Solar heaters - low flow

[dschembri]

Hi guys,

I wonder if someone could help me out with some advice. I had a pool installed a couple of years ago and added some solar pool heaters from arebos, as the pool is quite shaded. We have a very hot summer so I would have expected these to work very well, but I am struggling.

I have a 1.5hp pump and normally have 75% vac, 25% skimmer then leading to my inlets.

Without the heaters on, the pump is very comfortable at 10psi, but with 80% heaters, 20% inlets it is up at 18psi and the flow is visibly slow. If I reduce the valve to the heaters, no water goes to them and just goes to the pool. I believe the issue is here, in that the panels are on my flat roof (25 feet across, 28 feet up each run) so they require a lot of energy to run water through them. I've disconnected the panels and had the pipe on the roof just loop water back down and the issue is the same so I don't think its resistance in the panels.

Would a booster pump help in this case, and would it be placed after the filter prior to pumping water to the roof?

 

[ajw22]

Welcome to TFP.

The energy to pump the water up is offset by the flow back down and nets to zero.

Post pics of your equipment pad and solar panels.

Let's see what @mas985 thinks.

 

[mas985]

What is the pump make/mode?

What size is the pipe going to/from the panels?

It is normal to experience some reduction in flow rate when solar is engaged because there is extra head loss in the solar plumbing but usually it is only a minor reduction. But I would expect several PSI increase in pressure. 8 PSI change is a bit high so there may be something in the solar plumbing that is causing excess head loss.

The panels may not be priming properly that is why I need to know the pump make/model#. The pump's head curve may not be high enough to get good flow at 25' for priming.

Can you also provide some detail pictures of the plumbing setup include the solar plumbing?

 

[dschembri]

hey @mas985, appreciate the feedback!

I realise I made a mistake in my previous message, the pump is actually a 0.75hp - Hayward SPK12607XY1 (K-Flo Pump - Single Speed Pumps | Hayward). The plumbing to/from the panels on the roof is all in 42mm.

In terms of plumbing, it looks roughly like the below -



The odd corner at the bottom left is because I have a beam in the garage, it looks like this -



Then on my roof, it looks like the below -





Thanks again!

 

[mas985]

The head curve is not all that high but it should be good enough although at 18 PSI, the pump would be producing less than 25 GPM.

But with that size pipe, you should not exceed 51 GPM anyway so putting a larger pump on that size plumbing is probably not a good idea.

I think the issue is there is too much head loss in that plumbing. Pipe diameter is fairly small and you have a lot of bends. Larger pipe would certainly help but I don't know if that is an option for you.

 

[dschembri]

Yeah unfortunately increasing the size of the pipes is not something I am likely to be able to do to be honest. Would you say the biggest issue is in the U type bend around the beam that I've posted a seperate photo of?

Failure to fix this, could a booster pump, or a seperate pump entirely for the solar run potentially work in this case?

Appreciate the advice

 

[mas985]

Yeah unfortunately increasing the size of the pipes is not something I am likely to be able to do to be honest. Would you say the biggest issue is in the U type bend around the beam that I've posted a seperate photo of?

Every bend adds head loss and every foot of pipe adds head loss and the narrower the pipe the worse both are.

Failure to fix this, could a booster pump, or a seperate pump entirely for the solar run potentially work in this case?

The problem would be forcing more water through that highly restrictive plumbing. It can be done but is very inefficient, will cause very high water pressure and not something I would recommend.

I ran a few more calculations and the current pump at 18 PSI actually is probably closer to 25 GPM rather than the 30 GPM I said earlier. But the thing is that even with the largest pump in that pump line (SPK12630XY), you would only get a few more GPM (~30 GPM). The problem is that the plumbing curve is so steep, no mater what pump you put on the system, you won't gain that much flow rate.

The proper solution is to upsize the pipe.

 

[Bill1974]

Is this a new issue? Did it work fine before?

Check to make sure none of the pipes have got to warm and collapsed.

If there is air in the system it would also add to the restriction, is there anyway to bleed the system to other than running the pump and hoping the air works its way out?

It looks like all the panels are in series as opposed to parallel. Running them all in series is more restrictive and less thermally efficient (probably minimally).

If the panels can be replumbed to run in parallel it will flow more easily. Valves may need to be added to balance the flow so each panel gets a similar amount of flow.

 

[mas985]

I've disconnected the panels and had the pipe on the roof just loop water back down and the issue is the same so I don't think its resistance in the panels.

 

[dschembri]

Thanks for the feedback guys.

I feel like I always had this issue to be honest, but all of it is relatively new. Last summer I kind of accepted it, but it didn't warm up as much as I would have wanted it to. I've now decided to switch them off until I can fix the flow, as I feel its way too slow and I'm also concerned of potential damage to the pump running at that psi.

I do not currently have any non-return valves on either side, so I'm also thinking if this could be causing an issue?

