Power consumption of 2 spd pump measured with and w/o solar

#1
There seems to be a lot of talk these days about saving electricity. And rightly so! Electric rates have gone way up, and people are starting to feel it in their checkbooks! I thought this to be appropriate for the "deep-end". (Even though I don't have one :( ) I have learned so much here at TFP, I thought I would share some of my experiments.

My recently completed AGP is 15x30 (12,000 gal) and I am using a Tagelus TA-60D (300lb) sand filter with a 2-speed Waterway Supreme HI-FLO pump 3/4 HP. Also installed are 2 Fafco "Solar Bear" panels each 4x20 plumbed using PVC. I can switch the solar on and off using a 3 way valve. The 2 panels are currently plumbed in series only because I didn't have all the PVC fittings I needed. I will make the change to parallel flow soon to increase GPM flow.

The pump data-plate specs are:
Model #: PSP2075-6R
Volts: 115
RPM: 3450/1725
Amps: 8.8 (Hi) and 2.6 (low) which calculates to 1012 watts (hi spd) and 299 watts low speed.

Using a Kill-A-Watt meter, I was able to determine that my pump uses significantly less power than its data-plate suggests :p

Hi-speed without solar (less head; higher flow): 745 watts
Hi-speed with solar (more head; lower flow): 662 watts
Low-speed without solar: 138 watts
Low-speed with solar: 127 watts

Let's calculate how much this will cost per month if the pump is run 10 hours per day on low speed with the solar turned on:
Cost per KwH: $0.185
KwH per day: 1.27 (127 watts div 1000 * 10 hours/day)
Days per month: 30

Cost to run pump on low speed per month: $7.05

Initial flow rate measurements seem to indicate I am only getting about 15 GPM. Hopefully this will increase when I switch the solar to parallel flow. But even this seems sufficient to keep my pool clean and warm.

Of course this does not take into consideration electric-motor startup surge, or running the pump on high-speed for cleaning or back washing, but I expect this to be a rather small cost.

I attached the pumps head/flow graph.

So the whole point of this is you can save significant money by running a 2 speed pump. I still need to do more precise flow rate measurements. Hopefully I can have those for the forum soon.

Jason M
 

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Titanium

LifeTime Supporter
Jun 26, 2007
441
SF Bay Area
#2
Jason,

Great post!

I have a Kill-A-Watt meter also, but I can't use it to measure my pool pump electrical usage since it is 240 Volt. :(

Using a Kill-A-Watt meter, I was able to determine that my pump uses significantly less power than its data-plate suggests
This is not too surprising. The motor HP rating is how much HP the motor can supply to the pump without overheating. The actual HP load is determined by the characteristics of the pump itself (impeller, head, etc.) So the pump "demands" a certain level of HP and the motor supplies that amount of demanded HP. In fact, your motor would probably supply a much greater amount of HP that its nameplate HP - perhaps as much as 1 1/2 or 2 HP. It is just that the motor will overheat at anything over 3/4 HP (or maybe a little more if the motor SF is over 1.0).

Of course this does not take into consideration electric-motor startup surge
While it is true that an electric motor will use 6-8 times normal electrical current on startup, it is also true that this startup time is only a fraction of a second. Except for very limited and special cases in industrial facilities, the "startup surge" of an electrical motor does not cost a homeowner even a fraction of a cent.

Thanks again for your great post. Can we see pictures? (We love pictures !!)

Titanium