AU2007232984A1

AU2007232984A1 - Outdoor unit

Info

Publication number: AU2007232984A1
Application number: AU2007232984A
Authority: AU
Inventors: Katsunori Murata; Hideki Sangenya
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2006-03-31
Filing date: 2007-03-29
Publication date: 2007-10-11
Anticipated expiration: 2027-03-29
Also published as: EP2012078A1; JP2007292439A; EP2012078A4; AU2007232984B2; WO2007114243A1; JP4270274B2

Description

Applicant: DAIKIN INDUSTRIES, LTD. Title: OUTDOOR UNIT PCT Application No.: PCT/JP2007/056847 TRANSLATION VERIFICATION I hereby verify that the attached papers are a true English translation of the International Application identified above as originally filed. The undersigned declares further that all statements made herein of my own knowledge are true and that all statements made on information and belief are believed to be true. October 7, 2008 Hidetada KATO SPECIFICATION OUTDOOR UNIT TECHNICAL FIELD The present invention relates to an outdoor unit of an air conditioner that includes an 5 outdoor fan that applies air to an outdoor heat exchanger to promote heat exchange and which controls the rotational speed of the outdoor fan during frost formation on the outdoor heat exchanger. BACKGROUND ART An outdoor heat exchanger and an outdoor fan that generates an air flow are LO disposed inside an outdoor unit of an air conditioner. During heating operation, the outdoor heat exchanger becomes an evaporator, and as operating time elapses, frost begins to cover the surface of the outdoor heat exchanger. When frost formation further progresses, ventilation resistance occurs, and the potential for this to lead to performance degradation is high. In order to prevent this performance degradation, control for increasing input to the L5 motor that causes the outdoor fan to rotate and maintaining the rotational speed at a constant or increasing the rotational speed is widely employed (e.g., see Patent Document 1). <Patent Document 1> JP-A No. 2004-218936 DISCLOSURE OF THE INVENTION <Problem that the Invention is to Solve> W0 However, when the outdoor fan is maintained at the same rotational speed while ventilation resistance is large, sometimes the blowing noise of the outdoor fan increases and imparts a feeling of unpleasantness to the user. Further, although an increase in the blowing noise can be eliminated by performing defrosting operation early, operating efficiency drops, so this is not preferred. 5 It is an object of the present invention to provide an outdoor unit of an air conditioner that can suppress the blowing noise of a fan without lowering operating efficiency. <Means for Solving the Problem> An outdoor unit pertaining to a first aspect of the present invention is an outdoor unit 30 of an air conditioner to which an indoor unit is connected, with the outdoor unit comprising an outdoor heat exchanger, an outdoor fan and a controller. The outdoor heat exchanger performs heat exchange with air as an evaporator during heating operation. The outdoor fan generates an air flow that passes a surface of the outdoor heat exchanger. The controller performs in-frost fan control for lowering the rotational speed of the outdoor fan when frost -1

