Pool pump "feet of head" quandry...

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Backglass

Backglass

0
Jun 4, 2007
139
Putnam County, NY
Hi all...first post. Great forum!

I just bought a house with an older in-ground pool. It was a foreclosure/eviction so the previous owner stripped the house of everything not tied down, including the pump and filter multi-port valve (he did leave the filter however, too heavy to move I guess).

Anyway, I am having a hard time figuring out the correct size pump to buy. I have had two pools in the past, but both were above ground with hardly any pipe. This one is quite different. As best I can figure the pump is 60-65 feet from the pool (pipe is buried). Of course the rule of thumb is "replace the pump with the same size" but I have no idea what that size was and no local pool places have records of selling/installing at this house. Also I have read that oversizing is often worse than undersizing so I am not sure what to do.

Here are the specs:

* Approx. 21,000 gallons.
* 15' X 30' with deep end (average depth 5.5')
* 60-65 feet of 1-1/2" PVC from pool to pump area (both directions).
* There is no rise from the pool to the pump...in fact if anything the pump might even be almost a foot below the pool.
* Hayward S244S 300lb Sand Filter (50psi Max)


I would like to add a heat pump in the future, so I am leaning toward the Hayward Super Pump 2610X15 which as far as I can tell is a 1.5HP up-rated pump (1.0/1.5).

Is this too big? Does the long 65 foot horizontal run add a lot of "head"?

Sorry about the rambling post...and thanks for any advice!
 
Backglass,

Welcome. You'll get a ton of good advice here....(Most of it not from me!! :lol: :lol: ) Mas985 is the guru of pool hydraulics and I'll bet he'll chime in here soon.

Meanwhile, your filter seems about right for a 21k pool. My experience tells me that a 3/4 hp pump will be fine for that pool and filter and piping. You are correct....better to be just a little under than to oversize your pump.....even tho that doesn't make much sense 'til you dig into it a little.
 
Backglass,

Doesn't sound like you need a high HP pump so pick the smallest you can. If you have a single line for suction and a single line for return then the largest I would go with is a 3/4 HP full rated or 1 HP uprated pump. 65' of 1.5" line can create a lot of head loss so it is best to keep the flow rates as low as possible.
 
Backglass said:
This pump rating business is insane...they should have a standard!
Click to expand...

They actually have several different standards, which is where much of the problem comes from. Check out the WikiPedia article on horse power. The original definition seems to have been 150% of what a pony could do, nothing to do with horses. And after that things just got worse.

When comparing motors you should look at the brake HP, which is the rated HP times the service factor. That is the power available to the pump. "Full rated", "up rated", and "max rated" are terms which give you hints about what the service factor is. I find it simpler to ignore them and always work with brake HP.
 
I'm no pool pump guy, but if my old hydraulics experience is any help, here goes:

Horizontal piping doesn't really affect head pressure.

Head pressure is the resultant of the height of a column of water - naturally, the higher the column, the greater the pressure at the bottom. Depth, or negative height, has the opposite effect. It requires a pressure reduction (suction) to move it.
The common factor is height, in other words, where is the water level relative to where you WANT it.

While there are losses in horizontal piping, it tends to be frictional losses. It shouldn't affect the pump sizing appreciably.

Size of pipe may impact the capacity of a pump system, as bigger pipes can FLOW more, but the pressures remain the same.

Basically, you want to size your system to turn over the water in your pool. If you intend to run it 4 hours a day, it'll need to move 21,000 gallons in that time or less. Find a pump with the flow rate you need, and match or slightly oversize the filter. You can always ask a pool builder what he'd put on a new 21k @ 5.5 foot pool...

There is a relationship between motor and pump, as far as hp, speed, flow, and pressure, but since in the pool world, the motor and pump come together, you really don't need to worry about it much. If you are curious, there is a good article on the Affinity Laws here: Affinity Laws (PDF)
 
The frictional losses in a pipe, especially the larger losses in a smaller diameter pipe, do make a huge difference in the pressure relative to using a larger diameter pipe. The reason is that for a given single-speed pump, its RPM is constant so there is a pump curve that relates pressure vs. flow rate. The intersection of the system curve which also relates pressure to flow rate with this pump curve determines the actual pressure and flow rate.

