heating with solar air collected by transparent glazing of the roof

[erbstef]

In this website heatingwithsolarair.com I've put a description of how I can imagine that a system can work in an adequate climate. Any comments are welcome!!! Stefan

[Mike90250]

I have a pretty wild imagination. yet most of it is not practical.

Have you actually put any of your theory to practice or test ? How did it work for 4 seasons ?

[erbstef]

Hi Mike,
thanks for the comment. You obviously haven't read until the end. It's all answered there.

[Mike90250]

It's a FAIL
poly carb panels will never pass any city fire resistance regulation.

When new, wood's auto ignition temp is over 200C Baked and heated for a couple months, and it starts to drop, but that's OK, the roof panels will have softened and fallen off at that point.

In the winter, how do you prevent condensation inside the roof (I didn't read the whole thing, waste of time)

Just about every point you make, fails. Air is not an ideal conductor of heat, it's actually one of the better insulators. You can stick your hand in a 200c oven and it does not burn because air transfers very little heat. But it's easy to move around

[azdave]

You obviously haven't read until the end. It's all answered there.

I started to read it but it was 154 pages so I skipped to the end.

My home in Indiana had a solar hot air circulation system. It came with the house and worked quite well on cold, sunny days to send some gentle warm down to the basement living area. It did reduce our heating costs but not by dramatic amounts. We lived there 10 years and I never had any issues with it.

I'm in Phoenix now and the first home I bought here had a solar domestic hot water system that was a disaster in maintenance costs and care. I then moved to another home in Phoenix where I installed a grid-tie PV system and that has worked out perfectly and has paid for itself after about 6.5 years.

[erbstef]

Hello Mike,
I understand the text is long and nobody has time to waste, but I've written there that that's the big problem of non-glass translucient roof panels not being standardly permitted almost nowhere, which absolutely doesn't mean that they're dangerous, as they have been utilized in roofs to bring light under the roof since many decades. So many good things are forbidden, especially in our industrialized countries. This is one point that needs an individual solution depending on the place.

"When new, wood's auto ignition temp is over 200C Baked and heated for a couple months, and it starts to drop,"
How much?
The roof structure doesn't need to be from wood. I think I've actually written that steel might generally be the better option.

"the roof panels will have softened and fallen off at that point."
Have you ever seen that? At the temperatures the system would work? Normal roofs get (much) hotter!

"In the winter, how do you prevent condensation inside the roof"
In case there is some condensation, which might occur during the night, it definitely dries again during the day. So condensation doesn't need to be prevented and actually can't be with the whole system being so simple and thus robust.

I wrote a lot about the prejudices about air as a medium of heat transport. The numbers don't lie, but there is a lot more to a medium than only heat capacity.

[J.P.M.]

In this website heatingwithsolarair.com I've put a description of how I can imagine that a system can work in an adequate climate. Any comments are welcome!!! Stefan

Welcome to the forum of few(er) illusions.

You write that you are an engineer. What discipline ? What design experience ? How long have you been a working engineer. Are you certified/licensed ?

What you've referenced reminds me of me when I first got the solar bug about 45+ years ago. I had a lot of ideas and experimented some. One day, when designing/building one of my first designs, an air cooled flat plate collector with a blower, I had a question in my mind about how turbulence at the entrance to the collector affected the (local) heat transfer rate and so the collector efficiency. Being near the local university, I walked a few blocks and found someone (a grad student as it turned out) sitting next to a heavily instrumented water cooled flat plate collector operating in the sun collecting energy. "Hooray" I thought - a kindred spirit. So, I politely asked if I could speak to him. He said yes. As I described what I was doing and asked about what I later learned to be entrance effects, he proceeded to spend about 10 minutes ripping me a new one and trying (as it appeared to me at the time anyway) to humiliate me because I didn't know what something called a Reynolds Number was as well as a lot of other engineering heat transfer stuff I'd need to know about before I could do much more than piss into the wind with perhaps admirable but mostly non productive efforts at advancing the cause of alternate energy. While I was pissed and my ego was bruised, I also knew deep down he was right in the sense that, while I'd read a lot of stuff that touched on the subject of alternate energy, I was in way over my head but didn't know it (yet). So, I returned to school, learned some basics with respect to engineering and then started to learn stuff. In so doing, I slowly discovered how really ignorant (and arrogant) I'd been. I see a lot of the same enthusiasm and also subject ignorance in what I read from your 154 pages so far.

