Using main filter pump for solar heating is stupid?

[rlab]

Hi,

Based on research on TFP and elsewhere, for new build I was planning on solar heating run by main filter pump (Intelliflo), with automation to switch 3 way valve and increase VS speed when solar is active.
The catch is *every* installer has told me flat out they never install that way on a new build and basically it's a stupid idea. They want a dedicated pump and suction/return for the solar.

The arguments against using filter pump are:
1. I have to run the full filter loop at higher flow rate when solar is on. = way more TDH and hence electricity use
2. TDH on solar is too high for standard filter pumps, they will wear much faster.

These points kinda make sense to me, but then it seems like most people on TFP are just using the filter pump? Suspect this may be another US versus Australia thing?

 

[ajw22]

The arguments against using filter pump are:
1. I have to run the full filter loop at higher flow rate when solar is on. = way more TDH and hence electricity use

So they think running two pumps are more energy efficient then running one at the necessary flow rate for the solar?

2. TDH on solar is too high for standard filter pumps, they will wear much faster.

And which part of the pump do they think will wear faster?

I think both of their arguments have no factual basis.

@mas985 thoughts?

 

[AusPhil]

I think the points put forward as cons are rubbish but on a new build i'd think there are some benefits of at least plumbing for an independent system .... here is one blog that has some logical pro's and con's

Recommended plumbing for swimming pool heating | Pooled Energy

There are 3 recommended pool plumbing methods for swimming pool heating. You can learn more about these pool plumbing methods by reading Pooled Energy's guide.

www.pooledenergy.com

Depending where you are in Oz you may also want to use the solar to cool the pool at night ....

 

[proavia]

Two pumps sounds like a waste of electricity. And not sure I want to be pumping unfiltered water thru my solar panels. Thinking the debris would eventually clog the panels.

 

[rlab]

Two pumps sounds like a waste of electricity

I'm not sure that's the case. Here are the 2 options when solar is active:

1. Separate Solar pump and filter pump:
- TDH(filter loop) at low flow rate
- TDH(solar loop) at higher flow rate (solar flow rate)

versus

2. Combined solar+filter pump:
- TDH(filter loop) at higher flow rate
- TDH(solar loop) at higher flow rate
= TDH (filter loop + solar loop) at higher flow rate

Electricity usage is proportional to TDH * flow rate, therefore option (1) (separate pumps) actually uses less electricity. Furthermore electricity usage goes up non linearly against TDH and flow rate, therefore option (2) (combined pump) uses even more electricity than you would expect as it is having to run the full combined TDH of the solar+filter loop at the higher solar flow rate.

This is why I originally posted this in the Deep end section.... I think its actually more complex than just 2 pumps = more electricity.

 

[Pool_Medic]

LOL. You have to admire pool people who’s knowledge base is formed by archaic teachings.

No, one pump will suffice if properly planned.

 

[rlab]

I am surprised by how closed minded people are. The discussion is not about whether a single pump can work (clearly it can), it is about whether using 2 pumps is more efficient, and is less wear on the main pump.

So I decided to do the math, and here is what I got (Electricity usage when solar is active):
Combined pump for Solar + Filter - TOTAL Electricity usage = 1665W
Separate Pumps for Solar + Filter - TOTAL Electricity usage = 1280W

Clearly using separate pumps is significantly more efficient.

Here are the calculations. I used high end Hayward pumps, as unlike Pentair they actually publish electricity usage for their pump curves. TDH is based on various estimates floating around, and published figures for solar panel TDH. However it doesn't really matter what TDH estimates you use, the result is always the same because you are always having to run a higher combined TDH at a higher flow rate when using a single pump.

** If anyone can get the pump curve electrical usage for IntelliFlo, I would be happy to redo the calculations for that pump

Filter loop TDH = 33 feet (10m), flowrate = 20 gpm (75 lpm)
Solar loop TDH = 33 feet (10m), flow rate = 40 gpm (150 lpm)

Combined pump for Solar + Filter
TDH = 66 feet, Flow rate = 40 gpm
VS Speed = 3000RPM
TOTAL Electricity usage = 1665W

Separate Pumps
Filter TDH = 33 feet, Flow rate = 20 gpm
VS Speed = 2100 RPM
Electricity usage = 670W

Solar TDH = 33 feet, Flow rate = 40 gpm
Fixed Speed 0.5HP pump
Electricity usage = 610W
TOTAL Electricity usage = 1280W

 

[cfherrman]

Are the pumps ran in series?

By the way, power is power and it will take the same amount of power to do this, overkill and efficiencies are what matters.

 

[borjis]

I was so excited when I got my first home with a pool that had solar.
On the pool inspection day, the pool co hired for the inspection right off the bat told me the new
pump motor recently installed was insufficient power for solar. I came here and the resident hydraulic
specialiast told me that motor rating was fine for single story. and it was.

 

[Pool_Medic]

Rlab, you’ve been lead down the garden path.

I install all brands and Hayward is the worst out there.

