RPM vs GPM

[jmcmd1980]

Check the heater inlet temperature and compare it to the outlet temperature to see what the temperature rise is.

The SWG temperature is the heater outlet temperature.

The Temperature rise is Outlet - Inlet = Temp. Rise, which should be 16.8 degrees or less.


You can use this formula to estimate the flow based on the temperature rise.

Y = temperature rise.

X = flow in gpm.

Y = 672/X

X = 672/Y.

For example a flow of 40 gpm should be a temperature rise of 16.8 degrees.

A temperature rise of 11.2 degrees should be about 60 GPM.

As you can see, flow below 40 gpm results in a big temperature rise.

If the water temperature is 86 degrees and water boils at 212°F, then a temp rise of 126 degrees will result in boiling of the water and the heater will probably explode or be seriously permanently damaged.

A flow of 5.3 GPM or less will likely cause the water to boil and seriously damage the heater.

plot Y = 672/X, y from 6 to 60 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

plot Y = 672/X, y from 6 to 150 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

At 2750 RPM, in Pool Heat Mode, heater bypass closed, Spaool Makeup off the spa:

Inlet temperature 77 degrees
Outlet temperature into pool 88 degrees

Thanks.

Jim

 

[jmcmd1980]

Haven't we already covered a lot of this?

Setting heater bypass valve

My pool is about 5 weeks from fill. The pool installer gave very little information and training and I have been using TFP for expert assistance. Could someone advise me on setting my heater bypass valve? Should I open it completely to the heater during seasons I use the heater for the pool...

www.troublefreepool.com

Gas heater needs 2750 RPM to fire

The pool builder set my Jandy filter pump to run at 2250 in pool heater mode and 3450 in spa mode/spa heater mode. They set the system to run at 2750 RPM from 9 AM to 6 PM and gave no further instruction. I have been experimenting with variable pump speeds to save electricity. I have been...

www.troublefreepool.com

Yes, but I never really understood what the answer was and I have had 4-5 months experience with my pool now.

Pool builder set pump at 2750 RPM x 9 hrs, 3450 RPM Prime, 3450 RPM spa heat, 2250 Pool Heat, manual heater bypass about 30% open, Makeup to champagne spa 50:50 Pool to spa overflow continuous.

My desire is to run pump slower to save energy, close the heater bypass completely and not have to fuss with it unless to isolate the heater for a reason, set spaool makeup to 100% to pool, use 3 spillovers per day to refresh spa water, run prime at 2750 and pool heat at 2250, spa heat at 2750, so heater never gets over recommended GPM. I was trying to NOT modify my equipment as setup is under warranty by pool builder.

I would like to put this issue to rest also, believe me, just confused.

Jim

 

[JamesW]

At 2750 RPM, in Pool Heat Mode, heater bypass closed, Spa/pool Makeup off the spa:

Inlet temperature 77 degrees.

Outlet temperature into pool 88 degrees.

Temp rise = 11 degrees.

Flow = 672/11 = 61 GPM.

Y = temperature rise.

X = flow in gpm.

Y = 672/X

X = 672/Y.

Below is an estimate of your system curve.

So, the flow at full speed is estimated to be between about 78 GPM and 95 GPM.

 

[jmcmd1980]

At 2750 RPM, in Pool Heat Mode, heater bypass closed, Spa/pool Makeup off the spa:

Inlet temperature 77 degrees.

Outlet temperature into pool 88 degrees.

Temp rise = 11 degrees.

Flow = 672/11 = 61 GPM.

Y = temperature rise.

X = flow in gpm.

Y = 672/X

X = 672/Y.

Below is an estimate of your system curve.

So, the flow at full speed is estimated to be between about 78 GPM and 95 GPM.


View attachment 537122

So, I would assume that the slower 2700 RPM speed and GPM flow rate would be ok to run through the heater with the bypass closed? I am trying to get away from the pool builder settings to a more efficient use. Sorry to beat this issue. Thanks so much!

 

[JamesW]

So, I would assume that the slower 2700 RPM speed and GPM flow rate would be ok to run through the heater with the bypass closed?

I think that you could go as low as 1,900 RPM with the bypass closed.

Make sure that the temperature differential is not higher than 16 degrees.

 

[jmcmd1980]

I think that you could go as low as 1,900 RPM with the bypass closed.

Make sure that the temperature differential is not higher than 16 degrees.

Thanks, I will give it a try and monitor the in and out temps.

Jim