But as a couple of specific points meant as what might hopefully be considered as constructive criticism/comment, and not meant to discourage you or your efforts, and while not reading all you've written (yet), I'd say a lot of what you write has already been covered by others many times over and many years ago - sometimes thousands of years in the past (See: "A Golden Thread, 2,500 years of solar architecture and Technology", Butti & Perlin, ISBN #0-442-24005-8). A lot of what you write of is in that tome.

I'd respectfully suggest you seek what's already been done because in so doing you'll spend less time reinventing stuff. Besides, it's good to look before you leap if for no other reason than you'll never live long enough to make all the mistakes yourself (although you seem to be off to a good start at doing so). That applies to a lot of what I've read of your stuff so far in the sense that others have already discovered what you write about and then found out by doing rather than just reading/thinking about it.

I'd also suggest you see if any of what you've read about actually works by doing/building some of it rather than simply reading - both are necessary - or by exploring what others have learned works/doesn't work by doing some of it yourself (there's a lot of B.S. written by ignorant people for what seem to be their own reasons having nothing to do with advancing the state of the art - Caveat Lector). Usually, the devil is in the details and the circumstances and in the particulars of what's being attempted. A lot of what you've written has been tried and done by others and found lacking. Leaving such details out, either by ignorance or in the interest of saving time can be dangerous.

BTW, on Mike's comment about kindling temp. of wood and an example of how what you may not know being perhaps dangerous: That first collector of mine was meant as a test bed done before I returned to school. Some of the particulars such as glazing type and number, absorber materials and flow pattern as well as air flowrate could be changed somewhat easily. With the exception of the glazing, absorber materials, gasketing, insulation, bolts/screws and the blower, the thing was wood. After about 6 months of playing with it, learning or confirming what I'd read and learned and getting a fair amount of satisfaction, I decided to check the overall loss coeff. by stagnating the collector and measuring the temperature differential between ambient air and the collector interior while monitoring the irradiance with a small hand held pyranometer. So, I buttoned up the collector, unplugged the blower and started recording temps. and irradiance. Because the wood had been desiccated over the past 6 months or so by mostly being at elevated temps and exposed to hot air - essentially making the collector a wood dryer - after about an hour or so in bright sun, the collector interior reached a temp. of ~ 175 C. After about another hour, the collector side of the 2d glazing got real dark and smoke was present at the collector frame seams. No real harm done because It was a small collector, not near anything and I was on site measuring a bunch of temps. etc., but the experience sure put the fear of the almighty in me about what not being experienced can lead to.

Take what you may want of the above. Scrap the rest.

[Mike90250]

more about several studies regarding wood:

http://web.mit.edu/parmstr/Public/NRCan/CanBldgDigests/cbd189_e.html

2/3 down:
Wood subjected to prolonged periods of heating and cooling cycles may ignite spontaneously. The alternate heating and cooling processes may chemically decompose the wood to produce pyrophoric carbon, which oxidizes rapidly. Many incidents of spontaneous ignition have occurred with wood in contact with hot surfaces such as hot water and steam pipes.


and

The purpose of this paper is to report
on certain empirical case studies,
research activities, and experiments
undertaken which clearly demonstrate that wood will ignite when
exposed for an extended period of
time to temperatures well below its
commonly recognized published
ignition temperature of approximately
482ºF (250ºC). In particular, it was
concluded for the conditions studied
that ignition of wood occurred under
exposure temperatures of as low
as 256ºF when exposed 12 to 16
hours per day in as little as 623
days or approximately 21 months.
Data from three well-documented
restaurant kitchen fires and observations of wood located behind
heated wall mounted appliances
in three operating restaurants,
combined with laboratory and
manufacturer testing are used to
demonstrate that low temperature
ignition of wood clearly occurs.

Elevated exposure temperatures,
typically above 170ºF,7 but below
the published short-term ignition
temperatures of wood, act to thermally deteriorate or “cook”8 the wood.
“Cooking wood” is heating the wood
sufficiently to cause physical and
chemical changes without initially
causing ignition. After a period of
cooking time, the wood becomes
more reactive to the oxygen in the
atmosphere, creating conditions
favorable for self-heating to occur
at low exposure temperatures.

[Mike90250]

Don't get us wrong, but when anyone comes along with ideas that "seem" so obvious, and yet are not being implemented, it requires a 2nd look. Like who would think that after 2 or 3 years of heating, wood would ignite at 170F !!

And i have seen plastic panels get soft and melty, and pull out of the mounting, dumping the heat.

But when something known dangerous (wood in heating boxes) comes along, we speak out about it

[erbstef]

Hi J.P.M. and others,
"You write that you are an engineer. What discipline ? What design experience ? How long have you been a working engineer. Are you certified/licensed ?"
Why don't you want to know nothing about my sex-life?

