Method for operating laundry dryer, and laundry dryer

Abstract

To automatically set an appropriate inlet temperature of drying air; and to change an exhaust circulation rate at stable appropriate timing.SOLUTION: A method for operating a laundry dryer includes: after starting drying operation, fully opening a temperature adjusting valve for controlling an inlet temperature of drying air and monitoring the inlet temperature; automatically setting, as an inlet temperature set value, in a controller, a peak temperature detected during that time, a temperature obtained by subtracting a preset differential temperature from the peak temperature, or an inlet temperature average value after detecting the peak temperature; performing the drying operation while controlling the temperature adjusting valve so as to maintain the set value; and changing a circulation rate of exhaust circulation according to a change in laundry temperature or exhaust temperature during the operation.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a control method or operation method for a dryer for laundry such as towels and bedding, particularly a laundry dryer for commercial use that washes the same type of washed laundry collectively, and a laundry dryer capable of executing said method. [Background technology]

[0002] Washing / drying machines that perform washing and drying in succession and laundry dryers that are dedicated to drying (both are collectively referred to as "laundry dryers" or simply "dryers" in this application) dry laundry placed in a rotating drum installed in a drying chamber using drying air heated by a steam heater or burner. The dehydrated laundry is loosened by the rotation of the drum and then dried by the heated air passing through the drum. It is known that the drying process goes through a preheating period, a constant rate drying period, and a decreasing rate drying period before the drying is completed.

[0003] During the preheating period, the temperature of the laundry containing moisture is raised to the constant rate drying temperature. During the constant rate drying period, the moisture content decreases at a constant rate, and the temperature of the laundry and the drying speed are almost constant. Therefore, the exhaust temperature is also almost constant. During the falling rate drying period, the moisture on the surface of the laundry disappears, and the drying speed is limited by the rate at which the internal moisture moves to the surface. As the drying progresses, the drying speed gradually decreases, and the temperature of the laundry and the exhaust temperature gradually increase.

[0004] The heating temperature of the drying air (the temperature when it flows into the drying chamber, hereafter referred to as the "inlet temperature") is generally changed depending on the type of laundry, for example 150°C for synthetic fibers and 120°C for futons. 100% cotton towels are often operated without temperature regulation (control of the inlet temperature), and the inlet temperature depends on the steam pressure on the equipment side, with the steam pressure of typical commercial laundry equipment being 0.7-0.8MPa and the inlet temperature being 160-170°C.

[0005] Even when temperature control is performed (for example, Patent Document 7), the inlet temperature is set manually, and if the setting is not done properly, the drying speed will drop significantly. Therefore, in order to prioritize productivity, the inlet temperature is set high so that the temperature control valve is always fully open, which often results in wasted heat energy.

[0006] The temperature of the laundry (hereinafter referred to as "item temperature") and the rise in the exhaust air temperature during the falling-rate drying period are used to detect the point in time when the laundry is dry, i.e., the point in time when the drying operation is to be terminated. For example, when the item temperature or the exhaust air temperature reaches a set temperature, the drying operation is terminated immediately or after a predetermined time has elapsed (e.g., Patent Documents 1, 2, and 5).

[0007] In order to efficiently use the energy consumed, a method called exhaust gas recirculation is used, in which part or all of the exhaust gas whose temperature has risen during falling-rate drying is recirculated to the intake side. That is, an opening and a damper that opens and closes the opening are provided in the partition that separates the exhaust passage from the intake passage, and the degree of exhaust gas recirculation is adjusted by the opening degree of this damper.

[0008] For example, Patent Document 2 describes a method of continuously controlling the amount of exhaust circulation by detecting the supply air temperature, exhaust air temperature, and item temperature, while Patent Document 3 describes a method of determining that a constant rate drying period has begun based on a change in exhaust air temperature, and reducing the amount of heat generated by the heater.

