Two speed Pump selection for system with Solar

[murban7]

I need assistance with a system question…
I have a combination pool (25k) and spa (4 jets) with ground mounted solar panels (7 FAFCO panels (4' x 8') -top of solar panels are 10' above pool level)
System currently uses :
1 HP Northstar pump (SF is 1.85) with
Single 2” suction line (~20’ length to skimmer) and
Single 2” discharge line (~ 40’ to pool) with 5 eyeball outlets.
Solar panels are directly adjacent to the pump equipment - overall size is roughly 28 ft by 8 ft-
System includes a Pentair cartridge filter (300 or 400 sf), check valve and Lars heater

Question:
To reduce energy costs, I am considering replacing the single speed pump with a 2 speed pump; I am considering a Whisperflo WFDS 3 and 4 (or 24/26)
I am designing system for ~30 gpm in the filter mode (with solar) and 60+ gpm in the spa mode
My concern is related whether low speed pump discharge will have enough volume/head to overcome the static head to reach the solar panels.
Pump curves show shutoff head is ~20 ft which appears to show sufficient head to reach the top solar header
Your thoughts/concerns would be most appreciated-
Note: I am not ready to go to variable speed pump due to initial costs (would need any expensive upgrade of RS system to use these pumps)

 

[Brentr]

Welcome to TFP There are a lot of people here both who work in the industry and not so knowledgeable like myself who are always ready and willing to help.

Funny I was about to post for the same question so I would be interested in following this thread. I know that mas985 says that it can be done and I was about to post the question as what would be the parts that I would have to purchase and how to wire the system up.

 

[mas985]

I use to have a 1 HP NS pump as well and I replaced the impeller with a 1/2 HP NS impeller and then I replaced the motor with a two speed superpump motor. I call it my frankenpump. Works great and I reduced the energy consumption by close to half. Also, most people can't believe that I run a two story solar system off such a small pump but it is possible.

Anyway, there are lots of possibilities. The cheapest solution is to just replace the impeller. This will give you a lot of benefit for very little cost. You can run a smaller impeller off a larger motor without any problems. In fact, sometimes it is more efficient as larger motors tend to be more efficient and have larger operating ranges than smaller motors. Then you can decide if you want to change the motor to a two speed later or not. One thing I have found is that low speed is really only good for filtering and skimming is reduced by quite a bit so I really don't know how much time I will run the pump at low speed. Probably only when there is no solar demand which during the summer is pretty small.

You can replace the entire pump but if your current pump is in good condition, it can be much easier to do what I described above without any plumbing changes.

[EDIT]

Just noticed that you have spa jets. If the current pump produces decent feeling jets, then I would not downsize the pump. I would just replace the motor with a two speed.

As for priming the panels on low speed, I think that could be iffy at best. The pump needs to deliver both head and flow rate to prime the panels. The head loss is the height of the panels plus the dynamic head in the plumbing. That could be up to 15-20' of head. Also, the critical flow rate in 2" plumbing is around 15 GPM so I would think you need at least 30 GPM to prime the panels. That is tough to do with low speed.

 

[murban7]

thanks for your thoughts

New pump vs new motor
Current pump is 5 years old and runs fine
However, a new pump is ~$550 vs switch to a 2 spd motor is ~$350; so am thinking a new pump would be better choice- your thoughts?

REgarding priming the panels on low speed
I have a Aqualink RS6 One touch to control the system-
One potential solution is for the controller to switch the pump to high speed for a couple of minutes should the solar temperature turn on the panels during the day; after priming, pump would return to low speed

Do you think this would work? do you know if this is possible with this controller? Other ideas?

 

[mas985]

The choice between a new pump and new motor is a tough one. The wet end on a pump will usually last much longer than the motor so you could probably go for another 10 years with just a new motor. The only reason I would suggest a new motor is that it is a much easier swap out than changing the entire pump. When changing the pump, especially to a new pump line, the fittings will not be in the correct location and the correct type so you will be doing a lot of plumbing changes. Just changing the motor is much easier.

If the Aqualink controls the solar valve as well, then it will likely prevent you from using low speed with solar but I am not entirely sure. You might want to query Hayward on that. My Aqualogic will only use high speed with solar.

