Patent Publication Number: US-2010126032-A1

Title: Ductless dryer

Description:
TECHNICAL FIELD 
     The present invention relates to a ductless dryer, and more particularly, to a ductless dryer which is capable of minimizing an amount of water used for dehumidifying humid air exhausted resulting from drying objects to be dried and of preventing stop of a gas combustion or turning on/off of a heater that frequently occurs when air volume in the dryer is reduced. 
     BACKGROUND ART 
     Generally, a clothes dryer is an apparatus performing a drying operation on objects such as wet laundry to be dried by blowing hot air generated by a heater into a drum to absorb moisture from the objects therewithin. Dryers can be categorized as exhausting type dryers and condensing type dryers depending on the method employed for dealing with the humid air generated as the objects are dried by absorbing moisture therefrom. 
     In the exhausting type dryer, humid air exhausted from a drum is exhausted outside the dryer. However, an exhaust duct is required for exhausting the moisture evaporated from the objects in the drum to the outside of the dryer, and especially, the exhaust duct should be installed being extended a long distance to the outside of a room or building, because products of combustion such as carbon monoxide etc, are exhausted together with the moisture. 
     Meanwhile, in the condensing type dryer, the moisture in the humid air exhausted from the drum is condensed at a heat exchange unit to remove the moisture therefrom, and the dried air is recirculated back into the drum. However, a condensing type dryer does not facilitate to use gas as a heating source because a closed loop may be formed due to the flowing of the drying air. 
     In a ductless dryer, these disadvantages of the exhausting type and the condensing type dryers may be improved upon. That is, the ductless dryer has a configuration that it is not required to have an exhaust duct for exhausting the moisture evaporated in the drum installed to be extended a long distance to the outside of the room and to recirculate the dried air back into the drum after condensing the humid air exhausted from the drum in the heat exchange unit to remove the moisture. 
     However, in the ductless dryer, the air from the outside flows into the drum in a hot and dry state resulting from heating by a gas combustion or an electric heater. Here, in order to prevent damage on laundry or a fire, when the air volume in the dryer is reduced, the gas combustion is stopped or the heater is turned on/off, frequently, causing bad influence on the laundry or a safety of the dryer. 
     Also, the ductless dryer is provided with the heat exchange unit for removing the moisture contained in the humid air exhausted after drying the objects to be dried. The heat exchange unit is provided with a tube passing between fins. In order to remove the moisture, water having a temperature below a dew point temperature of the humid air flows through the tube, thereby condensing the humid air contacting with the fins. However, in the related art, even though it doesn&#39;t need to flow the water into the tube when the temperature of water is lower than the dew point temperature of the humid air, the water still flows into the tube without any control, thereby wasting the water. 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     Therefore, it is an object of the present invention to provide a ductless dryer which is capable of preventing stop of a gas combustion or turning on/off of a heater that frequently occurs when air volume in the dryer is reduced. 
     Further, it is another object of the present invention to provide a ductless dryer which is capable of controlling an amount of water used for dehumidifying in a heat exchange unit according to a dew point temperature of humid air. 
     Technical Solution 
     To achieve these objects, there is provided a ductless dryer comprising a main body, a drum rotatably installed at the main body, a hot air supply unit providing hot air into the drum, and a heat exchange unit dehumidifying humid air exhausted from the drum and controlling an amount of water for dehumidifying according to a dew point temperature of the humid air. 
     Here, preferably, the hot air supply unit may control the amount of heat supplied to heat air according to the amount of air introduced into the drum. Here, when time taken for the temperature of the air to reach a predetermined maximum temperature value after the initial drying process, the amount of heat supplied to heat the air may be reduced. 
     To perform this, preferably, the hot air supply unit may comprise a gas combustor for generating hot air by igniting gas after mixing with air, a gas valve for performing or stopping the gas supply to the gas combustor, a hot air supply duct by which the hot air generated from the gas combustor is introduced into the drum, and at least one hot air temperature sensor measuring a temperature of the hot air introduced into the drum. Alternately, preferably, the hot air supply unit may comprise a plurality of fixed heaters, a hot air supply duct by which the hot air generated from the fixed heaters is introduced into the drum, and at least one hot air temperature sensor measuring the temperature of the hot air introduced into the drum. Alternately, preferably, the hot air supply unit may comprise a fixed heater, at least one variable heater, a hot air supply duct by which the hot air generated from the fixed heater and the variable heater is introduced into the drum, and at least one hot air temperature sensor measuring a temperature of the hot air introduced into the drum. 
