Energy Efficient Pool Pump?

Pool pumps, pool filters and the plumbing of
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chem geek
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Postby chem geek » Mon 12 Jan, 2009 23:30

Doubling the pipe length doubles the head loss. So just for the 100' of pipe each way (200' round-trip) at 5 GPM for each of 16 panels in parallel, that's 80 GPM. In 1.5" pipe the head loss in 200' is 60 feet (26 PSI) which is quite a lot. In 2" pipe the head loss would be 18 feet (8 PSI) which is much more reasonable. I suspect that with your current pump, you may not be at 80 GPM because of the high head loss so your heating may not be quite as optimal.

I assumed that each panel truly needs or is optimal at 5 GPM and that they are plumbed in parallel. Though that's how it is normally done, you could instead plumb two banks in series which is less efficient for heating since the second bank is hotter and radiates out more heat, but it would have about half the flow rate requirement though a little more loss of head through two sets of panels. The net result would be less total head which in your situation would be better. However, getting larger pipe would be a better option.

So having your pipe replaced with larger pipe would certainly save a lot more energy, perhaps over 1000 Watts. I'm quite surprised that you have a solar system hooked up with 1.5" pipe in the long runs to/from the system.

Richard


Rick Sass
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Postby Rick Sass » Tue 13 Jan, 2009 13:26

Thanx again Richard -

I'm not sure what serial and parallel piping is, but I do have two banks of "panels." One bank is above the other bank and there is piping going to the lower panel which has a tee and then another pipe goes from the tee up to the other sets of panels. The same scenario holds true for the other piping except that tee is at the upper panel. The reason I have two sets of panels is because I ran out of roof area in a straight line so they were doubled up.

I should have asked questions about piping and head loss on this forum first, but I really didn't know what to ask.

So, would you suggest that I replace all the 1.5" piping with 2" piping and go with a different pump to handle both the system and solar pumping and eliminate the solar booster pump?

Just to clarify, I have 11 panels that flow 5 gpm and 5 panels that flow 4 gpm.
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Postby chem geek » Tue 13 Jan, 2009 14:44

The diagram shown here has 3 individual solar panels plumbed in parallel. This means that the cold water input to the panels is evenly distributed among all of the panels and that the output from the panels is collected equally from all of the panels.

You will also notice that in order to have the total pipe length be the same regardless of which panel water goes through, that the plumbing input goes in the opposite direction from the plumbing output. That is, the input pipe at the bottom of the panels is going from left to right while the output pipe at the top of the panels is going from right to left.

If these panels were connected in series, instead of parallel, then the output of one panel would feed the input to the next panel so you'd have a pipe at the top of the first panel go to the bottom of the second panel, etc. Connecting in series creates a higher flow resistance (head), but a lower total flow requirement since the total flow is equal to the flow through each panel. When you connect in parallel as shown in the diagram, the flow resistance (head) is lower, but the total flow requirement is higher since it is the sum of the individual panel flows.

If your panels are connected in parallel, then the total flow needed is 11*5 + 5*4 = 75 GPM which is close to the 80 GPM I used in the previous post's calculation. The way you described the piping with a Tee sounds like the two banks of panels are connected in parallel.

Anyway, as to what to do, you really do need to speak to a professional about this. I do not work in the pool industry. However, moving to 2" pipe should help a lot in your particular system and is what should have been done in the first place (in fact, if you're replacing the pipe anyway, you could even go with 2.5" pipe if you wanted to). If you do this, then you should be able to run with a single variable-speed or variable-flow pump, such as the Intelliflo, and not need a separate booster pump for the solar and you should save quite a bit on energy costs and possibly improve your solar efficiency as well (depending on current flow rates in your system).

Richard
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Postby Rick Sass » Fri 16 Jan, 2009 12:27

Thanx Richard -

Based on your description, I am using a parallel system. Since, the headers for the solar panels are 2" should I continue with 2" returns and supplies or should I increase to 2.5" piping? Would the increase in piping size to 2.5" produce a noticable benefit or is just that if I'm replacing the piping I should go with 2.5".

The contractor has already been paid about 6 months ago - do you think I have any recourse with the contractor to replace the piping or is it going to be "if I know so much, then you do it" scenario.

Thanx again for your help.
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Postby chem geek » Fri 16 Jan, 2009 13:29

There is absolutely nothing wrong with having parts of the piping be larger than other parts, especially if the longest pipe run can be larger. In fact, the most common situation is to have 2" pipe out of the pump that then gets split into individual 1.5" pipes near the pool where each goes to a separate return (since the flow is split, smaller pipes can be used to each return). Another common situation is for separate 1.5" pipes to come from the skimmer(s) and floor drain(s) and then go to separate manual valves and then come together into a short 2" pipe that feeds the pump. Basically, the resistance to flow in a pipe is non-linear with respect to the flow rate and to the pipe diameter.

