Most efficient pool plumbing

[smallpool]

I'll be installing a new pool shortly and want to create the "most efficient" pool plumbing, as my current electrical rates 31 cents/Kwh. I'm trying to conserve head feet and 90 degree turns. Note that where I live in CA, I have to keep 3 ft between the filter and heater (for eventual solar addition), and I have to program my pump to be 36 gpm or less (I have a 12,000 gal pool). All lines will be 2' and my filter will be a 320 sq ft one.

Is there a more efficient way to plumb than below? There's only 3 90, "+" degrees in the below. BTW, the pool pump will be below the water line of the pool. Also note that both the heater and filter have their inlets and outlets stacked on top of each other (not to the side/back as this diagram might suggest).
skimmer
|
5 feet to pump
|
pump
pool returns +
| |
| filter
+ heater ----------------+

 

[mas985]

The most important factor in energy savings is flow rate. High flow rate equates to high energy use and visa versa. This is why two speed a VS speed pumps are important in controlling energy use. Running on lower speeds is really what saves energy.

Also, one thing to be aware of when reducing head loss in plumbing is that it will actually increase the amount the pump draws in terms of electricity. You will only save energy if you compensate for that increase in flow rate and energy use with a decrease in run time.

Lastly, in terms of head loss, pipe diameter is by far more important than the number of 90s. Reducing a 90 has almost no effect but increasing pipe size can reduce head loss by a lot. It just isn't worth the effort to try and design out 90s. If you have only one suction line, I would make sure it is 2.5". A minimum of 2" on the return side but you could go with 2.5" for everything.

I would design the plumbing based upon convenience, ease of installation and maintenance and then use a two or VS pump to minimize energy use.

 

[smallpool]

Thanks for the information about pipe sizes and 90's. However, I don't see that lowering speeds saves energy, given that I can't go over 36 gpm (CA rules for a 12,000 gal pool). For example, I got the specs for an intellflo; at 10 head, 35 pgm draws 200 W, while at 20 gpm, it draws 150 W. That means to move 700 gal, it'll take 4Kw @ 35 gpm and 5Kw @ 20gpm. That's a pretty significant savings going at the higher (and top end of my legal limit) speed.

 

[mas985]

However, I don't see that lowering speeds saves energy, given that I can't go over 36 gpm (CA rules for a 12,000 gal pool).

There is no such rule for residential pools. And it is the other way around. A commercial pool needs to turnover the pool in at least 6 hours which means the flow rate is a minimum of 33 GPM, not a maximum.

For example, I got the specs for an intellflo; at 10 head, 35 pgm draws 200 W, while at 20 gpm, it draws 150 W. That means to move 700 gal, it'll take 4Kw @ 35 gpm and 5Kw @ 20gpm. That's a pretty significant savings going at the higher (and top end of my legal limit) speed.

I don't think you are doing the analysis correctly. Head loss is not a constant with flow rate or RPM so you must solve for the head curve and the plumbing curve intersection.

On 2" plumbing (Plumbing Curve-C = 0.0082*GPM^2), here is what I get for those two flow rates:

35 GPM, 1200 RPM, 10' of head, 205 watts, EF=10.29
20 GPM, 700 RPM, 3.4' of head, 102 watts, EF=12.10

20 GPM at 700 RPM has a higher energy factor (EF=GPM*60/watts) so it will be more efficient to operate at that flow rate.

 

[smallpool]

However, I don't see that lowering speeds saves energy, given that I can't go over 36 gpm (CA rules for a 12,000 gal pool).

There is no such rule for residential pools. And it is the other way around. A commercial pool needs to turnover the pool in at least 6 hours which means the flow rate is a minimum of 33 GPM, not a maximum.
From 2010 CA Energy Code Requirements (https://bulk.resource.org/codes.gov/bsc ... 10.06.html):
(C) Filtration pumps shall be sized, or if programmable shall be programmed, so that the filtration flow rate is not greater than the rate needed to turn over the pool water volume in 6 hours or 36 gpm, whichever is greater

For example, I got the specs for an intellflo; at 10 head, 35 pgm draws 200 W, while at 20 gpm, it draws 150 W. That means to move 700 gal, it'll take 4Kw @ 35 gpm and 5Kw @ 20gpm. That's a pretty significant savings going at the higher (and top end of my legal limit) speed.

