Saving electricity - replacing an old pump/motor

[pauster]

Hi,

I am trying to figure out if it makes sense to replace the motor/pump on our pool to save electricity. It seems to run smoothly (but is a tad louder than I like).

Can someone please help me make sense of this ?

According to the plate the pump is a Hayward Super pump, 1.0 HP, HS-125-JS using 6.0 amp (110 V), made in 1987 (year decoded per "The Ultimate Pool Guide"). The filter is a 27 inch / 70 GPM sand filter with 3.5 sq m.

It is a fairly basic 32x16' 22000 gallon vinyl pool - 1 main drain, 2 skimmers, 2 returns. I want a 10 hour turnover, which means 36.7 gpm (let's say it is 40 gpm).

The pump is 6 ft from one skimmer, so I have about 10+30+30 feet of pipe on the suction side (2 skimmers + main drain)

The discharge side is about 60 ft total.

According to my book 1 1/2" PVC pipe has 8.9 feet of head per 100 ft length at 40 gpm, so that adds up to 11.6 ft of head.

The filter adds about 7 ft of head, 5 for skimmers and main drain, and, say, 3 for the chlorinator

This would be under 27 ft of head. Can this be ? (in the visible plumbing there are 7 elbows which are supposedly equivalent to 7.5 ft of straight pipe each, adding another 4.4 ft of head. There is also a T-shaped valve that adds say another foot of head So we may end up at 33 ft of head total.

If I chose, say a 1/2 HP Hayward Northstar SP4005NS, I could get 70 gpm of flow. Since it is a .37kw, this would be a 3.36 amp motor ?

If the motor runs 10 hours a day I could save 2.9 KWh per day (at about 15 cents per KWh on Long Island, NY) - $13 a month, or $65 per 5 month season.

BTW the previous owners also had 2 returns integrated on the stairs but these two were disconnected behind the filter, probably because of a leak in that line a long time ago (I am guessing)

Can someone help me wit a sanity check on this ?

Thanks a lot

Patrick

[mas985]

If I chose, say a 1/2 HP Hayward Northstar SP4005NS, I could get 70 gpm of flow. Since it is a .37kw, this would be a 3.36 amp motor ?

No, kw is euro units for horse power, it does not include the efficiency of the pump. The 1/2 HP northstar uses the same current as the 3/4 HP so no energy savings. In fact it is worse since you need to run it longer for the same turnover.

If you really want to save money, then I would suggest a 2 speed pump. Your savings could be as high as 30%.

[pauster]

Thanks mas985 !

How can I calculate the actual electricity used by a certain pump ? Which models would you recommend as an energy-efficient replacement ? For 2 speed pump, what additional timers/switches would I have to install ?

I can measure what I am using to day by looking at my meter, but I have a feeling that the current pump is somewhat oversized...

Thanks

Patrick

[mas985]

You can get an estimate of energy use from the pump specifications. Normally pumps will specify the service factor amps for a given voltage (115 or 230). For example, my 1 HP Northstar pump has a 1.85 service factor which makes the pump braking HP 1.85 and is the actual HP of the pump. Labeled HP has little meaning so just ignore it. The amp rating is 7.8 amps at 230 volts which I verfied with a clamp on amp meter. So the wattage is volts times amps or 1.8 kilowatts. You will notice that this is very close to the braking horsepower. This can also be used as a good estimate.

A very good 2 speed pump is the Pentair Wisperflow but Hayward also makes a good 2 speed. In fact, you may be able to replace only the motor to get the 2 speed function of your existing pump. Just choose the same HP.

If you don't already have one, a 2 speed controller would be advisable. Most controllers have this funtion built in so if you already have one, it probably can support a 2 speed pump.

