How do I know if my pump can handle the head height for Solar?

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dannieboiz

Well-known member
Jan 16, 2015
306
San Jose, CA
I plan on installing a solar heater this season. it's a two story house, my guess is the peak of the roof will be about about 25feet high. The pump is a Hayward SP2302VSP @ max speed 0 head it's said to do 110gpm based on the chart below.

I used an online calculator and put in all my "current" pumping and the results is below. I'm more confused now looking at this chart. I'm guessing that i can fit 7 or 8 4x10 panels on the roof. if I can sneak a few more on another roof, I'll do that as well. I'm at the planning stage now, will still need to climb the roof to take measurements. Based on what's below, do we know if I'll need a bigger pump? My pool has 1.5" plumbing FWIW

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Dannie,

Looks like the pump experts are busy for the moment so I'll add this information. Not sure which online calculator you're using but the curve looks to be the performance curve for the VSP pump. You will need to contact the panel manufacturer for specific pressure loss charts for each type of panel. None of them seem to provide this online. They do however give you a "typical flow rate per panel". It varies a lot (3-6 gpm per panel) depending on the model so you really do need to contact them for your specific installation. You'll want to this anyway so you have something they have to perform to hydraulically after you purchase their panels. There is an optimization calculation they will perform to size your installation. As a rough approximation you can take your current discharge pressure at each pump speed and find this on the curve to get your flow rate for that speed. Then add the additional vertical height. So for example suppose your current discharge pressure is 10 psi at 3450 rpm. Multiply 10 times 2.31 to get Ft of head. 23.1 ft of head. At this discharge pressure and pump speed you're running about 100 gpm (wow a lot of flow!). But when you add 25 additional of vertical head for your roof you'll be closer to 50 gpm. Heliocol's manual indicates 30 gpm max for 1 1/2" header piping. You could probably increase to 2" which is good for 50 gpm. Again I would contact them with the specific layout diagram and confirm all your measurements.

This is a crude estimate and again, you need to contact the panel supplier for specifications on your specific installation. One thing that you should realize from this calculation (assuming my 10 psi discharge pressure is correct) is that you'll very likely need to run on high speed to get adequate flow for the 7-8 large panels through your system and up to the roof. I found this to be true for my installation. A way to deal with this is to bypass the solar array when you are outside of the peak solar heat period each day (say from noon to 5 pm during summer in my location). When you close the bypass you can run SWG or water features at low flow rates if needed and not burn up a lot of electricity for this time.

Unfortunately, I only have a 2-speed pump which means the motor is not the permanent magnet type you have so my power is not reduced anywhere near as much as yours will be when the panel bypass valve is closed. But I do get a LOT of benefit from the solar when it runs. On partly cloudy to sunny days I get pool temps of 86-87 deg F by late afternoon this time of year. Great for me and only a little gas heat required to make my wife happy. Late spring to early fall we're both happy with no gas heat. We use the pool a LOT so this has been a good investment for us. If you don't use the pool a lot this is not such a good investment compared to the gas heater.

I hope this is helpful.

Chris
 
dannieboiz said:
I plan on installing a solar heater this season. it's a two story house, my guess is the peak of the roof will be about about 25feet high. The pump is a Hayward SP2302VSP @ max speed 0 head it's said to do 110gpm based on the chart below.
Click to expand...
Right but there is no way that a plumbing system has 0 ft of head at 100 GPM. For that pump on full speed and with a typical 1 1/2" plumbing the flow rate without solar would be about 59 GPM @ 45' of head.

dannieboiz said:
I used an online calculator and put in all my "current" pumping and the results is below. I'm more confused now looking at this chart. I'm guessing that i can fit 7 or 8 4x10 panels on the roof. if I can sneak a few more on another roof, I'll do that as well. I'm at the planning stage now, will still need to climb the roof to take measurements. Based on what's below, do we know if I'll need a bigger pump? My pool has 1.5" plumbing FWIW
Click to expand...
With 8 4x10 panels, that is 320 sq-ft so the flow rate target should be about 32 GPM after the panels are primed. I ran a similar pump with a two story install so you have plenty of margin. At full speed (3000 RPM) with solar engaged, the maximum flow rate should be around 51 GPM (47' of head) so technically you could run at about 2050 RPM and still be ok depending on VRV placement.

