Materials That Are Transmissive To White Light, But Not Infra-red?

"The problem is the amount of infra red heat in the sunlight."

No, the problem is how to bury enough farm land to grow food for the third world.

The shear magnitude of the excavation project would stun China. Piping light below the surface of the earth to grow food is idiotic.

Why not just develop a taste for kelp?

Good luck.

It wouldn't be for staples, ie rice, wheat, soya, corn etc. These seem to grow quite happily in fields and make up over 60% of global calorie intake.

This would be for most of the other stuff, including possibly aquaponic integrated micro fish farms.

At the moment I'm in Australia and we have the same problem; it's too hot to grow most edible plants outside. This would be a simpler solution than the current approach of electrically powered cooling and shading systems. But the main problem remains heat build up due to solar infra red.

This isn't meant as a universal solve all solution, but it'll help.

"At the moment I'm in Australia" Cry me a river.

OK, Your goal is a good one. People should be able to eat.

My understanding is that laminated glass, like the one used residences, cut 90% of UV light. Check it out PVB films for glass lamination.

The problem of too much heat and not enough good quality water can be solved in most cases by structures such as the seawater greenhouse. This plastic tunnel house design produces climate control, filtered air and surplus fresh water- all from saltwater and sun/solar operated (or mains powered) fans, of which we have unlimited supplies of both.

All budding environmentalists should consider the possibility of duplicating natural processes to alleviate more than 1 problem at once, thus generating economically productive and eco freindly solutions!

See http://www.seawatergreenhouse.com/

Tim Chirgwin Kangaroo Island S.A.

Hi TimKI

Very impressive Tim. I will get in touch with you during the next week. I think that the technology I have could be of interest to you and your enterprise. Using it in your or the OP's application has accured to me in the past. It has other, even more important applications in the insulation world though.

Kangaroo Island should be getting warmer by now if not really hot over the next months.

I'll be in touch, Ky.

There are IR reflecting and absorbing films.

Did a cursory search for 'spectrally selective films' and turned up a few viable possibilities.

As this is mainly for use in the developing world tho I was ideally looking for something, or combination of things, which are fairly basic and common.

Realise this may be hopeful...

You better take note of the fact that IR filters don't just filter out IR, they filter out visible light as well, just to a lesser extent. This means that the amount of light available for photosynthesis will be greatly reduced, so you'll need to grow plants that required lower levels of sunlight.

Most plants prefer light levels of about 30% intensity, so we'll be diffusing the light anyway. A darker filter will just mean we have to collect that much more light to bring in.

Pilkington makes a few different types of relatively inexpensive architectural-grade single-layer IR absorbing glass, 'Azure Glass' is one. They also make low-emissivity multiple-layer windows that include an IR-reflective coated film. Many of these types of glass have high visible light transmittance in the range of 80 percent or better. Corning also produces some similar types of glass.

Schott, Hoya and Isuzu make filter glass that is even better at absorbing IR and transmitting visible light, but they don't usually produce it in large sizes like Pilkington. But if you just need it for skylights, their smaller sizes might be sufficient.

Vacuum? i.e. use double glazing? this will allow sunlight but insulate from IR radiation.

Actually, IR loves a vacuum -- it zooms right through. A vacuum reduces both conduction and convection.

Oohh, thanks.

Shows you're never too old to be wrong :)

Tony

Were in Australia are you? She's a big one, you know, and with different climate zones so it would be important to know where you are trying to set this up.

Sounds all a bit improvised and you will have to supply a lot more information for any one to even start guessing what you are trying to achieve. I used the word improvised so not to offend, it is more "dreamlandu" really.

See what happens and if I can be of help, Ky.

Indium Oxide will reflect a large proportion of the heat and is transparent to light. But this sounds like a strange project as if you reflect most of the heat why would you have a need to go underground for reducing the temperature to a level to support the crop?

