JP2001153397A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently dehumidify while suppressing rising of a condensing pressure when reheat dried in a heating cycle. SOLUTION: In the air conditioner comprising a heat exchanger 20 and a blower 25 arranged in the casing 2a of an indoor unit 2, the exchanger 20 is constituted of a first indoor heat exchanger 21 and a second indoor heat exchanger 22 disposed to be superposed with each other by laminated heat exchangers. The exchanger 21 and the exchanger 22 are connected in series through an indoor expansion mechanism 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner, and more particularly to a device arrangement in an indoor unit suitable for performing a dehumidifying operation in which a decrease in room temperature is suppressed in a heating cycle.

[0002]

2. Description of the Related Art Conventionally, an air conditioner capable of performing a dehumidifying operation (hereinafter, referred to as reheating drying) while suppressing a decrease in room temperature is disclosed in, for example, Japanese Patent Publication No. 53-3580. In some cases, a reheat dry operation is performed in a cooling cycle in which refrigerant discharged from a compressor is circulated from the outdoor side to the indoor side. In the air conditioner capable of performing the reheat dry operation as described above, the indoor heat exchanger includes two heat exchangers for dehumidification (evaporator) and heat exchanger for reheating (reheater). It consists of a heat exchanger.

In the reheat drying in the cooling cycle, the outdoor expansion valve is fully opened, the refrigerant flows from the outdoor side to the indoor side, and is condensed by the reheater. By evaporation. At this time, since the room air passes through the reheater from the evaporator, it is dehumidified by the evaporator, and then heated by the reheater and blown out into the room.

[0004] However, when reheating and drying is performed in the cooling cycle as described above, since the refrigerant for reheating is first flown to the outdoor side, the refrigerant partially condensed on the outdoor side is reheated. Therefore, there is a problem that the amount of reheat is reduced and efficiency is deteriorated.

On the other hand, as described in JP-B-61-533, a reheat dry operation is performed in a heating cycle in which refrigerant discharged from a compressor is circulated from the indoor side to the outdoor side. There is also. When performing reheating drying in the heating cycle in this way, use the reheater as a condenser,
After passing through the condenser, the refrigerant is depressurized by the indoor expansion valve, evaporated by the dehumidifying evaporator, and further evaporated outside. At this time, since the room air passes through the condenser from the dehumidifying evaporator, it is heated after being dehumidified and blown out into the room.

[0006]

When reheating and drying is performed in a heating cycle as described above, high-pressure hot gas enters the reheater (condenser). Due to the small area of the vessel, the condensation pressure will increase. Therefore, if the opening degree of the indoor expansion valve is adjusted so as to prevent the condensing pressure from rising, the differential pressure across the expansion valve becomes small, and sufficient dehumidification cannot be achieved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to perform sufficient dehumidification while suppressing an increase in condensation pressure during reheating and drying in a heating cycle. Is to do so.

[0008]

According to the present invention, the stacked heat exchangers are arranged side by side so as to overlap in two rows, and an expansion mechanism is connected between them.

Specifically, a solution taken by the present invention is an air conditioner in which an indoor heat exchanger (20) and an indoor blower (25) are disposed in a casing (2a) of an indoor unit (2). It is intended for. Then, the indoor heat exchanger (20) is divided into a first indoor heat exchanger (21) and a second indoor heat exchanger (22) arranged so as to overlap each other by a laminated heat exchanger made of aluminum or the like. The first indoor heat exchanger (21) and the second indoor heat exchanger (22)
Are connected in series via an indoor expansion mechanism (23).

In the above configuration, the first indoor heat exchanger (2
Either 1) or the second indoor heat exchanger (22) is an evaporator for dehumidifying air
(21) and the other can be used for a reheater (22) for heating air.

In the above configuration, a centrifugal blower is used as the indoor blower (25), and the indoor heat exchanger (21,
22), the reheater (22) is a centrifugal blower (25) rather than the evaporator (21).
It is preferable to adopt a configuration arranged closer to the suction side.

