Keep 1.5HP or go to 1HP

[trublue]

I have a Dura Glass 1.5HP original motor on a Dura Glass P2RA5F-125L pump. It was installed in May 1997 and I have changed the bearings once. Now making noise again I looked into changing the bearings, but have decided to rebuild the pump and buy a new motor. I am not interested in a 2 speed but would like some thoughts on maybe changing to a 1HP motor and impeller. Pool is 20x40 inground (35000 gal.) with a 800lb 36" sand filter. I have a SWG and now run about 8 hours a day. Pool stays beautiful with this runtime. If I go to smaller motor would I have to increase the runtime to get the same results?

I guess my question is would I save enough kwh by going to smaller motor to justify the change. I can buy a exact replacement motor and rebuild kit for $260. There is about $25 difference in price of motors if I went with 1HP. Amps on 220 are 9.6 vs 7.6.

ps/ my plumbing presents a problem for going to a different pump or I would be open to pump suggestions.

Thanks for any thoughts.

Mark

 

[jblizzle]

You will save substantially more money by going to a 2-speed and running on low speed. Low moves half the water for 1/4 the cost.

Likely you could still drop to a 1HP 2-speed which will be cheaper than the 1.5HP 2-speed and use less power ... this assumes that you do not need the higher flow rate that comes with the 1.5HP.

You are correct that if you lower the HP on the pump you need a smaller impeller.

 

[mas985]

If I go to smaller motor would I have to increase the run time to get the same results?

Not necessarily. There is no evidence that a certain amount of water needs to be turned over per day. That was an old rule of thumb that doesn't appear to be true for most pools. In fact, most pools need only 3-4 hours per day and that is independent of pump size. So the same run time may work just fine. How long are you currently running your pump?

 

[trublue]

I am running 8 hours. I mainly run that long to get the chlorine production I need from the SWG. I still have to add bleach from time to time.

 

[jblizzle]

Sounds like you would benefit from running a low speed for longer than 8 hours as it would allow more SWG output.

Please add your pool details to your signature and location to your profile as described HERE as it will help us help you.

Which SWG do you have? It is surprising that the output is maxed out unless it is undersized.

 

[mas985]

I agree with Jason. I only need 4 hours for the SWG at 65% for a 20k pool so I am surprised that you need 8 hours for a 35k pool.

 

[trublue]

Not sure about the runtime. This is only the 3rd. year that I have had the SWG. I get full sun all day and I may not be correct in the gallons, but the pool calculator seems to confirm that it is in that range.
I have Cya between 70 and 80 and keep chlorine between 5 and 6. I am running the generator at 85%.

 

[linen]

Put me in the group that suggest a 2-speed.

Your pool is large and your cell is only rated for 40000 gallons (that is assuming 24 hour swg run time). So theoretically (35000/40000)*24 hours= 21 hours of run time needed, so no wonder you have to supplement with another chlorine source. I would think you would be better off running on 2-speed pump on low for much longer.

In the future you may want to look for a larger swg cell.

 

[jblizzle]

We typically recommend a cell that is sized for 1.5-3 times the size of you pool. The T-15 is a 40k pool, so just barely bigger than your pool, so you will indeed need more run time.

A little math: The T-15 ideally generates 1.45lbs chlorine gas in 24hours at 100% output.

For 8 hours @ 85% you are creating .4108 pounds/day = 6.57 oz/day and using the poolcalculator.com that would be adding 1.4ppm of FC to your 35k pool each day

That could be reasonable. Mark apparently adds 0.9ppm/day and I am at 1.7ppm/day (although my CYA is still a little low for the amount of sun I get).

You could either increase the % output or increase the run time to avoid having to add bleach. Also realize that the minimum FC is 4ppm, so staying around 5ppm would be reasonable.

If you want to determine if there is something in the water consuming the FC, you can Perform the Overnight Chlorine Loss Test.

 

[trublue]

Not losing any chlorine overnight. I test daily with tf-100 and speedstir. As you can see I am not a rookie. Been keeping this pool for 29 years now.

I am wondering if you get enough circulation with a 2 speed on low to do justice with the skimmers. Also what impact does the lower flow have on the SWG. (does it make the same amount of cl on low and high per hour??)

 

[jblizzle]

The SWG will produce the same amount regardless of flow rate, as long as low speed makes enough flow ... my small 1HP Superflo does.

You can always run on high for a couple hours to help the skimming if needed and then low for a longer period of time ... of course you will need an extra timer to automatically switch the speeds.

 

[trublue]

Thanks for all of the replies. I ordered a 1.5-1/4HP 2 speed and an overhaul kit. Will definitely give the low speed a try.

Thanks again,
Mark