GB2516336A

GB2516336A - Air-conditioning apparatus

Info

Publication number: GB2516336A
Application number: GB1406482.8A
Authority: GB
Inventors: Kiyoshi Yoshimura
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2013-06-13
Filing date: 2014-04-10
Publication date: 2015-01-21
Anticipated expiration: 2034-04-10
Also published as: MX2014007073A; CN203940582U; CN104236027A; CN104236027B; MX342141B; JP2015001310A; JP5975937B2; GB2516336B; GB201406482D0

Abstract

An air conditioning apparatus 100 comprises an outdoor unit 10 including a compressor 1, an outdoor heat exchanger 3 and an expansion valve 5, and an indoor unit 20 including an indoor heat exchanger 6, an indoor fan 7, a sucked-in indoor air temperature sensor 31 and a controller 30 to control the rotation speed of the indoor fan. If an air temperature difference ÎT between the sucked-in air temperature Tin and a set temperature Tset is greater than a thermo-threshold, the controller determines the number of revolutions per minute Nf for the indoor fan. If the air temperature difference ÎT exceeds a fan threshold T2, a heat exchanger temperature Te exceeds a coolwarm threshold T3, and an air humidity Hin is lower than a dry-wet threshold H1, the controller stops the indoor fan. After the indoor fan has been stopped, if a supercooling temperature ÎTedp, which is a difference between the heat exchanger temperature Te and a dew-point temperature Tdp, is lower than a supercooling threshold T4, or if a re-rotation period has elapsed since the stop of the indoor fan, the controller rotates the indoor fan again. The aim of the invention is to achieve dehumidification and prevent freezing of the indoor heat exchanger.

Description

DESCRIPTION

AIR-CONDITIONING APPARATUS

[0001] The present invention relates to an air-conditioning apparatus, and particularly relates to an air-conditioning apparatus having a dehumidifying function.

[Background Art]

[0002] For example, Patent Literature 1 discloses an operation control device for an air-conditioning apparatus having a dehumidifying function. The air- conditioning apparatus includes a variable capacity compressor, a heat-source-side heat exchanger (corresponding to an outdoor heat exchanger), an expansion mechanism, and a use-side heat exchanger (corresponding to an indoor heat exchanger) provided with a use-side variable air volume fan (corresponding to an indoor fan). First, in an indoor temperature control loop, the operation control device controls a compressor frequency to bring a sucked-in indoor air temperature closer to a set temperature. After the sucked-in indoor air temperature becomes close to the set temperature, the operation control device switches to a humidity control loop. Then, the operation control device increases the frequency of the compressor, decreases the number of revolutions per minute (reduces the air volume) of the indoor fan, lowers the sensible heat capacity (reduces the cooling load), secures the latent heat capacity, and thus prevents overcooling.

[Citation List] [Patent Literature] [0003] [Patent Literature 1] Japanese Patent No. 2909955 (pages 5 to 6, Fig. 6)

[Summary of Invention]

[Technical Problem] [0004] In the operation control device for the air-conditioning apparatus described in Patent Literature 1, after the sucked-in indoor air temperature reaches the set temperature, the operation control device switches to the humidity control loop and reduces the air volume of the indoor fan. The reduction in air volume lowers the discharged air temperature. Therefore, high humidity around an air outlet promotes condensation in the air outlet, and may cause dew condensation water to drop into an air-conditioned space.

Also, if the sucked-in indoor air temperature is low, the temperature of the indoor heat exchanger may be excessively lowered and become 0 degrees C or less. As a result, condensed water adhering to the indoor heat exchanger may freeze and damage the indoor heat exchanger.

[0005] The present invention has been made to solve the problems described above. An object of the present invention is to provide an air-conditioning apparatus capable of not only reducing overcooling, but also preventing condensation in an air outlet and preventing an indoor heat exchanger from freezing.

