Pump sizing for SWCG?

[Sammy2]

Any thoughts on buying a "Used - Like New" pump from Amazon Warehouse Deals? I've bought quite a bit of electronics from them this way and have never had an issue at all with them. Some of them even look to be new and just re-labeled as such or as "Refurbished" so that the manufacturer can get some sort of a tax break by selling them this way.

 

[pooldv]

Side bar: I bet the original pool contractor didn't do a very good job of estimating pump size requirements in the first place and just threw in a bigger than necessary pump without consideration of the end user's continuous cost.

As far as energy use (cost) goes, when choosing between running the pump longer or turning up the SWG percentage to make the necessary FC in my pool I intuitively come to the conclusion that turning up the percentage is cheaper. Is this an accurate assumption? Does doing this have other costs such as "wearing out" the catalyst in the cell quicker?

100% right on the throw in a bigger pump theory.

Also right that increasing percentage output is cheaper than increasing run time. SWG cells wear out based on "on" time generating chlorine. It will be "on" the same amount of time either way. So, no impact to cell life either way.

 

[JamesW]

If you're interested in the engineering data for your system, you can get a vacuum gauge and use it in conjunction with your pressure gauge to see what your system head loss is at different flow rates.

Graph the points and you will get a curve that looks like the cell curve above. This is your system curve.

Then you overlay the pump curves for the pump at different speeds. Then you can see what your flow rate will be at different speeds.

The pump curves start high and curve down whereas the system curve will start low and curve up. The operating point is where the lines intersect.

 

[Sammy2]

If you're interested in the engineering data for your system, you can get a vacuum gauge and use it in conjunction with your pressure gauge to see what your system head loss is at different flow rates.

Graph the points and you will get a curve that looks like the cell curve above. This is your system curve.

Then you overlay the pump curves for the pump at different speeds. Then you can see what your flow rate will be at different speeds.

The pump curves start high and curve down whereas the system curve will start low and curve up. The operating point is where the lines intersect.

How to change the flow rate right now with a single speed 3450RPM pump?

 

[JamesW]

I'm assuming that you're going to get the variable speed pump. That's when you do it.

You can get a rough idea by measuring your current flow rate and head loss and assuming that the head loss is (flow1/flow2)^2.

 

[Sammy2]

I see. I'm in process of determining the expected flow rate for my pool based on the TDH. To do that, I need to calculate the TDH.

OR.. Am I over-analyzing this and should just spring for the VS Pump? As in my first post, I can just replace the motor and seal for far less outlay of capital but if having a properly sized VS Pump for my pool will do what I need and pay for itself in a year or two I'll go that route. If I do go that route, do I really need 3HP or can the 1¹/₂ HP motor suite my needs.

 

[JamesW]

You can get a rough idea by measuring your current flow rate and head loss and assuming that the head loss 2 =(head loss 1)(flow1/flow2)^2. The cell graph follows this basic rule.

Current head loss is determined by vacuum pressure converted to feet of head + return pressure converted to feet of head. Flow rate can come from a flow meter or from using the existing pump curve to determine flow rate based on feet of head.

 

[xyz]

As far as energy use (cost) goes, when choosing between running the pump longer or turning up the SWG percentage to make the necessary FC in my pool I intuitively come to the conclusion that turning up the percentage is cheaper. Is this an accurate assumption? Does doing this have other costs such as "wearing out" the catalyst in the cell quicker?

This is only true if you consider the standby energy to run the SWG. If you take into consideration the cost of running the pump, the lowest energy cost will be the lowest pump RPM that still has everything working well.

Energy use for your pump changes non linearly with RPM. And pump energy will dominate your electric costs. At some point, running at too low RPMs will not give you good enough skimming, may not trip your flow meter on your SWG, and could get into an inefficient RPM range. With my VS pump, I think it starts to lose efficiency below 1000 RPM.

So I'd suggest you figure out how slowly you can run your pump and still get good skimming, etc. Then set your SWG at the percentage that is going to get you the FC you need.

For example, If your SWG makes 2lb/day, and you figure out you want to run your pump at 1200 RPM, and that you want to run it for 12 hours/day [based on the 1200RPM], that means @100%, you would get 1lb per day.

In reality, you don't need to do this calculation because FC use is variable; so you start with an educated guess, and then up it if FC is dropping, and lower it if FC is raising.

So lower your pump RPM, run it longer within reason, and the SWG will not wear out any more quickly.

 

[mas985]

I see. I'm in process of determining the expected flow rate for my pool based on the TDH. To do that, I need to calculate the TDH.

You really don't need to calculate TDH or flow rate. It really doesn't matter that much.


But if you insist, you can use one the spreadsheets in my sig and you don't need a vacuum gauge or any other extra equipment. You just need a working filter gauge.

I do go that route, do I really need 3HP or can the 1 1/2 HP motor suite my needs.

The 2.7 THP Inyo motor is fine. You don't need an Intelliflo. However, if you have a Pentair controller, you may want a Pentair VS so you can program the speeds through the controller.

 

[Sammy2]

Learning, learning more.

