evacuated tubes Vs. Flat plates again url comparsion

Unknown

It would be a cool project to build a house that could maintain above freezing with solar. I would consider tubes for such a project. I like the idea of an awning or pergola that provides dappled shade. I'd rather have better winter performance from the collector than large storage tanks and larger collector areas.

Grafting this on to the average obsolete energy hog that most people live in is another story. It's the same with geo these approaches depend on better building envelopes.

michael_34

evacuated tubes Vs. Flat plates again url comparsion

Here is a web site that is data logged with evacuated tubes and flat plate collectors side by side. Have fun!
Michael
LINK

Paul Pollets

Great solar software!

Who is selling the program and software? Very neat way of showing all the parameters.

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Wayco Wayne_2

Very

interestink. They are closer than I would have guessed. WW

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Metro Man

flat plates

Been saying this all along. Think evac tubes get better than they should #'s because of how they are tested @ the SRCC.

Can't beat a good old flate plate.

Metro Man

WV EGBERT_2

Good link

Interesting to see two flat panels at a slightly larger surface area about equal that of the evac tube surface area.

Once again, labor, cost and pay back is .....

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J.C.A._3

Interesting Email conversation last night....

With Jon Klima, from Conifer-Solar-Controls.

He told me a few things I was and am aware of, but I got to hear it from "The Teacher".

Both have their places. There isn't a doubt about that part...but figuring which will work best is the goal.

Long exposures and steady sun will make flat panels a better choice....unless you need higher temperatures. This seems to be where the evac. tubes shine.

I say, as always....It Depends! Chris

To quote Leo..."The More you know....the more you DON'T know!"

Metro Man

old dog

Yea, Jon's been around a while. Great resource for repairing older controls. I think he likes to keep those old C-30's alive.

Still haven't drank the cool-aid yet for evacs. Long term loss of that all important vacuum could be a major problem that may or may not play out. Used to think that space was the best asset for installing tubes but have since changed my mind after comparing performances of these systems.

High temps also is kind of a misnomer. Flat plates will still get you to 180*F pretty easily. Not sure how much hotter you would need for residential or commercial applications.

But... it's all up to what you are comfortable installing and standing behind.

Metro Man

michael_34

data loggers

Here is the guy that does the data log system.
-
Chuck Wright
Chuck Wright Consulting, LLC
http://cwc-das.com
ph: (512)255-4067
cell: (512)434-9692

Unknown

Misnomer?

Dave, The issue of high temperature is a misnomer if it's not defined properly. it's not as much about high temperature as it is about temperature above ambient. Since ambient temperatures on a roof in the summer are already very hot even an unglazed collector can produce relatively high temperatures at a reasonable efficiencies.

I think your skepticism is generally justified, however these collector types do have significantly different performance characteristics as return temperatures rise significantly above ambient. As to how these different characteristics average out in terms of annual performance is the important question.

As well considered as an system might be, actual and theoretical performance can be quite different, especially given the wild card of user behavior. Obviously the performance of a DHW system on a weekend house is going to be vastly inferior to an identical house that is fully occupied. This kills a great potential market, as the second home market in my region is a big deal, and many in this demographic are both financially capable and ideologically motivated to make alternative energy investments. But you would be stretching the truth to sell a solar DHW system to a weekender as a green investment. Wouldn't you agree?

Mi39ke

good start

Would like to see more parameters. The other data logging comparisons wouldn't work for me and my old computer. Seems to be letting the PV shade the evac tube? Not as scientific as I would like at this point. -- Mike

Larry Weingarten

That wasn't a disparaging remark...

... about the C-30s was it? :~) Suppose I'm a solar gray-beard. In the 70s and 80s I installed many collector types including evacuated tube. Things always happened to the tubes. They broke too easily in shipping or even just with too rapid temperature change. System controls starting up at the wrong time did real damage. All of those systems are long gone, but some of the flat plates are still working. No doubt design has improved.