[Solution to Problem] [0006] An air-conditioning apparatus according to the present invention includes an outdoor unit and an indoor unit installed in an indoor space. The outdoor unit includes a compressor capable of varying a compressor frequency for compressing a refrigerant, an outdoor heat exchanger configured to exchange heat with outdoor air, and an expansion valve configured to expand the refrigerant. The indoor unit includes an indoor heat exchanger configured to exchange heat with indoor air, an indoor fan configured to supply indoor air to the indoor heat exchanger, a sucked-in indoor air temperature sensor configured to detect a temperature of indoor air sucked in from the indoor space, a sucked-in indoor air humidity sensor configured to detect a humidity of indoor air sucked in from the indoor space, a heat exchanger temperature sensor configured to detect a temperature of the indoor heat exchanger, and a controller configured to control at least the compressor and the indoor fan. If an air temperature difference (AT) which is a difference between an air temperature (Tin) detected by the sucked-in indoor air temperature sensor and a set temperature (Iset) which is a preset temperature is greater than a thermo-threshold (11) which is a predetermined temperature, the controller determines a number of revolutions per minute (Nf) from a relationship between an air humidity (Hin) detected by the sucked-in indoor air humidity sensor and a heat exchanger temperature (Te) detected by the heat exchanger temperature sensor, and performs a cooling operation which involves rotating the indoor fan at the determined number of revolutions per minute (Nf). In the cooling operation, if the air temperature difference (AT) exceeds a fan threshold (T2) which is a predetermined temperature lower than the thermo-threshold (Ti), the heat exchanger temperature (Te) detected by the heat exchanger temperature sensor exceeds a cool-warm threshold (T3) which is a predetermined temperature, and the air humidity (Hin) is lower than a dry-wet threshold (Hi) which is a predetermined humidity, the controller stops the indoor fan. After the stop of the indoor fan, if a supercooling temperature (ATedp) which is a difference between the heat exchanger temperature (Te) and a dew-point temperature (Tdp) of sucked-in indoor air is lower than a supercooling threshold (T4) which is a predetermined temperature, or if a re-rotation period which is a predetermined period of time has elapsed since the stop of the indoor fan, the controller rotates the indoor fan again.

[Advantageous Effects of Invention] [0007] In the present invention, the controller determines the number of revolutions per minute (Nf) from a relationship between the air humidity (Hin) and the heat exchanger temperature (Te), and performs a cooling operation which involves rotating the indoor fan at the determined number of revolutions per minute (Nf). If the air temperature difference (AT) exceeds the fan threshold (T2), the heat exchanger temperature (Te) exceeds the cool-warm threshold (T3), and the air humidity (Hin) is lower than the dry-wet threshold (Hi), the controller stops the indoor fan. After the stop of the indoor fan, if the supercooling temperature (Aledp) is lower than the supercooling threshold (T4), or if the re-rotation period has elapsed since the stop of the indoor fan, the controller rotates the indoor fan again.

Therefore, it is possible not only to reduce overcooling, but also to prevent condensation around an air outlet and prevent an indoor heat exchanger from freezing.

[Brief Description of Drawings]

[0008] [Fig. i] Fig. lisa refrigerant circuit diagram that explains an air-conditioning apparatus according to Embodiment 1 of the present invention, and schematically illustrates a configuration of a refrigerant circuit.

[Fig. 2] Fig. 2 is a lateral cross-sectional view of a part (indoor unit) of the air-conditioning apparatus according to Embodiment 1 of the present invention.

[Fig. 3] Fig. 3 is a block diagram that explains the air-conditioning apparatus according to Embodiment 1 of the present invention, and illustrates a configuration of a part (controller) of the air-conditioning apparatus.

[Fig. 4] Fig. 4 is a flowchart illustrating a control flow for explaining the air-conditioning apparatus according to Embodiment 1 of the present invention.

[Fig. 5] Fig. 5 is also a flowchart illustrating the control flow for explaining the air-conditioning apparatus according to Embodiment 1 of the present invention.

[Fig. 6] Fig. 6 is a table that explains the air-conditioning apparatus according to Embodiment 1 of the present invention, and shows compressor frequencies each determined by an air temperature difference.

[Fig. 7] Fig. 7 is a table that explains the air-conditioning apparatus according to Embodiment 1 of the present invention, and shows the numbers of revolutions per minute (indices) of an indoor fan, the numbers each determined by an air humidity and a heat exchanger temperature.

[Fig. 8] Fig. 8 is a table that explains the air-conditioning apparatus according to Embodiment 1 of the present invention, and shows dew-point temperatures each determined by a relative humidity and a suction dry-bulb temperature.

[Fig. 9] Fig. 9 is a lateral cross-sectional view of a part (indoor unit) of an air-conditioning apparatus according to Embodiment 2 of the present invention.

