Solar drain down plumbing to avoid suction collapse of header????

[CRUSH-IT!]

I will be re-plumbing my pad soon and installing solar. I have a two story roof and live in florida where the solar may shut off during the day with water in the panels allowing the pipes to be exposed to high temps without circulation. I am concerned about vacuum leading to pipe collapse. The header could easily see minus 8 or 10psig. The manufacturer's published install instructions demonstrate no concern about collapse. (They suggest putting the vacuum relief valve at about 5ft above ground) My prospective installer says, "Don't worry about it. Its not an issue." I suspect his real world experience is valid and lets face it... he's the one who will have to repair a collpase. Just the same I am concerned. I am seeking a low pressure pipe to which I can drain my solar. The blower line is convenient.

Is there any reason not to plumb the drain down of the solar to the blower line below, (distal to) the check valve?

I appreciate your thoughts. Thanks again.

PS: The manufacturer and installer have a great deal of experience but to paraphrase Scotty, "They can't change the laws of physics."

 

[MSchutzer]

A vacuum breaker installed on the highest point of the solar panels eliminates any potential for negative pressure on the panels. This is the breaker that I have on my panels.

https://www.amazon.com/dp/B01GSG2R8C/ref=cm_sw_em_r_mt_dp_EGP8VXVA84FV0PS8TCMV?_encoding=UTF8&psc=1

It’s also good for freeze protection as it lets all the water drain from the panels when the pump is off.

 

[mas985]

Having a lower VRV allows you to run a VS pump at lower speed while using solar. However, there is the risk that if solar is shut off during the heat of the day, the water temp can reach a point where the PVC softens and when the pump shuts off, the vacuum in the pipe can collapse the pipe. If you are not that concerned about energy use, then putting the VRV on the highest point of the panels will eliminate that issue. However, if energy use is a big consideration, there are ways to mitigate the risk such as using CPVC for the return side plumbing.

 

[Rocket J Squirrel]

You need a VRV. I have two, one for each set of panels. Mine plug into the panels just like an end cap and look something like this:

 

[CRUSH-IT!]

I appreciate all of your responses. I understand well the hydraulics involved and you are correct mas985. I was surprised that helicocol recommends placing the vacuum relief valve low, " above the top of the filter". they also do not recommend CPVC so they are clearly disconcerned in a way I find surprising. In Florida I think it would be asking for a collapse. I would like to install a drain down and am curious as to whether I will get into problems having it drain into the blower line that is plumbed to the jets on the spill over spa. I suspect it will be just fine.