Why not build a second level above where you want the minority crops to grow, and plant the upper level with rice, etc. Simply by reducing the amount of light getting to the lower level, the temperature will reduce a bit. The upper level will retain the rest. And if the temperature is still too high, put a third layer of solar panels to give some shading (there are several reports/dissertations about micro climates under solar panels)... of course, each layer must be spaced to allow enough light for the bottom crops to grow. The bottom level will need around 30%, the centre 60+%, so only 10% or so of solar, but the energy from that should be enough for the pumping - assuming you have enough water available.

This is what I am preaching from last seven years. Growth and invention is based on local need. If local need is also superimposed by making human life little easier than that technology is a global technology since all human inherently needs to make life easy. If one provide human control than that technology is bond to get global.

Technology developed for Rajasthan will be good for Africa and middle east as well as Arizona, Mexico, California and others

How?

Have you ever been to Rajasthan? Do you know the climate of Rajasthan?

Are you aware of the rather great differences in how things are done between there and Arizona for example?

Transfer to Africa possibly but transfer to the developed world?

Got birth in Bihar, India. Got B.S. in Metallurgy from Bangalore, India and worked in Railway and commerce before leaving India and settling in USA.

Have being in Rajasthan, India at least once a month when was working. Went Ajmeer Rajasthan every year. Full aware of weather and is saying with confidence if it works in Rajasthan it will work in area I said on earlier highlight.

I am one of the founding father for the materials used in solar power from cell to silver and back aluminum and boron aluminum, ITO and silicon aluminum

Not talking about solar PV there but the scope of agriculture that is acceptable in Rajasthan would never fly in the US.

Labor intensive agriculture is fine when the laborer is being paid 1 (or if real lucky) 2 dollars per day.

Comparing anything in agriculture between the US, Canada, Australia and Europe with much of the rest of the world doesn't work.

Labor is one part of equation other is providing local power using solar, motor run by solar generated power for irrigation.

Days are not far when we can dream farm Vachel's based on solar. Then comes labor When I was in California most of farmer hired illegal to pick tomato's and cauliflower and other vegetable and fruits We also not pay minimum wedge. Pay to Indian farmer labor when you take care of GNP will not be roughly 25 percent of US illegal labor pay we make in USA

Difference is in India there is nothing call minimum wedge and USA we do have it. In India we treat farm labor like animal in USA we still give some respect and farmer do believe they are sub human and these are reality of current affairs.

I think you are seeking for something which will increase your problem instead of solving it. Most of the energy of sun is in the visible part of spectrum. Greenhouse effect results from the conversion of visible light in infrared rays by dark materials. Normal glass is almosst transparent to visible light and opaque to infrared (by the way, exactly the answer to your question) and performs very good in increasing the temperature in the greenhouse.

Use thermal inertia to keep the cool of the night during the day.

A significant portion of the solar energy reaching earths surface is in the IR region.

Example of solar spectral content here...
http://en.wikipedia.org/wiki/File:Solar_Spectrum.png

Greenhouse glass passes the visible and most of the short IR wavelengths. Solar flux not reflected or converted by photosynthesis is absorbed and converted to heat. The warmed area now re-radiates (see Blackbody Radiation) this heat in LONGER wavelengths IR which IS blocked by greenhouse glass, trapping the heat inside. Example explanation here...
http://www.wisegeek.com/how-does-greenhouse-glass-work.htm

Special dielectric coatings/films can be used as selective wavelength filters. The blocked wavelengths are reflected away by the coatings. An IR "mirror"(reflects away any incoming IR) may not actually solve your problem.
Look at data regarding "hot mirror" (#38000) here...
http://www.rosco.com/australia/filters/permacolor.cfm

Interesting concept. Keep an open mind for alternate options and best wishes with the project.

Often nurseries use a coat of white wash over the covering to limit the incoming sun in the summer.

Cheaper than fancy glass if not as sexy.

> Were in Australia are you?

Perth. I should point out at this stage that this isn't really my project, I crossed paths with one of the guys working on it and he mentioned they were trying to solve the heat buildup problem, so I thought I'd do some research in case I could offer something useful. They're heading to Burma in January, possibly doing a test here first.
I was looking to put together a greenhouse project while I'm here:
http://solarflower.blogspot.com/2010/11/this-is-design-i-sort-of-threw-together.html
until finding out that it's more about keeping temperatures down in this country, not up. So I'll probably get that going when I'm back i nNew Zealand early next year.
Til then I'm thinking about these cooling options.

