Steam lock

mars_6

Hello all I have a 4 panel Viessmann 200T system direct flow through 18 tubes per panel. Got a call from the homeowner last week the Resol controller was reading 270 deg. Not good, went out and looks like a power failure had caused the panels to stagnate. Flushed out the burnt up viessmann tryfocal glycol with TXP and repurged. System ran over the weekend but got air locked. Burned up the new glycol but today was on site and trying to purge the old system and could not get flow throughout the array, before I was able to cover the panels I was seeing collector temps of 385 deg. Talked to some people and steam lock came up. I tried to blow the system out after covering the panels with a 1/2 hp purge pump as well as with 80 psi air to no avail. Any thoughts would be greatly appreciated. Thanks Matt

matt_sunwaysolar

Sounds more like a blockage than an air lock or "steam lock". Even if the pump was undersized, you would be moving some air or fluid from the system. When you blow out with a compressor, is any air coming through at all?

If it is a air or steam lock, a high-point air vent should help.

Not very familiar with the Viessman's but could the manifold be damaged at sustained high-temps, causing a blockage? Any other valves/ components that could be melted or seized?

In similar circumstances, I've isolated and tested different parts of a system by strategically placing ball valves and boiler drains to determine where flow is becoming an issue.

Also, and I know this is obvious and simple, but are the check valve and pump moving in the same direction of flow?

mars_6

So it was not a steam lock, we had glycol burnout. The array is a 60 tube direct flow through design that has a 3/8" outer tube that a 1/4" inner down flow tube fits into the individual tubes. It is designed to very tight tolerance. The glycol in the system got so hot that the sugars in the glycol solidified in some of the tubes. The resultant carbonized material has impeded some of the flow through some of the tubes completely. I suspect I will have to replace some of theses and am resined to that. My question is would anyone know of a method to flush out the tubes when there not collected to the collector manifold to try to salvage as many as I can. Thanks for any help mars.

mars_6

Okay I found a partial solution to the blocked inner down flow tubes, I have also at this point been able to get good flow out of 17 of the 19 tubes I have manually cleaned. 2 of the 1/4" down flow tubes cannot be cleared and I will have to fabricate new ones. It appears as though the glycol when it stagnated broke down into 2 types of solids, one being a black rather Carmel type of material and one that is reddish in color and looks more like a clay material. It is interesting to me that the two tubes with the clay material were at the hot end of the manifold. Just thought I would post this if anyone has any input it would be appreciated. Thanks Matt

matt_sunwaysolar

I've seen the black flakes that you're talking about in really broken down, stagnated glycol as well. Once on a 20 collector (flat plate) system with an undersized expansion tank and prv. Once on an oversized Solar Panels Plus evacuated tube system. Flow was not blocked though, like you experienced.
On the oversized evacuated tube bank (100 tubes to 80 gallons storage for industrial process heat)(not designed by me), which was not working at all, I added a mechanical three way, thermostatic valve (no electronics) with heat dissipaters that circulate through the fluid through the dissipaters when the fluid gets above 210F. Of possibly more interest, I also added a Zilmet SolarSafe Expansion tank, which is an expansion tank that has a cooling chamber for glycol in it, specifically for periods of stagnation. Larger expansion tanks help too. I have checked up on that system a few times and after three years, it's still running very well.

Noburst also makes a good hydronic system cleaner.

mars_6

Matt thanks for the help, I will look into this solution and see if it makes sence. Matt

mars_6

Ok at this point we know we have good flow throug the evacuated tube heat collectors, we went through each one and varified good flow through each one, I will need to manifucature down flow tubes for 2 of the collectors as I canot get them cleared. No big deal as I have that plan in the works. It seams that that these panels are so hot under stagnation that I need a secondary pumping station if I have a primary pump failure. I'm thinking a Johnson a 350 control that if it sees to high of a temp at the manifold of the solar array it will kick in a heat dump, I have a fabricated heat dum I am using for over temp of the tanks but am thininkig this is the wrong thought processes, I think I need to try to protect the solar array with the heat dump if the primarary circulator on the array fails. Any thoughts. Thanks Matt Rossi FSH

matt_sunwaysolar

If you're only trying to protect against power outage you may just want to go the route of an UPS (Uninterruptible Power Supply) that will power your pump/control in the event of an outage.

If you're only worried about a pump going bad, and not a power outage, the method you're describing should work using an additional controller and pump. I am not familiar with the control you mention, but I imagine a set point control would do.

If you're also trying to prevent overheating, the mechanical thermostatic three-way valve I mentioned earlier is a way to go. It is an enclosed, marine-grade valve, with no electronics involved. You order it at a specific temperature setting. I believe common temp. settings are 210 and 180. Like a typical three-way valve, it has an inlet and a normally open outlet and normally closed outlet. When the temp of the heated solar fluid I s under the set temp, the heated fluid returns to the HX through the normally open port, per standard operation. When the temperature of the heated fluid gets to the set temp, the normally closed port opens and diverts the heated fluid through the heat dump to dissipate the excess heat. The cool thing and also the trick is that because no electronics are used to operate the valve, the standard control/s and pump/s are used with no additional programming. The trick is that the high limit (upper limit) that turns off the pump when the storage temp gets too high must be set high enough that the solar fluid will reach the set temp of the three-way valve before the high limit of the storage is reached. That way the pump continues to operate and push fluid through the heat dump. If the solar fluid cools down and there is still a demand for heat, the valve will go back to normal operation. When the sun goes down, the system turns off. This is a great method, especially if stagnation/ overheating is not expected often. It will also work fine for periods of stagnation at regular intervals.
I had a few concerns when I used this method on a system, just because I had never seen it used before. After speaking with the product reps, I felt good enough about it to give it a shot and was very happy with the results. I was able to salvage a system that would not work as designed/installed relatively easily. While I cannot vouch for their full product line, I got the equipment pretty affordably from Solar Panels Plus.

Hope this helps. If you want more info about any of this, let me know.

plumb12

Air or steam problem.
My first thought was are the array's piped in a reverse return sequence, meaning first in last out? Which would equalize the pressure to each panel, along with balancing the energy production of each panel.
The next was is the purging happening on a bright sunny day? If so, the fluid will flash to steam. Also if an air vent is used at the top it needs to be valved off and it should be closed after you have commissioned the system.
As for the glycol protection an anti-stagnation loop is the best for efficiency, whereas you can utilize the excess heat i.e. remove it to a basement or crawl space.
To protect the system during a power outage the steamback method should be used. You need to account for all the solar fluid in the panels and all outdoor exposed and/or uninsulated piping plus 10% for safety. Once that has been determined the expansion tank needs to be sized for this amount. This way when the solar fluid flashes (+/- 240 deg F) to steam, it will force all the outdoor exposed fluid down into the expansion tank.
The steamback method can be employed without the use of a heatdump too. The piping which will be in steamback should be installed with a high temp solder or be brazed. Keep in mind though if the DHW calls, the solar thermal sytem can't work while in a steamback mode.

mars_6

Okay so after more than a hundred plus hours into this debacle I have come to the conclusion that the array canot be reclaimed. I will be working with the manufacture to see what warranty may be offered. This system only 4 years old and to have suffered a catastrophic event that is non recoverable is not cool. I now that the manufacture Viessmann has discontinued the product line and has a new line that is not as prone to the problems my client has experienced. Yet another thing i was suppoesd to learn today.

wellen

It could be a steam problem.