Solar Vacuum/Breaker Relief Valve Location

[woodsage]

The breaker/relief valve is not at the highest point of the piping on the roof but rather on the supply side piping near the equipment pad. The installer told me "that's the way we do it around here, if the valve leaks/fails, it's easier to replace the valve at ground level instead of climbing on the roof". Should the valve be relocated to the roof?

Thanx.

 

[ping]

Re: Solar Vacume/Breaker Relief Valve Location

Mine was installed in about the same place as yours. I haven't had any problems with the system at all in a years use.

 

[woodsage]

Re: Solar Vacume/Breaker Relief Valve Location

I'm wondering why a majority of the solar installs have the vacuum relief valve installed at the highest point? As for maintenance/replacement, it would seem easier at ground level.

 

[jblizzle]

So with the valve at the location you show, do you get a LOT of air pushed through the system and back to the pool? With the valve at the highest point, the only air that should end up in the pool would be from the return pipe up to the valve.

By putting it at the highest location, most of the air leaves the system through the valve as the water is pushed up. Also by having it at the highest location, I think there is less chance of air being stuck in a portion of the panels. Additionally, when the system turns off, air is let into the system at the top and the water can drain back down the supply pipe easier and not pull a vacuum in the panels (potentially crushing them). With the valve down low, maybe the thought is that the panels drain down the return side by a siphoning affect pulling in air up the supply piping.

I am no expert, but those are my thoughts.

 

[ping]

So with the valve at the location you show, do you get a LOT of air pushed through the system and back to the pool? With the valve at the highest point, the only air that should end up in the pool would be from the return pipe up to the valve.

By putting it at the highest location, most of the air leaves the system through the valve as the water is pushed up. Also by having it at the highest location, I think there is less chance of air being stuck in a portion of the panels. Additionally, when the system turns off, air is let into the system at the top and the water can drain back down the supply pipe easier and not pull a vacuum in the panels (potentially crushing them). With the valve down low, maybe the thought is that the panels drain down the return side by a siphoning affect pulling in air up the supply piping.

I am no expert, but those are my thoughts.

Yes, I do get air pushed through the system but it does get primed fairly fast. Note that I do have a good size pump and this may or may not help. Once my system is primed it runs fine on high or low speed. If I leave it on low speed all the time, I do believe I have some air in the panels. I don't know if the vacuum breaker would help me out if it was installed at the highest point. Good question.

 

[woodsage]

Additionally, when the system turns off, air is let into the system at the top and the water can drain back down the supply pipe easier and not pull a vacuum in the panels (potentially crushing them). With the valve down low, maybe the thought is that the panels drain down the return side by a siphoning affect pulling in air up the supply piping.

If there are check valves on the return, then how would the water drain back and pull a vacuum? So, should there not be a check valve on the return side to allow draining the water?

I don't get a LOT of air returning back to the pool.

 

[jblizzle]

In most systems, the return comes from the top of the panels so the only way for water to drain out of the panels this route would be a siphon effect being pulled up the panel and then back down to the pool. Which may be what happens with the air valve low. When the air valve is at the top, generally the panels drain back down the supply pipe through a small hole in the solar diverter valve.

You need a check valve on the return pipe so that when solar is off the water does not get pushed up the return (not really a drainage purpose to it).

About the vacuum ... if you have no way for air to enter the panels at the top and turn off the system, gravity is going to pull the water down (both the return and the suction pipes) ... Which will start to reduce pressure at the top. That is why you have to have a way for air to enter the system to avoid reduced pressure possibly crushing the pipes.

To me it just makes for this air to enter at the top where it is needed as the water drains down ... although apparently it is not too uncommon to have the breaker by the pad so I guess it must work.

 

[JasonLion]

If the vacuum relief valve is too far below the top of the system, the panels might simply not drain at all. The static head of the water in the pipe can be sufficient to keep the valve closed. This wouldn't necessarily be obvious, as they would drain in the winter when the rest of the plumbing was drained. But leaving the panels full of water does put more strain on the panel mounting system and more stress on the panels themselves.

There are also some minor problems with putting the vacuum relief valve right at the very top. Vacuum relief valves need a couple of psi to reliably close. But in a perfectly designed system the pressure at the very top of the system is just a little bit above zero. Forcing the pressure to be higher to insure closing the vacuum relief valve increases the dynamic head, and thus lowers the overall efficiency just a little bit. Additionally, if the valve is at the very top and the supply line is not feed by a leaky three way valve the return pipe can drain, but the supply side, along with the panels, may stay full of water. Sometimes they will drain anyway, but you can't count on it in that configuration.

The location of the vacuum relief valve also has some effect on the rate at which the panels drain down. When the valve is located towards the bottom of the system there is a longer path the water must traverse when draining, increasing the flow resistance and slowing the draining process a little.

In my opinion, best place to locate the pressure relief valve at the high end of the supply manifold pipe, as shown in the diagram on this page. However, the differences between that and several other locations aren't all that large, and many different locations are used in practice.

 

[Ken Hot Sun]

The way you need to think of it is less linearly. A vacuum breaker breaker the vacuum. In other words when the pressure at the vb location goes below zero the vb opens and lets air in. That breaks the vacuum. The reason we want to break a vacuum is that in a solar heater its a black thing made of plastic. The most vulnerable component is the pvc plumbing. It can collapse if it stagnates in high heat under negative pressure. When the vacuum breaker is down at ground level that is the point of zero pressure and everything above that point can go under negative pressure. The higher in elevation above the vb location the more severe the vacuum and the more potential for piping collapse. So you see its all about pressure. I say that 100 times a day in my solar business. Vacuum breakers are not really about drainage. We don't care if the system drains or not. We just care that the negative pressure is relieved. For winterizing the system it'll all drain even if there is no vacuum breaker in most cases. It'll just take longer. Any rigid panel solar system should really be blown out with a shop vac rather than emptied just by gravity. Any water left in those polypropylene tubes will cause an irrepairable burst. That is a major reason we always use flexible solar panels. They are repairable and water can freeze solid. We can use them on low slope and even flat roofs. Vacuum breakers are all about negative pressure protection. No big deal in these examples because the worst thing that can happen is some piping collapses. The piping is probably not painted black. If it was its more risky of course because it'll get hotter.

 

[henryting]

The breaker/relief valve is not at the highest point of the piping on the roof but rather on the supply side piping near the equipment pad. The installer told me "that's the way we do it around here, if the valve leaks/fails, it's easier to replace the valve at ground level instead of climbing on the roof". Should the valve be relocated to the roof?

Thanx.

Vacuum breaker should always be at the highest position. This will allow water to drain back to the pool if the pumps are off. Draining fluids back to the pool is essential for 2 reasons :

Firstly it relief the stress on the plumbing when water is all weighted by gravity.

Secondly, when the pump is off, and during the night, since the solar panels are outdoors and most likely on the roof, there is a potential danger of freezing in the cooler months if water is not drained back when the pumps are off.

I would advice re-installing the relief valves to the highest point within your system. Do it sooner than later because all it takes for the water in your solar panels to freeze and you would have cracks everywhere and need to replace all the panels if that happens.