Shading Coefficient / Glass Techie Stuff

[sadie]

Hey there! A question for those of you with greenhouses (or you smarties who just know these sorts of things )

What shading coefficient is desirable / acceptable in greenhouse glass?
How about Solar Heat Gain Coefficient?

Do I want to block the UV rays? My guess is no, at least not completely, but how much is too much to block?

Obviously the glass itself is the biggest expense in the greenhouse and I want to be sure I get the best stuff possible, but my concern is that some kinds of glass are treated/tinted to make the room cooler etc not necessarily to grow orchids. Any suggestions or thoughts would be appreciated! Thank you!

[orchid-man]

these days I don't use glass as it passes way toooooooo much light.
If glass is going to be used then you will still be needing to use a material for shading ,so why not just use a shading material.

For your area I would be looking at a shading factor of about 50%,BD can correct me if Im wrong.

[sadie]

Thanks orchid-man. You have answered one of my big questions -- that I was worried the glass wouldn't let in enough light. It sounds like that won't be the problem.

I guess I should be a little more precise in my question. Since the greenhouse is going to be attached to the house, glass is the best option. I do intend to use shade cloth of some kind (probably done more like "curtains" or "blinds"), but I wanted to know about the glass without the shade cloth.

[Gin]

Mine is glass,except for the roof . Without shade cloth anyone for cooked orchids under glass .?
In certain areas of the green house I use black fiber glass screen door wire over the glass on the wall or if not a cheap skate like me ,shade cloth .Aluminet on the roof 50% or 60% . It is heat that is the trouble .. Gin

[Brutal_Dreamer]

We have a lexan greenhouse. You probably remember the shad cloth over the top. It makes the gh look like a covered wagon. Our cloth is around 60 or 70% I believe.

Cheers,
BD

[sadie]

Can anyone translate this to footcandles or % shade? (or in otherwords can I grow higher light orchids in here?)

Now that we are underway, I am selecting the actual glass panels, level of shade cloth etc etc. Any help would be appreciated. The glass I am looking at has the following:

Roof Glass--shading coefficient of 0.18 (the advertisements etc say that "the lower the better). Does that mean only 18% of the light comes through meaning the glass blocks 82%? That would surprise me, but as you can tell, I am confused.

Wall Glass--shading coefficient of .38 -- this glass is cheaper than roof glass so I assume it is slightly lower quality.

The UV transmittance is 7% and 13% respectively. Is that going to be a problem for orchid growing? Thank you thank you!

[Phyrex]

Sorry, I don't have any advice for you, but thanks for starting this thread Sadie.
Even though my GH is a mere speck on the horizon it's great to know some of these things in advance.

[wetfeet101b]

Shading% and Shade Coefficient are two different material properties.

Shading% is the amount of light that is blocked by the material (some use the opposite term, Light Transmittance).

Shading coefficient is how much solar heat load penetrates the material. A value of 1.0 means all solar heat passes through, a value of 0.0 means no solar heat passes through.

Shading% is a different, but related property of the shading material.
You can have a material with low shading coefficient (less heat gets in) but still allow a lot of light to pass through.

Think of light, heat and UV rays as separate components of the solar rays. Modern materials can now limit each component independently by using multiple layers that block each component.

In your example, the shading coefficient is 0.18. Which means only 18% of the direct sun's heat will pass through the glass.
But it does not state the light transmission properties. Most untinted glasses are pretty transparent so it probably has less than 20% shading.

UV transmittance is another material property. In your example, only 7% and 13% of the UV rays passes through the glass.
Excessive UV rays are bad for humans, but a lot of plants thrive on direct UV rays. So UV filtering is a delicate balance.

[lyngarc]

Sadie - thanks for starting this thread! I got a GH kit _that has I really like, but wish I knew how to interpret all the %s, etc.
Wetfeet - thanks for the explainations, I'm going to dig out GH paperwork this weekend and see what I've got.
I use box fans and a small swamp cooler which keeps it in the 80s except in peak periods but have a hard time keeping humidity up. Any ideas there?

[sadie]

wet feet -- thank you for your insight, that is very helpful. Now I'll sit down with the charts again and make some sense of it. No wonder I was confused by shading coefficient. I knew there would be someone here smart enough to help me sort it all out. Thank you.