You are correct that normally the head loss in static head which is the change in elevation is normally larger than the head from frictional loss, but in a pool system there is usually no static head at all. The reason is that any elevation difference between the pump and the pool water is exactly the same on both sides of the pump -- the output (pressure) side and the input (suction) side so these cancel out. That is, whatever extra work is needed to bring water up to the level of the pump is exactly compensated by the lower amount of work need to bring the water back down to the pool. The same principle applies to solar panels on a roof after such panels are "primed" (filled with) water. It is true that when first filling the panels and pumping water up to them that more pressure is needed, but the flow rates can be slow. So for solar panels, one does need a pump large enough to handle this priming of the solar panels, but can do so at low flow rates (or one can have an additional priming pump that is only turned on during the priming).

60 feet of 1.5" pipe has a head (pressure) of around 1.5 feet at 20 GPM, 5.1 feet at 40 GPM, 10.7 feet at 60 GPM, and 18.2 feet at 80 GPM. A larger pump is going to output a higher flow rate and correspondingly higher pressure. The same numbers for 2" pipe are around 0.4 feet at 20 GPM, 1.5 feet at 40 GPM, 3.2 feet at 60 GPM, 5.4 feet at 80 GPM. So using a larger pipe makes a BIG difference in having far lower frictional losses.

Richard
 
Well through a comedy of errors (ordered, backordered, downsized the motor) my pump arrived, but it is the original larger one I spoke of (1.5hp/1.0sf). Evidently my change didn't get to the warehouse...yet I only paid for the 1hp. ;)

Should I keep it? Send it back for the smaller one? Do I risk all sorts of ugliness by using it anyway?

pumpspec2.jpg
 
Do I risk all sorts of ugliness by using it anyway?
Click to expand...

Check the gpm rating on your filter. It's probably a little less than the gpm that big pump is gonna' try to push into your filter.

If so, you will operate with increased psi, use more electricity, and (this could be an urban legend...not sure) possibly blow some sand out of the filter into the pool.

Matching those two elements is the key to a nice system. The pump gpm should not exceed the gpm rating of your filter and, in fact, would do nicely if the pump gpm was about 20% less than the filter.
 

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duraleigh said:
Check the gpm rating on your filter. It's probably a little less than the gpm that big pump is gonna' try to push into your filter.

If so, you will operate with increased psi, use more electricity, and (this could be an urban legend...not sure) possibly blow some sand out of the filter into the pool.

Matching those two elements is the key to a nice system. The pump gpm should not exceed the gpm rating of your filter and, in fact, would do nicely if the pump gpm was about 20% less than the filter.
Click to expand...

The "Max PSI" is listed as 50 and the only GPM rating I can find in the manual is the "Maximum Recommended System Flow Rate by Pipe Size" chart, which says:
  • 1" - 20GPM[/*:m:u04b6xkq]
  • 1.25" - 30GPM[/*:m:u04b6xkq]
  • 1.5" - 45 GPM[/*:m:u04b6xkq]
  • 2" - 80GPM[/*:m:u04b6xkq]
  • 2.5" - 110GPM[/*:m:u04b6xkq]
  • 3" - 160GPM[/*:m:u04b6xkq]
My pipes are 1.5, but this chart confuses me. It appears that the filter itself can handle a very large GPM...correct? Isn't my GPM limited by the pipe size anyway? You can only suck/push so much water through a 1.5 pipe anyway regarless of pressure...right?

Thanks for all the advice guys!
 
The recommended flow rate for that filter is 62gpm according to the manufacturer's info. Using the head for an average pool, it seems like the pump will push more than that.

You can only suck/push so much water through a 1.5 pipe anyway regarless of pressure...right?
Click to expand...
Nope. With enough energy, you can push as much water as you want. Your psi and electric bill will go through the roof but, in theory, I don't believe there's a limitation on how much water you can push thru a given pipe.

Mas985 is the guru and I would listen to him before listening to me but it does appear that big pump will overmatch your filter resulting in a somewhat inefficient system. Not horrendously inefficient, but I would opt for a smaller pump.
 
Whatever pump gives you about 50gpm with a head (for the average pool) of about 40.

50gpm is 80% of the filter capacity and will still turn your pool water three times in a 24 hour period.....looks like it's about a toss-up between the 1 and 3/4 based on the chart you posted.

Again, Mas985 will probably check in if you can wait. I'm not sure about that head value of 40 for the average pool....he'll know better.
 
duraleigh said:
Whatever pump gives you about 50gpm with a head (for the average pool) of about 40.

50gpm is 80% of the filter capacity and will still turn your pool water three times in a 24 hour period.....looks like it's about a toss-up between the 1 and 3/4 based on the chart you posted.

Again, Mas985 will probably check in if you can wait. I'm not sure about that head value of 40 for the average pool....he'll know better.
Click to expand...

I will wait for the gurus! Do heat pumps add any feet of head? There would be several 90's in the pipe to plumb it in and I think I found a great deal on a used one locally.
 
