Calculating Foot of Head?

cdc515 · Apr 29, 2017

I am trying to calculate my foot of head but i am unsure of exactly how to do it.

I have a 20,000 gallon pool.

I have 1 skimmer
2 return lines to pool and one split into two on steps for a total of 3 Direct lines to pool with one being teed off for the steps.
Filter is Hayward DE4820 Pro-Grid 48-Square-Foot Vertical D.E. Pool Filter
Pump is Hayward SP3400VSP EcoStar VS Variable-Speed Pool Pump Energy Star Certified
Heater is Pentair 460736 MasterTemp High Performance Eco-Friendly Pool Heater, Natural Gas, 400,000 BTU

the pool equipment is 70-80 feet away from the pool depending on which return you go to, I also do not have a bottom drain.

All piping is 1.5 inches wide.

I have a salt pool that i would like to turn over 2 times a day.

How can i tell what my foot of head is for my pool?

Also.... Not sure if this plays a part either but i have two more lines going to 2 Pentair Laminars.

kadavis · Apr 29, 2017

The pump has two plugs at the bottom, one is at the strainer trap and the other is a little closer to the motor. By removing these plugs you can put a vacuum guage in the strainer housing and a pressure guage in the volute. With the pump running at the speed you want record these readings, Multiply the vacuum reading by 1.13 and the pressure reading by 2.31. Add the two together and that is your total head

Jimrahbe · Apr 29, 2017

cd,

Why? Why are you trying to make things hard on yourself? There is no requirement for a pool to have x turnovers a day.

Are you having an issue you are trying to fix with increased flow?

Thanks for posting,

Jim R.

kadavis · Apr 30, 2017

As Jimrahbe stated you really don't need to be concerned with turnover rate. Since you have a VS pump you should find the lowest flow that you can that allows for decent skimming and run the pump as long as you like. Many people on this Forum will run their pump at 1500 rpm and under and achieve great results

cdc515 · May 2, 2017

i was trying to calculate the total head because i seem to need it for every aspect of the pool calculations and sizing of equipment etc....

jblizzle · May 2, 2017

There is hardly ever a need to know the total head ... which is not a single number.

Why don't you tell us what you are trying to calculate / size and lets see if we can help.

cdc515 · May 3, 2017

I am trying to do two things.

I would like to know what speed to run my Hayward Variable speed pump at.

I would also like to see if my 2nd pool pump for my waterfalls is sized correctly as i am not getting the desired flow.

pooldv · May 3, 2017

I decided to post a discussion about my pump speeds in this thread too for future reference.

My speeds for the 011018, Intelliflo, 3hp variable speed pump are as follows.

I started at 900 rpm and got flow errors on my SWG. I tried 1000 rpm and got an occasional flow error if the filter was dirty. So, I ended up at 1100 rpm, no flow errors in 4ish years. Then I worked on the eyeballs to get good skimming. I ended up reversing the flow to counterclockwise with the eyeballs pointing pretty much parallel to the water surface. So, at 1100 rpm I get good skimming, can make chlorine and be on standby for solar heat. The pump uses 150 watts at 1100 rpm. At 10.25c/kWh I can run 24x7 for less than 12 bucks per month.

For solar I started at 1800 rpm on a hot day. First is to make sure the flow can close the VRV, vacuum release valve, which it did. Then feel the solar panels to see if they are hot. And feel the water from the returns to see if it is hot. I went up 50 rpm until the panels felt fairly cool to the touch and the water in the returns didn't feel too hot. I ended up at 1950 rpm and it uses 550 watts.

For the waterfall we usually put it on the 1950 rpm speed, if it isn't already because solar is on and then adjust the water flow with the 3way valve that splits water flow between waterfall and returns.

Since we added the heat pump last fall I wanted a little more flow than the 1100 rpm to make sure I get as much heat from it as possible. So, I run the pump at 1500 rpm when the heat pump is on. For no particular reason. I need to check the inlet and outlet temps, Hayward recommends adjusting flow so you see a 2°c temp rise.

Then the 4th speed we use is 2500 rpm which is used for extra skimming and/or bottom drain suction when cleaning up a messy pool after a storm or something.

Max speed and priming speed is set to 3000 rpm, although I'm thinking about lowering that to 2500 also.

This set up has worked great since the summer of 2012, except for the heat pump which I installed in September, 2016.

Teald024 · May 3, 2017

cdc515 said:
I have a salt pool that i would like to turn over 2 times a day.

cdc515 said:
i was trying to calculate the total head because i seem to need it for every aspect of the pool calculations and sizing of equipment etc....

cdc515 said:
I am trying to do two things.
I would like to know what speed to run my Hayward Variable speed pump at.
I would also like to see if my 2nd pool pump for my waterfalls is sized correctly as i am not getting the desired flow.

I'm going to assume that you have equipment installed and in use. If you want to go through the extraneous task of calculating the head of your system at some desired flow, we can help you do that. But.... it is ultimately not really something that you need to do. Bear with me here for a minute, you may not like or expect to hear what is written below. Let me try to bridge the gap.

You have selected an arbitrary turnover of 2x per day. This is really a meaningless and unnecessary goal. I'll try to explain why.

There are many reasons to run a pump. The most important is to make sure the water is mixed sufficiently to distribute the chemicals throughout the pool. This is usually accomplished by running for 30 mins after adding chemicals. Any longer than this time isn't really necessary if you have decent circulation.

If you are using a SWG, then you have to run the pump long enough to pass enough water through the SWG unit to make the needed FC. Flow and head are not really important other than to have enough flow to operate the SWG properly.

Other reasons are to skim the surface, filter the water, push water through a heater / solar, run fountains, bubblers, laminar jets, etc. You get the picture. To be honest, these are more of a "creature comfort" than a necessity. You only need to run the pump enough until you are satisfied with the results. This is not tied to any x number of turnovers. I think if you polled the audience, you would find that sufficient filtering is accomplished with much less than 2x turnovers. There are many cases where filtering is not the controlling factor when deciding how long to run the pump. SWG and heating are usually more time consuming. For brevity, if you care to learn more about filter times, this has been discussed many times. Feel free to use the search function to look at some previous threads on the subject.

Generally, for equipment selection, some analysis is needed to be sure to pick the right size. But it is usually based on experience of the builder and not specific calculations by the builder. Again, each piece of equipment is selected based on certain criteria with flow & head not always being the parameters used. SWG and filters are generally oversized to extend their life or increase maintenance intervals. Pumps on the other hand should not be oversized.

Pump speed selection is more of an art than a science. Pooldv gave a great explanation on how he determined pump speeds. Much is trial and error to see what works best. Pick a speed, run it, check if you are happy, adjust if needed. No one here can tell you definitively what speed to use. There are just too many variables.
As for your 2nd pool pump, it seems that at least the valves are not set correctly. At worst the pump is not sized correctly. Again, knowing the head won't change this.