[Description of Embodiments]

[0009] [Embodiment 1] Figs. 1 to 3 illustrate an air-conditioning apparatus according to Embodiment 1 of the present invention. Fig. 1 is a refrigerant circuit diagram schematically illustrating a configuration of a refrigerant circuit, Fig. 2 is a lateral cross-sectional view of a part (indoor unit) of the air-conditioning apparatus, and Fig. 3 is a block diagram illustrating a configuration of a pad (controller) of the air-conditioning apparatus. Each drawing is a schematic illustration, and the present invention is not limited to the illustrated configuration.

[0010] (Refrigerant Circuit) Referring to Fig. 1, an air-conditioning apparatus 100 includes an outdoor unit 10 and an indoor unit 20 connected to each other by refrigerant pipes.

The outdoor unit 10 includes a compressor 1 capable of varying an operation frequency for compressing a refrigerant (hereinafter referred to as a "compressor frequency"), a four-way valve 2 for varying a direction of flow of the refrigerant, an outdoor heat exchanger 3 that exchanges heat with outdoor air, an outdoor fan 4 that supplies outdoor air to the outdoor heat exchanger 3, and an expansion valve 5 that expands the refrigerant. The indoor unit 20 includes an indoor heat exchanger 6 that exchanges heat with indoor air, and an indoor fan 7 that supplies indoor air to the indoor heat exchangerS.

[0011] For cooling an indoor space, a refrigeration cycle is executed in a refrigerant circuit in which a refrigerant discharged from the compressor 1 flows through the four-way valve 2, the outdoor heat exchanger 3, the expansion valve 5, and the indoor heat exchanger 6 in this order, passes through the four-way valve 2 again, and returns to the compressor 1.

For heating the indoor space, a refrigeration cycle is executed in a refrigerant circuit in which a refrigerant discharged from the compressor 1 flows through the four-way valve 2, the indoor heat exchanger 6, the expansion valve 5, and the outdoor heat exchanger 3 in this order, passes through the four-way valve 2 again, and returns to the compressor 1.

[0012] (Indoor Unit) Referring to Fig. 2, the indoor unit 20 is a "ceiling concealed unit" installed in an installation recess 92 of a ceiling 91 of an indoor space 90. The indoor unit 20 includes a rectangular housing 21 having an open bottom surface 22.

An indoor fan motor 7a is mounted in the center of a top surface 23 of the housing 21, and an indoor fan blade 7b is secured to the indoor fan motor 7a.

The indoor fan motor 7a and the indoor fan blades 7b form the indoor fan 7.

The indoor heat exchanger 6 is disposed to surround the indoor fan blade 7b. The indoor heat exchanger 6 is divided into four parts, which are parallel with respective side surfaces 24 (four surfaces) of the housing 21. Air paths 25 (at four locations) are provided between the respective four parts of the indoor heat exchanger 6 and the side surfaces 24.

[0013] Therefore, indoor air sucked in from the open bottom surface 22 by the indoor fan 7 passes through the indoor heat exchanger 6, flows along the air paths 25, and is discharged from part of the open bottom surface 22 near the side surfaces 24 into the indoor space 90.

A rectangular plate-like decorative panel 26 is removably attached to the open bottom surface 22. Along the edges of the decorative panel 26, air outlets 29 are provided at respective positions corresponding to the air paths 25. An air inlet 27 is provided in a center region of the open bottom surface 22 and surrounded by the air outlets 29. A trumpet-shaped shroud 28 that efficiently guides the indoor air to the indoor fan blade 7b is disposed between the air inlet 27 and the indoor fan blade 7b.

[0014] (Sensors) The shroud 28 is provided with a sucked-in indoor air temperature sensor (hereinafter referred to as an "air temperature sensor") 31 that detects a temperature of sucked-in indoor air, and a sucked-in indoor air humidity sensor (hereinafter referred to as an "air humidity sensor") 32 that detects a humidity of sucked-in indoor air. The indoor heat exchanger 6 is provided with an indoor heat exchanger temperature sensor (hereinafter referred to as a "heat exchanger temperature sensor") 33 that detects a temperature of the indoor heat exchanger 6.

The indoor unit 20 includes a controller 30 that controls the number of revolutions per minute (rotation speed) of the indoor fan 7 and the rotation frequency of the compressor 1 on the basis of the results of detection by the air temperature sensor 31, the air humidity sensor 32, and the heat exchanger temperature sensor 33.

The air temperature sensor 31 and the air humidity sensor 32 may be located anywhere as long as they can detect the temperature and the humidity of the sucked-in indoor air.

