Clean room

Abstract: The clean room arrangement (2) comprises a clean room (1) having an upper portion (4) and a lower portion (6). Clean air is introduced into the upper portion (4) of the clean room (1), flows downward and expelled from the lower portion (6) of the clean room (1). An air recirculation passage (7) is connected to the clean room (1) such that the lower portion (4) of the clean room (1) is communicated with the upper portion (4) of the clean room (1). A warm heat source (8) is provided in the air recirculation passage (7) to generate an ascending flow of air in the air recirculation passage (7) so that the air descends in the clean room (1) due to a natural convection.

Description: The present invention relates to a clean room arrangement according to the generic term of claim 1. Generally clean room arrangements have a clean room, an air feed chamber formed in an upper portion of the clean room and a recirculation chamber formed in a lower portion of the clean room. The air feed chamber is provided with a filter and feeds clean air into the clean room through the filter. The recirculation chamber is provided with a grating and sucks the clean air through the grating. Therefore, the clean air introduced into the clean room from the air feed chamber via the filter goes down and enters the recirculation chamber. Then, the clean air is recirculated to the air feed chamber. On the way to the air feed chamber, external air for the ventilation is added to the circulating clean air if necessary, and such a combination is recirculated into the clean room. Various types of clean room arrangement have been proposed. Figure 5 of the accompanying drawings shows one of such arrangements. An air conditioner a is placed outside a clean room f and used to recirculate the clean air. A filter e extends in an upper portion of a clean room arrangement l and defines an air feed chamber d above the filter e. A clean room f is defined below the filter e. In other words, the filter e serves as a ceiling of the clean room f. A grating g extends in a lower portion of the clean room arrangement l and used as a floor of the clean room f. A recirculation chamber h is defined below the grating h whereas the clean room f is defined above the grating h. An outlet of the recirculation chamber h is connected to an inlet of the air conditioner a by a recirculation duct i. An outlet of the air conditioner a is connected to the air feed chamber d by an air feed duct c. A blower b of the air conditioner a forces the air to flow into the air feed chamber d through the air feed duct c and the air is introduced into the clean room f after it is filtered by the filter e. The clean air entering the clean room f descends into the recirculation or air recovery chamber h, as indicated by the arrows in the drawing. The clean air flows through the grating g as it enters the recirculation chamber h. Then, the clean air returns to the air conditioner a through the recirculation duct i. Figure 6 shows another conventional clean air arrangement. The air conditioner a is joined with the clean room f. The clean air from the blower b directly enters the air feed chamber d from the outlet of the air conditioner a. The outlet of the air conditioner a communicates with the upper portion of the upper portion of the clean room f. Likewise, the clean air from the recirculation chamber h directly flows into the inlet of the air conditioner a. The lower portion of the clean room communicates with the inlet of the air conditioner a. Figure 7 illustrates an arrangement which has a blower j equipped with filters. The clean room f is defined in the clean room arrangement l with the recirculation space k being formed around the clean room f. The clean air is directly introduced into the clean room f by the filter-provided blower j and then expelled to the recirculation chamber h from the clean room f via the grating g. The clean air then flows upward in the recirculation chamber h and returns to the air feed chamber d. These conventional arrangements have following problems: If an air flow rate of the blower is raised in order to obtain a high cleanliness in the clean room f, a pressure loss across the filter becomes large and power for the blower becomes large. In addition, the recirculation of the clean air by the blower causes an imhomogeneous pressure profile in the recirculation system which in turn causes a drift current in the clean room. On the other hand, if air flow rate of the blower is lowered and a high cleanliness of the clean room is attempted, a turbulence is generated in the clean room and an ascending current is locally produced in the clean room. Therefore, a high cleanliness cannot be expected. A clean room arrangement which provides an airlock at the entrance to the clean room in order to prevent particle contamination of the clean room is known from DE-U-8 910 036. The air inside the clean room is sucked off by a ventilator. From there, the air is guided through a heating device and blown into the clean room via an air conditioner. Air circulation is thus generated by mechanical blower means. One object of the present invention is to provide a clean room arrangement which can provide a recirculating flow of clean air without blowers. This object is achieved by the features of claim 1. Advantageous developments are defined in the dependent claims. According to a variant of the present invention, there is additionally provided a cold heat source mounted or placed in the air feed chamber or the recirculation chamber for forming a more stable flow of air in the clean room. Since the air recirculation passage is provided with the warm heat source, the air in the air recirculation passages is