In the above solution, when reheating and drying in the heating cycle is performed, one of the first indoor heat exchanger (21) and the second indoor heat exchanger (22) is provided with the discharge gas of the compressor. Is used as a reheater (condenser) (22) into which water flows, and the other is used as an evaporator (21) for dehumidifying air. The refrigerant discharged from the compressor passes through the reheater (22), is decompressed by the indoor expansion mechanism (23), is evaporated by the evaporator (21), and then evaporates outside the room. Circulate. At this time,
The room air passes through the reheater (22) from the evaporator (21), is heated after dehumidification, and is blown into the room.

[0013] In the above solution, a laminated heat exchanger which can be configured to be thin is used for the reheater (22) and the evaporator (21), and these are arranged side by side so as to overlap each other. In addition, the reheater (22), which is a condenser, can be configured to have a larger size than before, and as a result, an increase in condensing pressure can be suppressed.

When the reheater (22) is disposed near the suction side of the centrifugal blower (25), it is assumed that drain water generated during dehumidification in the evaporator (21) has flown to the blower (25). Also, the water droplets evaporate in the reheater (22).

[0015]

Therefore, according to the above means, when performing reheating drying in a heating cycle, the reheater (22), which is a condenser, can be made large, so that an increase in condensing pressure can be suppressed. There is no need to adjust the opening of the expansion mechanism (23) to reduce the differential pressure before and after, and as a result, it is possible to sufficiently perform dehumidification.

Further, if the reheater (22) is arranged on the suction side of the centrifugal blower (25), even if the drain water generated in the evaporator (21) flies to the blower (25), the water droplets are regenerated. Since the water is evaporated by the heater (22), it is possible to prevent water from splashing outside the machine.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a refrigerant circuit diagram of an air conditioner of the present embodiment constituted by connecting an indoor unit (2) to an outdoor unit (1). As shown, the outdoor unit (1) is provided with a compressor (3). And the discharge pipe (4) of the compressor (3),
The suction pipe (6) provided with the accumulators (5, 5)
Each is connected to the primary port of the first four-way switching valve (7).

The secondary port of the first four-way switching valve (7)
The first gas pipe (8) and the second gas pipe (9) are connected to each other, and the first gas pipe (8) is connected to one of the primary ports of the second four-way switching valve (10). I have. In addition, the second four-way switching valve (1
A first liquid pipe (11) is connected to the other of the primary ports of (0). The first liquid pipe (11) has a check valve bridge circuit (1).
2), a second liquid pipe (13), and an outdoor heat exchanger (15) provided with an outdoor fan (14) are connected in order, and this outdoor heat exchanger (15)
Is connected to the second gas pipe (9).

The secondary side port of the second four-way switching valve (10)
The gas-side relay pipe (16) and the liquid-side relay pipe (17) are connected. The relay pipes (16, 17) are connected to the indoor heat exchanger (20) disposed in the indoor unit (2) through the gas-side communication pipe (18) and the liquid-side communication pipe (19). ) Is connected.

The indoor heat exchanger (20) is connected to a gas-side connecting pipe.
It is divided into a first indoor heat exchanger (21) connected to (18) and a second indoor heat exchanger (22) connected to the liquid side communication pipe (19). These indoor heat exchangers (21, 22) are connected to each other in series via an intermediate pipe (24) provided with an electric expansion valve for dehumidification (indoor expansion mechanism) (23). Further, these indoor heat exchangers (21, 22) are provided along the ventilation path of the indoor air sucked into the indoor unit (2) when the indoor blower (25) is operated, and the first indoor heat exchanger (21). 21) and the second indoor heat exchanger (22) are installed in the indoor unit (2) in this order.

FIG. 2 shows a specific arrangement example. The casing (2a) of the indoor unit (2) has a suction port (2b) formed on the front surface, and an outlet (2c) formed on upper and lower side surfaces and left and right side surfaces (not shown). And the casing (2a)
Inside, a first indoor heat exchanger (21), a second indoor heat exchanger (22), and an indoor blower (25) are arranged in this order from the suction port (2b) side.

First indoor heat exchanger (21) and second indoor heat exchanger
Each of (22) is constituted by an aluminum laminated heat exchanger. These heat exchangers (21, 22) are arranged in two rows before and after so as to overlap each other.
The indoor expansion valve (23) is arranged below the 22). The indoor blower (25) is constituted by a centrifugal blower such as a turbo fan. In this arrangement, the first indoor heat exchanger (21) serves as an evaporator during reheating and drying, and the second indoor heat exchanger (22) serves as a reheater (condenser). Therefore,
In the indoor heat exchanger (20), the reheater (condenser) (22) is arranged closer to the suction side of the turbo fan (25) than the evaporator (21).

