WO2014135517A1

WO2014135517A1 - A ventilation system

Info

Publication number: WO2014135517A1
Application number: PCT/EP2014/054128
Authority: WO
Inventors: Lars-Peter EKOLIND; Henrik SKREDSVIK
Original assignee: Avidicare Ab
Priority date: 2013-03-04
Filing date: 2014-03-04
Publication date: 2014-09-12
Also published as: DK2965015T3; PL2965015T3; EP2965015A1; ES2865652T3; SE1350259A1; EP2965015B1; SE539405C2

Abstract

The present invention relates to a ventilation system for a clean room (1 ), the system comprising: a first air supply system (100) comprising at least one displacement air supply unit, whereby said at least one displacement air supply unit is arranged to provide a volume of displacing laminar flow of clean air forming a first air zone (101 ), representing a work area (11 ), of the clean room (1 ); and a second air supply system (120) comprising at least one dilution air supply unit, whereby said at least one dilution air supply unit is arranged to provide a volume of diluting turbulent flow of clean air forming a second air zone (121 ) of the clean room (1 ); wherein said second air supply system (120) is arranged such that said second air zone (121 ) at least partly surrounds the first air zone (101 ). This application also discloses a corresponding method for providing ventilation to a clean room (1 ).

Description

A VENTILATION SYSTEM

TECHNICAL FIELD

The present application relates to the field of ventilation, and in particular to the field of ventilation systems and methods for providing ventilation to clean rooms, such as operating theatres. BACKGROUND OF THE INVENTION

In a clean room, such as an operating theatre, it is essential to reduce the number of airborne bacteria-carrying particles, also referred to as colony forming units (cfu), in order to alleviate contamination during activity in the room, such as surgery or production of ultra-clean products. In for example an operating theatre, airborne bacteria-carrying particles deriving from the surgery staff is the main reason for surgical site infections.

Airborne bacteria-carrying particles are substantially generated by the persons present in the room. Each person sheds roughly 10 000 skin particles/minute when moving and 10 % of these particles are carrying bacteria.

Depending on the intended activity in the clean room, different levels of air cleanliness are required. In clean rooms with an allowed maximum contamination level in the region of 100 cfu/m³ i.e. 100 airborne bacteria- carrying particles per cubic meter, ventilation systems based on turbulent air flows are used. The purpose of turbulent air flow ventilation systems is to mix the present air of the room comprising bacteria-carrying particles with clean supply air, such that the present air is diluted, thus reducing the

contamination level of the room.

In clean rooms requiring a higher level of cleanliness, such as in operating theatres for high infection sensitive surgery, the allowed maximum contamination level is typically below 10 cfu/m³. A turbulent air flow system needs to achieve very high air flows and in the range of hundreds air exchange rates, in order to keep the contamination to such a low level. Thus, the environment would not be work friendly. Therefore, flow ventilation systems based on laminar air flows are used instead of ventilation systems based on turbulent air flows. By laminar air flow ventilation systems, the contamination level of the covered area can be kept below 10 cfu/m³, without the need for very high air flows. Typically, a laminar air flow ventilation system comprises a ceiling installation providing a laminar flow of clean air, also referred to as a unidirectional flow ceiling (UDF ceiling). A laminar flow ventilation system is much more energy-consuming than the above-mentioned turbulent ventilation system. Therefore, a UDF ceiling is typically arranged to cover a limited region of the room, which is required to fulfill cleanliness requirements. The limited region is typically where medical staff and medical equipment is located.

For operating theatres, ventilation installations are increasing in size since greater work areas fulfilling the cleanliness requirements are needed due to more complex surgery requiring more medical staff and more space requiring equipment. In an operating theatre today, the UDF ceiling covers typically an area of 9-12 m².

The purpose of a laminar air flow ventilation system is to displace present air of the room by a supplied descending flow of clean air. Thereby, the present air of the room, comprising bacteria-carrying particles, is displaced downwards towards the floor of the room. Thus, the contamination level in the area covered by the laminar air flow ventilation system is reduced.