The controller 30 may be included in the outdoor unit 10.

[0015] (Controller) The controller 30 is configured to control the number of revolutions per minute Nf of the indoor fan 7 and the compressor frequency Hz of the compressor 1 on the basis of the results of detection by the air temperature sensor 31, the air humidity sensor 32, and the heat exchanger temperature sensor 33. The controller 30 includes the following means for executing each step of a control flow described below: means for computing an air temperature difference Al means for comparing the air temperature difference AT with a thermo-threshold Ti means for determining the compressor frequency Hz; means for instructing the compressor 1 to rotate or stop; means for determining the number of revolutions per minute Nf of the indoor fan 7; means for comparing the air temperature difference AT with a fan threshold T2; means for comparing an air humidity Hin with a dry-wet threshold Hi; means for computing a supercooling temperature ATedp; means for comparing the supercooling temperature ATedp with a supercooling threshold T4; means for comparing a stop time and a re-rotation period of the indoor fan 7; and means for comparing the air temperature difference AT with a dry thermo-threshold T5.

[0016] (Control Flow) Figs. 4 and 5 are each a flowchart illustrating a control flow for explaining the air-conditioning apparatus according to Embodiment i of the present invention.

With reference to Figs. 4 and 5, a control flow (operation) of the air-conditioning apparatus 100 during a cooling operation (which involves supplying cooling energy to the indoor heat exchangerS to cool the indoor space 90) will be described.

When the air-conditioning apparatus 100 is powered on (step Si), the air temperature sensor 31 starts to detect a sucked-in indoor air temperature (hereinafter referred to as an "air temperature") Tin, the air humidity sensor 32 starts to detect a sucked-in indoor air humidity (hereinafter referred to as an "air humidity") Hin, and the heat exchanger temperature sensor 33 starts to detect a temperature of the indoor heat exchanger 6 (hereinafter referred to as a "heat exchanger temperature Te") (step S2).

[001 7] (Thermo-OFF) An air temperature difference AT between the air temperature Tin and a set temperature Tset is determined (step S3), and the air temperature difference AT is compared with a predetermined thermo-threshold Ti (e.g., 1.5 degrees C) (step S4).

If the air temperature difference AT is equal to or less than the thermo-threshold Ti, that is, if the air temperature Tin reaches the set temperature Tset and there is no need to supply conditioned air, the compressor 1 is left at rest (off) (step S5). Then, unless a stop button on a remote control (not shown) or the like, for stopping the operation is pressed (step S6), the process returns to step S2 where the air temperature Tin, the air humidity Hin, and the heat exchanger temperature Te are detected, and the subsequent steps are executed.

If the stop button is pressed, the operation of the air-conditioning apparatus 100 is stopped (END). Stopping (or turning off) the compressor 1 is referred to as "thermo-OFF" [0018] (Therm o-O N) If the air temperature difference AT exceeds the thermo-threshold Ti, that is, if the air temperature Tin has not reached the set temperature Tset, the frequency of power for driving the compressor 1 (hereinafter referred to as a "compressor frequency Hz") is set in accordance with the magnitude of the air temperature difference AT (step S7), and the compressor 1 is rotated (turned on) at the set compressor frequency Hz (step S8). Starting (or turning on) the compressor 1 is referred to as "thermo-ON." That is, when the compressor 1 is started (or turned on), inverter control for controlling the compressor frequency Hz is performed. If the air temperature difference AT is large, the compressor frequency Hz is increased to increase the air-conditioning capacity, whereas if the air temperature difference AT is small, the compressor frequency Hz is decreased to reduce the air-conditioning capacity (see Fig. 6).

[0019] (Humidity Determination: High Humidity) Then, a determination is made as to whether the air humidity Hin exceeds a given level of high humidity (e.g., 78%) (step S9).

If the air humidity Hin is determined to be a high humidity, the number of revolutions per minute Nf of the indoor fan 7 is set to a value of the number of revolutions per minute Nf determined in advance from a relationship between the air humidity Hin and the heat exchanger temperature Te (see Fig. 7) (step Sb), and the indoor fan motor 7a is rotated at the set number of revolutions per minute Nf(step 511). Then, unless the stop button on the remote control (not shown) or the like, for stopping the operation is pressed (step S12), the process returns to step S2 where the air temperature Tin, the air humidity Hin, and the heat exchanger temperature Te are detected, and the subsequent steps are executed.

