JPH11248217A - Heat-exchange ventilator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a configuration related to a bypass ventilation path while promoting the thinning of a heat exchange ventilator. SOLUTION: A heat exchanger in a lamination type and in a hexahedron is arranged at a casing while two systems of fluid passages are in a nearly horizontal direction and in a nearly vertical direction, an air-feeding blower and an exhaust blower are provided at one and the other side of both small ports where the fluid passage does not face, respectively, the output end of the air-feeding ventilation passage and the input end of the exhaust ventilation passage are provided on the lower surface of the casing where the open surface of one fluid passage of the heat exchanger faces, a bypass ventilation passage 20 for connecting an indoor side suction port to the suction side of the exhaust blower and a partition box 10 for forming a connection port 19 at the downstream side of the heat exchanger of the exhaust ventilation path are provided at one small port side of the heat exchanger, and the wind path area of the exhaust ventilation path being formed by the upper surface of the partition box 10 gradually increases toward the suction side of the exhaust blower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ventilating system for exhausting indoor air to the outside of a room through a built-in heat exchanger, and supplying air by exchanging heat of the outdoor air into the room with the heat exchanger to supply and exhaust air. The present invention relates to a heat exchange ventilator for performing the following.

[0002]

2. Description of the Related Art Such a heat exchange ventilator is shown in FIGS.
As shown in the figure, a heat exchanger 5 for performing air-to-air heat exchange
0 is provided to perform ventilation by simultaneous supply and exhaust while performing heat exchange, and it is possible to perform ventilation with little variation in indoor state quantity. In such a heat exchange ventilator, a laminated heat exchanger 50 configured in a hexahedron is often used. The end face of the heat exchanger 50 has a parallelogram shape.
As shown in Japanese Unexamined Patent Application Publication No. HEI 2-267442, a box-shaped casing 51 is assembled so that one of two diagonal lines related to the fore-edge is oriented in the horizontal direction and the other is oriented in the vertical direction. . Therefore, the fluid passages through which the exhaust air flow and the supply air flow pass obliquely intersect, and the indoor air 52 sucked from the indoor air inlet formed on the lower surface of the casing 51.
Flows obliquely upward in one fluid passage of the heat exchanger 50, and the outdoor air 53 sucked from the outdoor suction port flows obliquely downward in the other fluid passage of the heat exchanger 50,
It is blown into the room from the indoor side outlet.

[0003] Some of such heat exchange ventilators are provided with a bypass ventilation path that bypasses the heat exchanger. The bypass ventilation path is a path for branching a part of the exhaust ventilation path, bypassing the heat exchanger, and exhausting room air, and can be opened and closed by an air path switching device. By opening the bypass ventilation passage, the indoor air bypasses the heat exchanger and is directed to the outdoor outlet, and normal ventilation without heat exchange suitable for an intermediate period such as spring and autumn is performed.

[0004]