SUMMARY OF THE INVENTION

An object of the present invention is to alleviate the above mentioned drawbacks and problems. A further object is to provide an improved ventilation system for a clean room such as an operating theatre. A further object is to provide an improve method for providing ventilation to a clean room such as an operating theatre. Definitions

In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

By laminar flow of air is meant a uni-directional air flow which has substantially the same direction within a volume of the laminar air flow. The laminar air flow has the purpose of displacing bacteria-carrying particles in an air zone covered by the laminar air flow. Without falling outside the scope of the present invention, it is to be understood that the laminar air flow due to for example surrounding disturbances may deviate from an exact uniform direction while still fulfilling its purpose of displacing bacteria-carrying particles.

In order to quantify how laminar a flow of air is it is possible to determine the turbulence intensity of the flow of air. The turbulence intensity may be defined as the measure of fluctuations in air velocity in relation to its mean value (relative standard deviation), i.e. the standard deviation of the air velocity divided by the mean value of the air velocity. This definition is set out by the German DIN (Deutsches Insitut fur Normung) standard DIN 1946-4 (see section 3.1 .13 in DIN 1946-4:2008-12). DIN 1946-4 deals with for example ventilation in rooms used for healthcare. A measurement period of three minutes is usually used for the turbulence intensity measurement.

As is seen from the definition, the ratio of the respective quantities will result in a value having no unit, why the turbulence intensity often is expressed in percents. By studying the above definition it will be understood that high air velocities will result in a low turbulence intensity as the standard deviation is divided by the mean velocity. The air velocity may be measured using various types of anemometers including hot-wire anemometers. One measurement method is set out in section E.6 of DIN 1946-4:2008-12.

For the purpose of this application, laminar flow of air is defined as having a turbulence intensity of not more than 30 %, when measured according to DIN 1946-4.

By displacement of bacteria-carrying particles is meant that a flow of bacteria-carrying particles are forced in the direction of a provided laminar flow of air, instead of following its otherwise natural direction due to the convection force. From a person standing in a room, which normally is much colder than the body temperature of the person, the convection force spreads the bacteria-carrying particles, shed from the person, in a direction upwards along with the flow of heat from the body. By a displacing laminar flow of air, this convection force is disrupted.

By turbulent flow of air is meant an air flow which does not flow in a uniform direction. Contrary to laminar flows of air, turbulent flows of air typically mix with the surrounding air. The turbulent air flow has the purpose of diluting the concentration of bacteria-carrying particles in an air zone covered by the turbulent air flow.

For the purpose of this application, turbulent flow of air is defined as having a turbulence intensity of above 30 %, when measured according to DIN 1946-4. By dilution of air is meant that the contamination level of the air is diluted in view of the concentration of bacteria-carrying particles.

By work area is meant an area of the clean room where the activity is intended to be performed. For an operating theatre, the work area comprises the operation table on which the patient is located, and further comprises an area surrounding the operating table. For a production clean room, the work area comprises a work station at which e.g. manual assembling of a product is performed, and further comprises an area surrounding the work station. In the surrounding area, staff is located when performing activity at e.g. the operating table or work station.

The invention

According to a first aspect of the invention, the above mentioned and other objects are achieved by a ventilation system for a clean room, the system comprising: a first air supply system comprising at least one

displacement air supply unit, whereby said at least one displacement air supply unit is arranged to provide a volume of displacing laminar flow of clean air forming a first air zone, covering a work area, of the clean room; and a second air supply system comprising at least one dilution air supply unit, whereby said at least one dilution air supply unit is arranged to provide a volume of diluting turbulent flow of clean air forming a second air zone of the clean room; wherein said second air supply system is arranged such that said second air zone at least partly surrounds the first air zone.

