Hot Water Drainback System in WI

[mojisimo]

Hello and thanks for any thoughts or input on this issue. We installed 2 systems on my mom's house in Northwest Wisconsin; one is a drainback system for the in-floor heating and the other is a pressurized system for her domestic hot water. We used Solargenix panels on both systems; 2 for the domestic hot water and 6 for the drainback system. The pressurized system has been running properly over the past three years, but the pipes in all six of the Solargenix pipes have burst.

I have two questions:

1. Has anyone ever repaired the innards of a Solargenix concentrating panels? My friend has done it before and he used silver brazing to fix the pipes and he said it was a huge pain. He also said that he realized afterwards that the pipes on the inside are 3/4" and 1" standard pipes and that it is reasonable to think that you could just cut out the burst section of the pipe and solder copper pipe. Has anyone ever done this or have a strong opinion one way or the other. I talked to the manufacturer (very nice guy) and he indicated that they are indeed 3/4" pipe and 1" pipe, but that he would be wary of fixing them due to the exact placement needed for the pipes since they are in little concentrators and need to be at the focal point. I believe we could maintain the right positioning of the pipes, but would be very interested in hearing anyone else's input.  
   
2. How best can I prevent this from happening again once we fix the panels? Here are the specs for our project:
   
   

A. 300 gallon tank into which the water is taken to the roof and to which the hot water returns.

B. In the tank is a heat exchanger that heats the water in the in-floor heating system. There is an instant water heater (gas) that finishes off the hot water for the in-floor heating system if it is not hot enough (~85 degrees). This in-floor system had issues and the plumbers came out to work on it a couple of times and while they were at it they worked on our system.

C. there is 1/4 inch drop per foot through the whole house and the pipes are insulated in the unconditioned space of the attic.

D. We are using two pumps inline, a Taco 009 and a Taco 006.

E. There is a differential controller telling the pumps when to run and when to cut off.

The History:

The systems were installed in the summer of 2006. The pressurized system has been OK all along but the drainback system worked until the boiler that runs the in floor heat shut down in the middle of the winter. I assume that the water in the tank would stay pretty hot if it is not having the heat pulled off of it, but doubt this could hurt anything? When they (the plumbers) went to turn the system back on, water would not pump through the whole system. It would pump water up but then never far enough to go through the panels. The pumps were switched out because the plumbers felt that the pumps were bad. They later told us the pumps were OK and reinstalled them. The system was tested in summer 2007 and it worked (that is it pumped water through the panels). And it worked fine until sometime in January of 2008) the boiler/in floor heating system went down again. Same thing happened when the boiler was repaired the pumps would not pump water through the system.

In spring 2009 the system was tested and found that the pipes in the Solargenix panels had busted.

We don't know why they burst. Here are my thoughts on what could have gone wrong:

1. The plumbers filled the tank up too much and the water inlet pipe was below the water line, resulting in a slow drainback and possible freezing in the panels.
   
2. The differential controller went bad and pumped water to the panels when it should not have (at night).  
   
3. We have 3 right angles in one location (to get around air heater ducts) this is in a place where the pipe drops straight down for about 17 ft. Maybe the flow is slowed down by these sequential right angles, enough so to allow water to freeze in the panels.
   
4. There may be a slight sag in the roof such that the panels themselves are out of plane with each other. Causing a spot for water to get caught?
   
   

I have one other random question. Is replacing the cartridge in the taco pumps enough to fix them and fix them right? The plumbers when testing the system in spring 2009 left the system on and the pumps ran without water in the tank for an undetermined number of hours.

Thank you for your thoughts,

Mike D

[GaryGary]

Hi,

I don't have any experience with these collectors -- so this is just opinion from looking at the diagram.

