Air conditioner and control method of the same

Abstract: An air conditioner comprises a freezing cycle circuit, which includes, successively proivided on a main duct line 11 in the mentioned order, a compressor 10, a four-way valve 12, an external heat exchanger 13, a pressure reducer 14, and an internal heat exchanger 15, the main duct line 11 branching into at least an upper and a lower part coolant flow line 20 and 30 in the internal heat exchanger 15, and an on-off valve 16 provided on the upper part coolant flow line 20 and closed in a low capacity cooling operation. The air conditioner can gently cool and gently dry a room without causing chillness to be felt.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to air conditioners and methods of controlling the same. More particularly, the invention relates to techniques concerning an air conditioner, which can provide a gentle cooling mode for gently cooling a room while the temperature thereof is held in the neighborhood of a predetermined temperature, and a gentle drying mode for drying air in the room while substantially maintaining the present temperature of the room, in addition to a cooling mode and a heating mode. 2. DESCRIPTION OF THE PRIOR ART Air conditioners are roughly classified into a separate type in which an interior unit and an exterior unit are separated from each other, and an integral type in which the two units are accommodated in a same housing. In either type, a freezing cycle circuit of heat pump type is provided, in which a compressor, a four-way valve, an external heat exchanger, a pressure reducer (or an expansion valve) and an internal heat exchanger are provided on a main duct line. The freezing cycle circuit is used in a heating mode and also a cooling mode by switching its four-way valve. The internal heat exchanger, however, is recently in a trend of increasing size for improving its heat exchange capacity and reducing the power consumption. The internal heat exchanger also has a coolant flow line diverged into a plurality of branches for increasing the heat exchange efficiency in the cooling operation and also in the heating operation. Correspondingly, the air conditioner can be set in a plurality of operating modes such as a "strong cooling" mode, an "intermediate cooling" mode, a "weak cooling" mode and a "drying" mode (or commonly termed substantial weak cooling mode). In the drying mode, intermittent operation of the internal unit fan or like control is provided. Such a measure, however, has a problem that it cannot permit sufficient drying. Another well-known method for drying uses an expansion valve, which is provided on the coolant flow line in the internal heat exchanger and permits drying by re-heating. In this case, however, the coolant flow line cannot be branched. Therefore, the heat exchange efficiency in the cooing and heating operations is inferior to the case where the coolant flow line is branched. Accordingly, a construction as shown in Fig. 16 is proposed in Japanese Laid-Open Patent Publication No. 8-105646. In this construction, an internal heat exchanger 4 is provided in an internal unit housing 1 such that it faces air suction holes 2 formed in the front wall of the housing 1. A fan 5 is provided adjacent the housing rear wall to take air from the air-conditioned room into the housing through the air suction holes 2 and blow out air having been heat exchanged in the internal heat exchanger 4 through an air blow-out opening 3 provided in the bottom of the housing adjacent the front wall thereof. The internal heat exchanger 4 has a coolant flow line 9, which is branched into a first branch line 9a extending upward from the side of a substantially central inlet of the internal heat exchanger 4 and a second branch line 9b extending downward. On their outlet side, the two branch lines 9a and 9b are joined together by a coupler 9c provided outside the internal heat exchanger 4. An on-off valve 10 is provided on the second branch 9b and closed when a predetermined temperature is approached by the temperature of the air-conditioned room. In this system, when the temperature of the room becomes the neighborhood of a predetermined temperature during a cooling operation, the on-off valve 10 is turned off, and coolant is allowed to flow through the first branch Line 9a. Thus, the cooling air is reduced to one half for gently reducing the temperature in the air-conditioned room. In this operation, drain water produced as a result of condensation in an upper part of the internal heat exchanger 4, falls as drops and is gasified by air passing through a lower part of the internal heat exchanger 4. Therefore, the drying of the room is prevented. As shown, by the closing of the on-off valve 10 on the second branch line 9b in the neighborhood of the predetermined temperature, a substantial drying effect can no longer be expected due to the gasification of drain in a lower part of the internal heat exchanger 4, although the cooling air output is reduced to one half. For this reason, the on-off valve is opened when drying the room. Therefore, this prior art system still has the problem of excessive reduction of the temperature of the air-conditioned room. The invention seeks to solve the above problems inherent in the prior art air conditioner. Specifically, it is a first object