     Preferably, the heat exchange unit may comprise a heat exchanger, an air temperature sensor and a humidity sensor for calculating a dew point temperature of the humid air passing through the heat exchanger, a water temperature sensor measuring the temperature of water flowing in the heat exchanger, and a water amount valve by which the amount of water flowing in the heat exchanger is adjusted according to the dew point temperature of the humid air and the temperature of water. Here, preferably, the temperature and a humidity of the humid air measured by the air temperature sensor and the humidity sensor may be outputted as volt values, and the values are calculated into the dew point temperature through an operating formula pre-stored in a mi-com. 
     Preferably, the water amount valve is installed at an outlet of a tube passing through a first heat exchanger or at an inlet of a tube passing through a second heat exchanger, and accordingly, the water amount valve is closed in case that the temperature of water flowing in the tube of the first heat exchanger is lower than the dew point temperature of the humid air passing through the first heat exchanger and/or in case that the temperature of water flowing in the tube of the second heat exchanger is lower than the dew point temperature of the humid air passing through the second heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a ductless dryer in accordance with one embodiment of the present invention; 
         FIG. 2  is a planar view showing the ductless dryer of  FIG. 1 ; 
         FIG. 3  is a block diagram showing a first variation of a hot air supply unit in  FIG. 2 ; 
         FIG. 4  is a block diagram showing a second variation of the hot air supply unit in  FIG. 2 ; 
         FIG. 5  is a graph showing an air temperature at an inlet of a drum and an on/off cycle of a heater in case of the heater having a capacity of 5400 W; 
         FIG. 6  is a graph showing an air temperature at an inlet of a drum and an on/off cycle of a heater in case of the heater having a capacity of 4600 W; 
         FIG. 7  is a graph showing an air temperature at an inlet of a drum and an on/off cycle of a heater in case of the heater having a capacity of 4150 w; 
         FIG. 8  is a table comparing a drying performance according to a heater capacity; 
         FIG. 9  is an extracted view of a heat exchange unit in  FIG. 2 ; 
         FIG. 10  is a graph showing a temperature and a humidity of humid air at a first position and a third position in  FIG. 9 ; and 
         FIG. 11  is a graph showing a dew point temperature of humid air at a first position and a temperature of water flowing out a first heat exchanger in  FIG. 9 . 
     
    
    
     MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS 
     Description will now be given in detail of the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  is a schematic view showing the ductless dryer in accordance with one embodiment of the present invention, and  FIG. 2  is a planar view showing the ductless dryer of  FIG. 2 . Arrows indicate flowing of air, 
     Referring to  FIGS. 1 and 2 , the ductless dryer in accordance with one embodiment of the present invention includes a main body  110 , a drum  120  rotatably installed at the main body  110 , a hot air supply unit  140  providing hot air into the drum  120  and controlling heat for heating the air according to air volume, and a heat exchange unit  200  dehumidifying humid air exhausted from the drum  120  and controlling the amount of water for dehumidifying according to a dew point temperature of the humid air. 
     A door  111  for putting clothes into the drum  120  is installed at a front side of the main body  110 . And, a foot  113  supporting the main body  110  is installed at a lower side of the main body  110 . The main body  110  has an inner space provided with a belt  131  rotating the drum  120 , a fan  133  installed in a circulation duct  114 , for providing a blowing force for air in the ductless dryer and a motor  135  providing the belt  131  and the fan  133  with a driving force. A pulley  137  by which the belt  131  is stopped is installed at a rotation shaft of the motor  135 . Here, the motors  135  may be configured to be plural so as to provide the belt  131  and the fan  133  with the driving force, respectively. And, the circulation duct  114  is provided with a filter (not shown) for filtering lint such as a fluff and a waste thread contained in hot and humid air flowing out the drum  120 . 
     The drum  120  is a container having an inner space for objects to be dried, such as clothes. A plurality of lifters  121  for lifting the clothes are installed therein. 
     The hot air supply unit  140  includes a gas valve  141  by which gas is supplied or blocked, a gas combustor  143  for generating hot air by igniting gas exhausted from the gas valve  141  after mixing with external air, a hot air supply duct  145  connecting the gas combustor  143  with the drum  120  so as to supply the generated hot air to the drum  120 , and a hot air temperature sensor  147  measuring a temperature of the hot air introduced into the drum  120 . 
     The hot air supply unit  140  is provided with a flame rod extended from an edge portion of a flame so as to detect a flame current and indirectly measure the amount of carbon monoxide (CO) through a value of the flame current. 
