using suntuf as the only roofing on a large shop?
 

Hello all!
I am contemplating a large shop build for equipment and woodworking.
We have used standing seam hidden screw metal roofing on all the other structures and really love the security.
I had not given heating much thought, I figured it would be only heated when in use, and have a dehumidifier running for tools and such.
Now I see all these hot air solar systems with suntuf and I am a little excited :D
So, do I build fully independent collectors and install them over my roofing, or take a big leap and go with the suntuf roofing/collector integrated system?
Cons:
1) I do get some wind. I am down in the trees so that helps some...
2) when it is not launching limbs at my roof!
3) the metal is said to last 50 years or more. With cleaning and painting I think it has no measurable service life. The same cannot be said for acrylic.

The pros are obvious, cost and simplicity.

My design already has the roof facing the proper way, but the south wall below it must be mostly doors. No big solar love to be had there.
I have an asymmetrical design with a 3' high wall between the roof pitches, so I can have south facing clerestory windows all the way across.
Nothing like natural light to work by.
That wall will be very easy to plumb all the air tubing through, and there is a generous eave projecting from the back roof to help with keeping weather off my windows and the plumbing.
So what say you folks?
Obviously I would still use metal on the north facing roof.

Its a very interesting idea. If you go with the integrated design, which I like the idea of, you will have to think about summer (when you don't want heat) and how to deal with that.

I'd still have copious insulation below the roof sheeting, and just turn out the hot air. I could also devise a reflective blind that would cover the black surface under the suntuf. that could get complicated.

Haha, yeah that sounds cool but complicated. If you had an 'attic' area in the garage, you could vent it during the summer, and close up the vents when you wanted heat. Then just stick a fan up in the attic to blow hot air down like a few of us have been doing.

http://ecorenovator.org/forum/solar-...-basement.html

http://ecorenovator.org/forum/solar-...eat-house.html

http://ecorenovator.org/forum/solar-...bottom-up.html

Skyking,
I think you have the right idea. No need for Suntuff. Many of us would kill for a standing seam metal roof. Those are the ideal solar collecters because they get HOT. All you have to do is paint them black on both the top and the bottom. Painting the top might be optional but you definitely should paint the bottom black. Black is the perfect energy reradiator and any energy radiation that is absorbed will then be reradiated downward.I would expect Suntuff would age, get brittle, and crack after not too long anyway.

Like Daox said, just put in a movable damper going to the roof vents. If I had it to do over again I wouldn't have put an electric damper in that position, because you will probably only move its position twice a year. Its function is too important in my opinion to be left to a motor that could fail. Just make sure you have access to the manual damper without tearing things apart too much. Then add insulation of your choice and stir.

I had a friend who had a house & garage. The garage had a questionable roof. So he tore off the old roof and nailed a bunch of corrugated fiberglass on the roof because it was so cheap.

Now, I'm not saying that this is a great idea for a serious roof, but it was quite amazing how much warmth the garage had in the winter, even on an overcast day. He ended up using the garage a a place to produce edible seed sprouts on a medium size scale... it was enough to support his family in a modest fashion.

I'm not championing corrugated fiberglass roofing or even edible seed sprouts, but the heat gain was well worth taking note of.

Something like THIS STUFF might be superb.


-AC

I will elaborate on what I had in mind.
Imagine a 6/12 roof with OSB sheeting, with a black vapor barrier.
Then put on stringers to nail the suntuf on, forming a 4" air gap. Imagine a wall at the top edge of that roof to take the hot air into the building, with controls. Either turn the air in or turn it outside when things get too hot.
I would insulate under the OSB to minimize heat loss overnight and heat coming in when you don't want it.
funny how you think things through as you type :D
I can use traditional underlayment over the OSB sheeting, and seal it up good. Maybe even black roll roofing. It is cheap, absorbs heat like crazy, and will last indefinitely under the suntuf.
Punch a couple of curbed holes through near the bottom to admit the cool air. Curbed and sealed up nice so condensation from the bottom of the suntuf is properly channeled.

Now if the suntuf gets damaged, at least my structure is waterproof below till I replace the damaged panel. I can build drains into that system for both condensation and any damaged or deteriorated roof leakage.
Replace the suntuf periodically. I think it would pay off even if it had to be done every 10 years or so.