If the stop button is pressed, the operation of the air-conditioning apparatus 100 is stopped (END).

[0020] (Humidity Determination: Low Humidity) If the air humidity Hin is determined to be a low humidity, the number of revolutions per minute Nf of the indoor fan 7 is set to a value of the number of revolutions per minute Nf determined in advance from a relationship between the air humidity Hin and the heat exchanger temperature Te (see Fig. 7) (step S13), and the indoor fan motor 7a is rotated at the set number of revolutions per minute Nf (step 514).

Then, the air temperature Tin, the air humidity Hin, and the heat exchanger temperature Te are detected (step S15), and the air temperature differenceM (AT = Tin-Tset) is determined (step S16).

[0021] (Stop of Indoor Fan) If the air temperature difference AT exceeds a predetermined fan threshold 12 (e.g., 1.0 degree C) (AT> 1.0 degree C), the heat exchanger temperature Te exceeds a predetermined cool-warm threshold T3 (e.g., 1.0 degree C) and is relatively high (warm) (e.g., Te> 8 degrees C), and the air humidity Hin is less than a predetermined dry-wet threshold Hi and relatively low (dry) (e.g., Hin c 68%) (step Si7), then the indoor fan 7 is stopped (step 518).

On the other hand, if the above-described conditions ("AT > T2," "Te > T3," and "Hin < Hi ") are not satisfied, the rotation of the indoor fan 7 is continued and the process returns to step S13 where the number of revolutions per minute Nf of the indoor fan 7 is set to a value of the number of revolutions per minute Nf determined in advance from a relationship between the air humidity Hin and the heat exchanger temperature Te (see Fig. 7), and the subsequent steps are executed.

[0022] (Re-Rotation of Indoor Fan) After the indoor fan 7 is stopped (step 518), the air temperature Tin, the air humidity Hin, and the heat exchanger temperature Te are detected (step 519).

Then, a dew-point temperature Tdp of sucked-in indoor air and a difference between the heat exchanger temperature Te and the dew-point temperature Tdp (hereinafter referred to as a "supercooling temperature") ATedp (ATedp = Te-Tdp) are computed (step S20). The dew-point temperature Tdp may be calculated by an approximate expression obtained from an air diagram, or may be determined from a table, such as that in Fig. 8, which is organized with respect to the air temperature (dry-bulb temperature) Tin and the air humidity (relative humidity) Hin.

[0023] If the supercooling temperature Aledp is less than a predetermined supercooling threshold T4 (e.g., -3.0 degrees C) or if a predetermined re-rotation period (e.g., 30 seconds) has elapsed since the stop of the indoor fan 7 in step Si 8 (step 521), the indoor fan 7 is rotated again for the purpose of preventing the indoor heat exchanger 6 from freezing (step S22).

Then, the air temperature Tin is detected (step 523), the air temperature difference AT is determined (step S24), and the air temperature difference AT is compared with a predetermined dry thermo-threshold T5 (e.g., -0.5 degrees C) (step S25).

[0024] If the air temperature difference AT is equal to or less than the dry thermo-threshold Tb, that is, if the air temperature Tin is lower than the set temperature Tset, the compressor 1 is stopped (turned off) (step S26). Then, unless the stop button is pressed, the process returns to step S2 where the air temperature Tin, the air humidity Hin, and the heat exchanger temperature Te are detected, and the subsequent steps are executed.

On the other hand, if the air temperature difference AT exceeds the dry thermo-threshold T5, that is, if the air temperature Tin reaches the set temperature Tset or is slightly less than the set temperature Tset, then the process returns to step S13 where the number of revolutions per minute Nf of the indoor fan 7 is set to a value of the number of revolutions per minute Nf determined in advance from a relationship between the air humidity Hin and the heat exchanger temperature Te (see Fig. 7), and the subsequent steps are executed.

[0025] (Compressor Frequency) Figs. 6 to 8 explain the air-conditioning apparatus according to Embodiment 1 of the present invention. Fig. 6 is a table that shows compressor frequencies each determined by an air temperature difference. Fig. 7 is a table that shows the numbers of revolutions per minute (indices) of an indoor fan, the numbers each determined by an air humidity and a heat exchanger temperature.

Fig. 8 is a table that shows dew-point temperatures each determined by a relative humidity and a suction dry-bulb temperature.

