Heat Reflective Coating for Roof

I would have thought that the aluminum would be good by itself, unless it's painted black.

Maybe this:

https://www.texcote.com/wp-content/uploads/2016/12/aia.pdf

The texcote looks good, but what is the cost?...and can it be rolled on...?

Not quite as reflective as this mixture...texcote tops out around .8 TSR, according to the documentation...

Fig. 3

Spectral reflectance in coatings (dry thickness 0.6 mm ± 0.05 mm) containing 1.6 vol% TiO2 and 30 vol% hollow thermoplastic microspheres with different average particle size. (A) 20 μm, (B) 80 μm

Found this...

https://patents.google.com/patent/EP3075799A1/en

I also ran across this. I don't know if it is close to being available and whether it would be practical and affordable.

https://www.sciencedaily.com/releases/2018/09/180927145555.htm

I'm thinking we discussed this not too long ago. If the efficiency of a solar panel is, say, 35 percent, then the albedo is 35 percent, absorbing 65 percent. This is equivalent to a dark gray, and not very good at rejecting heat.

"... If the efficiency of a solar panel is, say, 35 percent, then the albedo is 35 percent, absorbing 65 percent. ..."

.

Something is off. 'Albedo' is the amount of incoming radiation that bounces off. That radiation would not be available to be converted to energy.

Additionally, those would be some very dark panels...if all the incident radiatikn that was not converted to electricity was absorbed and conveted to heat, there would be no glare...no reflection at all.

While your point is solid...solar panels aren't necessarily great at keepi a roof cool, more than just efficency comes into play.

https://blogs.scientificamerican.com/solar-at-home/the-albedo-effect/

Hmmm...that seems like a rather unfortunate misuse of the term albedo.

Albedo: "ratio of light reflected from a surface," 1859, from Latin albedo , literally "whiteness," from albus "white"

^{Online Etymology Dictionary, © 2010 Douglas Harper}

Not interested in solar panels on this roof for several reasons....

Super Therm! I need it on my roof

https://www.greenbuildingadvisor.com/article/an-insulating-paint-salesman-is-tripped-up-by-his-own-product

On my roof.. Not IN my roof!?

That's a terrible and informative story..

His cluelessness is what drove his success at sales and distribution. such a pity.

A scale model test before should have been done by somebody at some point (before signing off) with or without the claims made by the MFG.

I'm not one for frivolous lawsuits, but I'd say a counter suit for lost business and defamation etc would be appropriate. If ONLY it could be done quickly and efficiently in the client's best interests and NOT just for the case lawyer's.

I would LOVE to take a FLIR camera around this guys treehouse.. I mean fort. I mean house. yeesh.

I've been in old homes where ~2" holes are drilled in the top and bottom of every stud bay to allow a hose to blow insulation into the empty cavity..

wow wow wow WOW.

There was a guy on CR4 ~8 years ago who advertised a reflective paint system that looked quite good, but he was claiming R values that were hard to substantiate, and then complaining that he couldn't get UL or some similar approval.

Maybe a silvered Mylar tarp might be the way to go, if tacked down enough not to flap too much.

I don't think a space blanket would last a week with the wind and rain...the secret to a space blanket is it's reflectivity of some 97%, without a way to maintain that clean surface, even if you could attach it securely, the effectiveness would fade quickly...They do sell a similar product in roll form for attic installation which does work well, but that is not an option here...

Ha ha , maybe I was wrong....You go girl...!

SE, if you check your 2015 R. E. Michael catalog, page 1213 & 1214, you will see that there are two different types of reflectix wraps. One is for inside [non uv ; catalog # 7H400 (a)] & one is for outside ( catalog # 7H394 ) mfg # CDW 48050

I actually plan to bring a couple boxes of fast spreading seasonal vines on a portion of the rooftop. The shade from the leaves cascading across the roof should help.

Unfortunately this destroys the roof....

I can't say my roof was made for this, but a large low pitch area is certainly well suited for a few. The vines I've used are non-attaching, light, and easy to train. They also wither away in the fall. I also enjoy a little roof repair. I need to get up there and enjoy some gutter work soon.

SE,

if you say heat reflective what do you mean by that?

The way you introduce heat to a roof from the outside/from the sun is that the roof material absorbs the short wave radiation, as you already found out, the energy then increases the temperature of your roof material and then it radiates heat away in longer wave forms as there is infrared (check also out Wien displacement law)

The worst you can do is use a material that does not absorb heat in infrared or near infrared because it nearly does also not radiate in this spectrum with mostly emission factor the same as absorption.

Also I do not think you need to reflect much of heat radiation coming from the atmosphere.

Reflective roof material is mostly meant to reflect short wave radiation to prevent heat build up by short wave absorption.

Best would be if you have a material that reflects and absorbs badly in short wave and is almost perfect in heat radiation and absorption. This means heat cannot build up in your roof material.

Some of this might sound counter intuitive until you read up on the reasons why the Bedouins in the desert wear white clothing (reflective) under black (fully absorbing) clothing.

