Bubble Foil Bubble Trouble (ME

Nate Greenleaf

I feel that I should weigh in on this topic due to my "inside" knowledge on the issues at hand...

We at EOS Solar manufacture an evacuated tube solar collector, so it would seem that I can offer a better educated opinion than most.

1.What many people don't understand about the SRCC data is that the tests are preformed at an ambient temperature nowhere near a real world application in a colder climate. The efficiency models seen on an SRCC chart start at an ambient temperature of 77°F. This means that if you were to look at the column labeled (C) of an SRCC chart where the Delta T is 36°F, the ambient temperature of the air is 77°F and the solar fluid temperature is 113°. In column (D) this would be a 90°F Delta, or 77°F ambient and a fluid temperature of 167°F. What does this mean? It represents that the test data is good... for Florida, and does little to respond to the query as to what the performance output of a collector would be at say: 15°F ambient in category (D).

The SRCC is run by the University of Central Florida so it should be no surprise that the data that they supply is sound for their climate. Unfortunately, the data does little to aid in the selection of a collector for space heating in New England or Canada.

This sound data has no basis for these arguments, as it does not account for the actual collector losses to ambient air temperatures. Studies published in various solar trade publications have substantiated the claim that Evacuated Tube systems can be up to 40% more efficient than a comparably sized flat plate system in ambient conditions below 50°F. Why is this?

This is due to the fact that the evacuated tube is exponentially a better insulator than any form of glazing on a flat plate collector. Why do you think the flat plate collector manufactures and proponents gleefully will declare that that the flat plate collector will shed snow. Clever marketing to offset product deficiencies. A flat plate collector will shed snow because the energy that it is supposed to be collecting and transporting into the home for use, is re-radiating back out into the colder air surrounding it. I personally would not want to advertise that my collector was dumping heat back into the environment at a level that it would "melt snow". See the attached picture of an Evacuated tube panel beside a flat plate. It was taken using a thermal imaging camera at an ambient temperature of 30°F under 1000W/m2 solar gain. Needless to say a picture is worth 1000 words. (how many have I used so far?)

2.There are different types of Evacuated Tube Collectors.
-"Super Tubes" like Viessman and Sunda.
- Twin glass evacuated tubes like EOS or Apricus.

The collection surface on a "Super Tube" is essentially a flat plate collector crammed into a vacuum tube. This is a clever way of reducing those pesky ambient air losses. Unfortunately, the tracking abilities of the twin glass form are not seen here either.

The collection surface on a twin glass tube is the entire tube itself, due to the sputtered surface coating on the outside of the inner tube.

This means that the collector surface on the Twin glass tube is round, and unlike any flat plate collector, it provides you with a passive tracking device built into the design of the collector.

The downside? A twin glass collector is less efficient than a flat plate collector at solar noon because the spaces between the tubes provide a loss of energy to the roof below. Fortunately, this only lasts for about an hour. Then the passive tracking design of a twin glass tube shines. Performance curves accelerate beyond the flat plate for both pre-noon and post-noon values. The best output a flat plate can provide is at noon and is measured at 100%. A performance curve will represent this as a Bell shape. Whereas a twin glass tube collector will will represent itself more like a camel back with two humps. A steady incline in the morning, a slight dip at noon, then another increase in the afternoon. These morning and afternoon bumps can be upwards of 40% MORE output than a flat plate collector. Not only that, but if you have a cloudy day at noon, you just lost your "window" of opportunity for solar collection, as your efficiencies will start to decrease. Not so with a twin glass evacuated tube. They collect energy during the "meaty" parts of the day.


Sigh... I could go on and on, and I will if probed accordingly.

[Deleted User]

From the famous Mr Bean's wonderful web site...

http://healthyheating.com/Page 55/Page_55_o_bldg_sys.htm

Save the aluminum for the construction of intelligent things, like beer cans and beer kegs.

If you have never been to Roberts site, I STRONGLY suggest you do so.


www.healthyheating.com

Definately worth the time. Thanks for the education Robert!

And thank you for your ongoing contributions to man kind.


ME

Dave Yates (GrandPAH)_8

I always

learn there.

hot_rod

Excellent!

