DIY solar pool heater - air lock issue

[Jfwetz]

Hi all - see attached photo of my home grown solar heater. 3 arrays, flow is in the bottom, out the top of the panels. Works pretty well - measured a 5-8° temp increase depending on conditions.

Have a problem with the top row getting an air lock on the two highlighted panels. Added a VRV this season but the problem persists. I manually disconnect the panels and purge air out of them and they work fine for a while then flow stops through them again.

Pressure at the filter is consistently about 15psi. Pump is a 1 HP Hayward superpump.

Any ideas to fix

 

[mas985]

Are the outer panels hot to touch?

Is the solar valve adjusted for 100% flow into the panels?

I think the issue you may have has more to do with pressure differentials. Basically, the outer panels are not getting enough flow rate to purge the air out of the panels and the reason they are not getting enough flow rate is because there is not enough pressure differential between the inlet and outlet of those two panels.

This is likely due to the configuration of the feed pipes as they are currently on the same side of the panels. They really should be on opposite sides of the panels to ensure a more equal distribution of pressure. The ground slope does not help the issue either.

Can you also post a picture of the rest of the plumbing connections to the equipment?

How much tubing is in each sub-panel?

What is the pipe size for the supply and the return? The supply looks smaller than 1 1/2"

How does the solar exit into the pool?

 

[Flying Tivo]

Could you have a sucction side leak that is pumping air into the system?

 

[Jfwetz]

Are the outer panels hot to touch?

Is the solar valve adjusted for 100% flow into the panels?

I think the issue you may have has more to do with pressure differentials. Basically, the outer panels are not getting enough flow rate to purge the air out of the panels and the reason they are not getting enough flow rate is because there is not enough pressure differential between the inlet and outlet of those two panels.

This is likely due to the configuration of the feed pipes as they are currently on the same side of the panels. They really should be on opposite sides of the panels to ensure a more equal distribution of pressure. The ground slope does not help the issue either.

Can you also post a picture of the rest of the plumbing connections to the equipment?

How much tubing is in each sub-panel?

What is the pipe size for the supply and the return? The supply looks smaller than 1 1/2"

How does the solar exit into the pool?

Thanks for your response.

The supply branches are 1” pvc fed from 1.5 inch. Supply happens after the filter via Jandy 3 way valve set at about 50%. Returns are 1.5” through a Jandy check valve to pool returns.

The panels each have 100 feet of 1/2” rainbird tubing. In and outs of the panels are 1/2 “ connections.

I’ll get some more pictures tonight -thanks for your help!

 

[mas985]

Thanks for your response.

The supply branches are 1” pvc fed from 1.5 inch. Supply happens after the filter via Jandy 3 way valve set at about 50%.

That is likely your issue. You are are not redirecting enough flow to the panels. A 50% valve setting does not mean half the water goes to the panels and half is bypassed. It is much more complicated than that due to head loss differences in the paths.

The main issue is that there is not enough flow rate to fully prime the panels.

One way to test this is to slowly increase the flow to the panels and watch the pool returns and see if air comes out. At some point, the air will stop and that is going to be your new setting.

 

[mas985]

Works pretty well - measured a 5-8° temp increase depending on conditions.

Is that inlet to outlet temperature increase?

That is too much and indicates flow rates that are too low.

Heat transfer from the panels to the pool is dependent on not only the heat rise from inlet to outlet but also the flow rate. If you halve the flow rate, the heat rise doubles but the amount of potential heat to the pool remains the same. However, the heat loss from higher outlet temperatures also increases so it is much less efficient to run at lower flow rates with higher temperature differentials as it is to run at high flow rates at lower temperature differentials.

Here is a typical solar panel efficiency curve vs flow rate:

 

[1poolman1]

Hi all - see attached photo of my home grown solar heater. 3 arrays, flow is in the bottom, out the top of the panels. Works pretty well - measured a 5-8° temp increase depending on conditions.

Have a problem with the top row getting an air lock on the two highlighted panels. Added a VRV this season but the problem persists. I manually disconnect the panels and purge air out of them and they work fine for a while then flow stops through them again.

Pressure at the filter is consistently about 15psi. Pump is a 1 HP Hayward superpump.

Any ideas to fix

First find the source of the air, there really shouldn't be any in a properly sealed system.
Second, it looks like those panels are on a slight slope. Does each array feed from the bottom or top. If from the top there will always be a problem with trapped air.

 

[Jfwetz]

The panels feed from the bottom and out the top. Yes - the panels get very hot when the flow is not happening. The diverter is set to about 50 % thru the solar panels. Just the top row is the problem. The VRV I added this season hasn’t helped

 

[mas985]

Again, have you tried adjusting the solar valve so more flow goes to the panels?

 

[Jfwetz]

That is likely your issue. You are are not redirecting enough flow to the panels. A 50% valve setting does not mean half the water goes to the panels and half is bypassed. It is much more complicated than that due to head loss differences in the paths.

The main issue is that there is not enough flow rate to fully prime the panels.

One way to test this is to slowly increase the flow to the panels and watch the pool returns and see if air comes out. At some point, the air will stop and that is going to be your new setting.

Thanks so much for your help. Did that this morning - immediately got air bubbles in the check valve and pool. The panels are cool to touch. Pressure at DE 4800 filter bumped to about 18psi Would have thought the VRV would let air escape as the system powers up. Attached feed and return picture

 

[Jfwetz]

Thanks so much to everyone that responded - great help and info. My solar heating system has been cobbled together as a series of prototypes and iterations. Any suggestions on how to improve, let me know.

It’s been a good pool season here in the Cincinnati area - very sunny and hot. I don’t cover the pool and the heat pump has only run a few times for very short periods. I do notice a lower electricity bill than last year.

 

[mas985]

Thanks so much for your help. Did that this morning - immediately got air bubbles in the check valve and pool. The panels are cool to touch. Pressure at DE 4800 filter bumped to about 18psi Would have thought the VRV would let air escape as the system powers up. Attached feed and return picture

If the pressure is less than atmospheric at the VRV, which can happen because of elevation changes and low flowrate/pressure, then the air will not escape from the panels.

 

[mas985]

Thanks so much to everyone that responded - great help and info. My solar heating system has been cobbled together as a series of prototypes and iterations. Any suggestions on how to improve, let me know.

The solar capture area is only around 60 sq-ft and for a 25k pool, that is not going to capture much energy.

Maximum solar radiation hitting a flat surface at your latitude is around 2500 BTU/sq-ft/day. So at 80% efficiency, the heat getting to the pool would only be about 120k BTU/day which would raise the temperature of a 25k pool about 0.6 degrees F. So with those panels, you are not really adding that much heat.

You would probable get more solar capture area in the same ground area if you had used conventional panels. Plus they are more efficient and not aways that much more expensive than DIY systems per sq-ft.

For example, these panels:

Amazon.com

Are $4.50/sq-ft so if you paid more than $270 for just the panels (tubing, fittings, wood, valves, etc), then these would have been more cost effective.