Lots of things to ponder here.
Condensation + mold spores = very bad warm air.
I worry about how to keep the surfaces in my collector from growing anything bad.
Possibly a paint or coating?
automated damper system to cool the collector to ambient temperature at sundown, thus avoiding the temperature differential needed to form condensation?

Just tossing this out to see what others have experienced/dealt with.

If the sun shines on your roof on a semi-regular basis, it will dry out and heat up everything to the point that mold will die.

So, you might be over-thinking this thing.

-AC

you're from Portland, so you know what happens around here. We get serious bad spells with no sun.
I have kicked it around all morning. I think the thing to do is build wall air collectors where I can, and put HDPE tubing under the standing seam metal for a liquid based collector. I was going with a dark green roof so that will deliver some heat OK.

Interesting physics factoid
 

Ever wonder why steam radiators aren't usually black, but instead are white? Kind of counter intuitive right. The reason is radiators are meant to heat the entire room, not just around the radiator only. Because white doesn't reradiate energy nearly as well as black does the radiator gets a lot hotter than a black radiator would for the same energy input. That means a strong convective loop in the air is created.

The radiator creates a strong energy transference through conduction to the air molecules next to the superheated radiator. Those air molecules move up to the ceiling then and new air molecules rush in and are in turn heated through conduction by the superheated radiator. A convection cycle is created through this process that theoretically heats the entire room. It wouldn't work if the radiator was at the ceiling because the heated air would already be at the ceiling and it would have no where to go for other air molecules to replace it. No convection cycle then.

The color doesn't matter. Color affects how something absorbs light, not how it radiates or convects heat. Unless the radiator in a path to receive sunlight, the radiator will have the same output and the pattern of output will be the same.

Stealth Solar Heating...
 

You're talking about sun exposure from time to time. Your air will be about as mold-laden as the air you breathe when you walk around outdoors.

That is a very viable plan. I even have a lab report laying around here someplace about doing that very thing.

It's been a while since I read the report, but as I recall, the big advantagea are that your solar collector is totally hidden and protected from the elements and from complaining neighbors, if that is relevant. Also, your incremental cost is very small if you are already doing a roof.

The biggest disadvantage is that the amount heat that will be collected is much lower than from a full on flat plate collector or evacuated tubes... something in the neighborhood of 8% to 10% as opposed to 40% or slightly higher for evac tubes. But if your whole roof is your collector, it all adds up. I have no data for heated air to use as a comparison.

If you're gonna do it, put some rigid foam under the roof/tubing setup.

And don't use HDPE, it's too likely to melt. PEX would be a better bet.

And if you're gonna do it, you only need to do it to the faces of the roof that receive significant sun.

I wish I had done this when I did my roof.

BTW, my roof is dark green and yest, it gets very hot... even on a sunny winter day.

Take lots of pix.

-AC

It will have a south facing roof at 6/12 or better. 12/12 is ideal in our latitude, but a little daunting to install.
The trick is to get good contact with the metal, and still protect whatever tubing used from being abraded. The metal roof expands and contracts every day, and moves slightly. I can hear our other roofs move from time to time.
One method had the tubing in a metal hat channel that the roofing sat on, so the roofing was not touching the tube directly.

mn,
Your ignorance is quite astounding. Rather than waste my time correcting your lack of knowledge line by line I'll just say that I've treated you with respect in all my previous comments even when I disagreed. Your lack of same to me and others here is obvious.

I realize someone with your arrogance will interpret my lack of refutation as not knowing what I'm talking about. My background is physics and your armchair physics is not worth refuting. In other words, you just don't know what your talking about most of the time and especially here.

Shall we review your claim here?
You posted an off topic comment in my shop heating thread. Check.
Did I care? No, not really. This thing happens all the time and no need to get feathers ruffled. You on the other hand have the ruffled feather thing going on just fine.

Somebody else disagreed with your science, in no disrespectful manner, he simply said no. No personal references, no accusation of ignorance, nada.
You get your panties in a wad, IN MY THREAD, and go off.
Next time you feel the need to vent, make your own thread.
Next time you want to start a new topic about radiating bodies, make your own thread.
Thank you :)

It's not a "claim". It's physics and I thought people would find it interesting. I did not put it there to divert attention from your thread. If you feel that way then I'm sorry. I'm always sorry when someone with genuine knowledge about something is disrespected just because it is not conventional wisdom.

