Sizing Solar and pump efficiency

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fengshui

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Jun 30, 2011
30
Santa Barbara, CA
I'm re-doing the solar on my system, and it's brought up to me the issues I have with my pumping. Here's an overview:
Intelliflo VF 3 Horsepower Pump
2 Intake pipes (One spa drain, and one pool skimmer, usually set to 100% pool)
2 Outflow pipes (One into 4 jets on the spa, and one into two jets in the main pool, usually set 50% pool/50% spa)
Both the Intake and Outflow pipe pairs go into Jandy 3-way valves into single pipes into the pump and outflow equipment.
All pipes appear to be 2".

After the pump I have a 60 sq-ft DE filter, a 8-panel Solar Heating system on my roof, and a 400k BTU Gas Heater (rarely used, and plumbed around when not used)

The pool has a suction crawler and debris bag attached at the skimmer, which takes nearly all of the flow through a speed control valve, and which blocks most of the skimmer action. In the winter, I aim to run the system at 15-20 GPM for the crawler. In the summer, I open the speed control valve appropriately and run at 32GPM (for the solar).

When I tested the system earlier this year, I reached a maximum flow of 40GPM with the pump running full out at 3450rpm and 1945 watts. Is that reasonable for a system of this sort? The solar panels recommend 4 gpm per panel. With 8 panels, that requires 32GPM, 2750rpm and 1000 watts. 10 panels would require 40GPM and a pump running full-out to optimize their heating.

Questions:
Is this a reasonable flow/power/speed rate for the system as described?
I see graphs and other pools reporting flow rates in the 80-100GPM range. This system can't get anywhere near that. Why? What part of the setup is causing the lower GPM I'm seeing?
I'd enjoy having the two additional panels, but not with a doubling of power required. Why does it take so much more power to get those last 8GPM?
Are there other steps I should consider taking to improve the efficiency of the system?
I always have air in the system outflow at startup. My assumption was that that was from the solar system vacuum breaker valve. Is that correct? Do I need to keep anything in mind regarding that?
The DE pressure gauge is hard to read, given the changing flow. At full-flow for summer, it usually starts at about 20PSI, and I backwash at about 30PSI. Is that right?
 
How did you measure the flow rate? Sounds like your are trying to use a table to tell you what the flow rate is as a function RPM, but it does not work that way. The flow rate is a function of your specific equipment and plumbing.

I think your flow rates must be higher than you think. I estimate that my little pump puts out 40gpm for my solar with no issues.

As far as cleaning the filter, we recommend doing so when the pressure rises 20-25% over the clean pressure ... so around 36psi.
 
I measured the flow rate by setting the Intelliflo VF to the flow I wanted, then waiting a minute or so for the speed to stabilize. I did this for flows from 15GPM through 40 GPM in 5GPM increments where I stopped because I was at max RPM. I hadn't seen tables before my research started tonight, although the the calculations generated from mas985's Intelliflo excel calculator did match my numbers to within 15%.
 
Ah, sorry I read VS and not VF which is much less common.

I am really surprised your flow is so low. You must have a lot of head loss, but interesting you match Mark's calculation.

It is likely that being limited to a single suction line is large contributor to the low flow rate.

Heaters can also add head loss, do you have a bypass around the gas heater?

How much does the flow rate rise with solar off?
 
jblizzle said:
Ah, sorry I read VS and not VF which is much less common.

I am really surprised your flow is so low. You must have a lot of head loss, but interesting you match Mark's calculation.

It is likely that being limited to a single suction line is large contributor to the low flow rate.

Heaters can also add head loss, do you have a bypass around the gas heater?

How much does the flow rate rise with solar off?
Click to expand...
I do have a bypass around the gas heater, and it's used maybe 8 times a year.

I expect those numbers are with the solar off (I did the measurements on New Years Eve and marked them as my "Winter" measurements), but I'm not sure.

I'm surprised too, given what others are seeing. Is there a test I could do during the day tomorrow to ascertain where the head loss is? Would I be better off running with the intake split 50/50 between pool and spa?
 
You generally should not split the suction like that as you may drain the spa if you are not returning more to the spa than you are removing. But if you ensure you still have spill over, that could show if the suction is the driver.

If that is without the solar, then the flow rate will drop even more with it on.
 
jblizzle said:
You generally should not split the suction like that as you may drain the spa if you are not returning more to the spa than you are removing. But if you ensure you still have spill over, that could show if the suction is the driver.

If that is without the solar, then the flow rate will drop even more with it on.
Click to expand...
Yeah. Right now, I'm not splitting suction.

One additional data point I should mention. I have no idea what the piping is underground. This is an old pool, and it's entirely possible that the underground piping is 1.5" or smaller. I hope not, but the only way to know for sure would be to dig, AFAIK. The bottom of the skimmer feels like 1.5", but I can't check in the dark. :)
 
My pool was built in the 70s and only had one suction line from the skimmer that was 1.5" I have made it increase to 2" above ground on the pad. And was lucky to find an abandoned pipe for a waterfall pump that I tied in as a 2nd suction line for when I run on high speed for solar.
 
It sounds like you have something setup wrong, blocking most of the water flow. An IntelliFlow running at full speed should be able to get over 100 GPM in nearly any reasonable situation. Is it possible some valve is mostly closed somewhere, blocking most of the water flow? Or are you running 100% of the flow through the solar panels? (Which is a bad idea with a pump that large.)