Yours, Larry

Unknown

yes, but on the other hand, at unoccupied temperatures solar could do a much more outstanding job at offsetting the weekly heating costs (assuming you are in a heating zone) than it does for full 70 degree rooms.

Metro Man

See 30's

Larry, not bashing C-30's at all. In fact with all these new controls that have all the new functions, still (in my mind) have a long way to go in proving they're worth. If all you need is a differential temerature controller to turn the system on and off you can't beat those old work horses. We'll see what works and doesn't work in the next 20 years.

I know what you mean about the old evacs. We pulled many of those out in the day. Lots of issues. Not against the new evacs but I have not been convinced with any installed systems of the claimed superiority. I have heard sales reps at shows claim 2 - 3 times efficiency. I Just haven't seen it and we still won't spec them out in any new installations.

It takes more than a data sheet for us to switch product line. I need some field testing and hammer tests.

Metro Man

Paul B_5

Hi Scott : Lots of them do exist. Owner says this one went down to 50 degrees while he was away 2 weeks in the winter .7700 Degree day climate.But this is a partial solar home with Efficiency to the max. 1/2 strawbale to r-70 beautiful inside and out. ( also off the grid) see attached photos. enjoy : Paul

Metro Man

Miss no mere

Scott, What we try to do is to design for the yearly heating load when putting a solar heating system together. If the system is less efficient in the summer that the winter.... so be it. As long as the end result is a yearly savings in energy..... which is the goal.

A larger system will run far less in the summer months than winter. But when you look at the energy produced yearly we are heating homes close to 100% w/solar during the shoulder months and this may drop off to 50% or even less in the dead of winter a low sun angles.

For clients who are using costly propane and are heating 7 months out of the year these system have a relatively quick pay back.

Not too concerned with ambient.... but pay more attention to the energy costs of the home and what solar energy can (or cannot) do to meet those needs.

As these home become tighter and tighter our system can get smaller. Look forward to the day that I can heat a 5000 sq ft home with 100 sq ft of collector area w/ 200 gallons of storage that will provide heat for 3 days of no sun.

Metro Man

ALH_4

Evacs

The only advantages to evac tubes that I see are ease of installation for small roof-mounted systems and freight savings on smaller systems. Otherwise I agree that flat-plates are the way to go in most situations, particularly when one considers the much higher cost of evac tubes.

Unknown

Paul,

Thats a very nice looking instal. Personally (performance issues aside) I like the look of tubes. This was just the sort of application I was referring to. I think the fact that some air and light can pass between the tubes provides unique architectural options. (in the photo)The steep angle seems to somewhat limit the amount of useful shade produced, but I really like this idea of bonus shading. Who manufactures the tubes in that photo?

I know that there are lots of good drain-back systems with a proven records. But when I here that some people are using glycol in these systems (just in case, or to avoid tricky pipe work) I start to think maybe closed loop makes more sense. Once you make this conceit you give up the ability to size for a significant aspect of the heating load unless you want to incorporate a inelegant heat dump. So if you want to get some heating but you don't want to do drain back or heat dumps your sizing is essentially dictated by your summer DHW loads. Seems to me that winter optimized pitch and the generally higher (winter) efficiency of tubes is a nice approach in this case.

What is the back up heat for that house, any clever techniques used for integrating the solar.

Is Anybody aware of a good book that showcase working solar homes, something technical and design oriented? I think there would be a strong market for such a book.

Tim_34

The world is not flat...but my collectors are

Until the makers of evacuated tube systems can come up with an effective way to deal with too much sunshine, I will stay with my flat plate systems.

How can I possibly tell my customers to stay home on a hot July or August day and let hot water go down the drain by opening their taps to deal with times when the sun is producing more hot water than we want or need? I haven't found a good strategy from any evacuated tubes manufacturers to handle these conditions.

