Gut check Dynamic Head and pipe size redo

zbull

Member
Mar 27, 2020
13
Atlanta, Georgia
In an effort to get an idea of TDH and since it's hard to measured buried pipe, I installed a vacuum gauge on the suction side of my 1.5HP WhisperFlo pump (WFE-6) that has a 1.5HP (2.25 THP) motor. It’s reading 6.5 inches Mercury.

The filter pressure gauge is reading 22 PSI (recently backwashed).

Using the calculations from a post by mas985 I ended up with:

Return Dynamic Head = 2.31 * 22 (Filter PSI) + 3 = 53.82

Suction Dynamic Head = 1.13 * 6.5 (Inches Mercury) = 7.345

Total Dynamic Head = 53.82 + 7.345 = 61.165

Based on the curve for the WFE-6 pump it looks like GPM would be about 95 GPM:
pentair-whisperflo-specs.gif

My IG pool is freeform and is about 20K gallons with two skimmers and one bottom drain with 1.5” piping. From what I have read the plumbing flow rate would be 3 * 42 GPM (each 1.5” pipe max flow rate) = 126GPM.

The filter is a FNS DE 60, which has a max flow rate of 120GPM. Taking the lesser of the pipe and filter flow rate, it seems the 95GPM the pump is supposedly pushing, I’m getting decent flow rate. But I would like to get more flow to my spa spillover and the bubbler on my tanning ledge (it’s just a return pointing upwards). I can’t seem to get good flow at both the spillover and the bubbler return at the same time.

I mentioned in a previous post that I am considering replacing the two skimmer baskets and piping and the two pool return runs with 2” pipe since I’ll have the pool deck torn up. Is this worth it and will I be able to get more flow for my waterfall or at least the reduced TDH from the 2” pipe may provide future flow rate if needed?

I’m thinking reducing the TDH with larger pipe will allow more flow rate. Is this right?
 

jimmythegreek

TFP Expert
Bronze Supporter
In The Industry
Aug 10, 2017
2,177
Morris Cnty NJ
It's very hard to run a bubbler and have good overflow with any pump. You would be running it full blast. Would be easier to add a second pump just for the bubbler for the times you want them both on. A seperate suction point would be ideal
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,238
Pleasanton, CA
From what I have read the plumbing flow rate would be 3 * 42 GPM (each 1.5” pipe max flow rate) = 126GPM.

The filter is a FNS DE 60, which has a max flow rate of 120GPM.
Neither filters nor pipes nor anything else has a limit to flow rate. Those are simply recommendations. Given a large enough pump, there is no fundamental limit to flow rate other than the pump.

I’m thinking reducing the TDH with larger pipe will allow more flow rate. Is this right?
Increasing pipe size will only take you so far. The rest of the plumbing will also affect the flow rate and at some point become dominant so increasing pipe size will have no effect. The single biggest contributor to head loss is probably the multi-port valve.

Also, I am surprised that the plumbing has that operating point. It is more indicative of 2" plumbing rather than 1 1/2" plumbing.

How far is the equipment from the pool?

How many suction lines are coming from the pool all the way to the pump (i.e. # parallel lines)?

How many return lines are going from the pump all the way to the pool (i.e. # parallel lines)?

Note: 2x1.5" lines has a little less head loss than a 1x2" line.
 

zbull

Member
Mar 27, 2020
13
Atlanta, Georgia
Thanks for the replies!

It's very hard to run a bubbler and have good overflow with any pump. You would be running it full blast. Would be easier to add a second pump just for the bubbler for the times you want them both on. A seperate suction point would be ideal
I have a single speed pump, so it runs full blast anyway. How would I add a separate suction line to an existing pool? What kind of second pump would I use?

Neither filters nor pipes nor anything else has a limit to flow rate. Those are simply recommendations. Given a large enough pump, there is no fundamental limit to flow rate other than the pump.
So, if I were to replace my 1.5HP pump with a 3HP pump I could increase flow rate without increasing any pipe size?

Also, I am surprised that the plumbing has that operating point. It is more indicative of 2" plumbing rather than 1 1/2" plumbing.
The pool was built in 2000. All I know about the pipes is what I can see coming out of the ground at the equipment pad. Looks to be 1.5" returns and suction lines, then 2" between equipment.

How far is the equipment from the pool?
The nearest point between the equipment and the pool is a pool return that is 17 feet. The bottom drains are about 25'. The nearest skimmer is 24', furthest is 48'. The bubbler return is 50'. The spa is about 45' away. Here is a picture:
pool1.jpg

How many suction lines are coming from the pool all the way to the pump (i.e. # parallel lines)?
As far as I can tell there are 3 suction lines from the pool: Bottom drains (I assume join as one) and two skimmers. I don't know if there are other lines that join underground. The spa has two bottom drains (I assume join as one).

How many return lines are going from the pump all the way to the pool (i.e. # parallel lines)?
Looks like two return lines, and one cleaner return. One return to the spa and one to the pool, that must split underground between the bubbler return and the regular return. We had the pool renovated this past fall and added the tanning ledge where they extended the return about 10' to the center of the ledge to create the bubbler.

Here is a labeled picture of the equipment pad piping and overall picture.
equip2.jpg

equip1.jpg

Thanks for your time!
 

Attachments

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,238
Pleasanton, CA
So, if I were to replace my 1.5HP pump with a 3HP pump I could increase flow rate without increasing any pipe size?
It depends on the shape of the head curve compared to the one you have now. But in most cases, yes, the flow rate will increase some. For example, replacing your pump with an Intelliflo would raise the flow rate from 95 GPM to about 107 GPM. That would be about a 13% increase in flow rate but an increase in energy use of a little over 30%.