of the invention to provide an air conditioner, which permits drying of a room without substantially reducing the temperature thereof, i.e., without causing any chillness to be felt, and can improve the comfortablity of the room. A second object of the invention is to provide a method of controlling an air conditioner, which can realize a gentle cooling mode in which the air-conditioned room is dried while holding the temperature thereof in the neighborhood of a predetermined temperature, and also a gentle drying mode in which the room is dried while substantially holding the prevailing temperature. SUMMARY OF THE INVENTION To solve the above first object, the invention features an air conditioner, which comprises a freezing cycle circuit including, provided on a main duct line, a compressor, a four-way valve, an external heat exchanger, a pressure reducer and an internal heat exchanger, the main duct line branching into at least an upper and a lower coolant flow line in the internal heat exchanger, and an on-off valve provided on the upper cooling flow line and closed in a low capacity cooling operation. The low capacity cooling operation is an operation at a reduced operating frequency of the compressor and under an increased pressure in the coolant flow line in the internal heat exchanger, in which only sensible heat is available for change so that it is impossible to expect substantial cooling (or drying) capacity. According to the invention, in the low capacity cooling operation the on-off valve is closed to allow coolant to flow solely through the lower coolant flow line. It is thus possible to obtain cooling or drying without spoiling the heat exchange efficiency of the internal heat exchanger, and hence without substantially reducing the temperature of the room. Besides, since no drain water falls from the upper part of the internal heat exchanger, the blown-out air has not been humidified, and it is possible to provide a dry and comfortable condition with less relative humidity. According to the invention, the cooling operation and drying operation which permits such a dry condition to be obtained while suppressing the chillness, are referred to as gentle cooling operation and gentle drying operation to distinguish them from the conventional cooling and drying operations. The on-off valve may be provided on a portion of the upper coolant flow line on the inlet or outlet side thereof. However, where the on-off valve is provided on the outlet side, its closing would result in stagnation of coolant in the upper coolant flow line. For this reason, the on-off valve is preferably provided on the inlet side. In order that the room should not be cooled down excessively when it is gently cooled or gently dried, the upper coolant flow line preferably has a greater length than the lower coolant flow line. When the on-off valve is closed, a temperature difference is produced between air flowing through the upper part of the internal heat exchanger and that flowing in the lower part. In this state, therefore, condensation may occur in a lower end portion of the internal heat exchanger, in which air from the fan and these air streams join together. According to the invention, the length of a portion of the lower coolant flow line corresponding to a lower end portion of the internal heat exchanger is made to be less than that of the other portion, thus making the cooling capacity of the lower end portion to be lower than the other portion. Preferably, a less length portion of the lower coolant flow line is made up for by leading a portion of the upper coolant flow line to the lower end of the heat exchanger. By so doing, the heat exchange efficiency is not reduced in the normal cooling and heating operations performed with the on-off valve held open. To attain the above second object, the invention also features a method of controlling an air conditioner which comprises a freezing cycle circuit including, provided on a main duct line, a compressor, a four-way valve, an external heat exchanger, a pressure reducer, an internal heat exchanger, a controller for controlling the freezing cycle circuit according to signals from a temperature sensor and a predetermined temperature detector, said main duct line branching at least into an upper and a lower coolant flow line in the internal heat exchanger, and an on-off valve provided on the upper coolant flow line and closed in a low capacity cooling operation, which method has a gentle cooling mode for gently cooling a room while the temperature thereof is held in the neighborhod of a predetermined temperature, as well as a cooling mode and a heating mode, the on-off valve being closed by the controller when the gentle cooling mode is selected. When the gentle cooling mode is selected, the controller sets a plurality of temperature zones with predetermined temperature ranges with reference to predetermined temperatures, and closes the on-off valve when the temperature of the room is in a gentle cooling temperature zone lower than a predetermined temperature for a redetermined period of time. Preferably, the on-off valve is closed under a further condition that the operating frequency of the compressor is too low to provide the cooling capacity. Preferably, the case where the pressure reducer is an electronic expansion valve, the controller