Variable Speed or Not?

[peachy]

Hi guys. New member here. We're about to get a contractor to build a 25,000 gallon in-ground pool and was looking at using the variable speed pumps by either pentair or hayward. it seems according to their energy calculator that the savings on electricity is quite substantial that in fact one can recoup the purchase cost in a year's time. is this too good to be true?

i was calculating manually the cost of running a 3/4 hp pump and i came up with just $650 while their websites calculates at $1800 and $2100. what gives?! now i'm starting to question their energy savings claim. did i miss something on my calculation?

single speed 3/4 hp = 560W or 0.56kW
0.56kW x 12 hrs = 6.72kWh x 365 days = 2453 kWh/year x $0.27/kWh (rate) = $662

 

[Bama Rambler]

Look at the number of turnovers. They use 2.1 for the single speed and only 1 for the Ecostar. So they're fudging the savings by 50% right there. In order to compare apples to apples you'd have to use the same number of turnovers. You can reduce the runtime of the single speed to get one turnover and that'll make it closer. They're also not taking into account any baskwash or vacuuming time in the calculation.

 

[JasonLion]

Welcome to TFP!

Our rule of thumb is that a variable speed pump is only worth it compared to a two speed pump if your electric rates are $0.20/kwh or higher. A two speed pump is always better than a single speed pump.

As Bama already pointed out, that particular comparison is misleading at best. The minimum run time per day slider seems to have been invented solely for the purpose of biasing the results, as there really isn't any requirement for a minimum run time as such. A slider for minimum turnovers would have made far more sense.

 

[peachy]

our electric rate is $0.27/kWh. so i guess i'm in the right direction with the variable speed pump. seems like there are more members here saying that pentair is better than hayward.

my question though is how they calculated the single speed pump. the turnover of 2.1 is only a result of the hrs the pump is used. the hours, the hp and the rate should dictate the cost per season and i'm not getting the $1800+. anyone? at $600 that's 300%.

 

[jblizzle]

WAIT ... ignore everything below here while I figure out what I screwed up

OK ... now it is fixed ... ignore the warning above to ignore this :? :?

The difference is the amount of watts assumed the pump uses you say 560W and they say 1528W:

Using their "known" numbers:
$1807/365 days/12 hours = $0.413/hr ... assuming a season = 365 days
$0.418/0.27$ per kWh = 1528 Watts

 

[scooperhsd]

Where are you getting 560 Watts for a 3/4 HP ? I was using an older (like - 28 years old) 3/4 HP Hayward Powerflo II last summer for 2 weeks. I put it on my Kill-a Watt and it was showing a runtime of closer to 1KW. My current 1.5 HP energy efficient Pentair SuperFlo also shows about 1.2-1.4 KW running. In any event - running for about 1 turnover per day should net out the 3/4 HP for about 12 hours/day runtime (maybe a bit more since your pool is a bit larger than mine) (I'd figure the 3/4 HP to be doing about 30 Gallons per minute = 1800 gallons / hours => just under 14 hours / day)

Will a 2 speed or variable speed save you money ? Yes. But be realistic about what you are looking at.

 

[peachy]

The difference is the amount of watts assumed the pump uses you say 560W and they say 1528W:

jblauert,

where did you get the 1528? i went with the 3/4 hp and did a conversion from my iPhone conversion app.

 

[JasonLion]

Name plate HP has only a tenuous relationship to the actual amount of power a pump draws. Anything from 650 watts to 1400 watts is plausible based on real world measurements of many different pumps all with a name plate listing 3/4 HP. I suspect they used name plate peak amps to calculate their watts number. Peak amps will normally be well above actual real world amps.

There is a specific relationship between HP and watts that gives 560 watts for a 3/4 HP motor. But HP isn't really a well defined thing in the pump world and name plate HP has only a very loose relationship with the kind of HP that the electrical conversion factor applies to.

 

[jblizzle]

The difference is the amount of watts assumed the pump uses you say 560W and they say 1528W:

jblauert,

where did you get the 1528? i went with the 3/4 hp and did a conversion from my iPhone conversion app.

The 1528W comes from doing the math in my previous post ... starting with their season cost estimate and working backward to calculate what they had to use for the motor power usage to arrive at that cost.

 

[peachy]

seems like the number 1528 is around the max limit that jasonlion posted. i guess i can't just rely on the hp rating. I can find anything else though that would indicate the power use.... no wattage or amperage.

would you guys recommend the pentair variable speed for my 25,000 gallon pool? the pump room is about below the pool if that makes any difference.

 

[jblizzle]

I would not consider a single speed. But the advantage of the variable over a 2 speed is more of a gray area.

My electric is half the cost of yours so I am getting a 2 speed. Run high for solar and low when not needing solar. A variable pump would just allow me to dial back the high speed some for solar although I then loose heating efficiency. I am not sure a variable at low speed saves much over the low of a 2 speed.