I think that is really the entire reason for the reaction to my comment. Correct but non conventional wisdom seems to often be threating to many individuals here. I'm very happy that not all commenters on this forum feel that way. I assure you my factoid comment was not meant to hijack your thread and I will refrain from further interacting here.

PEX expands much much, more than metal... about 1"/100'/10 degrees F. But as long as the pipe doesn't run over a metal edge, it shouldn't be a problem.

If you are really worried about abrasion, go and haunt some radiant floor heating blogs to see how they handle the problem, and much more likely, is there an abrasion issue at all?

I think that a more suitable problem to resolve is how are you going to accomplish the 180 degree U-turns at the top & bottom, and not expose your PEX to sun light?

-AC

I'd put an edge on the cavity that the pex will occupy. Make the turns inside that edge. Put some insulation blocking between the loops to support the roof.
Fasten the metal roof to blocks of solid wood or ply as needed.
So, you are thinking insulating board or something similar over the roof sheeting?
Like this?
3/4" Foil Faced Insulation Panel at Menards
That does pose a fastener question regarding the metal roof. I'd have to get a long enough fastener to reach through to the OSB to tie the metal down well.

And One More Bit...
 

Since factiods are being featured here, here's another one...

When the 1973 OPEC embargo happened, many countries were affected by the sudden unavailability of cheap fuel.

The United States launched a big solar initiative, including cash incentives to people who chose to go solar. Jimmie Carter even put solar collectors on the roof of the White House (some of these very solar-collectors are in a museum in China today).

Today, you can get perfectly serviceable solar collectors for free or very cheap, that are from that era. At the same time, home heat loss standards were improved only to some modest degree.

Sweden chose to go after home heat loss head on, did major studies, totally revamped the building techniques and codes and also laws that affect home heat loss. So, today in Sweden you can't build a home that is not what we call a high efficiency home (very similar to a Passive House). If you can't afford it, the government will weigh in to make sure that everyone has a high efficiency home.

Net result is that Sweden has been transformed, with regards to home heat efficiency, while in the US, solar incentives come and go with the administration, and the solar industry is constantly whiplashed by government subsidies (or lack thereof), so US solar has never actually grown into a mature industry. Which leaves the interested fringe like us who are doing interesting things as best we can.

There are very many lessons from this story, but to me, the big one is to focus your best attention on the structure of your house, insuring maximum tightness, over-generous insulation (see Daox's office project for ideas)... but to keep an eye out for solar, too.

If you can seriously reduce the rate of heat loss from your house, amazing things are possible with alternative energy techniques, including solar.

Best,

-AC

Yeah, I was thinking of something like that... not any kind of super-insulation strategy (unless you want to be a certified insulation hero) but enough to allow the heat to build up for the water or water/glycol fluid.

The fastener issue is not a big deal, metal roofs go on over much thicker insulation than you are considering, all the time.

But where on the metal roofing will your fasteners go? Will that intrude onto your PEX channel?

-AC

Here is what I am imagining:
Roof joists->OSB sheeting->3/4" foil board.
Hero-style R-26 minimum insulation between the joists below the OSB :D
there is a 1.5"x1.5" nailed around the roof perimeter, nailed to the OSB sheeting. The 3/4" foil is inside that.
Now we have a 3/4" space for pex. 3/4" pex might not be needed, but the dimension works for many reasons.
Lay out the pex and clip it down with U-clips and fasteners.
Use a horizontal pattern so you can see the pex. Don't worry about roof fastening yet.
Use small pieces of insulation to block between loops. Lay roofing over that, and shoot the screws down to the OSB. The standing seam roofing only gets screws on one edge, then the next sheet clips onto that piece and hides the screw.
It is easy to put in screws and not hit your tubing. Nothing is covering it.
Finish out the metal as normal.

R-26 for vaulted roofs isn't even code anymore in our fair PNW states. But since it's a shop, you should be due your proper respect.

Otherwise, it all sounds quite reasonable.

