wire a two speed pump as slow only for solar

[bolinas]

I replaced my single speed whisperflow 3/4HP pump motor with a two speed motor last year. I am thrilled with the results. However, now I have installed a fancy new solar heater and the two speeds are a problem. Slow speed is perfect, but fast is too much pressure. I really don't need high speed at all, but my Jandy Aqualink RS always runs the high speed for a few mins before going to low speed. I don't think you can have it start in slow speed.

What I'd like is to have it start in slow speed all the time. it would be great to have a manual switch that I could use to go high speed if possible, but if all I got is allow all the time, I'm happy. I don't use the vacuum much anyway, which is the only time I'd want high speed.

Any thoughts appreciated.

 

[carlscan26]

It's running on high speed to prime the panels. If it's only for a few minutes what's the problem?

 

[JasonLion]

One option is to add a spring loaded bypass valve that allows water over a certain flow rate to bypass the panels. Alternatively, you can change the wiring on the pump so the speed is controlled manually instead of by the automation system.

 

[bolinas]

It's running on high speed to prime the panels. If it's only for a few minutes what's the problem?

problem is that the high speed creates too much pressure at the very worst time, i.e. when the panels are hot. I'm now trying to figure out if I can have the solar valve open only during times the pump isn't running. Not sure that's possible as it uses a temp sensor on roof so that when roof is hoter than pool and pool is too cold, it open the valve. Not good to have solar running when roof is colder than pool when pool is too cold as it will chill it.

Best solution is having pump turn on high to prime, then once it drops to low speed, allow solar valve to open, if temp is correct, else solar is always closed. Might end up being a controller problem and not a pump problem.

 

[JasonLion]

The controller is operating as designed. Most solar systems won't prime properly unless the pump is on high. That many not be appropriate for your setup, but I don't think you are going to be able to change this behavior of the controller in any simple way.

 

[jblizzle]

What makes you think the pressure is too high? Solar efficiency goes up as you increase the flow rate.

General desired flow rate is around 1 gpm per 10 sqft of panel. How big is your setup and what is your new pump?

 

[mas985]

With most setups, low speed is not flow rate and pressure to prime the panels and keep the VRV closed so it is difficult to get the panels to work properly on low speed.

How high are the panels?

Do you have a vacuum release on the roof or some place else?

 

[bolinas]

I got lucky. I can set the solar 3 way valve to only operate after the pump has had time to settle down to low speed. This way I get the ability to use high speed to prime the pump system. Solar systems do NOT need a prime and flow rate and pressure are not the same thing. Ideal is high flow but zero pressure. The pump on low speed gets the water up the head no problem. I plumbed in a bypass valve so I close it sending all water to solar with a pressure gauge at the input to the panels. Then I gradually open the bypass until I get zero psi at the panels. I plumbed the panels in multiple banks with 2" pipe leading up so flow rate is quite high. The pool increased temp by 2 degrees in the last half hour I ran it before the sun got too low. Pretty exciting stuff. More tuning to go, but I'm hopeful I won't need the gas heater again!

 

[JasonLion]

You want the pressure to be slightly above zero at the top of the panels when the system is running. Most vacuum release valves require a couple of psi to fully close. Also you don't want the pressure going negative in the panels as the tubes in the panels can pinch closed when the pressure is negative. Since the pressure will go down as the filter gets dirty, the clean filter pressure at the panels should be several psi above zero. Also, it depends on where you are measuring the pressure. The pressure at the very top of the system needs to be slightly above zero, lower down on the supply side the pressure will be higher than it is at the very top.

Priming, in the sense of priming a pump does not apply to solar panels, but there are two other effects that often get called priming which do apply. First, there needs to be enough pressure to raise a static column of water up to the top of the panels to get the water flow to start. And second there needs to be enough flow rate to flush the air out of the panels. Some people call that priming the panels. Depending on the height of the panels above the pool water, that process often requires high speed, but that varies depending on many factors.

 

[carlscan26]

That's exactly what I meant (priming solar panels) Of course Jason said it 100X better

 

[bolinas]

Thanks, guys. I'm getting it. The vacuum release is at the input to the panels. The top of panels is 22 feet above pool surface. The pressure gauge is threaded into the vacuum release when I want to test (removing after to avoid negative pressure). The pressure on high speed reads 6 psi with the solar bypass valve open. Only the back pressure from the fas heater then diverts water to the roof and still the 6psi and this with a 3/4 hp pump motor. On low speed with filter clean, and bypass open, I get water coming through only if i open the vacuum release. It doesnt have the power to blow the air out otherwise. However, if i close the bypass by about 25%, i get about 0.25 PSI at the gauge and that's enough to "prime". I think I will close the bypass a bit more taking pressure up to maybe 2psi now that I know I can control the high speed. My fear is that with the bypass closed I may forget to turn solar off when servicing the system, thus putting high speed through the panels with the bypass partly closed and causing pressure over 8psi. Manufacturer says not to exceed 5psi for longest life.

 

[mas985]

I don't want to get bogged down in sematics here but according to Webster's dictionary, the definition under verb #4:

4 a: to put into working order by filling or charging with something <prime a pump with water>

Priming solar panels means to fill with water or in other words removing the air. This is not unlike priming a pump where it is filled with water thus removing the air. So priming DOES apply to solar panels.

 

[bolinas]

Priming solar panels means to fill with water or in other words removing the air. This is not unlike priming a pump where it is filled with water thus removing the air. So priming DOES apply to solar panels.

I agree. However, I wonder what the pump was priming before I had the new solar system? Also, I only just learned that the pump needed more power to push the air out. I installed the system myself and it isnt actually panels at all, but rather long extruded tubing I cut to length and bonded to headers custom made. I did all the design and engineering and install, but am just now learning how it works. The tubing manufacturer really doesn't like the idea of hot plastic tubing under pressure.

The latest is that I found that low speed cannot "prime" the solar. I also found that with the bypass valve fully closed directing full flow to solar, the pressure was still comfortably low and flow improved. I decided to test pressure under high speed with the bypass closed and it registered only 6psi. While above the tubing limit of 5 psi, it is for a brief, albeit the worst time, and it is with clean filter. The pool temp increased 9 degrees on the first day with these settings so I am pretty happy.