Changing 50 cycle fan motor to 60 cycle

[ohbie1]

Power draw for a fan (or a pump) is related to [flow rate] x [pressure rise] for the fan. For fans under normal operation (i.e. not around 0 flow or around max unrestricted flow) small changes in flow through the fan do not cause much, if any, change to the pressure rise across the fan. For this reason, adding a restriction to the fan outlet (the adjustable damper on your Tarm) will lower the flow rate at an almost constant pressure rise and result in a lower power consumption.

Eric

Eric,
Thanks. That clarifies. Next question......The Innova is meant to run full throttle only, so there is no outlet or inlet damper. If I blocked some of the intake or cut down on primary or secondary air would that achieve the same result? I'm thinking yes?

 

[jdavi581]

I don’t understand what you mean about closing the fan inlet. Wouldn’t this action cause it to be more difficult for the fan to suck air, and therefore raise the amperage needed?

This is a common misunderstanding. It (be it a shop vac or whatever fan you are using) will speed up when you put your hand over the tube. We commonly think this is the motor working harder, but actually it is moving air in a circle, not actually moving it. The sound you hear is the motor RPMs increasing because its load has been reduced. I am not familiar with your boilers setup, but I would think you could hold a piece of cardboard over the intake of the fan to try it. Good Luck!

 

[dirttracker]

Sorry Frank, I thought your Tarm was like mine. I did not realize the Innovas don't have a damper in the duct on the fan outlet. My Solo Plus 40 does and I use this to control the airflow by throttling down the fan outlet. I suppose you could do the same by shutting down both the primary and secondary air or block the fan inlet. Does your Tarm have a problem with too much airflow? I suspect you may be fine without any modifications depending on the fan performance. If it's available, get a copy of the fan performance curves and try to gage the difference between 60Hz and 50Hz operation. The pressure vs. flow map should have 2 curves on it, one for 50Hz and one for 60Hz. If the 2 lines are close together, then no problems, the increase in flow should be small. Keep in mind, as the air flow increases through your Tarm, the pressure drop of the Tarm also increases. If you have a 20% increase in fan speed, you will not have a 20% increase in flow through the system as the system pressure drop will increase. The actual flow increase may be less than 10%, but it will be tough to quantify without making detailed measurements on your Tarm.



Eric