In the above-mentioned conventional heat exchange ventilator, the height of the casing 51 is determined by the diagonal dimension of the small opening of the heat exchanger 50, and it is difficult to promote the reduction in thickness. Met. Heat exchanger 5
In the case where the air supply path 0 is rotated by 90 degrees with respect to the casing 51, the air path configuration of the ventilation path is simple when air is supplied and exhausted from below the heat exchanger 50, and this installation form has been followed. Was. However, there is a problem that it is difficult to maintain and inspect the air filter 54 and the like for purifying the supplied air and preventing the fluid passage from being clogged. Therefore, there are still strong demands for thinning. The reason that the maintenance and inspection of the air filter 54 is difficult is that the surface of the heat exchanger 50 facing the inlet of the fluid passage is located in the closed space, and the air filter 54 attached here is removed, cleaned and the like is attached again. This means that the bulky heat exchanger 50 must be rotated or removed as shown in FIG. In the case of a device having a bypass air passage, the configuration of the air passage switching device tends to be complicated, and there is a problem that noise easily leaks to the indoor side because the bypass air passage is close to the indoor-side suction port.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to simplify the configuration relating to a bypass ventilation passage while promoting the thinning of a heat exchange ventilation device. That is, it is to promote noise reduction and to improve the detachability of the air filter of the heat exchange ventilator.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, a first aspect of the present invention is a method of forming a path through one fluid passage of a laminated hexahedral heat exchanger built in a casing formed of a hexahedron. And a supply air passage through which an air flow from the outdoor to the room is passed by the blower, and an independent passage over the entire passage with respect to the supply air passage, and a part of the passage in the other fluid passage of the heat exchanger And a heat exchange ventilator provided with an exhaust air passage through which air flows from the room to the outside by a blower, wherein the heat exchanger has one fluid passage and the other fluid passage substantially horizontally and substantially vertically. A blower that forms a supply air flow on one side of both small openings where the fluid passage of the heat exchanger does not face is disposed on the casing so as to intersect in the direction of the direction, and a blower that forms an exhaust flow on the other side. Arranged at the outlet end of the air supply ventilation passage The inner air outlet and the indoor suction port, which is the inlet end of the exhaust ventilation passage, are separated from each other on the lower surface of the casing facing the surface where one of the fluid passages of the heat exchanger opens. A partition box that forms a bypass ventilation path that communicates with the suction side of the blower that forms the flow and a part of the exhaust ventilation path on the downstream side of the heat exchanger is provided on one of the small sides of the heat exchanger. The box is provided with air passage switching means for closing one of the bypass air passage and the exhaust air passage and opening the other, and when the air passage switching means closes the bypass air passage, a partition box is formed. The air passage area of the exhaust passage to be exhausted gradually increases toward the suction side of the exhaust blower.

According to a second aspect of the present invention, a part of a path is formed by one of the fluid passages of a laminated, hexahedral heat exchanger built in a casing having a hexahedral structure. An air supply passage through which air flows from the outside to the indoors by a blower, and the entire passage is independent of the supply air passage, and a part of the passage is constituted by the other fluid passage of the heat exchanger. A heat exchange ventilator having an exhaust ventilation passage through which air flows from the room to the outside is provided. The heat exchanger is arranged such that the fluid passage on the supply ventilation passage side is substantially horizontal and the fluid passage on the exhaust ventilation passage side is substantially vertical. The heat exchanger is arranged in the casing, a blower that forms a supply air flow is disposed on one side of both small openings where the fluid passage of the heat exchanger does not face, and a blower that forms an exhaust flow is disposed on the other side, Indoor side blowing at the outlet end of the air supply ventilation passage The inlet and the indoor suction port, which is the inlet end of the exhaust ventilation passage, are separated from each other on the lower surface of the casing facing the opening of the fluid passage on the exhaust ventilation passage side of the heat exchanger. An air filter is provided on the opening surface so as to be detachable from the lower surface of the casing, a bypass air passage connecting the indoor side suction port and a suction side of a blower that forms an exhaust flow, and a downstream side of the heat exchanger of the exhaust air passage. A partition box forming a part of the side is provided on one side of the heat exchanger, and the partition box is provided with air path switching means for closing one of the bypass ventilation path and the exhaust ventilation path and opening the other. In a state in which the air passage switching means closes the bypass air passage, the air passage area of the exhaust air passage formed by the partition box gradually increases toward the suction side of the exhaust blower. adopt.

In order to achieve the above object, a third aspect of the present invention adopts a means according to any one of the first and second aspects, wherein the partition box has a muffling structure.

According to a fourth aspect of the present invention, there is provided a blower for forming an exhaust flow in the means according to any one of the first to third aspects, wherein the blower is a double suction type centrifugal blower. The means to do is adopted.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. The heat exchange ventilator according to this embodiment shown in FIGS. 1 to 7 has a heat exchanger 1 for performing air-to-air heat exchange incorporated in a casing 2 having a hexahedral box shape with an open lower surface. In addition, the room is ventilated by simultaneous supply and exhaust while performing heat exchange, so that the ventilation with little variation in the state quantity in the room can be performed. In this heat exchange ventilator, a part of the path is constituted by one fluid path 3 of the heat exchanger 1, and an air supply ventilation path 5 through which an air flow from an outdoor to an indoor is supplied by an air supply blower 4; A part thereof is constituted by the other fluid passage 6 of the heat exchanger 1, and an exhaust ventilation passage 8 through which an air flow from the room to the outside is passed by an exhaust blower 7 is independently constituted over the entire passage.