controls the electronic expansion valve to increase the cooling capacity thereof when closing the on-off valve. Preferably, the case where the on-off valve is an electromagnetic valve, when the temperature of the room is reduced to be lower than the gentle cooling temperature zone, the controller outputs a signal to stop the compressor and, after a subsequent predetermined period of time, turns the electromagnetic expansion valve off to open it. By this control, it is possible to reduce power consumption and prevent heating of the electromagnetic expansion valve. In this control method, when the temperature of the room has been in a temperature zone higher than a predetermined temperature for a predetermined period of time, the controller opens the on-off valve. As a result, the operating frequency of the compressor is returned to the frequency for a normal cooling mode. When the freezing cycle is in a quick cooling operation, the gentle cooling mode is not performed until the temperature of the room reaches a neighborhood of a predetermined temperature. To attain the second object, the invention further features a method of controlling air conditioner which comprises a freezing cycle circuit including, provided on a main duct line, a compressor, a four-way valve, as external heat exchanger, a pressure reducer, an internal heat exchanger, a controller for controlling the freezing cycle circuit according to signals from a temperature sensor and a predetermined temperature detector, the main duct line branching at least into an upper and a lower coolant flow line in the internal heat exchanger, and an on-off valve provided on the upper coolant flow line and closed in a low capacity cooling operation, the method having a gentle drying mode for gently drying the room while substantially holding the prevailing temperature therein, as well as a cooling operation mode and a heating operation mode, the on-off valve being closed by the controller when the gentle drying mode is selected. When the gentle drying mode is selected, the controller sets a plurality of temperature zones with predetermined temperature ranges with reference to the temperature of the room at the time this mode is selected and operating frequencies of the compressor for the respective temperature zones, and drives the compressor at the operating frequency for the temperature zone, in which the temperature of the room prevails. In view of controlling the compressor (for instance detecting the position of a brushless motor), the temperature ranges of the temperature zones and the operating frequencies of the compressor are preferably set different depending on a reference atmospheric temperature. By this method, when the actual atmospheric temperature is higher than the reference atmospheric temperature, the temperature range is wider than that when the actual atmospheric temperature is lower. In view of the compressor control, it is also desirable that a change of the operating frequency of the compressor in accordance with a shift of temperature zone is performed after a predetermined waiting time. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the basic freezing cycle circuit of an air conditioner according to the invention; Fig. 2 is a sectional view showing the internal construction of an internal unit according to the invention; Fig. 3 is a schematic view showing an internal heat exchanger in the internal unit; Fig. 4 is a schematic view showing a modification of the internal heat exchanger; Fig. 5 is a basic block diagram showing the control of the air conditioner according to the invention; Fig. 6 is a view for illustrating temperature zones which are set in a gentle cooling mode in the method of control according to the invention; Figs. 7 and 8 are flow charts illustrating a routine in the gentle cooling mode; Fig. 9 is a flow chart illustrating a routine for cancelling the gentle cooling mode; Fig. 10 is a view for illustrating temperature zones which are set in a gentle drying mode in the method of control according to the invention; Figs. 11 to 15 are flow charts illustrating a routine in the gentle drying mode; and Fig. 16 is a sectional view showing an internal construction of an internal unit in an air conditioner of prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 illustrates an air conditioner according to the invention. The air conditioner comprises a compressor 10, across which a freezing cycle circuit is connected. The freezing cycle circuit comprises a main coolant flow line (i.e., main duct line) 11, on which a four-way valve 12 for switching the line for cooling and heating, an external heat exchanger 13, a pressure reducer 14, and an internal heat exchanger 15 are connected. In the cooling operation, coolant flows through the external heat exchanger 13, the pressure reducer 14 and the internal heat exchanger 15 as shown by solid arrows. In the heating operation, on the other hand, coolant flows through the internal heat exchanger 15, the pressure reducer 14 and the external heat exchanger 13 as shown by dashed arrows. The main duct line 11 branches into an upper coolant flow line 20 and a lower coolant flow line 30 in in the internal heat exchanger 15. An on-off valve 16 is provided on the upper coolant flow line 20. In this embodiment, the on-off valve 16 is provided on