So using simplified pump affinity laws I find the following simplified relationships.

Flow is directly proportional to pump RPM so my flow would be approximately 1/3 of what it is now. Will that be noticeable in the sheer descents and cascading waterfall from the spa into the pool? I think it might. I can add to my z-wave relay to turn the pump up to full RPM when I select the "Party Mode" which turns on everything including the descents (and lights, including patio bistro lights at night) but during normal runs for filtration and salt generation I will have a very slow cascading waterfall, right?

What about my pressure side automatic pool vacuum? Will that even work at all? Of course my pool guy is concerned about this. I recently installed security cameras on my house because, even though we're in a nice neighborhood, there's been an increase in crime (or just that we see it more on the neighborhood Facebook page, maybe it was always there?). With these cameras I see that he's in and out in 15 minutes which is only enough time to clean the steps where the vacuum doesn't get, check the chemical balance, do a quick skim with the rake and add a little CYA.. Maybe his biggest concern is that he's going to have to earn his money now and actually do more to clean the pool?

By simplified, I am assuming that the impeller diameter and efficiency is held constant and it falls out of the equations and the power demand relationship become is P₁/P₂ = (RPM₁/RPM₂)³. Solving for P₂ we find that P₂ = P₁ / (RPM₁/RPM₂)³ or in the case of running at 1200RPM vs 3450RPM this yields P₂ = .042P1. With P₁ = 11amps x 230volts = 2.5KW for my current pump this results in P₂ = 103 Watts for a new VS Pump, which is about what you guys have been saying all along.

The corresponding change in Head is H₂ = H₁ / (RPM₁/RPM₂)² or H₂ = 0.121H1. This is quite a drop It would seem. Am I missing something here? Which is more important? Pressure or Flow Rate? It would seem that at ~¹/₈ of the previous pressure that losses in fittings would be more amplified.

This is if I don't change the pump impeller diameter or efficiency. Do these VS pumps have more efficient impellers of a different diameter too?

 

[mas985]

The wet end of a VS pump is exactly the same as any other pump. In fact, the Intelliflo uses the same wet end as the WFE-12 Whisperflo.

The pumping efficiency does not change much with RPM. However, the motor and drive efficiency do change. This is why the affinity laws do not pertain to the motors only to the pumps. So the power equation relates to the impeller drive power (more specifically to the power delivered to the water) and not the motor input power.

Does your pressure side cleaner have a booster pump?

 

[Sammy2]

You really don't need to calculate TDH or flow rate. It really doesn't matter that much.


But if you insist, you can use one the spreadsheets in my sig and you don't need a vacuum gauge or any other extra equipment. You just need a working filter gauge.


The 2.7 THP Inyo motor is fine. You don't need an Intelliflo. However, if you have a Pentair controller, you may want a Pentair VS so you can program the speeds through the controller.

I will check out the spreadsheets for sure!

As far as the motor goes, I do not have a Pentair controller. I have a pretty old Jandy / Zodiac Model 8156 Type RS-8 Combo circa 2003 but I control it with my phone with a plug in for my Vera Home Automation System and an Autelis control module as discussed in the last paragraph of my OP and using the low voltage relay discussed here. I'm not sure if the motor recommended by Inyo Pools has that capability or not. Using this will allow me to control the pump speed on my phone, or even just automatically, based on the situation. I can have it run at low speed for basic filtration and then higher speeds for "show" when entertaining, which is quite often actually. We bought a house with a pool to enjoy it and have our friends and family enjoy it too!

- - - Updated - - -

The wet end of a VS pump is exactly the same as any other pump. In fact, the Intelliflo uses the same wet end as the WFE-12 Whisperflo.

The pumping efficiency does not change much with RPM. However, the motor and drive efficiency do change. This is why the affinity laws do not pertain to the motors only to the pumps. So the power equation relates to the impeller drive power (more specifically to the power delivered to the water) and not the motor input power.

Does your pressure side cleaner have a booster pump?

Okay. The power delivered to the shaft is what is put out by the motor so there's that relationship but what you are saying here is confirming my assumption to take the impeller diameter out of the equation though. Thanks for the confirmation!

I clicked on the spreadsheet page in your signature but it is a forum post. I was hoping to get an excel spreadsheet to manipulate so I can check my system design. For me I'm always wanting to work the solution. Did I miss something in the thread? Is there a link in there? TIA

 

[mas985]

Impeller diameter is similar to RPM in the affinity equations. Smaller impellers drop the head curve which is what lower RPM does. However, the efficiency of the pump is determined somewhat by the impeller size unlike RPM. Larger impellers tend to have better pumping efficiency but it depends on the design.

The links to the spreadsheet are within the post. Look for a blue Excel

 

[Sammy2]

Thanks. I'll go look now. I was re-reading posts from last August when I was helping a coder get the Autelis to work within Vera for home automation. It is still in "beta" but it just works. I'm going to look into seeing if he'll help me incorporate a VS Pump with relay switches (that Pentair model, I'm thinking the 1 ¹/₂ HP one will do what I need but need to confirm of course).

