Do I have the right pump (and filter)

Ufra

Member
May 27, 2018
6
Houston/TX
I was studying about pumps, to better understand options to save energy. 9 months ago, I bought the pool with the house and I'm looking to be more knowledged on the next season. From the information I found, the pump may be oversized respect to the filter, or the filter downsized respect to the pump and pool.

Average head space is 54 ft, with 1.5" pipes over two lines (drain and skimmer).
Looking at the manual of the pump (Pentair Challenger High Pressure 1.5HP), this results in a flow rate of 70 GPM.
My filter is a 24 sq ft DE one, I have no labels to identfy its max flow rate, but looking at the pentair FNSP24, which in my opinion shares the same grid set, this could be about 48 GPM.
It looks like the pump is oversized, also considering I have no water features to justify the High Pressure pump.

Would be worth to downsize the pump? If yes, should I better wait it dies?
Thanks for any help

Other observation, hoping may help understand the system: the pressure on a clean filter is 15 psi.
When I drained the water, thus just using the drain line, I calculated a flow of 2000 g per hour. When I normally run the pump and use only the single skimmer as intake, the pump evidently "cries" asking more water.
The water has always been clear (TFP method), running the pump 10 hours a day in summer (water temp around 92 F in Texas), and 4 hours in winter (water temp about 56 F).
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,477
Northern NJ
Your best option to be energy efficient and save money is a Variable Speed pump. A VS pump is effectively variable HP.

A VS pump can save you 80-90% running at 1200-1500 rpm compared to a single speed pump.
 

setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
3,511
Stuart/FL
Ufra,

Welcome aboard. Great questions you're asking! VS pumps almost always pay for themselves in very short order. I'm looking into this for my next upgrade after I covert to SWG. If you want to get an understanding of VS pump benefits read this article. In short, most of the benefit result from two aspects. The motor type used (permanent magnet Vs induction) and the ability to fine-tune to your exact speed you need instead of one or two speeds you have with typical induction type motors on the 1 and 2-speed pumps.. The less expensive pumps vary the motor speed by changing the number of poles in the motor. So once you buy it you only have two options for speeds. This can reduce the power consumption but only in a pretty crude way and the net savings are usually minimal. Variable speed pump motors are permanent magnet motors that are inherintly more efficient plus you can get the exact speed required by controling the frequency. Your exact performance characteristics are calculated using the Pump Affinity Laws. I'm no expert but in my early days as a plant engineer the experts at pump workshops used to say learn how to use the Affinity Laws or they will dominate you. I'm proof you don't need to be an electrical engineer to understand how to exploit the VS pump to optimize operating costs. There are many great practical articles on how to benefit and pump suppliers have added good information on their sites as well. All this said, you have to look at your specific situation as you're doing. For example, in my case I want to optimize use of my solar panels here in S Florida. This requires pumping to the roof and the lower speeds don't create sufficient head. This doesn't mean a VS pump won't work, since a small reduction in pump speed saves a LOT of energy but it does mean my payout period for the investment is less.

It's great to see you're really trying to understand your pool and there are plenty of true experts here that can help along the way.

I hope this is helpful.

Chris
 
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Ufra

Member
May 27, 2018
6
Houston/TX
Please explain how you got to 54' of head.

A very inexpensive fix would be to replace the impeller with a lower HP version.
I measured the geometrical distance of each inlet from the pump port in the three axis, assuming that who made the pool directed the pipes in directions perpendicular or parallel to the pool edges.
Even if they cut the corners, the difference would not be big.
54' is the average of the skimmer and drain head spaces.
 

setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
3,511
Stuart/FL
Ufra,

That's fine for estimating. When you do the final pump selection go to the website for specific equipment head loss. When you're estimating pump lengths that you can't see because they're underground it's common to add a design allowance of 10%.

I hope this helps.

Chris
 
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JamesW

TFP Expert
Mar 2, 2011
21,146
The easiest way to calculate the head loss is to use the pressure gauge. The psi x 2.31 gives you the feet of head on the return side.

You also have head loss on the suction side.

You can get a vacuum gauge if you really want to know, but it's usually not necessary.

I would recommend that a de filter be limited to about 1 gpm per square foot of filter surface area. 2 gpm per square foot of filter surface area is the maximum.

Unless you need a lot of flow for a specific reason, I typically recommend that you try to keep the flow rate as low as possible while still getting good skimmer action.

Note that the total dynamic head is dependent on the flow rate.

So, the head loss increases or decreases depending on if the flow increases or decreases.

Typically, it's a square factor. So, if you reduce the flow by 50 percent, you reduce the head loss by 4 times.

A variable speed pump is really a good choice. They are very quiet and they use about 1/5 the amount of power when you run them on low speed.

With a variable speed pump, you really don't need to know what the head loss is.

Just adjust the speed until you get good flow in the skimmer and from the returns.

Many variable speed pumps display the power usage in watts so that you can verify how much power you are using.

A 1.5 hp single speed pump will use about 1,500 watts but a variable speed pump will typically be closer to about 200 watts.

It's not uncommon for people to run a variable speed pump 24/7 for about $20 per month with good water quality.

Many utilities have rebates available. Example:

Austin Energy offers a $300 rebate per unit to customers who install qualified variable-speed pool pumps.
Pool Pumps
 
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setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
3,511
Stuart/FL
Good point James makes. Way more accurate than estimating pipe length if you already have the pool. Just make sure you don't have any valves in an unusual position when you take the pressure.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,778
Pleasanton, CA
Good to know.
I must have misunderstood my readings, as I thought that was the way to calculate it.
I'm just googling it and found the resource below
How Do I Calculate Feet of Head for My Pool? - INYOPools.com

Would be that ok or there's any other guide you recommend?
If you had read the comments, it is pretty clear the guy that wrote that has no clue what he is doing.

If interested, I have spreadsheet in my signature that can be used to estimate flow rates fairly accurately without the need of any extra hardware.
 

Ufra

Member
May 27, 2018
6
Houston/TX
Thanks all,
I-ll read the material you recommended and make a more accurate calculation.
Variable speed pumps look interesting too and will evaluate them.
Mark,
I saw your spreadsheet and I'm "studying" it :)