The present invention is based on the realization of the inventors that the bacteria particle generators, i.e. the present persons, of a clean room are typically concentrated in the work area. Thus, in clean rooms using laminar air flow ventilation systems, it may based on this realization be sufficient that the ventilation system is arranged to cover only the work area, thus displacing the substantial part of the generated bacteria-carrying particles.

However, it has also been realized that a laminar flow of air directed towards the floor of the room affects the area surrounding the laminar air flow zone by turning upwards when approaching the floor, and further turning inwards and back towards the work area. The turning laminar air flow brings along bacteria-carrying particles both from the work area and from the floor level which the air flow interacts with. There is thus a high risk of

contamination of the work area by these turning laminar air flows returning bacteria-carrying particles back into the work area. In order to alleviate this problem, a second air supply system is arranged to cover the area surrounding the first air zone formed by the laminar flow of clean air. The second air supply system comprises at least one dilution air supply unit being arranged to provide a volume of diluting turbulent flow of clean air. The turbulent flow of clean air forms an additional, second air zone surrounding the first air zone. The second air zone may be arranged such that the turbulent flow of clean air of this second air zone does not disturb the laminar air flow of clean air in the first air zone.

The turbulent flow of clean air suppresses the turning laminar air flows deriving from the first air zone. Further, the turbulent flow of clean air dilutes the air in the second air zone, thus providing a clean air environment also outside the first air zone.

It has further been realized that the first air supply system, providing a volume of displacing laminar flow of clean air and being e.g. a UDF ceiling, may be restricted to cover only the work area. In the work area, the majority of the present persons, i.e. bacteria-carrying particles generators, are located. By this arrangement of the first air supply system, the majority of generated bacteria-carrying particles is displaced. The ambient area surrounding the work area is covered by the second air supply system, providing a volume of diluting turbulent flow of clean air, which dilutes the air in view of bacteria- carrying particles generated by for example persons present in this ambient area.

This inventive combination of the first air supply system and second air supply system provides an area, being the work area and the ambient area, having a cleanliness which may be kept below a maximum allowed level. The work area and the ambient area preferably together make up the total room area.

Equipment may be arranged in the work area or in the ambient area, since both zones are kept clean by the ventilation system. Thus, the equipment does not need to be controlled such that it is not moved outside the area covered by the UDF ceiling as for known ventilations systems.

Further, the UDF ceiling does not need to be extended to cover areas in which equipment is located.

This is an energy efficient solution, since the first air supply system typically uses large volumes of air and may by the present invention be optimized in size. The second air supply system may comprise a plurality of turbulent air flow outlets. The volume of diluting turbulent flow of clean air may be provided through these turbulent air flow outlets.

The first air supply system and/or the second air supply system may be arranged in the ceiling of the clean room.

The ventilation system may comprise at least one, preferably a plurality of, discharge units arranged in the second air zone. Each discharge unit functions as an active or passive outlet for the air in the room. The ventilation system may comprise at least one air discharge unit arranged in a side wall and adjacent to the floor of the clean room.

The second air supply system may be arranged such that said second air zone surrounds the first air zone. This feature may be achieved by distributing a plurality of turbulent air flow outlets around one or more laminar air flow outlets of the first air supply system.

The clean room may be an operating theatre, or a production clean room.

The first air supply system may be arranged such that the first air zone, as seen in a horizontal plane, covers an area having e.g. a circular, rectangular or ovale shape. Other shapes are of course also feasible. In preferred embodiments, the covered area is in the interval of 0.5-16 m².

In case of a circular shape, the first air supply system may be arranged such that the first air zone, as seen in a horizontal plane, covers a circular area extending with a radius of 0.5-2 meters, preferably 0.75-1 .5 meters, as seen from the center of the work area.

An area extending with a radius of 0.5-2 meters as seen from the center of the work area, yields an area of about 0.75 to 13 m². An area extending with a radius of 0.75-1 .5 meters as seen from the center of the work area, yields an area of 1 .7 to 7.1 m². Thus, if other geometries than circular, the exemplified surface areas are applicable.