As shown in FIG. 3, each indoor heat exchanger (21, 22) has a plurality of flat porous heat transfer tubes (28) between upper and lower headers (26, 27) (see FIG. 4). Are arranged at regular intervals,
Corrugated fins (29) (see FIG. 5) are arranged between the heat transfer tubes (28).

The flat porous heat transfer tube (28) is formed by cutting a long member formed by extruding an aluminum material into a predetermined length, and has a large number of small holes (2) penetrating vertically.
8a) are arranged in a line. The upper end of each hole (28a) communicates with the upper header (26), and the lower end communicates with the lower header (27). The corrugated fins (29) are corrugated fins, and are disposed between the heat transfer tubes (28) to increase the heat transfer area.

In the above configuration, the pipe connection of each heat exchanger (21, 22) is performed as follows. For example, one end of the upper header (26) of the first indoor heat exchanger (21) is
8) is connected and the other end is closed. The first indoor heat exchanger (21) and the second indoor heat exchanger (22) have a lower header (27).
Are connected to each other via an intermediate pipe (24) provided with an electric expansion valve for dehumidification (23), and the other ends are closed. Further, the upper header (2) of the second indoor heat exchanger (22)
The liquid side communication pipe (19) is connected to one end of 6), and the other end is closed. As described above, the circuit configuration of FIG. 1 can be realized.

On the other hand, as shown in FIG. 1, the check valve bridge circuit (12) includes a first inlet / outlet port (12a) to which a first liquid pipe (11) is connected, and a second liquid pipe (13). The inlet pipe (31) and the outlet pipe (32) are connected in parallel with each other between the second inlet / outlet port (12b) and the first inlet / outlet port (12b). Stop valves (33, 34) are connected to the outlet pipe (32) by the third and fourth check valves (35, 3).
6) are arranged. A rectifying inlet port (12c) between the first check valve (33) and the second check valve (34) in the inlet pipe (31) and a third port in the outlet pipe (32).
A rectification outlet port (1) between the check valve (35) and the fourth check valve (36).
2d), a rectifying pipe (37) is provided.

The first check valve (33) and the second check valve (34) are respectively connected to the first port (12a) and the second port (12).
The inlet pipe (31) is provided in a direction allowing the flow of the refrigerant from the b) side toward the rectification inlet port (12c). Also,
The third check valve (35) and the fourth check valve (36) control the flow of the refrigerant from the rectifying outlet port (12d) side toward the first inlet / outlet port (12a) and the second inlet / outlet port (12b), respectively. The outlet pipe (32) is provided in an allowable direction.

The rectification pipe (37) has a rectification inlet port (1
2c) From the side, a supercooled heat exchanger (3
8) and a first electric expansion valve (39) whose opening is controlled so as to function as a pressure reducing mechanism during the cooling / heating operation is provided in order. The rectification inlet port (12c) and the subcooling heat exchanger (3
A first injection pipe (41) provided with a second electric expansion valve (40) is provided between the outer pipe inlet port and the outer pipe inlet port of (8). The outer pipe outlet port of the subcooling heat exchanger (38) is connected to the suction port of the compressor (3) via a second injection pipe (42).

With this configuration, the first liquid pipe (11)
Refrigerant flowing through the check valve (33) or the second liquid pipe (13)
The refrigerant flowing from the side through the second check valve (34) flows from the rectification inlet port (12c) according to the opening ratio between the first electric expansion valve (39) and the second electric expansion valve (40). Part of the flow branches to the first injection pipe (41). When the divided refrigerant passes through the subcooling heat exchanger (38), it flows from the rectifying inlet port (12c) through the inner pipe of the subcooling heat exchanger (38) to the rectifying outlet port (12d).
Heat exchange with the main refrigerant flowing to the
It is sucked into the compressor (3) through the injection pipe (42).

Further, a first liquid pipe (11) is provided in the refrigerant circuit.
A bypass pipe (43) is provided between the suction pipe (6). The bypass pipe (43) is provided with a bypass opening / closing valve (44) formed of a one-way solenoid valve.