[0009] Furthermore, Patent Document 4 describes controlling the drying time by determining the type, amount, and dehydration rate of the laundry from changes in the exhaust temperature during the residual heat (preheating) period at the beginning of drying, while Patent Document 6 describes reducing the amount of heat generated when the rate of increase in the item temperature becomes greater than the rate of increase in the exhaust temperature. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] European Patent Application Publication No. 1279760 [Patent Document 2] European Patent Application Publication No. 2657395 [Patent Document 3] Japanese Unexamined Patent Publication No. 14893 / 1983 [Patent Document 4] Japanese Unexamined Patent Publication No. 62-243595 [Patent Document 5] Japanese Patent Application Publication No. 10-96588 [Patent Document 6] JP 2005-168640 A [Patent Document 7] JP 2007-61411 A Summary of the Invention [Problem to be solved by the invention]

[0011] As mentioned above, laundry dryers use heated drying air to dry laundry, and consume energy to heat the air. Conventionally, energy-saving measures have been taken to reduce this energy consumption, such as adjusting the amount of steam from the steam heater according to the progress of drying or circulating exhaust air.

[0012] In a laundry dryer, laundry is placed in a drum, which is then rotated or swung, and the laundry is dried with drying air that is heated by a heating means and passes through the drum. Exhaust air circulation is performed to reduce the energy consumption required for drying by returning a portion of the drying air (exhaust air) that has passed through the drum to the air intake side of the drum. The exhaust air circulation rate, i.e., the proportion of exhaust air that is returned, needs to be changed at an appropriate timing according to the progress of the drying process.

[0013] Exhaust air circulation is an extremely effective means of saving energy consumed by laundry dryers, but experience and intuition are required to set the timing for changing the circulation rate (mainly to increase the circulation rate), and if the circulation rate is increased too early, excess moisture is returned, lengthening the time it takes to dry, and if the circulation rate is increased too late, reuseable exhaust heat is wasted, increasing steam consumption and reducing energy efficiency. In addition, it has been suggested that the frequent occurrence of natural disasters in recent years is due to global warming, and there is a demand for further reductions in energy consumption.

[0014] The first objective of this invention is to further reduce energy consumption by automatically setting an appropriate inlet temperature and maintaining the set inlet temperature in dryers, which are a type of laundry equipment that consumes a lot of energy, and the second objective is to enable changes to the exhaust gas recirculation rate to be made at a stable and appropriate timing. [Means for solving the problem]

[0015] In this invention, after the start of the drying operation, the temperature control valve 4 which controls the inlet temperature Ti of the drying air A is fully opened to monitor the inlet temperature Ti, and the maximum temperature (peak temperature) Tp detected during that time or a temperature slightly lower than the peak temperature, i.e., the temperature obtained by subtracting a preset difference temperature ΔTp from the detected peak temperature Tp or the average value of the inlet temperature Ti after the peak temperature Tp is detected, is automatically set in the controller as the set value of the inlet temperature, and the temperature control valve 4 is controlled to maintain that set value while performing the drying operation, thereby solving the first problem.

[0016] When using a steam heater as the heating means 3 for heating the drying air, if many machines use steam in a laundry factory where the steam pressure fluctuates greatly, the set inlet temperature can be maintained by increasing the set value of the differential temperature ΔTp. How low the temperature should be set is determined individually, taking into account the steam consumption and fluctuations of the machines installed in each laundry factory.

[0017] Considering the actual conditions of a laundry factory, the differential temperature ΔTp is preferably in the range of 0 to 10° C., and more preferably 0 to 5° C. The differential temperature ΔTp may be calculated according to the detected peak temperature Tp or the time that the temperature is maintained. The maximum value of the steam pressure may be detected, and the saturation temperature of the steam may be set as the peak temperature to determine the controlled temperature.

[0018] In a steam heater, when the temperature control valve 4 is not controlled to open or close, the latent heat of the steam is exchanged with the drying air to become drain at the saturation temperature, and the drain is discharged from the steam trap. On the other hand, when the temperature control valve 4 is controlled to turn on and off at a set temperature, a temperature difference is provided between the opening temperature and the closing temperature to prevent chattering, but after the temperature control valve is closed and the latent heat of the steam is exchanged with the drying air to become drain at the saturation temperature, the sensible heat held by the drain is also exchanged (the drain temperature is lower than when the temperature control valve is open, and the amount of heat discharged is reduced), which allows the amount of steam consumption to be reduced.

