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