six of one/half dozen...?

[OGrubber]

Or more precisely, have I just wasted my money?
It's a long story but in a nutshell;
I have 65% shade cloth over the peak and down the south side the whole length of my greenhouse. The problem is that the temps in there still average about 50+ degrees C during the day and I need to bring the temps down - down at least to 40, max. I don't want to shade the north side as well because some plants are full sun varieties and I need an area where they will be happy....
So, I just bought a 65% reflective cloth to cover the same area of my shade cloth over the length of the peak. Will it work better than the shade cloth?
Thoughts?

[Dumbo]

Sounds like a math question!

I say yes.

[Eeyore]

Definately not a mathemetician but I'd say yes as well. In order to keep the heat down you have to reflect the available sunlight on the south facing peak so in theory it should help. AS to whether you need both..... maybe not. I guess you'll have to see if it is too much shade. It might be.

[kelly_m]

Can't help you....but I do know we've had the shade cloth out since the May long weekend! now ours is just across the top....in the sun greenhouse. temps in the un shaded spots have been as high as 45C but i think the spots under the cloth have been a few degrees cooler.

[B_BQ]

50 degrees! That's hot! Enough to cook the plants I would suspect!
No experience here, but just thinking that vents and extractor and air circulation fans would be essential. Knowing you, you already have them.
~BBQ

[Katherine]

I would think reflective cloth would at least cut down on direct insolation but those temps are killer. Can you supply mist at the hot period of the day? What about moving the plants out of the greenhouse or is that not an option? Either way I sympathize. We have the exact opposite problem. Cool and very wet.

[OGrubber]

Thanks for your responses, everyone.

Katherine,
Extremes in weather are very hard to deal with both physically and emotionally. I feel for your situation as well.
Misting in those temps in a [basically] closed environment would just be an invitation to fungal problems. Unfortunately, moving everything outside is no longer an option at this point, either. A lot of things are trellised or in extremely large bottomless grow boxes.

Brenda,
Yes, six overhead fans that I can change the direction to draw prevailing winds through the house. It's adequate when the ambient air temps remain under 30 degrees. So far, everything seems to be hanging in ok, but I can't say I'm not worried.

Kelly,
My greenhouse, unlike the one you are working in, was never designed for or meant to be used through the summer months. In mine, there is very little head space [for heat collection] and the venting capabilities are very inferior to a high tunnel. I actually shouldn't be using it right now. I'm desperate. laf

Lyn,
The greenhouse is oriented east to west lengthwise, so basically the sun is on the peak all day, only shifting from just barely south to just barely north late afternoon. If I could re-orient the house lengthwise north to south, then my hotest part of the day would be 11 to 2, and much more manageable. Guess I won't know how this will work until I get the cloth and use it.

Marc,
Math? It doesn't make sense to me that 65% deflection of light is more effective than 65% shade.

[bluewillow]

I do hope you have been able to get this matter of shade under control, Inge. We sure have had our share of sun and warmth. Today is far more comfortable and hopefully some showers as much of the land is in bad need of. We had a dandy storm last Sunday but it was hit and miss in our area.

[OGrubber]

Thanks Sheila, I'm sure I'll get it all sorted out.
Some drizzle yesterday - not nearly enough - but hopefully enough to break the cycle of no rain.
I'm so used to the above norm temps, I had to break out a pair of sweat pants and a sweater yesterday. laf

[Dumbo]

I've never been that great at physics, but if you reflect it, shouldn't you also be reflecting the heat versus absorbing heat and shading?

I don't know what either of these things look like, never saw them (or never realized what I was looking at). So I'm going by the name of them.

A quick google seems to confirm this:
http://www.greenhousegrower.com/article ... ve-screens
http://twogreenthumbs.hubpages.com/hub/shade-cloth

Seems the reflective type decreases temp more, but also retains more heat in the greenhouse during the night.

Never saw any of these before. Don't know how good the info is.

EDIT:
Reflect (to me) = deflecting the suns radiant energy, thus cooler.
Shade=no radiant energy deflection.

That's how I read it.

EDIT 2:
Found some more PDF's on this, but it started going into PAR and Photon-Flux and the colour of the shade cloth... uhg coffee.