[0019] Furthermore, by combining it with exhaust gas circulation, the temperature of the air flowing into the heater can be increased, so that even when the inlet temperature is controlled and the temperature control valve 4 is throttled, the inlet temperature does not drop significantly, the inlet temperature is stable, and the impact on the drying time is reduced, resulting in further energy savings.

[0020] In this invention, the second problem is solved by detecting or estimating the decreasing rate transition point P1 at which the constant rate drying period (hereinafter referred to as the "constant rate period") F2 transitions to a decreasing rate drying period (hereinafter referred to as the "decreasing rate period") F3, and performing control to increase the exhaust gas recirculation rate at the detected or estimated point.

[0021] The ramp-down rate transition time point P1 is detected by detecting that the temperature gradient (which becomes nearly 0) of the item temperature Tw or exhaust temperature Ta during the constant rate period F2 has begun to rise. The ramp-down rate transition item temperature difference ΔT1 or ramp-down rate transition exhaust temperature difference ΔTa1 is set in the controller, and the item temperature Tw or exhaust temperature Ta during the constant rate period F2 is set as the reference temperature T0, Ta0, and the ramp-down rate transition time point P1 is when the detected item temperature Tw reaches a temperature obtained by adding the ramp-down rate transition item temperature difference ΔT1 to the reference item temperature T0 when the item temperature is set as the reference temperature Ta0, and when the detected exhaust temperature Ta reaches a temperature obtained by adding the ramp-down rate transition exhaust temperature difference ΔTa1 to the reference exhaust temperature Ta0 when the exhaust temperature is set as the reference temperature Ta0.

[0022] In this case, the determination that it is the constant rate period F2 for setting the reference item temperature T0 is made by determining the rate of change of the item temperature or exhaust temperature (almost 0), or by determining that the constant rate period F2 is the point at which the constant rate determination waiting time t1 set in the controller as the elapsed time from the start of operation or the transition from the preheating period to the constant rate period has elapsed.

[0023] At the decrease rate transition time P1 determined by the above method, the opening of the damper 11 is changed, for example, from 1 / 4 to 1 / 2 to increase the exhaust gas recirculation rate. In this invention, the inlet temperature Ti is controlled to maintain a set value, so there is no fluctuation in the product temperature or exhaust gas temperature caused by fluctuations in the inlet temperature. This makes it possible to more accurately determine the transition from the fixed rate period F2 to the decrease rate period F3 based on changes in the product temperature Tw or the exhaust gas temperature Ta, and the energy saving effect of the exhaust gas recirculation can be stably achieved.

[0024] This invention also focuses on the fact that a temperature difference occurs between the surface and the inside of the laundry fibers at the end of the falling rate period (hereinafter referred to as the "falling rate end period") F4, and by performing a temperature difference elimination operation to eliminate this temperature difference at the falling rate end period F4 and ending the drying operation after said operation, it is possible to reduce energy consumption at the drying end period. Effect of the Invention

[0025] This invention allows energy savings without significantly reducing the drying speed. Furthermore, by combining it with exhaust gas circulation, further energy savings can be achieved without extending the drying time. The results of the drying test showed that it was possible to reduce steam consumption by approximately 5%.

[0026] According to this invention, operation can be performed with the optimal inlet temperature setting according to the steam pressure on the equipment side, without having to set the inlet temperature before starting operation, and an excessive increase in the inlet temperature that does not contribute to improving the drying speed can be suppressed, so that steam consumption can be reduced without reducing productivity.