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formation on the outdoor heat exchanger is detected or estimated. In this outdoor unit, the amount of increase in the blowing noise is small even when ventilation resistance increases because of frost formation. For this reason, unpleasant noise is suppressed. 5 An outdoor unit pertaining to a second aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein the in-frost fan control is not executed until a predetermined amount of time elapses after the start of heating operation. Here, heating operation is maintained for a predetermined amount of time, so warm 10 air can be provided even when operation is started in low outdoor air. An outdoor unit pertaining to a third aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein lowering a target rotational speed of the outdoor fan that is set beforehand is included in the in-frost fan control. 15 Here, the rotational speed of the outdoor fan drops during frost formation and the amount of increase in the blowing noise becomes small. For this reason, noise is suppressed. An outdoor unit pertaining to a fourth aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein lowering an upper 20 limit of an input value that is supplied to the outdoor fan is included in the in-frost fan control. Here, the rotational speed of the outdoor fan drops during frost formation and the amount of increase in the blowing noise becomes small. For this reason, noise is suppressed. 25 An outdoor unit pertaining to a fifth aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and an evaporating temperature of the outdoor heat exchanger falls below a predetermined temperature. 30 Here, frost formation is detected without having to use a special device, and the blowing noise is suppressed. An outdoor unit pertaining to a sixth aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating -2operation and the outdoor air temperature falls below a predetermined temperature. Here, frost formation is detected without having to use a special device, and the blowing noise is suppressed. An outdoor unit pertaining to a seventh aspect of the present invention comprises the 5 outdoor unit pertaining to the first aspect of the present invention, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and a low pressure side falls below a predetermined pressure. Here, frost formation is detected without having to use a special device, and the blowing noise is suppressed. LO An outdoor unit pertaining to an eighth aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and an ON time ratio during one cycle of a drive voltage that is supplied to the outdoor fan exceeds an ON time ratio that is set beforehand. [5 Here, frost formation is detected without having to use a special device, and the blowing noise is suppressed. An outdoor unit pertaining to a ninth aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating 20 operation and the rotational speed of the outdoor fan falls below a target rotational speed that is set beforehand. Here, frost formation is detected without having to use a special device, and the blowing noise is suppressed. An outdoor unit pertaining to a tenth aspect of the present invention comprises the 25 outdoor unit pertaining to the first aspect of the present invention, wherein an average value of an input that is supplied to the outdoor fan is calculated at a previous stage when the in-frost fan control is started, and while the in-frost fan control is being executed, the average value of the input is supplied to the outdoor fan. Here, the rotational speed of the outdoor fan automatically drops because of 30 ventilation resistance resulting from frost formation. For this reason, the amount of increase in the blowing noise becomes small. An outdoor unit pertaining to an eleventh aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein when the in-frost fan control is being performed, defrosting operation is started when the rotational -3speed of the outdoor fan falls below a lower limit rotational speed that is set beforehand. In this outdoor unit, heating capability drops because of the in-frost fan control, so the rotational speed of the outdoor fan is monitored to prevent heating capability from dropping below an acceptable range. For this reason, when frost formation progresses to an 5 extent that an increase in the blowing noise cannot be suppressed, defrosting operation is timely started, so heating performance recovers before the user is caused to feel insufficient heating. An outdoor unit pertaining to a twelfth aspect of the present invention comprises the outdoor unit pertaining to the first aspect of the present invention, wherein when the in-frost 10 fan control is being performed, defrosting operation is started when a difference between the rotational speed of the outdoor fan and the rotational speed of the outdoor fan before frost formation exceeds an acceptable value that is set beforehand. In this outdoor unit, heating capability drops because of the in-frost fan control, so the difference between the rotational speed of the outdoor fan and the rotational speed of the 15 outdoor fan before frost formation is monitored to prevent heating capability from dropping below an acceptable range. For this reason, when frost formation progresses to an extent that an increase in the blowing noise cannot be suppressed, defrosting operation is timely started, so heating performance recovers before the user is caused to feel insufficient heating. An outdoor unit pertaining to a thirteenth aspect of the present invention comprises 20 the outdoor unit pertaining to the first aspect of the present invention, wherein when the in-frost fan control is being performed, defrosting operation is started when an integrated value of a difference between the rotational speed of the outdoor fan and the rotational speed of the outdoor fan before frost formation exceeds an acceptable integrated value that is set beforehand. 