heated and the ascending current of air flowing into the air feed chamber is generated. If the air feed chamber or the recirculation chamber is provided with the cold heat source, a more stable ascending current is produced and maintained in the air recirculation passage and as well as in the clean room. Figure 1 shows a sectional view of a clean room arrangement according to a first embodiment of the present invention; Figure 2 shows a sectional view of a second embodiment of the present invention; Figure 3 illustrates a sectional view of a third embodiment according to the present invention; Figure 4 is a section of a fourth embodiment according to the present invention; Figure 5 shows a sectional view of a conventional clean room arrangement; Figure 6 shows a sectional view of another conventional clean room arrangements; and Figure 7 shows a sectional view of still another conventional clean room arrangement. Preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following detailed description, same numerals are assigned to like elements in different figures. Referring to Figure 1, numeral 1 designates a clean room formed in a factory or a laboratory and a clean room arrangement is generally indicated by a numeral 2. An air feed chamber 4 is formed in an upper portion of the clean room 1. A filter 3 which extends in the upper portion of the clean room 1 generally in a horizontal direction defines the air feed chamber 4. A recirculation chamber 6 is formed in a lower portion of the clean room 1. A grating 5 which extends in the lower portion of the clean room 1 defines the recirculation chamber 6. The air chamber 4 and the recirculation chamber 6 are connected with each other by an air recirculation passage 7. The air recirculation passage 7 is provided with a heat exchanger 8 (warm heat source). An inlet pipe 9 is connected with the heat exchanger 8 such that a heating medium of high temperature such as warm water and steam may be fed into the heat exchanger 8. An outlet pipe 10 which is equipped with a heating medium flow rate control valve 11 is also connected with the heat exchanger 8. An external air duct 12 is connected to a circulation duct 7a of the circulation passage 7 connecting the circulation chamber 6 with the heat exchanger 8 such that external air can merge with the recirculated air. An exhaust duct 18 is connected to the circulation chamber 6 such that the air in the chamber 6 can be expelled out of the clean room arrangement. The exhaust duct 18 is provided with a damper (not shown) for adjusting an amount of exhaust. Preferably, an air feed duct 7b connecting the heat exchanger 8 to the air feed chamber 4 is covered with a heat insulating material. The air in the heat exchanger 8 is heated as the heating medium is supplied into the heat exchanger 8 through the feed pipe 9. Then, the heated air ascends in the feed duct 7a of the air recirculation passage 7 due to a buoyancy of itself and reaches the air feeding chamber 4. At the same time, the air in the recirculation duct 7b moves up toward the heat exchanger 8. Accordingly, an air circulation occurs in the clean room arrangement. Specifically, the hot air flowing into the air feed chamber 4 is clarified to the clean air by the filter 3 and then enters the clean room 1. Such clean air flows downward in the clean room 1 as indicated by the arrows 13. Then, the clean air is recovered by the circulation chamber 6 via the grating 5 and flows back into the heat exchanger 8 through the circulation duct 7a. A flow rate of the recirculated air can be adjusted by the flow rate control valve 11. Specifically, the recirculated air flow rate is adjusted by controlling a flow rate of the heating medium such as hot water flowing into the heat exchanger 8, i.e., by controlling an amount of heat exchanged between the air and the heating medium. The descending flow of air occurs in the clean room 1 due to the natural convection of the air caused by the buoyancy of the air. Thus, a stable descending flow of air is assured. Figure 2 shows another embodiment of the present invention. As compared with the clean room arrangement 2 of Figure 1 which the externally provided air circulation passage 7 is connected to the clean room 1 by the ducts 7a and 7b, the arrangement 2 of Figure 2 has an integrated recirculation passage 7. The passage 7 extends vertically next to the clean room 1 with an upper outlet of the passage 7 being directly communicated with the upper portion of the air feed chamber 4 and a lower inlet of the passage 7 being directly communicated with the lower portion of the air circulation chamber 6. In Figure 2, a section of the air circulation passage 7 can be designed arbitrarily. In Figure 1, generally standard pipes are employed as the pipes 7a and 7b. This means that a designer of the clean room arrangement should choose a pipe from ready-made ones. Further, a heat transfer area of the heat exchanger provided in the air passage 7 can be determined arbitrarily according to the arrangement of Figure 1. Consequently, a more precise natural convection is realized and a more precise air flow rate control becomes possible. Figures 3 and 4 illustrate other embodiments of the present invention, respectively. Arrangements of these figures are fundamentally similar to that of Figure 1. A major difference is a cooling heat exchanger 14 (cold heat source). In Figure 3, the cooling heat exchanger 14 is provided in the air feeding chamber 4 and extends just above and along the filter 3. In Figure 4, the cooling heat exchanger 14 is provided in the air circulation chamber 6 and extends just below and along the grating 5. A cooling medium such as cold water is supplied into the cooling heat exchanger 14 