Recomendations for SHW in WI

[mojisimo]

I have two questions:

1. Do you have a recommendation for % glycol solution to use in cold Northern WI. The temps are extreme. I have heard 30-50 % and at $21 a gallon 50% is hard to stomach. The system failed this past winter (innards of 6 concentrating SolarGenix panels burst, could have been many different reasons why they burst and we are going up to address them this next week). So I want to make it more burst proof in the future and think that adding glycol is a good idea. I would like to get away with 30% but don't want to invest in the 30% if it is going to end up falling short, might as well go with closer to 50% in that case. What do you think?

   
   

2. We have a pressure relief valve at the drain back point at the top of the last panel. It is a 125 psi air/coin vent. Should that not be there in our cold climate?

   
   
   

Thanks!

Mike Dooraghi

[chainsaw]

The anti-freeze that I use in my solar water system was obtained free by going to several auto repair shops and picking up used coolant that was changed out. They were happy to get rid of it. You then need to strain to remove any particles.

After I had collected a barrel full I then took samples of different combinations( diluted with water) in small bottles and placed in the freezer(-10f).

I found that even a very weak anti-freeze mixture would make mush ice but would not hard freeze enough to cause busting.

Your climate would be colder than mine so you would need to take that into account for your mixture.

Also my heat exhanger is designed that in case of a rupture it is impossible to enter the potable water system.

Hope this helps

[ghurd]

This was a Long time ago. From memory.

A friend worked at a huge car shop.

They had a machine that "spun" the used antifreeze at high speed.

It supposedly separated the dirt, oil, and water from the antifreeze.

Mostly the employees used the cleaned and de-watered antifreeze, and the rest was sent to wherever they sent it back then.

Saved the shop money not having to send watery antifreeze.

Not profitable to give customers there old antifreeze back if they can charge them for new.

If they still do that, might get some decent stuff free.

Might want to add some conditioner to keep the pump happy.

G-

[GaryGary]

Hi,

A well designed and installed drain back system should not need any anti-freeze.  

You have probably worked on this some already, but I'd have a look at the whole collector and plumbing system to make sure you have downslopes toward the tank everywhere.  Then test the system to make sure it drains back reliably.  I think that one way to be certain all the fluid is draining would be to turn the pump off, and let it drain fully on its own, then introduce some compressed air in the return line, and see if it pushes any more fluid out -- if it does, there is fluid being trapped in the system somewhere.

I guess that if you do use antifreeze as a backup, that it would have to be good for your coldest temp, otherwise its still going to freeze?

Is the valve a pressure relief, or a vacuum break?  There would really be no reason to have a pressure relief on a drain back system, as it is vented to the atmosphere, and should not be under pressure at all.  The vacuum break is used on some drain backs, but if the plumbing is right, it is not needed, and its just another failure point.

I've got two drain backs in MT (very cold) -- never had even a hint of a problem with them.

One problem with introducing anitfreeze into the system is that you have to be careful to check it each year and replace it when necessary.

Gary

[morglum]

Hi Gary,

I read your article on builtitsolar.com about the 1000$ solar water heating system (great stuff!) and a few of your posts here as well and you've got me thinking.  I really didnt need this: I'm already working on a wind turbine, solar panels and controller and I'm thinking about converting an old diesel tractor to electric (I've already got the forklift motor!  lol..)  

Anyway,

Just to make sure I understand your system correctly :

 You don't have antifreeze in your water even though it freezes in Montana because the water will drain back to the tank in your basement as soon as  the pump turns off.  This is because everything in your system has a slope and whatever water is left behind will freeze but there will not be enough for the water to break the pipes, correct?

Question:  On this picture of your collector (http://www.builditsolar.com/Experimental/PEXColDHW/P1000874.JPG)   I dont see the slope in the copper pipes.  They seem very horizontal, or is it just me?

Thanks!

S.