A thermal compensation module for a high-precision constant temperature environment and a control method thereof

Abstract

The present invention discloses a thermal compensation module for a high-precision constant temperature environment and a control method thereof. The thermal compensation module comprises a temperature sensor, a flow sensor, a controller, a PID regulator, a relay, a refrigeration device and a heating device; the signal output end of the temperature sensor is connected to the first signal input end of the controller, the flow sensor is connected to the second signal input end of the controller, the first signal output end of the controller is connected to the signal input end of the PID regulator, the second signal output end of the controller is connected to the signal input end of the refrigeration device, and the third signal output end of the controller is connected to the signal input end of the heating device. The control method is a control means for cooling the heat dissipation device and heating the heat absorption device. The present invention performs real-time thermal compensation on the heat-sensitive device that causes thermal instability and thermal unevenness in the constant temperature clean room, so that it is always in a thermal equilibrium state, thereby improving the uniformity and stability of the environmental temperature of the entire clean room.

Description

Technical Field

[0001] The invention belongs to the field of constant temperature control, and in particular relates to a thermal compensation module in a high-precision constant temperature environment and a control method thereof. Background Art

[0002] Clean room, also known as ultra-clean room, dust-free room, dust-free workshop, clean workshop, refers to a room specially designed to reduce pollutants such as particles, harmful gases, bacteria in the air to below the specified indicators within a certain space, and to control the indoor temperature, cleanliness, indoor pressure, airflow speed and airflow distribution, noise vibration, lighting, and static electricity within a certain required range. That is, no matter how the external air conditions change, the room can maintain the cleanliness and temperature and humidity performance originally set. Constant temperature and clean environment is an important guarantee for the production of semiconductor and electronics industries, and is also the basic condition for scientific research laboratories such as ultrafast laser laboratories. With the development of the semiconductor and laser industries, both production and scientific research have put forward higher requirements for environmental performance, such as higher cleanliness, ultra-high precision temperature and humidity control, better temperature uniformity, reasonable pressure distribution, more energy saving and noise reduction, etc. Therefore, how to design such an ultra-clean production / scientific research environment has become an urgent problem to be solved.

[0003] The environment of a traditional constant temperature clean room usually has a temperature gradient. Its temperature and temperature stability are actually only the temperature and temperature stability of the temperature measurement point, and cannot represent the temperature of the entire space. The temperature measurement points are only a few points, such as the air outlet and the return air outlet. For example, a person's normal body temperature, for example, 36.5℃, is only the temperature of the temperature measurement point, such as the armpit, mouth or anus, not the temperature of all parts of the body. In fact, from an infrared thermal distribution map of the body surface temperature of a human body, it can be seen that the temperature of the human body surface is not uniform. Similarly, if you take an infrared thermal distribution map of a clean room, there will also be a temperature gradient.

[0004] The Chinese patent with publication number CN103759391B discloses a constant temperature and humidity air conditioning system and a control method for improving the accuracy of indoor temperature and humidity. From the experimental data provided, it can be seen that when the constant temperature and humidity air conditioning system is in the cooling control process, the average value of the supply air temperature = 22.1°C, and the average value of the return air temperature = 25.2°C; when the constant temperature and humidity air conditioning system is in the heating control process, the average value of the supply air temperature = 27.9°C, and the average value of the return air temperature = 24.9°C. In other words, whether in the cooling control process or the heating control process, the temperature gradient in the constant temperature and humidity clean room is not less than 3°C. The spatial uniformity of temperature is even more unknown, especially when the airflow organization in the room is in a turbulent state.

[0005] For occasions such as semiconductor production workshops and ultrafast laser laboratories, the spatial uniformity of temperature distribution is very important. Since the production and scientific research environment is a dynamic environment, the equipment in the environment itself is also a heat source, which will affect the spatial uniformity of temperature. Therefore, improving the spatial uniformity of temperature distribution in constant temperature and humidity clean rooms, reducing the temperature gradient in the room, and reducing the energy consumption of constant temperature clean rooms are urgent issues to be solved.

