Two fan wiring

Hi guys,



At the moment I have FAN1 setup with a 4 minute timer. I wanted to increase Pa (air pressure) so have decided to throw in a FAN2 with no timer that will run in a serial configuration with FAN1.

I would only like FAN2 to run when the light is on. I would imagine putting L -> L and N -> N without a breaker would cause the fan to running continuously. Should I do FAN1 L -> ROSE S/L instead ?

Also, would I be able to run FAN2 off FAN1 and thereby cause it to run even when the fan is off for as long as FAN1's timer ?

Why not just put in a more powerful fan and if necessary increase the overrun? Would seem to be a much simpler option

Iggifer said:

Why not just put in a more powerful fan and if necessary increase the overrun? Would seem to be a much simpler option

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It sure would, except that I've spent quite a lot on ducting for 100mm (insulated/acoustic etc) and having to drill bigger holes and re-duct will be a pain in the backside.

Will two fans in series increase the flow?

Iggifer said get a more powerful fan; not one with bigger ducting and hole.

EFLImpudence said:

Will two fans in series increase the flow?

Iggifer said get a more powerful fan; not one with bigger ducting and hole.

Click to expand...

Yes, it will increase Pa thereby increasing performance. The MF100s are probably as fast as they go @100mm ducting, 245m3/hr. I should have gotten the MF150 with a pull of 500m3/hr but I was being an idiot and didn't do the math and dived in head first.

If you only want dan2 to run when the light is on the wiring couldn't be simpler.

N to n
L to switched live (the light)

If you have a three pole isolator wire fan 2 to that.

The other reason for ineffective fan ventilation is not having enough air INCOMING to the room.

If you have a 100mm dia duct, you'll need a space/hole that allows at least that much air in to the room. If you add another fan, then you'll need a hole twice the size. Or just take the door off its hinges.
Merry Christmas!!

National Ventilation recommends that fans be put in parallel to increase air volume, or in series to increase the pressure. Pressure for longer runs, volume for increased extract.

You could get a standalone timer module, and use that to feed both fans, link L and SL on the timed one to bypass the timer.

Timer modules are available from plenty of suppliers, think even S Fix do them.

The only way to get fan2 to follow fan1 is to take apart Fan 1 and get to the wire that the timer switches. For very cheap timers contained within the fan body there will be a two pole terminal block at one end of the printed circuit that feeds two black wire out to the fan motor, this is where you want to connect your second fan. its all very thin internal wiring so so you will need some thin wire which connects to a new terminal block into which you can fasten you .5mm cable.
Frank

Also…..if you have two fans then both will need to be fitted with backdraft flaps. Otherwise the stronger fan will suck air back through the weaker fan reducing the two-fan advantage.

I'm still thinking that Iggy's suggestion would be better…..

Iggifer said:

put in a more powerful fan and if necessary increase the overrun?

Click to expand...

Aren't the two fans planned to be in the same ducting - i.e. in-line?

Whilst still dubious that two fans in series will be of benefit, it will definitely be a hinderance if one is on and one is off - the off one being a restriction/blockage of the flow of the on one.

Taylortwocities said:

Also…..if you have two fans then both will need to be fitted with backdraft flaps. Otherwise the stronger fan will suck air back through the weaker fan reducing the two-fan advantage.

I'm still thinking that Iggy's suggestion would be better…..

Iggifer said:

put in a more powerful fan and if necessary increase the overrun?

Click to expand...

Click to expand...

Back draught shutters would be pointless if both fans are running, even if differing speeds. One would need to be completely stopped for them to be any use, surely?

ban-all-sheds said:

Pa?

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Pascals/static pressure.

In the main blade fans have a very limited pressure increase even with a blocked off input or output, the centrifugal fan as used in vacuum cleaners will give a far better pressure or part vacuum than blade fans. To get a better pressure differential step one is to seal any air holes like those under the door.

What I don't understand is why you want a pressure differential?

I have done this in medical manufacture with a positive pressure so air will always flow out of open doors so flies can't fly in. But it was a real pain when changing lamps they had to be stuck down.

I am trying to work out what a light has to do with fans running? I assume some UV light to kill bugs, but that does not make sense either as you would want it on when any fan is running.

Most people seem to think you are talking about a bathroom, however that also does not make sense as to remove moisture you want cold air (which will because it is cold have low moisture content in to some thing to warm up the air so it can absorb more moisture be directed around the room then once it has absorbed the moisture sent outside. The main method of doing this is to draw air into the house allow the central heating to warm the air then send it to bathroom with a grill in the bathroom door and finally send outside.

It really does not matter if you blow air into the house or suck it out, however it is better for circulating air to be warm, so blowing air in means you can direct the air to an air heater before it is circulated through the house so drafts are warm rather than cold.

The main point is you have to look at the house as a whole not just one room. In my house opening the bathroom window causes a thermosyphon to start, the radiators heat the air which rises up the stairs into the bathroom and out the open window being replaced with air from under the front door as with all thermosyphon systems once it has started it's very hard to stop. Closing the window means the upstairs pressure increases and air is forced out of the house through every crack in window or loft lid. Being open plan does not help.

Now in mothers house she has a hall with doors so air from front door goes past radiator and up the stair well and out of the bathroom window without causing a draft in the living rooms.

The main reason for a fan is when the bathroom is down stairs so there is no thermosyphon, the other is when one wants to conserve energy and the fans are connected to a heat exchanger or heat recovery unit. The other is to satisfy Part F building regulations or when more to do with removing odour than humidity. A well designed house should not need a fan. However try finding a humidity operated vent and one will be hard pressed. Opening a window is all that is required the problem is getting some one to close it after.

What I would like is a fan which switches on as the light is switched off for 15 minutes so removing humidity after one has finished in the bathroom not chilling one while actually using the bathroom. But that's being lazy window works well, she opens it and I close it as she has a shower every day but I just stay dirty!

I am sure you will now tell us what the fan is really for?