[0027] Furthermore, by controlling the inlet temperature, it is possible to ensure stability of the exhaust temperature and the product temperature, so that the transition to the constant rate drying period, the decreasing rate drying period, and the decreasing rate end period can be performed more accurately. Also, by adding an option for the automatic inlet temperature setting mode to the operating method options, it is possible to easily perform appropriate energy-saving operation without having to input the inlet temperature setting value individually for each drying program. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a front view showing an example of an internal structure of a laundry dryer; [Diagram 2] Side view [Diagram 3] A diagram showing the progress of the washing process and the change in temperature of the item [Figure 4] Block diagram of a control device according to a first embodiment [Diagram 5] FIG. 13 is a diagram showing an example of a screen for selecting an operation method. [Figure 6] Flowchart showing the control procedure of the first embodiment [Figure 7] Flowchart showing the control procedure of the second embodiment [Figure 8] Flowchart showing the control procedure of the third embodiment [Figure 9] FIG. 4 is a diagram showing the position of the symbols of the third embodiment on the diagram of FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, an embodiment of the present invention will be described with reference to the drawings showing the embodiment.

[0030] 1 and 2 are diagrams showing an example of a commercial laundry dryer. Laundry W is loaded into drum 1, which is rotated around a horizontal axis in drying chamber 12, and drying air A, which is sucked in through air inlet 2 and heated by steam heater 3, flows across drum 1 and dries laundry W, which is stirred up by rotation R of drum 1 and then falls. Steam heater 3 is equipped with temperature control valve 4, which adjusts the amount of steam, and bypass valve 5, which is used when a small amount of steam is allowed to flow. Temperature control valve 4 and bypass valve 5 are controlled to open and close by commands from a controller (not shown).

[0031] The drying air A that has passed through the drum 1 is discharged from the exhaust port 7 by the exhaust blower 6, but by opening a damper 11 that covers an opening 10 provided in the partition between the exhaust path 8 and the intake path 9, part of the exhaust air is returned to the intake path 9 (exhaust air circulation), and is heated by the heater 3 together with the intake outside air and reused as drying air.

[0032] The inlet temperature Ti of the drying air A that is heated by the heater 3 and flows into the drying chamber 12 is detected by an inlet temperature sensor 15.

[0033] The surface temperature (item temperature) Tw of the laundry W stirred up as the drum 1 rotates is detected by an item temperature sensor (infrared sensor) 13 provided in the drying chamber 12. The temperature of the drying air A passing through the drying chamber 12 is detected by an exhaust temperature sensor 14 provided in the exhaust path 8.

[0034] 3 is a graph showing the changes in the inlet temperature Ti, product temperature Tw, and exhaust temperature Ta detected by each sensor against the time elapsed from the start of operation, with the horizontal axis representing the elapsed time (minutes) and the vertical axis representing temperature (°C). Drying is completed through a preheating period F1, a constant rate period F2, and a decreasing rate period F3.

[0035] Since the inlet temperature Ti reaches the maximum temperature Tp immediately after operation starts, it is controlled to maintain it at a temperature slightly lower than that temperature (for example, a temperature 2 to 5°C lower). Specifically, the maximum temperature detected during the period from the start of operation until the lapse of the set peak detection time tp is used as a reference, and the reference temperature or a temperature slightly lower than the reference temperature (for example, a temperature 0 to 10°C lower, more preferably a temperature 0 to 5°C lower) is used as the set value of the inlet temperature, and the temperature control valve 4 is controlled to maintain the set value. Figure 3 is a diagram when the temperature control valve 4 is on / off controlled.

[0036] Fig. 4 is a block diagram of a device for automatically setting the inlet temperature Ti of drying air A, and Fig. 6 is a flow chart showing an embodiment of the automatic setting procedure. A controller of the laundry dryer is preset with a plurality of drying programs 21, an inlet temperature set value calculation program 22, and parameters 23 used in the programs. Program selection means 24 and temperature control condition selection means 25 display selection items on a display to prompt the operator to input.