There has been some new reflective paint product written up in Popular Science and a lot of the Renewable Energy rags that actually reflects / radiates so well it actully cools.

I don't think it is on the market yet in any fashion and it seemed to me me to be another one of those "New Li Ion battery fits in your cel phone and can power the city of L.A for a week" kind of articles --- I am still waiting for my flying car and Mr. Fusion that has been coming within the next ten years since I was in grade school and was it Kennedy or Johnson in the White House!

I lived in Vegas most of the time and the cool deck helps and is cheap -ish.

Insulated aluminum panels work the best if you want to keep the profile low and can afford them. They can keep it pretty much at ambient air temp below the deck.

So you think painting the roof black with that paint used in solar collectors and then painting it white over that would work well?

..." Thurmalox spray paint. This is a product intended for painting collector absorber plates and is said to provide a somewhat selective finish (ie a finish with high visible and near IR absorbency, but low emissivity in the far IR)."...

https://www.builditsolar.com/Experimental/PaintAbsorbancy/GlossvsFlat.htm

...or rather something like this with high emissivity...?

..."Aremco’s HiE-Coat™ 840-Series line of high emissivity coatings are black-body formulations designed to significantly improve the thermal efficiency of infrared heaters, furnaces, incinerators, and ovens used throughout the appliance, ceramics, chemical processing, metallurgical, and refining industries."...

https://www.aremco.com/high-emissivity-coatings/

...or all three in layers? Remember this an aluminum roof....

SE, the other way around.

The reflective material needs to be below the black absorbing/emitting material.

Think of it that way:

1. There is no material that reflects all radiation.

2. The material that does not absorb very well does also not emit very well

3. Your reflective will still absorb short waves and will not emit very well so it will heat up.

The way the double layer works is:

1. absorbs anything that comes in and transforms into heat

2. the heat is reflected from the reflector below and heat goes the other way

3. your absorbing material is also a very good emitter and will radiate the heat away.

4. you do not relay on convection alone for cooling

5. you can use special reflective material for particular wave length

6. absorbing material is black to make sure it has high emittance as well.

That is as much as I understand the Bedouin choice of clothing and should work for roofs as well.

Nope, not buyin' it...

There are problems with this line of reasoning...

"... 2. the heat is reflected from the reflector below and heat goes the other way ..."

Remember the material is not transparent to most radiation. The dominant mode of heat transfer downward will be conduction. Materials like aluminum or silver are very low emittance, and can be highly reflective, but offer very low resistance to heat transfer via conduction.

Radiant barriers typically specify an air gap. Perhaps this has something to do with Bedouin garb....or maybe dressing in black is akin to Zahavi's handicap principle, providing an honest signal that they are bad asses (don't mess with them/do mate with them...depending on who is receiving the signal).

Back on track....if you paint a roof high absorption high emissivity black,it is going to get hotter in the sun... not just on the top layer of paint. A layer of paint below that will not offer sufficient thermal resistance to stop what is below that next layer from being almost as hot at the surface....even if it is as low emissivity as silver.

A black roof could be cooler at night by radiating more efficiently out into the night sky.

The air gap is indeed an important factor and I rather think painting a tin roof black does not have the desired cooling effect.

When talking about radiative heat transfer the main issue is the capability of radiating away energy. A tin roof with a low absorption still gets very hot since it a) still absorbs heat b) needs to become much hotter than a black material to radiate the same amount of energy and c) in summary once it builds up heat relies on convection mainly to get rid of the heat.

When one searches for "Coolroof" there is some good information around.

The only way of making the insulation work the way I describe it is using a black thick material with a low heat conduction coefficient and if you want a airgap in between the black insulator and reflector.

A Paint will not quite achieve this! Main problem in OP request is to demand a Heat reflective material. My point is:

1. It needs to reflect short waves not long waves

2. it needs to emit almost perfectly long waves to get rid of heat easily.

3. Best material is a combination of the two above

If you staple foil up to insulated rafters, most of the heat is reflected back into that 6 or 8 inch space, and it accumulates there, how long do you think the wood and roofing materials can withstand that kind of heat? If your ceiling rafters are insulated then stapleing foil over the top works only if attic is well ventilated.

SE, can you show an image of the top and bottom of your roof.

Standing seam aluminum panels....

I have the same type. My seams are close to due west or the leading side is in the sun while the trailing side is not. 7 sides could be coated, while 3 could not. Not sure if your top is dirt or dried organic. I've seen where there has been condensation on either side where the opposite is dry.

There does seem to be some small amount of foreign material here and there, but mostly this is just loss of paint, it seems it was white at one time....I don't know how old this structure is, but it looks like it has been there for a long time...

The glass micropheres are very effective and their longevity is.....well glass. The "coating" over this metal roof is the weak link. and The metal would have to be "prepared" beforehand. The sun, rain, hail, plus the make up of the "glue" will in short time, put it on the ground. Also these polymers have a curing time, and the time and labor and expense, make this (in my mind) better spent, making sure this lightweight metal porch roof is strapped down and secure. The sun won't hurt you but the wind will.

I think a retractable awning above the metal roofing with an air gap might work.