the side, from which coolant enters in the cooling operation. However, it is also possible to provide the on-off valve 16 on the side, from which coolant leaves. In this embodiment, the on-off valve 16 is an electromagnetic valve. In the following specification, the on-off valve is described as an electromagnetic valve. Fig. 2 shows the internal construction of an internal unit 40, in which the internal heat exchanger 15 is accommodated. Fig. 3 shows the internal heat exchanger 15 removed from the internal unit 40. The internal unit 40 has a substantially rectangular housing 41. The front and top of the housing 41 have front and top air inlets 42 and 43. The internal heat exchanger 15 is disposed in the housing 41 such that it extends along the front and top air inlets 42 and 43. For reducing the size of the housing 41, the fins of the internal heat exchanger 15 are provided in three fin groups. More specifically, the internal heat exchanger 15 has a first fin group 151 which faces the front air inlets 42, a second fin group 152 which extends obliquely upward from the upper end of the first fin group 151 towards the top air inlets 43, and a third fin group 153 which extends obliquely downward form the upper end of the second fin group 152 to the rear wall of the housing 41. The second and third fin groups 152 and 153 are in the form of an inverted letter V. As shown in Fig. 3, the main duct line 11 branches into two branches at a position substantially corresponding to a central portion of the second fin group 152. One of the branches extends as an upper coolant flow line 20 from the second fin group 152 through the third fin group 153. An electromagnetic valve 16 is provided on the upper coolant flow line 20 near the branching thereof. The other branch extends as a lower coolant flow line 30 through the first fin group 151. Outlet portions of the two coolant flow lines 20 and 30 join together on the outside of the internal heat exchanger 15 and return to the four-way valve 12. As shown in Figs. 2 and 3, the upper coolant flow line 20 has a greater length than the lower coolant flow line 30. The housing 41 has an air blow-out opening 44 at the bottom corner adjacent the front wall. An air directing plate 45 is rotatably mounted in the opening 45. A fan 46 is disposed in the air passage leading from the internal heat exchanger 15 to the air blow-out opening 45. By the fan 46 air in the room is taken in the housing 41 through the front and top air inlets 42 and 43 for heat exchange in the internal heat exchanger 15 and then led out through the air blow-out opening 45. When the room is cooled down to reach the neighborhood of a predetermined temperature, a controller reduces the operating frequency of the compressor 10 so as to perform a low capacity cooling operation. At this time, the electromagnetic valve 16 is closed to permit coolant to flow solely through the lower coolant flow line 30, whereby the room can be cooled or dried without spoiling the heat exchange efficiency of the internal heat exchanger 15, and thus without substantially reducing the temperature of the room. Besides, according to the invention, no drain water is dropped from the second and third fin groups 152 and 153 in the internal heat exchanger 15. Thus, the blown-out air has not been humidified, and it is possible to obtain a dry and comfortable condition with less moisture. The closing of the electromagnetic valve 16 causes a difference in temperature between the air flowing through the second and third fin groups 152 and 153 in the upper part of the internal heat exchanger 15 and the air flowing the first fin group 151 in the lower part. Therefore, condensation may occur in a lower end portion A of the internal heat exchanger 15 where the air forced by the fan 46 and these air streams join together. A basic idea for preventing this is to make the duct line length (or duct line density) of the lower coolant flow line 30 on the lower end of the internal heat exchanger 15 less than that of the remaining coolant flow line, thus reducing the cooling capacity in the lower end portion A compared to that in the remaining portion. With this arrangement, however, the heat exchange efficiency of the internal heat exchanger 15 as a whole is inevitably reduced in the cooling or heating operation with the electromagnetic valve 16 opened. According to the invention, it is proposed that, as shown in Fig. 4, the reduced duct line length of the lower coolant flow line 30 is made up for by leading a portion 201 of the upper coolant flow line 20 toward the lower end of the first fin group 151. With this arrangement, namely with opened electromagnetic valve 16, the entire internal heat exchanger 15 contributes to the heat exchange, and the heat exchange capacity in the normal cooling and heating operations is not reduced. The method of controlling the air conditioner in the gentle cooling mode and also gentle drying mode will be described. Fig. 5 is a basic block diagram showing the control of the air conditioner. In this embodiment, various operating modes and redetermined temperatures can be set by a remote controller 50. A control unit 60 for the internal unit includes a predetermined temperature sensor 61 for receiving signals from the remote controller 50, an actual temperature detector 63 for receiving an actual