Water Pump for Cold Plunge Filtration System

[GeorgeMfg]

Hi,

I'm designing a cold plunge filtration system and looking for some advice on pump types. The system design is as follows:

cold plunge -> hair filter / catcher -> pump at floor level -> water filter + venturi injector -> exhaust

The pump will be running 24/7 and my priority is to make the pump last as long as possible. I see lots of options on the market for DC brushless motor centrifugal pumps - most of which are rated for 1-2 years at constant use. I also see circulation pumps that claim to last longer, for 3-5 years. I also see pool pumps seem to last for 10-15 years.

What makes a pool pump last so much longer than the others? I know the manufacturer and quality of the pump will have some influence on lifespan, but what other factors should be considered when selecting a pump? For example, does it make a difference if it's AC or DC? What is the best pump type for this application?

I apologize if these are simple questions, still learning and appreciate your replies.

 

[LittleInch]

My guess is simply that the vendors don't rate it for 8,500 hours a year use (24*365)

If you can get a guarantee based on those hours a year then go for it, but the likelihood of them paying up or replacing one is low IMO

I'm assuming this is fairly low pressure / low flow "domestic" sized pump here? (No details provided)
Most are built to a price point, but look for what bearings and seals they use. Those are what wears out. your motor choice is not normally the issue s long as there is good cooling air available

I would just install two in parallel and either run them one week on one week off or just run one until it beaks then swap it out.

So ask around, especially people like pool maintenance companies, to see which has a good reputation then don't buy the cheapest.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

If you want it to last, don't overload it and minimize the number of starts. Keep the motor housing cool. Run it at BEP or just a bit less.

Homework:

https://www.pumpsandsystems.com/calculating-pump-starts-and-cycle-time

https://www.pumpsandsystems.com/13-common-factors-affect-pump-life

https://www.zoellerengineered.com/w...e/Continuous-Duty-vs-Continuous-Operation.pdf

https://www.waterworld.com/home/article/14070832/pump-system-longevity-and-extreme-operating-regimes

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EdStainless]

Lower specific speed pumps (and less efficient) tend to last a lot longer.
But the above advice is crucial, run at 90-95% or the DEP flow rate.
Your pump will love you.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[georgeverghese]

Looks like these cold plunge pools run on a combination of ozone and chlorine for disinfection, so choose a pump that is suitable for small amounts of hypochlorite. Ozone alone is much less corrosive to metallic components, but apparently doesnt provide satisfactory disinfection.

 

[GeorgeMfg]

Thank you for your replies. To expand a little more - the pump needs to have a flow rate of around 10,000 l/hr.

I think it's an interesting point that lower specific speed and less efficient pumps last longer. Right now I could use a 24VDC centrifugal brushless pump that consumes about 80w. The alternative is a 120v AC centrifugal pump that consumes about 250w at the same flow rate.

I am ok with the energy costs of a 250w pump, however I am concerned that the added power will dissipate too much heat into the water, which is meant to be cold. We will have one system fighting to cool the water, and one system doing the opposite. Does anyone know how much heat is lost through the water with these pumps, vs off the body? Is this a valid concern?

 

[1503-44]

I wouldn't worry about heat from such a small pump offhand, but ambient temperature, water temp, pipe material, length of pipe, insulation, pool volume, surface area, number of people, evaporation rate, inside/outside location, wind, pool covers can all have some effects to consider, if you are concerned about that.

Lower efficiency pumps do not have such tight tolerance, so not so much friction and mechanical wear to deal with. Its the slack tolerance that makes them less efficient.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Look at the pump curve or duty for those two pumps to see if they are comparable.

The ac pump might be more powerful than the DC one or is a lot less efficient. But the max heat input is about 90% of the electrical input assuming the motor is air cooled.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Just to note that the"rated flow" of these pumps is highly variable depending on your back pressure/ friction losses. So a low head 10m3/hr pump might only do 3m3/hr if your pipework is small and has high pressure losses like filters or valves or chillers.

You need to match the pump to the system losses.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

Brushed motors will never last nearly as long as non-brushed motors. I would never consider one for a pool pump, around chorine vapors and high humidity.

 

[GeorgeMfg]

Thank you for the additional info.

I have the option to not run the pump 24/7. Instead, I could run it for 4-8 hours per day. This would decrease total hours run by 75%, but introduce 365 start/stops per year. Which would you prioritize for pump longevity?

 

[1503-44]

Change the question.

Will I save enough money by not running the pumps 24/7 to buy a new pump every year or 2.
If you save more money by stop start operation such that you can buy a new pump before the warranty runs out on the old one, well yes, you definitely want to do that.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[1503-44]

Found some restart info in NEMA MG 10

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Artisi]

Contact Grundfos pumps - their product should be ideal for your applications.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)