JP2004057986A - Dehumidification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform successful humidity control in a dehumidification apparatus for adjusting dehumidification capacity by using a separation membrane module and supplying purge air on a secondary side. <P>SOLUTION: The dehumidification apparatus has a humidity measuring means 21 for measuring humidity of dry air discharged from a separation membrane module 1, a flow rate adjusting means 20 for adjusting the flow rate of the purge air to a purge air supply part 8, and a control means 22. The control means 22 outputs a control signal which is continuously changed so that a humidity measured value measured by the humidity measuring means 21 can agree with a humidity set value set by a humidity setting device 23 to the flow rate adjusting means 20, and thereby the flow rate of the purge air is continuously adjusted. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dehumidifier having a separation membrane module, and more particularly to a dehumidifier capable of adjusting dehumidification performance by supplying purge air to a secondary side of a separation membrane.
[0002]
[Prior art]
It is necessary to stably supply dry pressurized air to pneumatic devices installed in factories and various plants. Pressurized air obtained by compressing air with an air compressor often contains moisture and cannot be directly supplied to load equipment. Therefore, a dehumidifier is generally provided between the air compressor and the load equipment.
[0003]
General dehumidification methods include a refrigeration method, a desiccant method, and a separation membrane method. Of these, the separation membrane method is widely used in recent years because of its high dehumidification efficiency and easy downsizing of the apparatus. In general, a separation membrane type dehumidifier is configured by connecting one or a plurality of separation membrane modules in which a number of hollow fiber separation membranes are bundled and accommodated in a container, and such a separation membrane module is, for example, manufactured by Ube Industries. CV10 module and BEKO 4020 module from Germany.
[0004]
FIG. 8 is a sectional view of a separation membrane module using a hollow fiber separation membrane, and FIG. 9 is a process flow diagram of a dehumidifier using the separation membrane module. As shown in FIG. 8, the separation membrane module 1 includes a cylindrical container 2 and a plurality of hollow fiber separation membranes 3 bundled and housed in the container 2. The hollow fiber separation membrane 3 has a large number of fine communication holes on its side wall, and the communication holes have a diameter large enough to allow moisture to pass but not gas. Both ends of a large number of hollow fiber separation membranes 3 formed in a bundle are supported by support members 4 and 5 resin-molded in the container 2, and open to an inlet 6 and an outlet 7, respectively.
[0005]
While the air introduced from the inlet 6 passes through the primary side (inside) of the hollow fiber separation membrane 3, the moisture contained by the partial pressure difference between the primary side and the secondary side of the water vapor penetrates the membrane and the secondary side. (Outside), dehumidified and dehumidified, dried as air, and discharged from the outlet 7 to the outside. A purge air supply section 8 and a purge air discharge section 9 are provided on the secondary side of the hollow fiber separation membrane 3. By supplying dry air from the purge air supply unit 8 as purge air and discharging it from the purge air discharge unit 9, the water separated on the secondary side is discharged to the outside together with the purge air. Side humidity (ie, the partial pressure difference of water vapor) can be reduced. Therefore, by increasing the flow rate of the purge air, the difference in steam partial pressure can be increased to increase the dehumidification performance. Conversely, by decreasing the flow rate of the purge air, the difference in steam partial pressure can be reduced to reduce the dehumidification performance.
[0006]
In FIG. 9, a pipe 10 from an air compressor is connected to an inlet 6 of the separation membrane module 1, and a pipe 11 to a load facility is connected to an outlet 7. When a plurality of separation membrane modules 1 are connected in parallel to constitute a dehumidifier, the pipes 10 and 11 connected to each separation membrane module 1 are branched in parallel.
[0007]
A purge pipe 12 is branched from the pipe 11, and the purge pipe 12 is provided with an electromagnetic on-off valve 13. The on-off valve 13 is ON / OFF controlled by a humidity controller 14 which measures the humidity (relative humidity) of the dry air flowing through the pipe 11 and outputs a control signal. The humidity controller 14 outputs a control signal for opening the on-off valve 13 when the humidity of the dry air is higher than a set value, and outputs a control signal for closing the valve when the humidity is low.
[0008]
FIG. 10 is a diagram illustrating an operation state of the dehumidifier of FIG. 9. Since the humidity controller 14 always outputs the ON-OFF control signal so that the humidity of the dry air always matches the humidity set value, the on-off valve 13 always repeats the open-close operation, and as a result, the humidity of the dry air Greatly overshoots above and below the set value.