Thus, when arranging a conventionally sized operating table in the work area, and according to the above realization, the substantial part of the number of present medical staff in the room is covered by the first air zone, i.e. by the displacing laminar flow of clean air.

According to a second aspect of the invention, the above mentioned and other objects are achieved by a method for providing ventilation to a clean room, the method comprising: providing, by at least one displacement air supply unit of a first air supply system, a volume of displacing laminar flow of clean air forming a first air zone, covering a work area, of the clean room; and providing, by at least one dilution air supply unit of a second air supply system comprising, a volume of diluting turbulent flow of clean air forming a second air zone of the clean room, wherein said second air supply system is arranged such that said second air zone at least partly surrounds the first air zone.

The steps of providing a volume of displacing laminar flow, and of providing a volume of diluting turbulent flow is preferably performed parallel to each other.

The above disclosed features and corresponding advantages of the first aspect is also applicable to this second aspect. To avoid undue repetition, reference is made to the discussion above.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the enclosed drawings showing embodiments of the invention.

Figure 1 illustrates a clean room comprising a ventilation system according to one embodiment of the present invention.

Figures 2a-2b illustrate effects achieved by the ventilation system according to the present invention, in comparison to a ventilation system of known type.

Figure 3 is a view from above of an operating room in which a ventilation according to the present invention is arranged.

Figure 4 illustrates a method for providing ventilation to a clean room.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and for fully conveying the scope of the invention to the skilled person. A ventilation system according to one embodiment of the present invention is illustrated in figure 1 . The ventilation system is arranged in a clean room 1 . The clean room 1 could be e.g. an operating theatre, a production room for clean products, or a room for handing sterile products, such as unpacking and preparation of sterile instruments before an operation.

The ventilation system comprises two air supply systems based on different air flow principles - a first air supply system 100 providing a laminar air flow and a second air supply system 120 providing a turbulent air flow.

Lower discharge units 13 are arranged in the clean room 1 . These are arranged in side walls of the clean room 1 , and adjacent to the floor. Upper discharge units 14 are also arranged in the clean room 1 . These are arranged in the side walls of the clean room 1 , and adjacent to the ceiling.

The lower discharge units 13 and the upper discharge units 14 are adapted to, actively or passively, guide air out from the clean room 1 .

The first air supply system 100 is arranged in the ceiling above an intended work area 1 1 of the clean room 1 . In an operating theatre, an operating table (not illustrated) is typically arranged in the work area 1 1 . In an production room, a production table (not illustrated) is typically located in the work area 1 1 . As disclosed above, the work area 1 1 extends to an area surrounding e.g. the operating table or productions table, in which area staff is present.

The first air supply system 100 is based on a laminar air flow principle. The first air supply system 100 comprises one or more air displacement air supply units (not shown). The displacement air supply units provide, through an laminar air flow outlet 10, a displacing laminar flow of clean air directed downwards in the clean room 1 , and directed towards the work area 1 1 . The laminar air flow of clean air forms a volume forming a first air zone 101 of the clean room 1 .

The laminar air flow has a substantially uniform direction, in contrary to tubular flows. However, due to disturbances in the flow path, such as persons or equipment, the direction of the laminar air flow will increasingly turn outwards from the center of the laminar air flow volume with an increasing distance from the laminar air flow outlet 10. Thus, the first air zone 101 gets a funnel-shaped form.

The laminar flow of clean air forming the first air zone 101 has a displacing effect on bacteria-carrying particles, among other particles, generated by persons located in the first air zone 101 . The laminar flow of clean air carries with it particles downwards and towards the floor of the clean room 1 . Thus, the otherwise occurring effect of bacteria-carrying particles being transported upwards by convection, and thereafter downwards towards the patient, and in particular towards infection sensitive open wounds of the patient, is at least weakened.