The heat exchanger 1 is a laminated type as shown in FIG.
The fluid passage 3 on the side of the supply air passage 5 is oriented substantially horizontally, and the fluid passage 6 on the side of the exhaust air passage 8 is oriented substantially vertically, and is incorporated in the center of the casing 2. Both sides of the casing 2 facing the small opening where the fluid passages 3 and 6 of the heat exchanger 1 do not face are separated from the heat exchanger 1 side by a partition wall 9 and a partition box 10, and a lower surface of the closing plate 11 is detachable. The air supply chamber 12 and the exhaust chamber 13 which are closed by are defined respectively. An outdoor-side suction port 14 is provided on the front surface of the casing 2 that defines the air supply chamber 12, and a duct connection port 15 is provided so that the air-supplying chamber 12 can communicate with the outside (often outdoors) by a duct. In the air supply chamber 12, a double suction type centrifugal air supply blower 4 is installed with the rotation shaft 16 of the electric motor being substantially vertical. The outlet of the air blower 4 faces a vertically long communication port 17 formed on the front side of the partition wall 9 that separates the casing 2 from the heat exchanger 1 side, and the front face of the heat exchanger 1 and the casing 2 And a part of an air supply ventilation passage 5 formed between the inner wall surface and the front wall surface.

An outside air outlet 18 is provided in front of the casing 2 defining an exhaust chamber 13 on the opposite side of the air supply chamber 12, and a duct is provided so as to be able to communicate with the outside (often outdoors) by a duct. A connection port 15 is provided. Exhaust chamber 13
Inside, a double suction type centrifugal exhaust blower 7 is installed with the rotating shaft 16 of the electric motor substantially horizontal. The outlet of the exhaust blower 7 faces the outdoor outlet 18.
As shown in FIGS. 5 and 6, a horizontally long communication port 19 is opened in the upper part of the partition box 10 separating the exhaust chamber 13 and the heat exchanger 1 side of the casing 2, and the upper surface of the heat exchanger 1 and the casing 2 are separated. Exhaust ventilation passage 8 formed between the inner wall surface of the ceiling and
Some have contacted. The upper surface of the partition box 10 is inclined toward the exhaust chamber 13 at an angle smaller than 90 degrees, and an outlet of a bypass ventilation passage 20 formed at a lower portion is opened upward.

The bypass ventilation passage 20 is provided with an indoor side intake port 21.
And the exhaust chamber 13 to form a ventilation path that bypasses the heat exchanger 1. A muffling material 22 is stretched on the inner surface of the partition box 10, and the outlet of the bypass ventilation passage 20 is normally closed by an opening / closing damper 23 as an air passage switching means. The opening / closing damper 23 is rotatably supported on the side where the bypass ventilation passage 20 and the communication port 19 are adjacent to each other, and
The damper driving device provided therein closes one of the communication port 19 and the bypass ventilation path 20 and opens the other. The damper drive device includes a swing arm 26 having one end connected to the drive device 24 and the other end connected to the back surface of the opening / closing damper 23 by a link 25. The tension spring 27 is mounted on the swing arm 26. Normally, the opening / closing damper 23 is biased to bypass the ventilation passage 20.
Is held in the closing position. A heat insulating material 28 is provided on the rear surface of the opening / closing damper 23, and when the outlet of the bypass ventilation passage 20 is closed against the upper surface of the partition box 10, the exhaust ventilation passage 8 formed on the upper surface of the partition box 10 is closed. The area of the air passage gradually increases toward the exhaust chamber 13 side.

A rectangular cylindrical slide chamber 29 which can be slid up and down is connected to an open part of a lower part of the casing 2 facing the heat exchanger 1, and a decorative panel 30 is provided so as to cover an opening at a lower end of the slide chamber 29. Is installed. A horizontal partition plate 31 is provided between each of the front and rear bevels on the upper surface of the heat exchanger 1 and each of the front and rear inner wall surfaces of the casing 2. A horizontal partition plate 32 is provided between the front surface of the casing 2 and the inner wall surface so that the partition plate 32 can be attached and detached by an operation from an open portion of the casing 2. Further, a flexible and expandable and contractable partition wall structure 3 is provided at the rear edge of the lower surface of the heat exchanger 1.
3 is provided in a hanging state, and the lower end thereof abuts on the back surface of the decorative panel 30 to separate the indoor-side suction port 21 from the indoor-side outlet 34. The decorative panel 30 is provided with a suction grille and a blowout grill that communicate with the indoor-side intake port 21 and the indoor-side outlet port 34, respectively, so as to face the room.