Referring to Fig. 6, as the air temperature difference AT increases, the number of revolutions per minute Nf is increased to promote cooling of indoor air When the air temperature difference AT reaches the dry thermo-threshold T5 (e.g., -0.5), the compressor 1 is stopped.

[0026] (Number of Revolutions per Minute) Referring to Fig. 7, the number of revolutions per minute Nf of the indoor fan 7 corresponding to the case where the heat exchanger temperature Te is a lowest temperature and the air humidity Hin is a highest humidity is set to "100." The heat exchanger temperatures Te are divided into four levels, and the air humidities Hin are divided into five levels. In Fig. 7, the number of revolutions per minute Nf of the indoor fan 7 in each section corresponding to one level of the heat exchanger temperature Te and one level of the air humidity Hin is expressed as an index relative to "100" described above.

That is, when the air humidity Hin is determined to be a high humidity (78% < Hin), the number of revolutions per minute Nf of the indoor fan 7 is greater than that in the case where the air humidity Hin is determined to be a low humidity (Hin «= 78%). The number of revolutions per minute Nf of the indoor fan 7 increases substantially stepwise as the air humidity Hin increases. For the same air humidity Hin, the number of revolutions per minute Nf of the indoor fan 7 increases as the heat exchanger temperature Te decreases.

For the dry-wet threshold Hi of the air humidity Hin, the table (Fig. 7) is created on the basis of a relationship between humidity and air volume which is confirmed, by a test, not to cause condensation. The lowest threshold of the heat exchanger temperature Te is set to "4 degrees C," which is sufficiently higher than "0 degrees C," so as to prevent the indoor heat exchanger 6 from freezing and to lower the temperature of the indoor heat exchanger 6 to secure the latent heat capacity as much as possible.

[0027] (Dew-Point Temperature) Fig. 8 shows dew-point temperatures, each determined by a relative humidity and a suction dry-bulb temperature, in the form of a table instead of an equation. The higher the relative humidity (equivalent to the air humidity Hin) and the higher the suction dry-bulb temperature (equivalent to the air temperature Tin), the higher the dew-point temperature (Tdp).

[0028] (Operation and Effect) The air-conditioning apparatus 100 stops the indoor fan 7 when "AT> 1.0 degree C," "Te> 8.0 degrees C," and "Hin <68%" are satisfied (step Si8). This means that when the air humidity Hin is low, the indoor heat exchanger 6 is unlikely to freeze, and the air temperature difference AT (i.e., difference between the air temperature Tin and the set temperature Tset) is small, then the air-conditioning apparatus 100 stops the indoor fan 7 while continuing the operation of the compressor 1 to further reduce the sensible heat capacity and achieve dehumidification, and thus to further lower the heat exchanger temperature Te.

That is, when the indoor fan 7 is at rest, dehumidification cannot be achieved because the indoor heat exchanger 6 does not exchange heat with sucked-in air.

However, since the heat exchanger temperature Te is low when the indoor fan 7 is operated, the latent heat capacity can be secured even with a small air volume.

[0029] The indoor fan 7 that has been temporarily at rest is rotated again (step S22). This is because by keeping the heat exchanger temperature Te lower than the dew-point temperature Tdp, the latent heat capacity can be secured even when the indoor air-conditioning load is small. Also, by setting a time condition, the indoor heat exchanger 6 can be prevented from freezing even in the event of failure of the heat exchanger temperature sensor 33.

[0030] As described above, the air-conditioning apparatus 100 detects the air temperature Tin, the air humidity Hin, and the heat exchanger temperature Te, and controls the compressor frequency and the number of revolutions per minute of the indoor fan 7 on the basis of these detected values. Therefore, even when the indoor load is small, it is possible to secure the latent heat capacity. Also, the air-conditioning apparatus 100 determines the dew-point temperature Tdp, compares the dew-point temperature Tdp with the heat exchanger temperature Te, and rotates the indoor fan 7 again. Therefore, it is possible to prevent condensation and to prevent the indoor heat exchanger 6 from freezing.

[0031] [Embodiment 2] Fig. 9 is a lateral cross-sectional view of a part (indoor unit) of an air-conditioning apparatus according to Embodiment 2 of the present invention.

Parts equivalent or corresponding to those of Embodiment 1 are given the same reference numerals, and the description thereof will be partially omitted. Fig. 9 is a schematic illustration and the present invention is not limited to Embodiment 2 illustrated herein.