The laminar flow of air provided by the first air supply system 100, need a certain minimum level of momentum in order to weaken the

convection force and thus displacing bacteria-carrying particles. The level of momentum depends on a combination of weight and velocity of the laminar flow of air. A higher level of momentum may be achieved either by increasing the air flow velocity or by increasing the weight of the air in the air flow. By having a minimum level of momentum, the laminar flow of air has a sufficient velocity at working height, where the particles from present persons are shed, in order to disrupt, or at least brake, the convection force.

An air flow velocity of above 0.25 m/s at a working height (e.g. at the height of an operating table or of a work station), is typically needed to brake the convection force to a certain extent. Further, an air flow velocity of above 0.4 m/s at a working height is typcially needed in order to substantially disrupt the convection force of a person.

There are different ways in order to provide a laminar flow of clean air having the velocity needed at the wokring height for achieving displacing effect. Thus, the first air supply system 100 may be formed in different shapes and may have different constructions, in order to achieve the displacing effect.

As a first example, the first air supply system 100 may be arranged to provide a laminar flow of clean air with a predetermined velocity at the laminar air flow outlet, in order to achieve the desired velocity at the working height. As an example, the predetermined velocity lies typically in the range of 0,2- 0,4 m/s at the laminar air flow outlet, in order to have increased to 0.25 m/s when reaching the working height.

The velocity may preferably be measured at a distance of about 10 centimeters below the displacement air supply unit in the direction of the laminar air flow, in order to ensure that the velocity has the desired value.

As a second example, the first air supply system 100 may be arranged to provide a laminar flow of clean air having a controlled weight such that the laminar flow of clean air has has a desired velocity at the working height in order to provide a displacing effect. In order to ahcieve this effect, clean air having a lower temperature than the air in the room is let out, through the laminar air flow outlet 10, by the displacement air supply units. Due to the temperature difference between the outlet laminar air and the ambient air in the clean room 1 , the outlet laminar air sinks downwards, having a

unidirectional flow direction, towards the work area 1 1 .Further, a decreased temperature of clean air provides a higher momentum. Thus, the laminar flow of clean air having a decreased temperature may achieve the desired velocity at the working height without the need for an initial velocity when let out through the laminar air flow outlet 10. As an example, a laminar air flow may be controlled to have temperature of 1-2°C lower than the ambient air in the clean room 1 and let out with essentially no initial velocity. By these conditions, the laminar air flow may achieve a velocity of 0.25 m/s when reaching the working height.

The first air supply system 100 may be provided with means (not illustrated) for sensing the temperature of the ambient air in the clean room 1 . Thus, it may be determined which temperature the clean air to be provided by the displacement air supply unit of the first air supply system 100 should have in order to achieve the above mentioned desired temperature difference between the air, provided by the first air system 100 and the ambient air in relation to the first air zone 101 . Further, the first air supply system 100 may be provided with means (not illustrated) for adjusting the temperature of the clean air to be provided through the first air supply system 100 such that the desired temperature difference is achieved.

The second air supply system 120 is arranged in the ceiling and surrounds the first air supply system 100. The second air supply system 120 is based on a turbulent air flow principle, i.e. a different air flow principle than for the first air supply system 100.

The second air supply system 120 comprises one or more turbulent air supply units (not shown). The plurality of turbulent air supply units provides a turbulent air flow through a plurality of turbulent air flow outlets 12 or diffusers 12 being distributed around the air flow outlet 10 of the first air supply system 100.

The turbulent air flow of clean air, provided by the turbulent air supply units and through the plurality of turbulent air flow outlets 12, form a volume forming a second air zone 121 of the clean room 1 . The turbulent air flow outlets 12 are arranged in a spaced manner around the laminar air flow outlet 10, such that the second air zone 121 surrounds the first air zone 101 . The second air supply system 120 may be formed in different shapes and may have different constructions, such as conventional fans having rotating fan blades and/or having outlets formed such that let out air is turbulent.