25 In this outdoor unit, heating capability drops because of the in-frost fan control, so the integrated value of the difference between the rotational speed of the outdoor fan before frost formation and the current rotational speed is monitored to prevent heating capability from dropping below an acceptable range. For this reason, when frost formation progresses to an extent that an increase in the blowing noise cannot be suppressed, defrosting operation 30 is timely started, so heating performance recovers before the user is caused to feel insufficient heating. Further, because judgment to start defrosting operation is made based on the integrated value of the rotational speed difference, defrosting operation is not erroneously started even when a gusty backwind acts on the outdoor fan such that the rotational speed instantaneously sharply drops or even when the power source voltage drops such that the -4rotational speed of the outdoor fan sharply drops. <Effects of the Invention> In the outdoor unit pertaining to the first aspect of the present invention, the amount of increase in the blowing noise is small even when ventilation resistance increases because 5 of frost formation. For this reason, unpleasant noise is suppressed. In the outdoor unit pertaining to the second aspect of the present invention, heating operation is maintained for a predetermined amount of time, so warm air can be provided even when operation is started in low outdoor air. In the outdoor unit pertaining to the third aspect of the present invention and the 10 fourth aspect of the present invention, the rotational speed of the outdoor fan drops during frost formation and the amount of increase in the blowing noise becomes small. For this reason, noise is suppressed. In the outdoor unit pertaining to the fifth aspect of the present invention to the ninth aspect of the present invention, frost formation is detected without having to use a special 15 device, and the blowing noise is suppressed. In the outdoor unit pertaining to the tenth aspect of the present invention, the rotational speed of the outdoor fan automatically drops because of ventilation resistance resulting from frost formation. For this reason, the amount of increase in the blowing noise becomes small. 20 In the outdoor unit pertaining to the eleventh aspect of the present invention to the thirteenth aspect of the present invention, when frost formation progresses to an extent that an increase in the blowing noise cannot be suppressed, defrosting operation is timely started, so heating performance recovers before the user is caused to feel insufficient heating. BRIEF DESCRIPTION OF THE DRAWINGS 25 FIG. 1 is a refrigerant circuit of an air conditioner that includes an outdoor unit pertaining to an embodiment of the present invention. FIG. 2 is a control block diagram of the air conditioner that includes the same outdoor unit FIG. 3 is a graph showing the relationship between outdoor fan input, outdoor fan rotational speed and outdoor fan blowing noise in a case where the outdoor unit is controlled by in-frost 30 normal control. FIG. 4 is a graph showing the relationship between outdoor fan input, outdoor fan rotational speed and outdoor fan blowing noise in a case where the outdoor unit is controlled by in-frost fan control. FIG. 5 is a flowchart of in-frost fan control. - 5- FIG. 6 is a graph showing the relationship between outdoor fan input, outdoor fan rotational speed, outdoor fan blowing noise and frost formation amount in a case where in-frost fan control is continued. FIG. 7 is a flowchart from the start of in-frost fan control to until the start of defrosting 5 control. FIG. 8 is a flowchart from the start of in-frost fan control to until the start of defrosting control of an outdoor unit pertaining to a first modification of the embodiment of the present invention. FIG. 9 is a flowchart from the start of in-frost fan control to until the start of defrosting 10 control of an outdoor unit pertaining to a second modification of the embodiment of the present invention. <Description of the Reference Numerals> 1 Air Conditioner 2 Outdoor Unit 15 3 Indoor Unit 4 Controller 13 Outdoor Heat Exchanger BEST MODES FOR CARRYING OUT THE INVENTION <Configuration of Air Conditioner> 20 FIG. 1 shows a refrigerant circuit of an air conditioner that includes an outdoor unit pertaining to an embodiment of the present invention. An air conditioner I is a multi-type air conditioner and has a configuration where plural indoor units 3 are connected in parallel with respect to one outdoor unit 2. A refrigerant circuit 10 of the air conditioner 1 is one where mainly a compressor 11, a four-way switch valve 12, an outdoor heat exchanger 13, 25 expansion valves 14 and indoor heat exchangers 16 are connected in order, and becomes a vapor compression type refrigeration cycle. Here, the compressor II is a variable capacity inverter compressor that performs rotational speed control by an inverter. Further, an accumulator 20 that separates liquid refrigerant and gas refrigerant is disposed on a suction pipe side of the compressor 11. 