There are many UVC air purification systems available - but they are often expensive - and at the moment not readily available. This Instructable makes use of commonly available components and materials to make a low cost version.

UVC light is germicidal and in the right intensity, right range and for the right time it will reduce the amount of Coronavirus in the air. However, it must be used in conjunction with other hygiene measures such as washing hands, safe separation distance, disinfectant wipes, use of masks etc.

The UVC lamp (and reflections from metal) MUST NOT be viewed directly and must not be allowed to shine on the skin or it could do harm. It should only be switched on when the unit is completed and fully assembled and the lamp cannot be seen directly.

This unit operates on mains electricity and should only be assembled by a capable person and checked before use. Contacts and bare wires must not be accessible once the project is completed. Power should not be activated until the project is completed.

Supplies

18 mm plywood

44 x18 mm softwood

6 mm MDF

100 mm waste pipe cut to 800 mm long

Electrical components must be suitable for local region and mains voltage:

100mm bathroom extractor fan

18W 2G11 Germicidal UVC 4-pin lamp and socket and 18W electronic ballast

(or 9W G23 Germicidal UVC 2-pin lamp and socket and 9W magnetic ballast)

Screws

1.5 sq mm mains cable

10A isolating switch and 3amp plug

Step 1: Making the Base

Base board: Use 18mm laminated plywood and cut it to 375mm x 300mm.

Cross pieces: Use 44mm x 18mm wood and hold across pipe and mark off length to cut to just fit across diameter allowing for curvature of pipe (approximately 98mm). Make two of these.

Cut a slot in both base pieces the same width as the wood so that they can be fitted together to make a cross.

Assembly: Mark the centerline of the base board and loosely place the components to ensure there will be space for the on/off switch. Mark drilling locations 25mm from the center and drill through with 3mm drill hole. Countersink these holes on the underside of the base.

Step 2: Preparing the Cross Pieces

Mark up cross piece length by holding against the pipe. Mark up width of slot using wood as template. Saw out. Confirm fit of cross piece in pipe. Make 2 crosspieces.

Step 3: Marking Up the Cross Pieces for Assembly

Put the cross pieces on the base board together with the switch and ensure the layout looks good. Identify which cross piece is the lower and mark centers for drilling at 25mm from center. Mark location of drilling at 25mm from center on 'upper cross piece. Decide which is the 'lower' cross piece and which is the 'upper' and drill 2mm holes 25mm from the centre. These holes will help locate the cross pieces when the screws come through the base.

Step 4: Preparing the Pipe

Mark up the 500mm x 100mm wastepipe for attachment to base crosspieces and ventilation holes. Make a drilling template with 5mm spaced lines using a right angle and pencil. The drill locations will be at every other mm intersection. The ventilion grill is repeated at 4 locations between the cross pieces of the base. Drill To find the diameters at 90 degrees to each other, use masking tape. Mark drill locations with a sharp point. Drill pilot 2 mm holes. Re-drill the fixing holes to 3mm and the ventilation holes to 5mm. Drill and jigsaw an additional hole large enough for the power cables. The holes must not be drilled too high up - they must not allow UVC light to shine out directly onto fingers placed near the unit.

Step 5: Prepare Light Baffle

Use the extractor fan as a guide to mark out two baffles 8mm wider than the inner radius of the pipe from 6mm thick MDF or plywood. Drill a 2mm diameter hole to locate the baffle at the correct height. Cut out and mount 30mm apart in the pipe to ensure that the lamp cannot be seen directly but air can flow freely. Secure each baffle with two more screws.

Step 6: Prepare Ballast and Lamp Backplate and Install Fan

Use lamp ballast as template and lamp socket . 2 pin Compact Fluorescent Tubes require a magnetic ballast and 4 pin CFL lamps use an electronic ballast. Ensure that the ballast wattage and the tube wattage are compatible. Connect the wiring as shown on the ballast instruction/data sheet. Install tube. Install pipe and secure with screws. Install extractor fan. Complete wring from fan and lamp to switch and power cable with plug. Ensure baffles and pipe ventilation does not allow the lamp to be seen directly. Attach stickers with safety information and operating instructions:

"UVC light is germicidal and in the right intensity, right range and for the right time it will reduce the amount of Coronavirus in the air. However, it must be used in conjunction with other hygiene measures such as washing hands, safe separation distance, disinfectant wipes, use of masks etc.
The UVC lamp MUST NOT be viewed directly and must not be allowed to shine on the skin or it could do harm. It should only be switched on when the unit is completed and fully assembled and the lamp cannot be seen directly.

Disconnect from mains before disassembling of replacing the lamp"

Switch on and confirm operation. Position near in the middle of the room or on a table. Room air is drawn in at the top of the unit and cleaned air comes out through the ventilation holes at the base.