[0037] FIG. 5 is a diagram showing an example of a screen that allows the operator to select a program and temperature control conditions, and shows the state when the operator has selected "Drying 1" and "Temperature control." When "Temperature control" is selected, a button for selecting the temperature control conditions is displayed on the right side of the screen. When "Inlet temperature" or "Outlet temperature" is selected, the set values ​​for these are manually entered. "Fully open" is the mode in which the temperature control valve is kept fully open, and "fully closed" is the operation in which only the cooling process is performed. The button labeled "ECO" in FIG. 5 is the button for selecting the inlet temperature automatic setting mode 27 in FIG. 4, and is the button for selecting the operation method of this invention.

[0038] When the operator selects the drying program 26 and the inlet temperature automatic setting mode 27 to be used and starts the drying operation (see Figs. 7 and 8), the controller fully opens the temperature control valve 4 (steps s21, s31) and starts the drying operation (steps s22, s32). When the inlet temperature automatic setting mode 27 is selected, the controller calls the set value calculation program 22 and the parameters 23 to be used in the program at the same time as the drying operation starts (YES in step s11), and starts a timer count (step s12).

[0039] The inlet temperature sensor 15 sequentially sends the detected temperature to the inlet temperature storage memory 28 (step s13), and the calculation program 22 calculates (step s16) the set value of the inlet temperature from the highest value Tp (step s15) detected continuously during the peak detection time tp (e.g., 4 minutes) in the set parameters 23 and the integrated retention time (e.g., 30 seconds) in the parameters 23 (step s14) and the differential temperature ΔTp in the parameters 23, and automatically sets it in the inlet temperature setter 29 (step s17).

[0040] If the maximum inlet temperature is maintained for the set integrated hold time before the peak detection time tp has elapsed, the inlet temperature control is started with that temperature as the maximum temperature. If the inlet temperature has not stabilized until the peak detection time tp has elapsed, the maximum temperature detected during the peak detection time tp is used.

[0041] For example, when the cumulative peak temperature retention time (time when the temperature drops below the peak temperature is not counted) exceeds the set time (30 seconds), the peak temperature at that time is used as the reference temperature and inlet temperature control is started. If the peak temperature is updated during the process, the cumulative time is reset.

[0042] In the example of Figure 3, the maximum inlet temperature Tp = 159°C detected 2 minutes after the start of operation is set as the reference temperature, and operation is performed under the conditions of a differential temperature of 0°C and an inlet temperature setting (controlled temperature) of 159°C. The temperature control valve 4 used for inlet temperature control is an on-off valve that is fully closed when the detected inlet temperature is 159°C and fully open when the detected inlet temperature is 157°C (reference temperature minus 2°C).

[0043] The temperature control valve 4 used for inlet temperature control may be a motor valve whose opening can be continuously changed. However, it is believed that a greater energy saving effect can be obtained by using an on-off valve to perform the control of the present invention.

[0044] In other words, when the temperature control valve 4 goes from open to closed, the saturated vapor pressure inside the heater 3 drops from the steam pressure when it was open (assuming the gauge pressure was 0.8 MPa) to saturated water (drain: 175°C) as the steam (175°C) removes latent heat, and as it continues to remove heat the saturated vapor pressure drops, for example to 0.6 MPa, resulting in approximately 80% saturated steam (165°C) and approximately 20% saturated water (drain) by mass. At this time, the latent heat of the approximately 20% of the steam that became drain and the sensible heat difference due to the drop in drain temperature are used (recovered) to heat the drying air (compared to when the temperature control valve is not closed).

[0045] On the other hand, if steam is constantly supplied, 0.8 MPa of drain (sensible heat) will be discharged, and the energy saved will be the aforementioned heat recovery from that sensible heat; if the pressure drops to 0.8 to 0.7 MPa, the energy saving rate will be approximately 3%, and if the pressure drops to 0.8 to 0.6 MPa, the energy saving rate will be approximately 6%.

[0046] Therefore, it is preferable to use an on-off valve as the temperature control valve 4. Even if an opening-adjustable valve is used, it is believed that the same energy-saving effect as on-off control can be obtained by controlling the opening to vary at regular intervals (changing the set temperature at regular intervals).