They don't cost that much either: retractable+patio+awning

It's about 70' long......so no...

Speculation for the Floridian

SE,

Traffic signs use retro reflective glass spheres to send visible light back where it came from. They obviously do a really good job since headlight illuminated signs appear to be a light source at night. Glass is great for visible but unfortunately absorbs too much near infrared and infrared to reject much of that >50% of heat you mention. However, there are heaters which use quartz tube enclosures for their heating elements. Quartz is both more heat resistant and more transparent in the longer wavelengths than glass. It all makes sense. We just need some quartz spheres of varying sizes to see if we can retro reflect that >50 to any substantial extent. Clearly, it would be optimum if we had nice perfect quartz spheres so they would not leak at anomalies but.... Beach sand grains are roughly spherical due to abrasion for deep time and you are a Florida resident where there is lots of sand. Perhaps the grains could be automatically sorted with a FLIR or maybe even a WiiMote and an air jet grain selector for good retro reflective behavior.

I know that sand has been added to paint for weather resistance since the time of Washington and Jefferson because of the tour guide narratives they recite at Mount Vernon and Monticello. This also may mean that retro reflection is sending the UV away from the paint. Selecting for IR is likely to be mostly a grain size tweak. Anyway, I'll bet you are the kind of guy who could test out this speculation to see if a practical sorting technique is feasible. Just mount your IR source near your sensor at a non 90 degree angle to your tray of a single layer of sand grains to detect retro reflection. If there are simply not enough near spherical quartz grains to be practical, then the usual industrial process for making glass spheres(dropping molten material to a hard surface and size sorting the flash cooled spatter) can be used instead of sorting the beach. Quartz will be molten at a higher temperature but I suspect will otherwise behave like glass in the industrial solid micro sphere maker machine.

If you achieve success then all you have to do is paint your roof and disperse a thin layer(one grain thick) of sorted retro reflective sand grains on it before it dries.

_____________

thewildotter

The weak link is "paint" and how it adheres to roof. Sunshine will break down most glues and paints over time. I kinda like, "Growing" the roof has the advantage of absorbing sunlight, the leaves create an air space, then it gives back oxygen.

Craig,

The green approach indeed has its advantages. The weak link for it is, unfortunately, the roof which is aluminum for light weight. It is not designed to carry a bioload nor designed to be against wet, possibly acidic, decaying plant material. If we start over with concrete with lots of cover(marine rated) over any reinforcement then I am with you. It is a far bigger project at that point. It would be cool from transpiration and thermal mass but it would initially cost a bundle more since an adequate foundation would need to be part of the design to carry the far greater weight. It would have the advantage of outlasting any of us and so the costs could be viewed as far lower since they could be amortized over deep time.

I am in Texas so I am well aware of the sunshine decay of paints and glues. The retroreflectors most likely slow that deterioration but it will still have a brief life span compared to bare aluminum. Others have already mentioned multi layer aluminum including the video from SE of the trailer wrapping lady. Multi layers is not without its problems as well since creatures will seek to inhabit the space between layers. The creature problem is also an issue with the green approach. Note that the retro reflectors could work well embedded in the surface of concrete as an alternative to a kudzu mound to discourage resident creatures and remain thermally moderated.

______________

thewildotter

Yes, and starting over is not an option, so back to saving time, mess, and money by doing nothing more than adding a window swamp cooler.

And I thought I was OT

I window swamp cooler? In Florida?

Plants are relatively dark and photosynthesis is inefficient (on the basis of energy used in creating and maintaining biomass to total incident radiation). The amount of heat from sunlight at the surface of a grass roof is likely very similar to the heat from sunlight at the surface of a solar roof.

A shade tree will always perform as a shade tree. One leaf at a time.

Well, not always. Sometimes shade trees perform much more like wrecking balls, all leaves and branches at once....

Had that happen many years ago....now I cut down any tree within striking distance straight away....

I've got it down to 2 choices....

Sunshield radiant barrier

Henry Tropi-cool 100% silicone

Google : home insulation with the stroke of a brush

Yes the sunshield has that....but there are other factors to consider, such as cost, area coverage per gallon, longevity, ease of application, positive feedback from users of this product, as well as effective heat blocking characteristics....all these together equal value for dollar spent... I'm leaning towards the Tropi-Cool...

https://reflectivebeads.com/Large-Bags-of-Reflective-Beads_c9.htm

It occurs to me that the glass beads, while good for reflecting light at night, are useless for reflecting infrared unless aluminum coated...since my roof is aluminum, that in itself reflects infrared, it then seems the problem is in the visible spectrum heating the roof panels through radiative heat and then transferring the heat via conduction and radiative emission to the space below....the solution then lies in reflecting the visible spectrum with a bright white surface that ideally can maintain that highly reflective quality over a long period of time.....100% silicone type coatings seem to be the best at doing that....what remains is proper surface preparation and application to achieve the goal...

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

A couple things:

The link you provided earlier list hemispherically aluminum coated glass beads.

The reflectivity of glass beads (half coated or otherwise) in the IR region might be affected by the size of the bead and the material in which the bead is.

