New well question

[Joevano]

Not really a garage question but there is so much knowledge here I thought I would throw this out.

I need a new well drilled at my house. The existing casing is cracked and well is pumping lots of sand. Besides the house, we do have an lawn irrigation system.

The pump and expansion tank I have are fine, but I'm kind of a "while your at it" kind of guy when it comes to repairs.

Is there any real advantage to a Grundfos constant pressure system? (add $1,675)

Alternately, same question for a Goulds variable speed controller on my existing pump? (add $1,441)

 

[Cyberbear]

In 1995 my well was drilled down 500 feet and they used PVC pipe casing, and I've never had any problems. I live on a mountain of granite, and except for the first 15 feet, all of my well casing is in solid rock and I pump about 30 GPM.

 

[ssdave]

I've designed many of these constant pressure systems; I was designing them for community water systems and trailer parks and using VFD's (variable frequency drive) and custom controllers before Grundfos put out the package systems. I also did two massive system designs for golf courses, where we used VFD constant pressure pumping plants to feed valve in head, individually controllable sprinkler systems, and used water features on the course for water storage. I really enjoyed designing these type of systems.

The advantage to them is that you can have storage in a much more compact space than pneumatic bladder tanks, if you need the storage. Your well pump also pumps against a constant pressure instead of a variable pressure, so you can design it to pump more efficiently.

The constant pressure systems, ideally are pumping from a non-pressurized tank, through a small (usually less than 3 gallons) pressure tank, to the house. The small pressure tank is to avoid water hammer as the pump starts and stops, and to allow for a small amount of leakage (like a dripping faucet) or someone getting a glass of water to drink without the pump coming on. The pump is a variable speed pump, that varies how much it pumps to keep the pressure at a set value. It shuts off entirely when no water is being used.

The downside to a constant pressure pump is that it is a bit more complex, and costs a bit more. You have two pumps to buy (well and constant pressure booster), and a tank. The tank costs a bit less than a pneumatic tank, though. The benefits are:
You get more even pressure, and greater capacity for water use without running out (you can size the holding tank as big as you want).
The well pump is working against a lower, more standard pressure so it generally lasts longer and is more efficient.
You can store more water for irrigation and peak use, if your well can't keep up with that peak use.

Addendum: Reading your question again, you asked about a vfd to control the downhole pump. I see very little benefit to those, it puts the complex and expensive pump down the hole, where it is harder and more expensive to maintain. The only advantage I see to constant pressure systems is if you use a non-pressure storage tank, with a level control that runs the well pump instead of a pressure switch. I see very little benefit to using a VFD pump down the well, except possibly if you had essentially unlimited well capacity, so you use it as your "storage" to meet peak capacity. In that case, you'd be trading off more costly maintenance against having above ground storage.

 

[brownbagg]

i dont think u have a problem, our wells are in pure sand, just clean the well. let it run constant for about six hours, pump the sand out

 

[Falcon67]

I would just say that we lived in the sticks for 4 years on a well - 180', 32~40 gallon pressure tank, 35 on / 50 off pressure switch. Never had any issues and after reading the discussion above I'd be on the side of "KISS", keeping the system as simple as possible. Easier to maintain and easier to troubleshoot. We currently have a well for irrigation only. It's about the same deal except with a smaller tank. The house is on city water and pressure in the house can vary more than the 35/50 on the well if one of the water towers is acting up.

 

[larry_g]

The constant pressure systems, ideally are pumping from a non-pressurized tank, through a small (usually less than 3 gallons) pressure tank, to the house. The small pressure tank is to avoid water hammer as the pump starts and stops, and to allow for a small amount of leakage (like a dripping faucet) or someone getting a glass of water to drink without the pump coming on. The pump is a variable speed pump, that varies how much it pumps to keep the pressure at a set value. It shuts off entirely when no water is being used.

The downside to a constant pressure pump is that it is a bit more complex, and costs a bit more. You have two pumps to buy (well and constant pressure booster), and a tank. The tank costs a bit less than a pneumatic tank, though. The benefits are:
You get more even pressure, and greater capacity for water use without running out (you can size the holding tank as big as you want).
The well pump is working against a lower, more standard pressure so it generally lasts longer and is more efficient.
You can store more water for irrigation and peak use, if your well can't keep up with that peak use.