[0009]
[Problems to be solved by the invention]
When the on-off valve 13 repeatedly opens and closes as described above, there is a problem that the life of the on-off valve 13 is shortened and the reliability of the device is reduced. Further, since the fluctuation of the flow rate of the purge air is large, the change in the humidity of the dry air (overshoot) also increases, and it is difficult to say that the controllability is always excellent. Then, this invention makes it a subject to solve the problem in such a conventional dehumidifier, and aims at providing the new dehumidifier for that.
[0010]
[Means for Solving the Problems]
The dehumidifier according to the present invention for solving the above-mentioned problems, an inlet for introducing air to be dehumidified to the primary side of the separation membrane, an outlet for discharging dehumidified dry air from the primary side of the separation membrane, A separation membrane module having a purge air supply unit for supplying purge air to the secondary side is provided. The apparatus further includes a humidity measurement unit for measuring the humidity of the dry air discharged from the separation membrane module, a flow adjustment unit for adjusting a flow rate of the purge air to the purge air supply unit, and a control unit. Outputs a control signal that continuously changes so that the humidity measurement value by the humidity measurement means matches the humidity set value to the flow rate adjustment means, so that the flow rate adjustment means continuously changes the purge air flow rate. It is characterized in that it is configured (claim 1).
[0011]
In the above dehumidifier, the control means can perform a P operation, a PI operation or a PID operation (claim 2).
[0012]
In any of the above dehumidifiers, the humidity set value may be variable (claim 3).
[0013]
In any of the above dehumidifiers, at least one of a flow rate measuring unit, a pressure measuring unit, a temperature measuring unit, and a humidity measuring unit for air to be dehumidified is provided, and a deviation signal proportional to a change rate of the measured value is provided. It can be configured to input to the control means and thereby perform a predictive control of a change in the humidity of the dry air affected by those changes.
[0014]
Another dehumidifier according to the present invention that solves the above-mentioned problems includes an inlet for introducing air to be dehumidified into the primary side of the separation membrane, an outlet for discharging dehumidified dry air from the primary side of the separation membrane, A separation membrane module having a purge air supply for supplying purge air to the secondary side of the membrane is provided. The apparatus includes a humidity measuring unit that measures the humidity of the dry air discharged from the separation membrane module, a temperature measuring unit that measures the outside air temperature, and a flow rate adjusting unit that adjusts a flow rate of the purge air to the purge air supply unit. Control means, the control means so that the dew point value corresponding to the humidity measurement value by the humidity measurement means is a value lower by a preset difference than the outside air temperature measurement value by the temperature measurement means to measure the outside air temperature. A continuously changing control signal is output to the flow rate adjusting means, whereby the flow rate adjusting means is configured to continuously change the purge air flow rate (claim 5).
[0015]
In the case where the temperature measuring means is provided, a limiter means may be provided for limiting the measured outside air temperature input to the control means so as not to exceed a preset upper limit (claim 6).
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process flow chart showing an embodiment of a dehumidifier according to the present invention. 8, the separation membrane module 1 has a structure in which a hollow fiber separation membrane is housed in a container, a pipe 10 from an air compressor is connected to an inlet 6 thereof, and a load is A pipe 11 to the equipment is connected.
[0017]
A purge pipe 12 branched from the pipe 11 is connected to a purge air supply unit 8 communicating with the secondary side of the separation membrane module 1. The purge pipe 12 has an electric control valve, a hydraulic control valve, a pneumatic control valve, or the like. Is provided with a flow rate adjusting means 20 capable of continuously adjusting the flow rate. In order to monitor the dew point of the dry air flowing through the pipe 11, the pipe 11 is provided with a humidity measuring means 21 such as a humidity (relative humidity) measuring transmitter, and the detected value is transmitted to the control means 22 as an electric signal. Instead of the humidity measurement transmitter, a dew point measurement transmitter configured to directly measure the dew point may be used.
[0018]
The control means 22 is constituted by a microcomputer device including, for example, a CPU (Central Processing Unit), a storage unit, an input / output unit, and the like, and a predetermined control operation is executed by a control program stored in the storage unit.
