Pentair SolarTouch controller falls back to solar hold after a few mins due to low temp

[gerombo]

Hi,
I'm using a Pentair SolarTouch controller with my IntelloFlo VSF pump. I notice that my controller falls back to solar hold after just a few minutes, because it picks up a sudden drop in "solar temp" (roof temp).
As a result, my valve opens and closes multiple times over the span of a few minutes, my pump spends most of the time in solar hold (ext4) with the valve closed, and I'm using a fraction of my roof solar capacity.

Some details:

• pool
  • current temp: 18C
• solar touch settings:
  • target temp: 31C
  • diff to start: 4C (=22C)
  • diff to stop: 1C (= 19C)

My initial hypothesis was: cold pool water goes up to the roof and cools down the sensor too much. Hence I changed the Diff to start (increased to 4C) and Diff to stop times (decreased to 1C).

I started monitoring the Solar/roof temp on the controller. Typical sequence:

1. start roof temp: 25C
2. starting solartouch with Solar Heating Enabled
3. start solar hold (since 25 > 31-4)
4. 5 min hold (pump in ext 4, solar valve closed, expected)
5. solar heating enabled (pump in ext2, solar valve enabled, expected)
6. roof solar temp drops a few degrees (21-22C still above Diff to stop, expected)
7. after a few minutes roof solar temp drops suddenly to 15C for a few seconds, triggering solar hold (for 5 minutes)
8. repeat

Could this be a faulty sensor or a bad contact? (since the measured 15C is even lower than my pool temp this seems like an anomaly)

My temp sensor on the roof is at the top/cold side of the first panel, this seems counter intuitive to me. Shouldn't it be at the bottom/hot side of the panels?

I would welcome any suggestions (including corrections to my understanding of how the system works)

Side question: what's the point of solar hold for 5 minutes, especially if there is no separate solar booster pump to prime?

 

[Rocket J Squirrel]

The probe of the solar sensor should not be touching the panels. Your symptoms sound like it is. If so, move it a little so it's measuring the air temperature at the panels, not the panels themselves.

 

[gerombo]

The probe of the solar sensor should not be touching the panels. Your symptoms sound like it is. If so, move it a little so it's measuring the air temperature at the panels, not the panels themselves.

Thanks @Rocket J Squirrel

I got up the roof to investigate. The sensor is actually not touching the panels or pipes at all. Wrong assumption on my part.

So I wonder if it is picking up cold bursts of wind. The 15C aligns with the ambient air temperature at the time.

 

[ajw22]

@Dirk Should the solar temperature sensor be lying flat on the roof like this is....

 

[Dirk]

I could never find a definitive answer to that, as I had the same question. Should it be touching the roof? Or touching the little tubes? Or the manifold?

It's supposed to be measuring the temperature that is available to heat the water, but again, does that mean air temperature or the temperature of the solar panel material. I think it's supposed to measure ambient air temperature, but in direct sunlight.

Mine is in an upside-down glass pickle relish jar, affixed to the jars lid, which is affixed to the roof. It is sticking straight up from the lid. So its probe is not really touching anything but air. The jar is mounted a couple inches away from the upper manifold of my panel array.

I used an undocumented theory, from someone that pretended to know, that the jar shields the sensor from cooling winds, which left unblocked can affect the sensors sensitivity to temperature change.

All a long-winded way of saying I really don't know.

The bottom line is, the sensor determines when the system should kick on and off, based on available heat at the panels. A solar heater controller should have user-adjustable sensor threshold settings, which allow you to fine tune how that works. If your system kicks on, and after a reasonable amount of flushing (a few minutes) you should be able to put your hand in front of a return and feel the return water slightly warmer than the rest of the pool. If the water is cool to the touch, or the same temp as the pool, then the system engaged sooner than it should have, and sensor settings, or its placement, need to be adjusted.

The only way to determine if the system is coming on later than it should, is to fool with the sensor settings to find out at what point it's not working as intended, and then back off the settings from there. I never did that, so I don't know that my system is optimized in that regard, but it comes on around 8am when the sun hits the roof, so I figured "close enough."

