PVC size for solar heating panels

[parkland]

Howdy! I'm new to the forum.

I'm installing a solar heating system and had everything picked out, FAFCO panels with 2" pvc pipe. Long story short the guy that was selling the panels actually had 1.5" instead of 2", and I've already installed the PVC up to the roof. Should I just get some other panels with 2" headers or will it be no big deal and just use an adaptor for the 1.5".

I was just wondering if the flow would be much different. I plan on having 1 row of seven 4x10s and a second row of 4x12s above it.

thanks!

 

[JasonLion]

Welcome to TFP!

With seven panels in the row the size of the header pipe is going to make a difference. Everything will work with the 1 1/2" pipe, but 2" is better.

 

[parkland]

Thanks Jason. I'm not a fluid dynamics expert but felt 2" would be the way to go as well. Hard to resist the deal on the 1.5s, but I don't want to screw my pump/system up.

 

[joenj]

I thought the FAFCO panels only had the 2" header, that is why i went with them. I have the Sun Savers. Also like having the return and feed on the same side, up to 7 panels. Provides an easier plumbing run.

Make sure the two banks are in the parallel supply/return setup.

 

[mas985]

Thanks Jason. I'm not a fluid dynamics expert but felt 2" would be the way to go as well. Hard to resist the deal on the 1.5s, but I don't want to screw my pump/system up.

You won't damage anything with the 1.5" header, it will just have a bit more head loss than 2" headers. So the filter pressure will be a little bit higher and flow rates lower. This is more of an energy efficiency consideration than anything else.

 

[parkland]

thanks for the replies. looks like i'm either going with FAFCO clones with 2" headers or the techno-solis panels, also with 2" headers.

one question about how the panels drain. i plan on having two rows of panels, the lower one on my patio cover, and the upper on the roof (in parallel). the pvc (in and outflow) comes in on the roof (between the two rows), and the inflow heads down to the lower bank and outflow heads up. vacuum release valve will be placed as well.

what i'm wondering is: will the panels on the patio area drain once the system is off? or will this water get trapped in this area since it is lower then the outflow piping exits the area. or will the gravity/vacuum effect pull this water out. does this even make sense?

 

[JasonLion]

You don't want to create localized low spots like that! The pipe should run "downhill" from the vacuum breaker valve all the way to the pool. Localized low spots can collect water that won't drain out and localized high spots can collect air that may block the pipe and prevent proper circulation.

 

[parkland]

hmmm...so if the vacuum breaker valve is above this area it will drain? i was planning on placing it in the top corner as the manufacturer suggests.

i'm not really sure that i can place panels on my patio cover otherwise, which is interesting as both of the professional bids from heliocol and the FAFCO rep has panels placed on the patio with pvc in/outflow above this area on the roof.

 

[dschlic1]

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).

 

[mas985]

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.

 

[mas985]

thanks for the replies. looks like i'm either going with FAFCO clones with 2" headers or the techno-solis panels, also with 2" headers.

one question about how the panels drain. i plan on having two rows of panels, the lower one on my patio cover, and the upper on the roof (in parallel). the pvc (in and outflow) comes in on the roof (between the two rows), and the inflow heads down to the lower bank and outflow heads up. vacuum release valve will be placed as well.

what i'm wondering is: will the panels on the patio area drain once the system is off? or will this water get trapped in this area since it is lower then the outflow piping exits the area. or will the gravity/vacuum effect pull this water out. does this even make sense?

I wouldn't rely on the suction to remove water but instead design the plumbing for proper draining. First, avoid any type of u trap in the plumbing where water cannot drain downward by gravity alone (i.e. not reliant on suction). However, there are a couple of configuration options.

Dual Vacuum Release Option:

Use a vacuum release at the upper most point of the return side of each set of panels. Connect the supply and return side pipes from each set of panels to a point below the lowest point of the lower panel. Hopefully that makes sense. This is like having two separate solar panel systems which are connected at the pad or slightly above the pad.

Single Vacuum Release Option

Place one vacuum release at the top of the upper panel near the return pipe. Connect the two supply side pipes at a point below the lowest panel as above. However different than above, connect the return side pipes at a point just above the highest point of the lower panel. This ensures that no water will be trapped in the lower panel.

Low Elevation Vacuum Release Option (not generally recommended)

I don't recommend this unles you will avoid the problems pointed out in my last post. Plumb the pipes as in the dual vacuum release option but instead use only one vacuum release on the supply side at least 5 feet above the pool water level.