The control means 22 compares the humidity measurement value from the humidity measurement means 21 with the humidity set value set by the humidity setting device 23, and continuously sends it to the flow rate adjustment means 20 so that the measured humidity value matches the humidity set value. Output a changing control signal.
[0019]
That is, the measured humidity value and the set humidity value are subtracted as shown in the figure, and the deviation is input to the control unit 24. The control unit 24 sends a control signal continuously changing to the flow rate adjusting means 20 so that the deviation becomes zero. Is output. The control unit 24 of the control unit 22 is configured by a control program as software, and the calculation of the deviation is also executed according to the control program. The control operation of the control unit 24 is configured so that proportional control (P control), proportional integral control (PI control), or proportional integral derivative control (PID control) can be selected. The humidity setting device 23 can be constituted by an input unit such as a keyboard which is a peripheral device of the microcomputer device.
[0020]
Here, when the deviation of the humidity measurement and humidity set value e, time T, Kp a proportional constant, Td a derivative time, the control output m, the base value of the control output and m _0, the control of the control unit 24 The output m is m = Ke + m ₀ in the case of P control, m = K (e + 1 / T · ∫edt) + m ₀ in the case of PI control, and m = K (e + 1 / T · ∫edt + Td · de) in the case of PID control. / dt) + _{m 0} become.
[0021]
FIG. 2 is a diagram showing an example of a control result by the control means 22. The control means 22 selects the PI control, and when the measured humidity value falls below the set humidity value as shown in the figure, the opening degree of the flow rate adjusting means 20 becomes continuous as shown in the figure by the PI control operation according to the deviation e. Gradually decrease. As a result, when the deviation gradually decreases, the control means 22 gradually returns the flow rate adjusting means 20 to the original opening. In the process, the humidity causes some overshoot, but the degree of the overshoot is significantly suppressed as compared with the conventional method shown in FIG. In general, this overshoot slightly increases when P control is selected, but may be further suppressed when PID control is selected.
[0022]
FIG. 3 is a process flow chart showing another embodiment of the dehumidifier according to the present invention. This example differs from the example of FIG. 1 in that the humidity control uses a measured value of the flow rate of the air to be dehumidified in addition to the measured value of the humidity of the dry air. Therefore, the same parts as those in FIG. 1 are denoted by the same reference numerals, and overlapping description will be omitted.
[0023]
In order to measure the flow rate, pressure, temperature and humidity of the pipe 10 through which the air to be dehumidified flows, a flow rate measuring means 30 such as a flow meter type or a capacity type flow rate transmitter, a bellows type or a Bourdon tube type pressure measuring transmitter, etc. A pressure measuring unit 31, a temperature measuring unit 32 such as a thermocouple type or a resistance type temperature measuring transmitter, and a humidity measuring unit 33 similar to the humidity measuring unit 21 are provided, and the measured values are transmitted to the control unit 22 for control. Parameters. In practice, at least one of these measuring means can be selected and provided according to the situation of the process.
[0024]
Further, if desired, a temperature measuring means 34 for measuring the temperature of the outside air and a humidity measuring means 35 for measuring the humidity of the outside air are provided in place of the temperature measuring means 32 and the humidity measuring means 33, and the measured values are controlled. 22 to be used as control parameters.
[0025]
Fluctuations in the flow rate, pressure, temperature, humidity, etc. of the air to be dehumidified affect the dehumidification capacity of the separation membrane module. For example, when the air flow rate increases, the required dehumidification amount increases, and therefore, when the purge air flow rate is constant, the humidity (dew point) of the dry air flowing out of the pipe 11 increases. Similarly, when the pressure, temperature, humidity, etc. of the air increase, the humidity of the dry air also increases.
[0026]
As described above, the humidity measurement value from the humidity measurement unit 21 provided in the pipe 11 is input to the control unit 22, so that when the humidity of the dry air rises, the control unit 22 returns the flow rate to the original value. A control signal that changes continuously is output to the control signal 20. However, there is a considerable time lag (time lag) before fluctuations in the flow rate, pressure, temperature, humidity, etc. of the air to be dehumidified appear as changes in the humidity of the dry air. Therefore, when these fluctuations occur rapidly, the humidity of the dry air greatly overshoots from the set humidity value.
