Solar overheating issues

Unknown

work really well. You get to use tubes and drainback. Here is a couple of pics. My drainback system on the roof(15 degrees right now) and my mini unit on the porch just stagnating away every day....no problems. So far the one on the porch has also been St. Bernard proof and thats really amazing. The panels are laid out on the roof for an additional 3 more but being this is my first winter with them on my house I can see already that trying to heat in the winter is out of the question. There just isnt enough sunny days to make it worth while. In my opinion Wayne, dont over complicate this stuff, its really easy and works great for getting lots of free hot water in summer and spring and early fall and maybe with 5 panels I will get more hot water in the winter when the sun shines. We are unwittingly doing exactly what the oil companies want, overcomplicating these things and selling to people who have more money, which is very few. They only way we as installers can help those arabs drink their oil is get alot of simple low cost systems on the roofs of everyday American homes.
TONY

Wayco Wayne_2

It seems to me

that closed loops are pretty easy except for the rare occasion that you may face an extended power outage, such as a hurricane knocking out power for days like we had 6 years ago. In Tom Lanes book he seems to like PV panels running DC circs as a protection and an energy savings. A local solar contractor I know sez he has not had good luck with these and sometimes has trouble getting enough capacity. I have been turning this over in my mind and looking for solutions. I read that putting a DC circ and an AC circ in parallel is sometimes done. I thought, why not in series. Make the DC circ the main one and back it up with a variable speed AC circ. That way you can save on electricity and have enough capacity, and have protection in an extended power outage. I think about Bob up in Mass and all those evac tubes. What a disaster if the power goes out for an extended period. What do you do. Drain and replace all the glycol? Do the Evac tubes get damaged in the overheating situation? What if you drained the system would that be better or worse?

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Derheatmeister

Drainback

WW,How about doing a drainback then you do not have to worry about the power failures!

How many panels are you planing on installing 2 to 3 for domestic? Or more,for Heating?

I have worked on some PV powered Systems (Heliodyne)Gobi,and they work just fine for Domestic.

As of the Evac tubes: they are not any good in a "Drained" or empty system!

Up here in Colorado (10000+ feet) i am seeing massive failures to Evac tubes and i am not sure Why!
Maybe a bad batch ? Altitude or overheating in a power failure ? They are supposed to be able to handle Stagnating !

Back to Flat plates and or KISS (Keep it simple st....)

Time for some Data logging on the evac systems! Richard

Mark Eatherton

What kind of failures are you seeing Richard?

Not much to go wrong with these puppies...

ME

Unknown

Like Mark ask

What kind of failures on what type of tubes? Double wall heat pipe? single wall? What brand? Were they installed properly? How old were they? Can you post some pics?
TONY

Simply Rad_2

Evac tubes

I can agree with the meister on the evac tube failures. We have had about a 15% failure rate on the vacuums. The gray smoke on back and condensate are tell tail signs. Meister and I are both using the Viessmann tubes(thermomax). So the quality is there. I spoke to the thermomax rep and have not heard back. I also think that for low temp applications the flat plates can't be beat. Tubes seem to work best with large delta Ts. I am going to try drain back with flat plates on our next solar DHW system.
Jeffrey

Unknown

Are Viessmann tubes

single wall or double wall tubes? And where do you find the glass breaks?
TONY

Wayco Wayne_2

I am considering

going tubing. My house's solar site is not so good. I looked at my roof from the MS Virtual Earth. My back roof faces SE. about 40 degrees off South. There is a high tree line that diffuses the light in the Winter Months. I read some charts that showed that tubes gather more from the side than flat plates. This is important given my angle to Solar south. Also I am a small company with not much man power. Tubes are easier to get on roofs. I'm going with 3-30 tube arrays standing at 59 degrees pitch. I have a radiant slab in a shed behind my house I can use as a dump zone. I could also use my snow melt sidewalk if need be. I looked at the Apricus line of tubes this weekend at a Solar Conference. They have collector all around the inside of the tube, not a flat plate inside the tube like the Thermomax so It seems more multi directional. SSPC charts showed them more efficient than Thermomax also. I have also been looking at a Laing DC circulator.

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Unknown

Apricus tubes are

double wall like the sunmax. I went to the Viessmann site and looked at their tubes, it appears they are still making the older style tubes, single wall with a seal between the metal and glass. This is the weak point because of the coefficient of expansion between the glass and the metal alloy. post pics when your done.
TONY

hot_rod

Mike over in Aspen

has been seeing some unusual evac tube failures also. 25 tube failed in less than 5 years on a 125 tube array as I recall.

It would be nice to documant some of these failures.

Another long time installer in Canada claims a 30% failure rate in evac tube systems he has installed.

A conractor in Wisconsin has a seriously underperforming evac tube system on his own home.

I get to meet and talk with a lot of old time solar installers these days, so I ask the folks about there experiences, and generally get some excellent first hand info from those that have walked the walk.

3 areas of concern with tubes, in my opinion.
Loss of vacumn, easy to determine by cloudness of the tube. Loss of fluid or vacumn in the heat pipe tube inside some styles, and poor connection between the condensor and the dry wells.

Evac tube glass is thinner and more fragile than tempered plate glass used on flat panels.

I have heard countless real life examples of 20- 30 year old flat panels still performing as well as the day they were installed. Can someone show me evac tube systems with that track record?

hr

hot_rod

If you need the higher temperatures

or run in cold ambient temperatures , yes the tubes do enjoy a small advantage. I'd say from all the data I have seen about a 10% difference is about right. Under certain conditions.

For DHW preheat and radiant tempeartures, in conditions above 15F, I still feel the panels perform as well, and in some cases better.

The data exists to make this comparison and actual online data logged systems are out there to show in real time the performance difference.

There is a place for both types of collectors, just be sure you are comparing them fairly at YOUR operating condition, not just a snapshot performance number.

hr

Derheatmeister

Mark ,I am going to remove a thermomax 60 tube system up in Montezuma ,it had a petty serious failure:about 60% of the tubes are Broken or full of water and freezing and then Breaking..

That is not so good for a 7 year old system !

This system is interfaced with domestic hot water and a Heating system so it has plenty of heat dump..

I also have seen the Smoke in the tubes on Viessmann tubes( Like Jeffrey)in Breckenridge and in Camp Hale Leadville (About 20 % Failure)

So for now i am a little skeptic about the evac tubes in Altitude ??

I have been working on one of Mike's large systems in Keystone(Novan flat plates got to love them !), it is about 20 to 25 years old and still strong if they (Keystone resorts) will not let it freeze again!

Wayco Wayne_2

Here's an ariel view of my house

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"As you can see my back roof is South East. My house is the one with the light colored shingles.

Eric_6

re:Thermomax tubes

I travel the state of Colorado and look at installations as
a field representative for a wholesaler of solar thermal and hydronics.
In most cases for Thermomax tubes it could be that the thermal limiter has a limited life and then the high heat that the condenser tube is putting out on a undersized storage system or undersized heat exchanger is
destroying the vacuum. Saw Heatmeister's system and have talked to Mike @ Aspen Solar and have seen another 150 tube system w/30-36 tubes failed at year 1(which had 5000 gallon storage but with only a 100 ft x 3/4" smooth coil).

Heat kills everything in time. Annual maintenance required no matter what (closed loop, drainback, mod/con, or vehicle).
All the best to you. Eric