In order to realize the turbulent air flow of the second air zone 121 various types of air flow outlets 12 may advantageously be used. Today, there is a large number of different types of air flow outlets 12, producing a turbulent air flow, commercially available from a large number of suppliers such as Lindab®, Halton® and Flakt Woods®.

For instance, flow outlets 12 or diffusers of the Lindab® NS19 series may advantageously be used to realize the turbulent air flow of the second air zone 121 . The flow outlets of the Lindab® NS19 series are flow outlets comprising a plurality of nozzles used to discharge air such that a turbulent air flow is realized. The nozzles of the flow outlets 12 are individually adjustable meaning that the dispersion pattern of the flow outlets 12 may be adjusted, so as to discharge air in a specific way. This is advantageous as the

characteristics of the flow of turbulent air may be adjusted to suit a specific need. For instance, the adjustable nozzles bring about that the flow outlets may be used with both under tempered air and over tempered air and still realize a turbulent flow of air. Further, the outlets may be adjusted so as to take the geometry of the room where they are positioned into account.

In order to characterize or describe the turbulent air flow exiting the flow outlets 12, various parameters may be specified. However, the throw length or throw of a specific flow outlet 12 may be of relevance, as it gives information concerning the air flow exiting the flow outlet 12 and hence indirectly how the air flow will affect the surrounding air. The throw length L₀.2 indicates the distance at which the air velocity of the core of the air flow has reached a limit velocity of 0.2 m/s. The throw length for other limit velocities such as 0.25, 0.3 and 0.4 m/s may also be specified.

The turbulent air supply units may be arranged to provide turbulent air flow in a predetermined direction. For example, the turbulent air flow may be directed slightly outwards in view of the first air zone. Thus, any disturbing effect the turbulent air flow may have on the laminar air flow of the first air zone, may be alleviated.

The turbulent flows or clean air have a diluting effect on the air in view of bacteria-carrying particles. The turbulent flows of clean air also have a weakening effect on air flows deriving from the first air zone 101 . These diluting and weakening effects will now be described in detail with reference to figures 2a and 2b.

Figure 2a is a side view of an operating theatre in which a conventional ventilation system is installed. A patient is located on an operating table 21 , and medical staff 22, 22' are located nearby the operating table 21 . An air supply system, comprising an laminar air flow outlet 20, is arranged in the ceiling above the work area, comprising the operating table 21 and the medical staff 22, 22' located nearby. The air supply unit is also arranged to extend above an equipment table 23.

The air supply system comprises one or more displacement air supply units. The displacement air supply units are arranged to provide, through the laminar air flow outlet 20, a volume of displacing laminar air flow of clean air, thus forming a clean air zone. The provided laminar air flow has a

unidirectional direction illustrated by flow arrows 25.

Initially, when clean air is let out from the laminar air flow outlet 20, the laminar flow of clean air sinks downwards and towards the floor of the room. When approaching the floor, the laminar flow have gained speed, and will deviate from its substantial unidirectional direction and turn outwards due to the approaching floor surface. When approaching the side walls of the room, the flow will turn upwards and further turn inwards back towards the air zone of laminar flow of clean air. This turn effect of the laminar flow of clean air is illustrated by flow arrows 26 and 27. Even though the air flow deviates from its substantial single direction, it will still flow in a unidirectional manner when compared to turbulent air flows which have essentially no unidirectional flow characteristics. Therefore, the turning air flows are in the present context still regarded as laminar since the turning air flows are unidirectional on the whole and in relation to the turbulent air flows of the second air zone 121 .

When turning inwards and back towards the air zone of laminar flow of clean air, the turning laminar air flow does not only bring with it bacteria- carrying particles generated by the medical staff 22, 22', it also brings with it contaminated particles originating from the floor area of the room. Thus, there is an imminent risk that the air zone of laminar flow of clean air, in particular open wounds of the patient present therein and being susceptible to infection, is contaminated.