 

[Dirk]

Sorry, read the last post first, then went back to read the rest. My system experienced that same kicking on and off whenever the temperature on the roof was close to the threshold. Cold or very hot out the system worked as expected, but it would kick on and off too much when the air temp was borderline. I asked around and found the pickle jar trick, which did solve it for me. Give it a shot.

I probably should go up there and see how the lid is doing. Maybe it's rusted out by now.

Some tips (pardon if I mentioned this to you in another thread). Those zip ties are going to fail. As is the exposed sensor wiring. The UV and heat up there are brutal. I located my wires under the pipes as much as possible, to take advantage of the shade they throw, and I only use stainless steel wire now outside, wherever I used to use zip ties. Even the UV ones won't hold up indefinitely. The wire will.

https://www.amazon.com/gp/product/B005VR49D6/

 

[ajw22]

@Dirk Next time you get on the roof get some pics of the pickle jar trick and show us.

 

[Ahultin]

Mine is likely a bit "extra" (but also ground mount) so the sensor and wire is all in conduit with the sensor run thru a drilled and tappped pvc cap. I've not had the cycling problem, maybe the metal sensor reacts slower?

 

[gerombo]

Thanks @ajw22 and @Dirk !

My system experienced that same kicking on and off whenever the temperature on the roof was close to the threshold. Cold or very hot out the system worked as expected, but it would kick on and off too much when the air temp was borderline.

That sounds very similar indeed. I also din't have any issues during peak summer. only noticed it late fall and now early spring.

I asked around and found the pickle jar trick, which did solve it for me. Give it a shot.

Genius. Will give it a try! I had been thinking putting some type of cover over it to shield it from the wind. This would create a glasshouse effect so I might have to increase the start up threshold.
I'm curious to know how you fixated the pickle jar. Roof flashing sealant?

Those zip ties are going to fail. As is the exposed sensor wiring.

Thanks for the tip! New owner here. Lots of discoveries

Side question: what's the benefit of the Solar Hold in the first place, if you don't have a solar booster pump that needs to be primed?

 

[gerombo]

found this related post introducing the pickle jar concept:

Solartouch roof sensor questions

Hi everyone, New to the forum. Recently had heliocol panels installed with the pentair solartouch control system. It is set up by the manufacturer to turn on when there is a 6 degree difference with the pool water. For example the roof sensor was showing 84 and the water was 78, obviously it...

www.troublefreepool.com

 

[Dirk]

found this related post introducing the pickle jar concept:

Solartouch roof sensor questions

Hi everyone, New to the forum. Recently had heliocol panels installed with the pentair solartouch control system. It is set up by the manufacturer to turn on when there is a 6 degree difference with the pool water. For example the roof sensor was showing 84 and the water was 78, obviously it...

www.troublefreepool.com

I had forgotten that thread. Yah, we explored the issue quite a bit, didn't we...

 

[Dirk]

I'm curious to know how you fixated the pickle jar. Roof flashing sealant?

That's what I wrote in that other thread. I thought I remembered screwing down the lid, flat on the roof, and then threading the glass jar into its lid, but maybe I just used glue. I have a concrete tile roof. I may have used both, a screw plus sealant. Maybe I used he same screw to hold the sensor to the lid and the lid to the roof.

I do remember slotting the lid, to pass the wire through it. And taping the wire so that it wouldn't abrade on the cut metal.

It'll be a while before I can get up there, to get a pic and see what I did. I was talking about getting a pic in that old thread, that was five years ago, and still haven't been back up there! I was fortunate, and very careful, and managed that install without cracking a tile. I'm not keen on pushing my luck unless I have to. Where's somebody with a drone when you need one?

 

[Dirk]

Side question: what's the benefit of the Solar Hold in the first place, if you don't have a solar booster pump that needs to be primed?

Sorry, I don't know. I've never used the SolarTouch, and I'm not sure my controller has that feature. It does have the adjustable thresholds, which I played with once upon a time, but don't remember much about them, or what I settled on.

Some time last year I did a hard reset of my controller, so if those thresholds were ever adjusted to something other than the factory default, they are probably factory default now. I probably didn't consider those while I redid all my settings after the reset. When I engage solar this year I'll have to pay attention to how the system is working. Which means I'll have to get up a few times when it first comes to see if it's outputting warm water as it should.