30 The compressor 11, the four-way switch valve 12, the outdoor heat exchanger 13 and the expansion valves 14 are included in the outdoor unit 2, and the indoor heat exchangers 16 are included in the indoor units 3. Further, the four-way switch valve 12 and the indoor heat exchangers 16 are interconnected by refrigerant communication pipes 17a, and the expansion valves 14 and the indoor heat exchangers 16 are interconnected by -6refrigerant communication pipes 17b. The refrigerant communication pipes 17a and 17b are disposed between the outdoor unit 2 and the indoor units 3. A gas side stop valve 18 and a liquid side stop valve 19 are disposed in the refrigerant circuit inside the outdoor unit 2. The gas side stop valve 18 is disposed on the four-way switch valve 12 side, and the liquid side 5 stop valve 19 is disposed on the expansion valves 14 side. The refrigerant communication pipes 17a are connected to the gas side stop valve 18, and the refrigerant communication pipes 17b are connected to the liquid side stop valve 19. These stop valves 18 and 19 are placed in a closed state when the outdoor unit 2 and the indoor units 3 are to be installed. Then, the stop valves 18 and 19 are placed in an opened state after the outdoor unit 2 and the 10 indoor units 3 have been installed on-site and the refrigerant communication pipes 17a and the refrigerant communication pipes 17b have been connected to the stop valves 18 and 19. Further, an outdoor fan 29 that generates an air flow in order to promote heat exchange between air and the outdoor heat exchanger 13 is disposed in the outdoor unit 2. Further, the air conditioner I that includes the outdoor unit 2 of the present 15 embodiment is disposed with many temperature sensors that comprise thermistors. An outdoor temperature sensor 102 detects the ambient temperature where the outdoor unit 2 is installed, and a discharge pipe temperature sensor 111 is attached to a discharge pipe of the compressor 11 and detects a discharge pipe temperature To. An evaporating temperature sensor 113 during heating operation is attached to the outdoor heat exchanger 13 and detects 20 an evaporating temperature Te, and liquid pipe temperature sensors 117 are attached to exit sides during heating operation of the indoor heat exchangers 16 and detect a liquid pipe temperature TI. Further, a low pressure side pressure sensor 213 that detects a low pressure side pressure is disposed between the four-way switch valve 12 and the outdoor heat exchanger 13. 25 A controller 4 controls operation of the air conditioner I on the basis of the detected values of these temperature sensors and the detected value of the pressure sensor. <Operation of Air Conditioner> (Cooling Operation) Next, operation of this air conditioner 1 will be described. During cooling 30 operation, the four-way switch valve 12 is held in a state indicated by solid lines in FIG 1. High-temperature high-pressure gas refrigerant that has been discharged from the compressor 11 flows into the outdoor heat exchanger 13 via the four-way switch valve 12, exchanges heat with outdoor air, and condenses/liquefies. The refrigerant that has liquefied is depressurized to a predetermined low pressure by the expansion valves 14, exchanges heat with indoor air -7in the indoor heat exchangers 16, and evaporates. Then, the indoor air that has been cooled by the evaporation of the refrigerant is blown out into the indoors by unillustrated indoor fans and cools the indoors. Further, the refrigerant that has evaporated and gasified in the indoor heat exchangers 16 returns to the outdoor unit 2 through the refrigerant communication pipes 5 17a and is sucked into the compressor 11. (Heating Operation) During heating operation, the four-way switch valve 12 is held in a state indicated by dash lines in FIG. 1. High-temperature high-pressure gas refrigerant that has been discharged from the compressor 11 flows into the indoor heat exchangers 16 of the indoor 10 units 3 via the four-way switch valve 12, exchanges heat with the indoor air, and condenses/liquefies. The indoor air that has been heated by the condensing of the refrigerant is blown out into the indoors by the indoor fans and heats the indoors. The refrigerant that has liquefied in the indoor heat exchangers 16 returns to the outdoor unit 2 through the refrigerant communication pipes 17b. The refrigerant that has returned to the 15 outdoor unit 2 is depressurized to a predetermined low pressure by the expansion valves 14, exchanges heat with the outdoor air in the outdoor heat exchanger 13, and evaporates. Then, the refrigerant that has evaporated and gasified in the outdoor heat exchanger 13 is sucked into the compressor 11 via the four-way switch valve 12. <Outdoor Fan of Outdoor Unit> 2 0 The outdoor fan 29 is disposed with a motor 29a. The motor 29a is a long-lifespan DC brushless motor and can change the rotational speed by controlling (DUTY controlling) the ON time ratio (DUTY ratio) during one cycle of a power source input. The rotational speed is detected by a rotational speed sensor 129 comprising a Hall IC that is disposed on the motor 29a. 2 5 For example, when ventilation resistance increases because of frost formation on the outdoor heat exchanger 13, the rotational speed of the outdoor fan 29 drops, but this drop in the rotational speed is detected by the rotational speed sensor 129. Further, when the DUTY ratio is increased, the input that is supplied to the motor 29a of the outdoor fan 29 increases, so the rotational speed of the outdoor fan 29 increases. 