US20160076780A1

US20160076780A1 - Process For Operating A Clean Room And Control Device

Info

Publication number: US20160076780A1
Application number: US14/847,732
Authority: US
Inventors: Karl-Heinz Lotz; Bernd Sommer; Christoph Hammer
Original assignee: Weiss Klimatechnik GmbH
Current assignee: Weiss Klimatechnik GmbH
Priority date: 2014-09-11
Filing date: 2015-09-08
Publication date: 2016-03-17
Also published as: CN105423479A; RU2015138284A; EP2995875B1; EP2995875A1; RU2646200C2

Abstract

The invention relates to process for operating a clean room and to a control device for a clean room, the clean room (10) comprising a work room (12, 13, 14), a room ventilation system (15) and a control device (16), the room ventilation system being controlled and/or regulated by means of the control device, an air exchange rate in the work room and a pressure difference between the work room and an environment (25) being generated by means of the room ventilation system, the control device comprising at least one sensor device (19) for registering an actual value representing an operating parameter, wherein the air exchange rate is adjusted by means of the control device in such a manner that the actual value is in the range of a target value.

Description

The invention relates to a process for operating a clean room and to a control device for a clean room, the clean room comprising a work room, a room ventilation system and a control device, the room ventilation system being controlled and/or regulated by means of the control device, an air exchange rate in the work room and a pressure difference between the work room and an environment being generated by means of the room ventilation system, wherein the control device comprises at least one sensor device for registering an actual value representing an operating parameter.
Processes and control devices of this kind for clean rooms are commonly employed to control and regulate room ventilation systems. By way of a room ventilation system, supply air is supplied to and exhaust air is discharged from a room, an air temperature or also a relative humidity, for example, being monitored by means of corresponding sensors in the room. A change in air temperature will then cause the room ventilation system to be controlled via a control device in such a manner that the supply air for the room is cooled or heated so as to maintain or achieve the desired air temperature.
Moreover, in a clean room, the intention is to generate a particularly clean air atmosphere in a self-contained accessible work room or in a work booth in order to prevent lab samples or microelectronic components from being contaminated with germs, microorganisms or dust particles, for example. To this end, a room ventilation system is used to generate a particle concentration in the work room that is substantially reduced in comparison to an environment of the work room. Also, a permanent pressure difference is generated between the work room and the environment in order to prevent particles from entering the work room or also from exiting the work room. Furthermore, it is necessary that individuals enter the work room to perform work activities. Despite appropriate work clothing and possibly special work equipment, these individuals commonly represent the largest source of particles and other pollutions.
Apart from an appropriate air flow in the work room, which is supposed to guide pollutions away from a workplace, the air supplied to the work room is filtered several times and continuously supplied to the work room in order to keep a particle concentration below a limit value. Said limit value depends on a classification of cleanliness of the work room according to a standard such as ISO 14644-1. To ensure the required pressure difference and the particle concentration in the work room at all times, the room ventilation system is operated permanently; that includes times during which no work activities are performed in the work room and times during which individuals are present in the workroom. An air exchange rate is selected such that the work room can be entered by a number of individuals, which leads to a sharp increase in particle concentration without exceeding an admissible particle concentration for the relevant clean room class. Optionally, a light signal device such as a stop light may be arranged at an entrance to the work room, which controls access or permits and stops production as a function of a particle concentration.
Ensuring a sufficiently low particle concentration hence requires a correspondingly high air exchange rate. The particle concentration is substantially determined by a speed of rotation of running ventilators of the room ventilation system. Since the ventilators are operated continuously and are in permanent use, this leads to comparatively high energy costs and thus operating costs for the clean room.
Hence, the underlying object of the present invention is to propose a process for operating a clean room and a control device by means of both of which the operating costs of a clean room can be reduced.
Said object is attained by a process incorporating the features of claim 1, by a control device incorporating the features of claim 14 and by a clean room incorporating the features of claim 15.
In the process according to the invention for operating a clean room, the clean room comprises a work room, a room ventilation system and a control device, the room ventilation system being controlled and/or regulated by means of the control device, an air exchange rate in the work room and a pressure difference between the work room and an environment being generated by means of the room ventilation system, the control device comprising at least one sensor device for registering an actual value representing an operating parameter, wherein the air exchange rate is adjusted by means of the control device in such a manner that the actual value is in the range of a target value.
By way of the process according to the invention it is ensured that a particle concentration that is reduced in comparison to the environment of the work room is available in the accessible work room at any time during the operation of the clean room. At the same time, an air exchange rate is permanently provided in the work room that does not drop below a minimum value, the pressure difference also being permanently maintained at the same time. It is initially immaterial whether there is a positive or a negative pressure in the work room relative to an environment of the work room. During the continuous operation of the clean room, at least one operating parameter of the work room is registered by means of the sensor device. It is immaterial how said operating parameter is registered or also measured. The substantial aspect is that an actual value of the work room is registered, which may also happen outside of the work room in or on the room ventilation system, for example. The actual value of the operating parameter registered by the sensor device is processed by the control device and is used to adjust the air exchange rate in such a manner that the actual value is in the range of a target value of the operating parameter.