-Operation- Next, the operation of the air conditioner will be described. <Heating operation> In this air conditioner, in the heating operation, the electric expansion valve for dehumidification (23) is fully opened, the bypass on-off valve (44) is closed, and the first four-way switching valve (7) and the second Four-way switching valve (10)
Are switched to the positions shown by the solid lines in FIG. 1, and the compressor (3) is driven in this state.

At this time, if the second electric expansion valve (40) is also in the fully closed state, the refrigerant discharged from the compressor (3) will receive the first four-way switching valve as shown by the solid arrow in the drawing. (7) First gas pipe
(8), supplied to the indoor unit (2) side via the second four-way switching valve (10) and the gas-side relay pipe (16), and transferred from the first indoor heat exchanger (21) to the second indoor heat exchanger. After passing through the vessel (22) in order, the liquid side relay pipe (17), the second four-way switching valve (10), the first liquid pipe (11), the first check valve (33), the supercooling heat exchanger (38), the first electric expansion valve (39), the fourth check valve (36), and the outdoor heat exchanger through the second liquid pipe (13).
(15), and after passing through the outdoor heat exchanger (15), is sucked into the compressor (3) via the second gas pipe (9) and the first four-way switching valve (7). You.

In this heating cycle, the first and second indoor heat exchangers (21, 22) function as condensers, and the outdoor heat exchanger (15) functions as an evaporator, and releases the amount of heat absorbed from outside to the room. Then, indoor heating is performed. During the heating operation, the first electric expansion valve (39) is opened so that the evaporative refrigerant drawn into the compressor (3) through the outdoor heat exchanger (15) is maintained at a predetermined degree of superheat. The degree is controlled. <Cooling operation> On the other hand, the cooling operation is performed by driving the compressor (3) by switching the first four-way switching valve (7) to the switching position shown by the broken line in the figure. At this time, the refrigerant discharged from the compressor (3) is supplied to the first four-way switching valve (7), the outdoor heat exchanger (15), the second liquid pipe (13), It passes through the second check valve (34), the supercooling heat exchanger (38), the first electric expansion valve (39), the third check valve (35), and the first liquid pipe (11) in order, and After sequentially passing through the second indoor heat exchanger (22) and the first indoor heat exchanger (21) from the second four-way switching valve (10) and the liquid side relay pipe (17), the gas side relay pipe (16) The gas is sucked into the compressor (3) via the second four-way switching valve (10), the first gas pipe (8), and the first four-way switching valve (7).

In this cooling cycle, the outdoor heat exchanger
(15) functions as a condenser, and the second and first indoor heat exchangers (22, 21) function as evaporators, and the amount of heat sucked from the room is released to the outside to perform indoor cooling. During the cooling operation, the first electric expansion valve (39) is operated so that the evaporated refrigerant passing through the first indoor heat exchanger (21) and being sucked into the compressor (3) is maintained at a predetermined degree of superheat. ) Is controlled. <Gas Injection> For example, when the second electric expansion valve (40) is opened during the heating operation, the high-temperature and high-pressure liquid refrigerant condensed in the first and second indoor heat exchangers (21, 22) becomes the first liquid. Tube (1
1) When passing through the first check valve (33) and reaching the rectifying inlet port (12c), the first electric expansion valve (39) and the second electric expansion valve (4
A part of the liquid refrigerant is diverted to the first injection pipe (41) in accordance with the opening degree ratio with respect to (0). The divided liquid refrigerant is decompressed by the throttle action when passing through the second electric expansion valve (40), becomes a low-temperature low-pressure gas-liquid mixed refrigerant, and flows into the outer pipe of the supercooling heat exchanger (38).