temperature signal from a room temperature sensor 62, a central controller 64 in the internal unit for executing various control routines according to the received signals, and an electromagnetic valve drive circuit 65 for on-off driving the electromagnetic valve 16. The central controller 64 is a CPU (central processing unit) or an MPU (microprocessor), and it sets operating frequencies of the compressor 10 and generates an expansion valve bit signal for controlling the pressure reducer (or electronic expansion valve) 14 according to the signals from the predetermined and room temperature sensors 61 and 62. Another control unit 70 for the external unit includes a compressor drive circuit 71 for driving the compressor 10 according to a compressor operating frequency signal from the internal unit central controller 64, a temperature sensor 73 for receiving a compressor suction side temperature signal from a suction sensor 72, an expansion valve drive circuit 74 for driving the pressure reducer (or electronic expansion valve) 14, and an external unit central controller 75 for controlling the expansion valve drive circuit 74 according to a temperature signal from the temperature sensor 73 and an expansion valve bit signal from the internal unit central processor 64. Figs. 7 and 8 are flow charts illustrating a routine in the cooling operation. In a normal cooling mode, in a step SC1 the electromagnetic valve is "OFF" and also the expansion valve bit signal is "H". Then, in a step SC2 when a gentle cooling mode command from the remote controller 50 has been received, the central controller 64 sets temperature zones for room temperature control and compressor operating frequencies for these temperature zones, for example as shown in Fig. 6, with reference to the predetermined temperature Ts detected at the predetermined temperature sensor 61 (step SC3). In this embodiment, when the temperature of the room is being decreased, a temperature range above Ts + 1.5 is referred to as X zone (14-code, operating frequency: 57 Hz), a temperature range between Ts + 1.5 and Ts - 1.0 as F zone (code variable signal from 4- to 13-code, operating frequency: variable), a temperature range between Ts - 1.0 and Ts - 2.0 as G zone (3-code, operating frequency: 15 Hz), and a temperature range below Ts - 2.0 as V-zone (0-code, operating frequency: 0 Hz). When the temperatures of the room is being increased, a temperature range above Ts + 2.0 is referred to as X zone, a temperature range between Ts + 2.0 and Ts - 0.5 as F zone, a temperature range between Ts - 0.5 and Ts - 1.5 as G zone, and a temperature range below Ts - 1.5 as Y zone. The operating codes and operating frequencies for the compressor are the same as those when the temperature of the room is being decreased. In a subsequent step SC4, the central controller 64 checks whether the air conditioner is under a room temperature gradient ignored control or so-called quick cooling operation. When the result of the check is "YES", it executes a step SC5 of checking whether the temperature of the room is below F zone and also the operating frequency of the compressor 10 is, for instance, below 7-code. When the result of the check is "NO", the control program 64 goes back to the step SC4. When the result of the check is "YES", it executes a step SC6 of starting a 5-minute timer. Then, until it finds in a step SC7 that 5 minutes has passed, the central controller 64 executes a step SC8 of checking whether the operating frequency of the compressor 10 has increased over 8-code. When the result of the check is "YES", i.e., when the frequency has increased, the central controller 64 executes a step SC9 of resetting a 5-minute timer and then the program goes back to the step SC4. As above, when the gentle cooling mode is selected during the quick cooling operation, it is waited the temperature of the room is below F zone and the operating frequency of the compressor 10 is below 7- code for 5 consecutive minutes. When 5 minutes has passed without increase of the operating frequency of the compressor 10 beyond 8-code, the central controller 64 executes a step SC10 of resetting the 5-minute timer and then the program jumps to a step SC12 to allow outputting an electromagnetic valve bit signal "L" from the internal unit central controller 64 to the electromagnetic valve drive circuit 65 and the external unit central controller 75. Then in a step SC13, it turns on, i.e., "closes", the electromagnetic valve 16, thus allowing coolant to flow solely the lower coolant flow line 30. At the external unit, the expansion valve drive circuit 74 enhances the capacity of the electronic expansion valve 14 to perform a gentle cooling operation. When in the step SC4 the result of the check is "NO", i.e., the air conditioner is not under quick cooling operation, the central controller 64 in a step SC11, likewise as in the step SC5, checks whether the temperature of the room is below F zone and the operating frequency of the compressor 10 is below 7-code. When the result of the check is "YES", the central controller 64 outputs an expansion valve bit signal "L" to control the electronic expansion valve 14. When the result of the check is "NO", the program returns to the step SC4. When the temperature of the room is reduced down to Y zone in the gentle cooling operation, the