[0047] When performing on / off control, it is common to set a temperature difference between the on and off temperature to prevent valve chattering, and in the example in Figure 3, this temperature difference is set to 2°C, and the temperature control valve is controlled to close at a detected temperature of 159°C and open at 157°C. Because there is a time lag between when the temperature control valve is opened and when the detected temperature rises, the inlet temperature Ti in the diagram in Figure 3 drops to around 155°C.

[0048] In actual on / off control, it is believed that it is necessary to set not only the differential temperature but also the temperature difference between the on temperature and off temperature (preferably in the range of 1 to 3°C). By setting the temperature drop from the inlet temperature set value to 2 to 10°C (more preferably 3 to 6°C) and the on / off interval to 10 to 60 seconds (more preferably 20 to 45 seconds), it is possible to reduce steam consumption without reducing the drying speed.

[0049] It is believed that the same effect can be obtained by installing a steam pressure sensor on the secondary side of the temperature control valve, detecting the maximum pressure, and controlling the steam pressure to vary within a certain range, instead of controlling the inlet temperature.

[0050] For example, if the maximum pressure is 0.8 MPa, the difference is 0.05 MPa, and the pressure difference for on / off operation is 0.15 MPa, the set pressure will be 0.75 MPa, and the temperature control valve will close when it reaches 0.75 MPa and open at 0.6 MPa.

[0051] 3, the item temperature Tw detected by the item temperature sensor 13 rises sharply in the preheating period F1, remains almost constant in the constant rate period F2, and gradually rises in the falling rate period F3. The exhaust temperature Ta detected by the exhaust temperature sensor 14 changes in a similar manner to the item temperature, except for the preheating period.

[0052] The small fluctuations in the item temperature Tw are thought to be due to uneven drying of the laundry, with a peak appearing when the driest part is measured and a valley appearing when the wetter part is measured. The item temperature of the entire laundry inside the drum (strictly speaking, the surface temperature of the item) can be smoothed by taking the average of consecutive measurements or by placing multiple sensors and taking the average of their measurements.

[0053] In the constant rate period F2, the product temperature Tw and exhaust temperature Ta remain almost constant throughout the period, so it can be determined that the period is a constant rate period because there is no change in the product temperature Tw or exhaust temperature Ta. When the falling rate period F3 begins, the product temperature gradient and exhaust temperature gradient rise again, so it can be determined from this change in temperature gradient that the period has left the constant rate period F2 and entered the falling rate period F3.

[0054] In the falling rate period F3, the moisture content of the laundry fibers gradually decreases, and therefore the moisture that migrates from inside the fibers to the fiber surfaces also gradually decreases, so that the temperature gradient of the item temperature Tw is not linear but quadratic, that is, it is considered that the temperature gradient changes so that it becomes steeper with time. In the example of Figure 3, the exhaust temperature Ta exceeds the item temperature Tw after the start of the drying process, but it can be seen that the item temperature Tw, especially its peak value, exceeds the exhaust temperature Ta in the latter part of the falling rate period F3.

[0055] In falling-rate drying, a temperature difference occurs between the surface and the inside of the laundry fibers, and as the fibers dry, the thermal conductivity decreases, so the temperature difference between the surface and the inside increases as the drying progresses. By utilizing this temperature difference in the final falling-rate stage F4 to evaporate the moisture inside the fibers, it is thought that the energy consumption in the final falling-rate stage can be reduced.

[0056] In this invention, the set value of the inlet temperature is automatically set and the inlet temperature Ti is controlled to be maintained at the set value, so that it is possible to reduce fluctuations in the temperature of the drying air A caused by fluctuations in the steam pressure supplied to the heater, and fluctuations in the temperature of the product and the exhaust temperature during drying are also reduced. Therefore, by determining the transition to the fall rate period F3 and the fall rate end period F4 based on these temperatures and controlling to change the exhaust gas circulation rate, it is possible to reduce the energy consumption of the heater 3.

[0057] Furthermore, when the start point P2 of the ramp-down rate end period F4 is detected or estimated, the heating of the heater 3 is stopped with the exhaust gas circulation rate at its maximum, and the drying operation is terminated after operation is continued in that state, thereby achieving further energy savings.

