# Thread: Variable speed vs. single speed

1. ## Variable speed vs. single speed

Hi all,

I have an aging pump that I think may be a culprit in my electricity consumption problem (>3000 kWh / month with just two people). It's an 11 year old AO Smith 177474 single speed. I see ads that claim that a variable speed pump can save a lot of electricity, but was hoping to get some advice on that before spending the extra \$\$\$.

Intuitively, it seems to me that what counts is how much water is pumped through the filter and chlorine dispenser per day. If so, wouldn't a pump that slows down periodically just need to run longer to pump the same number of gallons?

Also, there's nothing wrong with the water flow. A pool guy told me that it's actually exceptional. I hate to replace something that works well. Is the variable speed function in the motor? Can I just get a different motor and convert my existing pump to variable speed?

Thanks for any advice you can offer!

2. ## Re: Variable speed vs. single speed

You will see a better return on investment with a 2-speed pump over VS pump. You can generally direct fit a replacement 2-speed motor to your current wet end with very little effort. Adding a VS motor to a wet end not made for a VS motor isn't always as easy or possible and much more expensive. A two speed when running on low will use roughly 30% of the energy than your single speed uses when its running at full speed. Without knowing the how your pool is plumbed I cant say for sure but it s pretty good bet you will have enough water flow on low speed to circulate and chlorinate your pool. You would probably only use the high speed on the pump to vacuum the pool. The extra cost for the VS pump, which would likely be a full pump replacement for you, is hard to offset if your electricity rates are lower than \$0.18/KW.

3. ## Re: Variable speed vs. single speed

Thank you! I hadn't actually thought about the distinction between 2-speed and VS. Our rates are quite a bit lower than that. It's on a sliding scale where you pay more per unit if your electricity consumption is higher. From my bill:

Energy Charge − first 500 kWh (500 kWh at \$0.076) \$38.00
Energy Charge − next 500 kWh (500 kWh at \$0.0864) \$43.20
Energy Charge − over 1000 kWh (2,055 kWh at \$0.0971) \$199.54

(Edit: I forgot there's an additional \$0.0063 / kWh added to each of those for a "Power Cost Adjustment, whatever that means, so the total is about \$300 even for energy charges)

I currently run my pump for eight hours a day with the dial on the chlorine dispensing cylinder thingamabob about half open. This was on the pool shop's advice. He said that it takes about that to cycle a pool the size of mine, and said it needs a daily complete cycle. I saw another post here just now that a complete cycle isn't necessary as long as you're happy with how much it cleans and there's enough chlorine. We have a screened pool cage and don't get much debris, so maybe I'm just overkilling it. I'll try a shorter cycle with the dispenser wide open to see how it works out. I appreciate the advice!

4. ## Re: Variable speed vs. single speed

Does anyone know of a cross reference chart that will tell me what motors I can directly fit to my Whisperflo WF-24? Am I tied to AO motors, or is there usually a variety of brands that will fit a given pump?

5. ## Re: Variable speed vs. single speed

You can use a Century B2980 for 230v or a B2981 for 115v.

6. ## Re: Variable speed vs. single speed

I would calculate what your cost is now for running the current pump and then take the best case scenario to figure out what a 2 speed & VS would cost for the same time period. I've pasted a formula I use when comparing things. My electricity bill went crazy this year but after looking at it, I kept the AC 2 degrees lower and the charge was increased over last year. So consider other sources of your high electric use too. When I saw the total bill I assumed it was my gas heater usage but turns out to be electricity.

In order to calculate the average operating cost for any electrical appliance you can use the following formula:

watts/1000 = kW x hours of operation = kWh x kWh rate = cost

Watts can usually be found on the appliance nameplate. If the nameplate lists amps:
volts x amps = watts

Example: How much does it cost to operate a portable electric heater? An electric heater wattage is usually given on the unit itself, or with the literature that comes with it. Our example is 1000 watts. Say you use the heater an average of 45 hours during winter months (1/2 hour per day for the three winter months). The City Electric Service electric rate during the winter is \$.068 (found on your bill).

So -
1000 watts/1000 = 1 kW x 45 hours of operation = 45 kWh x \$.068 = \$3.06
Now take an 8 amp heater. The calculation changes just a bit:
8 amps x 120 volts household current = 960 watts/1000 = .96 kW x 45 hours = 43.2 kWh x \$.068 = \$2.94

My own pool pump (single speed):

1,840 watts (115 volts X 16 amps per Jandy)
1840 / 1000 = 1.84 kW X 8 hours of operation = 14.72 kWh X \$.10 (cost/kWh) = \$1.472 per day to run pool pump (\$44.16 / month & \$185.47 for summer of 2016 (May 14 – September 17).

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