VS pump worth it in my Caretaker+SWG+Fountain system?

[dbbarron]

I have an inground system currently with a whisperflo 1.5hp pump. DE filter, heater+Jandy Aqualink RS system
It has to drive a caretaker system, a fountain (four deck jets) and a SWG.

I was working the math and it seems like the energy savings might be worth it.
Instead of running the Caretaker and pump on full for 10 hours or so,
I was thinking
2 hours at 60GPM, essentially full speed for the Caretaker (only return is caretaker and fountains)
8 hours at 30GPM, min flow for the SWG - uses 1/4 energy as full speed - run fountains at this time (2pm-10pm) - some flow will pass through caretaker also.
14 hours at 15GPM for circulation - uses minimal energy.

If I do the math, this saves me about 1/2 on electric and should give better mixing, etc.

However, I am concerned about running the Caretaker too little and having to run 30GPM for the SWG to work requiring flow that minimizes any advantage from the VS pump.

Thoughts?

db

 

[jblizzle]

I am surprised that the SWG required 30 GPM, does the manual state that?

How are you estimating costs? I would avoid any of the calculators on the manufacturers websites as they can be quite misleading.

I do not think the Caretaker will do anything useful if your pressure is too low. The nice thing about the VS would be that you could determine the minimum speed to adequately run the system.

There is no reason you need to be running the pump 24/7 and likely 10 hours is more than you currently need with your existing pump.

What is your electrical cost? With a Caretaker system, I think it will be harder for the VS pump to be cost effective since you do not have the benefit of being able to run at the low flow rates most of the time. Although you may some some $ on electricity, how many years will it take to save $900 worth?

If you wanted to save some $, you could just change the motor to a 2-speed and run the Caretaker long enough to keep the pool clean on high and run low for more hours through the fountains (might have enough power???).

 

[JasonLion]

It very much depends on what your electric rates are. If you have very high rates (say $0.40/kWh) it is worth getting a variable speed pump, but somewhere below that (roughly $0.30/kWh) you will never make back your original investment in the variable speed pump.

A couple of things to keep in mind. The better variable speed pumps (Pentair and Hayward) are more efficient even at high speed, though not nearly as much better as they are at low speed, so you save something even at 60 GPM. None of the current crop of variable speed pumps are at their peak efficiency at their lowest speed. The IntelliFlo is optimal right around 1000 RPM, while the EcoStar does best at around 800 RPM, those speed usually move more than 15 GPM and may even be enough for the SWG.

The Caretaker system doesn't need all that much total time to do it's job, half an hour is often good enough, though it varies a bit, however it can benefit from running more than once a day. Your best bet might be to run the Caretaker for half an hour to an hour two or three times a day, rather than in one block.

 

[mas985]

2 hours at 60GPM, essentially full speed for the Caretaker (only return is caretaker and fountains)

Are you sure that is all the Caretaker requires. Your current pump is probably delivering a lot more than 60 GPM. What is the filter pressure when the cleaner is running and what is the pump model # (WF-6 or WF-26)?

 

[dbbarron]

2 hours at 60GPM, essentially full speed for the Caretaker (only return is caretaker and fountains)

Are you sure that is all the Caretaker requires. Your current pump is probably delivering a lot more than 60 GPM. What is the filter pressure when the cleaner is running and what is the pump model # (WF-6 or WF-26)?

The Pump is a WFE-6.
The clean pressure of the (DE) filter is about 27psi. It only goes up a little when dirty, maybe to 30-31.
The Caretaker likes about 20-25psi on its gauge.
Only a heater (and diverter valve for the deckjets&spa) between the pump and the caretaker.
2" pipe from pump to caretaker, 1.5" from caretaker to heads.

I think the pump is capable of much more than 60psi, but I think between the caretaker and 1.5" pipe it is hitting a head limit. Thus, I might get just as effective operaion from a VS at a lower speed than the WFE-6.

And I pay $.20/kwh but only run 6 mo of the year.

Thoughts?

 

[mas985]

27 PSI is about 62' of head and if the suction adds another 8' that would be around 70' of head which means the pump is producing about 85 GPM.

But let's compare the options.

A) VS Pump (~$900)
B) New two speed pump (~$700)
C) Replace motor with a two speed motor (~$350)

I wouldn't even consider B since you have a working pump already and it is much cheaper to replace just the motor. Since the VS is about $550 more than the two speed motor, it would need to save that much more in energy.

The VS would save about 185 watts vs the two speed on higher speed at the same flow rate. On lower speed (1000 RPM for the VS), the VS would save about 285 watts over the two speed on low speed. So assuming 2 hours on high and 8 hours low, the VS would save about 2.658 kwh per day. It would take about 1000 days for the VS to overtake the two speed in terms of cost savings (~6 yrs). So I think it would probably be worth it although I don't think you probably need 8 hours of run time on low speed. You can get away with much less than that. How big is your pool?

 

[dbbarron]

Pool is 23k gal.
I think I would need to add the cost of a two speed relay to the two speed solution which helps justify the VS a bit more.
The current pump is about 5 years old so it probably has good life ahead of it, but when it goes, sounds like the VS is a no brainer.
Will have to think about replacing it sooner.....

 

[mas985]

For that size pool, 8 hours on low speed is probably overkill. My own pool, I run 1-2 hours on high speed and 2 hours on low speed and that seems to be enough to keep the pool clean. If you did the same, then there is less of an advantage to the VS. You would be saving only about 1 kwh per day and then the break even is almost 10 yrs even with a two speed controller (~$200).

The biggest savings you get is by simply reduce run time so until your current pump gives out, you shouldn't need more than about 3-4 hours of run time per day.

 

[dbbarron]

I have found in the past that reducing runtime leads to some incremental algae growth.
However, that was before switching to SWG and being far more diligent about chemical levels.
I will experiment with runtime this season (opening in 2 weeks).
db

 

[mas985]

Pump run time should have very little impact on algae growth. That was probably due to a drop in FC. With automatic feeders, including SWGs, it is important to compensate for the reduced run time in order to get the same FC residual. With a SWG, you might find that is the limiting factor because even at 100%, it will add only so much FC.