That list should pretty much clear the air once and for all on bubbles and use of aluminun under radiant tube as a energy reflector.

hot rod

Paul Pollets

Thanks...!!

I thought so, now we know so. Forunately, I used the foil bubble stuff only once in 1999. I wasn't impressed by the performance, and it was used under a gyp overpour on top of concrete.

I'm hoping the solar biz won't be inflicted with the snake-oil claims, as it becomes more popular. I expect to be hearing that flat panels are just as efficient as vaccuum tubes.

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Dave Yates (GrandPAH)_8

nasty grams here

Paul,

Following my article on my vacuum tube array, I received several nasty-grams that pretty much said as much!

hot_rod

Actually...

flat panels are more efficient under certain conditions. Plenty of third party data to support that conclusion

hot rod

Paul Pollets

Huh??

What conditions?

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Unknown

evac tubes are pretty much only better in the north.

Down in more direct isolation areas, flat plates work just fine.

at least, that's what everything I've read on it says... I don't have the direct knowledge to say that it's true or not.

hot_rod

low temperature conditions

where SDHW and radiant systems operate. Use the SRCC data to see the efficiency differences.

There are applications where evac tubes "shine" high temperature systems, areas that don't get a lot of snow are a few

Keep in mind the evac tubes are about 3 times the cost of the flat panels, also.

hot rod

scott markle_2

nit picking

Paul,

At peek insolation and high ambient temperatures Viessman flat plate collectors are actually slightly more efficient than their evac. tube model of the same surface area. Seasonal averages are lower, still considering the price difference and questions about the longevity of vacuum seals I question wether evac. tubes have an economic advantage. Certainly in southern california, Florida and other similar areas flat plat collectors make more sense than tubes, Wouldn't you agree?

I hope that the Schot all glass tubes are available in NA eventualy, these tubes circulate transfer fluid directly through the collector, no heat pipe, no minimum pitch,no hx losses(at collector) also the all glass construction seems to me to be much more bomb proof, I'm suspicious of the long term viability of mechanical seals given the extreme thermal conditions, even with the mysterious and cool sounding Barium getter in side. Siedo (a Chinese manufacturer ) (they make the Oventrop collector) makes a direct circulating tube collector but it is not an all glass design.

ALH_4

Flat Plate vs Evacuated Tubes

A blanket of snow that does not melt has a pretty significant effect on evacuated tubes. In cloudy areas where snow is not common, I could see evac tubes outperforming flat plate collectors.

In general, in direct sunlight flat plate collectors will hold their own with evacuated tubes. However, transportation and installation of flat plate collectors is much more difficult, particularly for roof installations.

scott markle_2

Andrew, Very helpful information,thanks.

As of yet I have no experience installing solar thermal. I had forgotten the obvious installation advantages of tube collectors. There sure are a lot of factors to consider. As a one man outfit I can see where I would be much better off advocating for tubes (roof mount). Unfortunately this would be based on my comfort and safety not necessarily performance or payback.

Paul Pollets

Great!!

Thanks for the info and charts, Andrew. Very interesting!

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hot_rod

A good study

but it is a bit skewed by the location of the two types of collectors. And the actual collection area is not equal. A 32 square foot flat panel exposes most of that area to the energy source, where as a 32 square foot evac tube, due to the shape and space between the tubes would expose less surface to the sun.

It's a surface area game no matter how you slice it. Running the numbers, all the numbers, is the only fair way to compare and make a decision.

Use the data from the SRCC Solar Rating and Certification Corp. They test and rate various panels, under identical conditions.

Here is an example

Model a SDHW panel, assume a 30F outside temperature at the collector. Use a incoming water temperature (my well water actual) of 55F. Use the SRCC graph I posted above and you will see the flat plate at 54% efficiency while under the same conditions the tubes are running 38%.

Nothing against eveac tubes, properly applied they are superior. Ii've had evac tubes on my shop for about 6 months now. DHW production mainly. The 4X10 flat panel I removed provided quite a bit more SDHW.

If your design is for SDHW or low temperature radiant, anything below 140F flat plate would be my suggestion.

Now run the life cycle cost tables. It's possible the evac tubes could lose their vacumn, and warranty before the payback.

