Things No One Asks About Variable Speed And 2 Speed Pumps

[Dranonymous]

So I have a really old 3/4HP Hayward single speed motor. I'm going to replace it with either a 2 speed or a VS. The current setup gets pretty hot and in the middle of the summer, its thermal cut out will trip. There's no doubt that a 2 speed or VS will save me money. Most discussions are always about how long to break even when buying either of the pumps, which isn't that interesting right now. I have some off beat questions that I'd really like help with.

- Is there any reason you can't run a VS pump 24 hours a day? The idea being to set the flow so that it takes that long to turn over the pool volume. Wouldn't this be the cheapest way to run the pump?

- Turning on a motor and most devices is the hardest time (roughly I think) due to current surge. Would running a VS 24 hours a day make it last longer?

- If I get either the 2 speed or VS pump, how do I know when to back flush my DE filter, since the pressure will be half or lower? Would I need to use it at full speed once a week, so I get the normal pressure readings compared to a clean filter?

- Is there a minimum flow rate or pressure I need to have for proper DE filtration?

I bet some folk thought this was just going to be another thread arguing over which pump is better!

 

[Isaac-1]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

I will only address the first part, there are various reasons why you might need to run a variable speed pump for limited hours at above minimum speed instead of continuously at minimum speed. First off many pieces of pool equipment require a certain minimum flow or minimum pressure to operate, this could be anything from an SWG or pool heater to a water feature or even simply having strong enough flow from your return jets for good water circulation currents.

On your second point while high inrush loads are a major wear factor on conventional single phase electric motors, variable speed motors work much more like 3 phase motors, and can (I am not saying do) have very gentle starting torque profiles.

I don't have a good answer for your last one, other than to say your baseline rise in pressure does not need to be based on full speed operation of the VS pump, it could be based on something like half or 3/4 speed, as the VS speed pump could be tuned to the optimal flow dynamics of the filter.

I have no idea if there is any baseline minimum flow for DE

Ike

 

[jhalpinjr]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

I agree with Isaac- while most pumps are rated for continuous use- even at low speed running 24 hours is probably a bit long. At some point use lose the battle between efficiency and cost. I'd be more concerned with bearings and brushes long before the small inrush to start the motor.

Finding the optimal speed is what you really need. One must not just be concerned with accessories like fountains etc...but also skimmer efficiency.

Your suggestion about using a higher speed to check your filter is one method.. As most of these pumps available have many timer options the occasional higher speed will help in that matter. As I have a sand filter, backwashing is not as big of a job for me.

 

[duraleigh]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

How big is your pool?

 

[JasonLion]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

You don't generally want to use the lowest available speed on a variable speed pump. Variable speed pumps have an ideal efficiency speed, which is nearly always faster than their slowest speed. For example an IntelliFlo moves more water per watt at 1000 RPM than it does at 600 RPM, so you save money by running it a little faster.

In theory running 24/7 will give you a longer lifetime. In practice the difference is so small that it really doesn't matter.

You always want to check the filter pressure for cleaning on the same speed, and it should be a medium speed, fast enough to get a reasonable pressure, but not too high that might stress the system.

There is a fairly high minimum flow rate to properly coat the grids, but once coated ideal filtration happens at a far lower speed. Most variable speed pumps startup at a faily high speed, to prime the pump, which is sufficient to coat the grids. After that you can run at whatever speed is good for other reasons.

 

[Dranonymous]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

My apologies for not posting my specs before.

- 23000 gallons
- Hayward 3/4hp with a 1.5sf
- 1 1/2 inch lines
- no water features, solar, etc
- zodiac g3 cleaner (kreepy crawly)
- my pool is older, so it has the small outlets which used to be used with the whips.
- 3 returns
- single floor drain which you put a plate in the skimmer to use
- Hayward DE6020 pool filter
- I have a valve connected to the water return line so I can shut off the small returns. I will put 2 PVC pipes in the normal returns to make small aerators to,raise my ph sometimes, so I use the valve to raise my pressure.

I didn't realize the pump would be most efficient at above minimum speed. That's a good thing to know.

Other thoughts?

 

[jkurl]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

I have a jandy VS pump and we run ours only 8hrs a day. The first hour is for cleaning w/ a Polaris 280 which has a booster pump. We run the vs pump at 3150 rpm. The other 7hrs are at 2200 w/ the pump and solar running. If we don't run solar the pump runs at 1800. If we run the waterfall it runs at 3150. Our electrical bill is not too high. I live in California so we can have high rates at times. I will see what our kw per hour is on our bill. I will try later to post if I can gotta go back to the hospital and see the wife and the new baby girl. You will get some great answers about 2 speed and vs ultimately it is your choice but it is a great choice to have versus only having one option.


Sent from my iPad using Tapatalk HD

 

[Dranonymous]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

You shouldn't be worrying about my pool, just that new baby girl you mentioned! My two 'baby girls' (8 and 11) were out enjoying the water this afternoon. Gotta love pool covers ability to get the water warm out here in Az pretty quickly.

Is there any danger of running a VS at the same speed as my single speed, if the VS is rated at a higher HP? The pressures should be approx the same right? Though maybe some higher for the VS if its got a better impeller?

 

[JasonLion]

Re: Things No One Asks About Variable Speed And 2 Speed Pump

Variable speed pump come in different sizes. Most of them are much larger than most single speed pumps and should never be run at full speed on a typical pool. But there are some smaller ones where full speed is quite appropriate in some situations and there are some pools that really need a larger pump and so might make use of full speed.