Unless the materials applied above your aluminium roof are subatantially transparent to IR then your aluminum roof will not be reflecting downcoming IR. The exposed lower surface of your aluminum roof could provide a low emissivity surface that is easy to keep clean....so you might consider polishing the underside.

Global Warming Dilemma

One of the great problems with GW is that visible and near infrared light, once absorbed by anything on earth, gets re-radiated at lower frequencies. At lower frequencies the atmospheric gasses, especially the so-called greenhouse gasses are less transparent. The whole earth then experiences the greenhouse effect and warms up.

A Modest Proposal

I assert that the most effective, long-term way to reduce the average earth temperature is to reflect some small fraction of the higher frequency solar radiant energy back into space prior to absorption. I am an older guy who thought of this as a young adult. If one delays acting until the radiant energy is absorbed and hope for sufficient re-radiation, you are spitting into the wind and will be smacked in the face with your own blivet. I have in recent decades read papers where other scientists, actually in the field have said the same thing a lot less colorfully and with almost no apparent assimilation by the media, the public, or even the popular scientific community. My fused quartz retroreflectors could be benignly distributed on the earth's surface since they are, at their essence, very little different than natural sand. An extremely good way to do it would be to use the retroreflectors on roof shingles to replace the fine gravel coating them today. Roof surfaces are human protected, replaced, and maintained surfaces, mostly above vegetative cover, and represent significant temperate and tropical surface area. Intercepting solar radiation in the frequency ranges well discussed by SE, the OP of this thread with ir rr(infrared retro reflective) shingle coatings is my modest proposal. Since I am older now, jaded wrt the patent process, and concerned that no one is visibly championing this technology, I am giving up the thought of getting rich on this (save the) world class idea in favor of just getting anyone to actually do it for the sake of my descendants. You will likely judge me as a crackpot lunatic with too inflated an opinion of himself, and I do not care as long as someone does it. The popular press said similar things about Tesla and almost every other world class inventor so it seems to come with the territory. I fear I have already alienated SE with my insensitive opinions regarding the algae plaguing him but at least in this forum he is the one who appears to have the best inclinations and handle toward addressing these solar gain issues. I hope he can see through his wadded up, provincial, toxic algae shorts that in this one I am on his side. I use the reverse psychology, shock jock, approach here because I have become weary with the classical, more civilized "invent a new mouse trap and they will come" logic as glacially(ironic) more slow. I am perceiving my own mortality and have exhausted my patience with the scientific community mule and realize that I have to hit them with a two by four just to get their attention instead of just shouting gee or haw. I choose SE BECAUSE I RESPECT his ability to recognize and test a good idea when he sees one and sincerely hope that besides mentally investigating the glass beads I mentioned, he will take that great leap of faith and look into quartz. So I whisper just one word, not plastic, but quartz. I have other priority projects and I need to focus on them, so I want a disciple who is lucid and invested. I wish that I had not offended him in the other thread with my algae comments but that gong has already sounded. I know others will recommend more diplomacy and I will recommend to them reading poems by Sir Andrew Marvell. So SE, I hand the IR RR reigns over to you on using retro reflectors to finely adjust earthly albedo. I name you the senior partner since you will be assuming the mantle of cat herding the unwashed. If you merely test the idea out on a small patch of your roof, I will be appreciative. I am confident that, if it works well on your roof that you will communicate that success. I will, beyond that, be available as the lunatic consultant should you want additional topical conversation.

Think Globally, Act Locally

The IR RR scheme is separable. That is, SE can treat and temp measure a small chunk of his roof and generalize that to planetary issues with simple proportional scaling. This post, while perhaps excessively long, is still on topic even though there are those in this forum who delight in denying relevance exactly on those posts which are clearly, if one understands the process of generalizing, the very ones most relevant in a lot of these threads. These critics seem oblivious to their own inclination to issue twitter twaddle(short, social button touching fluff.)

_________________

thewildotter

I tend to agree with you. There are studies that use models to predict the gobal effect and show that reflective cool roofs might have a cooling impact locally but cause heating globally. That make me think the models might not be as useful as they assumed.

Truth Wins(in the long run, no matter what)

Well, thank you truth inac for that info. I am aware of studies that show reflective windows in urban settings simply transfer the solar gain onto the neighbors. They, unfortunately were not testing retro reflectors which would send IR back roughly toward the sun(up, not down and sideways.) The mental model serves well. If your building reflects heat at your neighbors, you have not had a positive impact on your urban heat island. If instead, you send it into space you will emit less carbon running your AC than you would otherwise have needed and you will have directed less AC condenser exhaust(hot) into the surrounding air.

A more difficult but no less important concept is that carbon is merely an energy reservoir. Ultimately, the ONLY long-term way to cool the planet is by reflecting more solar radiant energy back into space. All other factors are transient. Atomic energy, long the teachers' pet of the anti-fossil fuel crowd uses huge cooling towers or dumps large amounts of heat into rivers. This still warms the earth and is producing the long wave IR which cannot easily escape the atmospheric blanket. Photovoltaic panels may produce electricity from sunlight but it nearly all ends up as heat accumulating at the end use points. Retro reflection is direct, proportional and can be tuned for our preferred climatic average temperature by simple, scalable techniques.