Your math is flawed!

If pump two ramps up to x speed for solar while pump one shuts off, why couldn’t you just ramp up pump one? One running for x amount of time versus two running for the same amount of time is identical, except the clients pays for two pumps.

You’ve sold two pumps, plus fittings and labour, end of story!

 

[cfherrman]

I'm not seeing good math either, you can run your pool pump at 20 gpm and run the solar at 40 gpm if the pumps are in series.

 

[mas985]

I am surprised by how closed minded people are. The discussion is not about whether a single pump can work (clearly it can), it is about whether using 2 pumps is more efficient, and is less wear on the main pump.

So I decided to do the math, and here is what I got (Electricity usage when solar is active):
Combined pump for Solar + Filter - TOTAL Electricity usage = 1665W
Separate Pumps for Solar + Filter - TOTAL Electricity usage = 1280W

Clearly using separate pumps is significantly more efficient.

Here are the calculations. I used high end Hayward pumps, as unlike Pentair they actually publish electricity usage for their pump curves. TDH is based on various estimates floating around, and published figures for solar panel TDH. However it doesn't really matter what TDH estimates you use, the result is always the same because you are always having to run a higher combined TDH at a higher flow rate when using a single pump.

** If anyone can get the pump curve electrical usage for IntelliFlo, I would be happy to redo the calculations for that pump

I don't think your TDH calculations are correct. First and foremost TDH is dependent on flow rate so you can't just add head loss calculated from two different plumbing systems at different flow rates. So you really have to define the plumbing systems before you can calculate TDH. On my system, I run solar at 1550 RPM at 108 watts so my system beats both of your scenarios hands down and it runs both solar and filtering at the same time. A second pump would only increase the power usage.

So before you present fictitious scenarios, please define the plumbing systems in detail including all lengths, fittings, pipes sizes, valves, and everything else the water touches. Without the details your analysis is totally meaningless.

If one was to build a solar only system, it would have most of the components of the filtering system. Skimmer or MD, suction plumbing, pump, return plumbing, return eyeballs. A solar only system would only save the filter head loss and maybe a heater if one was installed. The additional solar plumbing and panel head loss would well exceed anything that was "eliminated". But even worse is the fact you are sending unfiltered water to the panels. You will have plugged panels in no time rendering the solar useless.

Filter loop TDH = 33 feet (10m), flowrate = 20 gpm (75 lpm)
Solar loop TDH = 33 feet (10m), flow rate = 40 gpm (150 lpm)

BTW, these are completely unrealistic head loss numbers for those flow rates. Head loss at those flow rates should be much lower than that for a typical system. At 24 GPM my filter + solar has 8' of head. At 40 GPM, my filter + solar has 24' of head and runs at 396 watts.

 

[JamesW]

Filter loop TDH = 33 feet (10m), flowrate = 20 gpm

How are you getting this? Unless you're using 1" pvc, it's not realistic.

As long as you size the pvc correctly, your head loss should be very low at 20 or even 40 gpm.

At 20 gpm without solar, your filter pressure probably won't exceed a 3 psi.

Your suction lines should be 2" minimum.

You should use a big cartridge filter.

What is the description of the plumbing and equipment that you're using to do the calculations?

Since this is a new build, you have the opportunity to do it correctly.

 

[Costas > DownUnder]

They want a dedicated pump and suction/return for the solar.

I think this is just because it is an easy option for them.

I note that many of our fibreglass pools available Down-under come pre-plumbed with a separate water circuit for the solar with the intakes usually located down at the deep end at around 3/4 depth.

My solar pump draws around 750W whilst my main pump draws 82W at 1000 RPM.

The trick here is that for good heat transfer efficiency you need to run a reasonably fast flow rate through the heating elements (my solar system is the black tubing type and not a panel array).

If I was running my setup with a single pump and say I set my pump to 2000 RPM the pump still only draws under 500W at this RPM so I would be in front by 200 to 300 W or so.

So while it may be a little tricky to calculate an accurate figure for overall power draw with a single pump it is certainly an option to build such a system.

On the flipside - One benefit of running two pumps on separate circuits is the redundancy that it affords.

I always have a pump in circuit to circulate water and in an emergency I can use the separate solar circuit & pump as a standby system - so if my main pump or water flow circuit fails for whatever reason and is out of action for a few days in the middle of a hot summer, there is no need to panic....

 

[rlab]

Ok yes apologies I should have increased the filter loop TDH at the faster flow rate.... but if I do that, things come out even more in favour of a dual pump system!!

That is the whole point here, that by having to unnecessarily run the filter loop at the higher flow rate required by solar, the overall TDH of the system is higher than a dual pump system.

The only way a single pump system can come out on top is if there is some fixed energy overhead in running the second pump that out weighs the increased energy use of running the single pump at a faster speed/higher TDH. That is where I am hoping someone can enlighten me... my general understanding was that fixed energy overhead in pumps is minimal, energy use is primarily from the speed the pump motor is spinning at.