30 In normal control, the controller increases/decreases the input in order to hold the rotational speed of the outdoor fan 29 at a constant and, with respect to increasing/decreasing the rotational speed, increases/decreases outdoor fan input to try to maintain a constant rotational speed. FIG. 3 is a showing "the relationship between outdoor fan input, outdoor fan rotational speed and outdoor fan blowing noise in a case where the outdoor unit is -8controlled by in-frost normal control", with the horizontal axis representing elapsed time after the start of heating operation and with the vertical axes representing, in order from the bottom, outdoor fan input, outdoor fan rotational speed and outdoor fan blowing noise. When a predetermined amount of time TD passes after heating operation has been started, frost 5 formation on the outdoor heat exchanger 13 begins and ventilation resistance begins to increase. In the case of normal control, the controller increases the outdoor fan input to try to maintain the rotational speed of the outdoor fan 29 at a constant such that the rotational speed does not drop because of ventilation resistance. For this reason, the blowing noise sharply increases. 10 <In-frost Fan Control> FIG. 2 is a control block diagram of the air conditioner 1 that includes the outdoor unit 2 of the present embodiment. In FIG. 2, the controller 4 receives, by a frost formation detector 41, the detected values from the outdoor temperature sensor 102, the evaporating temperature sensor 113, the outdoor fan rotational speed sensor 129 and the low pressure side 15 pressure sensor 213, performs detection or estimation of frost formation on the outdoor heat exchanger 13, and controls the outdoor fan 29 via an outdoor fan controller 42. The controller 4 maintains the outdoor fan input at a constant to ensure that the outdoor fan rotational speed drops when frost formation on the outdoor heat exchanger 13 begins and ventilation resistance begins to increase in order to prevent an increase in the 20 blowing noise of the outdoor fan 29. This is in-frost fan control, and the amount of increase in the blowing noise is suppressed thereby. FIG. 4 is a graph showing the "relationship between outdoor fan input, outdoor fan rotational speed and outdoor fan blowing noise in a case where the outdoor unit is controlled by in-frost fan control", with the horizontal axis representing elapsed time after the start of 25 heating operation and the vertical axes representing, in order from the bottom, outdoor fan input, outdoor fan rotational speed and outdoor fan blowing noise. When a predetermined amount of time TD elapses after heating operation has been started, frost formation on the outdoor heat exchanger 13 begins and ventilation resistance begins to increase. However, because the controller maintains the outdoor fan input at a constant, the rotational speed of 30 the outdoor fan 29 naturally drops because of ventilation resistance, and the amount of increase in the blowing noise becomes smaller than when the controller maintains normal control. <In-frost Fan Control Logic> FIG. 5 is a flowchart of in-frost fan control. When heating operation is started, -9counting of the elapsed time TD after the start of heating operation is started in Si. After standing by for a certain amount of time (TD2) in S2, it is determined in S3 whether or not the outdoor air temperature is less than a predetermined temperature (Doadef), and if YES, then an average value of the outdoor fan input is calculated in S4. Then, the controller 5 moves to S5 and determines whether or not the amount of time TD that has elapsed after counting has been started has reached a predetermined amount of time (TD 1), and if YES, then the controller determines in S6 whether or not the evaporating temperature (outdoor heat exchanger temperature) is less than a predetermined temperature (Tedef). If YES in S6, then the controller moves to S7 to ensure that the outdoor fan input is such that the average value 10 of the input that was determined in S4 is maintained. It will be noted that when the determination in any of S3, S5 or S6 is NO, then the controller enters normal control. SI to S7 are a starting condition of in-frost fan control, and S7 is in-frost fan control operation. <Operation after the Start of In-frost Fan Control> In the in-frost fan control, the input to the outdoor fan 29 becomes constant during 15 frost formation, so the rotational speed of the outdoor fan 29 drops in response to ventilation resistance and an increase in the blowing noise of the outdoor fan 29 is suppressed. However, the frost on the outdoor heat exchanger 13 continues to grow, so there is also a limit on blowing noise suppression resulting from the drop in the rotational speed of the outdoor fan 29. Further, the in-frost fan control is control that suppresses an increase in the 20 blowing noise while lowering heating performance, so indefinitely continuing the in-frost fan control significantly lowers heating performance and causes