I suspect they split the returns underground because the head loss is so low. Increasing the pipe size would probably not gain you much in terms of flow rate.

But if you want more flow to the bubblers and spillover, just cut off the main return or are the bubblers fed from the main return?

Also, the valve setting between the main return and spa spillover is half way between both which means you are reducing flow to both. If you set the handle such that it is in the direction of the return branch, the flow to both the spa and return would be fully open.
 

zbull

Member
Mar 27, 2020
13
Atlanta, Georgia
Thanks mas985

It depends on the shape of the head curve compared to the one you have now. But in most cases, yes, the flow rate will increase some. For example, replacing your pump with an Intelliflo would raise the flow rate from 95 GPM to about 107 GPM. That would be about a 13% increase in flow rate but an increase in energy use of a little over 30%.
Sounds like a larger pump wouldn't be worth it in terms of energy use. Bills are high enough as it is :)

I suspect they split the returns underground because the head loss is so low. Increasing the pipe size would probably not gain you much in terms of flow rate.
Sounds like here that I shouldn't bother replacing pipe when I have the pool deck torn up.

But if you want more flow to the bubblers and spillover, just cut off the main return or are the bubblers fed from the main return?
The bubbler is just one of the main returns extended to the ledge and turned upwards.

Also, the valve setting between the main return and spa spillover is half way between both which means you are reducing flow to both. If you set the handle such that it is in the direction of the return branch, the flow to both the spa and return would be fully open.
Good observation! I just moved it like this, wide open to both, but got no discernible difference:
IMG_3988.jpeg

Then moved it like this and have better flow to the spa. The bubbler is not very impressive but may be bearable, especially with the cleaner running. Tiny adjustments to the valve make a big difference in how the flow appears. I assume I'd have to adjust the spa mode so it knows where to turn when in spa mode now.
IMG_3989.jpeg

So outside of spending more electricity and the cost of a larger pump or having a dedicated bubbler pump, I'm stuck with this? Do you think a separate pump like jimmythegreek mentioned would be viable without another suction line? And the cost of running a separate pump may be as much as a larger main pump? If this were a new pool, would the bubbler be on its own pump? Would this pool call for a 1.5HP or larger pump?

Thanks again for your input.
 
Last edited:

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,238
Pleasanton, CA
If it were a new pool, I would have run a separate line from the bubbler to the pad so you would have separate control over the bubbler, spa and returns. I still think a single pump would work fine but you need the separate control over each feature.
 

zbull

Member
Mar 27, 2020
13
Atlanta, Georgia
Ok, so since I'm tearing up my pool deck to replace it with pavers, I could run a separate pipe for the bubbler and give it its own pump or at least a separate valve off the main return. And just leave the other piping as 1.5" alone?
 

jimmythegreek

TFP Expert
Bronze Supporter
In The Industry
Aug 10, 2017
2,177
Morris Cnty NJ
The problem lies in wanting to run it all at once. You mentioned running the cleaner and its effects. With water features and a single pump it's all about the zoning. Theres no pump that can handle waterfalls bubbler and returns at once. It's a choice of setting up scenarios. I have a 3 ft sheet decent and all 2" plumbing its reduced to 1.5 at waterfall input as that is what it accepts. I run my ecostar VS on 2200 rpm with nothing else flowing for what I like in flow. Doeant leave me much if I had a bubbler and other things to run. I dont have a spa so I have my panel use spa mode to shut down returns and open waterfall and adjust the rpms. In your case with 2 waterfalls and the bubbler its gonna be tight running all 3 on a single VS but it could work depending how wide the waterfalls are. Adding a pump is simple you just seperate a suction line like drains and feed new pump with it and supply the feature from the pump that you want.
 

zbull

Member
Mar 27, 2020
13
Atlanta, Georgia
In your case with 2 waterfalls and the bubbler its gonna be tight running all 3 on a single VS but it could work depending how wide the waterfalls are.
Actually there is the spa spillover and then two accent waterfalls on either side of the spillover. There is an auto-valve when the accent waterfalls are on and it splits flow from main return right before it enters the heater. I never run those accent waterfalls b/c it just makes the waterfalls and the spillover look like 3 weak waterfalls. Again, not enough flow. But sounds like a bigger pump would bump up my energy bill.

Adding a pump is simple you just seperate a suction line like drains and feed new pump with it and supply the feature from the pump that you want.
So I would add a pump and cut into the main drain suction line, then pipe that to return to the bubbler only? This water would never enter the filter then. Is there any issue with that? What type of pump would be good there?

Or what about using the cleaner booster pump? Could I split off the cleaner return and run the bubbler off the cleaner booster pump when the cleaner isn't running?

Thanks!
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,238
Pleasanton, CA
A larger pump or more pumps is going increase your power bill either way. You can't get something from nothing. The question is how many of the these features do you want to run at the same time? The more you want to run at the same time, the larger the flow rate requirement and the larger the energy use.
 
  • Like
Reactions: jimmythegreek

zbull

Member
Mar 27, 2020
13
Atlanta, Georgia
A larger pump or more pumps is going increase your power bill either way. You can't get something from nothing. The question is how many of the these features do you want to run at the same time? The more you want to run at the same time, the larger the flow rate requirement and the larger the energy use.
True. I'd like to have the bubbler and the spillover running during the normal running hours while we are enjoying the pool. I'm probably going to remove the accent waterfalls as we don't use them. So the easiest path is probably getting a larger pump (maybe this Intelliflo VS) and deal with increased energy use during peak pool use.