You will be saving a bit on energy costs with a VS but unless you have a controller that will automatically switch speeds when solar turns off, you won't be saving as much as you could. However, you may not need to run the pump longer than the solar demand anyway.

I can give you more accurate numbers if I know the exact length for each run (pool to pad, pad to solar), the number of returns you have and the eyeball size. Also, will you be using 1 1/2" for solar or 2"? And what manufactures are you using for the panels?
 
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I realize that I can fit 4x12 panels so that's what I'll do. it'll most likely end up being 8x 4x12 Fafco. They're 2" pipe, I can switch my pump discharge to 2" up through the panels then reduce it back to 1.5 before going back into the gas heater. I don't know if this will benefit anything. I don't have the exact fitting quantity but this is the number I'm guessing based on the layout and location of where everything are. All the number below has been slightly exagerated.

Total legnth - 80
90 - 17
45 - 4

Are there motorized gate valve? I do have a very intesive home automation system that I can
probably tie a motorized gate valve to to divert water at any given time based on the pumping/sun schedule.

We spend 200-300 in gas a month during the summer to heat our pool for only a a few days a week during the summer. That's with the solar cover on most of the time. I'm very religous with covering the pool after we use it. I also have PV solar, so running the pump on high during peak sun hour will cost me very little.

I should also note that my panel will be on the north roof. I know it won't be as efficient but some reported that it helped regardlesss so I'm going to go for it anyways. WIth just the solar cover, I can hit low 80's no problem. if I can add another 10 degrees with the roof solar, I'll never need the gas heater again.
 
dannieboiz said:
Total legnth - 80
90 - 17
45 - 4
Click to expand...
Sorry but what do these numbers mean? Can you be more specific:

Pool to Pad length supply & return?
Pad to solar panel length supply & return?
Number of eyeballs and the diameter?

Exact lengths would be more helpful instead of exaggerating.

Also note that from some literature, Fafco has some of the highest head loss of any panels in the industry because of they way their headers work (~4x). This will reduce the efficiency of your VS pump.
 
Sorry should have been clearer

Total PVC both intake and return combine legnth - 20ft intake and 60ft return.
90 degrees eblow - 17 pcs
45 degrees elbow - 4 pcs

From the pump to the lowest point roof it's approximately 20ft heights is about 25ft. and then 32ft of solar straight across and another 32ft back.
 

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The eyeball diameter should be smaller than the thread unless you don't actually have any eyeballs installed. Normally they are 1" or 3/4".
 
The original numbers are pretty close to what I have now:

Without solar, flow rate is about 57 GPM @ 46' of head, 970 watts

With solar, flow rate is about 45 GPM @ 49' of head, 880 watts

A bit higher head loss with the Fafco panels.

I would put the VRV on the supply side of the panels to allow you to lower RPM a bit and save a bit more on energy costs.
 
That sounds like I should be ok with this pump @ max speed. It'll take about 7.5 hours to turn the pool over one time. So if I ran the pump between 10am to 6pm then slow it down to 1500 rpmduring the last 2 hours of sunlight, I think it would be a good start.

Is it worth going 2" from the pump and through the panel before reducing it at the heater or just stick with 1.5" all the way and only reduce at the roof where it meets the panels and out?
 
dannieboiz said:
It'll take about 7.5 hours to turn the pool over one time.
Click to expand...
Turnovers aren't really important to maintain a pool. I run my pool at a fraction (1/3) of a turnover per day. See: Pump Run Time

The numbers I posted above were for 1.5" for the solar. At 2", the flow rate increases from 45 GPM to 50 GPM and head loss drops by about 1'. But at the same flow rate (different RPM), the 2" pipe saves about 200 watts in energy.
 
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