The air supply passage 5 has an outdoor side inlet 14 as an inlet end, and a communication port 17 from the air supply chamber 12 through the air supply blower 4.
To a part of the air supply passage 5 on the front side of the casing 2, further through the fluid passage 3 facing the substantially horizontal direction of the heat exchanger 1, and one of the air supply passages 5 on the rear side of the casing 2. Part to the indoor side outlet 34 on the lower surface of the casing 2,
This is configured as a series of ventilation passages having this as an outlet end, and a dust filter 35 is detachably mounted on the surface of the heat exchanger 1 facing the inlet of the fluid passage 3, and a high-performance filter 36 is detachably mounted on the surface of the heat exchanger 1 facing the outlet. It is installed. On the other hand, the exhaust ventilation passage 8
Passes through a fluid passage 6 which is directed to a substantially vertical direction of the heat exchanger 1 with the indoor side suction port 21 at a lower portion of the casing 2 as an inlet end, and from a part of the exhaust ventilation passage 8 on the top surface side of the casing 2. It reaches the exhaust chamber 13 via the communication port 19, reaches the outdoor air outlet 18 on the front surface of the casing 2 via the exhaust blower 7, and is configured as a series of ventilation paths having this as an outlet end. An air filter 37 for preventing clogging is detachably mounted on the surface of the passage 6 facing the entrance.

The heat exchange ventilator can supply outdoor air to the room through the heat exchanger 1 by the supply air passage 5, and simultaneously exhausts the room air to the outside of the room through the heat exchanger 1 by the exhaust passage 8. It is possible to perform heat exchange ventilation by simultaneous supply and exhaust while performing heat exchange. The indoor air that has exited the heat exchanger 1 flows from the communication port 19 of the partition box 10 toward the exhaust chamber 13, but the upper surface of the partition box 10 is inclined downward by the open / close damper 23 toward the exhaust chamber 13. Since it functions as a guide plate that smoothly guides the air flow to the exhaust chamber 13 side, wind noise and operation noise are reduced. When the driving device 24 of the damper driving device is operated to rotate the swing arm 26 against the bias of the tension spring 27,
The opening / closing damper 23 is pushed up by the link 25, the communication port 19 of the exhaust ventilation passage 8 is closed, and the bypass ventilation passage 20
Is released. When the bypass ventilation passage 20 is opened, the room air is sucked into the exhaust blower 7 through the bypass ventilation passage 20, bypassing the heat exchanger 1 from the indoor-side suction port 21, and is exhausted outside from the outdoor-side outlet 18. become. That is, ordinary ventilation without heat exchange is performed. The bypass ventilation passage 20 has a configuration in which the indoor-side suction port 21 is adjacent to the exhaust chamber 13 with the partition box 10 interposed therebetween, so that the bypass ventilation path 20 can be configured very simply.
It is difficult for the noise on the side to reach the room from the indoor side suction port 21, and it is possible to promote a reduction in noise.

The feature of this heat exchange ventilator is that the heat exchanger 1
Are incorporated in the casing 2 so that the two systems of the fluid passages 3 and 6 are oriented substantially horizontally and substantially vertically. Conventionally, since the diagonal line of the fore-edge is incorporated in the casing so as to be directed substantially in the horizontal direction and the substantially vertical direction, the cross-sectional shape of the air supply passage and the exhaust air passage in the portion where the heat exchanger is placed is substantially triangular. However, this embodiment has a substantially square shape. By adopting such a configuration, when the dimensions of the heat exchanger 1 and the air passage area of each ventilation path are the same, the height dimension of the casing 2 can be reduced, and thinning can be promoted. For example, the diagonal dimension of the small opening of the heat exchanger 1 is 200 mm, and the air passage area is 10 mm.
2,000 square mm, $ 2 in the conventional way
× 200 = 282.8 mm, but in the arrangement shown in this embodiment, 266.7 mm, which is about 1
A reduction in thickness of 6.1 mm is realized.