Addendum: Reading your question again, you asked about a vfd to control the downhole pump. I see very little benefit to those, it puts the complex and expensive pump down the hole, where it is harder and more expensive to maintain. The only advantage I see to constant pressure systems is if you use a non-pressure storage tank, with a level control that runs the well pump instead of a pressure switch. I see very little benefit to using a VFD pump down the well, except possibly if you had essentially unlimited well capacity, so you use it as your "storage" to meet peak capacity. In that case, you'd be trading off more costly maintenance against having above ground storage.

I disagree with what I highlighted in red above. I've had a constant pressure pump down the well for years. There is no difference between it an a regular submersible pump. What is different is that the pump motor is 3 phase and controlled by a VFD. One large advantage I discovered is that with the soft start feature of the VFD I can run the well pump off my portable generator as it does not have the huge inrush current of a single phase motor operated on/off. I chose and sized my system to handle the watering of lawns and gardens on our property. With the old on/off system I would have to pay attention to how many sprinklers were running to prevent he pump from to much cycling. With the constant pressure system I know the max number of sprinklers I can run and anything less than that the variable speed of the pump will handle. It works for me, and I would do it again.


When SSDave talks about holding tanks its foreign to me. I have a well that tested over 85 gpm so no need for a holding tank. If your in an area with low gpm wells that could be pumped dry then maybe a holding tank is necessary.

lg
no neat sig line

 

[ssdave]

Larry G is correct, in his context. My context is I have always been dealing with limited capacity wells, and storage was needed. If no storage is needed, a vfd controlling a well pump is a good option, as it eliminates the pneumatic bladder tank storage above ground. Only a very small surge tank is required. In that case, your trade off a pneumatic tank for a VFD controller. Both are somewhat equivalent in cost and maintenance/replacement costs. The features of a constant pressure system are therefore a selling point.

One thing I didn't point out in my first post is that constant pressure systems are less efficient. For pumping the same amount of water, they generally will take about 10 to 20% more power than a fixed power pump. Not in all cases, but in general that is true.


Larry G's observation on the soft start current required by vfd's is spot on. I had an installation that I did on generator, we were able to halve the size of the generator by putting in a 2 pump vfd system instead of a 3 pump, fixed hp system. Since there was no commercial power, and we did all pumping off the generator, the fuel savings was immense by going with a smaller generator designed for the operating load, and not having to design the generator to supply the starting current of a fixed power motor. In that particular case, the increased efficiency of the generator offset the lower efficiency of the VFD control system and resulted in a net savings in energy costs.

 

[Richard Cranium]

If your casing is split, why not just case it again in PVC pipe. When they drilled my well they went down into hardpan then drove the steel down to form a seal and from there they cased it to the top with a pvc casing to keep the well from collapsing onto my pump. They make a pvc just for casing wells with I am told.

 

[ssdave]

Here's another scenario where VFD's really pay off:

If you have a well that has high static water level, but draws down quickly, your power costs go up the longer you pump the well. So, if you don't have storage, and rely on the well for the supply volume, your pumping costs can be high.

In cases such as these, I do drawdown/capacity tests, and graph out the time run/volume produced for the well. Then, I design a timer system that toggles the pump on and off, allowing the static water level to recover. I then pick a pump that operates more efficiently in the drawdown level that I designed the system to operate in. I discharge the pump to a storage tank, and pressurize the water with a constant pressure VFD system.

The reliability of the system goes up, and the power costs go down by a large factor.

I designed a system like this for a small municipality, that rotated production between 5 wells, with production from each well tailored to it's most efficient production range. The savings in pumping costs totaled nearly $400,000 per year. The system cost less than $500,000 and my fees were nder $100,000, so the payback was less than 2 years.

 

[chris142]

In 1995 my well was drilled down 500 feet and they used PVC pipe casing, and I've never had any problems. I live on a mountain of granite, and except for the first 15 feet, all of my well casing is in solid rock and I pump about 30 GPM.

Where are you? My well is only good for maybe 10 gpm