Please look on the website under "About". If there are still doubts, you can ask in the Fachhochschule München, Lothstr. 34, if I actually studied there and even got the title.
In my humble opinion, the titles don't value as much as real knowledge and still more capacity, which of course I always try to improve. Actually, we were taught also absolute nonsense, which I had to find out later.

" A lot of what you've written has been tried and done by others and found lacking."

It's the system altogether, which I haven't seen or heard of anywhere.
Take you time to read and digest it. It took me an incredible time to put it together in a way that it is easily understandable for anyone. It's all based on physics, calculations,...


I'm sorry for the Americans who would have difficulties to understand the international system of units.
On the other hand I don't understand Fahrenheit, etc.

[sdold]

erbstef: We'd love to discuss your ideas, but we're not going to have much of a conversation if most of your replies are brief and simply direct us to your web site. It's much like listening to an interview with an author who answers most questions with "It's in the book." I would also like to know something of your background and experience to bring some context to what you are proposing, and your "about" page listing three titles provides none of that.

[Mike90250]

Hi J.P.M. and others,

...................
I'm sorry for the Americans who would have difficulties to understand the international system of units.
On the other hand I don't understand Fahrenheit, etc.

There are easily accessible tables for conversions, it doesn't bother me at all to use them as needed.

We're just stating that much of what you posit - has been looked at many times before

" Like who would think that after 2 or 3 years of heating, wood would ignite at 76.66 C " That should be an eye opener for you.

I wish you luck in your endeavors, while warning of the dangers you are not seeing.

[erbstef]

Hi azdave,
Yes, solar thermal with water is problematic, that's why air systems.
PV is much better moneywise, but its efficiency is low: about 10 to max. 20%. Please correct me.

[bcroe]

Hi azdave,
Yes, solar thermal with water is problematic, that's why air systems.
PV is much better moneywise, but its efficiency is low: about 10 to max. 20%. Please correct me.

The lower efficiency of the panels, can be compensated for by heat pump multipliers.
The Coefficient Of Performance can typically multiply electric energy by 3 to 5. Without
all the temperature problems of direct thermal. Bruce Roe

[erbstef]

@ J.P.M.
I've just ordered the book. I'm quite curious, as they say it has also the whole solar cooking story. I cook with the sun big part of the year.

@ sdold
" We'd love to discuss your ideas, but we're not going to have much of a conversation if most of your replies are brief and simply direct us to your web site. It's much like listening to an interview with an author who answers most questions with "It's in the book." I would also like to know something of your background and experience to bring some context to what you are proposing, and your "about" page listing three titles provides none of that."

I think I understand u quite well, but ...:
My main problem is time: I have endless work and things to do. Whatever I do, I try to do it as well as possible. Writing costs me especially a lot of time, first, because I want to avoid misunderstandings at any cost, and second, my English is not so well, as it might seem, as my vocabulary is quite reduced. So I often don't understand details, which if I looked them up, I'd spend the whole day with dictionaries, which applies also for when writing myself: I often cannot express myself as freely and precisely as I would want to.
The same happens with my Spanish.
The only language I speak really well is my Franconian dialect. That's the northern part of Bavaria.

My experience on what I write is in this case based also on my practical work as a plumber, including many repairs. And I've always read a lot of technical literature.

So you know only very few about me. However, I don't know anything about you, which means all of you, the forum.
You can see that I joined it in 2014, but forgot about it.
I just found it some days ago when looking for solar forums that were listed on builditsolar.com as I had contacted Gary and haven't received any answer until today. BTW, does anyone know about him? Has he discontinued the website-work???
So when I wanted to register here in this forum, it said that my name or e-mail was already used.

So, if we want to collaborate with each other, trying to help each other, finding better solutions, I think we'll automatically learn about each other. I don't like talking too much about me, as almost anything can easily be misunderstood. Also, I've sometimes found in forums not too friendly tones, competition...
I'd rather prefer no forum and collaboration than an unfriendly one.
I don't want and have to compete with anybody. I don't want to be neither the most intelligent one nor do I want to disabuse the forum.
I just brought this - let's call it project - to "paper" because I think I had to, without thinking of profiting from it in any form, just because I am a solar fanatic.
I think it's important to share and even have to accept criticism (though it can hurt and is often unjustified) in order to find better solutions for our planet and the people who care and really need better solutions.
I don't want to change the world, but bring in the contribution I can.

Best wishes!
Stefan