     When the amount of the carbon monoxide measured by the flame rod corresponds to a reference value high enough to badly influence on a human body, the gas valve  141  is closed to stop the combustion and an alarming sound informs a user of necessity to ventilate. 
     The gas combustor  143  connected to the gas valve  141  mixes gas exhausted from the gas valve  141  with the external air for the combustion and heats air using the heat generated therefrom. Hot air generated therefrom is provided into the drum  120  through the hot air supply duct  145 . 
     The hot air temperature sensor  147  is installed at a connect portion  145 a connecting the hot air supply duct  145  with the drum  120 . The hot air temperature sensor  147  may be provided plurally and be installed in the hot air supply duct  145 . 
     In case that the air volume in the dryer is reduced, such as lint caught in the filter interrupts flowing of the air, the air cannot be facilitated to flow due to too much laundry in the drum, the air volume in the dryer is reduced due to blocking of the duct connected to the outside, since the temperature of the air introduced into the drum  120  is higher than a reference temperature (i.e., a temperature applied to prevent damage on laundry or a fire), the laundry may be damaged. 
     To prevent the aforementioned, the hot air supply unit  140  adjusts the gas valve  141  according to the air volume and controls the amount of gas supplied to the gas combustor  143 . That is, if a temperature measured by the hot air temperature sensor  147  exceeds a reference temperature range resulting from that the air volume is reduced, the gas valve  141  is closed partially or entirely so as to reduce or block the gas introduced into the gas combustor  143 . In order to perform this, preferably, the gas valve  141  is implemented as a multiple stage solenoid valve by which an injection amount of gas can be minutely controlled. 
     Accordingly, the amount of heat supplied to the air introduced into the drum  120  can be reduced without frequently stopping the gas combustion so that the temperature of the air can be lowered. Accordingly, it is capable of preventing damage on the laundry and of enhancing a stability of the dryer. 
       FIG. 3  is a block diagram showing a first variation of the hot air supply unit in  FIG. 2 , and  FIG. 4  is a block diagram showing a second variation of the hot air supply unit in  FIG. 2 . 
     Referring to  FIG. 3 , the hot air supply unit  170  in accordance with the first variation includes a fixed heater  171  and a variable heater  173 . 
     The fixed heater  171  handles 50% of the heater capacity, and the variable heater  173  is adjusted to handle the heater capacity 0˜50%. In detail, when the temperature of the air introduced into the drum  120  (refer to  FIG. 1 ) is measured to be within a normal range by the hot air temperature sensor  147  (refer to  FIG. 1 ) due to a normal air volume, the heater is controlled to handle the capacity of 100%. That is, the fixed heater  171  having the capacity of 50% is operated, and the variable heater  173  is fully operated to have the capacity of 50%. 
     However, when the temperature of the air introduced into the drum  120  (refer to  FIG. 1 ) is measured to exceed the normal range by the hot air temperature sensor  147  (refer to  FIG. 1 ) since the air volume is reduced, the heater is controlled to have the capacity reduced. That is, the fixed heater  171  having the capacity of 50% is operated, and the variable heater  173  is adjusted to have the capacity less than 50%. Accordingly, the amount of heat supplied to the air introduced into the drum  120  (refer to  FIG. 1 ) is reduced so that the air temperature is lowered, thereby preventing damage on the laundry. 
     Here, whether or not the air volume is reduced is determined based on time taken for the temperature of the air introduced into the drum  120  (refer to  FIG. 1 ) that is measured by the hot air temperature sensor  147  (refer to  FIG. 1 ) to reach a predetermined maximum temperature value after the initial drying process. That is, the shorter the time duration is, the more the air volume is reduced. 
     Referring to  FIG. 4 , the hot air supply unit  180  in accordance with the second variation includes a plurality of fixed heaters. 
     In this embodiment, the fixed heaters include a first fixed heater  181  having the capacity of 50%, a second fixed heater  183  having the capacity of 30% and a third fixed heater  185  having the capacity of 20%. 
     In detail, when the temperature of the air introduced into the drum  120  (refer to  FIG. 1 ) is measured to be within the normal range by the hot air temperature sensor  147  (refer to  FIG. 1 ) due to the normal air volume, the heater is controlled to handle the capacity of 100%. That is, the first fixed heater  181 , the second fixed heater  183  and the third fixed heater  185  are operated all together. 
