Hydraulics 101 - Have you lost your head?

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chumbley,

In pool mode, you suction is very high. Do you have air in the pump basket when in this mode or is the pump loud?

Normally, it is best to keep the head loss on the suction side to less than 25% of the total head loss. Otherwise the pump gets loud and you start seeing air in the pump basket. Your PB should have used either 2 1/2" pipe or separate pool to pad runs for the skimmer and main drain. Especially with that size of pump.

If you have no plans to modify the plumbing, I probably wouldn't either, then I think you may be best off with a variable speed pump. That way you get the power when you need it but then you can optimize the flow rate for every day filtering. You can go with a two speed, but you won't get the lowest energy usage that way.
 
Thanks for the replies...

H20 - I would plan to stay at 220v. I'm not worried about plumbing changes - at least around the pad. I don't want to do plumbing changes back to the pool setup.

JasonLion - Yes, same pump for pool and spa.

mas985 - Yes, the suction seems high to me too. The pump is louder in pool mode than spa mode, and there are usually some air bubbles in the filter. I'm not sure how much of this is caused by how much higher the pump is than the pool. I think that 1" of mercury is equal to about 13.5" of water, so if the pump is 6' above the pool, it would make sense to me that at least 5" of my vacuum reading is just pulling water up to the pump level. Perhaps I'm missing something there. I too wish the builder would have plumbed the drain and skimmer separate. But he didn't, and doing so now would be, well, not impossible but not easy either. Would a lower speed (two speed or variable speed) still allow me to run the pressure side cleaner?

Thanks all.
 
Your absolutely right. The static head added to the suction side is 6'. Nothing you can do about it unless you move the pad or dig a deep hole. :shock:

Note too that the filter pressure is also affected and will read about 2.6 PSI lower because of the pad height. If you were at water level, the head balance would be much better.

Your best bet is a variable or two speed pump. The variable would give you a bit more flexibility in setting flow rates and probably save you more money over the life of the pump but even a two speed would help the situation.
 
mas985 said:
For a 16,000 gallon pool and a 8 hour turnover (i.e. 3x per day), you would only need 33 GPM from a pump. Even the smallest pump will deliver much more than 33 GPM so assuming you don't need a high flow rate for a spa, waterfall or other feature, either a two speed or variable speed pump might be a good solution.

If you go with a variable speed, the Intelliflo series is probably your best bet. The other variables have not had a lot of time out in the field so reliability could still be an issue. Depending on what you pay in electrical rates, the Intelliflo will likely pay for itself in a short period of time. If I were buying a pump today, this would be the pump.

If you go with a two speed, there are many options depending on the brand you want to use. You could go with a 1/2 HP but some manufactures use 3/4 HP motors in those pumps so the efficiency isn't that great which is why I usually recommend a 3/4 HP full rated pump as the smallest.
Click to expand...

mas985!
In the post above you talk about a "full rated" 0,75hp pump. I have found two different whisperflows both are rated as a 0,75hp pump but one is full rated and the other is not. What is the difference . Could you explain that please.
Whisperflow is a good pump from research, am I right about that observation? I had to give up the intellflo beacuse my project is about to burst it's budget. Not really that bad but I can't motivate the extra cost for a variable speed pump right now.

Thanks!
//Mats

Thanks!
 
There is an extra number, called service factor or SF, for motors that relates the advertised HP to the actual HP available to the pump. The HP available to turn the pump is called brake HP and brake HP = HP * SF.

A full rated pump has a relatively high SF, while a max rated pump as a relatively low SF. Typically a 3/4 HP full rated motor is the exact same motor as a 1 HP max rated motor, though this varies a little from manufacturer to manufacturer.

The entire system of rating motors in HP has a long and very confusing history, with a number of different standards for how to measure HP used at different times for different purposes and giving different results. As a result the advertised HP of a motor doesn't really tell you all that much. You also need to know the SF. Phrases like full rated, max rated, up rated, etc. give you hints about what the SF might be, though they are not really used consistantly.
 
Jason!
Not much of a difference in SF between the two, 1,65 SF for the regular pump and 1,67SF for the full rated pump.
It seems like a very little variation in actual brake hp between the two pumps, 0,015 hp.
 
Just to add to what Jason wrote:

A pump consists of two parts: The wet end and the motor. What most manufactures do is use the same wet end on different motors which gives the up rated vs full rated versions. However, if the wet end is the same, the performance or head curve will be the same. So for the Whisperflo line the following are really the same pump performance wise but have different motor labels and HP ratings. However, the BHP is the same (accounting for round off error).

Full Rated --------------------> Up Rated

WFDS-3 (0.75 HP, 1.67 SF) ----> WFDS-24 (1.0 HP, 1.1 SF)
WFDS-4 (1.0 HP, 1.67 SF) ----> WFDS-26 (1.5 HP, 1.1 SF)
WFDS-6 (1.5 HP, 1.47 SF) ----> WFDS-28 (2.0 HP, 1.1 SF)

All manufactures seem to do this and I believe it is primarily for marketing reasons and to give buiilders choices when selling to customers. Usually, they will group the full rated and up rated versions on the head curves so you can see they are really the same pump or at least identical wet ends. For most manufactures, the motor design is the same as well or at least has the same energy characteristics but this may not be true for all.
 
