Filter module

A filter module comprising:

• a housing including a first opening and a second opening;
• a filter inside the housing;
• a first electrode, which is a mesh panel, at an inside of the first opening and facing a first surface of the filter;
• a second electrode, which is a mesh panel, at an inside of the second opening and facing a second surface, opposite to the first surface, of the filter;
• and
• a spacer configured to maintain a space between the first surface and the first electrode,
• wherein the filter module is configured to be arranged in a flow path of air so that the air flows through the filter from the second surface to the first surface with the second opening and the second electrode at an upstream side of the filter along the flow path, the first opening and the first electrode at a downstream side of the filter along the flow path, the second electrode forming a ground electrode, and the first electrode forming a high voltage electrode, and so that the space maintained by the spacer prevents electrical conduction between the first electrode and the second electrode due to foreign substances collected in the filter upstream of the first surface.