     However, when the temperature of the air introduced into the drum  120  (refer to  FIG. 1 ) is measured to exceed the normal range by the hot air temperature sensor  147  (refer to  FIG. 1 ) since the air volume is reduced, the heater is controlled to have the capacity reduced. That is, the heater capacity is controlled by entirely or partially operating the first fixed heater  181 , the second fixed heater  183  and the third fixed heater  185 . Accordingly, the amount of heat supplied to the air introduced into the drum  120  (refer to  FIG. 1 ) is reduced so that the temperature of air is lowered, thereby preventing damage on the laundry. 
     Here, likewise the first variation, whether or not the air volume is reduced is determined based on time taken for the temperature of air introduced into the drum  120  (refer to  FIG. 1 ) that is measured by the hot air temperature sensor  147  (refer to  FIG. 1 ) to reach a predetermined maximum temperature value after the initial drying process. That is, the shorter the time duration is, the more the air volume is reduced. 
     Hereafter, an on/off cycle and a drying performance of the heater according to the heater capacity will be described, in case that the heater capacity is variable such as the first and second variations. 
       FIG. 5  is a graph showing the air temperature at an inlet of the drum and the on/off cycle of the heater in case of the heater having the capacity of 5400 W,  FIG. 6  is a graph showing the air temperature at the inlet of the drum and the on/off cycle of the heater in case of the heater having the capacity of 4600 W,  FIG. 7  is a graph showing the air temperature at the inlet of the drum and the on/off cycle of the heater in case of the heater having the capacity of 4150 W, and  FIG. 8  is a table comparing the drying performance according to the heater capacity. 
     Referring to  FIGS. 5 to 7 , the on/off cycle is approximately 3 minutes and the air temperature is 225° C. in case of the heater capacity of 5400 W, and the on/off cycle is approximately 10 mins and the air temperature is 215° C. in case of the heater capacity of 4150 W. Thus, the smaller the heater capacity is, the lower the maximum temperature of the air flowing into the drum  120  (refer to  FIG. 1 ) that is measured by the hot air temperature sensor  147  (refer to FIG,  1 ) becomes by more than 10˜20° C., and at the same time, the on/off cycle (ΔT) is increased, thus reducing the on/off frequency. But, the larger the heater capacity is, the shorter the time taken for the temperature to reach the maximum temperature at an early stage of the drying process (time taken to substantially and actively dried the laundry), accordingly it is more advantageous to shorten the drying time. 
     Referring to  FIG. 8 , when the air volume is insufficient, the drying time and a power consumption serving as main criteria for a drying performance show no degradation even when the heater capacity is reduced. That is, in case of the heater capacity of 5400 W, the drying time is 92.48 mins and the power consumption is 5,398 kwh, while in case of the heater capacity of 4150 W, the drying time is 90.78 mins and the power consumption is 5.404 kwh. Here, results from the two cases are not particularly different. 
     Accordingly, the amount of heat supplied to the air introduced into the drum  120  can be reduced without frequently turning on/off the heater so that the air temperature can be lowered. Accordingly, it is capable of preventing damage on the laundry and of enhancing a stability of the dryer. 
       FIG. 9  is an extracted view of the heat exchange unit in  FIG. 2 ,  FIG. 10  is a graph showing the temperature and a humidity of humid air at a first position ({circle around ( 1 )}) and a third position ({circle around ( 3 )}) in  FIG. 9 , and  FIG. 11  is a graph comparing a dew point temperature of humid air at the first position ({circle around ( 1 )}) and the temperature of water flowing out of a first heat exchanger in  FIG. 9 . A thick arrow indicates flowing of the humid air passing through the heat exchange unit, and a thin arrow indicates flowing of the water passing through a tube. 
     Referring to  FIG. 9 , the heat exchange unit  200  includes a case  210  forming a receiving space, at least one heat exchanger received in the case  210 , an air temperature sensor and a humidity sensor for calculating the dew point temperature of the humid air passing through the heat exchanger, a water temperature sensor  251  for measuring the temperature of water flowing in the heat exchanger, and a water amount valve  240  for controlling the amount of water flowing in the heat exchanger according to the calculated dew point temperature of the humid air. 
     A water container (not shown) for collecting condensed water generated in a condensing process and dropping is provided at the lower portion of the case  210 . 
     The heat exchanger includes a first exchanger  220  and a second heat exchanger  230 . The heat exchanger may be configured in single or the number of three or more if necessary. 