So before you start selling solar be sure to do all the research based on actual certified outputs, cash flow, and life cycle analysis.

Not just the glossy sales sheets

I have a hunch that their will be some excellent, contractor friendly, solar info available for the first time ever at the upcoming AHR show in NY. plan on being there Jan. 21- 25 I believe.

hot rod

ALH_4

Problems with the study

I agree that the location of the collectors is an issue with this study. For some reason, the flat plate collectors were installed in an area where shadows could be cast on them from the higher roof line. I wish they had mounted them closer to the ridge, or on the same side of the building as the evac tube collectors.

If you ignore the gross area bars on the graph and use the aperture area, it should be a better comparison. Insulation is probably a significant factor in the comparison during the winter months. However if the roof above the flat plate collectors partially shades one of the panels, as it appears would be the case, the numbers could very easily be skewed dramatically.

Unless installed in a location with a lot of diffuse light, I think flat plate collectors will perform as well as evacuated tubes, particularly in warmer climates. However, if there is not a lot of direct sunlight, it could be argued that solar heating does not make financial sense anyway, particularly with the added cost of evacuated tubes. Additionally, the evac tube collectors with the fluid completely contained in the header are almost certainly less efficient than tubes with the heated fluid running through them. More heat transfer steps and boundaries mean more loss. This may put these evac tubes more on par with a flat plate collector with higher insulation losses.

This has nothing to do with bubble wrap. ;-)

hot_rod

Andrew

I'm all for real life testing and comparisons. I do a lot myself with a grain of salt.

With so much data available from multiple sources across the globe regarding collector efficiency comparisons... Why model a comparison study with a shaded collector? Although he does come up with an answer I agree with:)

Reminds me of a couple of my favotite "Dale-isms"

"Framing real and appropriate questions and putting realistic answers to them is engineering."

"You can't use the output of a solar system twice."

Or
"As long as the building is under load, there is no solar system that is more efficient than a window that is gaining more than it's losing."

Where's ME with his super glass! Since we have completely hijacked his very useful thread, sorry Mark, we got carried away....

hot rod

[Deleted User]

No problem...

You guys change the topic, and I throw some timely photographs into the picture...

Here's a system we completed today. THere is another identical system to this one. This array is hooked to 2 each 80 gallons Steibel Eltron dual coil storage tanks. Both coils are being utilized for SDHW preheat.

The building is undergoing major changes, and numerous trades people were walking by, making comments and asking questions. I mentioned to the electrician that these things were so efficient that they could suck heat out of the clouds, on a cloudy day.. He leaves.

1/2 and hour later, a carpet layer walks by and sez "I understand them there things are so efficient they can suck heat out of a night sky..."

1/2 and hour later, the painter walks by and sez " I hear tell them things can pick up heat off the moon!

1/2 and hour later, the plumber walks by and sez, " I hear tell them thangs are so good they can suck the heat off the next planet..."

Funny how rumors get started...:-)

Truth is, in all my years, I have NEVER seen a flat plate collector pull heat out of a cloudy day, but HAVE seen these evacuated tube collectors do that.

THe good folks at Low Energy Systems provided the components and installation advice, and performed the solar calculations. THis sytem serves a 24 unit apartment complex. THe solar fraction as a whole was not very large (~ 20% of annual needs) but the solar efficiency was HIGH, around 76% if memory serves me correctly.

I'm a BIG fan of SMALL systems. Better utilization efficiencies.

Long hard day. 120 square feet of Viessmann Evacuated Tube solar collectors installed. Great product.

And kudos to my wild Irshman installer, Sean Smith, and his ever present side kick, soon to be lead man, Chris Nedrow. Great job guys.

ME

hot_rod

Nice work,ME

what a good job of finding a "spot" to place the array.

With over 300 days of sunshine over most of Colorado you probably don't get much chance to test cloudy day performance between the two types of collectors.

I have 3 different active solar systems running at my place. all have used flat plate collectors, over 16 years old!, that are still cranking out the BTU's.

Clarence Beaver, a solar veteran with over 50 years of hands on experience, sent me some pictures of evac tube installs in his area. Tube replacement is an ongoing and constant maintenance issue on the large arrays he showed me.