[0006] At present, the existing constant temperature and humidity control technology has roughly the same structure and single function; first, the constant temperature and humidity purification air conditioning unit used has low refrigeration efficiency; second, when the equipment in the constant temperature and humidity clean room is working, due to the dynamic change and uneven heat in the clean room space, it only relies on the constant temperature and humidity purification air conditioning unit and limited temperature measurement points to feedback and adjust the temperature and humidity, which is easy to produce temperature gradient and spatial distribution unevenness; third, the feedback and intelligent control efficiency of real-time temperature and humidity is low. Therefore, it is necessary to design corresponding technical solutions to solve this problem. Summary of the invention

[0007] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a thermal compensation module for a high-precision constant temperature environment with high temperature control accuracy, good temperature uniformity and energy saving. Another purpose of the present invention is to provide a control method for a thermal compensation module for a high-precision constant temperature environment with good real-time temperature and humidity feedback and high intelligent control efficiency.

[0008] Technical solution: The thermal compensation module for a high-precision constant temperature environment described in the present invention includes a temperature sensor, a flow sensor, a controller, a PID regulator, a relay, a refrigeration device and a heating device; the temperature sensor is used to measure the indoor temperature and the output temperature of the refrigeration device; the signal output end of the temperature sensor is connected to the first signal input end of the controller, the flow sensor is connected to the second signal input end of the controller, the first signal output end of the controller is connected to the signal input end of the PID regulator, the second signal output end of the controller is connected to the signal input end of the refrigeration device, the third signal output end of the controller is connected to the signal input end of the heating device, and the fourth signal output end of the controller is connected to the signal input end of the relay.

[0009] The refrigeration device is an air cooling device or a water cooling device. The refrigeration device includes an indoor unit and an outdoor unit. The indoor unit is arranged at the heat dissipation position of the heat dissipation device to facilitate temperature balance and save energy. The heat dissipation device is provided with a heat sink, and the indoor unit is arranged on or near the heat sink to facilitate temperature balance and save energy.

[0010] The heating device is a resistance heating device, an induction heating device or an infrared heating device, but is not limited to these heating methods. The heating output is achieved by controlling the output power of the heating. The controller module is equipped with a heating device power supply analog signal, and the heating output is adjusted in combination with a PID regulator. The heating device includes a heater, which is arranged at the heat absorption part of the heat absorption device to facilitate temperature balance and save energy. The heating device also includes a heat exchanger 2, which is arranged on the heat absorption device, and the heater is arranged on or near the heat exchanger 2 to facilitate temperature balance and save energy. An isolation cover is arranged outside the heat dissipation device and the heat absorption device, so that the temperature control accuracy and uniformity of the constant temperature and humidity clean room are improved, which is conducive to improving the refrigeration efficiency of the air conditioning unit that provides a constant temperature environment for the clean room, and is conducive to reducing the operating energy consumption of the constant temperature and humidity clean room. At the same time, a relatively independent constant temperature unit is formed in each isolation cover. The entire constant temperature and humidity clean room space is decomposed into a number of constant temperature units and the remaining temperature balance space, so that the temperature stability and uniformity of the entire space are better.

[0011] The control method of the thermal compensation module in the above-mentioned high-precision constant temperature environment includes the following specific steps:

[0012] Step 1: The controller determines whether it is a refrigeration device or a heating device. The refrigeration device executes step 2, and the heating device executes step 5;

[0013] Step 2: The controller determines whether the difference between the set temperature and the actual output temperature of the refrigeration device is greater than Δt. If it is greater than Δt, step 3 is executed; if it is less than or equal to Δt, step 4 is executed;

[0014] Step 3: The controller controls the refrigeration device not to change the compressor frequency or the output cold air or chilled water flow rate. When the difference between the set temperature received by the controller and the supply air or chilled water outlet temperature is less than or equal to Δt, the controller controls the refrigeration device to load the cooling capacity.

[0015] Step 4: the controller controls the refrigeration device to load the refrigeration capacity. When the difference between the set temperature received by the controller and the supply air or chilled water outlet temperature is greater than Δt, the controller controls the refrigeration device not to change the output cold air or chilled water flow rate;

[0016] Step 5, the controller determines whether the difference between the set temperature and the heater output temperature is greater than Δt, if it is greater than Δt, execute step 6, if it is less than or equal to Δt, execute step 7;

[0017] Step 6: The controller controls the heating device to not change the heating output. When the difference between the set temperature received by the controller and the heater output temperature is less than or equal to Δt, the controller controls the heating device to load the heating amount.