> Schott, Hoya and Isuzu make filter glass that is even better at absorbing IR and
> transmitting visible light

Had a look at some of those, seem viable.

> Sounds all a bit improvised

That's me just starting to get into this. I mostly work with concentrated solar. The last people the guy whose project this is spoke to were NASA. He's more up with the play on these things than me.

> if you reflect most of the heat why would you have a need to go underground for
> reducing the temperature to a level to support the crop?

I guess the earth is acting as an insulant, it'll keep the air heat out, but the solar heat in.

> Simply by reducing the amount of light getting to the lower level, the temperature
> will reduce a bit.

But so will the light. Shading is definitely not a bad way forward, I was talking to a guy in Germany a few weeks ago who's doing pretty cool stuff with pv panels as variable shading, but at the optimal 30% light you still get too much heat build up with fully insulated walls.

> We are implementing Solar Thermal Powered cooling system for Green House, to grow the Color Capsicum.

What kind of cooling? Evaporative?

> Normal glass is almosst transparent to visible light and opaque to infrared

Far IR yes, but I think most glasses transmit near IR, which is where most of the energy is.

> Use thermal inertia to keep the cool of the night during the day.

Which brings us to other options than filtering. Cooling is definitely a possibility, and actually what the guy favours, tho he wants electrical cooling units, which aggrivated my 'there must be an easier way' response, hence this thread. It's looking however that although specialty glasses exist, they might not be the easiest option.
Thermal intertia makes sense, and I was thinking today about ways of effectively using this as a cooling system, ie pumping heat from the air into, say, water, which could then be released at night.

I was thinking about heat pipes, ie evacuated copper tubes with an amount of liquid, probably water, which are very efficient at transportnig heat, and very easy to make.
http://en.wikipedia.org/wiki/Heat_pipe
Since the space would be below ground you could integrate tanks of water into the walls, and have a bunch of heat pipes coming out at a downward angle. (The hot end needs to be below the cold). You could set the internal pressure to something which would give you just the right boiling point, so the pipes would only start transfering heat to the water above a certain temperature.

sugarandfat,

Experiment: Nacl glass (no spectral blocking) and soda glass (IR blocking) on thermal box and black. Sun shines, boxes heat up.

Which was hotter?

Answer: Nacl glass.

Why?

Answer that you you will have to rethink your assumptions about IR "trapping" and how a "greenhouse" works...

Seaplaneguy

For residential window glass you generally use a coating on the inside to prevent UV light from entering the home. Easy with double pane window as the coating is between the panes and protected - double pane would not be cost effective for a green house.

The effect of the coating on the glass does show that UV can be greatly reduced though.

I have trouble understanding how the pit is going to be of much use - unless it is 10 meters deep or some such thing. Even then the heat transfer from the inside to the pit walls/floor will soon saturate it's capacity to absorb more.

Humidity of the area? High or low?

Hi sugarandfat

I am sure I have the solution for you and had planed to contact you through PM (internal Private Mail, here in CR4) but have thought other wise now.

I have decided not to but will see were this thread is going to lead. It is a bit all over the place and what I have to offer would be proprietary know how and not a freebie to give away on some web site.

For this information to flow I will need more information about you, your bosses, and a few other due diligence information. Knowing that the one day you are in Spain and the next in "where ever" makes me stand back and keep things close to my chest.

PM me and we can sort things out. I don't come cheap, so think again, Ky.

Try double layer glass,with water circulating between the layers.The hot water should be stored for use at night when temperatures drop, to stabilize temperature.Circulating the water at night cools it for use the next day.Seems I read about a similar process in use in Israel many years ago.

Good luck.

This is the best solution so far. The problem with filters is that they absorb whatever part of the spectrum, that they are designed for, and change the energy into heat. Water is a strong absorber of IR and is transparent to visible light and it can be circulated and evaporatively cooled.

see this... maybe it will help :)

http://www.cbc.ca/technology/story/2010/11/26/tech-glass-film-colour-energy.html