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PRESS
09-12-2007, 09:51 PM
Gentlemen

Here is another one which i have been wondering about for quite sometime. I have to upgrade a wing of an office building and install variable air volume diffusers to achieve my goal. This dictates that i should vary the air volume from the air handing unit as well. My problem is i should use the existing AHU and it has 3 single phase supply air fans. I have never seen a single phase inveter. Can someone tell me a brillliant idea to use.
Brian_UK
09-12-2007, 11:49 PM
Do you have a three phase supply available in the building that you could use ?
nike123
10-12-2007, 12:06 AM
You could connect these three fans in star as one three phase fan motor and regulate speed with one three phase inverter.
PRESS
10-12-2007, 05:54 AM
Do you have a three phase supply available in the building that you could use ?


Brian uk

yes the existing unit is supplied with 3 phase power which they distributed each phase among the 3 fans.
PRESS
10-12-2007, 06:06 AM
You could connect these three fans in star as one three phase fan motor and regulate speed with one three phase inverter if you have three phase supply.

I understand and agree with you in principle, but i have my fears. does this really work practically. i have never seen or tried it. have you done this before or seen such an installation.
PRESS
10-12-2007, 06:11 AM
You could connect these three fans in star as one three phase fan motor and regulate speed with one three phase inverter if you have three phase supply.

I understand and agree with you in principle but i have my fears. Have you done this before or seen such an installation. does it really work practically. please let me know.
nike123
10-12-2007, 08:39 AM
I didn't done that before but I don't see to many reasons why this should not be working satisfactory in practice if you carefully set min. and max. sped. It is similar to conventional PWM by thyristor or triac in conventional fan speed regulators

This could be of some value to you:
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TRASH101
10-12-2007, 10:17 AM
alternatively you could use a motorised damper in conjunction with a static pressure sensor to meter the air. Although this would involve some clever control.

You could also use a single phase stepped speed control (transformer type) or a three phase version but you would have to introduce protection on the transformer output side on each.

Phase chopper speed controllers are available for single phase applications but they are generaly only suitable for low load/ torque.

all that aside I would rip out the three fans and put a 3 phase fan in:D

good luck
TRASH101
10-12-2007, 10:23 AM
Nikes idea will work but....
an invertor will probabley pickle itself as you have a greater scope for phase balance faults as the 3 fans will inevitabley load up differently (especially when speed changes occur). My advice is dont do it unless you have time and money to spare:eek:
nike123
10-12-2007, 12:22 PM
Phase chopper speed controllers are available for single phase applications but they are generaly only suitable for low load/ torque.


This is exactly what the fan motors is, low torque and load is rising proportionally with speed.
If it is compressor, than I should be worried!
But as you said "advice is dont do it unless you have time and money to spare"
PRESS
10-12-2007, 07:23 PM
Thank you guys for all the insights that you are giving me. This forum is such a good idea.