[0018] Step seven, the controller controls the heating device to load the heating amount. When the difference between the set temperature received by the controller and the heater output temperature is greater than Δt, the controller controls the heating device not to change the heating output.

[0019] The above-mentioned high-precision constant temperature environment thermal compensation module can be applied to constant temperature and humidity clean rooms, such as clean factories, clean workshops, clean laboratories, and clean operating rooms, especially in places with high requirements for temperature control accuracy, temperature uniformity, and energy saving, such as semiconductor production workshops and ultrafast laser laboratories.

[0020] Working principle: Classify various equipment in the environment according to temperature characteristics, cool down the heat dissipation equipment, and heat up the heat absorption equipment, so that various equipment in the environment are in a thermally stable state and the temperature of the entire constant temperature and humidity clean room is in a balanced and equilibrium state.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. Perform real-time thermal compensation on heat-sensitive equipment that causes thermal instability and thermal unevenness in a constant temperature clean room, so that it is always in a thermal equilibrium state and its temperature is the same as the clean room ambient temperature;

[0023] 2. Adopt independent data detection feedback control methods to achieve precise control for each module. At the same time, based on the internal functional modules of the refrigeration device and the heater, hierarchical control is applied to further improve the accuracy (±0.01℃) and efficiency of the functional applications of the refrigeration device and the heating device;

[0024] 3. Install an isolation cover for each heat-sensitive device. In each isolation cover, a relatively independent constant temperature unit is formed. The entire constant temperature and humidity clean room space is decomposed into several constant temperature units and the remaining temperature balance space, so that the temperature stability of the entire space is better and the uniformity (±0.02℃) is better;

[0025] 4. Through the decomposition design, the temperature control accuracy and uniformity of the constant temperature and humidity clean room are improved, which is conducive to improving the refrigeration efficiency of the air-conditioning unit that provides a constant temperature environment for the clean room, and is conducive to reducing the operating energy consumption of the constant temperature and humidity clean room;

[0026] 5. Adding a heat sink or heat exchanger can make the temperature balance and stability provided by the thermal compensation module more efficient and the temperature control accuracy higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a first structural schematic diagram of the present invention;

[0028] Figure 2 It is a second structural schematic diagram of the present invention;

[0029] Figure 3 It is a third structural schematic diagram of the present invention;

[0030] Figure 4 is a circuit schematic diagram of the present invention;

[0031] Figure 5 It is a schematic diagram of a module of the present invention;

[0032] Figure 6 It is a flow chart of the constant temperature control method of the present invention. DETAILED DESCRIPTION

[0033] The directions shown in the drawings in the specification are up, down, left and right.

[0034] Example 1

[0035] like Figure 1 , a constant temperature and humidity clean room 12, the temperature and humidity are controlled by a constant temperature and humidity purification air conditioning unit 13, the production equipment or scientific research instruments inside the constant temperature and humidity clean room 12 can be mainly divided into three categories according to their thermal sensitivity: heat dissipation equipment 8, which refers to equipment whose working temperature is higher than the ambient temperature and releases heat to the environment; ordinary equipment 14, which refers to equipment whose working temperature is equal to the ambient temperature and does not release heat to the environment or absorb heat from the environment; equipment whose working temperature is equal to the ambient temperature and does not release heat to the environment or absorb heat from the environment; heat absorption equipment 10, which refers to equipment whose working temperature is lower than the ambient temperature and absorbs heat from the environment. The number and location of the three types of equipment are for illustration only and are not intended to be limiting.

[0036] Temperature sensors 1 are set at key temperature control points of the constant temperature and humidity clean room 12 (the temperature of the air outlet and water outlet, the temperature of the return air and water return, and the equipment equipped with the thermal compensation module, that is, the point on the equipment where constant temperature is desired). The temperature sensor 1 specifically includes an indoor environment temperature sensor, a refrigeration device output temperature sensor, and a heating device output sensor. The indoor environment temperature sensor is placed at multiple temperature measurement points inside the constant temperature and humidity clean room 12, and is used to detect the real-time temperature data of each device inside, and upload it to the controller 3.

[0037] The internal unit 601 (heat absorbing section) of the refrigeration device 6 is arranged at the heat dissipation part of the heat dissipation device 8 to achieve temperature balance and save energy. The heater 701 is arranged at the heat absorption part of the heat absorption device 10 to achieve temperature balance and save energy.

