Shade Net and Plastic Sheets

Replies to This Discussion

Permalink Reply by Mostapha Sadeghipour Roudsari on March 16, 2015 at 12:33am

Hi Rafat,

I leave the 3rd one to Chris. For the second one do they have the material specifications? You should be able to use Radiance's translucent material and EP's Honeybee_EnergyPlus Glass Material to generate them.

Permalink Reply by Rafat Ahmed on March 16, 2015 at 5:04pm

Dear Mostapha 

thanks for your reply but i could not implement it well, and i wish that the below information will be sufficient to help, bcz this is really important to me and otheres who deals with Horticulture and Landscape in same time.

The most common plastic materials used as agricultural films are the low density polyethylene (LDPE, with a density less than 0.93 kg m−3), the copolymer of ethylene and vinyl-acetate (EVA)

Also here you can find the characteristics of the flexible materials for greenhouse covers (adapted from CPA, 1992 and Tesi, 2001) as much as i get.

UV-PE Film ( UV-PE~ polyethylene Long life or UV)

Thickness (mm) = 0.18

Direct PAR transmissivity (%) = 90

Diffuse PAR transmissivity (%)= 86

Long-wave IR transmissivity (%)= 65

EVA Film ( EVA~Ethylene vinyl-acetate copolymer) 

Thickness (mm) = 0.18

Direct PAR transmissivity (%) = 90

Diffuse PAR transmissivity (%)= 76

Long-wave IR transmissivity (%)= 27

and here you will find the global heat transfer coefficient’ (K in W m−2 °C−1) for the above greenhouse covering materials, measured under normalized conditions (temperatures: exterior: −10°C, interior: +20°C, wind: 4 m s−1). (Source: Nisen and Deltour, 1986.)

Cover                       Clear sky       Overcast Sky

Single PE                 8.8-9.0             7.1- 7.2

Single EVA               7.8                   6.6

Note : the PAR radiation (photosynthetically active or photoactive radiation and its the amounts to 45–50% of the global radiation; Berninger, 1989)

The name PAR is used to designate the radiation with wavelengths useful for plant photosynthesis. It is accepted that the PAR radiation ranges from 400 to 700 nm (McCree, 1972), although some authors consider the PAR from 350 to 850 nm. 

The composition of the radiation changes with time, as a function of the Sun’s elevation and the cloudiness. When the Sun is low over the horizon, the short wavelengths are reduced (less UV and more red). The clouds reduce the amount of energy, greatly decreasing the NIR.

The PAR proportion in relation to the global radiation increases with scattering (diffusion). It is lower with clear sky and in the summer (45–48%).

 

kind regards 

rafat 

Permalink Reply by Rafat Ahmed on March 21, 2015 at 4:38am

Any News Bro 

Permalink Reply by Chris Mackey on March 24, 2015 at 3:49pm

Rafat,

I apologize for responding so late.  I have been so busy over the past week with my thesis.

I think that your best bet with the ventilation will be to use the SetEPAirflow component and make a custom ventilation object (Option 2 on the NautralVentilation Type).  With this custom object, you can really take control over all of the inputs using the area of the net, the height of it, etc.  You probably want to drop down both the wind discharge coefficient and the stack discharge coefficient to account for the fact that the netting will create additional friction and slow down the air slightly.  Also, you probably want to use two SetEPAirflow components in tandem and set the angle of the two ventilation objects to be opposite one another (to account for wind-driven cross flow).  Your final set of components should look something like this:

To clarify mostapha's comment on constructions and radiance materials, here is an image on how to assign them:

I made some guesses about what the reflectance of your film is.

You can find more info on constructions in this video:

https://www.youtube.com/watch?v=OWeoXlQyPxg&list=PLruLh1AdY-SgW...

And more on radiance materials here:

https://www.youtube.com/watch?v=M4MA82_CPPA&list=PLkjfDmSc5OryX...

Also, if you want to get really deep into PAR, you will probably have to find some of your own ways of accounting for the changing color of sunlight at different angles (just the lux and radiation values won't get you accurate results in moles of photons).  You might want to check out the Ladybug_Colored Sky Visualizer to get a better sense of sky color with changing sun altitudes.

Hope this helps,

-Chris

Permalink Reply by Rafat Ahmed on March 27, 2015 at 5:43am

Thanks Chris for the clear replay, i totally understand that you are so busy and i appreciate it so much.

with the best wishes all the way 

Permalink Reply by Rafat Ahmed on March 28, 2015 at 2:24am

Dear Chris and Mostapha

Can you kindly tell me whats wrong with is simulation, 

and the results so crazzy errors. 

Hey Bros i know how much good you are at this, but really my mind JAMMM now,

kind regards  

Attachments:

• Greenhouse ver 01.gh, 495 KB

Permalink Reply by Mostapha Sadeghipour Roudsari on April 4, 2015 at 6:28pm

Hi Rafat,

The error is because you assigned a window constructions to walls and roof. You need to create the glazing surfaces inside the wall/roof (parent surfaces) and assign the window construction to them. You can also simplify your geometry which will save you so much time. There were couple of other mistakes such as assigning adiabatic boundary condition to walls and roofs.

Hope it helps,

Mostapha

Attachments:

• Greenhousever01_msr.gh, 510 KB

Permalink Reply by Rafat Ahmed on April 5, 2015 at 3:41am

Its So Brilliant Mostapha, ya i agree and am always confused about this. 

Its so much helpful, and the point of this is to explore the horticultural aspects on the country who have food scarcity production. 

thanks so much for you Bro