 

[murban7]

I did confirm with Jandy that the Aqualink can be set to run low speed with solar (i havent demonstrated this yet)

Sequence might be== Initial filter pump start is on high speed to prime the lines followed by low speed during the balance of the filtration cycle
When solar is turned on during the middle of filter cycle, filter pump at low speed will shut off for ~30 seconds to allow the solar valve to cycle and then turn back on (pump comes back on at low speed i think)

If true the control system will be ok---

However, a lingering concern (not sure if this is a problem) relates to whether water will fill the line downstream of the
solar header to the pool return-
Since the high point at the solar header is 10' above the pool, I believe that the return line to the pool will only remain full
if the pressure loss in the return line is greater than 10' loss in elevation (at 30 gpm and 80 ft of 2" line, i would expect the pressure loss to be < 10')
If so, the return line will be only partially full (is this ok if true?)

 

[mas985]

Yes, that is a concern with low speed especially if you have a vacuum release at the 10' level. One solution is to move the vacuum release lower on the supply pipe to a few feet above the pad. That way, the pressure does not need to be as high to keep it closed. Once the VR is moved and the pump switches to low speed, the panels may operate under a partial vacuum but will not lose prime since the VR will remain closed.

 

[murban7]

great- thanks for the suggestion on relocating the VR

One other thing I noticed in the CEC data regarding the Whisperflo 2 speed pumps-
These pumps come in two flavors based on max or uprated motors

Since the high speed if for Spa jets or priming, i have assumed that an efficient 1 HP pump will provide sufficient power for 4 jets
Also, since low speed pump performance is expected to be similar models with 3/4 -1.5 hp motors based on manufacturers curves, efficiency might drive pump choice

But it appears that the efficiency of these pumps are much better with the max rated motors (wfds 24 or 26 ) as compared to their equals with uprated motors (wfds 4 and 6)
For instance, WFDS 26 (1 hp with, 2 speed 230v ) is much more efficient than WFDS4 (2 speed 230v ) with same performance curve (CurveC - 6 rating vs 4.8 at low speed, 2.5 vs 2.1 at high speed)
Also, WFDS 3 (3/4 hp 2 speed 115V) is much more efficient than WFDS4 with only small loss in volume-

But i am wondering about the accuracy of the CEC data- can i rely on the CEC efficiency ratings to choose a pump model ? (or said another way, do you trust the CEC data to make these choices?)

thanks in advance for your guidance

Mark

 

[mas985]

Be careful of the CEC data for the Whisperflo's. I notified them that there are some inconsistencies and they are looking into it. But what I found was the following pumps seem to be in error:

WFDS-3
WFDS-4
WFE-3/24
WFE-4/26

Not sure why just those pumps but I think they may have mixed up the data when entering it in the database. However, I do believe that the WFDS-24, 26 are correct. So use those as a proxy for the WFDS-3 & 4. I will put that information on the orginal posting.

Also, note that the WFDS-3 uprated version is the WFDS-24 and the WFDS-4 uprated version is the WFDS-26.

 

[murban7]

Seeking further clarification

The first question relates to the electrical efficiency of an uprated motor (used by WFDS26) vs a full rated motor (used by
WFDS4)
The CEC data suggests that a pump with the same impeller but different motors has significantly different efficiency
or said another way a pump with an uprated motor translates more watts to gpm than an pump with an full rated motor ...
To add to the confusion, the pump marketers identify an uprated pump/motor as energy efficient

Question #1-- I am seeking a pump which does the job on high and low speed (see my earlier posts) as well as most efficient (if possible)
Which would you choose? WFDS 26 or WFDS 4?

Question #2-- It appears that the 2 speed 115 V pumps (wfds 3 and 24) may provide enough gpm and HP to satisfy my demands
I have initially elected to choose the more powerful pumps to add to margin of error
But it appears that by choosing the more powerful pump, i am giving up ~20% efficiency based on CEC data-
do you believe this efficiency gap (ie wfds 24 to 26) is real or is this another error in the CEC data?

thanks in advance

 

[mas985]

#1 The WFDS-4 data is suspect and I assume that all the data is suspect so I wouldn't use any of it. Theoretically, the efficiency and performance should be identical between the WFDS-4 and WFDS-26 so when making a decision, assume both pumps perform as the WFDS-26 as I think that data is correct. Either pump is really the same pump so you could just go by price to choose.

#2 You are correct in your assessment. There is really no reason to use powerful pumps unless you have a feature which requires it. But in most cases, few features really require a lot a flow rate and if they do, they need to have plumbing to support those high flow rates and in most cases don't.

#2b As for the difference between the 24 and 26, pumps will tend to follow the affinity rules for RPM as well as impeller diameter. So the ratio of GPM cubed should be about the ratio of watts. This is one way to tell if the profile is correct and yeild the correct values.

(65/61)^3 ~ 1.2
1795/1480 ~ 1.2

So yes, they do seem to correct, at least in a relative way. So the Curve A efficiencies of 2.47 vs 2.14 should be pretty close to reality.