Well Pumps - Variable Speed?

Sprinklerman · Feb 15, 2015

TomSeller said:
Having a VFD on the pump alone is not going to allow the sprinklers to run and take a shower at the same time. The pump would have to be larger.

Dont know what a VFD is , but on the grundofos constant pressure systems , I have plenty of customers that love them .

One customer has a well , he has 4 rentals in addition to his house all on 1 well , he had booster pumps that were marginal at best , his sprinkler system was fair with 3 heads on a zone , With the constant pressure system he can shower while the irrigation is running and there is no drop in pressure .

TomSeller · Feb 15, 2015

Sprinklerman said:
Dont know what a VFD is , but on the grundofos constant pressure systems , I have plenty of customers that love them .

One customer has a well , he has 4 rentals in addition to his house all on 1 well , he had booster pumps that were marginal at best , his sprinkler system was fair with 3 heads on a zone , With the constant pressure system he can shower while the irrigation is running and there is no drop in pressure .

VFD = Variable Frequency Drive. It is what varies the electrical frequency to the pump. The Grunofos is a specialized VFD. To do what you describe, the pump would have to be increased in size to get more GPM. Unless of course the existing pump motor could take more than the 60 hz it would have been running at (doubtful).

What I am saying is that you can't just throw a Grunofos controller on an old pump and get more GPM out of it. The pump has to be rated for a VFD and it has to have the capacity in GPM to put out enough water to irrigate and shower at the same time. A larger pump running with the traditional tank and pressure switch would do the same thing, except the pressure would go up and down a little as the pump cycled.

Sprinklerman · Feb 15, 2015

The ones I have worked around they changed everything , pump included . I recommend them to my customers all the time.

TomSeller · Feb 15, 2015

Sprinklerman said:
The ones I have worked around they changed everything , pump included .

Makes sense. They would have put in a larger GPM pump at that time. I agree that the constant pressure would be a nice thing to have, particularly as costs come down. Reminds me of the old time clothes washers that have levers underneath to switch speeds. Clunk, clunk, clank clank. The new front loaders have a variable sequence drive motor that soft starts and switches direction. More reliable so far.

TheGoose · Feb 15, 2015

A Vfd can make a small pump big and a big pump small. A normal pump runs at 60 hz. A pump equipped with a vfd can run as low as 30 hz or as high as 80 hz. You have to be careful when sizing them or you'll end up wasting money.

TomSeller · Feb 15, 2015

TheGoose said:
A Vfd can make a small pump big and a big pump small. A normal pump runs at 60 hz. A pump equipped with a vfd can run as low as 30 hz or as high as 80 hz. You have to be careful when sizing them or you'll end up wasting money.

Only if the pump is rated to run at 80hz. The 80hz would be factored into the rated GPM of the pump. New ones rated for VFD at 80hz would be fine.

Professor Marvel · Feb 15, 2015

TomSeller said:
Only if the pump is rated to run at 80hz. The 80hz would be factored into the rated GPM of the pump. New ones rated for VFD at 80hz would be fine.

what determines the HZ a motor can run at? I have run motors up to 120HZ in drive class (sounded like a dentists drill :laughing

. But I don't think that was intended for constant use and I always wonder what a particular motor can really run at. where do we find the rating.
Also we typically run pumps as low as 15 HZ in my industry. Slower than fans.

TomSeller · Feb 15, 2015

Professor Marvel said:
what determines the HZ a motor can run at? I have run motors up to 120HZ in drive class (sounded like a dentists drill :laughing. But I don't think that was intended for constant use and I always wonder what a particular motor can really run at. where do we find the rating.
Also we typically run pumps as low as 15 HZ in my industry. Slower than fans.

It would be a manufacture's listing relating to voltage, current, mechanics and frequency. Better be safe than sorry. As was posted, if you have the pump replaced at the same time, you should be golden.

buickanddeere · Feb 15, 2015

TomSeller said:
Only if the pump is rated to run at 80hz. The 80hz would be factored into the rated GPM of the pump. New ones rated for VFD at 80hz would be fine.

As long as full load rated amperage is not exceeded. The 60Hz pump can have the hz and rpms dialed up until limited by current or the desired gpm is reached. The typical pump motor is not operating anywhere near it's rated capacity. Going 50% over on frequency and voltage together is not a problem for any typical motor up to 200 or so HP.

TomSeller · Feb 15, 2015

buickanddeere said:
As long as full load rated amperage is not exceeded. The 60Hz pump can have the hz and rpms dialed up until limited by current of the gpm is reached. The typical pump motor is not operating anywhere near it's rated capacity. Going 50% over on frequency and voltage together is not a problem for any typical motor up to 200 or so HP.

Then it would be rated as such.