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A radial fan comprises a casing having a side portion and a pot-like casing portion, an impeller wheel arranged therein and having radially extending blades, an electric motor arranged at the side portion, and a pressure chamber which is formed by the casing portion and the side portion. The pressur

A radial fan comprises a casing having a side portion and a pot-like casing portion, an impeller wheel arranged therein and having radially extending blades, an electric motor arranged at the side portion, and a pressure chamber which is formed by the casing portion and the side portion. The pressure chamber with the impeller wheel space between the blades forms in cross-section a nozzle in the manner of a venturi nozzle. The ratio of the greatest blade height H/greatest diameter D of the scroll is substantially between H/D=0.08 and H/D=0.3.

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1. A radial fan comprising: a casing having a front wall, an inlet, an outlet, a side portion defining a planar wall, a pot-shaped casing portion and defining a casing scroll,an impeller wheel in the casing including a hub, a cover disc and a plurality of radially extending blades extending between

1. A radial fan comprising: a casing having a front wall, an inlet, an outlet, a side portion defining a planar wall, a pot-shaped casing portion and defining a casing scroll,an impeller wheel in the casing including a hub, a cover disc and a plurality of radially extending blades extending between the hub and the cover disc each of the plurality of radially extending blades defining a straight edge disposed parallel to and immediately adjacent the planar wall of the side portion of the casing, the impeller drawing fluid in through the inlet at a radial center portion of the impeller wheel and blowing the fluid out the outlet at a radial outer portion of the impeller wheel,an electric motor at the side portion,a pressure chamber formed by the casing portion and the side portion, anda flow channel for said fluid extending between said inlet and said outlet being defined by said planar wall of said side portion of said casing, adjacent blades of said impeller wheel, said hub and said cover disc, said flow channel extending between the hub and the cover disc to form in a cross-section a nozzle in the manner of a venturi nozzle; whereina narrowest cross-section of the venturi nozzle is defined by a surface of the impeller wheel at an outer circumferential edge of the impeller wheel and a surface of the planar wall of the side portion of the casing, the narrowest cross-section extending perpendicular to the planar wall of the side portion;the ratio of the greatest blade height H/greatest diameter D of the casing scroll is between H/D=0.08 and H/D=0.3,the casing has a tongue portion extending into said pressure chamber; andsaid tongue portion is provided on the casing portion in the form of a ramp which rises in the flow direction on the front wall of the casing portion. 2. A radial fan as set forth in claim 1, wherein the ratio of the greatest blade height H/greatest diameter D of the casing scroll is substantially H/D=0.1. 3. A radial fan as set forth in claim 1, wherein the ratio of the greatest blade height H/greatest diameter D of the casing scroll is substantially H/D=0.12. 4. A radial fan as set forth in claim 1 including enlargement cavity portions in at least one of the casing portion and the side portion, the enlargement cavity portions continuously three-dimensionally enlarging the pressure chamber. 5. A radial fan as set forth in claim 4, wherein the casing portion and the side portion have said enlargement cavity portions and the enlargement cavity portion in the casing portion is larger than said portion in the side portion. 6. A radial fan as set forth in claim 1, wherein the height/diameter ratio of the casing is between 1:7 and 1:9. 7. A radial fan as set forth in claim 6, wherein the height/diameter ratio of the casing is substantially 1:8. 8. A radial fan as set forth in claim 1, wherein with a rotary speed of about n=5250 rpm a gas volume flow of about 11 l/s at a pressure of 1050 Pascals is delivered, which corresponds to a shaft power of about 21 W. 9. A radial fan as set forth in claim 1, wherein the casing defines a delivery duct for the discharge of gas from the fan and including: a connection means on the delivery duct of the casing, said connection means defining a first plane,wherein said first plane is at an angle α≦90° relative to a delivery direction. 10. A radial fan as set forth in claim 9, wherein said first plane is at an angle of 90°>α≧83° relative to the delivery direction. 11. A radial fan as set forth in claim 9, wherein said first plane is at an angle of 86.4° relative to the delivery direction. 12. A radial fan as set forth in claim 9, wherein said delivery duct is provided on said casing portion. 13. A radial fan as set forth in claim 9, wherein said delivery duct is of a trumpet enlarging configuration. 14. A radial fan as set forth in claim 1, wherein said impeller wheel and said blades are held only to said hub and to the cover disk. 15. A radial fan comprising: a casing having a side portion defining a planar wall, an inlet, an outlet and a pot-shaped casing portion and defining a casing scroll,an impeller wheel in the casing including a hub, a cover disc and a plurality of radially extending blades extending between the hub and the cover disc each of the plurality of extending blades defining a straight edge disposed parallel to and immediately adjacent the planar wall of the side portion of the casing, the impeller drawing fluid in through the inlet at a radial center portion of the impeller wheel and blowing the fluid out the outlet at a radial outer portion of the impeller wheel,wherein said casing portion has a front wall,an electric motor at the side portion, anda pressure chamber which is formed by the casing portion and the side portion,a flow channel for said fluid extending between said inlet and said outlet being defined by said planar wall of said side portion of said casing, adjacent blades of said impeller wheel, said hub and said cover disc, said flow channel extending between the hub and the cover disc to form in a cross-section a nozzle in the manner of a venturi nozzle; whereinwherein a narrowest cross-section of the venturi nozzle is defined by a surface of the impeller wheel at an outer circumferential edge of the impeller wheel and a surface of the planar wall of the side portions of the casing, the narrowest cross-section extending perpendicular to the planar wall of the side portion;wherein the ratio of the greatest blade height H/greatest diameter D of the casing scroll is between H/D=0.08 and H/D=0.3,wherein said casing has a tongue portion extending into said pressure chamber, andwherein said tongue portion is provided on said side portion in the form of a ramp which rises in the flow direction towards said side portion. 