Unknown

Paul, you can do drain-back with the oventrop tube collectors, so I'm told. They also told me they had a test station in nevada where they let a bank of tubes stagnate, and so far (forgot how long) there doing fine. Obviously a salesman will sometimes exaggerate the facts, but I think tubes have a place, the Chinese sure seem to like them

How much do flat plates like being idle? A flat plate collector is a glazed box and extreme temperatures are hard on glazing, water ingress, fogging, insulation degradation etc. They're not all built the same, but even the best wont last forever in such a punishing environment. I would imagine that when there is no heat being drawn off (a big heating array in summer shutdown) this aging is accelerated. What of the thermal stress and glycol issues when cool fluid is sent to this array at 2pm in blazing sunshine. There nothing like experience over theory and when you really mine this subject you find alot of the experienced practitioners in the field are doing flat plate drain-back there are I'm told 30 year old systems that are still chugging away. I'm a bit wary of the vacuum, but on the positive side if it is possible to maintain a vacuum for 20 years or more, these things do have some interesting qualities, one of which is that the vacuum protects the selective coating from oxidation. This means that until it fails it will maintain it's performance. Not true for the clouded up flat-plate. Obviously if a tube fails it can be replaced. In the case of a high quality unit most of the investment is in the tube manifold, piping etc. Swapping out the tubes when they loose vacuum is not hardly as much work as replacing a flat panel array. I could see getting 40 years out of a viessman tube manifold, even if the tubes only lasted a bit more than the 10 warrantee it's not a total deal killer because the tubes themselves are not the lions share of the systems cost and they can be swapped with relative ease. I'm not pitching for for one or the other just interested in bringing out the issues.

Tim_34

Good Points

Scott

You makes some good points. Only time will tell regarding the longevity of these systems.

My guess is that most of the evacuated tubes systems that are going in are not Viessman. Likely they are 90% Chinese. Will they still be working trouble free in 10 or 15 tears? I'm not willing to take the chance with my customers.

I hate callbacks. I want to put in systems that work trouble free for years. I suppose I will put up with a slight decrease in efficiency from a film that might build up on the inside of a flat plate collector over time.

I have 4- 3' x 8's on my roof that have been working since 1981. When the sun is shining at this time of year the system usually limits out at 160˚by 2 PM. The 120 gal storage tank w/ the 50 gal electric backup gives me 170 gallons of hot water. The collectors drain down and stagnate. Not sure why I would want or need an evacuated tube system. (Also, I think flat plate looks better on a roof).

Metro Man

extreme flat plates

Not sure why extreme temps on glazing would be harmful unless your melting glass. As far as degradation of flat plates, even painted surfaces over 25 years old seem fine not to mention the selective surfaces.

A good flat plate will have all the internals in the "box" run through a furnace to out-gas so this does not end up on the backside of the glass. I think they run them at 1000*F+. Stagnation temps for flat plates are below 340*F. Running cool water into a hot solar collectors shouldn't be an issues and is kind of fun... you have to see it. Lots of steam and rumbling then everything is fine.

As far as a few collectors clouded flat plates....a few did but ususally around the edges. Many collectors look as they did new aside from frame oxidation. You can always pop the glass off and clean if it bothers you after 25 years.

What I have seen on some inferior flat plates is the riser to plate connection fail. The cheaper collectors used a poor soldering process and the plates could separate if even slightly pulled on. Also poor brazing btw the riser and header could lead to leaks usually in higher pressure closed-loop systems. But these issues where common to a small number of collector manufactures and the new welding soldering processes are excellent.

So yes.... I think a well built flat plate could last forever in they're not so punishing environment. If you think of it the temps of all the components are well below melting and breaking points.

Copper, glass, aluminum and high temp insulation. Not a whole to worry about.