the user to feel insufficient heating. Consequently, it is necessary to switch to defrosting control under a predetermined condition. FIG. 6 is a graph showing the relationship between outdoor fan input, outdoor fan 25 rotational speed, outdoor fan blowing noise and frost formation amount in a case where in-frost fan control is continued. As shown in FIG. 6, when the frost formation amount increases excessively, the amount of increase in the blowing noise becomes large even if the rotational speed of the outdoor fan 29 were to continue to drop, and eventually the blowing noise reaches an acceptable limit value Qs. The rotational speed of the outdoor fan 29 at 30 this time is a lower limit rotational speed Ns. Normally, defrosting control is executed when the outdoor heat exchanger temperature falls in a predetermined amount of time below a "target outdoor heat exchanger temperature" that is calculated from the operating frequency of the compressor 11 and the outdoor air temperature. In addition to this, in the present embodiment, when the rotational - 10speed of the outdoor fan 29 falls below the lower limit rotational speed Ns when the controller 4 is performing in-frost fan control, the controller 4 judges that the frost formation amount has increased and that the blowing noise has reached the acceptable limit value Qs and switches from in-frost fan control to defrosting control. Below, operation after the start 5 of in-frost fan control will be described using the drawings. FIG. 7 is a flowchart from the start of in-frost fan control to until the start of defrosting control. In FIG. 7, the controller 4 maintains the input to the outdoor fan 29 at a constant in step Si1. In step S12, the controller 4 detects a rotational speed N of the outdoor fan 29. In step S13, the controller 4 determines whether or not the rotational speed N of the 10 outdoor fan 29 has fallen below the lower limit rotational speed Ns. When the controller 4 determines YES in step S13, then the controller 4 switches to defrosting control in step S 14. When the controller 4 determines NO in step S13, then the controller 4 returns to step S12. Because of this control, the rotational speed of the outdoor fan 29 can be lowered to an extent where a blowing noise controlling effect is obtained and without causing the user to 15 feel insufficient heating, so the effect of in-frost fan control can be exhibited to a maximum. <First Modification> In the preceding embodiment, the controller 4 determines that the blowing noise has reached the acceptable limit value Qs when the rotational speed of the outdoor fan 29 has fallen below the lower limit rotational speed Ns, but the present invention is not limited to 20 this; for example, the controller 4 may also determine that the blowing noise has reached the acceptable limit value Qs when the difference with the rotational speed of the outdoor fan 29 before frost formation has exceeded an acceptable value L. It will be noted that the rotational speed of the outdoor fan 29 before frost formation employs an average value of the rotational speed of the outdoor fan 29 that has been sampled after previous defrosting control. 25 Below, this will be described using the drawings. FIG. 8 is a flowchart from the start of in-frost fan control to until the start of defrosting control of an outdoor unit pertaining to a first modification of the embodiment of the present invention. In FIG. 8, the controller 4 maintains the input to the outdoor fan 29 at a constant in step S21. In step S22, the controller 4 stores a rotational speed Na of the 30 outdoor fan 29 before frost formation. In step S23, the controller 4 detects the rotational speed N of the outdoor fan 29. In step S24, the controller 4 determines whether or not the difference (Na - N) between the rotational speed Na of the outdoor fan 29 before frost formation and the rotational speed N of the outdoor fan 29 that has been detected exceeds the acceptable value L. When the controller 4 determines YES in step S24, then the controller 4 - 11 switches to defrosting control in step S25. When the controller 4 determines NO in step S24, then the controller 4 returns to step S23. <Second Modification> In the first modification, the controller 4 performs determination to switch to 5 defrosting control on the basis of the instantaneous rotational speed of the outdoor fan 29; thus, for example, when natural wind counter to the blowing direction of the outdoor fan 29 strikes the outdoor fan 29 such that the rotational speed instantaneously drops, or when the power source voltage drops and the rotational speed of the outdoor fan 29 instantaneously drops, there is the potential for the controller 4 to erroneously switch to defrosting control. 10 Thus, in a second modification, the controller 4 switches to defrosting control when an integrated value of the difference with the rotational speed of the outdoor fan 29 before frost formation exceeds an acceptable integrated value. FIG. 9 is a flowchart from the start of in-frost fan control to until the start of defrosting control of an outdoor unit pertaining to a second modification of the embodiment 15 of the present invention. In FIG. 9, the controller 4 maintains the input to the outdoor fan 29 at a constant in step S31. In step S32, the controller 4 stores the rotational speed Na of the outdoor fan 29 before frost formation. In step S33, the controller 4 detects a rotational speed Ni of the outdoor fan 29 i times (e.g., 5 times) every t seconds (e.g., 60 seconds). In step S34, the controller 4 determines whether or not an integrated value T (Na - Ni) of the 20 difference between the rotational speed Na of the outdoor fan 29 before frost formation and each rotational speed of the outdoor fan 29 that has been detected exceeds an acceptable integrated value M. When the controller 4 determines YES in step S34, then the controller 4 switches to defrosting control in step S35. When the controller 4 determines NO in step S34, then the controller 4 returns to step S33. 