[0058] 7 and 8 are flow charts showing an embodiment of the overall drying operation in which the inlet temperature Ti is automatically set and controlled, and the exhaust gas recirculation rate is controlled.

[0059] In the second embodiment shown in FIG. 7, the product temperature Tw at the time when the constant rate judgment waiting time t1 set in the controller has elapsed from the start of operation (step s23) is set as the reference product temperature T0 (step s24), and when the product temperature Tw reaches a temperature obtained by adding the decreasing rate transition product temperature difference ΔT1 (usually 5°C to 30°C) set in the controller to the reference product temperature T0 (step s25), it is determined that the constant rate period F2 has been transitioned to the decreasing rate period F3, and the exhaust gas recirculation rate is changed.

[0060] That is, a constant rate determination wait time t1 required from the start of the drying process until the constant rate drying becomes stable is set, and the article temperature during constant rate drying detected in step s24 is stored as a reference article temperature T0.Then, the time when the article temperature Tw exceeds a temperature obtained by adding the decreasing rate transition article temperature difference ΔT1 (for example, 5°C) to the reference article temperature T0 is determined to be the end of the constant rate period F2, the exhaust gas circulation rate is increased, and the temperature control valve 4 is correspondingly throttled to continue drying by the decreasing rate drying.

[0061] When the product temperature Tw reaches the reference product temperature T0 plus the end-determining product temperature difference ΔT2 (usually 15°C to 30°C) set in the controller (step s27), it is determined that the ramp-down rate end start point P2 has been reached and the temperature control valve is closed (step s28), and then an operation end signal is received to end the drying operation.

[0062] In the third embodiment shown in FIG. 8, by detecting that the exhaust temperature has stopped changing after operation has started, it is determined that the period is constant rate drying F2, the exhaust temperature Ta at this time is set as the reference exhaust temperature Ta0, and when the temperature reaches the reference exhaust temperature Ta0 plus the decreasing rate transition exhaust temperature difference ΔTa1 set in the controller, it is determined that the period has entered the decreasing rate period F3, and the exhaust gas recirculation rate is increased.

[0063] Thereafter, when it is detected that the item temperature has exceeded the exhaust temperature, or when the temperature difference between the item temperature and the exhaust temperature has reached the set end proximity temperature difference ΔT3 and the set end determination waiting time t3 has elapsed and the ramp-down end start point P2 has been reached, the exhaust gas circulation rate is further increased, the temperature control valve 4 (and bypass valve 5, if necessary) is closed to continue operation, and the drying operation is terminated upon receipt of an operation end signal.

[0064] Steps s31 to YES at s35 in FIG. 8 are a constant rate period (in terms of control), during which the reference exhaust temperature Ta0 for detecting the ramp rate transition point P1 (see FIG. 9 for the symbols in the third embodiment) is automatically set.

[0065] In the third embodiment, after starting the drying operation (step s32), the system waits until the exhaust temperature stabilizes (step s33), and the exhaust temperature Ta at that point is set as the reference exhaust temperature Ta0 (step s34). Alternatively, the exhaust temperature can be replaced by the item temperature as the reference item temperature, and the transition to the decrease rate period F3 can be determined by detecting the change in the item temperature.

[0066] The exhaust temperature Ta is constant during the constant rate period F2, but rises when transitioning to the falling rate period F3. Therefore, when the exhaust temperature Ta reaches a temperature obtained by adding the reference exhaust temperature Ta0 and the falling rate transition exhaust temperature difference ΔTa1 (step s35), it is deemed that the falling rate transition time point P1 has been reached, and the exhaust recirculation rate is increased (step s36) and a transition is made to the falling rate period F3.

[0067] In the third embodiment, the ramp rate end F4 is detected from the relationship between the product temperature Tw and the exhaust temperature Ta during the ramp rate period F3 (step s37), and the ramp rate end start point P2 is estimated based on that point (step s38).