By linking the air exchange rate to the registered actual value, which is controlled according to a target value, it becomes possible to lower the air exchange rate during the operating periods in which the work room is not accessed at all or by only few individuals. Regarding the registration of the actual value, it is substantial that said actual value can be influenced by a change in the air exchange rate. During operating periods in which the work room is accessed and used by a number of individuals, the relevant actual value or operating parameter is influenced to the effect that the control device initiates a comparatively higher air exchange rate so as to maintain the actual value in the range of the target value and to control the actual value accordingly. Through the air exchange rate being adjusted to the use of the work room in this manner, a ventilator speed of rotation of the room ventilation system can consequently be lowered during operating periods without or with little activity in the work room. As a result, energy can be saved during these operating periods and operating costs can thus be lowered.
In the process, it may be envisaged in particular that a permanent and continuous positive pressure is generated as a pressure difference in the work room during the entire operating duration. In this way, particles can be prevented from easily entering the work room because a continuous air flow that flows out of the work room is generated through the positive pressure. At the same time, it is also possible to generate a negative pressure in the work room if germs or microorganisms are to be prevented from escaping the work room.
Advantageously, the pressure difference and an actual value representing an air quality in the work room and/or representing an operating parameter or operating condition of the work room can be registered by means of the sensor device. The sensor device then can simultaneously register the pressure difference and the actual value. The actual value can directly represent an air quality in the work room or also an operating parameter or condition that is causally related to the air quality. It is also possible that the sensor device registers different actual values with different sensors, for example. Registration can preferably take place periodically or continually so that the control device can immediately react to changing actual values by adjusting the air exchange rate.
For example, an actual value for particle concentration or number, air temperature, relative air humidity, air exchange rate, air pressure, intensity of movement, number of individuals, CO₂concentration and/or door opening can be registered by means of the sensor device. In particular the actual value for a particle concentration can be used to control the air exchange rate because the particle concentration is highly reduced when there are no individuals in the work room. An actual value of the particle concentration can also be easily adjusted to a target value by varying the air exchange rate. The same applies to an air temperature, the air temperature in the work room being raised by the use of machines or also by individuals in the work room. For instance, it may be possible to adjust the air temperature by simply increasing the air exchange rate without the need for energy-intensive cooling of a supply air. Likewise, relative air humidity can be easily adjusted. The air exchange rate itself as well as the air pressure and the pressure difference may also be registered in order to ensure that these operating parameters do not drop below an at least required target value. Moreover, an intensity of movement or a number of individuals in the work room can be registered by a motion detector or sensor, for example, and these operating parameters may also be used to adjust the air exchange rate because an increased intensity of movement or number of individuals is accompanied by an increase to be expected in particle concentration and air temperature as well as relative air humidity. Furthermore, it is possible to register the number of individuals by measuring the CO₂concentration in the work room or in an exhaust air or by monitoring a door opening of the work room and to adjust the air exchange rate accordingly.
Preferably, the particle concentration can be measured at a work place in the work room or in an exhaust air of the room ventilation system. In particular at the work place, the particle concentration can be registered immediately at the work location substantial therefor, wherein a particle concentration for the entire work room can be registered by measuring the exhaust air. In this way, it is also possible to measure particle concentrations at different locations so as to safely preclude that a limit value is exceeded.
An even better adjustment of an energy consumption of the clean room to the operational conditions can be achieved if the control device selects a target value as a function of a time control and/or of an intensity of movement in the work room, wherein a target value for an operation period or a target value for an inactivity period can be selected as the target value. For example, if a clean room is operated in a two-shift operation, a target inactivity value may be selected or set during the inactivity period that allows a comparatively high particle concentration in the work room that is so high that the work room cannot be accessed by individuals during the inactivity period, for example.
Hence, preferably, a particle concentration, a temperature and/or a relative air humidity may be increased or the particle concentration may be increased and the temperature and/or the relative air humidity may be decreased during the inactivity period in comparison to the operating period, depending on which environmental conditions are present in this regard, such as summer or winter. For example, an air temperature of 20 to 22° C. at a relative air humidity of 40 to 50% may be provided during the operating period, and an air temperature of 8 to 25° C. at 25 to 60% relative air humidity may be provided during the inactivity period. Thus, an air exchange rate can then be substantially reduced. In the operating period, i.e. during the two shifts, the target activity value can be selected or determined that will lead to a particle concentration in the work room that permits access of individuals. It is also possible to register, discretely or additionally, an intensity of movement in the work room and to set the target activity value or the target inactivity value according to a degree of the intensity of movement. Thus, the air exchange rate and with it an energy consumption can be better adjusted to the operating requirements of the clean room. Likewise, it is possible to select and set the target values for one or more of the aforementioned operating parameters on the basis of actual values.
