Glycol turns to steam

rt_2

I have a closed loop system using two 25 evac tube system with a 80 gallon storage tank. The system is filled with glycol. I've always been concerned as to what would happen in case we had a power outage. I decided to hook up my controller to a battery back-up system which is also used to supply power to my pellet stove in an emergency. It happened today. We lost power for over an hour and the sun was just as bright. If I hadn't been connected to the back-up, I know tha the glycol would have boiled and would have venedt out to the atmosphere. I have a pressure regulating valve but it would have been useless because my well pump would not have worked. My question is could there have been any permanent damage caused by an outage if I didn't have the back-up? Thanks for any input.

rt 

Fortunat

No problem if the system is properly designed

RT,



As long as the system is properly designed (sufficient expansion volume) and doesn't have high vents on the roof, putting a solar hot water system into stagnation for a brief period of time due to a power outage or component failure is not a catastophic event.



The system gracefully goes to steam and then recovers once the sun sets or goes behind a cloud.



In fact, many (most) of the european Combi solar systems are designed using this as their primary overheat protection. see specifically the many articles published by Hausner and Fink et al regarding the  stagnation behaviour of solar thermal systems.



for example: www.aee-intec.at/0uploads/dateien119.pdf





best of luck,



~Fortunat

Bob Gagnon plumbing and heating

Tube Protection

My 120 tube system has boiled over a couple of times when we lost power. I cost a few bucks to replace my anti-freeze. I was thinking about adding a second redundant 12 volt pump to work alongside the main pump. This setup would protect me in a power outage, main pump failure, and sensor and control failure, this 12 volt pump will have its own sensor and high limit switch.



Thanks, Bob Gagnon

rt_2

12 volt pump

Bob,

How mwould you power the 12 volt pump?

rt

Bob Gagnon plumbing and heating

Back Up System

I would hook up the 12 volt pump to a deep cycle battery that I would put on a trickle charger a few times a year. Any thoughts on this setup?



Thanks, Bob Gagnon

Kevin_in_Denver_2

KISS

You might consider dumping the heat with a thermosiphon loop out by the panels. That way you wouldn't have any rarely used 12V devices backing up your 120V devices. The worst thing in the world for a pump is to make it sit idle but hot for two years at a time.



After you sell that house, the new owner will tear out all that stuff the second time he pays someone $300 to come out and refill the system, so keep it simple.

Kevin_in_Denver_2

Water feed on a glycol system?

rt,



You said you have a pressure regulating valve. Are you saying that if you have a small leak somewhere, your glycol system will eventually be full of 100% water?You may keep an eye on your system to prevent that, but always think about the poor guy who inherits your house and has no clue about how it works.

Mark Eatherton

You're missing some critical check valves Bob...

If someone were to install the two pumps as shown without check valves, they wouldn't do much good :-)



Oversight, I'm sure.



ME

rt_2

Check valve

Don't the pumps have a check valve built in? Mine had one but I removed it and installed a check valve which has a manual overide. I found that the spring in the pump check valve was not strong enough to hold the valve shut when the system shut down for the night. Then the system would thermal siphon all night long and I'd loose all the heat I gained the day before. The manual check valve has a much stronger spring which prevents thermal siphoning.

rt

rt_2

pressure regulating valve

Yes, the valve is just in case I develop a small leak. I check the strength of the glycol every 3 months to make sure it doesn't get diluted with water.

rt

Bob Gagnon plumbing and heating

Check Valves and Circulator Pumps

Mark, it's a conceptual drawing, I don't include every valve and device, the cad drawing would be too confusing. I use Grundfos 15-58 circulators with built in checks, and haven't had a problem, but I will check them again to make sure I'm not losing some heat at night. I'm hoping to find a 12 volt Lainge circulator with a built in check also. Mark, can I install the 12 volt circulator in line with the 120 volt circulator, right after it, not alongside it like in the drawing? It would be a lot easier to pipe it that way. I haven't had any problems with cartridge circulators freezing up, and I would exercise it two or three times a year to check the system. I don't think a thermosyphon loop would work in a power outage with my 120 tube system. If someone has experience with a thermosyphon working in this case let me know. I don't ever plan on selling my house I built it 22 years ago and I have great neighbors.

Mark Eatherton

Understood Bob....

I just want to make sure that other people viewing your drawings understands that they MUST have checks in there if there are two pumps in parallel. Otherwise you end up with a small pump powered circle jurk between the on and off pumps, with little flow going out to the system...



Regarding series pumps, yes you could but, the standby pump would turbine when not in use but seeing flow through the pump. It would turbine backwards, so IF your control logic was quick enough to immediately throw power to the standby pump upon power failure, it COULD be spinning backwards, and could continue to spin backwards. I know this goes against intuitive thinking, and I could be wrong as it pertains to brushless DC motors, but I HAVE witnessed this in PSC motors.



Other than that, the pump would present itself to the system as additional resistance value, but if like most systems, you have excess capacity, shouldn't be a big deal.



Way back when, I came across a two pump series system, and the pumps were of different size. IMSMC, there was a Taco 0011 with a 009 down stream of that.



I've always been told that if you are going to do pumps in series OR parallel, they MUST be of equal capacity,head and GPM wise. These two were obviously NOT a matched set, but he had a time delay relay on the bigger pump (DB solar system) and after 10 minutes, the big pump would drop out and the little pump would maintain flow.



It appeared to be working fine, although on start up, the little pump kinda made noises like it was being over run....



ME