Variable vs constant well pump
lookloan
| Posted in General Questions on
New 500 foot deep well put in and well person wants me to put in a variable speed pump vs a constant pressure pump. The pressure tank is only 32 gallons and says I don’t need a larger tank Aparently this variable speed pump has a box that goes in the basement that if it breaks is $1700 to replace. For some because they buy in buck so it doesn’t cost anywhere near that for when they install. Has anyone experienced a well pump decision in recent years.
House is 2100 SF – single story. Pump is 90 feet from house.
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Why are they recommending the variable speed pump (counterintuitively called a constant pressure pump) and that specific capacity for your pressure tank? How many GPM can your well generate? What's your rate of water consumption? Do you have a whole-house water softener? Did you solicit recommended water solutions from other well companies? If so, did they differ from what you've described above?
The following may be helpful for context:
https://www.poolesplumbing.com/pooles-special-offers/selecting-a-well-pump/
https://www.freshwatersystems.com/blogs/blog/how-to-size-a-well-pressure-tank
The variable speed systems are nice since they keep the water pressure pretty much constant regardless of use (within reason). “Regular” pumps will cycle over a larger pressure range, such as “on at 30PSI, off at 50PSI”. I run a 40/60 pressure switch on my own well for a bit higher average pressure, which helps the RO system to run more efficiently and is nicer for things like showers too. Variable speed systems can use smaller pressure tanks since the cycle time isn’t as much of an issue with them.
Personally, I would go with a conventional system and a larger pressure tank (I have an 86 gallon tank). It’s a simpler and cheaper system, and you have more water reserve in case of a power outage.
Don’t worry about energy use. A well pump of either type is not a big contributor to a home’s overall energy use, well pumps simply don’t run often enough to use much energy.
Bill
Are you sure its a choice between a variable speed pump and a constant pressure pump? Those terms describe the same type of pump, the speed of the motor is varied to deliver constant pressure during water usage regardless of the flow rate. The other common set up is a traditional pressure tank/pressure switch set up where the pump will kick on when pressure falls below the cut in pressure and then run until it hits the cut off pressure. During prolonged water use you may notice the rise and fall of the pressure and the pump may cycle several times. Frequent pump cycling is not great for the life expectancy of pumps. Especially newer ones which seem to be value engineered more than they used to.
Have you done a pump test to determine the draw down rate and recharge rate of the well? That's usually a good first step to take. Then size the pump based on number of fixtures, water usage, head required and distance. Don't forget to factor in irrigation.
If you go with a VFD then you wont need a larger pressure tank so the well person is correct, although 32 gal still seems on the large side.
I would strongly suggest looking in to a cycle stop valve. Best of both worlds, mechanical constant pressure device that allows for a much smaller pressure tank to be installed. No electronics to go wrong, lower price point and same outcome. The owner is also very helpful and will answer questions.
https://cyclestopvalves.com/
Get as big a tank as is practical. My tank will run the house without power for the better part of 24 hours. Knowing there is no power, no laundry etc, but toilets flush and hand washing, cooking.
Does sound expensive. 500 foot deep? Think I would put my money at the bottom of the well
As a well pump installer, I install VFD's all the time. There are a few compelling reasons for doing so. The big one is cost! Yes, the drives are about a grand, BUT: The larger tanks needed for a conventional system are not cheap. They can cost close to a thousand bucks up here. Add to that, the need for a dry well protection device on low-flow wells (basically any bedrock well), and a single-phase pump control box. Furthermore, VFD's operate three phase motors (even with single phase input power) , which means that your wire is smaller, and the savings on wire alone can often offset the cost of the drive, particularly on a deep well setting or one that is a long distance from the house.
As a pump installer, 80% of my service calls are for problems originating from the need for replacing pressure switches, control boxes or flooded pressure tanks. All the byproducts of old mechanical technology.
VFD's incorporate dry well protection, diagnostics for well, pump and motor issues, as well as being convenient and easy for adjusting pressure. The constant pressure is a nice feature, and some even argue they save money. In the long term they do: VFD's incorporate a "soft start" for the motor, which means that you are not restricted by the number of times your pump can be started in a day. Capacitor-driven starts are limited per day, meaning with a VFD, motors will last longer.
I am such a huge proponent of them, that it was a no brainer when it came to what I would use in my own house. At the risk of jinxing myself, I can tell you I have never had to replace a faulty VFD in the decade I have been installing them. I have laundry tubs full of old pressure switches.
Thanks for the report of your experience. It's great to hear they work well in the field.
Which brands/models have you had good experience with?
I'd be somewhat concerned about the increased risk of lightning induced surge damage.
>"I'd be somewhat concerned about the increased risk of lightning induced surge damage."
I would be too, VFDs are far more sensitive to power transients than a simple mechanical pressure switch is.
I wouldn't let this concern be a "don't use a VFD" issue though. I've installed lots (and lots) of VFDs commerically because they are HUGE money savers in many applications, make mechanical stuff last longer in addition to energy savings, and make everything capable of variable speed. We don't see lots of failures, VFDs are reliable devices.
I would recommend a whole-house type TVSS (surge protector) installed on the panel in the home to protect against transients from the utility, and if the well pump is a long way from the house, I'd install smaller protectors on both ends of the wiring to the well, or put the wiring in metal conduit along the entire length of the run (which has other advantages when using a VFD). The metal conduit will help to limit transients on the pump wiring from thinks like nearby lightning strikes.
Bill
hi well-guy,
facing this choice myself for a new build. one well guy i spoke to is a proponent of the vfd, another guy says they have been causing him trouble.
in my particular case, the well would be like 200' from the house (don't know how deep yet).
are you still a pro vfd at this point, and if so, any particular manufacturers you would recommend?
do the pump and the controlling-equipment come from the same company or are they usually different manufacturers?
any guidance appreciated!
i built a new 11,000 sq ft home in 2004 and well guys told me to go with a variable speed pump. i think it was 3hp. it wasnt cheap, but back then i didnt care about the $. all i wanted was reliable pressure for big house, sprinkler system, and entertaining. i also asked the contractor to oversize the water line from the well to the house. they told me 1 1/4" was standard residential so i said go 2". they laughed and said thats crazy over done, but it only cost me a few extra $100s.
anyway, the system has been running great. the pressure tank is a pumpkin size. i watch the pressure gauge in the basement when i winterize and check the system. the pump spins up or down and keeps the pressure generally within 5psi with any usage, and its set to shut off at about 70psi, and i never notice the pressure change using water. i told the contractor that i wanted to be able to wash clothes, shower, fill the tub, water the lawn and garden at the same time without loosing pressure--mission accomplished.
the more taps i open, the pumps just keeps spinning faster and water keeps coming. i have not yet been able to max out the system and detect falling pressures.
the only problem we had was the master computer box (controller) in the basement went bad at some point (accusations was power surge) and the pump ran without shut down at 70psi. the pressure built and blew out a domestic connection resulting in flooding. since then the control box has been fixed twice. and there is a manual pressure relief valve stamped '100psi' thats on the main line in the basement. theoretically, should the pump ever create pressure exceeding 100psi, the value opens and water in shunted into our sump.
love the water pressure and reliability!