[0038] Example 2

[0039] On the basis of Example 1, further, Figure 2, a heat sink 9 can be provided on the heat dissipation device 8, and the indoor unit 601 of the refrigeration device 6 can be provided on or near the heat sink 9, so as to achieve temperature balance and save energy. A heat exchanger 2 702 can be provided on the heat absorption device 10, and the heater 701 can be provided on or near the heat exchanger 2 702, so as to achieve temperature balance and save energy. The installation of the heat sink 9 or the heat exchanger 2 702 can make the temperature balance and stability provided by the thermal compensation module more efficient and make the temperature control accuracy higher.

[0040] Example 3

[0041] On the basis of Example 2, further, as Figure 3 , an isolation cover 11 can be installed on the heat dissipation device 8 and the heat absorption device 10 to reduce the heat exchange between the inside and outside of the isolation cover 11, thereby reducing the thermal impact of the heat dissipation device 8 and the heat absorption device 10 on the entire constant temperature and humidity clean room 12, improving the thermal stability and uniformity of the entire space, and reducing the adjustment requirements and energy consumption of the constant temperature and humidity purification air conditioning unit 13. At the same time, each isolation cover 11 forms a relatively independent constant temperature unit. The entire constant temperature and humidity clean room 12 space is decomposed into several constant temperature units and the remaining temperature balance space, so that the temperature stability and uniformity of the entire space are better.

[0042] The function of the controller 3 is mainly to collect data such as temperature and flow, and then transmit them to the PID module. The PID module calculates the feedback value, and the controller 3 then feeds back the feedback value to the refrigeration device 6, the heating device 7 or the relay 5 to control the refrigeration and heating power.

[0043] like Figure 4 The output port of the temperature sensor 1 is connected to the signal input port of the controller 3, and a temperature signal is output to it. The output port of the controller is respectively connected to the input port of the heating device 7, the input port of the PID regulator 4, and the input port of the valve 15. The output port of the flow sensor 2 is connected to the signal input port of the controller 3. The chilled water passes through the flow sensor 2, the valve 15 and the heat exchanger 603 in sequence along the water inlet pipe.

[0044] like Figure 5, the controller 3 determines the cooling output and heating output by comparing with the preset temperature and through the PID regulator 4 (proportional integral differential, also known as PID controller). The cooling output is achieved by controlling the flow of cold air or chilled water. The controller module is equipped with a refrigeration device output temperature sensor module and a flow sensor module, and the cooling output is adjusted in combination with the PID controller 4. The indoor real-time temperature data is transmitted back to the controller 3 through the temperature sensor 1, and the pre-processing temperature and output temperature data of the refrigeration device 6 are respectively transmitted back to the controller 3 through two temperature sensors 1. The controller 3 compares the real-time temperature with the set temperature and uses the PID algorithm to infinitely adjust the cooling output or heating output. Among them, the cooling capacity can be adjusted by adjusting the frequency of the compressor of the variable frequency air conditioner, or by adjusting the flow of the output cold air or cold water. The controller 3 controls the relay 5 to use the PID algorithm to adjust the cooling output or heating output. Using the existing PID algorithm, it can be integrated on a PID regulator 4, or it can be integrated on a single-chip microcomputer, or computer software to achieve temperature control.

[0045] For heat dissipation device 8: the output ends of controller 3, PID regulator 4, and relay 5 are respectively connected to the input end of the inverter of refrigeration device 6, and the output end of the inverter is connected to the air blower or water supply pipe inside refrigeration device 6, that is, controller 3 outputs power analog signal, combined with the control output of controller 3 through relay 5 to realize the control of inverter, and then the inverter controls the air blower or water supply pipe inside refrigeration device 6. For heat absorption device 10: the output ends of controller 3, PID regulator 4, and relay 5 are respectively connected to the input end of heater 701, and the output end of heater 701 is connected to the heating output such as heater 701, that is, controller 3 outputs power analog signal, combined with the control output of controller 3 through relay 5 to realize the control of heater 701, and then the heating amount is controlled.