At 75 GPM, the head (pressure) loss in 200 feet of pipe of different sizes is the following (I also show velocity of the water in the pipe):

SIZE . HEAD(FT) . HEAD(PSI) . VELOCITY(FT/SEC)
1.5" ...... 54 .............23 ................ 11.8
2" ......... 16 .............. 7 ................. 7.2
2.5" ........ 7 .............. 3 ................. 5.0
3" ........... 2.4 ........... 1 ................. 3.3

You can see that the biggest bang-for-the-buck is to move from 1.5" to 2" pipe. So that's a no brainer. Going to 2.5" would only make sense if the incremental cost of doing so were fairly low. If the bulk of the cost were the labor, for example, then it might be worth it. It certainly isn't a requirement and the amount of energy savings will be somewhat small (I estimate that below).

If we assume that you've got 40 feet of head (17.3 PSI) with the solar panels, returns and suction head excluding the 200' of pipe (and that's just a very rough guess; it could be more), then this is a difference in feet of head (at 75 GPM) of 56 vs. 47 which is roughly an output power difference of about 16% which might translate to an input power difference that is similar in proportion. If I assume 50% overall pump efficiency, then that could be a difference between 1580 Watts vs. 1327 Watts or a difference of about 250 Watts. Remember that I assuming you are using an Intelliflo VF pump that adjusts its speed to keep the flow rate constant.

As for recourse with your contractor, I have no idea. At a minimum, you might ask him why he used 1.5" pipe for such a long run and whether he knew the effect that would have on pressure head loss and therefore energy efficiency.

By the way, do you have a pressure gauge on your filter showing, for example, PSI? That could give us a good idea of the current overall flow resistance in your system. I want to make sure that the Intelliflo pump will be able to handle what you've got. It may not be able to at all with the 1.5" pipe and should be OK with the 2" pipe, but knowing your current PSI would let me better estimate the unknown head associated with the solar panels and the pool return lines and fittings as well as the suction line and fittings. Also, do you know your current pump brand and model number or have specs on it including Horsepower and service factor and/or have pump curves?

You should also verify your pipe diameter. I assume you have Schedule 40 pipe and if so then 1.5" is a nominal pipe size with an actual inside diameter of 1.610" and an outside diameter of 1.900". The circumference which you can more easily measure is 5.969" (about 6"). For 2" nominal pipe size, the actual inside diameter is 2.067", the outside diameter is 2.375" and the circumference is 7.461" (about 7.5").

Richard
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Postby Rick Sass » Sat 17 Jan, 2009 12:43

Wow - Thanx Richard.

I really regret not coming here first and asking questions before my solar system was installed.

Answers to your questions are as follows:

1. I do have 1.5" pvc piping for the supply and returns for the solar system. All the piping is the black piping which I'm assuming is ABS rather than PVC. I do not know what schedule it is. The supply and returns lines coming off the roof to the booster pump is 1.5" PVC, Schedule 40.

2. The system pump is a StaRite DuraGlas, P2RA5F-125L. This pump/motor combination is a 1.5 HP, but the motor was replaced some time ago before my ownership with a GE 1 HP motor.

3. The filter is a StaRite Posi Flo, PTM100.

4. The pressure gauge on the filter housing reads 15 psi without solar and 20 psi with solar enabled.

Thanx again for all your help - you would be a very valuable asset here in SW FL!
chem geek
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Postby chem geek » Sat 17 Jan, 2009 15:43

The Sta-Rite P2RA5F-125L is a 1-1/2 HP Dura-Glas PR2A series up-rated pump. The service factor for an up-rated pump is usually lower, say around 1.1 or so. Your replacement motor GE 1 HP is probably full-rated with a service factor of 1.5 to 1.65 or so. So basically it is the same. What is most relevant is the Total Brake Horsepower which is the product of the Horsepower and the Service Factor (SF) -- you can see the HP and SF on the plate that should be on the pump motor.

The pump curves for the Sta-Rite Dura-Glas may be found here where the P2RA5FL is curve "D". It shows that the maximum head is around 90 feet and the best efficiency sizing is between 43 GPM 85 feet and 80 GPM 47 feet. With your long 1.5" pipe runs, this means that you aren't getting near the 75 GPM that is more efficient for your solar panels and you are wasting a LOT of energy with friction in the "too narrow" pipe.

The Pentair Intelliflo should have no problem at least emulating your current pump, but could be fine tuned to the desired flow. That is, even with your existing pipe, the Intelliflo would work in your system but would be pumping at a flow rate that is lower than optimal for your solar panels, just like your existing pump is doing. By replacing the 200' round-trip pipe, you can increase your flow rate to your panels with lower electricity usage -- a real win-win. You can get a LOT of energy savings with the Intelliflo if you use a lower flow rate when the solar is off.

Your pressure reading when solar is on doesn't make sense. 15 psi with solar off is reasonable and is 35 feet of head so with suction head added it's perhaps around 40-45 feet of head and a GPM of 80. That's a higher flow rate than you need (with solar off), but is due to not having a variable speed pump. However, with the solar on, 20 psi is only 46 feet of head so with suction head it's perhaps around 55-60 feet of head so 70 GPM but there's no way that this is going only through your solar system. The psi should have been much higher. In my own pool, for example, my older 1 HP full-rated pump (somewhat similar to your 1-1/2 up-rated pump) had around 15 psi with the solar off and around 28 psi with the solar on with fairly long runs but using 2" pipe. A 10 psi increment is more typical, but 5 psi is strange given your long narrow pipe runs.

