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PostPosted: Mar 17th, '14, 17:05 
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It seems there is a lot of information about polycarbonate vs. plastic, but none of it is climate specific. Does anyone know what are the pros and cons of using either specifically in warmer climates. I am starting the design of a small commercial aquaponics system and am not sure which way to go, poly vs. plastic. I am located in an area where the temperature in summer can reach 40 degrees C (105 F) and am not sure if double walled polycarbonate is the way to go.

Does anyone out there have any experience with this, or can direct me to some information that is climate specific?

I would appreciate any help I can get on this topic, even a general discussion about what people have experienced with either system in general.

Hope you all out there are having a good growing season so far.

Sincerely,

Karim


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PostPosted: Mar 17th, '14, 18:29 
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My deck system can reach 100f on 50f days. No experience with plastic. I know most commercial GH's around here prefer double air filled plastic roofs with ploycarb sidewalls. Probably more for heat retention on cold days. Check into earth batteries where they pull air from top of GH into buried tubes to balance temps.

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PostPosted: Mar 17th, '14, 18:49 
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I am Gold Coast in QLD Aust, i have polly roof and finding it a bit hot in summer for delicates such as lettuce, but it is UV stabilised, i know nothing about plastic?

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PostPosted: Mar 17th, '14, 18:54 
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kitacooch wrote:
I am Gold Coast in QLD Aust, i have polly roof and finding it a bit hot in summer for delicates such as lettuce, but it is UV stabilised, i know nothing about plastic?


Thank so much for you response. What do you do to cool it? Are you using any sort of mechanical cooling? I am trying to avoid evaporative cooling since water is a scarce resource over here.

What are you typical indoor temperatures indoor at height of summer in relation to outdoor temperature?


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PostPosted: Mar 18th, '14, 01:07 
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Shade cloth is used around my area (south florida). The ones I have seen do not have any type of roofing which is of concern to me if starting a commercial project, due to heavy rains messing everything up. If anyone has any suggestions or if there are good examples out there to follow please share. Thanks.


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PostPosted: Mar 18th, '14, 02:12 
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SJ, you know Ryan has his GH covered. I will take mine off shortly..I judt use it for cold protection. My GH gets into mid -upper 90's during 70-80 degree weather...would be way too hot in Summer. I also don't have roof/gable vents. These would make a huge difference I'm sure, since every GH I've seen has them...most with temp controlled fans.


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PostPosted: Mar 18th, '14, 05:34 
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kij2 wrote:
kitacooch wrote:
I am Gold Coast in QLD Aust, i have polly roof and finding it a bit hot in summer for delicates such as lettuce, but it is UV stabilised, i know nothing about plastic?


Thank so much for you response. What do you do to cool it? Are you using any sort of mechanical cooling? I am trying to avoid evaporative cooling since water is a scarce resource over here.

What are you typical indoor temperatures indoor at height of summer in relation to outdoor temperature?


Sorry, still in my first year and have not taken any readings, i have only just recently learnt that it is the heat that is a problem for my lettuces and possibly my broccoli and collie's. I have fitted 60% shade cloth above my DWC and seems to have improved it greatly however it is still getting the afternoon sun through the wall. As it is cooling down now i am leaving it alone for the winter but will be looking seriously into shading for next summer.
My green house is half organic dirt garden and half AP, the entire GH is covered in Plant Guard see link below. The side over the AP has the Polly roof over the top of the mesh, the other side over the dirt garden and all the walls just have the mesh, so dirt garden gets rain and entire greenhouse has airflow.
I am now putting a diary together and will be monitoring water and air temps as i wish to grow a large variety of food for as much of the year as possible.

http://greenharvest.com.au/PestControlO ... ml#VegeNet

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PostPosted: Mar 18th, '14, 08:26 
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Seriously, this cant be healthy.
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If you are thinking commercial checkout glass. Might be cost effective might not depends on your local suppliers.

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PostPosted: Mar 18th, '14, 08:58 
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Roll up side curtains curtains or vent would be a good option. Shade cloth to avoid direct sunlight in the greenhouse would also reduce the heat and is probably a must. There are also inflatable side vents which use blowers to open and close. The greenhouse could be a mix of Polycarbonate and regular plastic. I'd look around your area and talk to others that have large greenhouses just to see what they do.

These are roll up side curtains in case you haven't seen them.
http://www.extension.org/pages/27782/natural-ventilation-in-high-tunnels


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PostPosted: Mar 18th, '14, 09:12 
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If you are serious don't use shade cloth. It is fine for BY systems but if you are thinking commercial you want a reflective screen.

Shade cloths provide shade but because they absorb the energy from the sun they get hot. Relfective screens don't so they don't.

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PostPosted: Mar 18th, '14, 13:44 
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I can't agree with Stuarts description of the differences. The recommendation is good and the rationale is correct but Reflective Screen is a type of Shade Cloth and you will find it listed as Reflective Screen Shade Cloth, Reflective Shade Cloth or Reflective Shade Nets.


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PostPosted: Mar 18th, '14, 14:39 
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Shade cloths provide shade and even the white stuff absorbs a fair bit of light as heat.

Yes reflective screens do provide shade but the they work primarily on the principle of reflecting the light not intercepting it.

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Last edited by Stuart Chignell on Mar 18th, '14, 14:50, edited 1 time in total.

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PostPosted: Mar 18th, '14, 14:48 
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Plastic, even dual wall is cheaper and works well but has short life and on big structures is difficult to replace. Prone to storm damage.
Plenty move to Poly Carbonate upgrades
Light transmission should be better and as mentioned glass is the best. Needs specific toughened glass or its dangerous.
More money upfront but lower life cost

Agree with Stuart re reflective screens. Generally fairly fragile so need good installation which lets them be moved/packed up without damage. Greenhouse guys get very involved in energy absorbtion/reflection.

Cooling basically needs ventilation, open sides maybe enough, some have opening roofs, rigid roofs have opening vents or sections in the roof to let out hottest air. In very dry climates evaporative may be needed. Other option is a whitewash on outside of structure.
Often commercial guys dont like open sides and roof vents specially designed and screened as it can let disease and insects in.


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PostPosted: Mar 18th, '14, 14:53 
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On poly being cheaper.

I got a quote for a 2000m2 GH in poly $220,000 and would cost about 30,000 to recover in 2-3 years. Glasshouse was $242,000.

One recovering wipes out the initial saving.

However, each market is different so you have to check out prices for yourself.

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PostPosted: Mar 18th, '14, 17:43 
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Stuart Chignell wrote:
Shade cloths provide shade and even the white stuff absorbs a fair bit of light as heat.


I agree that reflective screens are better for keeping a greenhouse cool because of heat absorption issues with regular Shade Cloth but they are just a type of Shade Cloth

Stuart Chignell wrote:
Yes reflective screens do provide shade but the they work primarily on the principle of reflecting the light not intercepting it.


In order to reflect the light, Reflective Screens have to intercept it. Even some of the regular shade cloths intercept and reflect light, particularly the white ones. It's mainly the lesser heat retention and the ability to have greater control over indirect light that I think makes these better than the normal shade cloth.


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