[0046] When the refrigeration device 6 is an air conditioner, an air conditioning supply air temperature sensor and an air volume sensor are also provided and connected to the controller 3. The air conditioning supply air temperature sensor and the air volume sensor are respectively provided at the air outlet position on the air conditioning outlet area, and are used to detect the temperature data and air volume data at the air outlet position on the air conditioning outlet area, and upload them to the controller 3 respectively.

[0047] When the refrigeration device 6 is a water cooler, a water outlet temperature sensor and a water flow sensor are also provided and connected to the controller 3. The water cooler water supply temperature sensor and the water flow sensor are respectively provided at the water outlet position on the water outlet area of ​​the water cooler, and are used to detect the temperature data and water flow data at the water outlet position on the water outlet area of ​​the water cooler, and upload them to the controller 3 respectively.

[0048] like Figure 6The control method of the thermal compensation module to improve the indoor temperature control accuracy and temperature distribution uniformity specifically includes the following steps:

[0049] Step 1: The controller 3 determines whether it is the refrigeration device 6 or the heating device 7, the refrigeration device 6 executes step 2, and the heating device 7 executes step 5;

[0050] Step 2: The controller 3 determines whether the difference between the set temperature and the actual output temperature of the refrigeration device 6 is greater than Δt (the value of Δt is a positive constant and can be set). If it is greater than Δt, step 3 is executed; if it is less than or equal to Δt, step 4 is executed;

[0051] Step 3: The controller 3 controls the refrigeration device 6 not to change the compressor frequency or the output cold air or chilled water flow rate. When the controller 3 receives that the difference between the set temperature and the supply air or chilled water outlet temperature is less than or equal to Δt, the controller 3 controls the refrigeration device 6 to load the cooling capacity, that is, to increase the compressor frequency / increase the output cold air or chilled water flow rate;

[0052] Step 4: the controller 3 controls the refrigeration device 6 to load the refrigeration capacity, that is, to increase the compressor frequency / increase the output cold air or chilled water flow rate. When the difference between the set temperature received by the controller 3 and the supply air or chilled water outlet temperature is greater than Δt, the controller 3 controls the refrigeration device 6 not to change the output cold air or chilled water flow rate / not to change the compressor frequency;

[0053] Step 5, the controller 3 determines whether the difference between the set temperature and the output temperature of the heater 701 is greater than Δt (the value of Δt is a positive constant and can be set). If it is greater than Δt, step 6 is executed; if it is less than or equal to Δt, step 7 is executed;

[0054] Step 6: the controller 3 controls the heating device 7 not to change the heating output. When the difference between the set temperature received by the controller 3 and the output temperature of the heater 701 is less than or equal to Δt, the controller 3 controls the heating device 7 to load the heating amount.

[0055] Step seven, the controller 3 controls the heating device 7 to load the heating amount. When the difference between the set temperature received by the controller 3 and the output temperature of the heater 701 is greater than Δt, the controller 3 controls the heating device not to change the heating output.

[0056] Whether the temperature of a workshop or laboratory can be maintained stable is related to the configuration of the air conditioner, the external environment, and the heat released by the dynamic working environment of the workshop or laboratory. The design of the present invention can make the heat released by the heat dissipation device 8 be accurately controlled through its independently working refrigeration device 6 and PID regulator 4, without causing temperature fluctuations in the large environment of the constant temperature and humidity clean room 12; at the same time, the heat absorbed by the heat absorption device 10 can be accurately controlled through its independently working heater 701 and PID regulation, without causing temperature fluctuations in the large environment of the constant temperature and humidity clean room 12. Through the temperature control method, very high temperature control accuracy (±0.01°C) and very good temperature uniformity (±0.02°C) can be achieved.

[0057] In addition, since each heat dissipation device 8 and heat absorption device 10 is subjected to separate heat compensation processing, the normal operation of the entire clean room temperature control system can be guaranteed even if there is a problem with the air conditioning unit; secondly, energy saving, the outside environment temperature is low in winter, and the refrigeration capacity required for the constant temperature and humidity clean room 12 is also low. The refrigeration capacity output can be controlled in multiple gears according to the season to achieve the purpose of saving energy consumption. It is estimated that for a 60 square meter constant temperature and humidity clean room 12, the temperature control method of the present invention can save about 50,000 to 100,000 yuan / year in electricity bills compared with traditional constant temperature clean rooms.