In one embodiment of the process, control of the pressure difference may be superseded by control of the air exchange rate. The pressure difference may then be an overriding control variable and the air exchange rate may be a subordinate control variable. In this manner, it can at lest be ensured at any time during the operation of the clean room that a pressure difference is generated between the work room and the environment of the work room. A minimum pressure difference may be set, for example.
Advantageously, the room ventilation system comprises a first ventilator for supply air and a second ventilator for exhaust air, wherein the control device can control the pressure difference by adjusting speeds of rotation of the respective ventilators. It may also be provided that a filter device is arranged between the first ventilator and the work room in a supply air duct, for example, so that filtered supply air with a low particle concentration can be supplied to the work room at all times. The filter device itself may have multiple stages and comprise a plurality of different filters. By controlling at least the speed of rotation of one ventilator as a function of the speed of rotation of the other ventilator, a difference in speeds of rotation between the ventilators can be continuously maintained, which in turn causes the pressure difference.
Furthermore, the control device can control a speed of rotation of the first ventilator as a function of the operating parameter, preferably of an air temperature and of a particle concentration. If then a particle concentration drops below a target value, for example, the air exchange rate and with it the speed of rotation of the first ventilator can be reduced. To maintain the permanent pressure difference, the speed of rotation of the second ventilator can be readjusted.
The sensor device can also register an air temperature of the supply air and an air temperature of the exhaust air, wherein the control device can then control a speed of rotation of the first ventilator and/or a treatment of the supply air as a function of the air temperature of the exhaust air. For instance, it is also possible to control a speed of rotation of the first ventilator and to potentially reduce the same as a function of an air temperature in the work room and of a temperature difference between the air temperature of the supply air and the air temperature of the exhaust air. Optionally or also additionally, the supply air may be treated as a function of the air temperature by heating or cooling the supply air by means of a heater or cooler of the room ventilation system. The control device may also chose between adjusting the speed of rotation of the first ventilator and treating the supply air depending on the energy consumption to be expected. The prescribed control according to the air temperature may supersede the control according to the particle concentration, meaning that the control according to the particle concentration may take precedence over the control according to the air temperature.
The control device can control a speed of rotation of the second ventilator as a function of the pressure difference, preferably of an air pressure in the work room and of a speed of rotation of the first ventilator. Thus, the speed of rotation of the second ventilator may not only be adjusted to the speed of rotation of the first ventilator, but the pressure difference between the work room and the environment can also be taken into account when controlling the speed of rotation of the second ventilator. In this way, maintenance of a continuous pressure difference can be ensured in any case.
An even better adjustment to operational circumstances becomes possible if the control device can store operating parameters registered during an operating period and if recurring sequences of operational conditions can be derived from the stored operating parameters by the control device, wherein then the control device can adjust the air exchange rate to an operating condition to be expected in the future. For example, the control device can then recognize regularly recurring work activities that lead to an increased particle concentration in the work room. In anticipation of such a situation, the control device can then increase the air exchange rate before the particle concentration rises or preventively lower the particle concentration. In this manner, a situation may be avoided in which, for example, access to the work room is only successively possible for individuals because it may be necessary to wait for an increase of the air exchange rate dependent on control due to control of the air exchange rate according to the particle concentration. The process thus allows improved adjustment to operational circumstances without having to accept limitations in the use of the clean room.
With regard to the control device according to the invention for a clean room, the clean room comprises a work room and a room ventilation system, wherein the room ventilation system can be controlled and/or regulated by means of the control device, wherein an air exchange rate in the work room and a pressure difference between the work room and an environment can be generated by means of the room ventilation system, the control device comprising at least one sensor device for registering an actual value representing an operating parameter, wherein the air exchange rate can be adjusted by means of the control device in such a manner that the actual value is in the range of a target value. The control device can be realized in particular as a device for data processing.
With respect to the advantages of the control device according to the invention, reference is made to the description of advantages of the process according to the invention. Other advantageous embodiments of the control device become apparent from the feature descriptions of the dependent claims referencing process claim 1.
The clean room according to the invention comprises a work room, a room ventilation system and a control device according to the invention.
In one embodiment, the clean room can comprise a plurality of interconnected work rooms having different pressure differences. The work rooms can be interconnected in such a manner that access to a work room with a largest pressure difference is only possible via work rooms with respective smaller pressure differences. The process according to the invention and the control device according to the invention can be used for one of said work rooms alone, respectively, or also for all work rooms of the clean room, wherein each of the different pressure differences and other operating parameters each differing between of the work rooms can be taken into account by individually adjusting an air exchange rate in the respective work rooms.
In the following description, a preferred embodiment of the invention will be explained in more detail with reference to the accompanying drawing.