In terms of series vs parallel as well as the airlocks discussion, I've thought about this last weekend to be honest. In order to test this, I disconnected all the solar sheets and just had the water pump outside on the roof without any of the panels. The pressure on the pump seemed equal to when I had the solar connected to be honest, so my assumption here is that there is no additional resistance that is being caused by the solar sheets themselves. Airlocks I would say are probably unlikely as well given the 'simple' straight lines now, but I can test this again just in case and consider filling the plumbing with water from the roof itself.

 

[mas985]

Airlocks are generally limited to gravity fed systems and/or very low pressure. The high pressure ensures that air locks are not an issue. 18 PSI can lift water almost 42 feet.

 

[Bill1974]

What size pipe is running to and from the solar? The 100 ft or so of pipe and a few fittings might be the sole reason.

 

[mas985]

The plumbing to/from the panels on the roof is all in 42mm.

 

[mas985]

With the pipe length and fittings at 25 GPM, based on the pump head curve @ 18 PSI, that solar plumbing should have about 5.5 ft of head loss which is 2.4 PSI and not the 8 PSI the OP has reported. The lift to the panels is 28' which would be 12 PSI if the panels were not priming but that would disappear after priming. There is clearly an issue with the plumbing somewhere.

Can you post more pictures of the pad plumbing?

If you turn the valve to 100% solar, what does the filter pressure rise to?

 

[Bill1974]

That is likely the reason. A 100 ft of pipe is 5.1 psi and 30gpm. Add in the fittings that could double easily. More than 30 gpm would be even more of a loss.

 

[mas985]

That is likely the reason. A 100 ft of pipe is 5.1 psi and 30gpm. Add in the fittings that could double easily. More than 30 gpm would be even more of a loss.

Re-read my post. The fittings are included and it is 5.5 ft of total head (2.4 PSI) round trip. That is what it should be but is not. Something else is adding to the head loss.

 

[dschembri]

I'm attaching photos of all the plumbing as well as the current valve setup. The plumbing is relatively straightforward, other than the previously explained beam in the garage, getting around this introduced 8 angles (each way). Unfortunately unless I consider core-drilling the beam to go straight through I do not have any other option at the moment.

In terms of the PSI itself, this ranges from 10 to 21 - 10 being with the other inlet entirely open, gradually increasing to 21 when its completely closed to force all water to go through the solar panels. I've also tried looping the pipes on the roof and eliminating the panels to check what resistance these have, and at the setting when the pump runs at 18psi it brought them down to 16psi so roughly 2psi 'lost' here.

I'm starting to wonder if I am trying to force too much water through the panels to begin with? How do I identify the sweet spot of having a good enough flow but not too much pressure? With the pump running at 14psi I can feel water passing through the solar pipes, but difficult to say how much.

 

[mas985]

I see some issues with your valve settings but I may not fully understand the setup either.

Why do you have the skimmer partially off. Those should always be 100% on. Especially if the pipe below that from the main drain that looks to be shut off. So you are drastically reducing suction side flow rate which could cause pump cavitation.

Also, in the picture of solar on, the path through the SWG is partially off while the parallel path is full off. That will increase the return side head loss which might explain why the pressure is high and the flow rate low. That valve should be fully on and probably always 100% open. Why ever restrict that path?

In the picture with solar off, it shows a valve partially close going to the inlets. Why would you do that? Again, adds head loss and reduces flow rate.

A valve that is partially off, increases head loss and reduces flow rate. Avoid that at all costs unless it is necessary like in the case of shutting off solar.

 

[dschembri]

For suction -

I have my vac 100% open and the skimmer partially open because if I open the skimmer 100% there is not enough suction in the vac for the robot to work properly (barely moves and doesn't climb walls) - it is a zodiac mx9. Does this make sense?

For the inlets -

With the main path fully open, majority of water seems to go through this path and to the pool so the chlorinator does not get enough flow (neither do the solar panels if open) so I've had to restrict this a little. With solar on, in order to get enough water to go here instead I've had to close this and also restrict the next one by a bit in order to increase the pressure at the solar pipe instead.

I was under the impression this was normal, or have I got it all wrong?

 

[mas985]

For suction -

I have my vac 100% open and the skimmer partially open because if I open the skimmer 100% there is not enough suction in the vac for the robot to work properly (barely moves and doesn't climb walls) - it is a zodiac mx9. Does this make sense?

Yes it makes sense but it does come at a cost. Those type of cleaners reduce pump performance.

With the main path fully open, majority of water seems to go through this path and to the pool so the chlorinator does not get enough flow (neither do the solar panels if open) so I've had to restrict this a little. With solar on, in order to get enough water to go here instead I've had to close this and also restrict the next one by a bit in order to increase the pressure at the solar pipe instead.

I was under the impression this was normal, or have I got it all wrong?

So is the solar return path to the pool separate from the main return path that goes through the SWG?