[0027]
In this embodiment, in order to suppress such overshoot as much as possible, measured values such as the flow rate, pressure, temperature, and humidity of the air to be dehumidified are transmitted to the control unit 22 as described above, and occurrence of a large overshoot is reduced. Predictive control for prevention is performed. In other words, the control means 22 is configured to output a control signal that fluctuates in advance to the flow rate adjusting means 20 assuming that a humidity deviation proportional to the rate of change of these measured values occurs temporarily.
[0028]
FIG. 4 is a block diagram illustrating a control system of the control means 22 of FIG. Output signals from the flow rate measuring means 30, the pressure measuring means 31, the temperature measuring means 32, and the humidity measuring means 33 are respectively inputted to parameter converting means 36 to 39 comprising a differentiating circuit, and the output signals of the parameter converting means 36 to 39 are added. Is done. On the other hand, the humidity measurement value from the humidity measurement means 21 is compared with the humidity set value set by the humidity setting device 23 as described above, and the above-mentioned added value is added to or subtracted from the deviation (e) as Δe. The parameter conversion means 36 to 39 and the addition / subtraction operation are configured and executed by software such as a control program stored in advance in the storage unit of the control means 22.
[0029]
FIG. 5 shows a change in parameters such as the flow rate and a state in which Δe generated thereby is added to or subtracted from the deviation e as time elapses. For example, when the flow rate of the air to be dehumidified suddenly increases at t1, the differentially generated + Δe (the same signal as when the humidity has increased) is input to the control unit 24, and the control unit 22 performs PI, PID control, and the like. A continuously changing control signal is output to the flow rate adjusting means 20 to increase the purge air and prepare for the subsequent increase in the humidity of the dry air. When the flow rate suddenly decreases at t2, the purge air is reduced in reverse to the above to prepare for a subsequent decrease in the humidity of the dry air. Then, when other parameters fluctuate, predictive control is performed by the same method. Note that the deviation e during the execution of the normal control operation is maintained at or near zero.
[0030]
In the case where a temperature measuring means 34 for measuring the temperature of the outside air and a humidity measuring means 35 for measuring the humidity of the outside air are provided as required instead of the temperature measuring means 32 and the humidity measuring means 33, the same predictive control as described above is performed. Done. That is, when the outside air temperature rises, the temperature of the air to be dehumidified which is sent by pressurizing the outside air with the air compressor also rises. Similarly, when the humidity of the outside air increases, the humidity of the air to be dehumidified also increases. Therefore, when predictive control is performed using these parameters, the outputs of the temperature measuring means 34 and the humidity measuring means 35 are connected to the control means 22 as shown by the dotted lines in FIG.
[0031]
FIG. 6 is a control block diagram showing a main part of still another embodiment of the dehumidifier according to the present invention. Although not shown in FIG. 6, this embodiment also uses the same separation membrane module 1 as that of FIG. 1, and provides the flow control means 20 shown in the purge pipe 12 to send dry air to the load equipment. The piping 11 is provided with a humidity measuring means 21 shown in the figure. Further, in the present embodiment, a temperature measurement unit 34 for measuring the outside air temperature, a temperature difference setting unit 40, and a humidity dew point conversion unit 41 are provided, and a limiter for setting an upper limit of the outside air temperature measurement value input to the comparison circuit as necessary. Means 42 are provided.
[0032]
The purpose of controlling the humidity (dew point) of the dry air is to prevent dew condensation or the like from occurring inside the pipe 11 to the load equipment as described above. This condensation depends on the temperature difference between the inside and outside of the pipe 11, and when the outside air temperature is high, the dew point also rises. Therefore, in order to control the humidity (dew point) of dry air so that dew is not generated in the pipe 11 throughout the year, it is necessary to set the humidity (dew point) lower than the winter temperature when the outside air temperature is the lowest. .
[0033]
However, in order to lower the humidity (dew point) setting, it is necessary to increase the dehumidifying capacity of the separation membrane module accordingly, so that the flow rate of purge air increases and the energy consumption increases. Therefore, in the present embodiment, the control means 22 controls the dew point corresponding to the humidity of the dry air to always maintain a value lower than the outside air temperature by a predetermined difference. Since the humidity (relative humidity) and the dew point correspond to each other, the humidity is converted to the dew point by the humidity dew point conversion means 41 shown in the figure. The humidity dew point conversion means 41 is constituted by software based on a conversion program stored in the storage unit of the control means 22.