 

[Sammy2]

Any thoughts on buying a "Used - Like New" pump from Amazon Warehouse Deals? I've bought quite a bit of electronics from them this way and have never had an issue at all with them. Some of them even look to be new and just re-labeled as such or as "Refurbished" so that the manufacturer can get some sort of a tax break by selling them this way.

What do you think? Potential of saving $100 or so.

 

[mas985]

Open box or refurbished are fine as long as the warranty is the same. Also, make sure you don't lose the power company rebate. Otherwise, not such a good deal.

 

[Sammy2]

Open box or refurbished are fine as long as the warranty is the same. Also, make sure you don't lose the power company rebate. Otherwise, not such a good deal.

That's a good point. I will factor that into my costs.

 

[Sammy2]

I'm going to post some pics and draw a sketch later but I finally ventured out in the dark this morning and triggered various devices with my Autelis Pool Control App.

This is what I found:

All supply and return lines are 2" or 2 ¹/₂". I didn't bring a tape out with me in the dark but the external diameter is slightly less than the width of a Galaxy S7 which is 2.74" plus the case so about 2.85". The distance from the equipment to the skimmer and closest edge of the pool is in the neighborhood of 30 feet and there's at lease one elbow. The deep end is nearest the equipment, is 7 feet deep and there's two drains down there. The return lines are scattered around the pool which is a rectangle about 18' W along the skimmer side and 30' L. The spa is pretty decent size and centered in the pool with a cascading water fall from it into the pool. It is about 7 feet wide along the long side of the pool and 5 feet in the other direction with the feet area maybe 4 feet down and an basic seat. The length of the waterfall spill is about 5 feet.

There's three pumps as follows:

Main Pump runs skimmer, floor drains and pressure side cleaner. It also runs the spa which when activated two Jandy Valves redirect the water, shutting off flow in the pool and putting it all into the spa, including the return. The waterfall stops functioning when the spa is on. It seems that one of these valves is to redirect supply and the other is for return. This pump is the one screaming for help.

Second pump looks to be isolated from the filter and probably gets it's pick up (supply) from the main supply line somewhere under the deck. This pump only runs for the sheer descents.

Third pump is only active as a booster pump in the spa. Typically, the spa runs with about 6 jets when on but the booster pump increases flow to these jets and activates 4 more jets.

Since the sheer descents and spa booster are on their own pump I am not going to be concerned with them and they can stay as 3450 RPM single speed for now.

The main pump will be replaced with a VS Pump and I'm thinking that 1 ¹/2 Hp should suffice but need some input here on sizing to make sure.

I'm going to go with the Pentair pump with the auxiliary cable for speed control with 4 relays. Most likely these will be Z-Wave relays but I think there's still room for a couple more relay controls on my Jandy iAqualink which I need to verify.

Again, thanks for all your prior assistance in figuring this out and TIA for further help in pump selection.

 

[mas985]

Typically, the spa runs with about 6 jets when on but the booster pump increases flow to these jets and activates 4 more jets.

This is a bit confusing. It sounds like the main pump is running 6 spa jets. Is that correct? But can you run the booster alone and does it run all 10 jets sufficiently?

If not, you want to make sure that whatever pump you choose has a head curve that is at least as high as the one you have now. Do not size a pump by HP alone. Not all 1 1/2 HP pumps are the same or have the same head curve. If you choose one with a lower head curve, those 6 jets will become weaker. If you go with the VS motor attached to your current pump's wet end, then no problem. If you go with the Intelliflo, no problem. But if you go with the SuperFlo, could be a problem. That will not be as strong as your current pump.

 

[Sammy2]

This is a bit confusing. It sounds like the main pump is running 6 spa jets. Is that correct? But can you run the booster alone and does it run all 10 jets sufficiently?

If not, you want to make sure that whatever pump you choose has a head curve that is at least as high as the one you have now. Do not size a pump by HP alone. Not all 1 1/2 HP pumps are the same or have the same head curve. If you choose one with a lower head curve, those 6 jets will become weaker. If you go with the VS motor attached to your current pump's wet end, then no problem. If you go with the Intelliflo, no problem. But if you go with the SuperFlo, could be a problem. That will not be as strong as your current pump.

IIR, the booster pump does increase the flow on those 6 jets and it kicks in 4 more jets. It's been a while since enjoying the spa but I do know the 6 primary jets are on either way and act as supply when the pool is just in normal mode but I'll need to verify this. I wanted to order a pump today! If I assume that the booster doesn't connect to the 6 jets at all then I need to be more careful in what I select if I'm reading you correctly.

I was considering getting this pump which by the picture includes the wet end and is the SuperFlo. So I have two choices here, I get a VS Pump Motor sans wet end and replace just the motor and seals using the existing wet end which can be either the Intelliflo or SuperFlo or I get an IntelliFlo complete.. Or is it such that the motors are the same (for each motor Hp but the differences lie in the wet end impeller size and efficiency). Do all the Pentairs work with the add-on cable and relays or only some of them?

BTW, I did play with the spreadsheets a bit last night but need to probably spend a little bit more time with them.