Optimal RPM for VS Pool Pump with solar panels

[crumik]

Hello,

Yesterday my old pump died on me after 20 years (Pentair SF-N1-2A, 2HP & 3450rpm). I'm planning to replace it with Pentair 342002 SuperFlo VS 2.2 HP - local Pinch & Penny is asking for $1979 for new pump and install. I'm in Orlando, FL. My plumbing looks like this:

https://imgur.com/a/MNKD42v

I have solar panels on the roof to heat the pool, house has a second floor. No idea about solar panels manufacturer or size (bought the home from someone). Regular timer, no automation. Pool size is 10,000 gallons.

I know that the biggest benefit of Variable Speed pump is the energy savings. But, the pool guy said he is planning to put it on 8h schedule with MAX rpm, and lower for the rest of the day - this seems like a complete waste for me in terms of energy savings, is it not? I would much prefer longer hours with lower RPM.

I was trying to do some research on optimal RPM and found those two links, article + 7min youtube:

Best Variable Pump Speed for Pool Energy Savings | David Mello

Learn how to calculate the best speed to run your variable speed pool pump at to efficiently keep your smart home's pool clean while saving energy and money by determining your gpm flow rate by calculating the total dynamic head without a flow meter.

www.davidmello.com

Few questions related to the whole situation:
1. What is the best way to perform an educated decision to set optimal RPM, to make sure water is heated properly while minimizing energy use? Is buying the vacuum gauge, measuring Hg, Psi and calculating TDH (like shown in the links above) plus comparing with manufacturer Performance Curve (e.g. https://www.pentair.com/en-us/produ...598/col2/image_copy.img.png/1607611270109.png) the only way to do it properly?
2. I saw some threads with people saying that 2100 - 2700 rpm is the sweet spot for solar panels. Can I just set it to a random & reasonable value, like 2400 RPM and monitor? And go down with RPM, say 100 less, and see the effect? What I'm missing here is the exact 'thing' I should monitor - just water temperature? Bubbles in the return vent? something else?
3. Am I right to say that the pool guy is not right with the proposed schedule of 8h per day on max speed and it completely defeats the purpose on VS Pump?
4. Am I hurting the solar panels by setting lower RPM in any way? Or they will be OK, as long as GPM is around 32 or more?

Thanks in advance.

 

[ajw22]

Read Solar Pool Heaters - Further Reading

You care about the flow rate and not the RPM. Most manufactures recommend 0.1 GPM/sq-ft. or about 5 GPM for a 4x12 panel. 30 GPM for 6 panels and 40 GPM for 8 panels. Lower than that and efficiency starts to drop off. Higher than that and efficiency doesn't improve much.

 

[Dave95602]

Every system is different, there is no universal RPM sweet spot. Looks like you have a valve actuator sitting unused, do you have any automation that can control the pump/actuator?

Install a flow gauge, use the flow rates per panel that AJW22 references and set RPM to achieve desired rate. Also note that initially priming the panels and pipes (getting all the air out), will require higher RPM, especially with a 2 story house. Once the panels and pipes are filled, you can usually drop to a lower RPM and still maintain flow. If your vacuum relief valve starts sucking air, you dropped RPM too much.

 

[crumik]

Thank you for the explanation and for the link, I will give it a read. 30 GPM for 6 panels or 40 GPM for 8 panels is something I can work with, at least to have a baseline. Only a matter of checking how many panels I actually have there.

Flow gauge mentioned is around $150 from what I see - so I assume the reason for the recommendations is that it's much more accurate than using the Pump Performance Curve graph + calculating TDH for specific RPM, right?

 

[ajw22]

I assume the reason for the recommendations is that it's much more accurate than using the Pump Performance Curve graph + calculating TDH for specific RPM, right?

Right.

You will never get the TDH calculation accurate.

 

[crumik]

Last one thing from me and I will try to not bother you guys any more. This is the photo of my solar panels:

https://imgur.com/a/9Jpo0rj

If anyone is able to estimate the total size in sqft just by looking at the picture, please let me know, it would help me. Thank you.

 

[ajw22]

Find out what the standard size for each roof rectangle we see.

Count the number high by the number wide of rectangles it covers.

Multiply the number of rectangles it covers by the sq in of the roof rectangles.

 

[crumik]

Thanks. I did the lazy way in the meantime: opened my house in google maps, switched to satellite view, zoomed in on the roof and got this:

https://imgur.com/a/gzecu3g

Then I clicked 'measure distance' from the Google Maps itself and measured each panel size - it seems each panel is 4" wide and 12" long. 6 panels total, each 48sqft, makes it a total of 288 sqft. Assuming 5 GPM for a single 4x12 panel, the total required GPM should be around 30 GPM. So you were exactly right with 30 GPM for 6 panels mentioned before. Thank you for your help.