-AC

I'll have a 15' by 56' roof pitch to work with, more or less. one 500' roll will give me a 14" spacing between runs. That's $400, the 3/4" foil backed board is another $400.
Under a grand difference. I will look at some charts and see if it would pay. We really don't do solar well up here :)

$400? how do you break that down?

I'd like to see what the charts tell you.

Roger that... but we do get low quality solar. You need to have a goodly amount of temperature difference between your heated water and your radiating structure. It just so happens that a homemade heat pump can extract the heat and give you the delta-T, quite happily. The question is, will it supply heat at the rate you require. This is where reducing infiltration and increasing insulation becomes so important.

Also, if you have the land and the gumption, a ground source loop field can provide heat for you during the chill months, but during warm months, your PEX in the roof can gather warmth that you can stash in the ground (assuming you don't have serious water movement in the ground)... and it will cool your roof at the same time.

randen used the loop field to heat his shop near Toronto, and he built a homemade heat pump for that purpose.

He left a fairly well-documented trail...

BTW, I've kind of come into this thread in the middle... does your shop exist already? Are you building new? Are you renovating or are you planning out your ultimate shop?

-AC

The Solar Study I was Referring To...
 

Hey skyking,

I was able to locate the study that I was referring to previously...



HERE IT IS!

It should provide much food for thought.

-AC

as they say "you are the man"!
To summarize, they were able to extract about half as much as an exposed collector. I don't believe it was an evacuated tube high efficiency system they were comparing to though.
This shop is in planning stages. It will not be heated to the extent our house is.
I am very familiar with ground loop systems.
This is my brother's system in Yakima. I did all the ground work there.
http://ecorenovator.org/forum/geothe...m-install.html
I am contemplating that as well. He jacks solar heat into his ground system too.

That 400 was for just the tubing and nothing more. Same for the insulation. I was talking about the bare bones that went under the metal.

[QUOTE=skyking;33144}...That 400 was for just the tubing and nothing more...[/QUOTE]

I can understand if you want to buy local and support your community, however there are some pretty good prices HERE.

-AC

Sorry; I'm a bit late to this party. The above statement disagrees with every scientific source I've checked. One source:
Thermal radiation - Wikipedia, the free encyclopedia

The concept of more efficient emission from a 'black' surface is supported even by the instructions for using non-contact thermometers, which say that more accurate readings can be obtained by painting the target black.

Can you back up your statement with scientific sources?

Charlie

I was thinking about this. Sometimes people wake up on the wrong side of the bed. I think both I and MnRenovator did on the particular day this interchange came up. I don't hold any grudges here and don't want to rehash this, though I appreciate the support for my view, regardless. But let's all let it go and move on and continue to be friends.;)

We need to distribute correct information, when possible, many readers here.

I agree with MnRenovator radiator color makes no difference (unless its metalic).

Look up the emissivity (range 0 to 1) numbers for different paints, most run .80-.90 & are not dependent on visible color

from that reference:

https://en.wikipedia.org/wiki/Thermal_radiation

"Surface effects

Lighter colors and also whites and metallic substances absorb less illuminating light, and thus heat up less; but otherwise color makes small difference as regards heat transfer between an object at everyday temperatures and its surroundings, since the dominant emitted wavelengths are nowhere near the visible spectrum, but rather in the far infrared. Emissivities at those wavelengths have little to do with visual emissivities (visible colors); in the far infra-red, most objects have high emissivities. Thus, except in sunlight, the color of clothing makes little difference as regards warmth; likewise, paint color of houses makes little difference to warmth except when the painted part is sunlit.

The main exception to this is shiny metal surfaces, which have low emissivities both in the visible wavelengths and in the far infrared. Such surfaces can be used to reduce heat transfer in both directions; an example of this is the multi-layer insulation used to insulate spacecraft."

Why don't threads on this forum close after a certain amount of inactivity? I thought this thread was dead. I imagine Skyking made his decision as to building methods and materials long ago...

There are gaps in between the lines for a reason. Yes, suntuf panels admit light. Yes, shiny surfaces make better reflectors. Yes, a flat black steel roof panel absorbs more heat in sunlight than a white one. Whether or not a casual surfer will care if they are giving up 2% heat gain to have a tan roof, well I haven't one clue!