  30  fan motor,  50  heat exchanger,  50   a  line of symmetry,  51  front side heat exchanger,  51   a  heat exchanger,  51   b  heat exchanger,  55  back side heat exchanger,  55   a  heat exchanger,  55   b  heat exchanger,  56  fin,  57  heat-transfer tube,  70  vertical wind direction control vane,  90  partitioning panel,  100  indoor unit,  110  front side drain pan,  111  drain channel,  111   a  tongue portion,  115  back side drain pan,  116  connecting port,  117  drain hose,  151  microphone amplifier,  152  A/D converter,  154  D/A converter,  155  amplifier,  158  FIR filter,  159  LMS algorithm,  161  noise detection microphone,  181  control speaker,  191  silencing effect detection microphone,  201  signal processing device