I do not deny that the earth exercises black body radiation. It is just that the daytime temperature you must reach before that can achieve equilibrium is far higher than most of us want to experience. The equations really do depend on how many people you have needing how much energy conversion per person. We MUST either reduce the per person or the number of people. The per person has a dramatic effect on quality of life and ultimately the number of people will become unsustainable no matter how much they deny themselves. The only question is, are we dumb enough to extinct ourselves just to make that ultimate number of people we temporarily attain higher. IR RR's can raise either the quality or the quantity of human life sustainable on our finite planet. I, for one, would choose to raise the quality of life for my descendants even if I had to expect fewer of them.

____________

thewildotter

"...Atomic energy, long the teachers' pet of the anti-fossil fuel crowd uses huge cooling towers or dumps large amounts of heat into rivers. ..."

The amount of direct heat produced by energy production is actually relatively small. If you consider the shadow the Earth makes and assume that 1kW of energy would reach the surface beneath every square meter of that shadow (perpendicular to line from the sun) Primary energy supply for the entire Earth averaged over the year would be equivalent to heat for a square area of that shadow about 140 km on a side. That is less than 0.016%. Even allowing for abysmal efficiency it will have trouble topping 0.1% of the incoming solar radiation.

Also, most of the papers I have seen suggest cool roofs do not cause higher temps in the local area.

I believe the dilemma has existed within the construction industry for a very long time. They build houses too fast and too cheap. For the most part, getting low bid rarely means you're getting an energy efficient house. Also with banking and credit the way it is, 20% is spent up front, then 80% is drawn out forever after, whereas if a well built "passive" house (or subdivision) used upfront money to create efficiency then utility bills remain low and "value" skyrockets. There is so much information out there that goes unnoticed about "home building." Retrofit existing houses and apartments is not cost effective, and "reflecting" energy only moves it next door. Houses that "pay attention" to the sun and the earth are few and far between. Sadly, most houses are built so fast, on top of the ground, and the southern exposure is not utilized. The real "global warming" is going on our homes and in our heads by not living within the natural cycles, and "fighting" it. The thermostat that runs heating and cooling all day every day uses untold amounts of "energy." There is no way around it except each and every one of us adapting to cycles and not having to live every minute in a "comfort zone." We seem to think so much about "global warming" and "climate change" which are beyond our "doing much about," but we can think and do much about how we keep our own homes and self warm. We should have a "good home building" revolution for "this cycle."

The underside of the roof is also painted....polishing it would probably take the rest of my life....so no...

Mechanisms

Transparent, high-index-of-refraction spheres behave as retroreflectors. See rainbows for a familiar example. Note that rainbows are formed opposite the light source(an indication that it is a retro reflection) and that there is some dispersion of frequencies indicating that the light passed through, rather than reflecting off of the outer surface of the water in the droplets. Transparent sphere retro reflectors need not be half silvered(aluminized) to function but silvering can expand the frequency range over which they can perform. Silvering cannot improve function if the material absorbs the frequencies of interest except that the spheres which are upside down can reflect light which has not passed through the inadequately transparent sphere. This is now a diffuse reflection rather than a retro reflection.

For cooler roof operation one should prefer retro reflection since that sends the radiant energy mostly back from whence it came. Reflection is somewhat less valuable since diffuse reflection may send a portion of the reflected light on to some other part of the roof surface. Absorption and attempts to selectively re-radiate are among the least effective mechanisms since the average wavelength of the energy thus radiated is far longer than the original incident frequencies. These longer wavelengths get absorbed by many materials very transparent(or reflective white) in visible(glass and the greenhouse effect) although this may hint that you could glaze under your roof to keep the roof radiated heat from making it to your floor. A thin under layer of fiberglass wool insulation is probably far cheaper, easier, and more effective than solid glazing under your roof. This is, of course, the traditional approach to a hot roof. Perhaps, few other builders have realized that sending most of the energy back toward the source is an even better(and complimentary to insulation) plan if you can do it. Most people will not be able to do it, first of all because they do not know what retro reflection is, but also because they are mislead by their eyeball experience to think that transparent materials in the visible will be similarly transparent in infrared. Quartz is more transparent in infrared than glass is. That is why I mentioned quartz tube radiant heaters in post #30. There are other materials transparent in infrared but quartz sand is cheap and available.

_____________

thewildotter

Will these work mixed in with the 100% silicone roof coat....?

It occurred to me that this additive will cause some thickening, I was considering this silicone oil as a thinner....

...thoughts?

White ?

The first question is do they operate as retro reflectors when not embedded in some material. If the white adjective is applied because they are internally crazed(lots of microscopic cracks) or rough surfaced, then they may not work even when not embedded. On the other hand, the fused quartz radiant heater tubes look kind of white in the visible so they may be ok. I recommend trying an experiment to see if they look bright in low visible light to some FLIR camera when illuminated with a TV remote from the direction of the camera.