In an indoor unit 220 of an air-conditioning apparatus 200 illustrated in Fig. 9, the decorative panel 26 of the indoor unit 20 of Embodiment 1 is provided with a floor temperature sensor 34 that detects a temperature of a floor surface (not shown) of the indoor space 90.

[0032] (Floor Temperature Sensor) The floor temperature sensor 34 is a thermopile sensor that detects infrared rays from a floor surface to measure a temperature of the floor surface (hereinafter referred to as a "floor temperature TV') in a noncontact manner. The present invention does not limit the types and shapes of the floor temperature sensor 34.

[0033] (Sensible Temperature) A sensible temperature perceived by humans is significantly influenced by air humidity and radiation temperature of the floor or wall surface, as well as by ambient air temperature. Therefore, whereas the controller 30 of the air-conditioning apparatus 100 according to Embodiment 1 performs control on the basis of the air temperature Tin and the like, the controller 30 of the air-conditioning apparatus 200 according to Embodiment 2 uses the sensible temperature Ta instead of the air temperature Tin.

The sensible temperature Ta can be determined by the equation "Ta = Tin + a x (Hin-60) + 13 x (Tf-Tin)" which is a function of the air temperature Tin, the air humidity Hin, and the floor temperature If.

In this equation, a represents a correction coefficient for taking into account the air humidity Hin (dimension: degree CI%), and 13 represents a correction coefficient for taking into account the air temperature Tin and the floor temperature Tf. Values between 0 and 1 obtained in a test by taking into account a comfort index are assigned to cx and (0 < a c 1.0, 0 c 13 < 1.0).

[0034] Effects will be described using specific numbers on the assumption that, for example, a is 0.003 (degrees CI%) and I is 0.25. If Tin is 26 degrees C, Hin is 50%, and Tf is 25 degrees C, then Ta is 25.45 degrees C. This is a result obtained by making a correction such that when the air humidity Hin and the radiation temperature (floor temperature Tf) are low, the sensible temperature Ta is lower than the ambient air temperature Tin. That is, in this case, using the sensible temperature Ta makes the air temperature difference AT smaller than that in the case of using the air temperature Tin ((Ta-Tset) < (Tin-Tset)).

Therefore, by using the corrected sensible temperature Ta instead of the air temperature Tin in the air-conditioning apparatus 100, the compressor frequency Hz of the compressor 1 is controlled at a lower temperature. Hence, this reduces the operating time of the compressor 1 or lowers the compressor frequency, and makes it possible to achieve energy-saving operation.

[0035] If Tin is 26 degrees C, Hin is 70%, and Tf is 27 degrees C when a is 0.003 (degrees CI%) and 13 is 0.25, then the sensible temperature Ta is 26.55 degrees C. That is, in this case, using the sensible temperature Ta makes the air temperature difference AT greater than that in the case of using the air temperature Tin ((Ta-Tset) > (Tin-Tset)).

Since the high air humidity Hin and the high floor temperature If cause more discomfort than the actual air temperature Tin, a correction is made such that the sensible temperature Ta is higher than the air temperature Tin.

Improved comfort can thus be provided by control based on the sensible temperature Ta.

[0036] (Controller) The controller 30 of the air-conditioning apparatus 200 is not shown, because it can be obtained by connecting the floor temperature sensor 34 to the controller 30 (see Fig. 3) of the air-conditioning apparatus 100 and by adding, to the controller 30 of the air-conditioning apparatus 100, means for computing the sensible temperature Ta and means for replacing the air temperature Tin with the sensible temperature Ta.

[Reference Signs List] [0037] 1 compressor, 2 four-way valve, 3 outdoor heat exchanger, 4 outdoor fan, expansion valve, 6 indoor heat exchanger, 7 indoor fan, 7a indoor fan motor, 7b indoor fan blade, 10 outdoor unit, 20 indoor unit, 21 housing, 22 bottom surface, 23 top surface, 24 side surface, 25 air path, 26 decorative panel, 27 air inlet, 28 shroud, 29 air outlet, 30 controller, 31 air temperature sensor, 32 air humidity sensor, 33 heat exchanger temperature sensor, 34 floor temperature sensor, 90 indoor space, 91 ceiling, 92 installation recess, 100 air-conditioning apparatus (Embodiment 1), 200 air-conditioning apparatus (Embodiment 2), 220 indoor unit (Embodiment 2)