Least noise/power pump rpm for reasonably efficient solar

[MattM]

I didn't get much help from the tech from the solar company that came out to ensure our 550 ft of heliocool solar panels was up and running (11 x 50ft panels, elevated 23-28 ft from the pump - the panels are spread across multiple roof sections). I have 3" main plumbing plus I think 2 or 2.5" plumbing on the roof and a single intelliflow vs+ pump. I do not have a flow meter yet.

Pump is on from 7am - 7pm, and solar is activated via roof temperature sensor and thresholds defined in our intellitouch automation controller.

I've confirmed that solar flows and bubbles disappear eventually with a pump rpm at 2400 or higher (haven't tested <2400rpm). At 2400rpm, the filter (quad de 100) pressure is roughly 14.5. I'm assuming our total head is somewhere between 40-55 but this is just based on guesses and various equations I've seen posted here on tfp or elsewhere. Unfortunately, I don't currently have any way to calibrate gpm.

Assuming the panels have an optimal gpm of 5 per, or 55 gpm total and that my goal is to keep solar panels running most of the day at the lowest reasonable gpm which generates the least noise and uses the least power while producing modestly efficient heating (even if suboptimal) - what rpm should I set the pump to?

I've tried 2400 and 2500rpm over the last few days and the results haven't been that great, we got a good bump from 51-55 degrees F one day but since have yet to exceed 60 degrees, mostly going up a few degrees during the day and losing nearly all of that at night. Yes, I'm in San Diego.

Solar heating will be supplemented by a safety pool cover being installed next week and a heat pump which we're troubleshooting. Solar will be the main heat source for the pool though. I understand winter won't produce swimable temps but am still trying to calibrate and work out kinks with the system prior to the start of our season in mid february.

I did some more calcs tonight, and while I can guess the optimal setting is somewhere between 2500 - 2750, I'm not sure what the lowest rpm I should use while still providing reasonable heating (as I am using an intelliflow pump, I am happy to just run the pump longer at a lower rpm - but it's unclear what the proper pump speed should be and there is a huge difference in noise and energy use of the pump between 2500rpm and 2750).

Any help/advice appreciated.

 

[mas985]

Re: Least noise/power pump rpm for reasonably efficient sola

You may need to reduce your expectations some for heat gain during this time of year. I wouldn't expect more than about 5 degree gain per day. Over time you might get up to 65 degrees without a cover and maybe 80 degrees with a cover but it depends heavily on wind, air temperature and insulation of the cover.

My guess right now is that your flow rate with solar will be around RPM/45 (53 GPM @ 2400 RPM) but if you want some more accuracy, I need to know a few more things about the pool.

What is the distance between the equipment and pool?

Does the equipment pad use 3" pipe as well?

What is the water level height relative to the pump?

What is the filter pressure at full speed without solar?

How many returns do you have and what size are the eyeballs?

Do you have a vacuum release valve on the solar panels and if so what is the height relative to the pump?

 

[MattM]

Re: Least noise/power pump rpm for reasonably efficient sola

From what I can tell after visually inspecting plumbing with tape measure and two helpful kids:
- Pipes directly to/from the pool are 3", other pipes - including solar, are 2.5"
- All water before returning to pool goes and returns from heat pump which is a quite a bit away and adds 37 ft x 2 = 74ft
- The pump is ~55ft from the pool, so ~110ft roundtrip
- The solar pipes going up to the roof are at the same place as the heat pump but plumbed separately, so add another 74ft there.
- I guess that means water is going 110ft + 74ft + 74ft before we even taken into account going up the roof
- There are no valves on the roof (according to the solar guy when I asked) - instead we have one check valve right after the filter, followed by an actuator, the panels, on the return trip going down the house wall there is something that adds air to the pipe (to keep pressure at a safe point for the panels?), and when the water returns to the equipment there is another check valve.
- The pump is likely no more than a few feet at most above the water, possibly very near water level as the concrete it is on is slightly lower than the main pool deck and the pump is not elevated off the ground at all.
- We have two sets of returns controlled by an actuator, the main set consists of 3 returns, very small - maybe 1", and there are no eyeballs (discussing this with pool builder)
- With solar off, the filter pressure at 2400rpm oscillates between 11 and 12, call it 11.5
- Not sure if it matters but when solar is turned on, we can have significant bubbles in the returns for up to 1hr, and the pipes on the roof seem to start each day empty of water so all the air up there comes back down slowly - when the pump turns off for the night, all the water falls back down which is quite noisy for about 30 seconds

 

[mas985]

Re: Least noise/power pump rpm for reasonably efficient sola

on the return trip going down the house wall there is something that adds air to the pipe (to keep pressure at a safe point for the panels?),

That would be the vacuum release valve. When the pump shuts off, the VRV allows air into the system so that the panels will drain. However, it is normally, plumbed near the top of the panels or on the supply side of the panels. Does the valve leak at all when the panels are priming?

Not sure if it matters but when solar is turned on, we can have significant bubbles in the returns for up to 1hr, and the pipes on the roof seem to start each day empty of water so all the air up there comes back down slowly - when the pump turns off for the night, all the water falls back down which is quite noisy for about 30 seconds

This may be due to the VRV location. Like I said it is normally not plumbed on the return side lower than the top of the panels.

My original guess is pretty close so with solar you will get around 53 GPM @ 2400 RPM (GPM~RPM/46) and for without solar, you should get around 69 GPM @ 2400 RPM (GPM~RPM/35).

 

[MattM]

Re: Least noise/power pump rpm for reasonably efficient sola

Thank you for your help and feedback. I'll bring up your comments about the VRV location with the pool builder and solar installer after confirming that the pipe it is on is indeed the return. Otherwise, based on your feedback, it seems like 2400-2530 would be reasonable rpm speeds to set on the pump long term.

Also, I'm unsure about whether I should ask for the heat pump to be on its own valve so that the distance to it and back is not always adding to head for normal filtration and solar - it does have some kind of internal bypass - and, perhaps for additional programming flexibility in the intellitouch. The heat pump will be only modestly used.

Thanks again for your help!