Figure 2b illustrates the same operating theatre, but in which a ventilation system according to an embodiment of the present invention replaces the conventional ventilation system in figure 2a. The ventilation system of figure 2b comprises a first air supply system 100 comprising a laminar air flow outlet 10, and a second air supply system 120 including a plurality of turbulent air flow outlets 12. These first and second air supply systems 100, 120 have been described in connection to figure 1 .

As for the displacement air supply units in figure 2a, one or more displacement air supply units are arranged to provide, through the laminar air flow outlet 12, a volume of displacing laminar flow of clean air. The provided volume forms a first air zone of the room. The first air zone covers the work area comprising the operating table 21 and area where the medical staff 22, 22' are located.

One or more dilution air supply units provides, through the turbulent air flow outlets 12, a volume of diluting turbulent flow of clean air, illustrated by flow arrow 28, of clean air. The first air supply system 100 and second air supply system 120 are arranged such that the second air zone is arranged adjacent to the first air zone. Preferably, the second air zone surrounds the first air zone.

Each turbulent flow of clean air has at least two advantageous effects.

Firstly, the turbulent air flow dilutes the air in the second air zone in view of bacteria-carrying particles, i.e. contaminated particles. The

contaminated particles are being transported to the second air zone by the turning flows originating from the laminar flow of clean air as illustrated in figure 2a.

Secondly, the turbulent flow suppresses the upward direction of the turning flows originating from the first air zone.

Thus, the turbulent flows of clean air have the effects of both cleaning the air surrounding the first air zone, and alleviating the effect that

contaminated particles are reintroduced in the first air zone. Positive consequences of these effects are that the first air zone may easily be kept clean, and that the ambient air zone outside the laminar air zone may be kept clean by providing the second air zone.

By the invention, the first air supply system, based on a laminar air flow principle, may be arranged so as to cover only the work area, in which the majority of present medical staff are located. The second air supply system, based on a turbulent air flow principle, may be arranged to cover the rest of the room. This improvement is illustrated in figures 2a and 2b, where the laminar air supply system in figure 2a is arranged to cover both the work area and the equipment table 23. In figure 2b, where the inventive ventilation system is illustrated, the laminar air supply system covers only the work area, while the turbulent air supply system covers the ambient area in which the equipment table 23 is located. Since also the cleanliness of the ambient area is controlled, it is possible to utilize also the ambient area.

This is further illustrated in figure 3, illustrating an operating room as seen from above. The operating room in figure 3 corresponds to the operating room illustrated in figure 2b. In the operating room, a ventilation system according to the present invention is arranged. The first air zone 101 is arranged to cover the work area. The work area comprises the operating table 21 and the medical staff 22, 22'. Further medical staff is also located in the work area. The second air zone 121 is arranged to cover the ambient area.

In this embodiment, the first air zone 101 covers an area having a circular shape. Further, the second air zone 121 covers an area also having a circular outer shape. The second air zone 121 may in other embodiments be arranged such that the whole area surrounding the work area is covered by the second air zone 121 . In that way, the total room area of the clean room is covered by the combination of the first air zone 101 and the second air zone 121 .

Equipment tables 23, 23' are arranged in the room. Each equipment table is covered by either the first air zone 101 or the second air zone 121 , or partly by the first air zone 101 and partly by the second air zone 121 . Since the cleanliness is controlled in both zones, the equipment tables may be arranged in any of the zones.

In a typical operating room, outer medical staff 32, 32' are located in the second air zone 121 . These persons are not as many as the persons located in the work area, and has typically a more passive role. Thus, the concentration of medical staff, and in particular the active medical staff, is in the work area around the patient on the operating table 21 .