25 <Characteristics> (1) This outdoor unit 2 is disposed with the outdoor heat exchanger 13, the outdoor fan 29 and the controller 4. The outdoor heat exchanger 13 performs heat exchange with air as an evaporator during heating operation. The outdoor fan 29 generates an air flow that 30 passes the surface of the outdoor heat exchanger 13. The controller 4 performs in-frost fan control for lowering the rotational speed of the outdoor fan 29 when frost formation on the outdoor heat exchanger 13 is detected or estimated. For this reason, the amount of increase in the blowing noise is small even when ventilation resistance increases because of frost formation, so unpleasant noise is suppressed. Further, the in-frost fan control is not - 12 executed until a predetermined amount of time elapses after the start of heating operation. For this reason, heating operation is maintained for a predetennined amount of time, so warm air is provided even when operation is started in low outdoor air. (2) 5 In the in-frost fan control of this outdoor unit 2, lowering the target rotational speed of the outdoor fan 29 that is set beforehand is included. Alternatively, lowering the upper limit of the input value that is supplied to the outdoor fan 29 is included. Thus, the rotational speed of the outdoor fan 29 drops during frost formation and the amount of increase in the blowing noise becomes small. For this reason, noise is suppressed. 10 (3) In this outdoor unit 2, the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and the evaporating temperature of the outdoor heat exchanger 13 falls below a predetermined temperature. Alternatively, the in-frost fan control is executed when a predetermined amount of time elapses after the start of 15 heating operation and the outdoor air temperature falls below a predetermined temperature. Alternatively, the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and the low pressure side falls below a predetermined pressure. Alternatively, the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and the ON time 20 ratio during one cycle of the drive voltage that is supplied to the outdoor fan exceeds an ON time ratio that is set beforehand. Alternatively, the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and the rotational speed of the outdoor fan falls below a target rotational speed that is set beforehand. For this reason, frost formation is detected without having to use a special device, and the blowing 25 noise is suppressed. (4) In this outdoor unit 2, the average value of the input that is supplied to the outdoor fan 29 is calculated at a previous stage when the in-frost fan control is started, and while the in-frost fan control is being executed, the average value of the input that has been previously 30 calculated is supplied to the outdoor fan 29. Thus, the rotational speed of the outdoor fan 29 automatically drops because of ventilation resistance resulting from frost formation. For this reason, the amount of increase in the blowing noise becomes small. (5) In this outdoor unit 2, when the in-frost fan control is being performed, defrosting - 13 operation is started when the rotational speed of the outdoor fan falls below the lower limit rotational speed Ns. In the in-frost fan control, heating capability drops, so the rotational speed of the outdoor fan is monitored to prevent heating capability from falling below an acceptable range. Thus, when frost formation progresses to an extent that an increase in the 5 blowing noise cannot be suppressed, defrosting operation is timely started, so heating performance recovers before the user is caused to feel insufficient heating. Further, when the in-frost fan control is being performed, even when defrosting operation is started when the difference between the current rotational speed of the outdoor fan 29 and the rotational speed of the outdoor fan 29 before frost formation exceeds the 10 acceptable value L, effects that are the same as described above are obtained. Further, when the in-frost fan control is being performed, defrosting operation may also be started when the integrated value of the difference between the rotational speed of the outdoor fan 29 and the rotational speed of the outdoor fan 29 before frost formation exceeds the acceptable integrated value M. Thus, even when a gusty backwind acts on the outdoor 15 fan such that the rotational speed thereof instantaneously sharply drops, or when the power source voltage drops such that the rotational speed of the outdoor fan sharply drops, defrosting operation is not erroneously started. INDUSTRIAN APPLICABILITY As described above, the outdoor unit of the present invention is effective as an 20 outdoor unit of an air conditioner and the blowing noise of the outdoor fan is small during frost formation. - 14 -