Although the ventilation passage has a rectangular cross-section, the surrounding length is longer than that of a triangle, and it seems disadvantageous in terms of pressure loss.
The suction distribution can be made uniform, whereby the pressure loss can be eliminated. The outside air inlet into the air supply passage 5 where the heat exchanger 1 is located is at the middle, and the outside air is taken in from the outdoor outside inlet 14 to the air supply passage 5 located at the middle by the air supply blower 4. It can be easily pushed in, and since it is a double suction type, it can be pushed in at a uniform wind speed, so that pressure loss can be suppressed. The exhaust blower 7 is also of a double suction type so that uniform suction is possible and the blowing performance is stabilized. In particular, by arranging the rotating shaft 16 of the electric motor of the air supply blower 4 that blows the heat exchanger 1 by pushing in substantially vertically, pressure loss relating to suction is improved,
Noise is also reduced. In addition, by installing the rotating shaft 16 of the motor of the exhaust blower 7 by suction substantially horizontally, the balance between suction from the motor side and suction from the non-motor side can be adjusted, and noise can be reduced.

Each of the dust filter 35, the high-performance filter 36, and the air filter 37
Can be detached without removing the heat exchanger 1 from the open portion below the dust filter 35, the high-performance filter 3
6. The air filter 37 can be easily cleaned. That is, if the partition plate 32 is removed as shown in FIG. 4, the dust filter 35 can be attached and detached from the open portion of the casing 2, and the high-performance filter 36 and the air filter 37 can be attached and detached from the open portion of the casing 2 as they are. The fact that the dust filter 35, the high-performance filter 36, and the air filter 37 can be attached and detached from the open portion of the casing 2 without operating the bulky heat exchanger 1 as described above means that the dust filter 35, the high-performance filter 36, and the air filter 37 can be installed in a narrow space such as the ceiling. This is very convenient for a heat exchange ventilator that has a lot of heat.

The outdoor air outlet 18 and the outdoor air inlet 1
The position of 4 does not have to be on the front side of the casing 2 and may be on the back side or the top side. In addition, as shown in FIG. 7, outdoor air is passed from the top to the bottom in the fluid passage 6 of the heat exchanger 1, which faces in the substantially vertical direction, and flows from the front side to the back side of the fluid passage 3 in the substantially horizontal direction. Even if a configuration of a ventilation path through which room air is passed is adopted, it is possible to promote the reduction in thickness of the device. However, in the case of this configuration, since the inflow side of the outdoor air into the heat exchanger 1 is a closed space, when the dust filter 35 is provided, the maintenance of the dust filter 35 cannot be performed unless the heat exchanger 1 is removed. Can occur.

[0021]

As is apparent from the above description of the embodiment, according to the first aspect of the present invention, it is possible to simplify the structure relating to the bypass ventilation passage while promoting the thinning of the heat exchange ventilator. , Reduce noise.

According to the second aspect of the present invention, the configuration of the bypass ventilation path can be simplified while promoting the thinning of the heat exchange ventilator, the noise is reduced, and the detachability of the air filter is improved.

According to the third aspect of the present invention, noise can be further reduced together with the effect according to the first or second aspect.

According to the fourth aspect of the present invention, in addition to the effects according to any one of the first to third aspects, the pressure loss relating to the suction of the blower is improved, and the noise can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing a heat exchange ventilation device according to an embodiment.

FIG. 2 is an exploded perspective view of a main part of the heat exchange ventilator according to the embodiment.

FIG. 3 is a right side view of FIG. 1;

FIG. 4 is an explanatory diagram showing an operation for attaching and detaching a filter in the heat exchange ventilation apparatus according to the embodiment.

FIG. 5 is a perspective view showing a partition box of the heat exchange ventilation device according to the embodiment.

FIG. 6 is a cross-sectional view of an exhaust chamber portion of the heat exchange ventilator according to the embodiment.

FIG. 7 is a configuration diagram illustrating another configuration of an air passage of the heat exchange ventilation device according to the embodiment;

FIG. 8 is a sectional configuration diagram of a conventional heat exchange ventilation device.