On the other hand, a rectification pipe is connected from the rectification inlet port (12c).
The main refrigerant flowing through (37) remains at a high temperature and a high pressure when flowing into the subcooling heat exchanger (38), and the subcooling heat exchanger (38) Heat exchange occurs during the passage through. As a result, the divided refrigerant absorbs heat and is gasified, and is compressed via the second injection pipe (42).
Inhaled. In a state where the temperature of the main refrigerant decreases and the degree of supercooling increases, the main refrigerant becomes a low-temperature and low-pressure gas-liquid mixed refrigerant by a throttling effect when passing through the first electric expansion valve (39). As the degree of supercooling is increased as described above, the overall refrigerant circulation amount is increased, thereby improving the heating capacity. Note that, even during the operation in the cooling cycle, by opening the second electric expansion valve (40), it is possible to achieve an operation state in which the cooling capacity is further improved by the same operation as described above. <Heating cycle reheat drying> Next, the first four-way switching valve
The dehumidifying operation in the heating cycle in which (7) is located at the switching position indicated by the solid line in the figure will be described. At this time, the second four-way switching valve (10) switches to the switching position indicated by the broken line in the figure. The first and second electric expansion valves (39, 40) are fully closed, while the bypass on-off valve (44) is opened. Then, the opening degree of the electric expansion valve for dehumidification (23) is controlled so as to function as a pressure reducing mechanism. Further, the outdoor fan (14) is set to the ultra low speed rotation state or the stop state.

In this operating state, the refrigerant discharged from the compressor (3) receives the first four-way switching valve (7), the first gas pipe (8), and the second refrigerant as indicated by the one-dot chain line in the figure. It flows into the second indoor heat exchanger (22), which is a reheater (condenser), via the two-way switching valve (10) and the liquid side relay pipe (17). Then, after passing through the second indoor heat exchanger (22) and radiating heat and condensing, the pressure is reduced by the electric expansion valve for dehumidification (23), and the first indoor heat exchanger (2
When passing through 1), it absorbs heat and evaporates. Thereafter, the gas flows into the first liquid pipe (11) from the gas-side relay pipe (16) and the second four-way switching valve (10), and from the first liquid pipe (11), the bypass pipe (43) and the suction pipe.
It is sucked into the compressor via (6).

Therefore, the indoor air sucked into the indoor unit (2) by the operation of the indoor blower (25) is first cooled when passing through the first indoor heat exchanger (21), which is an evaporator, to condense moisture. And dehumidified. Thereafter, the low-temperature indoor air is reheated when passing through the second indoor heat exchanger (22), which is a reheater. As a result, air whose humidity has been reduced without changing the temperature is blown into the room, and the reheating dry operation is performed. <Cooling cycle reheating drying> In this air conditioner, the dehumidifying operation in the cooling cycle in which the first four-way switching valve (7) is located at the switching position indicated by the broken line in the figure is also performed appropriately. It is possible. At this time, the second four-way switching valve
(10) is located at the switching position indicated by the solid line in the figure, and
The first electric expansion valve (39) is fully opened, and the second electric expansion valve (40) is fully closed. The bypass on-off valve (44) is closed, and the opening of the dehumidifying electric expansion valve (23) is controlled to function as a pressure reducing mechanism. Further, the outdoor fan (14) is set to the ultra low speed rotation state or the stop state.

In this operating state, the refrigerant discharged from the compressor (3) passes through the first four-way switching valve (7) and the second gas pipe (9) as indicated by the two-dot chain line arrow in the figure. Via outdoor heat exchanger (15)
Flows into. At this time, by keeping the outdoor fan (14) in an ultra-low speed operation or in a stopped state, condensation of the refrigerant when passing through the outdoor heat exchanger (15) is suppressed, and thereafter, the refrigerant is cooled in the same manner as in the cooling operation. It flows into the 2nd indoor heat exchanger (22) via a path. The refrigerant condenses when passing through the second indoor heat exchanger (22), and then evaporates when passing through the first indoor heat exchanger (21). Thereafter, the gas-side relay pipe (16) and the second four-way switching valve (1
0), the gas is sucked into the compressor (3) via the first gas pipe (8), the first four-way switching valve (7), and the suction pipe (6).

Therefore, also in this case, the indoor blower (25)
The indoor air sucked into the indoor unit (2) by the operation of (1) is cooled when passing through the first indoor heat exchanger (21), is reheated when passing through the second indoor heat exchanger (22), and is reheated. Thermal dry operation is performed.