Claims

1. An outdoor unit (2) of an air conditioner (1) to which an indoor unit (3) is connected, the outdoor unit (2) comprising: an outdoor heat exchanger (13) that performs heat exchange with air as an 5 evaporator during heating operation; an outdoor fan (29) that generates an air flow that passes a surface of the outdoor heat exchanger (13); and a controller (4) that performs in-frost fan control for lowering the rotational speed of the outdoor fan (29) when frost formation on the outdoor heat exchanger (13) is detected or 10 estimated during heating operation.

2. The outdoor unit (2) of claim 1, wherein the in-frost fan control is not executed until a predetermined amount of time elapses after the start of heating operation.

3. The outdoor unit (2) of claim 1, wherein the in-frost fan control includes lowering a target rotational speed of the outdoor fan (29) that is set beforehand. 15

4. The outdoor unit (2) of claim 1, wherein the in-frost fan control includes lowering an upper limit of an input value that is supplied to the outdoor fan (29).

5. The outdoor unit (2) of claim 1, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and an evaporating temperature of the outdoor heat exchanger (13) falls below a predetermined temperature. 20

6. The outdoor unit (2) of claim 1, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and the outdoor air temperature falls below a predetermined temperature.

7. The outdoor unit (2) of claim 1, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and a low pressure 25 side falls below a predetermined pressure.

8. The outdoor unit (2) of claim 1, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and an ON time ratio during one cycle of a drive voltage that is supplied to the outdoor fan (29) exceeds an ON time ratio that is set beforehand. 30

9. The outdoor unit (2) of claim 1, wherein the in-frost fan control is executed when a predetermined amount of time elapses after the start of heating operation and the rotational speed of the outdoor fan (29) falls below a target rotational speed that is set beforehand.

10. The outdoor unit (2) of claim 1, wherein an average value of an input that is supplied to the outdoor fan (29) is calculated at a previous stage when the in-frost fan control is started, - 15 - and while the in-frost fan control is being executed, the average value of the input is supplied to the outdoor fan (29).

11. The outdoor unit (2) of claim 1, wherein when the in-frost fan control is being performed, defrosting operation is started when the rotational speed of the outdoor fan (29) 5 falls below a lower limit rotational speed that is set beforehand.

12. The outdoor unit (2) of claim 1, wherein when the in-frost fan control is being performed, defrosting operation is started when a difference between the rotational speed of the outdoor fan (29) and the rotational speed of the outdoor fan (29) before frost formation exceeds an acceptable value that is set beforehand. 10

13. The outdoor unit (2) of claim 1, wherein when the in-frost fan control is being performed, defrosting operation is started when an integrated value of a difference between the rotational speed of the outdoor fan (29) and the rotational speed of the outdoor fan (29) before frost formation exceeds an acceptable integrated value that is set beforehand. - 16 -