VS Pumps and solar heating a pool

[wayner]

I have an older non-VS pump but am thinking about moving to a VS pump for noise and energy considerations. One consideration is that I have an evacuated tube solar heating system so I run my pool while the sun is up to take advantage of the solar heat. It also isn't good to leave still water in evac tubes in the summer. This will also, I think, require me to run the pump at a higher speed to keep up the flow through the tubes and also due to the fact that it takes more power to pump the water up to my roof.

Therefore is it still worth it to get a VS pump and if so what should I look for in a pump given my circumstances? My existing pump is 9 years old - do these pumps have a lifespan so that mine may need replacing soon? My pump runs for about 12-14 hours per day for about 5 months per year or roughly 90 pump days per year. My pool specs are in my sig.

 

[mas985]

It also isn't good to leave still water in evac tubes in the summer.

Do the panels have a vacuum release valve that will drain the panels when the pump is off?

This will also, I think, require me to run the pump at a higher speed to keep up the flow through the tubes and also due to the fact that it takes more power to pump the water up to my roof.

When priming the panels this is true but once primed, the lift head is canceled by the downward head. However, there are considerations for vacuum release valves and pressure.

My existing pump is 9 years old - do these pumps have a lifespan so that mine may need replacing soon?

Shouldn't. If the motor goes that is replaceable and you could replace the motor with a two speed motor and have most of the energy savings as a VS.

My pump runs for about 12-14 hours per day for about 5 months per year or roughly 90 pump days per year.

Any reason why you run your pump that long? You could save quite a bit by just reducing your run time.
Pool School - Determine Pump Run Time

 

[wayner]

I run the pump that long due to the solar panels. If you shut the pump off for more than a few minutes then you can't start it up until the next morning as pumping coolish (80s) water into the tubes when they contain boiling water will shatter the tubes - I have practical experience at this. So I could shut the pump a few hours before sunset but I still seem to be getting some heat from the panels. Note that currently sunrise is 6:24 and sunset is 8:20 - and days were about an hour and a half longer at the solstice.

The panels do have a pressure relief valve that will allow the water to boil off but the don't really drain unless you do so manually.

There is also an issue with the pressure as I get air bubbles introduced into the system by the panels as the pressure doesn't seem to equalize properly. I started a thread on this a few years ago.

 

[mas985]

If you don't have a vacuum release valve and you plan on continuing to run the panels for most of the day, then you could use a VS at reduced RPM to save on energy costs. You might lose a bit on panel efficiency but you could fine tune it for both energy efficiency and heat transfer efficiency.

There is also an issue with the pressure as I get air bubbles introduced into the system by the panels as the pressure doesn't seem to equalize properly. I started a thread on this a few years ago.

Link?

 

[wayner]

Solar heating panels introducing air into system

 

[wayner]

FYI - I checked last night and my pump is a Sta-Rite 1HP. Model number MPRA6E-147L

 

[mas985]

What is the filter pressure when the panels are running? Is all the water current going through the panels or is some bypassed around the panels?

Since you don't have a VRV, you shouldn't be getting air in the system unless the pressure valve is leaking.

 

[wayner]

I think the panels do have one, or more, pressure relief valves which is what introducing the water. There were photos in the old thread linked to above but they seem to no longer be around.

I have a valve that I adjust to send flow to the panels - I adjust this so that some flow is going to the panels as when I send 100% of the flow to the panels the pressure rises and the velocity of water coming out of the return jets is substantially reduced. My pressure is now about 16 PSI - it was a bit higher but I just replaced my cartridge filters with new ones a couple of days ago which caused the change. When I send zero flow to the panels the pressure drops - I think to about 10 PSI but I haven't tried that recently.

The guy that installed these panels has tried to adjust this to reduce the air coming out but he blames it on the high height of the roof and the fact that the panels are split between a flat roof and a sloped roof. I have a walk-out basement so the water must rise over two stories to get to the panels. The Pressure valves are at the top of each bank of water panels.

 

[mas985]

What is the upper most height of the panels above the filter gauge?

What kind of pipe is that being used to feed the panels?

 

[wayner]

If I understand your question correctly regarding height then I would say it is roughly 20' from the pool pump up to the top of the first panel, which is the uppermost panel on the right.

The pipe is basic black PVC pipe - I think it is about 1.5" in diameter.

 

[mas985]

Is that a single story house?

Anyway, a 20' rise drops pressure by about 9 PSI which means you have about 7 PSI (16') for dynamic head loss between the pump and the top most panel. That may or may not be enough. If the panels are sucking air, then most likely the head loss is higher than that and you have a partial vacuum in the panels. Running at lower RPM/flow is only going to make the problem worse. If you fix the air leak, then you could probably run at lower RPM without any issues.

If there are holes in the panels somewhere or the pressure valves are leaking, you should see water coming out when you redirect all of the water into the panels. If those are truely VRVs, then having a partial vacuum in the panels will most definitely draw in air. You need to keep the pressure higher to keep the VRVs closed.

 

[wayner]

It is a single story house, at least at that end of the house, but there is a basement that is level with the grade at the back of the house so the water is effectively going up two stories - the basement and the first floor, and then there is a small peak on the roof that the uppermost panel is resting on that would raise it another 5 feet or so.

I don't think there are any holes in the hose as I would see water leaking which I do not see. Are the VRVs supposed to be one way? That is that they can let air or steam escape, but not let air enter? So I assume the problem is that air is getting in somewhere, perhaps from the VRVs or maybe somewhere else.

 

[mas985]

VRVs (vacuum release valves) only allow air INTO the panels so that the water can drain away when the pump shuts off. However, if broken, the could allow water out as well.

VRVs are not the same as a pressure release valves (PRVs) like those used on a heater. When the pressure builds inside the plumbing, the pressure release valves allow the pressure to escape.

Most pool solar panel systems have VRVs and not PRVs.