     The first heat exchanger  220  is composed of a fin  221  and a tube  223 . In the first heat exchanger  220 , hot and humid air flowing out of the drum  120  is condensed by low-temperature water and dried by a heat exchanging manner between air and water. The first heat exchanger  220  is installed at a left side of the case  210  (refer to  FIG. 1 ) so as to be located in an outlet end of the circulation duct  114  (refer to  FIG. 2 ) connected with the drum  120 . 
     The fin  221  is implemented as a plurality of thin plates stacked to each other with a minute gap therebetween so as to pass through the hot and humid air by vertically contacting thereto. Here, the thin plate is formed by a metallic material having an excellent conductivity. 
     The low-temperature (22° C.) water is circulated in the tube  223 . And, the tube  223  is penetratingly formed at the fin  221  in a reciprocating manner. 
     Likewise the first heat exchanger  220 , the second heat exchanger  230  is composed of a fin  231  and a tube  233 . In the second heat exchanger  230 , the dehumified air flowing out of the first heat exchanger  220  is condensed by the low-temperature water and dried once more by the heat exchanging manner between air and water. The second heat exchanger  230  is installed at a right side of the case  210  so as to be located in an Inlet end of the exhaust duct  161  (refer to  FIG. 1 ). 
     The fin  231  is Implemented as the plurality of thin plates stacked to each other with the minute gap therebetween so as to pass through the hot and humid air by vertically contacting thereto. Here, the thin plate is formed by a metallic material having the excellent conductivity. 
     The low-temperature (22° C.) water is circulated in the tube  233 . And, the tube  233  is penetratingly formed at the fin  231  in the reciprocating manner. 
     And, the tube  223  of the first heat exchanger  220  and the tube  233  of the second heat exchanger  230  are connected with each other at a middle position between the first heat exchanger  220  and the second heat exchanger  230 . 
     And, an inlet  233   a  of the tube  233  of the second heat exchanger  230  and an outlet  223   a  of the tube  223  of the first heat exchanger  220  are connected to a water hose (not shown) connected to an external water supplying source so as to receive water from the outside. 
     The water introduced into the inlet  233   a  of the tube  233  of the second heat exchanger  230  through the water hose passes through the water amount valve  240  and the tubes  233 ,  223 , and then cools the fin  231  of the second heat exchanger  230  and the fin  221  of the first heat exchanger  220 . And after, the water flows into the water hose through the outlet  223   a  of the tube  223  of the first heat exchanger  220 . 
     Meanwhile, in order to dehumidify the humid air at the heat exchange unit  200 , a status amount of the humid air passing through the first heat exchanger  220  and the second heat exchanger  230  should be detected. 
     That is, the dew point temperature proper to condense moisture on the fin  221  of the first heat exchanger  220  and the fin  231  of the second heat exchanger  230  and corresponding amount of water to be supplied can be controlled only after detecting the status amount of the humid air. 
     There may be a plurality of factors to determine the status amount of the humid air, for example, temperature/humidity of external air introduced into the heater or a gas burner according to the season, the temperature of water supplied to the heat exchanger, variation in a moisture content of laundry in the drum during the drying process and the temperature/humidity of peripheral air of the dryer. 
     Thus, only if the status of the humid air is detected at the inlet of the first heat exchanger  220  (hereafter, the first position ({circle around ( 1 )})), between the first heat exchanger  220  and the second heat exchanger  230  (hereafter, the second position ({circle around ( 2 )})), and the outlet of the second heat exchanger  230  (hereafter, the third position ({circle around ( 3 )})) considering all the factors above, the water amount can be actively controlled, thereby being capable of reducing the amount of water used. 
     To perform this, an air temperature sensor  253  and a humidity sensor  254  are installed at the first position ({circle around ( 1 )}), and an air temperature sensor  255  and a humidity sensor  256  are installed at the second position ({circle around ( 2 )}). Also, an air temperature sensor  257  and a humidity sensor  258  are installed at the third position ({circle around ( 3 )}). 
     Referring to  FIG. 10 , an RH_air_outlet indicates a relative humidity of the humid air measured by the humidity sensor  258  at the third position ({circle around ( 3 )}), a T_air_inlet indicates the temperature of the humid air measured by the air temperature sensor  253  at the first position ({circle around ( 1 )}), and a T_air_outlet indicates the temperature of the humid air measured by the air temperature sensor  257  at the third position ({circle around ( 3 )}). 
     The temperature and the humidity of the humid air measured by the air temperature sensors  253 ,  255 ,  257  and the humidity sensors  254 ,  256 ,  258  are outputted as volt values. And, the values are calculated into the dew point temperatures at the first position ({circle around ( 1 )}), the second position ({circle around ( 2 )}) and the third position ({circle around ( 3 )}) through an operating formula pre-stored in a mi-com (not shown). 