I would think it would be worth trying the repair.  The reflectors are non-imaging, so you won't have to get the pipes back in to exactly the same spot they were.  Even if you miss a little bit in the burst area, the performance of that particular area might be down a little, but the rest of the collector should be fine.  You have little to lose by trying it.  

you might also just want to look at the burst section -- depending on the crack size and location, it might just be easier to solder it closed. I would think that in a non-pressurized drain back that any solder good for (say) 400F would be OK.

If all else fails, you might be able to get an absorber only to replace the whole absorber.  This could potentially be from Solargenix or even some other place with a regular flat plate absorber.

Obviously something is keeping the collector from draining back.  The return line going below the water level in the tank that you mentioned is a good candidate.  It has to end above the water line to let air go up it and replace the water.

All the plumbing has to have a good slope, but sounds like you did that.

The collectors or bank of collectors need to be "clocked" a little so that they drain toward the supply line.  

Beyond that, I don't know -- some kind of blockage in the plumbing?  Valve left in the wrong position?  

After you think its working right, you need to check in some way that its really draining back reliably.  Sometimes you can hear it pretty well.  

The drain backs I have experience with drain back quickly and they are fairly loud during the drain back -- I would think that a system with this much vertical would sound like a fright train when its draining.

Drain backs are pretty bomb proof if setup right.  I think that overall they are more reliable than antifreeze protected systems because of the antifreeze maintenance issues, so once you get things right you should be in for years of trouble free service.

I would think that replacing the pump cartridges would do it, but you can email Taco about it -- they are pretty good about answering support questions.

Gay

[scottsAI]

Mike D,

My first time designing a drain back system discovered most recirculating pumps do not LIFT water very high, Most would not lift the water up to the peak. The only way the recirculating pumps work, is by completely filling the system... NO longer a drain back system.

Could be why the pipes ruptured.

Check the lift capability of the pumps to determine if suitable for the application.

Lift is determined from the height of the source water to the highest point in the system.

http://www.kingsolar.com/catalog/mfg/taco/009.pdf

Taco 006, lift 9 feet, not suitable to fill system, OK for recirculating once system is sealed.

Taco 009, lift 34 feet, unless system is taller should be OK for filling system or recirculating.

Check pumps installed correctly. I suspect originally installed reversed locations. (the "why" it would not fill, yet did later...)

Verify the drain back valve is setup correctly and works.

When it gets cold it should drain system, completely.

I would test the system after you get it working.

Input temperatures to simulate and verify it drains and fills correctly.

No reason to baby-sit a system.

As Gary said, should work if set up properly, which your system is NOT.

Remember plumbers know how to plumb, found it very difficult to find a plumber that knew anything about a solar heating system let alone how it worked. Solar heating is not your typical system.

Have fun,

Scott.

[hydrosun]

I put in a drainback system for one customer. The weight of the panels caused the roof to sag more in one area and water was trapped and froze. I was able to open up the back of the panel to get to the rupture.  I pushed the hole back together to a crack. There wasn't enough room to solder it so I used a two part epoxy in a roll from the plumbing department at Lowes to seal it. It has been working since last spring. Not sure about the longevity of the fix in the higher temperatures of a concentrating panel. Just what worked for me.

Chris

[frackers]

I don't have a domestic drainback heating system but my swimming pool one is and the critical part is the air valve at the top of the solar panel. This allows air to enter the panel when the pump stops - its basically a well foot valve -  a sprung loaded valve that is normally closed but a small amount of suck (the weight of the water in the system above the tank) will allow it to open and let in air.

I had a sticky valve a couple of years ago and lost the manifold at the bottom of 50 square meters of panel as a result.

After the repair I insulated the manifold so even if the panel drains but the manifold still holds a small amount of water, it is unlikely to freeze - seemed like a good idea at the time!

[GaryGary]

Hi,

Some of the drain back solar water heating systems do use the vacuum break valves.  But, they are not really needed if the system plumbing is setup right.  I think they are best avoided for the very reason you had trouble -- if the system needs the vacuum break valve, and it fails, you can have a freeze and burst problem.

Gary