Thoose two pumps here http://www.poolandspasupplystore.com/se ... Categories
are the two I'm talking about. Both 0,75hp
I'm getting my filter from that store and shall ask them to ship a pump at the same time to me. So the question is which of them I should choose. Or perhaps should I look at the 0,5hp instead.

I'm not very bright here that I'm aware of, so I hope you could lead me in the right direction.
Thanks
 
I see, you are looking at the WhisperFlo WF-3 and the WFE-3. Both of those pumps move almost the exact same amount of water, but the WFE-3 does it with less electricity, 5.6 amps instead of 7.1 amps or a 21% savings. The WFE-3 has a special high efficiency motor. It costs more up front and uses less electricity to do the same job.

The prices are close enough and the electrical savings significant enough that I always wonder why they still sell the older less efficient model.
 
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Those are both full rated pumps. The difference is that the WFE is a high efficiency motor and the WF is a standard efficiency motor. They both have the same head curves but will consume different amounts of energy.
 

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Re:

Thanks for the tech. I'm trying to understand some of the spa assumptions you posted. In a one pump situation, I understand that the pool will use less pump than the spa, and so one needs to size the pump to the spa needs, and then run the pool on a lower speed. How do you determine what is optimal then for a six-jet, 8 foot circular spa? It seems like there would be one sweet spot for return size, suction size, and pump HP requirements. What are the variables in the calcs for just a spa? Only pad distance/altitude would vary by job site, right?

mas985 said:

  • - Spa jets usually require 10-25 GPM per jet and thus very high flow rates which are difficult to achieve with low SFHP pumps. Total required flow rate is the number of jets * the flow rate per jet.

    EXAMPLES:

    6 Jet spa requiring 90 GPM would probably require a 1 1/2 HP full rated pump or equivalent
    8 Jet spa requiring 120 GPM would probably require a 2 HP full rated pump or equivalent
    10 Jet spa requiring 150 GPM would probably require a 3 HP full rated pump or equivalent

    Note that multiple pumps can be used to achieve flow rates and may be better suited for certain pool designs. Multiple pumps also allow your to target pumps for specific jobs and better optimization. So a 10 jet spa may be better serviced with two 1 HP pumps with separate lines for each group of 5 jets than a single 3 HP pump.

    Pipe Sizing

    Generally, the bigger the better although too low of head loss can be a problem with pumps. They tend to get noisy if the head loss is too low. However, it is much easier to add head to plumbing via restriction valves then it is to reduce head after the plumbing is installed so it is best to err on the side of too little head loss.

    Below is an example of a two speed pump head curve complete with a series of plumbing design scenarios (A-F) overlaid on top. The chart shows how the plumbing system head will change with different flow rates and pumps. The points where the plumbing system intersect the pump head curve are the operating points for each pump and plumbing system combination.

    Again, when choosing pipe sizes, it is best to go with larger pipe diameters when in doubt. If a high HP pump is required for a spa or water features, then larger pipe diameters will usually be required to maintain efficiency.
Click to expand...
 
Head loss in the plumbing is one factor but that can be and should be mitigated by using large pipes. If the plumbing is designed properly, most of the head loss in a spa (60-70%) should be due to the spa jets. However, some systems will use the same pump for circulation and jets which I don't think is a very good idea. For one, the requirements for the pool and spa are very different and two, forcing a high volume of water through the filter for the jets is not good for the filter and wastes a lot of energy. A better design is to use a separate jet pump just for the spa jets but also have spa returns so the water can be separately filtered and heated. That way the circulation pump can be dimensioned much smaller, even a two speed, then the spa pump. Unfortunately, not all spas are designed this way.

Right sizing of the pump for spa jets is primarily dependent upon the type of jet used. Each jet has a flow rate requirement so that it feels strong. But normally jets specifications are given in a range where the low end is for weak jets and the high end for strong jets. Once you know the flow rate per jet and the number of jets, the total flow rate is then known and a proper pump can be chosen. That was what I was showing in the sticky but that was only for 15 GPM jets and 25 GPM jets will require larger pumps.
 
Mas985,
Would it be possible for you expand this little table to also include the next step up (3/2.5")? We are unsure about the plumbing sizes to go for in our new pool build.

RPM 3450 2500 2000 1000
2.5"/2.0" Head Loss 74 39 25 7
2.5"/2.0" GPM 104 74 59 28
2.5"/2.0" Filter PSI 25.2 13.4 8.6 2.2

2.0"/1.5" Head Loss 87 46 29 7
2.0"/1.5" GPM 72 51 40 19
2.0"/1.5" Filter PSI 30.2 16.0 10.3 2.6

Thanks in advance.
 