The next question is what is the index of refraction of the coating. If it is too high then it will frustrate the internal reflections required to achieve good retro reflection. If they retro reflect in air sitting on some hard, smooth surface then the same FLIR camera test could be repeated after dropping them onto a freshly applied layer of coating. There is also some chance that the index of refraction of the coating could change after drying/curing.

I also do not know what size spheres are optimal. Once again the FLIR camera test is a good initial means of checking performance. One may not need a high dollar commercial FLIR camera since many digital cameras are just inherently sensitive to near IR but one may have to eliminate the IR reduction filter a lot of digital cameras have in place. I see no reason to need a high resolution, expensive camera especially since the cheaper ones are less likely to use the IR filter. Just check to see if the camera sees the TV remote IR led as a bright flashy spot if you fire it directly at the camera from maybe twenty feet away. If it does then the camera and remote are probably fine to use at maybe three feet from the spheres. Sorry to be mentioning all these possible pitfalls but it is better to suspect them than to just mysteriously fail. I appreciate your initiative in discovering a source of quartz spheres and I think there is a better than even chance that you can be successful despite all of these possible issues.

If the spheres retro reflect in air then you might easily and immediately try them in a thin film of water which has a higher index of refraction than air which is also likely for any other coating. This easy test will give you another data point without actually expending any coating material. There could also be an issue with some coatings wicking up onto the top surface of the spheres and the water might shed light on that possibility. Wicking onto the top surface may not be very important if the coating is still transparent in IR. In all these tests I would recommend just a small pinch of spheres on some black in IR (or window glass or mirror finish metal if you work at say 45 degrees to the surface with your camera and IR source) surface so that you might be able to see distinct points of light at each sphere. Just drop the pinch from say 1" above the surface and let the beads scatter to get a gradient density single layer of application. Remember that retro reflection sends the light back roughly toward the illuminating light source so use a single point infrared source for less aliasing and best interpretation. Hold this source near and just a little behind the camera while still maintaining a straight(unobstructed) line of sight pointed toward the spheres. All of these distances and other swag parameters are quite variable depending upon the characteristics of the surface, camera, and TV remote so perturb them around a bit for best analysis.

I applaud your efforts and hope for a positive outcome. Thanks.

_____________

thewildotter

One Other Test

If the spheres seem white because they are retro reflecting visible, that may be a good characteristic. One could test that by seeing if the material lights up red in the retro reflective cone. That is, hold a red light behind your head but still illuminating the beads. If they light up red and seem to get less red if you move your head away from the light then they are retro reflecting the red light and that is very good. For this test you may not need to remove any beads from the jar but just open the lid and shine the red light toward the exposed bead surface.

__________

thewildotter

Use an LED or other Safe Emitter, not a Laser for Your Light Sources

It just occurred to me that shining a laser toward these beads may be very much like staring directly into the beam. Do not injure your eyes. If you are laser competent then you might place a piece of paper behind a visible laser light source to get some idea of the beam tightness achieved by these retro reflectors but that is dangerous. Do not attempt it if you are not very well qualified.

____________

thewildotter

If you coat the silica beads in a coating that is opaque to infrared (and other frequencies), the spheres will not be reflecting, retro or otherwise.

A coating in which you could use the beads would need to be transparent to the frequencies desired to be reflected, having an acceptable refractive index, and meet the requirements to perform well as a top layer for roofing including adhering to silicone coating below and weathering well.

Correct on all counts. They could be half silvered on the back side as we have previously discussed but I recommend against it since that adds to costs and they probably will work better without it.

I plead guilty to oversimplification but I needed buyin to experimentation before solving those non-conceptual problems. Please forgive my partial subterfuge.

__________________

thewildotter

Prior Art ?

Please note also that the bulk of these problems have been solved in the visible for road signs which have most of the same weathering, etc problems that roof applications have. One may have a bit more trouble with this much wider bandwidth for the application but it is encouraging that most road signs stay brilliant for a very long time. Perhaps some of our materials experts can weigh in on this wider bandwidth issue with some low index of refraction, transparent in IR, good weathering suggestions. Note that the coating thickness can be quite thin, easing the quantitative transparency problem some.

_____________

thewildotter

Strawman Cryolite

Here is an odd possibility to get things started:"

It has a Mohs hardness of 2.5 to 3 and a specific gravity of about 2.95 to 3.0. It is translucent to transparent with a very low refractive index of about 1.34, which is very close to that of water; thus if immersed in water, cryolite becomes essentially invisible." from https://en.wikipedia.org/wiki/Cryolite

I do not have a certain way of coating a quartz sphere with cryolite but it has good hardness(weather resistance ?) and a low refractive index relative to quartz. If I could not find some Urethane formulation or similar off the shelf transparent(in IR?) commercial coating, I would consider somehow trying to use cryolite. I do not know how IR transparent it is or whether it could be applied cheaply as a binder or in a matrix to affix the spheres to a roof but it has at least an initial attractively low index of refraction. These are all things I had in my outplan for IR RR study but for decades now have not had free time to pursue.