I think there is a place for evac tubes in some applications. I don't agree they are a replacement in most cases, however, for a good flat plate. Time will tell, just like instantanous water heaters, I suppose. Happy Holidays to you and your clan.

hot rod

ALH_4

Studies

I'm not holding this up as the definitive proof that flat plate collectors are better than evacuated tubes. It's just an interesting study with obvious flaws. Every study of heating I have seen has flaws. In this case, these flaws are fairly major, with the location of the flat plates being the most obvious. The location seems less than ideal, even if they weren't going to use them for a published study.

Solar energy is particularly difficult to study as the input and output both vary annually, seasonally, and even hourly. Also the climate can vary widely over small distances, so what holds for Butte, MT will certainly not hold for Helena, MT. I think I cross at least 5 distinctly different climates on my daily commute. Granted, the topography is a little more dramatic here than some other locations. I pass a fire station in Elk Park north of Butte each day with a PV array that has to be extremely ineffective. I havent seen an area that has much more weather of all kinds than Elk Park. Go 20 miles north to Boulder and that array could be very effective.

How can I look at the insolation maps published as gospel by many manufacturers to calculate the performance of solar systems when the climate can vary so dramatically over a space of 10, 20 or 60 miles?

As I understand things, the primary difference between evacuated tubes and flat plate collectors is the effectiveness of the insulation.

Critical thinking is essential in everything we do. It's particularly essential when evaluating how appropriate solar energy is in a particular location.

Unless someone is buying Chinese evacuated tubes, the price difference between evacuated tubes and flat plate collectors is very difficult to make up with the added efficiency of the evac tubes (if there even is added efficiency). Obviously ROI is absolutely critical with solar installations. Determining which type of collector is most appropriate for a particular job is far less straightforward than reaching for a Vitodens, and the study I posted technically only applies to that house during that year.

To bring this back on topic, I used bubble wrap to pack a few Christmas gifts for shipment this year, which is about all that bubble wrap is good for. ;-)

Larry Weingarten

grain of salt

http://taxshine.com/ is a collection of articles by Steve Baer of Zomeworks. He may sound curmudgeonly, but sees through the hype. I find his writing refreshing ;~)

Yours, Larry

ALH_4

Passive Solar

Passive solar is the most efficient way to save energy. However. solar hot water collectors are very different from, and much more efficient than PV panels.

Biofuel is far from being an answer. It may make the problem worse, but that's a completely different thread.

Todd S_4

Solar Question

I agree with you HR. I lived in Colorado and it does get the sun - When its not dumping that great snow! I was in Eagle County for a year and the only clouds we had were when it was storming. Anyway, I wanted to ask is the flat plate better vs. Vac tube in a snowy climate because you can't reverse the flow to melt the snow off the collector? I suppose if the vac tube freezes over, there is no practical way to melt it.

hot_rod

evac tubes

need to be pretty steeply mounted in snow country. 50 degrees or more I have been told. Even so the snow will tend to collect between the tubes as they never get warm.

Depending on the temperatures you need to have them provide, the flat panels may be plenty of power and under the right conditions more efficient as the graphs, design data, and real live experience listed above shows.

If you are looking for higher temperatures for panel rads, air handlers, maybe baseboards, evac tubes would be a good choice. Still the snow pack needs to be considered.

My favorite evac tube install is this one with the tubes used as a railing. I believe this house or a similar install is used in some Viessmann ads.

hot rod

ScottMP

May I add my minimal experience?

I visited the Viessmann plant last fall, on a cloudy day, and took their solar class. We went up on the roof to see the evacuated tube collectors. It was cloudy and misting and they where producing hot water. Can't remember the delta T but I was impressed they where making anything. Would a flat plate do this?

I also was impressed with the idea that (for my area, N.E.) that SDHW was the way to go. I will limit any installs we do to DHW.

We haven’t done any yet but I really want to get our feet wet. This type of discussion is very helpful, as The Wall does so well.

So... in New England, with snowy days, cloudy days, and some brief sun (July and August) what would be best for my customers? F/P or Evac. Tube??