Metro Man

Paul B_5

Evacs I believe are RW schott and so is the PV panels. I'm intrigued by this place due to its integration of some high tech, as well as old style Solar building ideas.(High Mass,extreme insulation,Radiant heat concrete floors throughout,a living roof(grass),tri-pane kryton windows,masonary heater,peat moss septic and the list surely goes on) Any GOOD solar builder would really feel at home here based on integrated design of so many things that WILL be our future. He's lightyears ahead for a cold climate build. Oh there no backup generator here for power what you see is what does it all power generation wise . I'll post more pics tomorrow as well as more detailed replies re evac questions. Paul

Dobber

Panel vs. Tube

I'm just starting to look at installing solar. I don't want to go through the same guinea pig crap I went through with mod-cons. I'm a one horse operation, so the tubes appeal to me. The comparison test is great,but what are the month to month comparisons.As for the overheating problems,what about solar dump or storage.If I was building an off the grid house I would definitely incorporate massive storage.

From The Outside Looking In
Dobber

Tim_34

Solar dump and Storage

Storage is great but it takes up lots of room.

One of the evac tube makers tells you to put in a couple of solenoid valves and dump the excess heat on a hot day. Makes no sense to me.

As far as being a one man operation and installing collectors, we started using a local crane operator for most of our solar jobs. Sure makes life easier and safer. Doesn't add too much to the cost of the system.

Dobber

Storage

You can bury the storage.In Europe they bury 5000L insulated tanks to store during the summer for use in the winter.I'm not talking about anything that extreme (yet), but has anyone really looked at alternative storage?

Dobber

Unknown

Schot makes receiver tubes for parabolic trough solar plants,as a leading glass manufacturer this is the sort of company I would be looking at for evac. tubes. Unfortunately when I inquired about availability in the US I was old that they are not being distributed here. Apparently the demand in europe is as much as they can handle at this point. The Schot tubes I was looking at were direct flow (no heat pipe) and all glass construction , which seems to me a benefit by eliminating seals between dissimilar materials.

Peat moss septic gives it away that your probably not in the states, it's just so hard to permit any thing like that here. Keep the pictures coming

michael_34

no call backs

I agree build a system that will last. 90% of our service call for solar thermal are for evacuated tubes. That's huge.
The other thing is that all tubes are made in Asia (I believe even the Viesmann's).
There is alot of flat plates that are made here in the states (AET, Heliodyne, Bubbling Springs etc...)

Tim_34

Call Backs and Solar

Agreed. Having to pay for even one service call on a solar thermal system can wipe out any savings that would be gained.

Reminds me that I went to a residence last week (it's a group home for mentally challenged folks) with a 1 year old solar thermal water heater. The system was shut down. It was 88˚ outside and full sun on the collectors at 1:00PM. Apparently someone living there did not like the sound of the pump humming away all day. - The on/off switch is now hidden from view.

jrc2905

I just finished installing a 20 tube system on my house. I wanted to do my house first to see what is involved before I sell a job. First full day of operation it was full sun and it met the hot water required for three people without using fossil fuel. Today is cloudy and rain so it will be a good comparison. I learned quite a bit and found out that it is not an easy install or cheap and more work that any boiler I have installed.
I am wondering how one covers themselves from the homeowner saying the roof was damaged by walking on it? On a hot day some damage to the asphalt shingles in inevitable.

michael_34

ground mount.

Unknown

paul,

what's up with fat coper pipe thats integrated into the backside of the collector?

I like those roof mounts, my carpentry experience makes me a bit uncomfortable with caulk only sealed mounts, the flashing boots are nice touch. Are the supports custom fabricated or off the shelf? any close ups? Always interested in seeing how people handle pipe penetrations and mounting details.

Seeing the nice velux sky lights in the picture makes me think it would be very cool if someone made a flat panel that was designed to be flashed directly into the roof. There's a limit to how wide the top edge flashing could be and still maintain good water tightness, ganging multiple panels directly together would probably not work. I picture a single large 5x10 collector. Eliminating pipe penetrations and being able to re-roof without removing the collector would be a real advantage, anybody ever see any thing like this?