I don't think you are doing the analysis correctly. Head loss is not a constant with flow rate or RPM so you must solve for the head curve and the plumbing curve intersection.

On 2" plumbing (Plumbing Curve-C = 0.0082*GPM^2), here is what I get for those two flow rates:

35 GPM, 1200 RPM, 10' of head, 205 watts, EF=10.29
20 GPM, 700 RPM, 3.4' of head, 102 watts, EF=12.10

20 GPM at 700 RPM has a higher energy factor (EF=GPM*60/watts) so it will be more efficient to operate at that flow rate.

The 150W is what Pentair quoted (taken from their e-mail):
for example the VF pump at 35gpm with 10 feet of head will use 200 watts. If its running at 20gpm with 10 feet of head it will use 150 watts.

Sounds like the Pentair people (like myself) didn't know about the head going down when the flow goes down.

Where's a good place to learn about head, since that directly impacts the pump power? In my pool, the pump will be about 1' below (11") the waterline and about 8 feet from the pool. Does it make any sense to go to 2-1/2' pipe (do I save much in head)?

 

[mas985]

In my signature are several links. Start with Hydraulics 101 which is a sticky I wrote and which is based upon the information in the articles on Pumped 101 which have a lot more detail.

As for pipe size, head loss occurs in every piece of equipment in the pool plumbing so not only pipes and fittings but also, filters, heaters, valves, chlorinators, etc. Everything adds head loss. Depending on the setup and equipment, the pipes and fittings can be as much as 80% of the head loss. Going from 2" to 2.5" reduces head loss by 60% so a about 50% decrease in head loss overall.

But I wouldn't really focus so much on head loss if you plan on going with a two speed or VS speed pump because most of the time you will be running on the lower speeds and the difference in energy use with 2" vs 2.5" would be quite small. It only really matters when you use a single speed pump or you need to run on high speed for solar. For example, here are the two operating points for 2" vs 2.5" plumbing at 20 GPM for each:

2" Plumbing - 680 RPM, 20 GPM, 3.2' of head, 97 Watts
2.5" Plumbing - 525 RPM, 20 GPM, 1.8' of head, 83 Watts

So 2.5" plumbing would save about 14 watts which isn't a whole lot. 20 GPM will turnover the pool in 10 hours so assuming you need 10 hours of run time, which you probably won't, on a monthly basis, the 2.5" plumbing would save you about $1.30. Again, not much to get overly excited about.

 

[linen]

From 2010 CA Energy Code Requirements (https://bulk.resource.org/codes.gov/bsc ... 10.06.html):
(C) Filtration pumps shall be sized, or if programmable shall be programmed, so that the filtration flow rate is not greater than the rate needed to turn over the pool water volume in 6 hours or 36 gpm, whichever is greater

The code also stipulates later:

F. Multispeed pumps shall have controls which default to the filtration flow rate when no auxiliary pool loads are operating; and
G. For multispeed pumps, the controls shall default to the filtration flow rate setting within 24 hours and shall have an override capability for servicing.

So it appears to me that they are saying when "just filtering" you must be below the rate listed. Generally even lower is better, depending on the system.

 

[mas985]

I would consider a skimmer or cleaner as an auxiliary load and therefore the pool never operates in "filter only mode".

Anyway those regs are not really enforceable after inspection so the PO can set flow rate to anything they want to. However, because of the inspection, they may force you to use swept 90s even though the benefit is minimal.

You can always count on government to over regulate everything.

BTW, I think the link is broken to those regs.

Full California regs: http://www.energy.ca.gov/2008publicatio ... 01-CMF.PDF
Pleasanton excerpt of the CA regs for pools: http://www.cityofpleasantonca.gov/pdf/b ... pa-req.pdf