Two fan or not two fan

[simonspark]

Hello everyone,
Could do with some advice. I've been working in a block of flats, 5 floors, 70's build. There is a central ducting system that takes out the waste air from each toilet and bathroom. On the roof is a housing with two fans. One is standby, the other is duty. These are swopped over every month by a switch.
Now all the residents complain that the fans are not working good enough to clear stale air. So, as an experiment, I have made both fans run at the same time. The air movement has now improved
My question is this. Am I overlooking something? Are two fans running together in the same housing going to conflict? And can anyone see if it's all going to go wrong?
Your ideas will be much appreciated
Thanks
Simon

 

[jeremy]

Has the circuit been designed to run both fans simultaneously? If the cables can handle it could more powerful fans be installed? I know next to nothing about HVAC but these are the questions I would ask.

 

[simonspark]

I think so! Mcb is 6 A, cabling 1.5. So thats ok. I did think of that, but considering these motors have to work so hard, the KW rating is pretty low

 

[Knobhead]

Are the fans mounted in line with each other or parallel? If in line you will loose airflow by one fan “wind milling” if in parallel they should have louvers fitted to stop fan 1 drawing air through fan 2. It’s a tricky one to get around.

Parallel operation is best if you’ve got louvers fitted.

View attachment 7336

 

[simonspark]

Wow! A drawing. Nice one. They are in parallel, but without the louvre or baffle or whatever its called. I wonder if I can install one. Good thinking
Simon

 

[Knobhead]

You need to fit a louvre to each fan.