Ron Huber_2

roof work

In the summer the shingles are soft, in the winter they are brittle. Stage along the bottom of the array and use a ladder with ladder hook over the ridge to go from bottom to top to minimize having to walk on the shingles, also helps to get the roof work done early in the morning and then retreat to the inside work by the time it gets hot up there. Good for the shingles and for avoiding heat stroke as well.

Cosmo_3

Great thread

I just sat through a presentation by Bill Gabriel from Infloor Heating Systems inc. They sell the Thermomax line. He was very informative, and even though I had a lot of questions he did take the time to answer each one.

I want to incorporate solar in my repertoire, but have a lot to learn.

Main question I have now is the dumping the excess heat issue. The one question I forgot to ask, and may be dumb is as follows;
Can evac tubes be installed with drain back? Would this be a "best of both worlds" thing, or must there always be fluid taking away the heat from evac tubes?

Tim_34

That fat copper pipe

Scott

This system is an off grid glycol drainback design. These collectors are 4 x 10's. They also come in a 4 X 14 version. I don't have a photo of this 2 collector system after it was completed. What goes between those 2 panels is an 18" x 18" PV panel that runs a small DC pump located beside the storage tank w/ heat exchanger. The 2" copper line at the bottom rear of the panels acts as a reservoir so that the circ pump only has to overcome the 4' head to get over the top of the panel at start up. There is no differential controller. The system ramps up and slows down as the sun traces its path across the sky. A very clever and trouble free design.

Tim_34

Roof mounts

We get these supports from the collector manufacturer. They come from the PV side of the industry as far as I can tell. All aluminum post with a threaded aluminum base lagged into the rafters, aluminum angle bracket on top with a stainless threaded bolt and lock washer. Stainless self tap screws hold the collectors in place.

Here's a couple of photos of some single panel systems of the same design.

Unknown

Thats very interesting, thanks for additional photos etc. I assume that the storage tank has a high limit switch that can cut power to the d.c pump. I'v been curious about sun synchronous dc systems like this. Thats a very clever idea integrating the reservoir in the collector to minimize head. How do you monitor the level of the fluid without a sightglass?

The fact the the pump modulates with insolation makes a lot of sense, this would help maintain supply and return deltas and thus control cycling that a standard differential control might experience (with a fixed speed circ.) in marginal sunshine. My concern would be extremely cold conditions with bright sunshine. Since P.V performs better in the cold is it seems possible that you could have a condition where the pump was active but the thermal component was unable to add any heat to the storage tank, worse yet you could end up pumping heat from the tank to the sky. How can you be sure that this is not possible if there is not a differential control?

Who makes that unique DC drainback panel anyway ? thanks again for all the information.

Tim_34

Some Details

The system does have a high limit switch. And, there is a clear flow meter on the supply line at the tank so you can monitor the system fluid.

Your concern about possibly pumping heat from the tank to the sky is a valid one. It was the one thing about this system that I questioned when we first looked at it. I have decided that the overall efficiency losses are minimal.

When a cloud moves across the sky between the sun and the PV panel you can watch the flow meter decelerate and listen to the pump as it slows proportionally.

The system is from a Portland, Oregon company called Mr. Sun Solar.

Bob Gagnon plumbing and heating

Paul Cooke- System Limits out

You say your solar domestic system limits out at about 2 PM.
I noticed my solar domestic does the same thing. But I notice my low temp space heating solar system collects energy all day long, until sunset. If you put a small radiant panel onto your system, you can keep the tank temperatures lower, around 95 degrees, you will collect more solar energy hour to hour, and you will harvest more solar energy all afternoon. We can make these systems a lot more efficient.

Thanks, Bob Gagnon

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Tim_34

Solar Efficiencies

Bob

Perhaps if I lived in Arizona where I would get some sun in the winter I might add a radiant panel to my solar set-up. My system will only limit out in July and August when the last thing I need is more hot water.

Maybe I can become a utility and sell the extra BTU's to my neighbors. ;-)

Bob Gagnon plumbing and heating

The low temperatures help you get more energy

In the winter, a lot more.

Thanks, Bob Gagnon

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