     More particularly, in order to detect the status amount of the air, data regarding to a dry bulb temperature and a wet bulb temperature (or relative humidity) at the first, second and third positions are collected by the air temperature sensors  253 ,  255 ,  257  and the humidity sensors  254 ,  256 ,  258 , and the mi-com (not shown) serves to calculate each dew point temperature at the first, second and third positions using the collected data. 
     The water temperature sensor  251  is installed on the tubes  223 ,  233  introduced into the second heat exchanger  230  from the first heat exchanger  220  so as to measure the temperature of the water flowing in the tubes  223 ,  233 . 
     The water amount valve  240  is installed at the inlet  233   a  of the tube  233  passing through the second heat exchanger  230  so as to control the amount of water introduced into the tube  233 . The water amount valve  240  can be installed at the outlet  223   a  of the tube  223  passing through the first heat exchanger  220  if necessary. Here, the water amount valve  240  may be selectively implemented as one of an analog type valve that can be consecutively switched and a digital type valve that is switched by on and off signals and relatively cheap. To perform a minute controlling, the water amount valves  240  may be used in plural. 
     Referring to  FIGS. 9 and 11 , since the dew point temperature (T_Dew_In_Hex 1 ) of the humid air at the first position ({circle around ( 1 )}) is lower than the temperature (T_Hex 1 _Out_Surf) of the water flowing in the tube  223 , the humid air is uniformly condensed at the entire fin  221  of the first heat exchanger  220 . Here, the water amount valve  240  is closed so as not to allow the water to flow into the tube  223  any more, thereby reducing the amount of water used. 
     If the water temperature measured by the water temperature sensor  251  is higher than the calculated dew point temperature, the water amount valve  240  is opened so as to allow the water to be supplied more, thereby lowering the temperature of the surface of the fin  221  of the first heat exchanger  220  and the temperature of the surface of the fin  221  of the second heat exchanger  230  to be lower than a condensation temperature. 
     According to the aforementioned configuration, the temperature of the surface of the fin  221  of the first heat exchanger  220  is maintained below the dew point temperature of the humid air at the first position ({circle around ( 1 )}) and the temperature of the surface of the fin of the second heat exchanger  230  is maintained below the dew point temperature of the humid air at the second position ({circle around ( 2 )}) with controlling the amount of water used, thereby reducing the amount of water used with a maximum efficiency of the heat exchanger. 
     Meanwhile, it is capable of reducing the amount of water used with simple and a low cost. 
     As the simplest method, when the dryer is cooled without any control, the water amount valve  240  may be entirely closed, thereby reducing the amount of water used. 
     And, by receiving the temperature of water supplied into the heat exchange unit  200 , the valve is adjusted by the plurality of stages corresponding to temperature ranges estimated through experiments performed for a product development, thereby controlling the amount of water used. 
     And, in the related dryer, it is started that the water amount is purposely reduced or the water supply is stopped from when the drying process is almost finished, that is when the graph is drastically dropped down, by analyzing signals of an electrode sensor or the humidity sensor that is used for the determination, thereby minimizing damage caused by the moisture exhausted to the outside of the dryer and reducing the amount of water used. 
     The ductless dryer in accordance with the present invention may have the following advantages. 
     First, when the air volume is reduced, and thus the temperature value measured by the hot air temperature sensor is greater than the reference value, the amount of gas introduced into the gas combustor is reduced or the gas supply is stopped by closing the gas valve partially or entirely. Accordingly, the heat supplied to the air introduced into the drum is reduced without frequently stopping the gas combustion thus the temperature of the air is lowered, thereby being capable of preventing damage on laundry and of enhancing the stability of the dryer. 
     Second, when the air volume is reduced, and thus the temperature value measured by the hot air temperature sensor is greater than the reference value, the heater capacity is varied. Accordingly, the heat supplied to the air introduced into the drum is reduced without frequently turning on/off the heater thus the temperature of the air is lowered, thereby being capable of preventing damage on laundry and of enhancing the stability of the dryer. 
     Third, the temperature of the heat exchanger is maintained below the dew point of the humid air with controlling the amount of water used, thereby being capable of maximizing the efficiency of the heat exchanger and of reducing the amount of water used. 
     The ductless dryer in accordance with the present Invention can be used domestically, commercially and industrially. 
     It will also be apparent to those skilled in the art that various modifications and variations can be made In the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.