[pauster]

excellent - so if I take this one Pentair WhisperFlo

# 012485 - DUAL-SPEED UP-RATED 230V 60 HZ HIGH-SPEED 3450 RPM, LOW-SPEED 1725 RPM

* SF : 1.25
* Full Load Amps : 14.6/4.7
* Wt. : 42
* Model : WFDS-24
* Voltage : 115V
* HP : 1

it will suck 1.25 KW at full speed. I read somewhare that at the low speed it would be about 30% of that - is that the right ballpark ?

Thanks again for all your help

Patrick

[mas985]

Full speed is 14.6 Amps @ 115V = 1.7 kw and low speed is 4.7 amps @ 115V = 540 Watts. In this case, the pump uses a bit more in power than the breaking HP would suggest. The reason for this is that the efficiency is a bit less than the Northstar but still a fairly efficient pump. Better to use amps * volts to calculate power.

Note that this is an up-rated pump which would be identical to the 3/4 HP full rate. Either way it is probably more than enough pump.

You should also double check the voltage requirements. It may be able to operate at both 115v & 230v but the title says 230v while the details say 115v.

[pauster]

I'd really like to understand how these motors work in general ...

So a standard motor (under reasonable conditions, i.e. while hooked up to pool) will always run at maximum power and constanly draw the rated amps ? Even if the mechanical resistance of the pump varies due to e.g. a more or less clogged filter the amp draw is the same ? I am not questioning it, just want to understand the basics ... This would mean that the pump "tries to get the maximum flow it can achieve at the given head" and consumes always a constant amount of energy per unit of time.

I am trying to calculate cost saving / ROI for various replacement pumps and want to model actual consumption.

Regarding sizing the pressure gauge at the filter shows 15 psi (35 ft of head), so if I add suction side head of 8 ft I am at 43 ft of head - does that make sense ? The pipes around the filter and in the ground are all 1 1/2 inch PVC so I should not go higher that 44GPM which is fine for the 8-10 hour turnover.

Pump options are (some might be a little crazy)

- a regular EE pump, .5 HP such as the Northstar NS4005 although flow at 40 ft of head would be a tad too high for the plumbing

- a two-speed pump such as the smaller Pentair WhisperFlo WFDS-3
very tempting - a 115V - means I don't have to run new cables.

- PMSM based pumps such as Pentair IntelliFlo 100, 160 or the big one. They are expensive but might work out IF the energy savings are close to what Pentair claims. Do you have any idea how to estimate this ?

Thanks

Patrick

[mas985]

I'd really like to understand how these motors work in general ...

So a standard motor (under reasonable conditions, i.e. while hooked up to pool) will always run at maximum power and constanly draw the rated amps ? Even if the mechanical resistance of the pump varies due to e.g. a more or less clogged filter the amp draw is the same ? I am not questioning it, just want to understand the basics ... This would mean that the pump "tries to get the maximum flow it can achieve at the given head" and consumes always a constant amount of energy per unit of time.

More or less. The current will change slightly (<10%) with load but this can only be measured so as a first order, just use the rated amps. Also, the impeller of the pump is designed such that the motor operates near at the service factor load (i.e. full load)

The biggest impact to the pump with load changes is it's efficiency. How much work it does vs. the braking HP (BHP = HP * service factor) or energy use. Generally, if you are in the range of 45-65 feet of head, the energy efficiency of the pump may vary from 40% to 50% peaking somewhere in the middle depending on the HP of the pump. BHP efficiency can be determined by (GPM * Head (ft))/(3960*BHP). Energy efficiency is similar = (GPM * Head (ft))/(5315*KW)
Energy efficiency is a bit less than BHP efficiency depending on the pump.

So you might ask where does the extra energy go. Heat! This is why a pump will burn out if loaded too lightly or heavily.



I am trying to calculate cost saving / ROI for various replacement pumps and want to model actual consumption.

Regarding sizing the pressure gauge at the filter shows 15 psi (35 ft of head), so if I add suction side head of 8 ft I am at 43 ft of head - does that make sense ? The pipes around the filter and in the ground are all 1 1/2 inch PVC so I should not go higher that 44GPM which is fine for the 8-10 hour turnover.