I provide this dump of intentions so the thoughts are not lost. I see that Urethane also has an index of refraction in the 1.3 neighborhood but most of the sources I checked for transmittance did not report values for wavelengths longer than 800nm. I am sure that some of you have easy access to wider data which I could probably also have found with some time to dig. Urethane may be a front runner. I also did not check to see what they used on road signs. I do not believe that it is necessary to coat the quartz spheres with anything. The point is to get them well attached to some surface without messing up internal reflection.

I do not know if SE's proposed formulations have a chance or not. You can see why I had interest in using a film of water in one of my suggested tests for retro reflector operation since water, cryolite, and urethane all have a ballpark similar index of refraction while quartz has 1.4 or above across most of its transparency range.

____________

thewildotter

Here is an interesting paper promoting the idea of using retroreflector film on windows....this would have the same orientation as streetsigns.

Study Confirmation of Local Urban Improvement through Stylish Retro

Truth in AC(love that handle especially with my corruption of the acronym for relevance to this thread),

Thank you for finding that info. It does confirm the outdoor heat island mitigation operation of the mechanism of retro reflectors on windows in a theoretical and well simulated manner. The figure 1 drawing is something which should be propagated more into the popular scientific press for the masses to begin to assimilate. For the masses, the point should be made that big buildings no longer have to look like a GInormous mirror aimed at the sun to those on the sidewalk below.

Here in Texas, walking down the street in summertime beneath mirrored windows can easily result in heat stroke(not to mention "snow blindness") and this paper does a reasonable job of making that point to those not put off by having to wade through the geometric analysis details. The paper is thin on the construction details of their retro-reflective window treatment in terms of materials, etc. that might be useful to SE but with the heat ray retro-reflective film descriptive name one could likely get to their underlying patents with some effort. The paper is similar to some from decades ago which properly, if somewhat inaccessibly to most people, get the basic point of the primary geometric truth regarding retro reflection. It is comforting that they at least still talk about it in 2014.

I am concerned about the following fractionally true but misleading excerpt:

----------------------------------------------------------------------------------

Thus, adopting these countermeasures has a positive impact on mitigating global warming; however, it has a negative impact on adapting to urban warming because reflected solar radiation from a building surface worsens outdoor thermal environment (Fig.1). Hence, in this example, simultaneous evaluation of the two perspectives (mitigating global warming and adapting to urban warming) is important in selecting the proper countermeasures against urban warming.

-------------------------------------------------------------------------------------

I am concerned about the excerpt because it does not make the important point that most of the reflected light from the alternative window treatments ends up being absorbed by the (dazzled eyes of the) people, the street, the surrounding air mass, the coating itself, etc. The urban heat island effect itself is prima facia evidence that the more traditional treatments are lowering the frequency of the absorbed solar radiation. Even small amounts of water vapor in the atmosphere will trap these longer wavelengths and suppress valuable night time radiant loss of that heat into space. The urban heat island effect does negatively impact the global situation and their statement re global mitigation misleads people into believing that the other treatments are good enough globally despite the fact that the urban heat island increases the need for more air conditioning energy to offset the locally accumulating heat.

On the other hand, retro reflection sends the higher frequency radiant energy easily back through the atmosphere into space promptly, at the same angle through the atmosphere at which it entered, and does not lower its frequency so the atmosphere presents the same transmittance to the radiant energy on its way back out as it did on its way in. The bottom line is that even these scientists did not communicate (nor perhaps even perceive) these additional truths and thus implied that the non-retro reflector window treatments are better mitigation for global temperature control relatively than they really are. I understand that individual buildings with traditional window treatments will consume less energy for AC than untreated, but that is not the comparison of interest even in this paper. The comparison is between non-retro and retro reflective window treatments. Retro wins decisively both locally and globally without even counting the cross terms. Cross terms include secondary effects such as total relative carbon emissions from AC use. Retro wins on those as well and exhibits compounding leverage.

This lack of perception of the totality of significant mechanisms at play wrt retro refection benefits to the global issue is disheartening. It is something that I am dismayed to see persisting. I realize that the concepts are not evident to the general population and I yearn for the scientific community capable of analyzing them to do it. Ultimately, I charge them with communicating the results of careful study to the masses in a way everyman can digest. I believe that everyman will become jaded with approaches that demand resource he can ill afford from him with mixed or even counterproductive results(eg. the alcohol in gasoline controversy, I do not care about who has it right, so do not wad your shorts defending it to me.) The goal should be as it always should be, how do we get the most bang for the buck over the lifetime of the actual use of the technology. My approach is to seek out the ones with very low bucks first to see just how much bang we can get out of them.