If your current pump were just flowing through the 200' round-trip of 1.5" pipe with nothing else (and no suction head), it would be at around 73 GPM with 52 feet of head or 22.4 psi. So adding in everything else (the solar, the suction head, the baseline head to the pool without the solar), there's no way that all the water is going through that 1.5" 200' round-trip of pipe. When the solar is on, is ALL of the water going through the solar or is there a bypass valve that only has only SOME of the water going through the solar?

A psi increment of 5 is 11.6 feet of head. If there were no friction in the solar panels themselves (which isn't true), then the 200' of 1.5" pipe would have a flow rate of about 32 GPM to produce that head loss. So this implies that the flow rate through the panels (overall, not per panel) at <32 GPM is less than the flow rate from the pump overall at around 70 GPM. This is why I'm asking if some of the flow bypasses your solar when it is "on".

Richard
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Postby Rick Sass » Mon 19 Jan, 2009 21:37

Richard -

Here are more details of my system:

1. I do not have a bypass for the solar. The solar is controlled by a valve actuator which is controlled by the Aqua Logic.

2. The GE system pump is 1 HP with a SF of 1.25.

3. The booster pump for the solar is a Waterway SVL56, A.O. Smith motor, 3/4 HP and a SF of 1.65.

4. With the solar enabled and no booster pump the psi is 28.

5. With the solar enabled and the booster pump on, the psi is 20.

6. With solar not enabled and just running the system pump, the psi is 17.

Does using the booster pump change your previous psi concerns from your earlier reply?
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Postby chem geek » Tue 20 Jan, 2009 02:07

Rick,

Thanks for the info. I forgot about the booster pump and even if I had remembered, I didn't realize that (apparently) it is coming after your filter (probably just on the line to the solar) so it would reduce the pressure reading at the filter when it was on. The pump curve for your main pump with the smaller GE motor is probably closer to the "C" curve in the link I gave.

With the solar off, 17 psi pressure head is 39 feet of head so with suction head it might be around 45-50 feet of head and 65-70 GPM. Again more than you need when solar is off so the Intelliflo would clearly help there. If your pool was 15,000 gallons, then your current turnover rate with the solar off is under 4 hours. With the Intelliflo, you can run the pump for a longer time at a lower flow rate for a lot of energy savings (at least when the solar is off). The implied equivalent 1.5" pipe length is 190-240 feet which sounds about right going to/from your pool and fittings.

With the solar on and the booster pump off, 28 psi pressure head is 65 feet of head so with suction head it might be around 75 feet of head and 35 GPM. This implies a 1.5" pipe length of around 1200 feet. It's possible that the pump with your new motor has a higher GPM and also flowing through the booster pump with it off could have significant resistance. With the booster pump on, the 20 psi is from the first pump and about 46 feet of head which with suction head is around 55 feet of head and 60 GPM. The second pump is similar to the 1st (with the replacement motor) in HPxSF so the 60 GPM means another 55 feet of head. 60 GPM with 110 feet of head implies 600 feet of 1.5" equivalent pipe length and that sounds about right given the roughly 200 feet equivalent to/from the pool and fittings leaving 400 feet for the solar -- 200 feet to/from the solar and 200 feet round-trip through the solar panels.

So with your booster pump, the 60 GPM is a decent flow through the panels -- less than ideal, but not bad. It's pretty clear that if you replace your two pumps with the Intelliflo and don't change your piping, then you won't be able to achieve this flow rate. Even at peak 3450 RPM with the Intelliflo, the 600 feet of 1.5" equivalent pipe length implies around 55 GPM with 91 feet of head and around 2100 Watts. If you replace your 200' round-trip with 2" pipe, then you could get your current 60 GPM with 82 feet of head at around 3300 RPM and around 1850 Watts which may be only a little more than half of what your current pumps are using in energy.

Well, that makes a lot more sense so thanks for straightening me out. There's no question that your plumbing should have been using 2" for long runs. I'm a little surprised that your solar panel headers are 1.5", but that depends on the manufacturer. My Fafco solar panels have 2" headers (at least -- they are awfully thick and could be even larger). Anyway, it seems pretty clear that if you want to replace your two pumps with one Intelliflow, you're going to have to replace your 200' of round-trip piping to/from your solar panels with 2" pipe.

Richard
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Postby Rick Sass » Tue 20 Jan, 2009 11:32

Well thanx again Richard for your input and explanation. Just to make it clear, the headers for my solar panels are 2". Also, the pool is about 15,000 gallons.

You are correct, the BP is after the the filter and is on the line to the solar only.

The electric rate on my bill is about 6.5 cents per kw.

By replacing the 1.5" piping with 2" piping and replacing the two pumps with one IntelliFlo pump, it's clear there would be an energy savings and a lower electric bill to go with it. Would this scenario also give me more "heated" pool water and would it heat the pool quicker?

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