Yes but remember without a suction measurement, this is only approximate but probably within +- 3 ft. Also, if you have pipes plumbed in parallel, they can each handle 44 GPM. So depending on design, the flow could be more.

Pump options are (some might be a little crazy)

- a regular EE pump, .5 HP such as the Northstar NS4005 although flow at 40 ft of head would be a tad too high for the plumbing

Ah but this is the funny thing about hydraulics. If you reduce the pump HP, the head the pump sees is reduced as well. Here is a good rule of thumb:

RPM ~ GPM
Head ~ GPM^2
BHP ~ GPM^3
Head ~ BHP^2/3
~ means proportional

So

New head = Old Head * (New BHP / Old BHP) ^ 2/3


- a two-speed pump such as the smaller Pentair WhisperFlo WFDS-3
very tempting - a 115V - means I don't have to run new cables.

- PMSM based pumps such as Pentair IntelliFlo 100, 160 or the big one. They are expensive but might work out IF the energy savings are close to what Pentair claims. Do you have any idea how to estimate this ?

You would need to get the pump curves and amp usage for each of the RPM settings. Perhaps on their web site.
Thanks

Patrick

See above.

[pauster]

Hi Mark

this was most helpful (I am a SW engineer so I lenjoy this kind of thing ) it is now MUCH clearer how thie pieces fit together.

The Intelliflo curves can be found at pg 47 of

http://www.pentairpool.com/misc/owne...User_Guide.pdf

So if today I have 40 ft of head at 40 GPM (my return is a single 1 1/2 inch PVC pipe; the previous owners deactivated the other 1 1/2 inch return; the piping around the pump and filter is a single 1 1/2 inch pipe, too, coming from 2 1 1/2 inch suction side)

If I understood yo correctly the power (KW) is proportional to GPM*Head, so I approximate .4 kW in the diagram for 35 GPM/30 ft of head.

GPM Ft head KW
40 40 0.597
35 30.625 0.400
30 22.5 0.252
25 15.625 0.146
20 10 0.075
15 5.625 0.031
10 2.5 0.009

If I run this baby 18h at 15 gpm and 2 h at 35 gpm per day, I'll use 41 KWH per month instead of 410. In a 5 month season (yes, I use the pool if the water is warmer than 67 deg here on Long Island, NY) . At $.195/kwh that's a savings of $358 per season !

Can this be true ?

Patrick

[mas985]

Unless I got your current pump curve wrong, I think your flow today with the Hayward pump is closer to 60 GPM based upon the Hayward pump curve @ 45ft of head (rounded up): http://www.haywardnet.com/products/d...m?ProductID=10

That Hayward pump has a BHP of about 1.24 because it is a max rated pump.

I am not quite sure how you did your calculations for the new pump but this is how I would do it. You current plumbing is defined by the head and GPM no matter what type of pump you use (power formulas cannot be used between pumps because efficiency curves are different). So first you need to iterate this formula for a solution that falls on the new pump curve:

New GPM = 60 * sqrt (New Head/45) where new GPM & Head must fall on new pump curve.

So for the intelliflow here are my estimates for each of the RPM settings:

3450 RPM - 85 ft head - 82 GPM - 2.6 KW - 31 GPM / KW
2070 RPM - 30 ft head - 50 GPM - 0.6 KW - 83 GPM / KW
690 RPM - 3.4 ft head - 16.4 GPM - Hard to read power

Each of these should fall on their respective curves.

This pump has a pretty high head at the top setting so you may not use it much. It also costs a lot so the payoff may be longer than a two speed pump.

A 0.75 HP Wisperflow would have the following economics:

High Speed - 55ft Head - 65 GPM - 1.7 kw - 38 GPM / KW
Low Speed - 14 ft head - 33 GPM - 0.5 kw - 66 GPM / KW

Not as good as the other pump but payoff may be sooner.