[0034]
In the case where the dew point of the dry air is changed to follow the outside air temperature as described above, when the outside air temperature becomes extremely high in summer or the like, if the dew point of the dry air is maintained too high according to the outside air temperature, the dry air Therefore, it is desirable to set an upper limit for the value of the dew point to be controlled, since troubles may occur in the additional equipment that consumes. Therefore, in the present embodiment, a limiter means 42 as shown is provided on the output side of the temperature measuring means 34 for measuring the outside air temperature, and the measured outside air temperature whose upper limit is limited by the limiter means 42 is input to the control unit 24. The dew point is compared with the dew point. The limiter 42 is also configured by a control program in the controller 22.
[0035]
Next, the operation of the control system shown in FIG. 6 will be described. The humidity measurement value of the dry air from the humidity measurement means 21 is converted into a dew point value by the humidity dew point conversion means 41, and the dew point value is measured by the outside air temperature measurement from the limiter means 42. Is compared to the value. Further, the comparison value is compared with a temperature difference set in advance by the temperature difference setting device 40, and the comparison value is input to the control unit 24. As a result, the control means 22 outputs a continuous control signal to the flow rate adjusting means 20 so that the comparison value becomes zero. That is, the control means 22 continuously controls the flow rate adjusting means 20 by control operations such as P control, PI control, and PID control so that the dew point converted from the humidity of the dry air becomes lower by the temperature difference set by the temperature difference setting device 40. Control.
[0036]
FIG. 7 is a diagram for explaining the control operation of the control means 22 of FIG. For example, when the outside air temperature rises with time as shown in the figure, the humidity (dew point) of the dry air automatically follows a value lower by the temperature difference set by the temperature setting device 40. At t3, the measured outside air temperature exceeds the value set by the limiter means 42, so that the measured outside air temperature is limited to a constant value, and the humidity of the dry air does not rise accordingly.
In this way, by controlling the fluctuation of the humidity of the dry air so as to follow the outside air temperature, it is possible to eliminate useless use of purge air and suppress energy consumption.
[0037]
【The invention's effect】
As described above, in the dehumidifier of the present invention, the control means continuously sends a control signal that continuously changes to the flow rate adjusting means of the purge air so that the humidity of the dry air obtained by the separation membrane module becomes a set value. Output, whereby the flow rate adjusting means continuously changes the purge air flow rate of the separation membrane module to control the humidity. Therefore, the operation frequency of the flow rate adjusting means is reduced and its life is prolonged, and at the same time, a large overshoot of humidity is prevented, and as a result, high-quality dry air can be stably supplied to the load equipment.
[0038]
In the dehumidifier, the control means can perform the P operation, the PI operation, or the PID operation, whereby a stable control system can be configured.
Further, in any of the above dehumidifiers, the set value of the humidity can be made variable, whereby an arbitrary humidity can be set from outside the control means.
[0039]
In any one of the above dehumidifiers, at least one of a flow measurement unit, a pressure measurement unit, a temperature measurement unit, and a humidity measurement unit for air to be dehumidified is provided, and a deviation signal proportional to a change rate of the measured value is controlled. The means can be configured to provide predictive control of changes in dry air humidity that are affected by those changes. With this configuration, when the flow rate, pressure, temperature, humidity, etc. of the air to be dehumidified changes rapidly, the purge air flow rate is controlled early so that it does not greatly affect the change in humidity of the dry air. Can be.
[0040]
Further, another dehumidifying device according to the present invention, the control means so that the dew point value corresponding to the humidity measurement value of the dry air discharged from the separation membrane module is lower than the outside air temperature measurement value by a preset difference. Is output to the flow rate adjusting means, and the flow rate adjusting means is configured to continuously change the purge air flow rate of the separation membrane module by the control signal. With such a configuration, by controlling the fluctuation of the humidity of the dry air in accordance with the outside air temperature, it is possible to eliminate useless use of purge air and suppress energy consumption.
[0041]
When humidity is controlled by providing the temperature measuring means, limiter means may be provided for limiting the measured outside air temperature input to the control means so as not to exceed a preset upper limit. With this configuration, when the outside air temperature becomes extremely high in summer or the like, the dew point of the dry air is suppressed from becoming too high following the outside air temperature, and troubles in load equipment that consumes the dry air are prevented. Generation can be effectively prevented.
