variable speed vs dual speed pump

[terriolsen]

When I remodeled my pool last year I purchased all new equipment.

Even though I'm in SoCal with the high electricity rates (.33 per kwh), I have no water features, no heater or solar (yet), no spa... so I got the dual speed 3/4 hp Whisperflo pump rather than the variable speed. Since my previous pump was a decades-old single-speed, I expected my electrical bill to decrease substantially but it really hasn't... so now I'm wondering if I made a mistake and should have gotten that variable speed pump after all.

I run the dual speed daily at high (3450 rpm) for 2 hrs then at low (1725 rpm) for 6 more hrs. I'm looking into getting solar heating installed and my understanding is that I will need to run the pump at high for a lot longer than 2 hours if I want to get the full benefit of the solar heat since running at low won't have as much impact (please correct me if I'm wrong). No doubt that will increase my electric bill even more!

The solar panels (8 4x12s) would be on my single-story roof, ~10 feet from the equipment pad which is also about 10 feet from the pool.

I'm assuming that it costs me more to run at higher rpm than at lower. Are the variables more energy efficient at 3450 rpm than the dual at high (3450 rpm)? If I remember correctly, I'd heard the variables are more efficient at the lower speeds... but if the dual-speed can't handle the solar thing at low, then why would the variable speed be any better at it? Unless the variable is significantly more efficient at the higher rpm of 3450, then maybe I am okay with the dual. Or maybe its the 6 hrs at 1725 that's costing me more and that's why I should consider a variable instead of the dual... I'm so confused! :?

And speaking of 3450, how would I determine what speed to run the variable at and for how long during the day to get the most out of the sun?

I have seen other postings with calculation numbers but they were greek to me. I have not been able to figure out what my rates are for the dual compared to the variable. Can anyone please help me, in layman's terms, figure that out? Specifically, how much it costs me per hour at high and per hour at low, on the dual vs the variable.

Many questions, I know! Gosh, it would be so much easier if these pumps just had bottom-line price tags on them... Thanks for your help!

 

[Bama Rambler]

How long did you run your old pump?

Why are you running the pump on high for two hours?

 

[mas985]

Solar requires higher flow rates than general circulation so you are correct in that respect. However, the variable has the advantage of multiple speeds so you can fine tune the flow rates in panels for optimum heat efficiency and optimum energy consumption. You are pretty much stuck with the high speed of a two speed pump. However, if you choose the size of two speed pump accordingly, then you can get pretty good efficiency. With a 3/4 HP Whisperflo, I bet your pretty close to optimum flow rate and energy use so a variable might be better by only 10% or less for same flow rate. However, at lower speeds, the variables become much more efficient than low speed of a two speed pump so a variable could end up using half the energy of low speed but since low speed is already using 1/4 the energy of high speed, saving half as much again may not be all that much money.

 

[terriolsen]

Good call Dave -- I didn't run the pump that long before, only maybe 4 hours a day. So that could very well be part of it. I have a TightWatt timer on the pump that I have set to run in the winter for 1 hr on high and 3 hrs on low, then it changes in the Summer to 2 hrs on high and 6 hrs on low. It gradually increases/decreases to reach its maximum or minimum run time depending on the season. I have from 1 to 2 hrs on high because the skimmer, PoolCleaner and Liquidator work best on high.

There are also times when I brush the pool or add chemicals (usually acid) and run the pump on high for an hour to circulate. Do you think it would circulate just as well if I ran it on slow instead?

Mark, it was comforting to read your response! I tried to pick my equipment very carefully so I agree with you, I think I'm as close to optimum as I can be without spending twice as much for equipment that may take quite some time to break even on. I think I may be giving the variable too much credit, especially when comparing it with a dual-speed rather than a single-speed pump. If I understand you correctly then, based on my set-up, a variable would only save me 10%, maybe 20%, each month?

 

[susa]

>>There are also times when I brush the pool or add chemicals (usually acid) and run the pump on high for an hour to circulate.

While my acid dosing is fully automated with the Simpool pH system, when brushing, testing or adding some baking soda for TA, normally my VF runs at just 95 watts @ 900 rpm. I leave the system on for 24 hours due to the low power profile and retest water a couple times. Pump runs automatically in this mode 3 days a week and I make any changes or tests during those days.

 

[Bama Rambler]

At 2 hrs on high and 6 hrs on low you're using about the same amount of power as you were with 4 hrs on the old pump. I would run it on low except when I absolutely had to have high. You could run it for 8 hours on low and still save money over the 4 hours on high with the old one. If you add solar you'll have to run it some on high but if you get a good solar controller it'll only run on high when it needs to and that'll save you a little money over trying to run it on a timer.

 

[susa]

Could solar be initialized on high and then allow the system to slowly back off in speed, over a staggered sequence of slowdown events ?

 

[mas985]

I'm not sure I understand the last comment. The OP has a two speed and on low, it would open the vacuum release valve and prime would be lost in the panels.

 

[susa]

With a variable speed, is it possible ?

 

[mas985]

The placement of the VRV will determine how low of a speed you can go but there really is no need to step down the speed. Having one speed for priming the panels and a second speed for operation would be sufficient. However, if the VRV is installed at the top of the panels and the panels are installed on top of a two story roof, the priming speed will be about the same as what is required to keep the VRV closed so probably not much difference for the that scenario. The lower you plumb the VRV, the lower you can run the pump speed but priming speed will remain about the same.