Am I getting too cheap??

[Bad Wolf]

I'm amassing all of the components to install my wood furnace (TARM) and some solar panels, and I'm running out of money. I have to make a 80' run out and back to the solar panels and I had bought a 300' roll of PEX (OX barrier of course) will insulate place in 4" pipe and bury. Now I read that I should use copper for the hot side of the solar panels becaurse there are times when the water can exceed 200 degrees and the PEX could fail. The last thing I want to do is dig up the piping again, but copper pipe is like gold right now.
While pondering all this I looked up to the basement ceiling and saw all of the 3/4 in. copper pipe already installed for my radiators.

So does this make any sense: strip out 3 or 4 runs of copper pipe and replace it with the PEX that I lready have? I plan on switching the first floor over to radiant heat next year so that was going to be replaced anyway.

For the cost of a few fittings I could scrounge an easy 120' of pipe.

Thoughts?

Thanks
Greg H
TARM Excel 2000 almost installed
1200 gallon storage

 

[BrownianHeatingTech]

Pex is a no-no for solar.

Copper or corrugated stainless steel tubing are the practical ways to go.

Joe

 

[MrEd]

Why not pex? Do the temps get too high and uncontrollable? I'd like to add panels someday, but if I need to run copper all the way back I may need to reconsider...

 

[webbie]

All you need is for the power or pumps to go out for 10 minutes on a sunny day and solar panels will boil - I have seen temps over 200 degrees regularly when the pump sticks or fails.

 

[BrownianHeatingTech]

Why not pex? Do the temps get too high and uncontrollable? I'd like to add panels someday, but if I need to run copper all the way back I may need to reconsider...

Stagnation temperature on some panels is over 400 degrees.

Far in excess of what pex can handle.

Joe

 

[BrownianHeatingTech]

at what distance from the panel is it safe to transition from copper to pex?

Nowhere within the panel loop. The entire connection from the panel to the heat exchanger at/in the storage tank should be metal (copper or stainless).

In cases where the availability of sunlight has dictated that the panels be mounted in an outbuilding, or even at the far end of a single building, I've found that installing the thermal storage tank in that location (then running the pex from the tank to the point of use) is a viable alternative to running a significant length of copper or CSST.

Joe

 

[BrownianHeatingTech]

galvanized pipe?

Copper or stainless. Heat transfer fluid is expensive stuff, and introducing contaminants which might shorten its life is a bad idea. Threaded joints are a bad idea, as well - you don't need a 400-degree leak. Personally, I only use CSST now, because it allows long runs (at least 50 feet) between joints. Caleffi's SolFlex does a good job of providing two pipes, a control wire, and insulation all in one easy-to-use 50-foot run. At this point, I don't use anything else for solar - it gives the ease of pex, with the quality/durability of CSST, and having two pipes and a wire inside a pre-insulated run of pipe cuts installation time dramatically.

Joe

 

[solarguy]

We use pex for underground runs to solar systems all the time & have had no problems. Just be sure to terminate the pex a couple of inches above grade & convert to copper at that point for all panel connections. Be sure you allow sufficient copper piping between the pex to copper connection even if it means taking the long way around the barn. Heat trap your supply & return connections at the panel, set your solar controller for 200 degree emergency shutdown. Be careful when you're charging the solar loop, you need to allow for expansion. You do not want to exceed 80 psi when the system is in stagnation or you'll blow the pex. If you have a system that is reaching 400 degrees in stagnation mode, you do not have enough storage.

Bob

 

[BrownianHeatingTech]

We use pex for underground runs to solar systems all the time & have had no problems. Just be sure to terminate the pex a couple of inches above grade & convert to copper at that point for all panel connections. Be sure you allow sufficient copper piping between the pex to copper connection even if it means taking the long way around the barn. Heat trap your supply & return connections at the panel, set your solar controller for 200 degree emergency shutdown. Be careful when you're charging the solar loop, you need to allow for expansion. You do not want to exceed 80 psi when the system is in stagnation or you'll blow the pex. If you have a system that is reaching 400 degrees in stagnation mode, you do not have enough storage.

400 degrees is stagnation on many/most evacuated tube panels. Stagnation temp is based upon the design of the panels, not the size of the storage or the settings of the controller - stagnation is, by definition, what happens after the storage is fully charged (regardless of how large the storage tank is). Adding more storage or re-setting the controller may sometimes prevent you from entering stagnation, but it will never change the stagnation temperature of the panels. And, as Craig points out, in the case of a power failure, the size of the tank or settings of the controller will become irrelevant.

Using pex in that application will void the warranty on the pex and most likely the warranty on the collectors, as well. It may also be against code, since code requires that installations conform to the manufacturer's installation instructions, and many/most manufacturers only allow metallic piping.