In the figures:

FIG. 1 shows a schematic illustration of a clean room by means of a block diagram;

FIG. 2 shows a functional diagram of a clean room;

FIG. 3 shows a control diagram of a first controller of the clean room of FIG. 2;

FIG. 4 shows a control diagram of a second controller of the clean room of FIG. 2;

FIG. 5 shows a control diagram of a third controller of the clean room of FIG. 2;

FIG. 6 shows a control diagram of a fourth controller of the clean room of FIG. 2;

FIG. 7 shows a control diagram of a fifth controller of the clean room of FIG. 2;

FIG. 8 shows a control diagram of a sixth controller of the clean room of FIG. 2; and

FIG. 9 shows a control diagram of a seventh controller of the clean room of FIG. 2.

FIG. 1 shows a schematic illustration of a clean room 10, the clean room 10 comprising a work room arrangement 11 having a plurality of interconnected and accessible work rooms 12, 13 and 14, a room ventilation system 15 and a control device 16. The room ventilation system 15 itself comprises a ventilator device 17 and a treatment device 18. The ventilator device 17 is formed by a supply air ventilator and by an exhaust air ventilator (not illustrated), the treatment device 18 comprising a heater, a cooler and/or a humidifier and a dehumidifier (not illustrated). The control device 16 comprises a sensor device 19, a processing device 20, a memory device 21 and a time control device 22.
The work rooms 12, 13 and 14 are supplied with treated and filtered air by the room ventilation system 15 via a supply air duct 23 and an exhaust air duct 24, a pressure difference to the environment 25 being generated in the work rooms 12, 13 and 14 while the air is continuously exchanged. The sensor device 19 receives an actual value of an operating parameter from the work rooms 12, 13 and 14 and from the ventilator device 17 and the treatment device 18 via respective signal lines 26. The respective actual values of the operating parameters are transmitted to the processing device 20, the processing device 20 storing the actual values in the memory device 21 and simultaneously accessing the target values stored therein. The time control device 22 initiates access to target values in consideration of an operating period. The processing device 20 calculates an adjustment of the air exchange rate in the work rooms 12, 13 and 14 on the basis of the determined actual values and of the selected target values so that the control device provides control signals to the room ventilation system 15 via a signal line 27, the room ventilation system 15 effecting an adjustment of the relevant air exchange rate in such a manner that the actual values are in the respective ranges of the target values and substantially meet them. Energy consumption of the ventilator device 17 and of the treatment device 18 can be substantially reduced and a cost-effective operation of the clean room 10 can thus be achieved in particular by effecting said control by way of the air exchange rate.
FIG. 2 shows a functional diagram of a clean room 28 comprising a work room 29, a room ventilation system 30 and a control device 16. The room ventilation system 30 comprises a supply air duct 32 and an exhaust air duct 33 having an outgoing air outlet 34 and a fresh air inlet 35, respectively. A first filter 36 and a second filter 37 are arranged in the supply air duct. A first ventilator 38 for supply air as well as a cooler 39 and a heater 40 are arranged upstream thereof. A third filter 41 and a second ventilator 42 for the exhaust air are arranged in the exhaust air duct 33. The supply air duct 32 and the exhaust air duct 33 are connected to a heat recovery unit 43 having a bypass 44. The first ventilator 38 and the second ventilator 42 are operated continuously so that a pressure difference or a positive pressure in comparison to an environment 45 and an air exchange rate are generated in the work room 29. The work room 29 has a lockable entrance 46 including an opening sensor 47. Individuals may access or leave the work room 29 via the entrance 46 and perform a work activity within the work room 29 at a particle concentration that is reduced in comparison to the environment 45. A number of individuals present in the room can be determined via the opening sensor 47, for example.
A sensor device 48 of the control device 31 comprises a first air temperature sensor 49 in the supply air duct 32, a second air temperature sensor 50 in the exhaust air duct 33, a third temperature sensor in the fresh air inlet 35 and an air difference pressure sensor 52 and a particle concentration sensor 53 in the work room 29. Furthermore, the control device 31 comprises a first controller 54, a second controller 55, a third controller 56, a fourth controller 57, a fifth controller 58, a sixth controller 59 and a seventh controller 60. The aforementioned components of the control device 31 are interconnected by signal lines, which are illustrated by dashes in FIG. 2 and are not specified further.
