New Equipment TDH Calc - Am I way off?

julietalpha

New member
Jul 5, 2019
2
Las Vegas, NV
HI everyone. New pool and new equipment. Pump is Hayward TriStar VS SP3202VSP. I'm trying to get accurate TDH calculations so I can properly configure this to be energy efficient.

I picked up a vacuum gauge and a pressure gauge and hooked them up to the pump ports and got the following readings. I'm just not sure my vacuum readings are accurate, as they seem extremely low. Plumbing is 2.5" suction and 2" returns. Pool / Spa combo. Do these seem reasonable?

Pool/SPA Mode
3450 RPM = 4 in hg / 17 PSI (TDH 43.79 after 1.13 / 2.31 multipliers)
3000 RPM = 3 in hg / 14 PSI (TDH 35.73 after 1.13 / 2.31 multipliers)
2400 RPM = 1 in hg / 9 PSI (TDH 21.92 after 1.13 / 2.31 multipliers)
1725 RPM = 0 in hg / 5 PSI (TDH 11.55 after 1.13 / 2.31 multipliers)

SPA ONLY Mode
3450 RPM = 4 in hg / 23 PSI (TDH 57.65 after 1.13 / 2.31 multipliers)
3000 RPM = 3 in hg / 18 PSI (TDH 44.97 after 1.13 / 2.31 multipliers)
2400 RPM = 1 in hg / 12 PSI (TDH 28.85 after 1.13 / 2.31 multipliers)
1725 RPM = 0 in hg / 6 PSI (TDH 13.86 after 1.13 / 2.31 multipliers)

Thanks for any info!
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
14,222
Bedford, TX
Julie,

For the life of me I can't figure out why anyone would care about TDH???

What is it that you are trying to do?

If you have a VS pump you want to run it as slow as you can to get the job done.. Since you do not have a SWCG, your low speed would be what it takes to make your skimmers work well.

In my case, I run mine at about 1200 RPM about 90% of the time..

Let's see what @mas985 has to say..

Jim R.
 

JamesW

TFP Expert
Mar 2, 2011
16,384
I would say that the numbers seem reasonable. How many suction lines are open during the test?

2.5" suction plumbing indicates that the builder is probably smarter than most.

At 44 feet of head, the flow rate will be about 105 gpm.

Speed......feet.....gpm
3450.........44.......105
3000.........36.........90
2400.........22.........65
1725.........12.........45

As noted above, the best way to operate is to run as slowly as possible.

For skimming, you just need enough flow to get visible movement in the skimmer.

For a SWG, you just need enough flow to close the flow switch plus about 200 rpm for margin.

For a gas heater or solar, you need about 40 gpm

When running the heater, try to get about 40 to 45 gpm. Otherwise, go as slow as possible.

I would suggest 2,400 rpm for heating and 1,200 to 1,400 when not heating.
 
Last edited:

julietalpha

New member
Jul 5, 2019
2
Las Vegas, NV
Julie,

For the life of me I can't figure out why anyone would care about TDH???

What is it that you are trying to do?

If you have a VS pump you want to run it as slow as you can to get the job done.. Since you do not have a SWCG, your low speed would be what it takes to make your skimmers work well.

In my case, I run mine at about 1200 RPM about 90% of the time..

Let's see what @mas985 has to say..

Jim R.
I'm simply trying to get an accurate flow rate by utilizing TDH. I want this data so that I can set my VSP schedule with some level of efficiency.

I would say that the numbers seem reasonable. How many suction lines are open during the test?

2.5" suction plumbing indicates that the builder is probably smarter than most.

At 44 feet of head, the flow rate will be about 105 gpm.

Speed......feet.....gpm
3450.........44.......105
3000.........36.........90
2400.........22.........65
1725.........12.........45

As noted above, the best way to operate is to run as slowly as possible.

For skimming, you just need enough flow to get visible movement in the skimmer.

For a SWG, you just need enough flow to close the flow switch plus about 200 rpm for margin.

For a gas heater or solar, you need about 40 gpm

When running the heater, try to get about 40 to 45 gpm. Otherwise, go as slow as possible.

I would suggest 2,400 rpm for heating and 1,200 to 1,400 when not heating.
JamesW, thanks for the information. With the "SPA+POOL" numbers provided, I have the main drain open at 25% (2 drains connected to one line), skimmer open at 75%. With SPA numbers, only the SPA drain is open at 100%.

Again, just trying to get flow rates down so I can be economical.
 

JamesW

TFP Expert
Mar 2, 2011
16,384
Ok, seems like you have a pretty good understanding of what you're doing. :goodjob:

I think that the speeds that I indicated should work for you.

I would leave the skimmers open 100% all the time and the main drain about 10 to 15% open.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,736
Pleasanton, CA
I'm simply trying to get an accurate flow rate by utilizing TDH. I want this data so that I can set my VSP schedule with some level of efficiency.
You don't need to know TDH or flow rate to do that. In fact, most equipment specifications are quite conservative so if you are trying to set flow rates based upon those requirements, you may be sub-optimal for efficiency. I have found with my own equipment that the actual operation minimum flow rates where significantly lower than the specifications.

It is far better to find the minimum flow rates by trial and error. Heaters and SWGs will tell you when the flow rate is too low with low flow alarms. For skimmers, you want the water to flow over the weir door instead of around the sides to skim properly. Knowledge of the flow rate will not help you much in this case.

But you also need to take into account the state of the filter. If you do these measurements right before a cleaning, you can be assured that they will work when the filter is clean as well. However, if you do this measurement when the filter is clean, there is a good change you might be under flow when the filter is dirty. Although if your filter is clean and you determine proper RPM levels at the clean state and you normally clean the filter when the pressure rise is 25% or less (TFP recommendations), then a 15% in RPM margin at any RPM level should be sufficient to compensate for when the filter gets dirty.