[Brief description of the drawings]
FIG. 1 is a process flow chart showing an embodiment of a dehumidifier according to the present invention.
FIG. 2 is a diagram showing an example of a control result by a control unit 22 of FIG.
FIG. 3 is a process flow chart showing another embodiment of the dehumidifier according to the present invention.
FIG. 4 is a block diagram illustrating a control system of a control unit 22 in FIG. 3;
FIG. 5 is a diagram showing, as a lapse of time, a change in a parameter such as a flow rate in the control system of FIG. 4 and a relationship obtained by adding and subtracting Δe generated accordingly to a deviation e.
FIG. 6 is a control block diagram showing a main part of still another embodiment of the dehumidifier according to the present invention.
FIG. 7 is a view for explaining the control operation of the control means 22 of FIG. 6;
FIG. 8 is a sectional view of a separation membrane module using a hollow fiber separation membrane.
FIG. 9 is a process flow diagram of a dehumidifying device using the separation membrane module of FIG.
FIG. 10 is a diagram illustrating an operation state of the dehumidifying device of FIG. 9;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Separation membrane module 2 Container 3 Hollow fiber separation membrane 4,5 Support member 6 Inlet part 7 Outlet part 8 Purge air supply part 9 Purge air discharge part 10,11 Pipe 12 Purge pipe 13 Open / close valve 14 Humidity controller 20 Flow rate adjusting means 21 Humidity measuring means 22 Control means 23 Humidity setting unit 24 Control unit 30 Flow rate measuring means 31 Pressure measuring means 32 Temperature measuring means 33 Humidity measuring means 34 Temperature measuring means 35 Humidity measuring means 36 to 39 Parameter converting means 40 Temperature difference setting unit 41 Humidity dew point conversion means 42 Limiter means

Claims (6)

An inlet 6 for introducing air to be dehumidified to the primary side of the separation membrane, an outlet 7 for discharging dehumidified dry air from the primary side of the separation membrane, and purge air for supplying purge air to the secondary side of the separation membrane. In the dehumidifier provided with the separation membrane module 1 having the supply unit 8,
A humidity measuring unit for measuring the humidity of the dry air discharged from the separation membrane module, a flow adjusting unit for adjusting a flow rate of the purge air to the purge air supply unit, and a control unit;
The control means 22 outputs to the flow rate adjusting means 20 a control signal which continuously changes so that the humidity measured value by the humidity measuring means 21 matches the humidity set value, whereby the flow rate adjusting means 20 adjusts the purge air flow rate. A dehumidifier characterized by being configured to be changed continuously. 2. The dehumidifier according to claim 1, wherein the control unit 22 performs a P operation, a PI operation, or a PID operation. 3. The dehumidifier according to claim 1, wherein the humidity set value is variable. 4. The method according to claim 1, wherein at least one of a flow rate measuring unit 30, a pressure measuring unit 31, a temperature measuring unit 32, and a humidity measuring unit 33 for air to be dehumidified is provided. A dehumidifier, characterized in that a proportional deviation signal is input to said control means 22, thereby performing a predictive control of a change in humidity of the dry air affected by those changes. An inlet 6 for introducing air to be dehumidified to the primary side of the separation membrane, an outlet 7 for discharging dehumidified dry air from the primary side of the separation membrane, and purge air for supplying purge air to the secondary side of the separation membrane. In the dehumidifier provided with the separation membrane module 1 having the supply unit 8,
Humidity measuring means 21 for measuring the humidity of the dry air discharged from the separation membrane module 1, temperature measuring means 34 for measuring the outside air temperature, flow rate adjusting means 20 for adjusting the flow rate of purge air to the purge air supply unit, And control means 22.
The control means 22 continuously changes such that the dew point value corresponding to the humidity measurement value by the humidity measurement means 21 becomes a value lower than the measurement value of the outside air temperature by the temperature measurement means 34 for measuring the outside air temperature by a predetermined difference. A dehumidifier, wherein a control signal to be output is output to the flow rate adjusting means 20, whereby the flow rate adjusting means 20 continuously changes the purge air flow rate. 6. The dehumidifier according to claim 5, further comprising limiter means for limiting the measured outside air temperature input to the control means to not exceed a preset upper limit.

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