It has been realized that the work area in which the majority of the medical staff in an operation room are present extends about 1 m from the operation table. Based on this realization, the first air supply system of the present invention may be arranged to cover only this area. The second air supply system is arranged to cover the ambient area. Both the work area and the ambient area may be kept below a maximum allowed contamination level, e.g. below a contamination level of10 cfu/m³. Depending on the application, the laminar air supply system may be minimized to cover an area of about 0.5-8 m², instead of the conventional 9- 12 m² which is common today, while still keeping the cleanliness of the clean room below the maximum allowed level. It is understood that the laminar air supply system may be arranged to cover larger areas, such as in the range of 10-15m², in applications where this is required. The ambient area is also in these embodiments covered by the second air supply system, thus providing a controlled cleanliness of both the work area and the ambient area.

In an alternative embodiment (not illustrated) of the present invention, the ventilation system may be arranged in a clean room comprising a plurality of work areas. Above each work area, an air supply system corresponding to the first air supply system disclosed above, may be arranged. In the one or more areas surrounding the air zones formed by the laminar air flows from the first air supply systems, one or more air supply systems corresponding to the second air supply system disclosed above, may be arranged.

A method for providing ventilation to a clean room is illustrated in figure 4. The method comprises providing 401 a volume of displacing laminar flow of clean air. The displacing laminar flow is provided by at least one displacement air supply units of a first air supply system. The displacing laminar flow forms a first air zone. The first air zone covers, as seen in a horizontal plane, a work area of the clean room. The method further comprises providing 402 a volume of diluting turbulent flow of clean air. The diluting turbulent flow of clean air is provided by at least one dilution air supply unit of a second air supply system. The diluting turbulent air flow forms a second air zone of the clean room. The second air supply system is arranged such that said second air zone at least partly surrounds the first air zone. The method may be performed by the ventilation system and in a manner as disclosed above in connection to figures 1— 2b. The method steps 401 , 402 may be performed in parallel.

It will be appreciated that numerous variants of the above described embodiments of the present invention are possible within the scope of the appended claims.

Claims

A ventilation system for a clean room (1 ), the system comprising:

a first air supply system (100) comprising at least one displacement air supply unit, whereby said at least one displacement air supply unit is arranged to provide a volume of displacing laminar flow of clean air forming a first air zone (101 ), covering a work area (1 1 ), of the clean room

(I ) ; and

a second air supply system (120) comprising at least one dilution air supply unit, whereby said at least one dilution air supply unit is arranged to provide a volume of diluting turbulent flow of clean air forming a second air zone (121 ) of the clean room (1 );

wherein said second air supply system (120) is arranged such that said second air zone (121 ) at least partly surrounds the first air zone (100).

The ventilation system according to claim 1 , wherein the second air supply system (120) comprises a plurality of turbulent air flow outlets (12) through which the volume of diluting turbulent flow of clean air is provided.

The ventilation system according to claim 1 or 2, wherein the first air supply system (100) is arranged such that the first air zone (101 ), as seen in a horizontal plane, covers a circular area extending with a radius of 0.5-2 meters, preferably 0.75-1 .5 meters, as seen from the center of the work area (1 1 ).

The ventilation system according to claims 1 -3, wherein the work area

(I I ) has an area of 0.75 to 13 m².

The ventilation system according to any of claims 1-4, wherein the first air supply system (100) and the second air supply system (120) are arranged in the ceiling of the clean room (1 ).

The ventilation system according to any of claims 1-5, further comprising at least one air discharge unit (13, 14) arranged in a side wall of the clean room (1 ). The ventilation system according to any of claims 1-6, wherein the clean room (1 ) is an operating theatre.

A method for providing ventilation to a clean room (1 ), the method comprising:

providing, by at least one displacement air supply unit of a first air supply system (100), a volume of displacing laminar flow of clean air forming a first air zone (101 ), covering a work area (1 1 ), of the clean room (1 ); and

providing, by at least one dilution air supply unit of a second air supply system (120), a volume of diluting turbulent flow of clean air forming a second air zone (121 ) of the clean room (1 );

wherein said second air supply system (120) is arranged such that said second air zone (121 ) at least partly surrounds the first air zone (101 ).