central controller 64 outputs a 0-code signal for stopping the compressor 10 to the compressor drive ciruit 71. When this signal is sent at in a step SC14 during the gentle cooling operation, it executes a step SC15 of starting a 20-minute timer and then executes a step SC17 until in the step SC16 20 minutes pass. In the step SC17, it checks whether an operating frequency of 1-code or more has been sent out. When the result of the check in the step SC17 is "YES", i.e., when a frequency of 1-code or more has been sent out, it executes a step SC18 of resetting the 20-minute timer and the program returns to the step SC14. When any operating frequency of 1-code or more has not been sent out in the 20 minutes, it executes a step SC18A of turning off, i.e. opening the electromagnetic valve 16, then executes a step SC19 of resetting the 20-minute timer, and the program goes back to the step SC4. When the result of the check in the step SC14 is "NO", i.e., when no 0-code signal has been sent out, the central controller 64 executes a step SC20 of checking whether the temperature of the room has increased up to X zone. When the result of the check is "NO", the program returns to the step SC14. When the result of the check is "YES", it executes a step SC21 of starting a 30-minute timer. Then, until in a step SC22 30 minutes pass, it checks whether the temperature of the room has been reduced to be below X zone (step SC23). When the result of the check is "YES", it executes a step SC24 of resetting the 30-minute timer and then the program returns to the step SC14. When in the step SC22 time is over without reduction of the temperature of the room to below X zone, the central controller 64 executes a step SC25 of turning off, i.e. opening the electromagnetic valve 16 and then executes a step SC26 of sending at an expansion valve bit signal "H" to the electromagnetic valve drive circuit 65 and the external unit central controller 75. In a subseqent step SC27, it resets the 30-minute timer. Then in a step SC28, after waiting for 3 minutes, the program returns to the step SC4. When a command for cancelling gentle coding operation is sent out from the remote controller 50, the internal unit central controller 64 executes a routine as shown in Fig. 9. Specifically, it sends out a 0-code signal for stopping the compressor 10 to the compressor drive circuit 71. Then, it turns off the electromagnetic valve 16 and sets the expansion valve bit signal to "H", and thereafter operation according to the setting of the remote controller 50 is performed. The operation in the gentle drying mode will now be described. As shown in the flow chart of Fig. 11, in a step SD2 before the gentle drying mode is selected, the electromagnetic valve 16 is off and the expansion valve bit signal is "H". Then in step SD2 when a gentle drying mode command is received from the remote controller 50, the internal unit central controller 64 executes a step SD3 of sending out an expansion valve signal "L" to the electromagnetic valve drive circuit 65 and the external unit central controller 75. Then, in a step SD4 it sets temperature zones for room temperautre control and compressor operating frequencies for these temperature zones, for example as shown in Fig. 10, according to the temperature Tr of the room as detected by the temperature detector 63 and the the atmospheric temperature To. In this embodiment, the predetermined temperature Ts is represented as Ts = Tr - 1.0, and when the atmospheric temperature To is higher than 30°C (A mode), a temperature above Ts is referred to as A zone (4-code, operating frequency: 18 Hz), a temperature range between Ts and Ts - 2.0 as B zone (3-code, operating frequency: 15 Hz), and a temperature range below Ts - 2.0 as E zone (0-code, compressor: "off"). When the atmospheric temperature To is lower than 30°C (B mode) a temperature range above Ts is referred as A zone (4-code, operating frequency: 18 Hz), a temperature range between Ts and Ts - 1.0 as B zone (3-code, operating frequency: 15 Hz), a temperature range between Ts - 1.0 and Ts - 1.5 as C zone (2-code, operating frequency: 12 Hz), a temperature range between Ts - 1.5 and Ts - 3.0 as D zone (1-code, operating frequency: 9 Hz), and a temperature range below Ts - 3.0 as F zone (0-code, compressor: "off"). In a subsequent step SD5, the central controller 64 checks whether the gentle drying mode command input is the first one. When the result of the check is "YES" (first one), it executes a step SD6 of starting a 3-minute timer. Then, in a step SD7 it sends out a 3-code signal to the compressor drive circuit 71 for setting the operating frequency of the compressor 10 to 15 Hz. In a subsequent step SD8, the central controller 64 turns on, i.e., closes the electromagnetic valve 16, and then the control program jumps to a step SD11. The 3-minute timer is started in the step SD6 because the waiting time for switching each temperature zone is set to 3 minutes. When the result of the check in the step SD5 is "NO", the central controller 64 checks in a step SD9 whether the compressor 10 is "ON". When the compressor is "ON", it executes the next step SD10 of detecting the atmospheric temperature, setting a temperature zone corresponding to the detected atmospheric temperature, and starting a 3-minute timer. Upon confirming in a subsequent