Carbon credits is on the other end of that spectrum since our existing economy is very sensitive to fuel costs and poor people suffer a big impact if their heat goes out in winter. Special dispensations for the poor just angers those not quite poor enough and discounts their initiatives and investments toward improving their own life. It builds a long term glass ceiling for those who have the potential and just need the opportunity to flourish. I am not even sure it is an unintended effect since the poor are the easiest to oppress politically and the more poor you have to oppress the more globalist oppressors can do their thing. The middle class will elect to purchase slightly more special shingles if they win economically over the lifetime of their shingles. Retro reflective shingles(and window treatments) are a win for everyone except those with oppressive ambition who are already super wealthy and want to enlarge and perpetuate the gap between their elite buddies and everyone else by running the petro dollar/credit exchange tables. My stigmata is trying to overturn those tables with cheap and effective alternatives. I perceive that the less effective traditional window treatments might lead people to believe that they are more effective than they really are in reducing fossil fuel requirement and I dread the possibility that all reflective technology including retro will be perceived as yet another globalist lie when retro is, in my judgement, genuinely and significantly effective for its (albeit unconfirmed/theoretical ubiquitous use low) cost both for the building owner and for the earth. No, I do not own stock in any company selling these products.

______________

thewildotter

This must be microspheres in clear acrylic...

..."Albedo100 Reflective Spray consists of transparent glue, reflective microspheres and propellant gas (butan/propan gas-mixture). In order to optimize adhesion to different surfaces, the formula differs between the sprays."...

https://www.albedo100.co.uk/about/

https://www.ncbi.nlm.nih.gov/pubmed/28518100

http://solutions.3m.com.tr/3MContentRetrievalAPI/BlobServlet?lmd=1370888546000&locale=en_WW&assetType=MMM_Image&assetId=1361623393356&blobAttribute=ImageFile

SE,

Yeah, one can tune random angular reflectance and perhaps win locally. You will have to have some idea of where the preponderance of the reflected energy goes to know. I have added white(with high titanium dioxide) paint to small projects and I have used aluminum dust fillers in transparent paint on roof surfaces with measurable reduction in maximum temperatures reached on those surfaces. One does have to be vigilant to insure that you are not just sending the heat somewhere else that will suffer as a result. Your next to last post with the cyclists shows the dramatic difference between retro reflective coatings and simple white paint which reflects into more random directions. We have already discussed the fact that the white paint has to be white across a wide bandwidth to work even locally. I will also note that silver looking paint has the same issue as white looking paint in that you must know whether the silvering material actually reflects solar radiation across a wide enough bandwidth or you may do nearly nothing.

Any study which asserts that you want to worry about emittance misses the point that you first want to absorb just as little energy as possible. 3M does good work but they are falling into that trap of worrying about how much energy total leaves a surface but ignoring where it is going and whether it is likely to be adversely re-absorbed. If it re-emits from a house surface only to overheat you as you work in your garden, I do not count that as a win. This is where retro reflectors perform almost magically since you are seldom toward the sun from your house surface except at sunrise or sunset. Similarly, if you really want the sun's radiant energy to get back to space from whence it came, the path it follows to return after retro reflection will approximate the path it took to arrive at the retro reflector. This path is likely far better than some other path with some other angle of travel. I assert that it is optimum if you have no other solar tracking mechanism. That is one could do a little bit better with a big heliostat installation controlled to send the radiant energy out through the least absorbent path through the atmosphere, dodging clouds and such.

Hollow spheres of non-IRtransparent glass are likely absorbing higher frequency light and re-radiating IR at lowered frequencies from their outer surface. Their internal dead air space makes them a better insulator reducing the local ill effect one would expect if significant conduction also occurred but re-radiation is not at optimum angles. It is like a tiny little two layer roof with insulation between the layers. It performs better locally than a lot of alternatives but not better than retro reflection with its optimized reflection angle of approximately zero degrees from the angle of incidence. Retro is better than angle of reflection from surface equal to but opposite the angle of incidence(like mirrored glass buildings) and better than diffuse reflection from random geometry refractive index interfaces inside white paint and far better than absorption and re-radiation at lowered frequencies in material geometry dependent directions according to bremsstrahlung behavior.

So, the take away is that for the best temperature under your roof your better option is still the layer of fiberglass wool underneath and as much reflection as you can get for the money off of the top. If retro reflection can be achieved on the top surface with comparable cost to paint with random geometry refractive index interfaces, then you can add the benefit of contributing less energy load to the earth for roughly the same cost as the traditional approaches at the same time. 3M's glass micro spheres will re-radiate heat which may keep your roof cooler but unless they have a glass much more transparent in UV and IR than normal glass and have designed the geometry of their hollow sphere to retro reflect, your urban heat island will be adversely affected to some degree by that heat being unable to adequately escape your suburb. Due to ocean breezes you probably will not be immediately, personally impacted by this trapped energy but those famous drowning polar bears eventually will. Can you hear them sputtering ?

____________

thewildotter

Well it's clear that microspheres mixed in with paint is not the way to go, the spheres must be mounted or stuck to the surface, so the possibility of coating the wet surface of the silicone with the spheres would seem to have the best chance of reaching 90%+ reflectivity across the spectrum...The white coating alone might do the job....we'll see...In any case it will be an interesting project...

Just browsing and I came across this.

the term you’re looking for is called Albedo which is the measure of a surface's ability to reflect solar energy

Now that you know the term, you can look at coatings using this.

Such as this…

Hi SE, why do you want to use a silicone paint? Why not simply a silver or gold foil ?