Joe

 

[Bad Wolf]

OK I think I have the gist of it. PEX on the leg coming from the collectors- bad. These are old flat plate collectors I got from a friend. No warrenties. I have an expansion tank in the loop, and I'll set the high limit for 200 degrees.
I think to be on the safe side I think I'll swap out the pipe in the house for PEX and use it on the collector side of the loop. I have a 150' coil in a 1200 gallon tank so I would hope it could dump what ever heat it has and be no more that 180 going back to the panels.

Once I get the solar loop hooked up I can move on to the furnace.

Thanks for the tips

Greg H

 

[heaterman]

I'll side with Joe on this one. Pex on any kind of a solar panel system is a no-no. Automatic code violation here in Michigan. Stick with the copper my friend. If you're not going to do it right either don't do it at all or wait until you can swing it financially. The Callefi product is sweet. Not cheap, but sweet.

 

[solarguy]

I'm not trying to mislead anyone & using pex for this application isn't for the typical DIY so I'm sorry I put it out here on this list.

Putting the pex issue aside, any system that is allowed to stagnate for a prolonged period of time is not a good thing. If people are seeing temperatures of 400 degrees in their collector system during stagnation, you've got trouble. Stagnation occurs when there is no place left to dump solar energy & the typical cookie cutter, over the counter solar system does not really address this. The key to any good solar installation is to not allow stagnation to occur in the first place. You can accomplish this by having adequate storage, additional storage to act as a dump zone or bleeding off solar energy much like a geo system depending upon your application.

Solar, like any other mechanical system has no brain, you need to tell it what you want it to do.

Bob

 

[heaterman]

A person always has to design for the worst case scenario because I've never seen a job where Mr Murphy didn't show up at one point or another. When he does he always finds the weak point in the system and it's never a "good thing".

 

[brad068]

heaterman,

I know you install Garns. have you ever hooked up a solar system to a garn?

 

[heaterman]

heaterman,

I know you install Garns. have you ever hooked up a solar system to a garn?

No I have not. The Garn does however come from the factory with tappings for solar input. I saw one on a farm by Lake Michigan that was 24 years old and had two panels connected to it. I think it was a 1300 gl model and the owner said that the tank never dropped below 100-105* all summer. It was basically piped to provide preheat for the DHW during the summer and winter IIRC. Not much solar input here in Michigan from Sept to March so we don't do a lot of it.

 

[brad068]

Another ? for ya. Has the supply and return ports been reversed on the new garns? The old manual I have show the return high in the back and supply low in the front.

 

[BrownianHeatingTech]

I'm not trying to mislead anyone & using pex for this application isn't for the typical DIY so I'm sorry I put it out here on this list.

Putting the pex issue aside, any system that is allowed to stagnate for a prolonged period of time is not a good thing. If people are seeing temperatures of 400 degrees in their collector system during stagnation, you've got trouble. Stagnation occurs when there is no place left to dump solar energy & the typical cookie cutter, over the counter solar system does not really address this. The key to any good solar installation is to not allow stagnation to occur in the first place. You can accomplish this by having adequate storage, additional storage to act as a dump zone or bleeding off solar energy much like a geo system depending upon your application.

Solar, like any other mechanical system has no brain, you need to tell it what you want it to do.

A system can be designed perfectly, but that won't solve the issue of mechanical failures. Lose power briefly, and the fluid will stagnate. Power comes back on, and 400-degree fluid is now flowing through pex, causing property damage and potentially injury or death, depending upon where the pex runs, and where it fails.

A properly-designed system under normal conditions should rarely or never stagnate. But a proper installation has to account for abnormal conditions, as well.

Joe

 

[Bad Wolf]

I see enough people warning of elevated temps as a result of a system being off that I'm not going to take any chances.

However I'm at a loss to understand how it could achieve 400 degrees. These are old flat plate units, not the newer evacuated tube ones. Stagnation is limited by the boiling point. If it were straight water it woild boil at 212 degrees, if its under pressure the boiling point is higher and if it has antifreeze then that point is higher still. The pressure relief valve should blow at 30 psi. With out going back to my engineering books, a quick search gives me 265 degrees for a 50/50 mix at 15psi. Now thats well over the 200 upper limit I see for pex so I WILL be going to copper pipe.

Part of my original question was should I swap out existing copper pipe from my baseboard system that will probably be removed in a year anyway with pex in order to save money, and I take it that the answer is yes.


Thanks
Greg H

 

[BrownianHeatingTech]

Part of my original question was should I swap out existing copper pipe from my baseboard system that will probably be removed ina year anyway with pex in order to save money, and I take it that the answer is yes.

Re-using existing pipes is never guaranteed, since there is no practical way to know the condition of the pipes. Check if they are M or L copper, for one thing. M has red writing, and L has blue/black writing, typically. If wouldn't even consider using type-M copper pipes on solar, even if they were new, and definitely not if they were used.

Joe

 

[heaterman]

Another ? for ya. Has the supply and return ports been reversed on the new garns? The old manual I have show the return high in the back and supply low in the front.

Return high and supply low is correct. You want as much head as possible for the circ to operate with. That factor dictates using the lower port as the supply.