step SD11 that 3 minutes has passed, then in a step SD12 the atmospheric temperature is again detected, and in a next step SD13 it is determined whether the temperature zone is of B mode. When the result of the check is "NO", an A mode control in a step SD20 and subsequent steps in Fig. 12 are executed. When the result of the check in the step SD13 is "YES" (B mode), the central controller 64 executes a step SD14 of checking whether the operation has been in B mode continuously for 30 minutes. When the result of the check is "NO", the central controller 64 executes an A mode control in the step SD20 and subsequent steps in Fig. 12. When the result of the check is "YES", it executes a B mode control as shown in Fig. 13. In the A mode control, in a step SD20 the central controller 64 checks whether the temperature is in B zone. When the result of the check is "YES", it in a step SD21 sends out a 3-code signal to set the operating frequency of the compressor 10 to 15 Hz. Then, it executes a step SD22 of resetting the 3-minute timer and the program returns to the step SD9. When the result of the check in the step SD20 is "NO", it executes a step SD23 of checking whether the temperature is in E zone. When the result of the check is "YES", it executes a step SD24 of resetting a 3-minute timer and turns off the compressor 10. When the result of the check in the step SD23 is that the temperature is not in E zone, the central controller 64 in a step SD25 sends out a 4-code signal to set the operating frequency of the compressor 10 to 18 Hz of A zone. Then, it executes a step SD26 of resetting the 3-minute timer and the program returns to the step SD9. In the B mode control, the central controller 64 first executes a step SD30 of checking whether the temperature is in B zone. When the result of the check is "YES", it executes a step SD31 of sending out a 3-code signal to set the operating frequency of the compressor 10 to 15 Hz. Then, it executes a step SD32 of resetting the 3-minute timer and the program returns to the step SD9. When the result of the check in the step SD30 is "NO", it is determined in a step SD33 whether the temperature is in C zone. If the answer is "YES", the central controller 64 in a step SD36 sends out a 2-code signal to set the operating frequency of the compressor 10 to 12 Hz. Then, it executes a step SD35 of ressetting a 3-minute timer and the program returns to the step SD9. When the result of the check in the step SD33 is "NO", the central controller 64 in a step SD36 checks whether the temperature is in D zone. When the result of the check is "YES", it executes a step SD37 of sending out a 1-code signal and setting the operating frequency of the compressor 10 to 9 Hz. Then, it executes a step SD38 of resetting a 3-minute timer and the program returns to the step SD9. When the result of the check in the step SD36 is "NO", the central controller 64 executes a step SD39 of checking whether the temperature is in F zone. When the result of the check is "YES", it executes a step SD40 of resetting a 3-minute timer and turns off the compressor 10. When it is determined in the step SD39 that the temperature is not in F zone, it executes a step SD41 of sendng out a 4-code signal to set the operating frequency of the compressor 10 to 18 Hz of A zone. Then, it executes a step SD42 of resetting a 3-minute timer and the pragram returns to the step SD9. When the central controller 64 finds in the step SD9 in Fig. 11 that the compressor 10 is not "ON", it executes a step SD50 shown in Fig. 14 of checking whether the compressor 10 is "ON". When the result of the check is still "NO", the program returns to the step SD10. When the compressor 10 is found "ON", it executes a step SD51 of detecting the atmospheric temperature, setting a temperature zone corresponding to the detected atmospheric temperature and starting a 3-minute timer. Then, it executes a step SD52 of turning on, i.e., closing the electromagnetic valve 16 and the program returns to the step SD12. Fig. 15 shows a control for turning off the compressor 10 in the case of E zone in the A mode control and also in the case of F zone in the B mode control. The central controller 64 first executes a step SD60 of sending out a 0-code signal for turning off the compressor 10, and then a step SD61 of checking whether the temperature is in E or F zone for a predetermined period of time (in this embodiment, 20 consecutive minutes). When the result of the check is "NO", the program returns to the step SD9. When the result of the check is "YES", it executes a step SD62 of turning off, i.e. opening the electromagnetic valve 16 and then a step SD63 of resetting the 3-minute timer for 20 consecutive minutes and thereafter the program returns to the step SD9. The gentle drying mode is terminated in the same manner as described earlier in connection with the flow chart of Fig. 9 in response to the reception of an end command from the remote controller 50. As shown above, in the gentle drying mode according to the invention, the air in a room can be dehumidified without substantilly reducing the temperature of the room at the time when the command of this mode is received. This is particularly effective in such case as when one goes to bed, and it is possible to realize healthy drying operation while suppressing chillness.