 

[cfherrman]

Your solar loop will require the same amount of energy regardless of how many pumps you have. The way you save money is by putting the correct flow to the solar and not going over. Two pumps will always require more energy than one due to efficiencies. A single speed will require more energy over a vsp due to higher efficiency in the vsp and the vsp will not be over flowing the solar.

Your filter loop adding energy really in a non issue, it's like comparing the mpg of two cars, one with a 1.9l engine and one with a 2.0l engine.

The only concern of the filter loop is the head reducing the flow of the system and you don't put enough flow to the solar, vsp fix this as you buy the big one, set it, go swim.

It's your pool do what you think is best but I believe you had your answer before you even asked the question.

 

[JamesW]

In your two pump design, you're moving 60 gpm total vs 40 gpm.

That's going to take more energy.

As long as you size the plumbing correctly, the head loss is negligible.

If you use a 420 square foot cartridge filter, the head loss will be negligible.

In my opinion, the best way is to use a single variable speed pump that is controlled by the solar to change from 20 gpm to 40 gpm when the solar is activated.

As noted previously, you want to use filtered water in the panels or the panels can get clogged with debris.

In my opinion, two pumps just don't make sense.

 

[JamesW]

I'm not understanding how you're getting 33 feet of head to move 40 gpm through the solar loop using a separate pump and 66 feet of head to move 40 gpm through the filter plus solar loop with a single pump.

The head loss should be basically equivalent.

What am I missing?

What are your calculations?

 

[mas985]

The only way a single pump system can come out on top is if there is some fixed energy overhead in running the second pump that out weighs the increased energy use of running the single pump at a faster speed/higher TDH. That is where I am hoping someone can enlighten me... my general understanding was that fixed energy overhead in pumps is minimal, energy use is primarily from the speed the pump motor is spinning at.

And that is exactly why this does not work.

First, the head loss of Solar+Pool is not the sum of Solar Only + Pool Only. The Solar+Pool plumbing share the same suction and return lines plus most of the pad pluming of Solar Only. So in fact, Solar + Pool head loss is only slightly higher than Solar only plumbing. Add to that the wire to water efficiency of a small single speed pump (~25%) and you can easily see that the excess head loss of Solar+Pool is far less than the efficiency loss of the extra pump. Add to that, that there is no RPM adjustment so you cannot optimize flow rate for best efficiency. Therefore the the solar flow rate will likely be higher than necessary with a single speed pump.

For example:

Common plumbing: 2" Plumbing, 40' pump to/from pool. 5x90's each side and 5x90s on the pad with 5' of pad pipe.

Pool Only: Intelliflo Pump, Cartridge Filter, 4x3/4" eyeballs + Common Plumbing

Solar Only: SuperPump SP2600x5, 20' supply length, 65' return length, 10 4'x10' Fafco Panels, 10x90s, 1x 1 1/2" return outlet + Common Plumbing

Pool+Solar: Intelliflo Pump, Cartridge Filter, Filter check valve, 20' Supply length, 65' return length, 10 4'x10' Fafco Panels, 10x90s, 4x3/4" return outlet, return check valve + Common Plumbing

Here are the operating points and power usage:

Pool Only: 20 GPM, 1.75' Head, 525 RPM, 64 Watts (Note: Dual skimmer systems may require more flow rate for effective skimming)
Solar Only: 52 GPM, 17' Head, 3450 RPM, 667 Watts (Note: Flow rate is higher than required but no RPM control)

Pool+Solar: 40 GPM, 14' Head, 1415 RPM, 250 Watts

Pool+Solar 250 Watts vs Pool Only + Solar Only = 731 watts, almost a 500 watt deficit for the two pump setup.

However, it you use another Intelliflo for Solar Only, the new operating point would be: 40 GPM, 10' Head, 1215 RPM, 186 Watts

There is still no benefit in terms of energy efficiency. This is because each pump has it's own overhead and with a two pump system, you double the overhead. Plus with the extra cost of the pump and duplicate pluming (suction and return lines), there is more lifetime cost for a dual pump system.

But I still would argue that you want a filter in line for the solar system. You are just asking for trouble without one.

 

[rlab]

Pool+Solar 250 Watts vs Pool Only + Solar Only = 731 watts, almost a 500 watt deficit for the two pump setup.

However, it you use another Intelliflo for Solar Only, the new operating point would be: 40 GPM, 10' Head, 1215 RPM, 186 Watts

Thanks for the detailed analysis, good to have some more realistic figures! Where are you getting your IntelliFlo energy use numbers from? I couldn't find any published power use curves for IntelliFlo.

Also its interesting how much it comes down to the efficiency and TDH match of the solar pump. I suspect that in the dual pump systems that builders are offering me, they will just be throwing any old 0.5HP pump on the system and throttling it to get a reasonable flow rate. That in itself is probably a major reason to go with a single pump setup *if* the filter pump is a high quality variable speed pump (i.e. IntelliFlo).