Pump Questions

[raschkec]

First off I want to thank everyone for the great information on this forum. It is a big help.

I posted my first thread on my new pool a few weeks back and got a lot of feedback on my pools pump configurations - but it has raised more questions for me and I am hoping someone can help clarify. To be honest I'm completely confused as to which way to go.


First, it was suggested that I go with a 2-speed pump rather than a 1 speed for my primary pump. The suggestion noted that I would save money by running on the lower speed. My electric rates are rather low $.09/kwh

Questions:
If I would save money by running at a lower speed why wouldn't I just need to buy a smaller pump and run it at full speed? Are we saying the extra HP is unnecessary? Or is the extra HP just to get the pump started then it runs at a lower speed?
Would the pump just need to run longer if I ran at the lower speed and only used for the higher speed when using the suction side cleaner?
​

It was additionally noted that the water feature pump might be too large. If that is the case - how would I calculate the pump needs?


Pool Size:
455 Sq ft
92 Per
16'x 38'
Depth 3.5 -> 7'
21,000 Gallons
Features:
1 Bench
Top Existing Patio
Tanning Ledge with 2 bubblers
23' of raises wall w/ 3 sheers (2 - 3', 1 - 4')
Structural Specs:
100 % Gunite 6 1/2 sack mix min 4500psi
12x12" beam construction with .5" rebar every 4' around perimeter of beam
8" walls and 6" floors
(4) Bars of 1/2" rebar pool walls/floor on 8" center
Covers and drain at 6" center
Plumbing:
Schedule 40 PVC
CPVC at pump and connections
Valve Four (4) 2" x 2.5" Jandy 3-way
Auto-Fill Line 3/4" sch 40 PVC with valve and vaccumm braker
Main Drain Paramount MDX
Six (6) pool returns
2" sch 40 PVC overflow
Control flow for weeping wall
Two Skimmer s - Pentair Bermuda with equalizer
2" direct plumbing for each skimmer and main drain with independant valves
Equpiment Specs:
(All Pentair - unless noted)
Filter 420 sq ft cartridge filter
Pump: 1.5 HP Whisperflo pump
Water Feature Pump: 1.5 HP superflo
Hayward Suction Side Automatic Cleaner
Dual Timer
Salt Water Sanitizer
Two 500 Watt Lights
Plaster:
Standard White
Tile and Coping:
Travertine

 

[JohnT]

If I would save money by running at a lower speed why wouldn't I just need to buy a smaller pump and run it at full speed? Are we saying the extra HP is unnecessary? Or is the extra HP just to get the pump started then it runs at a lower speed?
Would the pump just need to run longer if I ran at the lower speed and only used for the higher speed when using the suction side cleaner?

You need the higher speed to handle running the cleaner or vacuuming. It can also come in handy to increase skimmer action if you get a lot of debris blowing into the pool in the spring.

 

[raschkec]

Gottcha - thank you JohnT that makes a lot of sense.

Any thoughts on the water feature pump question?

 

[JamesW]

For the 3 sheer descents, you shouldn't need a separate pump. You could use the main pump. Just valve the returns so that you can divert some of the flow from normal return to the sheers.

 

[bobodaclown]

X2 what was previously posted.
The high/low speed thing is a pretty cool savings.
It's due to the Pump Affinity Law
The Pump Affinity Law is a term used to express the relationship between motor speed, flow rates, and energy consumption. While some energy savings come directly from improved motor efficiency, the majority of energy savings gained by replacing a single-speed pump with a variable speed pump is due to the Pump Affinity Law. This law quantifies that power consumption drops at a nonlinear rate as you reduce pump speed and water flow. When you cut the motor speed in half, the flow rate is also reduced to half, but the power consumption of the pool pump is reduced to 1/8th of the original draw. (Cut and Paste from: http://www.nrel.gov/docs/fy12osti/54242.pdf)

VSP/VSM (Variable Speed Pump/Motor) do get better efficiency rates than 2-speeds but with the significant higher cost your monthly savings never pay for the higher cost in the life of the motor if your electric cost are less than $.20 KWH. I think it's works out to be questionable between $0.20 and $.40 KWH, less than $.20 cents a two-speed is better, greater than $.40 a Variable Speed Motor is better.

Some reading:
http://www.troublefreepool.com/content/159-pool-pump-basics
http://www.poolplaza.com/two-speed-pumps.shtml
http://www.nrel.gov/docs/fy12osti/54242.pdf

Hope the info helps. It will probably raise more questions, but that's good. Knowledge is power.