through a feed pipe 15 and discharged from the heat exchanger 14 through a discharge pipe 16. The discharge pipe 16 is provided with a flow rate control valve 17 to adjust a flow rate of the cooling medium. In the embodiments of Figures 1 and 2, the flow rate of the recirculated air is generally determined by an amount of heat exchanged in the heat exchanger 8, a temperature drop of the air due to heat radiation to outside from the clean room 2 and an amount of ventilation with the external air. However, this flow rate is easily affected by for example a temperature of the external air. According to the arrangements of Figures 3 and 4, on the other hand, since the air in the air feed chamber 4 or the air circulation chamber 6 is cooled by the heat exchanger 14 in order to effectively cause the natural convection due to the buoyancy, the temperature of the air flowing into the other heat exchanger 8 can be controlled more precisely and therefore the circulation of the air due to the buoyancy occurs more effectively. In case of Figure 3, the hot air entering the air feed chamber 4 is cooled therein before it is introduced into the clean room 1. In case of Figure 4, the hot air entering the air feed chamber 4 is introduced into the clean room 1 as the hot clean air and cooled in the recirculation chamber 6. It should be noted that the present invention is not limited to the illustrated arrangements. For example, the cooling heat exchanger 14 may be located in both the air feed chamber 4 and the air recirculation chamber 6. The flow rate control valve 17 may be mounted on the feed pipe 15 instead of the discharge pipe 16. Although the heat exchanger 8 is used as the hot heat source, an electric heater may be used instead thereof. As described above, the present invention has following advantages: (1) Since blowers are not used, no turbulence occurs in the descending air in the clean room; (2) Further, as compared with a case where the air circulation is caused by the blowers, less energy is consumed in the circulation of the air; and (3) A stable descending flow of air is ensured in the clean room even if a pressure profile in the air circulation system is not controlled.

Claims: A clean room arrangement (2) including: a clean room (1) having an upper portion (4) and a lower portion (6), clean air being introduced into the clean room (1) from the upper portion (4) thereof, flowing downward and expelled from the lower portion (6) thereof; an air recirculation passage (7) for recirculating the air of the lower portion (6) of the clean room (1) into the upper portion (4) of the clean room (1); and a warm heat source (8), characterized in that the warm heat source (8) is located near the lower portion of the recirculation passage (7) and generates an ascending flow of air in the air recirculation passage (7) without the use of blowers. The arrangement of claim 1, characterized in that the clean room (1) includes a filter (3) provided in the upper portion (4) of the clean room (1) and a grating (5) provided in the lower portion (6) of the clean room (1), and the filter (3) serves as a ceiling of the clean room (1) and the grating (5) serves as a floor of the clean room (1). The arrangement of claim 2, characterized in that an air feed chamber (4) is defined above the filter (3) in the upper portion of the clean room (1), an air recirculation chamber (6) is defined below the grating (5) in the lower portion of the clean room (1), the air recirculation passage (7) includes a duct (7a, 7b) connecting the air feed chamber (4) with the air recirculation chamber (6) and the warm heat source includes a heat exchanger (8) provided on the duct (7a, 7b). The arrangement of claim 1, 2 or 3, characterized in that a heating medium feeding device, preferably a warm water feed device (9, 10), is connected to the heat exchanger (8). The arrangement of claim 4, characterized in that the heating medium feeding device includes a flow rate control valve (11) for adjusting a flow rate of the heating medium introduced into the heat exchanger (8) in order to change a speed of the ascending air in the duct (7a, 7b). The arrangement of claim 5, characterized in that an external air feed line (12) is connected to the duct (7a) upstream of the heat exchanger (8) such that external air may be added to the recirculating air. The arrangement of any one of the foregoing claims, characterized in that the air recirculation passage (7) is formed next to the clean room (1) for recirculating the air of the lower portion (6) of the clean room (1) into the upper portion (4) of the clean room (1). The arrangement of any one of the foregoing claims, characterized in that a cold heat source (14) is provided in the air feed chamber (4) or the air recirculation chamber (6) for assisting a formation of the descending flow of air introduced into the clean room (1) from the air feed chamber (4). The arrangement of claim 8, characterized in that the cold heat source includes a cooling heat exchanger (14) extending above and along the filter (3) or extending below and along the grating (5), the cooling heat exchanger (14) is provided with a cooling medium feeding device (15, 16) for supplying a cooling medium into the cooling heat exchanger (14) and the cooling medium feeding device (15, 16) has means (17) for controlling a flow rate of the cooling medium.

Inventors: ABE HIROAKI C O ASAHI KOGYOSHA, HONDA SHIGEO C O ASAHI KOGYOSH, ISONO KAZUTOMO C O ASAHI KOGYO, ABE, HIROAKI, C/O ASAHI KOGYOSHA CO., LTD., HONDA, SHIGEO, C/O ASAHI KOGYOSHA CO., LTD., ISONO, KAZUTOMO, C/O ASAHI KOGYOSHA CO., LTD.
Applicants: ASAHI KOGYOSHA, ASAHI KOGYOSHA CO., LTD.
Application year: 1991
Main classification: F24F3
IPC codes: F24F7, F24F3