FIG. 9 is an explanatory view showing an operation at the time of maintenance of a conventional heat exchange ventilation device.

[Explanation of symbols]

1 heat exchanger, 2 casing, 3 fluid passage,
4 air supply blower, 5 air supply passage, 6 fluid passage,
7 exhaust blower, 8 exhaust ventilation path, 10 partition box,
Reference Signs List 12 air supply chamber, 13 exhaust chamber, 14 outdoor air inlet, 18 outdoor air outlet, 19 communication port, 20 bypass ventilation path, 21 indoor air inlet, 22 sound deadening material, 23 open / close damper, 32 partition plate, 34 rooms Inside outlet, 35 dust filter, 36 high-performance filter, 37 air filter.

Claims (4)

[Claims] 1. A part of a path is constituted by one fluid passage of a heat exchanger having a hexahedron structure, which is built in a casing having a hexahedron structure, and an air flow from an outdoor to an indoor is passed by a blower. Exhaust through which an air supply passage and a part of the passage are independent of the entire passage with respect to the supply air passage, the other fluid passage of the heat exchanger forms part of a passage, and an air flow from a room to the outside is blown by a blower. A heat exchange ventilator including a ventilation path, wherein the heat exchanger is disposed in the casing such that one fluid passage and the other fluid passage intersect in a substantially horizontal direction and a substantially vertical direction, The heat exchanger is provided with the blower for forming an air supply flow on one side of the small opening where the fluid passage does not face, and the blower for forming the exhaust air flow is provided on the other side, and the air supply passage is provided. An outlet on the indoor side, which is an outlet end, and the exhaust ventilation passage And an indoor side suction port which is an inlet end of the heat exchanger is formed separately on a lower surface of the casing facing a surface where one of the fluid passages of the heat exchanger opens, and the indoor side suction port and an exhaust flow are formed. A partition box that forms a bypass ventilation path that communicates with the suction side of the blower and a part of the exhaust ventilation path on the downstream side of the heat exchanger is provided on one fore edge side of the heat exchanger. Is provided with air path switching means for closing one of the bypass air path and the exhaust air path and opening the other. When the air path switching means closes the bypass air path, the partition is closed. A heat exchange ventilator having a configuration in which an air passage area of an exhaust air passage formed by a box gradually increases toward a suction side of the exhaust blower. 2. A part of a path is constituted by one fluid passage of a laminated, hexahedral heat exchanger incorporated in a hexahedral casing, and an air flow from an outdoor to an indoor is passed by a blower. Exhaust through which an air supply passage and a part of the passage are independent of the entire passage with respect to the supply air passage, the other fluid passage of the heat exchanger forms part of a passage, and an air flow from a room to the outside is blown by a blower. A heat exchange ventilator provided with a ventilation passage, wherein the heat exchanger is disposed in the casing with the fluid passage on the supply ventilation passage side substantially in the horizontal direction and the fluid passage on the exhaust ventilation passage side in the substantially vertical direction. The heat exchanger is provided with the blower for forming an air supply flow on one side of the small opening where the fluid passage does not face, and the blower for forming an exhaust air flow is provided on the other side, and the air supply and ventilation are provided. The indoor outlet at the outlet end of the road, An indoor suction port, which is an inlet end of the air passage, and a lower surface of the casing facing a surface on which the fluid passage on the exhaust air passage side of the heat exchanger is open, are configured separately. An air filter is detachably provided on the surface to be opened from the lower surface of the casing, and a bypass ventilation path that connects the indoor side suction port and a suction side of the blower that forms an exhaust flow, and a bypass ventilation path that communicates with the exhaust ventilation path. A partition box forming a part on the downstream side of the heat exchanger is provided on one side of the heat exchanger, and one of the bypass ventilation path and the exhaust ventilation path is closed and the other is closed. In the state where the air passage switching means closes the bypass air passage, the air passage area of the exhaust air passage formed by the partition box is smaller than that of the exhaust fan. Gradually toward the suction side Configuration and the heat exchange ventilator to be. 3. The heat exchange ventilator according to claim 1, wherein the partition box has a muffling structure. 4. The heat exchange ventilator according to claim 1, wherein the blower for forming the exhaust flow is a double suction type centrifugal blower.