FIG. 3 shows a control diagram of the first controller 54, the first controller 54 receiving an input signal from the first air temperature sensor 49 and from the second air temperature sensor 50. As a function of a target value T_sollof the air temperature, an actual value of the air temperature causes the actual value to be corrected or adjusted according to a characteristic 61 by being cooled with the cooler 39 and, in case of an air temperature rising further according to a characteristic 62, by increasing the air exchange rate or signal transmission to the third controller 56. If the actual value of the air temperature drops, first the heat recovery unit 43 is activated according to characteristic 63 by way of the seventh controller 60 and then the heater 40 is activated according to characteristic 64. The Y-axis shown in each of the diagrams relates to a signal strength of the respective controllers 54 to 60.
According to FIG. 4, the second controller 55 receives an input signal with a particle number n from the particle concentration sensor 53. An output signal is continuously increased starting from a set particle number according to a characteristic 65 of the second controller 55.
According to FIG. 5, the third controller 56 receives an input signal according to characteristic 62 from the first controller 54 and an input signal according to characteristic 65 from the second controller 55, corresponding to which an output signal of the third controller 56 controls a value of a speed of rotation of the first ventilator 38. Characteristics 66 and 67 relate to the input signals from the first controller 54 and from the second controller 55, respectively, characteristic 68 resulting from the two characteristics 66 and 67 and representing the output signal of the third controller 56. The output signal is transmitted to a drive control 69 of the first ventilator 38.
FIG. 6 relates to the fourth controller 57, which receives an input signal according to characteristic 70 from the third controller 56. By subtraction, the fourth controller 57 generates a characteristic 71 with an output signal that is to substantially ensure a speed of rotation of the second ventilator 42 that causes a pressure difference in the work room 29.
FIG. 7, which relates to the fifth controller 58, shows a characteristic 72 that causes an output signal as a function of a pressure or pressure difference in the work room 29. The fifth controller 58 receives an input signal, i.e. an actual value, from the air difference pressure sensor 52, said input signal or actual value generating a weaker or stronger output signal in case of deviation from a target value P_soll.
As illustrated in FIG. 8, the sixth controller 59 itself receives the output signal of the fourth controller 57 and of the fifth controller 58 according to characteristics 73 and 74, an output signal of the sixth controller 59 arising from a resulting characteristic 75. The output signal acts on a drive control 76 of the second ventilator 42 so that the required pressure difference in the work room is maintained at all times even if the air exchange rate varies.
FIG. 9 relates to the seventh controller 60, which can open or close a bypass valve 78 by means of a motor 77 according to characteristic 79 subject to the input signal from the first controller 54 and from the third air temperature sensor 51. According to characteristic 79, a minimum fresh air percentage of 15% is provided.


List of reference signs

10	clean room
11	work room arrangement
12	work room
13	work room
14	work room
15	room ventilation system
16	control device
17	ventilator device
18	treatment device
19	sensor device
20	processing device
21	memory device
22	time control device
23	supply air duct
24	exhaust air duct
25	environment
26	signal line
27	signal line
28	clean room
29	work room
30	room ventilation system
31	control device
32	supply air duct
33	exhaust air duct
34	outgoing air outlet
35	fresh air inlet
36	first filter
37	second filter
38	first ventilator
39	cooler
40	heater
41	third filter
42	second ventilator
43	heat recovery unit
44	bypass
45	environment
46	entrance
47	opening sensor
48	sensor device
49	first air temperature sensor
50	second air temperature sensor
51	third air temperature sensor
52	air difference pressure sensor
53	particle concentration sensor
54	first controller
55	second controller
56	third controller
57	fourth controller
58	fifth controller
59	sixth controller r
60	seventh controller
61	characteristic
62	characteristic
63	characteristic
64	characteristic
65	characteristic
66	characteristic
67	characteristic
68	characteristic
69	drive control
70	characteristic
71	characteristic
72	characteristic
73	characteristic
74	characteristic
75	characteristic
76	drive control
77	motor
78	bypass valve
79	characteristic

