Well Pumps - Variable Speed?

[Sprinklerman]

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]

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]

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

 

[TomSeller]

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]

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]

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]

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]

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]

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]

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.

 

[avillahdw]

TheGoose With your experience then I have a question or series of them. Due to code I have to put a fire suppression system in the new house we are going to build. Option A I can put a large pump set deeper and get the flow I need. or Option B I can put a smaller pump say 5-10 gpm set more shallow (dynamic level at 10 gpm is a little bit higher than at 50 gpm) and put in a 2000-3000 gal tank with another pump which is high gpm to supply the system. Option A the well pump is more expensive with more copper in the hole (set deeper) but less complex as only one pump and no storage tanks. Option B has a cheaper well pump but the extra tanks and extra high flow pump are not cheap. Either way would have a pressure tank for the system. Money aside which do you think is better in the case as I describe it? Tradeoffs for certain but what is your opinion as a long time pump installer. I have had installers give me absolutely positive answers both ways. They each think there is only one way, their way, each one being the opposite of the other. By the way the well can support either option. Required flow is 50 gpm.

In response to this, take in consideration that normally one of the first things done in fighting a fire is to disconnect the power. Thus a separate meter would truly be the only way to provide for the fire suppression system.

 

[techman]

The hz limitation of a motor is usually limited by the voltage. To run a motor faster requires a higher voltage than nominal, due to the inductance of the motor. So as the hz goes up, so does the voltage required to push the current (called V/HZ in VFDs). At some level you will reach the insulation limit of the windings and the breakdown will occur. Other factors such as iron losses also increase with frequency, but usually just lower the efficiency. Industrial motors rated for VFD operation usually have 150% to 200% insulation ratings above the nominal nameplate voltage.

paul

 

[TheGoose]

Normally when using a true VFD pump/motor matched system you use a bigger motor and a smaller pump. For example, you would use a 1.5 HP motor with a .75 HP pump head. The motor will be a 3-phase motor even if you are using single phase power (the controller will convert it).

 

[TheGoose]

If you go with option A you still need a tank big enough to keep your pump from cycling. For a 50 GPM pump you need a tank with a drawdown of 50 gallons to keep the cycle time at one minute. That gets expensive. This is if you are not using a VFD of CSV to control the cycling.

I guess the main question is "How well do you want it to work when the SHTF?" Is there a back-up power source?

TheGoose

With your experience then I have a question or series of them.

Due to code I have to put a fire suppression system in the new house we are going to build.

Option A I can put a large pump set deeper and get the flow I need.
or
Option B I can put a smaller pump say 5-10 gpm set more shallow (dynamic level at 10 gpm is a little bit higher than at 50 gpm) and put in a 2000-3000 gal tank with another pump which is high gpm to supply the system.

Option A the well pump is more expensive with more copper in the hole (set deeper) but less complex as only one pump and no storage tanks.
Option B has a cheaper well pump but the extra tanks and extra high flow pump are not cheap.

Either way would have a pressure tank for the system.

Money aside which do you think is better in the case as I describe it?

Tradeoffs for certain but what is your opinion as a long time pump installer. I have had installers give me absolutely positive answers both ways.
They each think there is only one way, their way, each one being the opposite of the other.

By the way the well can support either option. Required flow is 50 gpm.

 

[buickanddeere]

Then it would be rated as such.

Sorry but I'm not certain what you mean .

 

[Silvic]

If you go with option A you still need a tank big enough to keep your pump from cycling. For a 50 GPM pump you need a tank with a drawdown of 50 gallons to keep the cycle time under one minute. That gets expensive. This is if you are not using a VFD of CSV to control the cycling.

I guess the main question is "How well do you want it to work when the SHTF?" Is there a back-up power source?

The code is quite specific in just about all areas except power which is laughable. When asked about backup power requirements the answer is none required. What a joke that is.
My plan/design has backup power and yes if I go option A it is a constant pressure design which bumps the cost of the well set pump but either way there is a constant pressure system involved so not cheap.

As to the response from the other poster on the FD first killing power, as you may or may not know the fire suppression systems are required so as to provide initial occupant escape time and to provide some fire suppression prior to the FD arrival. Once they are there, obviously they are there.

 

[TheGoose]

I would go with the option that has the least amount of equipment to maintain (one pump, one tank, etc). My advice is to skip the constant pressure stuff and go with the biggest tank you can afford. What horsepower pump are they proposing?

 

[Silvic]

That is kind of my thinking go with least equipment ie one pump no storage just pressure tank. The motor in the well now is a test pump and is 5 hp (3/phase) and the numbers say that if I go option A I will have a 5 hp motor. I can't remember the stages on the test pump in the hole. The constant pressure system we have been looking at is 11 stages, yes no typo.

Why would you go large pressure tank vs constant pressure?