Seems like variables are only useful to dial back the speed to reach a minimum required for a certain application. If your setup is simple and rarely need a lot of power then you may find you only run it at low speed anyway.

I am no expert but that is my impression.

 

[peachy]

i see what you're saying with running low anyways. is it possible that the low speed setting of a 2-speed be too low to be usable? if i have a variable then i have several clicks that would allow me to set the right speed.... how i would determine that is another issue.

how come the wattage isn't posted on the specs of the pumps? any idea? seems like that would represent the electric consumption better.

 

[susa]

Having recently completed my 6th complete pool renovation, a few comments and observations.

1. I'm not a pool professional, but I can do all the installations including plastering and electrical work
2. Equipment companies greatly exaggerate the performance of their tools
3. The silence of operation is worth more than the savings in power
4. The savings in power is in the hands of a capable owner who understands the full operation and programming
5. Pentair pumps beat any other maker, any day, any time (I have no stock in company..)

With all that, I run a 4br, 4soul, house in deep south, highest temps year round, 1 acre of land, sprinkler pumps, 4 heatpumps for cooling and heating and my FPL bill monthly average is below 100 USD and house is generally below 20 C year-round.

 

[JasonLion]

is it possible that the low speed setting of a 2-speed be too low to be usable?

how come the wattage isn't posted on the specs of the pumps?

It is remotely possible for a two speed on low to be too slow. That is fairly rare however. The only common situations where that comes up are solar panel systems and pressure/suction side cleaners that don't use a booster pump.

Peak watts are easy to calculate from the name plate specs (amps times volts), but real world watts vary quite a bit depending on several different factors.

 

[mas985]

Typically, the best efficiency for the Intelliflo is around 1000 RPM and that tends to have a lower flow rate than even the smallest IG two speed pump.

 

[peachy]

mas,

you're the author of that write-up regarding piping efficiency right? that's a really good deal you posted on the other thread. i think i may just go for that option as well.

http://www.poolsupplyworld.com/poolsupp ... 011018.htm

i don't have the design in front of me but my pool guys spec'd the suction line to be using 2" pipes and the return to be 1.5". there are several lines on the suction as well as the return. Do i have to make sure that each 2" equals two 1.5" on the other side to allow as little loss as possible? or were your examples basically meant for just one suction line and one or two return lines?

 

[jblizzle]

mas,

you're the author of that write-up regarding piping efficiency right? that's a really good deal you posted on the other thread. i think i may just go for that option as well.

http://www.poolsupplyworld.com/poolsupp ... 011018.htm

i don't have the design in front of me but my pool guys spec'd the suction line to be using 2" pipes and the return to be 1.5". there are several lines on the suction as well as the return. Do i have to make sure that each 2" equals two 1.5" on the other side to allow as little loss as possible? or were your examples basically meant for just one suction line and one or two return lines?

I think I recall the chart you are talking about and what is says was that the flow through one 2" is the same as two 1.5" pipes. NOT that if you are using one 2" on suction you have to use 2 1.5" on the return ... at least I think that is what you are saying.

 

[mas985]

i don't have the design in front of me but my pool guys spec'd the suction line to be using 2" pipes and the return to be 1.5". there are several lines on the suction as well as the return. Do i have to make sure that each 2" equals two 1.5" on the other side to allow as little loss as possible? or were your examples basically meant for just one suction line and one or two return lines?

The examples are not meant to be hard fast rules. There are infinite number of ways to plumb a pool, some good, some bad. The general rule of thumb is that the larger the pipe and/or the more pipes you have, the lower the head loss. I like to see either larger suction pipes or more suction pipes than the return. Do you have more details on the number of suction vs return pipes?

 

[peachy]

hi jblizzle, yeah that's what i meant.... two 1.5" equals one 2". i realize that it's a general rule and i'm just trying to apply it on multiple pipes. so since the pump only has a 2" pipe on it's in and out anyways wouldn't that be the bottleneck then?

the design calls for.....
RETURN: six 1.5" and two 1.5" of jets. every two returns (each with gate valve) are paired together.... and paired again.
SUCTION: two 2" main drains and three 2" vacuum.

btw, a cartridge filter wouldn't no longer need a multi-port valve correct?

 

[mas985]

hi jblizzle, yeah that's what i meant.... two 1.5" equals one 2". i realize that it's a general rule and i'm just trying to apply it on multiple pipes. so since the pump only has a 2" pipe on it's in and out anyways wouldn't that be the bottleneck then?

No bottleneck, smaller pipe just has more head loss per foot of length.

RETURN: six 1.5" and two 1.5" of jets. every two returns (each with gate valve) are paired together.... and paired again.
SUCTION: two 2" main drains and three 2" vacuum.

I am not sure I understand what you are describing.
Does this mean you have 8 separate return lines going from the equipment pad to the pool and 5 separate suction lines going from the pad to the pool? Also, why do you have three vacuum lines?

btw, a cartridge filter wouldn't no longer need a multi-port valve correct?

Correct, that is why cartridge filters are more energy efficient.