16. A radial fan as set forth in claim 15, wherein the ratio of the greatest blade height H/greatest diameter D of the casing scroll is H/D=0.1. 17. A radial fan as set forth in claim 15, wherein the ratio of the greatest blade height H/greatest diameter D of the casing scroll is H/D=0.12. 18. A radial fan as set forth in claim 15 including enlargement cavity portions in at least one of the casing portion and the side portion, the enlargement cavity portions continuously three-dimensionally enlarging the pressure chamber. 19. A radial fan as set forth in claim 18, wherein the casing portion and the side portion have said enlargement cavity portions and the enlargement cavity portion in the casing portion is larger than said portion in the side portion. 20. A radial fan as set forth in claim 15, wherein the height/diameter ratio of the casing is between 1:7 and 1:9. 21. A radial fan as set forth in claim 20, wherein the height/diameter ratio of the casing is 1:8. 22. A radial fan as set forth in claim 19, wherein with a rotary speed of about n=5250 rpm a gas volume flow of about 11 l/s at a pressure of 1050 Pascals is delivered, which corresponds to a shaft power of about 21 W. 23. A radial fan as set forth in claim 15, wherein the casing defines a delivery duct for the discharge of gas from the fan and including: a connection means on the delivery duct of the casing, said connection means defining a first plane,wherein said first plane is at an angle αα>83° relative to the delivery direction. 25. A radial fan as set forth in claim 23, wherein said first plane is at an angle of 86.4° relative to the delivery direction. 26. A radial fan as set forth in claim 23, wherein said delivery duct is provided on said casing portion. 27. A radial fan as set forth in claim 23, wherein said delivery duct is of a trumpet enlarging configuration. 28. A radial fan as set forth in claim 1, wherein said blades are held only to said hub and to the cover disk. 29. A radial fan as set forth in claim 1, wherein a widest cross-section of the venturi nozzle is disposed at a radially inward portion of the radially extending blades and the narrowest cross-section of the venturi nozzle is disposed at a radially outward position of the radially extending blades. 30. A radial fan as set forth in claim 15, wherein a widest cross-section of the venturi nozzle is disposed at a radially inward portion of the radially extending blades and the narrowest cross-section of the venturi nozzle is disposed at a radially outward position of the radially extending blades. 31. A radial fan as set forth in claim 1, wherein the narrowest cross-section being defined by a surface of the cover disc and the surface of the casing. 32. A radial fan as set forth in claim 15, wherein the narrowest cross-section being defined by a surface of the cover disc and the surface of the casing. 33. The radial fan as set forth in claim 1, wherein each of the plurality of radially extending blades includes a curved edge disposed on a side of the blade immediately adjacent the inlet and a straight edge disposed on a side of the blade opposite the curved edge, the cover disc being disposed on the curved edge, the hub being disposed on the straight edge. 34. The radial fan as set forth in claim 15, wherein each of the plurality of radially extending blades includes a curved edge disposed on a side of the blade immediately adjacent the inlet and a straight edge disposed on a side of the blade opposite the curved edge, the cover disc being disposed on the curved edge, the hub being disposed on the straight edge. 35. The radial fan as set forth in claim 1, wherein said hub is directly attached to a first side of said plurality of blades and said cover disc is directly attached to a second side of said plurality of blades opposite to said first side, said flow channel extending between said first and second side of said plurality of blades. 36. The radial fan as set forth in claim 15, wherein said hub is directly attached to a first side of said plurality of blades and said cover disc is directly attached to a second side of said plurality of blades opposite to said first side, said flow channel extending between said first and second side of said plurality of blades. 37. The radial fan according to claim 1, wherein the flow channel includes a first section defined by the hub and not by the adjacent blades and a second section defined only by the adjacent blades of the impeller wheel, the cover disc and the planar wall of the side portion of the casing, the second section being disposed immediately after the first section in a flow direction of the fluid. 38. The radial fan according to claim 15, wherein the flow channel includes a first section defined by the hub and not by the adjacent blades and a second section defined only by the adjacent blades of the impeller wheel, the cover disc and the planar wall of the side portion of the casing, the second section being disposed immediately after the first section in a flow direction of the fluid. 39. The radial fan according to claim 1, wherein the cover disc begins at an innermost radial end of the plurality of radially extending blades and ends at an outermost radial end of the plurality of radially extending blades. 40. The radial fan according to claim 15, wherein the cover disc begins at an innermost radial end of the plurality of radially extending blades and ends at an outermost radial end of the plurality of radially extending blades. 41. The radial fan according to claim 1, wherein a radially inner end of each of the plurality of radially extending blades extends between an innermost radial end of the cover and an outermost radial end of the hub. 42. The radial fan according to claim 15, wherein a radially inner end of each of the plurality of radially extending blades extends between an innermost radial end of the cover and an outermost radial end of the hub.