Solar Woes… System in low speed cannot overcome panel drain down!

[david.del.rio]

This system was plumed based on this diagram from Pentair, with modifications found on this forum.



There are two differences in my system. It does not include the check valve between the solar panels and the return, and does include manual bypass and shutoff valves as shown in this diagram and photo.





Here are some photographs of the installation:





First let me describe the system operation at startup. The two speed pump is run by the electronic controller. I set the unit to run the pump on high speed for five minutes, and then switch to low speed for the rest of the day. During the high speed interval the solar system which has drained down over night is primed and all air is forced out.

Unfortunately during the one minute interval it takes for the timer to switch as programmed from high to low speed, the solar system drains down enough that the pump at low speed cannot force the air from the system and so water does not move through it. If I make the switch from high to low speed manually, with just a few seconds interval the system runs just fine. In other words, the solar system works fine on low speed if the panels have not been drained down.

A fix that just addresses the drain down during the start-up switch from high to low speed alone will not resolve the problem entirely. The same issue arises during normal daytime operations while the pump is in low speed mode and the solar valve closes, causing a drain down and then later opens automatically.

In short, they system runs great with the pump in the desired low speed mode …IF… the solar panels are primed. The pump in low speed mode simply does not have enough oomph to overcome the resistance of the air in the solar panels if they have drained down.

I look forward to any advice you can offer, and wish to acknowledge and say thank you for all the information and inspiration this forum and its members have provided.

 

[jblizzle]

Why is there any down time on the pump?
The valve should switch the solar on while the pump is on high and then instantaneous switch to low speed. The pump should not turn off for a minute.

In reality, you get better heating when the solar gets higher flow rate. On mine, the controller will always switch the pump to high speed when solar is needed. If the solar is not needed, then it will run in low speed. I have it set up similar to yours where I run on high for a while and then switch to low, but the solar will override the pump speed to high if the solar is needed.

Is the Solartouch controlling the speed? It might be able to do what my system is doing.

You should also add a check valve on the solar return so that the panels are not back fed when the solar is off and the pump is running.

 

[Isaac-1]

I agree your problem is the delay, not sure why it is there, or exactly how you have things set up, also as Jason said, your optimal heat transfer from the solar will tend to be with the pump on high.

 

[david.del.rio]

The pump is either in high, or low speed depending on which of two terminals are energized. Each of the two terminals is wired to the an output of the electronic switch. The switch 'could' be programmed so that the high and low speed outputs overlap for a time, but the pump is not designed to handle this. Doing so makes a bad noise and the manufacture says it will damage the pump.

Also, note that the problem also happens when the pump is in the low position, and the solar controller has turned off (closed) the three way valve, then later decides to open that valve. So this problem would persist even if the start up issue were resolved.

I prefer the low speed mode because at high speed it seems way overpowered for the pool, noisy, and because running at low speed saves on energy costs.

The Solartouch is only controlling the open/closed status of the 3 way valve. The motor speed is determined by the electronic switch. The Solortouch can only control the speed of an variable speed motor, not a two speed one. I wish I had purchased their Variable Speed Pump because the controller as described in the manual is smart enough to ramp up the pump when it opens the solar valve for five minutes, then return the pump to a desired pre-programmed RPM. I could add and control a solar booster pump with this unit, but would rather not add another pump! Here is the manual > http://www.pentairpool.com/pdfs/solartouchOM.pdf