How are your panels plumbed? Are they in parallel or serial?
 
JasonLion said:
It sounds like you have something setup wrong, blocking most of the water flow. An IntelliFlow running at full speed should be able to get over 100 GPM in nearly any reasonable situation. Is it possible some valve is mostly closed somewhere, blocking most of the water flow? Or are you running 100% of the flow through the solar panels? (Which is a bad idea with a pump that large.)

How are your panels plumbed? Are they in parallel or serial?
Click to expand...
The panels are plumbed in parallel. They were installed by a professional, and are going to be moved to a different roof in the coming weeks (the origin of this inquiry), so that setup can be changed, if appropriate.

There no valve closed that I can see, certainly. The piping all around the pump is visible and intact. I'm going to try some tests later today. I'll bypass out both the solar and gas heaters, disconnect the crawler, and see what sort of performance I see from both the pool and spa intake and outflow valves. When I have that data, I'll post it here.
 

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fengshui said:
There no valve closed that I can see, certainly. The piping all around the pump is visible and intact. I'm going to try some tests later today. I'll bypass out both the solar and gas heaters, disconnect the crawler, and see what sort of performance I see from both the pool and spa intake and outflow valves. When I have that data, I'll post it here.
Click to expand...
I measured the flow at lunch today. Here's what I found, with both solar and gas heaters bypassed, and a fully open skimmer:
40 GPM, 1640 W, 2155 RPM (Pool In and Outflow)
40 GPM, 2040 W, 3450 RPM (Spa In and Outflow)

Looking at this, It looks like I have some headroom on the Pool side, but it's still not great. Thoughts? Should I test again with just the pool and see what flow I can get at full power?

I've attached 3 photos. The two big ones show the system from above, with the filter just out of frame on the bottom right corner of the second image. The last image shows the far side for reference. Of the collection of pipes on the right side of the frame, there's the pair of outflow pipes immediately connected to a 3-way valve, then the two inflow pipes plumbed to the 3-way valve over on the left side of the image. The final pipe is to an old school jet system for the spa which I don't use. The pipes going into the ground on the left are the solar panels.
 

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fengshui said:
40 GPM, 1640 W, 2155 RPM (Pool In and Outflow)
40 GPM, 2040 W, 3450 RPM (Spa In and Outflow)
Click to expand...
Something strange is going on. The first line shows GPM and Watt numbers that should not be able to happen at the same time at that RPM, if the RPM and GPM are correct the power should be around 500 watts, while there is pretty much no way it can draw 1.6 kW at 2155 RPM. The second line show consistent power, GPM, and RPM numbers but suggests about 95 feet of dynamic head, which is a huge amount (possible but unlikely at 40 GPM).

Unfortunately, I can't think of anything obvious that could account for these inconsistencies.
 
JasonLion said:
Something strange is going on. The first line shows GPM and Watt numbers that should not be able to happen at the same time at that RPM, if the RPM and GPM are correct the power should be around 500 watts, while there is pretty much no way it can draw 1.6 kW at 2155 RPM. The second line show consistent power, GPM, and RPM numbers but suggests about 95 feet of dynamic head, which is a huge amount (possible but unlikely at 40 GPM).

Unfortunately, I can't think of anything obvious that could account for these inconsistencies.
Click to expand...
Here is my data from December. Do you see the same inconsistency here?

40gpm 3450rpm 1945 watts max
35gpm 2895rpm 1275 watts
30gpm 2575rpm 926 watts
25gpm 2360rpm 725 watts
20gpm 2170rpm 570 watts
15gpm 1905rpm 400 watts
 
That is a mess of pipes :D

Can you add some more to get the entire picture? Maybe label what you can?
Best to host them on Photobucket (or similar site) and post the links here.
 
I think you have a broken piece of plumbing somewhere. That amount of head loss for that RPM is quite excessive. But given that you have only 20 PSI for filter pressure, that accounts for only about 1/2. The other half is before the filter so I would focus in that area. Do you have any check valves in the plumbing and have you checked to make sure they are all operating properly? Also, check the backwash valve because those have been known to cause problems.
 
I did further testing this morning. With both the heater and solar bypassed and confirmed, I was able to get to 55 GPM flow, 3450 RPM, and about 2200 kW on the system. Pressure on the filter was 32 PSI. That seems somewhat better. These settings remained regardless of how I set the valves for water inflow and outflow. Since there seems to be two independent sets of pipes from the equipment to the pool (one pool, one spa), and no equipment between those pipes and the pump, the possibility of an intake-side problem seems unlikely to me. Could this all be due to a filter that needs backwashing or that's overloaded with DE? I have a Pentair SMBW 4060 and have been loading it with 6 lbs of DE when backwashing it. The manual for the 4060 lists an expected head loss of 2 ft of water at 45GPM. If its not the filter, where else should I look?

I'll post an annotated picture later today.
 
Filters that are several years old can get throughly blocked up inside. If you have not opened it up and cleaned it out in the last year then I recommend you do so. On the other hand, if it has been cleaned in the last year then odds are we need to look elsewhere.

You wouldn't happen to have an in-floor cleaning system?
 

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