This is very informative - however I am seeing an error when I enter my numbers in the spreadsheet GPM Estimate v4.xls

I have a newly installed Intelliflo VS3050 and when I use the PSI22GPM sheet and enter the RPM, PSI etc I get #NUM! errors in the lines 20 and below. The issue seems to come from line 22 when it is trying to calculate the square root of a negative number. It only happens with lower RPM (1500 and below) and associated lower PSI. However these are the RPM and PSI my installer set my system to run at most of the time.

Am I doing something wrong - or is my new set up in some kind of imaginary number universe......

here is wheat I am entering

PSI GPM Estimate
Pump Model IntelliFlo VS-3050
RPM Setting 1500
Pool to Equipment Pad Distance (ft) 10
Number of Suction Runs Pool to Pad 1
Suction Pipe Diameter (in) 1.5
PSI Gauge Height Above Water Level (ft) 3
Filter Pressure (PSI) 7
Suction (in-Hg.) #NUM!
Flow Rate (GPM) #NUM!
Head (ft) #NUM!
Input Power (Watts) #NUM!
Gallons per Watt-Hr #NUM!
Plumbing Curve Constant #NUM!
 
The reason is that it cannot find a solution for the PSI and RPM given. In other words, it doesn't fall on the curves. This quite possible at low RPMs because the PSI gauges tend to have very high inaccuracies at low PSI.

To prevent this from happening, you need to use a higher speed for calibration in Column B, preferably full speed. Then use columns C and above for other RPMs but only change the RPM. The information in the grey cells is not meant to changed. The idea here to determine your plumbing curve from near full speed operation and then use that plumbing curve for all other RPMs.
 
Thanks - at 2500RPM the numbers look better. 14PSI at the pump indicates 41GPM (with the solar on). This also suggest the flow rate at 1700, 1500, 1000 RPM (the RPM that my installer preset for non-solar, solar, and when Polaris booster pump runniing) should be 28, 24, 16 GPM respectively (I know the non-solar may be a little different). All sound good - but my Blue-White flow meter in the piping going to solar isn't registering anything like this. I do have a diverter valve but the installer of the Intelliflo/Suntouch said he had set it to send most/all water to the solar.

Putting my hand over the outlets into the pool also suggests the flow may be lower - but frankly I don't know what 16GPM would feel like anyway.

Is it possible that the Blue-White Flow Meter is clogged? Is it cleanable? It had seemed to be working with my old single speed 1HP pump - however in the old set up most water was being diverted back to the pool with only some going through the solar (the flow through the solar was much too high otherwise) - so I am not really comparing like to like.

Note I didn't want to run the Intelliflo at above 2500RPM - if the 41GPM is right that is max I would want to send through my 7 Sunburst EP40 panels.
 
Flow meters must be installed with 10xD straight length before the meter and 4xD after the meter. Otherwise, it may not read the correct flow rate. But if it is only measure part of the flow rate, that makes it more difficult to take into account. Also, flow meters are rated at full scale so tend to have a lot of error on the lower end of the scale.

So are you saying that you are running solar only at 16 GPM? How big are your panels and are they installed on a roof?
 
mas985 said:
Flow meters must be installed with 10xD straight length before the meter and 4xD after the meter. Otherwise, it may not read the correct flow rate. But if it is only measure part of the flow rate, that makes it more difficult to take into account. Also, flow meters are rated at full scale so tend to have a lot of error on the lower end of the scale.

So are you saying that you are running solar only at 16 GPM? How big are your panels and are they installed on a roof?
Click to expand...

Garage roof very close to the pool - and yes it is a flat run within multiple feet each side of the flow meter. I took the flow meter out and cleaned it but still no reading - I will order a new one.

There are seven Sunearth EP40 panels http://sunearthinc.com/wp-content/uploa ... Empire.pdf - as you can see the design flow rate for each panel is ~ 1GPM with max flow rate of 12 GPM.

For the seven panels my solar installer recommended a flow rate of between 10 - 25 GPM.

Some more testing today - (I cleaned the DE filter to make sure it wasn't an issue).

It turns out the Suntouch controller can get status from the pump. Here is what it got.

1000 RPM (solar off) 116W (from the Watts2GPM seems like 8 GPM)
1550 RPM (solar on) 286W (from the Watts2GPM seems like 33 GPM)
1700 RPM (solar on) 347W (from the Watts2GPM seems like 35 GPM)
2500 RPM (solar on) 944W (from the Watts2GPM seems like 44 GPM)

My sense is that at the lower RPM there is still little flow through the panels - but the numbers above suggest otherwise... I am most worried if the 1500 RPM is priming the solar.

As reported earlier using the PSI2GPM (based on 2500RPM - 14PSI) indicates 41GPM (with the solar on). This also suggest the flow rate at 1700, 1500, 1000 RPM should be 28, 24, 16 GPM respectively.

I know there are approximations in the models and measurements - does this seem within the bounds of reason.
 

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