[0068] The temperature differences ΔT2 and ΔT3 differ depending on the type of laundry and the individual dryer, and in practice it is necessary to make a judgment based on the temperature difference with, for example, +-10°C added as a discrimination margin.

[0069] The fall rate end F4 can also be determined when the item temperature Tw reaches the fiber temperature for proper drying of the laundry. The end determination waiting time t3 is the time until the heat quantity required to dry the moisture inside the undried fibers is accumulated on the fiber surface, and is the time required to eliminate the difference in dryness between the fiber surface and the fiber interior.

[0070] Since the end-determination waiting time t3 and the above-mentioned temperature differences ΔT1, Ta1, ΔT2 may be affected by the amount of laundry loaded, in such a case, it is possible to detect the temperature rise during the preheating period and adjust them. This adjustment is automatically performed by detecting the length of the preheating period F1 and the gradient of the item temperature Tw during the preheating period. In other words, the end-determination waiting time t3 is set as a function that decreases the end-determination waiting time t3 and the temperature differences ΔT1, ΔTa1, ΔT2 as the preheating time is shorter and the item temperature rises faster. [Explanation of symbols]

[0071] 3 Steam heater 4 Temperature control valve 11 Damper A Drying air F2 Fixed rate period F3 Declining rate period F4 Declining rate end P1 Decreasing rate transition point Ti inlet temperature Tp Maximum temperature (peak temperature) tp wait time Ta Exhaust temperature Tw Item temperature T0, Ta0 reference temperature t1 Fixed rate judgment waiting time ΔT1 Decreasing rate transition product temperature difference ΔTa1 Decreasing rate transition exhaust temperature difference ΔTp differential temperature

Claims

1. Automatic setting of inlet temperature A method for operating a laundry dryer equipped with a heating means for heating air flowing into a drying chamber and a temperature control valve for adjusting the temperature of the drying air that has passed through the heating means, comprising the steps of: after starting a drying operation, fully opening the temperature control valve to monitor an inlet temperature; automatically setting in a controller a maximum temperature detected by an inlet temperature sensor during the monitoring period or a temperature lower than the maximum temperature by a difference temperature previously set in a controller as a set value for the inlet temperature; and controlling the temperature control valve to maintain the set value while performing the drying operation.

2. 2. The method for operating a laundry dryer according to claim 1, wherein the control of the temperature control valve is an on-off control.

3. A method for drying laundry by exhaust gas circulation in which a part of exhaust gas passing through the drying chamber during a drying operation is returned to an air inlet side of the heating means, 2. The method for operating a washer / dryer according to claim 1, further comprising the steps of: storing an exhaust temperature during constant rate drying, in which the exhaust temperature remains substantially constant; and determining that a transition has been made from a constant rate drying period to a falling rate drying period when the exhaust temperature exceeds a temperature obtained by adding a temperature difference preset in a controller to the stored temperature, and increasing the exhaust circulation rate.

4. A method for drying laundry by exhaust gas circulation in which a part of exhaust gas passing through the drying chamber during a drying operation is returned to an air inlet side of the heating means, 2. The method for operating a laundry dryer according to claim 1, further comprising the steps of: storing the item temperature during constant rate drying, during which the item temperature detected by a sensor installed in the drying chamber remains substantially constant; and determining that a transition has been made from a constant rate drying period to a decreasing rate drying period when the temperature detected by the sensor exceeds a temperature obtained by adding a temperature difference preset in a controller to the stored item temperature, and increasing the circulation rate of the exhaust gas circulation.

5. A laundry dryer comprising a heating means for heating air flowing into a drying chamber, a temperature control valve for adjusting the temperature of the drying air that has passed through the heating means, a temperature sensor for detecting the temperature of the drying air, a control means for controlling the temperature control valve by comparing a detection value of the temperature sensor with a set value set in a controller, and a setting screen for setting an operation method, The laundry dryer is provided with a display item on the setting screen that displays a selection item suggesting automatic setting of the set value or energy-saving operation to prompt the operator to input the selection item, and when the operator selects the selection item and starts operation, the laundry dryer is operated in the operating method described in claim 1.

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