Foldable air filter unit

1. An air filter unit for purifying air, the air filter unit comprising:

a filter body extending along an axis,

a first filter frame and a second filter frame arranged on opposite ends of the filter body,

each of the first and second filter frame comprising four elongated frame members turnably secured to each other, and

the first filter frame is arranged on the top side of the filter body and the second filter frame is arranged on the bottom side of the filter body, and no filter frames or frame members are arranged between the top side of the filter body and the bottom side of the filter body

wherein the four elongated frame members are turnably secured to each other such that the filter body can be arranged in a first and a second state,

wherein the first state is such that the filter body is folded to reduce the volume of the filter unit and the second state is such that the filter body is assembled.

2. The air filter unit as defined in claim 1 , wherein the filter body, the first filter frame and the second filter frame in the second state have a rectangular cross section transverse to the axis.

3. The air filter unit as defined in claim 1 , wherein the filter body comprises four side walls.

4. The air filter unit as defined in claim 3 , wherein the side walls are rectangular and turnably secured to each other along the sides parallel to the axis.

5. The air filter unit as defined in claim 3 , wherein each elongated frame member comprises a recess such that the frame members are fitted to the corresponding wall of the filter body.

6. The air filter unit as defined in claim 1 , wherein the elongated frame members have a substantially rectangular shape and are turnably connected to each other by a thin elastic and/or flexible element in the inner corners of adjacent frame members.

7. The air filter unit as defined in claim 1 , wherein each of the first and second filter frames are formed by first and second substantially identical filter frame sections, the first filter frame section comprising two of the four elongated frame members of a respective filter frame and the second filter frame section comprising the remaining two of the four elongated frame members of the respective filter frame.

8. The air filter unit as defined in claim 7 , wherein the two elongated frame members of each filter frame section are connected via a foldable element to be turnably connected within a range of 90-180 degrees.

9. The air filter unit as defined in claim 7 , wherein the first and the second filter frame sections are connected via a turnable coupling mechanism, the turnable coupling mechanism is turnable within a range of 0-90 degrees.

10. The air filter unit as defined in claim 9 , wherein each coupling mechanism comprises a male part arranged on one of the first or second filter frame section and a female part arranged on the other filter frame section, wherein the male and female parts are arranged to turnably secure the first and second filter frame sections to each other.

11. The air filter unit as defined in claim 9 , wherein each coupling mechanism comprises a central hub arranged on one of the first or second filter frame section, the central hub defining the axis of rotation for the coupling mechanism.

12. The air filter unit as defined in claim 11 , wherein the coupling mechanism further comprises an arc-shaped recess extending around the central hub and a corresponding arc-shaped protrusion arranged on the other filter frame section, wherein the arc shaped protrusion is slidably arranged in the recess when the first and second filter frame sections are assembled.

13. The air filter unit as defined in claim 1 , wherein the filter unit is a disposable filter unit.