Air Gap in Pump Filter with Solar Panels

[jblizzle]

The heat added to the pool will always increase with increased flow rates .... but, once you get past about 1GPM / 10sqft the additional added heat is very low. So at that point you are just running at higher flow rates and pressures than you need to in order to get MOST of the solar heating available.

You can certainly run at lower flow rates and you will add heat to the pool, but just not as much as you could be adding.

 

[Dirk]

Thanks Jason for clarifying. This is starting to sound like The Great Drip Tube Debate. There's no way to test this all out, and truly optimize a system, unless you had two identical pools, using two identical systems, in two identical environments, where you could compare 2200RPM to 2250RPM to determine which pool gets warmer and at what cost in electricity. You get as close as patience and equipment allow, and then just go swimming!

 

[jblizzle]

The most basic way to test if you have enough flow is to touch the panels while running. If they feel warm, you need more flow rate. If they feel cool, you have enough flow rate.

 

[Poolzzz]

Dirk, indeed efficiency is on a curve. The point is that there is a broad range of acceptable efficiency and there is in fact no single "optimum" point in that it always keeps getting better with flow.

It's also important to realize that around the nominal optimum point it is relatively flat in that a 100% increase in flow might only add 5% increase in efficiency. So fairly insensitive to flow errors.

Also efficiency losses due to flow rate errors are typically much smaller than the rest of the system losses.

At the same time pressure is significantly affected by flow and can actually damage panels. That's why I think it's best to monitor pressure to make sure you aren't overdoing it which is the exact issue the OP had in this thread.

Ultimately it is the safe working pressure that puts a limit on efficiency.

 

[Dirk]

I think there are two curves going on, right? As the heat exchange improves with flow rate, the gain is negated by the cost of moving the water.

I agree there is an acceptable range for flow. I understand it flattens as flow gets higher (diminishing return). I now better understand there is no optimum point for heat exchange. I presume the optimum point recommended by the manufacturer is some sort of intersection of heat exchange and pumping expense. And that the high end of the recommended range is there to protect the panels from being damaged, and to some extent to account for the flattening curve: because above x-amount of flow, you're not doing much other than wearing everything out faster.

I think I better understand now what you meant by "More important is pressure." He can adjust the bypass all the way up to the max recommended flow, to eek out more heat exchange, because reducing the flow below the max won't save him any pumping expense, because without a VS pump, that expense is pretty much fixed. So it's a matter of determining how close to the max he wants to ride, presumably the closer to the max the more the risk of damage. Which, if I may, is what you were saying?

No matter. It would seem the OP's system is pumping too much water into the panels, and the various solutions have been discussed to reduce that to a better level (bypass or VS pump), and by doing so will hopefully clear his pump of air.

Since I can't offer any way to determine the amount of bypass without a FlowVis (the only method I know how to perform), then I'll leave the math, or the "panel feeling" advice, to others. Is it as simple as increasing the bypass until the panels start to feel warm, and then backing off the bypass a few notches? If that clears the pump of air then he's done?

Hopefully I got a little closer with that attempt!

Sidebar: where I got off the rails: There is an optimum flow rate for my system, because with a VS pump I'm balancing heat exchange against watts. I lost sight of the fact that the OP doesn't have the same variables.