Claims

1. A process for operating a clean room (12, 28), the clean room comprising a work room (12, 13, 14, 29), a room ventilation system (15, 30) and a control device (16, 31), the room ventilation system being controlled and/or regulated by means of the control device, an air exchange rate in the work room and a pressure difference between the work room and an environment (25, 45) being generated by means of the room ventilation system, the control device comprising at least one sensor device (19, 48) for registering an actual value representing an operating parameter,

characterized in that

the air exchange rate is adjusted by means of the control device in such a manner that the actual value is in the range of a target value.

2. The process according to claim 1,

characterized in that

a positive pressure is generated in the work room (12, 13, 14, 29) as a pressure difference.

3. The process according to claim 1 or 2,

characterized in that

the pressure difference and an air quality in the work room (12, 13, 14, 29) and/or an actual value representing an operating parameter of the work room are registered by means of the sensor device (19, 48).

4. The process according to any one of the preceding claims,

characterized in that

an actual value for particle concentration, air temperature, relative air humidity, air exchange rate, air pressure, intensity of movement, number of individuals, CO₂concentration and/or door opening is registered by means of the sensor device (19, 48).

5. The process according to claim 4,

characterized in that

the particle concentration is measured at a workplace in the work room (12, 13, 14, 29) or in an exhaust air of the room ventilation system (15, 30).

6. The process according to any one of the preceding claims,

characterized in that

the control device (16, 31) selects a target value as a function of a time control (22) and/or of an intensity of movement, a target activity value for an operating period or a target inactivity value for an inactivity period being selected as the target value.

7. The process according to claim 6,

characterized in that

during the inactivity period, a particle concentration, a temperature and/or a relative air humidity are increased or the particle concentration is increased and the temperature and/or the relative air humidity are decreased in comparison to the operating period.

8. The process according to any one of the preceding claims,

characterized in that

control of the pressure difference is superseded by control of the air exchange rate.

9. The process according to any one of the preceding claims,

characterized in that

the room ventilation system (15, 30) comprises a first ventilator (38) for supply air and a second ventilator (42) for exhaust air, the control device (16, 31) controlling the pressure difference by adjusting speeds of rotation of the respective ventilators.

10. The process according to claim 9,

characterized in that

the control device (16, 31) controls a speed of rotation of the first ventilator (38) as a function of the operating parameter, preferably of an air temperature and of a particle concentration.

11. The process according to claim 10,

characterized in that

the sensor device (19, 48) registers an air temperature of the supply air and an air temperature of the exhaust air, the control device controlling a speed of rotation of the first ventilator (38) and/or a treatment of the supply air as a function of the air temperature of the exhaust air.

12. The process according to any one of claims 9 to 11,

characterized in that

the control device (16, 31) controls a speed of rotation of the second ventilator (42) as a function of the pressure difference, preferably of an air pressure in the work room (12, 13, 14, 29) and of a speed of rotation of the first ventilator (38).

13. The process according to any one of the preceding claims,

characterized in that

the control device (16, 31) stores operating parameters that are registered during an operating period and derives regularly recurring sequences of operating conditions from the stored operating parameters, the control device adjusting the air exchange rate to an operating condition to be expected in the future.

14. A control device (16, 31) for a clean room (12, 28), the clean room comprising a work room (12, 13, 14, 29) and a room ventilation system (15, 30), wherein the room ventilation system can be controlled and/or regulated by means of the control device, wherein an air exchange rate in the work room and a pressure difference between the work room and an environment (25, 45) can be generated by means of the room ventilation system, the control device comprising at least one sensor device (19, 48) for registering an actual value representing an operating parameter,

characterized in that

the air exchange rate can be adjusted by means of the control device in such a manner that the actual value is in the range of a target value.

15. A clean room (12, 28) comprising a work room (12, 13, 14, 29), a room ventilation system (15, 30) and a control device (16, 31) according to claim 14.

16. The clean room according to claim 15,

characterized in that

the clean room (12, 28) comprises a plurality of interconnected work rooms (12, 13, 14, 29) having different pressure differences.