Claims

1. A high-precision constant temperature environment thermal compensation module, characterized in that: The thermal compensation module is arranged in a constant temperature and humidity clean room (12); the production equipment or scientific research instruments in the constant temperature and humidity clean room (12) include a heat dissipation device (8) and a heat absorption device (10) according to their thermal sensitivity; the thermal compensation module includes a temperature sensor (1), a flow sensor (2), a controller (3), a PID regulator (4), a relay (5), a refrigeration device (6) and a heating device (7); the temperature sensor (1) is used to measure the indoor temperature and the output temperature of the refrigeration device (6); the signal output end of the temperature sensor (1) is connected to the first signal input end of the controller (3), the flow sensor (2) is connected to the second signal input end of the controller (3), the first signal output end of the controller (3) is connected to the signal input end of the PID regulator (4), the second signal output end of the controller (3) is connected to the signal input end of the refrigeration device (6), the third signal output end of the controller (3) is connected to the signal input end of the heating device (7), and the fourth signal output end of the controller (3) is connected to the signal input end of the relay (5); The heating device (7) comprises a heater (701), and the heater (701) is arranged at a heat absorbing location of the heat absorbing device (10); The output end of the PID regulator (4) and the output end of the relay (5) are respectively connected to the input end of the frequency converter of the refrigeration device (6) or are respectively connected to the input end of the heater (701); The refrigeration device (6) comprises an indoor unit (601) and an outdoor unit (602), wherein the indoor unit (601) is arranged at a heat dissipation location of a heat dissipation device (8).

2. A high-precision constant temperature environment thermal compensation module according to claim 1, characterized in that: The refrigeration device (6) is an air cooling device or a water cooling device.

3. A high-precision constant temperature environment thermal compensation module according to claim 1, characterized in that: A heat sink (9) is provided on the heat dissipation device (8), and the indoor unit (601) is provided on or near the heat sink (9).

4. A high-precision constant temperature environment thermal compensation module according to claim 1, characterized in that: The heating device is a resistance heating device, an induction heating device or an infrared heating device.

5. The high-precision constant temperature environment thermal compensation module according to claim 1, characterized in that: The heating device (7) further comprises a second heat exchanger (702), wherein the second heat exchanger (702) is arranged on the heat absorbing device (10), and the heater (701) is arranged on or near the second heat exchanger (702).

6. A high-precision constant temperature environment thermal compensation module according to claim 5, characterized in that: An isolation cover (11) is provided outside the heat dissipation device (8) and the heat absorption device (10).

7. The control method of a thermal compensation module in a high-precision constant temperature environment according to any one of claims 1 to 6, characterized in that The specific steps include: Step 1: the controller (3) determines whether the device in the constant temperature and humidity clean room (12) is a refrigeration device (6) or a heating device (7); the refrigeration device (6) executes step 2, and the heating device (7) executes step 5; Step 2: The controller (3) determines whether the difference between the set temperature and the actual output temperature of the refrigeration device (6) is greater than Δt. If it is greater than Δt, step 3 is executed; if it is less than or equal to Δt, step 4 is executed; Step 3: the controller (3) controls the refrigeration device (6) not to change the compressor frequency or the output cold air or chilled water flow rate. When the difference between the set temperature received by the controller (3) and the supply air or chilled water outlet temperature is less than or equal to Δt, the controller (3) controls the refrigeration device (6) to load the cooling capacity. Step 4: the controller (3) controls the refrigeration device (6) to load the refrigeration capacity. When the difference between the set temperature received by the controller (3) and the supply air or chilled water outlet temperature is greater than Δt, the controller (3) controls the refrigeration device (6) not to change the output cold air or chilled water flow rate; Step 5, the controller (3) determines whether the difference between the set temperature and the output temperature of the heater (701) is greater than Δt, if it is greater than Δt, executing step 6, if it is less than or equal to Δt, executing step 7; Step 6: the controller (3) controls the heating device (7) not to change the heating output. When the difference between the set temperature received by the controller (3) and the output temperature of the heater (701) is less than or equal to Δt, the controller (3) controls the heating device (7) to load the heating amount. Step seven, the controller (3) controls the heating device (7) to load the heating amount. When the difference between the set temperature received by the controller (3) and the output temperature of the heater (701) is greater than Δt, the controller (3) controls the heating device not to change the heating output.

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