Scott

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hot_rod

Hi Scott

Happy Holidays.

The correct answer to your question is It depends.

You first need to define the load. What temperatures are needed, is it a seasonal heating load or yearly DHW. Location of the installation. Location of the panels and their orientation to solar south. Expected return on investment. Which "look" do they prefer on the roof or in the yard. Reputation and actual case histories of the products you are considering. Installation cost difference, and more.

You may find a need to offer several choices, it's not an either or choice with panels or tubes.

You might be amazed how much a simple inexpensive, $200.00 mat type swimming pool heater can crank out in the right application. Maybe more than a evac tube array

Luckily there s some excellent information available to guide you. Some free software and some for purchase to nail down the answers.

Plenty of first hand experience from solar installers here on the wall. Dave, Mark, and Metro Solar alone have 100 years of combined hands on solar experience check out the RPA member list and many of the solar mags and originations.

Attend the AHR show in January for some excellent access to manufacturers and installers.

Research like crazy. I just bought a handful of thermal solar books from Amazon. They even offer used book outlet sources. Paid under two bucks for some solar classics.

Thermal solar is an excellent next step for hydronic contractors and plumbers looking to offer SDHW, and some hydronic component.

There are some amazing products just hitting the market for solar thermal installation.

Pump station modules, new DC circs, great new controls to run and maximixe the energy, new collectors both evac and flat panel are being designed and built as we speak.

China cranked out over 20 MILLION square meters of collector surface last year! Around 18 million was sold in China, a huge solar thermal market, according to a recent article in Sun & Wind Energy.

Let me know if I can offer any help or ideas.

hot rod

Metro Man

Bursting vacume

I still haven't seen any reason to switch to vacuum tube tech-no. Flat plates also will collect in semi-cloud conditions. Even better they will collect with a foot of snow over them... seen it - done it. You'll have to wait a long time for snow and/or frost to melt off a cold tube. As Mr Hot Rod mentioned above the cost are triple-ish of flat plates, more parts, and they do not stand up to hail and abuse as flat plates will. Used to work with a salesman that would walk across the glass to show clients the strength. We have a large stock of used and rebuilt flat plates that we sell to clients that don't need new and will warranty for 5 years if we install.

One big question I have always posed to the vacuum reps is how do I know if the vacuum (or what level) is in them thar tubes? Some say they will cloud but????? Kind of like the argon gas in "high eff" windows....

We in Colorado DO have an advantage with the 300 + days of sunshine... pretty easy to justify a solar installation.

For my money I would purchase 3 X the flat plates.

All that being said it's all good and really all about what design parameters you have for each system. Demand, collector area to storage tank sizing, fluid type, flow rates, tilt angle, etc... all need to be factored in b4 hand. For example we have started super-insulating our ground mount systems just because of the heat loss..... measure a 20* drop from output of return to return to solar storage tank on a system... kinda defeating the porpoise.

Maybe we should start using bubble insulation since there may soon be a surplus???

My 2.5 c

Metro Man.... alias... Mr Flat Plate Drain-Back Stainless Steel Storage Tank Dude

Nate Greenleaf

I feel that I should weigh in on this topic due to my "inside" knowledge on the topic. We at EOS Solar manufacture an evacuated tube solar collector, so it would seem that I can offer a better educated opinion than most.
1.What many people don't understand about the SRCC data is that the tests are preformed at an ambient temperature nowhere near a real world application in a colder climate. The efficiency models seen on an SRCC chart start at an ambient temperature of 77°F. This means that if you were to look at the column labeled (C) of an SRCC chart where the Delta T is 36°F, the ambient temperature of the air is 77°F and the solar fluid temperature is 113°. In column (D) this would be a 90°F Delta, or 77°F ambient and a fluid temperature of 167°F. What does this mean? It represents that the test data is good... for Florida. Coincidently, the SRCC is run by the University of Central Florida so it should be no surprise that the data that they supply is sound for their climate. Unfortunately, the data does little to aid in the selection of a collector for space heating in New England or Canada.
This data has no basis for these arguments, as it does not account for the actual collector losses to ambient air temperatures.

Dennis Bellanti_2

Buderus - Best of both worlds??