Claims: An air conditioner comprising a freezing cycle circuit including, provided on a main duct line (11), a compressor (10), a four-way valve (12), an external heat exchanger (13), a pressure reducer (14), an internal heat exchanger (15), said main duct line (11) branching into at least an upper and a lower coolant flow line (20,30) in said internal heat exchanger (15), and an on-off valve (16) provided on said upper (20) coolant flow line (20) and closed in a low capacity cooling operation. The air conditioner according to claim 1, wherein said on-off valve is provided on a portion of said upper coolant flow line on an inlet side in a cooling operation. The air conditioner according to claim 1, wherein said upper coolant flow line has a greater length than said lower coolant flow line. The air conditioner according to one of claims 1 and 3, wherein the length of a portion of said lower coolant flow line on a side of a lower end of said heat exchanger is less than the length of the other portion. The air conditioner according to claim 4, wherein a less length portion of said lower coolant flow line is made up for by leading a portion of said upper coolant flow line to the lower end of said heat exchanger. A method of controlling an air conditioner which comprises a freezing cycle circuit including, provided on a main duct line (11) a compressor (10), a four-way valve (12), an external heat exchanger (13), a pressure reducer (14), an internal heat exchanger (15), a controller (64) for controlling said freezing cycle circuit according to signals from a temperature sensor (62,63) and a predetermined temperature detector (61), said main duct line (11) branching at least into an upper and a lower coolant flow line (20,30) in said internal heat exchanger, and an on-off valve (16) provided on said upper coolant flow line (20) and closed in a low capacity cooling operation, said method having a gentle cooling mode for gently cooling a room while a temperature thereof is held in a neighborhood of a predetermined temperature, as well as a cooling operation mode and a heating operation mode, said on-off valve being closed by said controller when said gentle cooling mode is selected. The air conditioner control method according to claim 6, wherein when said gentle cooling mode is selected, said controller sets a plurality of temperature zones with predetermined temperature ranges with reference to predetermined temperatures, and closes said on-off valve when a temperature of the room is in a gentle cooling temperature zone lower than a predetermined temperature for a predetermined period of time. The air conditioner control method according to claim 7, wherein said on-off valve is closed under a further condition that an operating frequency of said compressor is too low to provide a cooling capacity. The air conditioner control method according to claim 7, wherein said pressure reducer is an electronic expansion valve, said controller controlling said electronic expansion valve to increase a cooling capacity thereof when closing said on-off valve. The air conditioner control method according to claim 7, wherein said on-off valve is an electromagnetic valve, and when a temperature of the room is reduced to be lower than said gentle cooling temperature zone, said controller outputs a compressor stop signal and, after a subsequent predetermined period of time, turns off said electromagnetic expansion valve to open said on-off valve. The air conditioner control method according to claim 6, wherein said controller opens said on-off valve when the temperature of the room has been in a temperature zone higher than a predetermined temperature for a predetermined period of time, said controller opens said on-off valve. The air conditioner control method according to claim 11, wherein when said on-off valve is opened, the operating frequency of said compressor is returned to the frequency in the cooling operation mode. The air conditioner control method according to claim 6, wherein when said air conditioner is in a quick cooling operation mode, said gentle cooling mode is not performed until the temperature in the room reaches a neighborhood of a predetermined temperature. A method of controlling an air conditioner which comprises a freezing cycle circuit including, provided on a main duct line (11), a compressor (10), a four-way valve (12), an external heat exchanger (13), a pressure reducer (14), an internal heat exchanger (15), a controller (64) for controlling said freezing cycle circuit according to signals from a temperature sensor (62,63) and a predetermined temperature detector (61), said main duct line (11) branching at least into an upper and a lower coolant flow line (20,30) in said internal heat exchanger (15), and an on-off valve (16) provided on said upper coolant flow line (20) and closed in a low capacity cooling operation, said method having a gentle drying mode for gently drying said room while substantially holding the prevailing temperature thereof, as well as a cooling operation mode and a heating operation mode, said on-off valve being closed by said controller when said gentle drying mode is selected. The air conditioner control method according to claim 14, wherein when said gentle drying mode is selected, said controller sets a plurality of temperature zones with predeterrmined temperature ranges with reference to a temperature of the room at this time and operating frequencies of said compressor for said respective temperature zones, and drives said compressor at an operating frequency for a temperature zone, in which the temperature of the room prevails. The air conditioner control method according to claim 15, wherein the temperature ranges of said temperature zones and the operating frequencies of said compressor are different with reference to a reference atmospheric temperature. The air conditioner control method according to claim 16, wherein when the actual atmospheric temperature is higher than said reference atmospheric temperature, the temperature range is greater than that when the actual atmosphere temperature is lower. The air conditioner control method according to one of claims 15 to 17, wherein the operating frequency of said compressor is changed in accordance with a shift of temperature zone after a predetermined waiting time. The air conditioner control method according to claim 14, wherein said pressure reducer is an electronic expansion valve, said controller controlling said electronic expansion valve to increase a capacity thereof when closing said on-off valve.

Inventors: IGARASHI HIROKI, ITAGAKI ATSUSHI, TAKAHASHI TOMOMI, IGARASHI, HIROKI, ITAGAKI, ATSUSHI, TAKAHASHI, TOMOMI
Applicants: FUJITSU GENERAL LTD, FUJITSU GENERAL LIMITED
Application year: 1997
Main classification: F24F11
IPC codes: F25B41, F24F11, F24F1, F25B13