Backglass,

For the most part, you are getting pretty good advice from everyone. If you want to learn a bit more about pumps and head loss, I put together a sticky on the topic located here.

Half way down in the second post shows a typical pump head curve with different plumbing system overlaid on top. Unfortunately, the superpump is not nearly as efficient as the pump shown there so you will not be able to use that curve directly although the plumbing curves are still valid. It is probably close to the 3/4 HP pump shown.

However, we may be able to get to an answer with a bit more information:

Number of parallel suction lines from pool to pad?
Number of parallel return lines from pool to pad?
Current filter PSI?

The 3/4 HP pump would probably have ensured you were under 62 GPM but you may still be ok.

If you do need to swap pumps, I would suggest looking at the Super II and Northstar pump since they are a bit more efficienct and yes, expensive. The Super is a very good pump but the others have a higher GPM/Watt and will more than pay for the extra money over the life of the pump. However, since they are more efficient, they tend to have more GPM for a given head loss so sizing is very important. Either way you can't go wrong.

As for the heat pump, they tend to add about the same head loss as a filter with is 5-10 feet depending on flow rates.

Post back with the above answers and we can zero in on a solution.
 
You should consider an Intelliflo pump so you dont have to figure all this out.

With the Intelliflo you can just set it at 30GPM (your pool 21000/12hours pump run time) and the pump runs at the lowest RPM to achieve 30PGM. You dont have to figure out your feat of head, water feature usage, etc.

The Intelliflo costs more but in the long run it pays itself out. The pump runs at the lowest speed for the GPM you need to adequately filter your water.
 
mas985 said:
Number of parallel suction lines from pool to pad?
Number of parallel return lines from pool to pad?
Current filter PSI?
Click to expand...

It's pretty basic. One suction line, one return line. Both 65 feet. I don't know the current filter PSI, as there was no existing pump (previous owner took it with him...no way to contact).

Thanks!
 
If you look ONLY at your two 65-foot 1.5" lines, then they intersect your pump curve near 35 feet of head with 70 GPM or thereabouts. However, as mas985 stated, you need to look at your actual pressure on your filter since there will be additional head from the filter and other components of your system (elbows in your piping, resistance in the outlet into the water and from the skimmer on input, etc.). So the 70 GPM would be best case and your system is likely lower than that with higher head (but maybe not by very much). With your larger pump, you aren't going to get anywhere near low flow rates and as pointed out it will cost more in electricity.

Richard
 
There are several rules of thumb you can get to total head loss. It turns that the distance from the pool to pad is the lowest contribution of head loss.

Like I said before, the pad equipment contributes about a 1/3 of the head loss, 1/3 in suction and 1/3 in the return lines. In the suction and return plumbing most of the head loss is in the fittings and not the pipe.

I can only go by my pool which I have characterized in some detail. So as an example, the "equivalent" lengths of straight pipe for each contribution are:

2.5" Suction Pipe actual length: 35 ft
2.5" Suction Fittings equivalent length: 150 ft
2.0" Pad Equipment equivalent length: 185 ft
2.0" Return Fittings equivalent length: 150 ft
2.0" Return Pipe actual length: 35 ft

Total of 555 ft. At 85 gpm, that is about 58 feet of head which I have measured. I also confirmed the pressure drop of my pad equipment so the ratios are about right.

For your pool, I would suggest these values.

1.5" Suction Pipe actual length: 65 ft
1.5" Suction Fittings equivalent length: 90 ft
1.5" Pad Equipment equivalent length: 140 ft
1.5" Return Fittings equivalent length: 100 ft
1.5" Return Pipe actual length: 65 ft

Equivalent pipe length for fittings scale with diameter and I assumed the same for the pad equipment. So this is about the equivalent of 460 ft of straight 1.5" pipe.

This plumbing curve will cross the Super Pump 1.5 HP curve at about 60 feet of head and 45 GPM.
So from a flow perspective, you should be ok. From an efficiency standpoint, you will not be anywhere close to the best efficiency point of 47 feet of head at 67 GPM but then again that would exceced the flow rate of the filter.

If you were to drop down the the 1 HP uprated pump, you would be at 54 feet @ 42 GPM and for a 3/4 HP, you would be at 46 feet @ 37 GPM.

These are approximations but should be within 10-20%. Without the filter PSI, this is about as good as it gets.

If you did not have the pump in hand, my recommendation would be to go with the smallest pump possible to keep head loss down and flow rates to a minimum.

The pump you have should work ok. I am not sure it is worth the effort of exchanging it for a lower HP pump.
 

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