Pump Efficiency, Head, Flow, and related technical info

[mas985]

One more point that I think you touched on in your last post but I wanted to make sure it was not lost.

As you pointed out, energy use drops off as a cube of RPM so I think you will find that you will use the least amount of energy per GPM at the lowest RPM even if the efficiency drops somewhat with RPM. Assuming the maximum energy use is 3200 watts, here is my reasoning.

Watts / GPM = 3200 * (RPM/3450)^3 / GPM = 3200 * (RPM/3450)^3 / (.033 *RPM)

Watts / GPM = RPM^2 /405322.5

So the efficiency is not likely to roll off at a rate of RPM^2, so the lower the RPM the less energy is used.

Like I said before, if you operate at 750 RPM, you can do 2 turnovers in 24 hours and use the least amount of energy possible.

[chem geek]

Just FYI. I verified that the pump in the IntelliFlo and the IntelliFlo 4x160 are identical with identical curves and efficiencies. The only difference in the full version is the addition of a flow meter plus associated electronics to keep track of total volume so that the pump can shut off after a designated number of turnovers. That is what leads to much greater savings for certain configurations where multiple features are present (needing different flow rates) or where the system curve changes (e.g. filter gets dirty).

Richard

[waterbear]

Just FYI. I verified that the pump in the IntelliFlo and the IntelliFlo 4x160 are identical with identical curves and efficiencies. The only difference in the full version is the addition of a flow meter plus associated electronics to keep track of total volume so that the pump can shut off after a designated number of turnovers. That is what leads to much greater savings for certain configurations where multiple features are present (needing different flow rates) or where the system curve changes (e.g. filter gets dirty).

Richard

Actually, the actual pump itself is identical with the WhisperFlo. The only difference is the motor with all it's bells and whistles.

[msm859]

Can someone give me the short answer? Would it be more efficient(least costly to run) with the Intelliflo to have the slowest GPM to turn over 1x per day AND have the largest pipe with minimum 90's to have the lowest pressure/head???

I am having a pool built and using the Intelliflo and my builder thinks I am too concerned with the over use of 90's and pipe size. He indicates in the past--with the regular Whisperflo he has to use eyeballs to get the head up.

[mas985]

Low head loss in plumbing is a good thing up to a point. As head drops, flow rates increase but so does the power draw of the pump. The peak efficiency of a pump (GPM/Watt) is generally near the middle of the pump head curve.

Another consideration is if you have too little head on the return but too much head on the suction side, you run the risk of sucking in air or worse, pump cavitation.

The only down side of the opposite case (too much return head) is that it reduces the potential flow. So it is best to error on this side which is why most pool plumbing has larger suction pipes than return pipes.

So you really need to match your plumbing system with the pump. To do it properly requires a bit of work which is why most pool builders simply do what they have done before.

If you look at the curves for Richard's pool and the Intelliflow, with the solar off is about as low a head I would go on that pump and with solar on is about as high as I would go so I think it would be well suited for his pool.

Usually 1 - 2 1/2" suction line and 1 - 2" return line is sufficient for most pools. If you have mutliple suction lines from pool to pad I would go with 2" lines and if you have more than 2 return lines, I would go with 1 1/2" return lines.

2 - 2" lines is about the same head loss as 1 - 2 1/2" line.
2 - 1 1/2" lines are about same head loss as 1 - 2" line.

Having said all that, it is much easier to add head to a plumbing system then it is to reduce it as your PB pointed out. So I would always error on the side of large pipes and use ball valves at the pad to control and balance the head for the suction and return. This way you can adjust the plumbing system to get the most GPMs/Watt no matter what pump is put on. Plus, it is difficult to predict exactly how much head a plumbing system will have and is best to measure it after the fact.

Also, post the details of your pool and equipement so we can comment further on the design.

BTW 2 x 45 degree bends are only slightly better than 1 x 90 degree.

[msm859]

Thanks for the explanation. It is an 18 x 36 pool with separate built in spa 6 jets, both have 400 sq" cartridge filters, 2 - intelliflo pumps, single 400 btu mastertemp heater, water feature with Pentair waterfall pump, still debating final finish.

[mas985]

You did not mention your plumbing. What does the pool builder want to put in and what do you want? Lines sizes, number lines, returns, skimmers, main drains, etc. Also, how far from pool to pad.

Your pool size is pretty close to mine and I have two skimmers, a split main drain and 4 returns.

Ideally, I would have each skimmer and the main drain pair on a separate 2" lines all the way back to the pad. 3, 2" lines are equilvalent to a single 3" line plus it will allow you to turn on just one of the three to isolate a suction line for repair or to drain the pool via the main drain only.

For the returns, you could go with one 2.5" line, two 2" lines or four 1.5" lines. Each configuration is equilvalent in terms of head loss. If the pad is close to the pool, you could go with 1, 2" or 2, 1.5" lines.

This should give you pretty close balance between suction and return. Adding ball valves at the pad to control flow will allow you to fine tune your flow rates.