Understanding variable pump speeds and their effects on flow rate and my system

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dailygenesis

dailygenesis

Gold Supporter
Nov 19, 2022
235
Oklahoma City
Pool Size
21000
Surface
Plaster
Chlorine
Salt Water Generator
Hello everyone. I am looking for some help understanding variable pump speed settings and their effects on flow rate and my system overall. I am a new pool owner as of Summer 2022. Details of my system are in my signature.

Specifically, my questions are:
  1. If my pump is running at its highest speed (which is where my builder set its "high speed" setting for both pool and spa), is it possible that the flow rate could be too high and do damage to any part of the system?
  2. Can I lower the "high speed" pump speed and, if so, how do I determine the appropriate speed to maximize efficiency but also to make sure my flow rate is within the parameters for my equipment (especially the heater)?
  3. Will this lowering of the speed have any effect on the pump's ability to self-prime and/or the effectiveness of "freeze protect" mode (which runs at the "high speed" setting)?
The heater documentation specifies a minimum flow rate of 40 GPM and a maximum of 125 GPM.

My filter system specifies a "design flow rate" of 150 GPM (I'm not sure if this is relevant but including it just in case).

My pump is a Hayward Tristar 2.7HP VSP. I am controlling it via a Hayward E-command so my options for speed settings are in percentages (100, 95, 90, etc) rather than actual RPMs.

I have been trying to research this but I get super confused about the relationship between feet of head and flow rate and pump speed, etc., etc. I haven't been able to figure this out to any degree of confidence so I'm hoping someone can. help.

Thank you in advance!
 
1. You can overdrive the filter but it your case, that is not a problem. That pump will never get near 150 GPM.

2. Lowest speed possible while still maintain good skimming action and satisfying the heater requirements. Generally, this can only be done through trial an error. For the heater, lower RPM until the heater alarms and shuts down. That is the minimum for the heater. For the skimmers, make sure water travels over the weir door instead of around it. Is the heater running all the time? If not, you can usually program a different speed for the heater when it is on vs off.

3. Priming speeds are separate from programmed runtime speeds. You can set both independently. Check the manual for programing instructions.
 
Thank so much for the reply. That is very helpful. Just a couple of follow ups:

mas985 said:
That pump will never get near 150 GPM.
Click to expand...

That's good to know. But, the heater has a max flow of 125 GPM. Is there any risk that my pump will get near that range?

mas985 said:
Is the heater running all the time? If not, you can usually program a different speed for the heater when it is on vs off.
Click to expand...
It's not running all of the time. With my controller I am limited to a few pre-programmed speed settings -- spa high speed (50-100%), pool high speed (50-100%), spa low speed (10-50%), and pool low speed (10-50%). I can also set the heater to only operate in the "high speed" settings and then, if the heater needs to come on, it will automatically switch to high speed even if programmed to run in low speed. Thus far, both of the high speed settings have been 100%, so I think more than anything I'm trying to figure out if I can lower these high speed settings. This helps.

mas985 said:
Priming speeds are separate from programmed runtime speeds. You can set both independently. Check the manual for programing instructions.
Click to expand...
I'll have to test this. From what I've seen thus far when the pump comes on it will run in whatever the "high speed" setting is for three minutes to reach prime. Not sure if the "prime" will use 100% regardless of what the "high speed" setting is. Also, same concern about freeze protect, but will have to wait for the next freeze protect event to really test that. But I assume if the flow rate is meeting the 40GPM minimum for the heater that should be plenty for freeze protection as well. My only concern about priming is really when I have to remove the pump cover and clean the filter basket in there -- re-priming after this is the only time I could see it being a problem. But if needed I could change the setting whenever that is needed.
 
dailygenesis said:
That's good to know. But, the heater has a max flow of 125 GPM. Is there any risk that my pump will get near that range?
Click to expand...
Unlikely when going through the heater as it adds enough head loss to prevent that from happening.

dailygenesis said:
It's not running all of the time. With my controller I am limited to a few pre-programmed speed settings -- spa high speed (50-100%), pool high speed (50-100%), spa low speed (10-50%), and pool low speed (10-50%). I can also set the heater to only operate in the "high speed" settings and then, if the heater needs to come on, it will automatically switch to high speed even if programmed to run in low speed. Thus far, both of the high speed settings have been 100%, so I think more than anything I'm trying to figure out if I can lower these high speed settings. This helps.
Click to expand...
The high speed does not need to be at 100%. I would set high speed just above where the heater alarms and set low speed to just above where the water goes around the weir door in the skimmer. Heater will generally be at a higher speed than the skimmer

dailygenesis said:
I'll have to test this. From what I've seen thus far when the pump comes on it will run in whatever the "high speed" setting is for three minutes to reach prime. Not sure if the "prime" will use 100% regardless of what the "high speed" setting is. Also, same concern about freeze protect, but will have to wait for the next freeze protect event to really test that. But I assume if the flow rate is meeting the 40GPM minimum for the heater that should be plenty for freeze protection as well. My only concern about priming is really when I have to remove the pump cover and clean the filter basket in there -- re-priming after this is the only time I could see it being a problem. But if needed I could change the setting whenever that is needed.
Click to expand...
I believe that controller will run the priming at full speed no matter what the high speed is. See page 3:


Also explains freeze protection.
 
mas985 said:
I believe that controller will run the priming at full speed no matter what the high speed is. See page 3:


Also explains freeze protection.
Click to expand...
Thanks again. You are right on the priming. Hadn't noticed that the manual says it will prime at "high(est)" speed. There's a separate setting in the config to set the highest allowable speed. I have that still set at 100% but then I have the high speed pool setting at 90% currently. Just tested it and it does indeed start up and prime for 3 minutes at 100% before lowering to 90%.

I guess the next thing I need to figure out is whether the highest allowable speed should be less than 100%. I would think as long as it's high enough to prime correctly, I could lower it, but probably not much harm in leaving that at 100% if you're saying I'm not going to be overpowering my equipment or plumbing.

With regards to freeze protection, I don't think it'll run at 100%. In that part, the manual says you can choose whether to run at high or low setting. My guess is that will use the high setting for the pool and the spa independently as it rotates between them but I'll have to test next time it gets below freezing to be sure.
 
JamesW said:
I would probably set a maximum speed of about 2,750 rpm and set priming time to 0 minutes unless you need priming for some reason.

If the pump stays primed while off, there is no reason to enable priming.
Click to expand...
Thanks. With my controller, I have to set the speed in percentages. If I want to achieve a particular RPM is it as simple as taking the percentage of the highest RPM? Example -- 2750/3450 = ~80% ??

Also, the only reason I really need the priming is if I am doing maintenance like cleaning the pump filter basket. It stays primed at all other times. I suppose I could just manually override to prime it if needed.
 
mas985 said:
I would set high speed just above where the heater alarms
Click to expand...
I just noticed there is a code readout on the heater unit that will show "LO" if the temperature switch or the water pressure switch throw an error. Currently, this only triggers when the pump is off entirely. Even on low speed (50%) the heater is still operable according to this code readout. Can I assume from this that even my low speed (50%) pump is sending enough flow through the heater?
 
Yes, as long as the heater runs and does not alarm, you should be fine. 50% for the heater would be reasonable given the pump and your setup. However, you might want to set the high speed at 50% and low speed even lower for when the heater is off.
 
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