I recently installed a "test" Buderus solar system at my house. They are flat plate collectors that are filled with Argon gas. I have seen them perform very well on cloudy days. One day, the tank was satisfied, the collector temperature was 350 degrees F and I could put my hand on the glass! The attached pictures show ice hanging from the frame on a clear day and a photo of the control showing temperatures. These were taken mid-morning.

The system is glycol filled but when the system is satisfied, the glycol evaporates into the expansion tank so you don't have to worry about stagnating the panels. The storage is a tank within a tank design. The inner tank is 80 gal. stainless DHW and the outer is 120 gal. storage. The solar heat exchanger is in the bottom of the 80 gal. DHW. It heats the DHW which in turn heats the water surrounding it in the outer tank. That water is used to heat my house, hot tub and garage.

Buderus expects to have these panels available in January.

Nate Greenleaf

Estimated cost of the system?

Dennis Bellanti_2

I have not heard yet. They expect to have pricing out early January.

hot_rod

Interesting

what is the sensor below the panel for? And the plate hx? Quite a control line up Buderus, Taco, tekmar..

It sounds like the Schuco steam back system. Does it require a special fluid?

Is that tank available in the US of A? Does it hold 120 gallons or does the 80 gallon tank reside inside the 120?

Thanks for the great pics.

hot rod

Dennis Bellanti_2

Hot Rod;

I am not sure which sensor you are referring to. If you mean the one below the Taco pump that's hanging in space, it's a delta T pump that I am playing with and have the sensor temporarily unmounted. The plate hx heats the outdoor hot tub via the Tekmar setpoint control. The fliud was provided by Buderus and all labels are in German. It has a similar viscosity and smell of glycol. I'm guessing that it has a certain amount of alcohol in it for the evaporation process??

The tank will be available in the US in the future. They have dual coil tanks ready now. The total volume is 200 gallons, 80 DHW and 120 in the exterior tank. The DHW tank has a baffle system that is patented and sends the hot water immediately to the top of the tank so it can be used right away. The baffles stage open to distribute the heat in layers.

Sorry to be so vague, but I have only had it running for two weeks and I am learning about it as I go. They are finishing up the English instructions so I had to learn as much as I could from the German guys who helped install the panels. They were here for two days. By the way, the panels have a really slick mounting system. Took us 4 hours to mount 5 panels including getting them on the roof. Very easy and sturdy.

Give Ellen a hug for me!

Cosmo_3

This has been a great thread, I am interested into entering the solar arena myself.

Merry Christmas everyone

Cosmo

Dennis Bellanti_2

Grundfos Test Pump

On another interesting note, I am testing a Grundfos UP15-58 variable speed delta T pump in the house. It is a single pump continuous circulation system that flows through Panel radiators with non-elec t-stats, then through 150 ft. of eco-flex into the detached garage, through the solar tank, back to the house, and through a GB boiler. (No boiler pump) It has a digital display showing watts being used and most of the time it hovers around 11 watts!

Dennis Bellanti_2

Sorry

Delta "P" not delta T.

Dennis Bellanti_2

If a dumb wholesaler can do it, you sure can!

[Deleted User]

Dumb Wholesaler???

It's not nice to talk about your competition that way...

:-)

But you DO need to stay off the roofs and in the race car. At least there, you have a CAGE wrapped around you...

ME

ALH_4

Shedding Snow

So what happens with an evacuated tube in a climate that frequently sees a light nightly snow and high temperatures well below freezing? Sure the flat plate will lose more heat, but at least there is heat to lose. Am I way off base in saying that a flat plate losing a portion of its heat is more efficient than an evac tube not collecting any heat?

hot_rod

Exactly, Andrew

if days or weeks go by and a snow packed evac tube doesn't collect any solar... hmmm doesn't sound like that efficiency gain does much good.

You only get one chance a day to harvest that solar energy...

I don't agree with Nate that it is a product deficiency of the flat panels. Depends on what you have to sell, I suppose

hot rod

Dennis Bellanti_2

Here in Colorado

We generally use latitude plus 15 degrees to set the panels for year-round use. That equates to 55 degrees here in Denver. The snow slides off flat panels pretty quickly at that angle.