We have one centrally mounted fan which exhausts via a short pipe though the roof. The tin hat on the outside is visible from space!
The fan lives inside a plenum situated on the mezzanine over the metal shop. Ducts lead towards the centre of the wood shop and through the wall into the digital room. Three inlets are fitted with either closable bulkheads or butterfly valves.
The fume extraction for the laser cutters tees into the duct in the digital room.
The fan is remotely controllable from each room, with a button by the main exit to allow the fan to be turned off by the last person exiting. The remote controls at each location consist of a momentary switch and an indicator. Each of these assemblies is wired in parallel.
Power to the fan is controlled by a relay mounted in a box situated over the plenum.
Two DPDT relays are wired as a bistable with a toggle input. A pair of contacts on one of them is used to control current to the fan.
The relays are both standard 10A DPDT 125V coil and are mounted in rectangular bases with screw terminals.
Retractive switches and neon indicators are mounted in a modular grid mounting frame alongside the regular light switch in each room. The main door has an additional bright indicator with a legend to remind users to switch off the fan when leaving.
Each switch and indicator is connected to the relay box using three-core and earth cable, colour-coded as:
| colour | function |
|---|---|
| brown | switch & neon L |
| grey | switch return |
| black | neon N |
The indicator is a 3D printed cover which replaces the plastic trim ring of a 120mm LED puck light.
This is mounted on the back of the inside of the double door with screws and a short two core flex connects back to a junction behind the light switch. It is connected between the brown and black wires from the relay box and replaces the neon at this location.