dschlic1 said:
You don't really need the vacuum breaker at the top. Mine is localed close to the filter and pump. Water shipons up from the breker through the panels and down the other side. Been through two winters with no problems (freezes both winters).
In principle that will work but it may cause the solar return pipe to collapse under certain conditions. Several months ago, I had a discussion with a solar installer who recently started to put their vacuum release valves near the pad. He said soon after, they started to get reports of return pipe collapse on the roof. This makes sense when you consider the pressures involved and how solar controllers work.
Because of the placement of the vacuum release, the plumbing at the top of the house, especially a two story house, will be under a very high vacuum when the pump is turned off. This vacuum is proportional to the distance between the top of the panels and the vacuum release valve (i.e static head). Normally, this is not too much of a problem because PVC can withstand negative pressure fairly well as long as the temperature of the PVC does not get too high. The maximum service temperature for PVC is 140 deg F so it will start to soften quite a bit even before it reaches this temperature.
During the run cycle a solar controller may turn off the solar if the water temperature gets too high which usually happens during very hot days. However, the run cycle of the pump may not be over so the water may get trapped in the panels because the water pressure at the vacuum release is still above 0 PSI. So the water in the pipe and panels will continue to heat up and it will soften both the PVC and panel plastic. As soon as the pump shuts off, there is a high vacuum in the pipe and if the pipe is soft enough, it may collapse.
Placing the vacuum release at the top of the panels prevents a high vacuum from occurring within the pipe so collapse is less likely to occur. Another way prevent this is to use CPVC for the solar runs. However, the panels may still be subject to high vacuum but they are usually rated at much higher temperatures than standard PVC.
If you constantly run your solar system with the pump, there should not be a problem. But if allow a controller to shut off the solar system before pump run time is over and your installation is fairly high relative to the vacuum release valve, then you could potentially have a problem.