-Effects of Embodiment- As described above, in the air conditioner of this embodiment,
A first indoor heat exchanger (21) which is an evaporator on the upstream side and a second indoor heat exchanger (a reheater (condenser) on the downstream side along the direction of air flow in the indoor unit (2). By disposing the 22), the reheating dry operation in which the room air is cooled once, dehumidified, and then reheated by switching the four-way switching valves (7, 10),
It can be performed by both the cooling cycle and the heating cycle. Thereby, for example, by appropriately selecting the cooling cycle dehumidifying operation and the heating cycle dehumidifying operation according to environmental changes such as the outside air temperature, the reheating dry operation with good reheating capability and dehumidifying efficiency is performed more stably. be able to.

In particular, in the present embodiment, the reheater (22) and the evaporator (21) use a laminated heat exchanger that can be configured to be thin, and these are arranged side by side, so The second indoor heat exchanger (22), which is a heater, can be configured in a larger size than before. As a result, when performing reheat drying in the heating cycle, the increase in the condensing pressure can be suppressed, so that it is not necessary to adjust the opening degree of the indoor expansion mechanism (23) to reduce the differential pressure before and after, and as a result, Dehumidification can be sufficiently performed by the heating cycle dehumidification operation.

A first indoor heat exchanger (21), which is an evaporator,
Since the second indoor heat exchanger (22), which is a reheater, is disposed closer to the suction side of the turbo fan (25), the evaporator (21)
Even if the drain water generated at the time of dehumidification flies to the turbo fan (25) side, the water droplets will evaporate in the reheater (22), so that it is possible to prevent water from splashing outside the machine.

[0044]

Other Embodiments of the Invention The present invention may be configured as follows with respect to the above embodiment.

For example, in the above embodiment, the reheating and drying in the cooling cycle can be performed in addition to the reheating and drying in the heating cycle. However, the reheating and drying in the cooling cycle are not necessarily performed. You may. By doing so, the circuit configuration can be further simplified.

[Brief description of the drawings]

FIG. 1 is a refrigerant circuit diagram of an air conditioner according to an embodiment of the present invention.

FIG. 2 is a device layout diagram in an indoor unit in the air-conditioning apparatus of FIG.

FIG. 3 is a perspective view showing an external shape of a laminated aluminum heat exchanger used in the indoor unit of FIG.

FIG. 4 is a partial perspective view showing a flat perforated heat transfer tube of the laminated aluminum heat exchanger of FIG. 3;

FIG. 5 is a partial perspective view showing a corrugated fin of the laminated aluminum heat exchanger of FIG. 3;

[Explanation of symbols]

 (1) Outdoor unit (2) Indoor unit (2a) Casing (2b) Inlet (2c) Outlet (3) Compressor (14) Outdoor fan (15) Outdoor heat exchanger (20) Indoor heat exchanger (21 ) 1st indoor heat exchanger (evaporator) (22) 2nd indoor heat exchanger (reheater (condenser)) (23) Electric expansion valve (indoor expansion mechanism) (25) Turbo fan (indoor blower (centrifugal) Blower)) (26,27) Header (28) Flat perforated heat transfer tube (29) Corrugated fin

Continuing on the front page (72) Inventor Yutaka Shibata 1304 Kanaokacho, Sakai City, Osaka Prefecture Daikin Industries, Ltd. Inside the Kanaoka Plant of Sakai Seisakusho Co., Ltd. in the factory

Claims (3)

[Claims] An air conditioner comprising an indoor heat exchanger (20) and an indoor blower (25) disposed in a casing (2a) of an indoor unit (2), wherein the indoor heat exchanger (20) ) Are connected to the first indoor heat exchanger (21) and the second indoor heat exchanger (21) arranged so as to overlap each other by the stacked heat exchanger.
An air conditioner comprising an indoor heat exchanger (22), wherein the first indoor heat exchanger (21) and the second indoor heat exchanger (22) are connected in series via an indoor expansion mechanism (23). . 2. One of the first indoor heat exchanger (21) and the second indoor heat exchanger (22) is constituted by an evaporator (21) for air dehumidification, and the other is a reheater for air heating. The air conditioner according to claim 1, wherein the air conditioner is configured as (22). 3. The indoor blower (25) is constituted by a centrifugal blower, and the indoor heat exchanger (21, 22) is a reheater rather than an evaporator (21).
The air conditioner according to claim 2, wherein the (22) is disposed near the suction side of the centrifugal blower (25).