Roof PV

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abcd
Posts: 35
Joined: Wed Jun 03, 2020 11:43 am

Roof PV

Post by abcd »

Hi,

Please advise.

In order to simulate the impact of solar panels on building temperatures, I intend to create a roof with different layers, including solar panels as described in the schematic above.

Because Envi-met only allows for 3 layers, I thought of calculating the average of the roof materials into a material 1. Material 2 will be air (since the panels are installed on a 30° incline). And finally the third material will consist of the average of the PV layers.

According to the building walls tutorial, we're supposed to average the parameters values of the inner materials into a single material layer, leaving only the outermost and innermost material layers as is.
Following this rule, I have 3 questions:

1- Would joining the wall materials, air and bottom layers of the panel in one material distort the results?

2- For the calculation of the average of the parameters, does the rule applied to "Specific heat" explained in the tutorial, apply to all the other parameters: transmission, reflection, absorption, emissivity, thermal conductivity and density ?

3- If I understood correctly in the tutorial, the calculation of the outer layer is based on reflection, transmission and absorption since it receives direct solar radiations. But the layers of the medium depend specifically on transmission and absorption.

In my case, if I put the Glass alone on the outside, it may distort the results because it has a lower albedo than silicon. While the main characteristic of solar panels is the high albedo value of silicon, which allows them to reflect a minimum of rays.

Should we therefore calculate the average of the first 3 layers in a single outer layer (Glass, EVA, Silicon)? Or simply calculate the average of the 5 layers of the panel into one?
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Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Roof PV

Post by Tim »

Hi,

1. In this case, I would not follow the rule of the tutorial because of the air layer in the middle. As you already said, it would distort the results. Joining all wall materials in one as inner wall material, air as middle wall material and all PV materials as outer wall material as you suggested in your schematic is the best idea in my opinion.

2/3. In this case, yes. In standard cases, I would take the reflection, absorption and transmission values from the outer most material for the whole wall layer and only average the other parameters. Since you do have transmissive glass at the outside, I would not recommend that since the other PV layers below would then not be represented correctly as you also mentioned in 3.

Best regards,
Tim

abcd
Posts: 35
Joined: Wed Jun 03, 2020 11:43 am

Re: Roof PV

Post by abcd »

Hi Tim,

Thank you for your advice. You really help me to sort through the choices.

Another question please. For the creation of PV materials (notably EVA and Silicon), I found in the literature the values ​​of thikness, specific heat, thermal conductivity and density. But I did not find those of absorption, transmission, reflection and emissivity. Can I neglect them? if not, do you have any idea of ​​their values?

Thank you in advance.

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Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Roof PV

Post by Tim »

Hi,

Reflection is the albedo. Transmission can be neglected if it is a non-tranmissive material. And Absorption = 1 - reflection - transmission. Emissivity should also be found somewhere for similar materials, probably around 0.9.

Best regards,
Tim

abcd
Posts: 35
Joined: Wed Jun 03, 2020 11:43 am

Re: Roof PV

Post by abcd »

Hi,

Thank's a lot for your explanations and clarification. :D

I may find some difficulties to define the right values of absorption, transmission, reflection and emissivity ​​for each material (building and photovoltaic materials). So I thought about using a wall in the Envi-met database.
My question is: In the "Materials" window -> Misc -> moderate insulation, does this option represent an insulation material or rather a complete wall (brick, concrete, gypsum .. + insulation material )? If it is a wall, can I know the different layers making up these walls for the three options (good insulation, moderate insulation, no insulation).

Thank you in advance.

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Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Roof PV

Post by Tim »

Hi,

It is an already averaged material consisting out of the materials mentioned in the brackets (concrete, moderate insulation and plaster). Those materials are found in the Default folder.

Best regards,
Tim

abcd
Posts: 35
Joined: Wed Jun 03, 2020 11:43 am

Re: Roof PV

Post by abcd »

Hi,
Thank you again for your help.
I have another question please:
Does the concrete mentioned in "moderate insulation wall" mean concrete brick or simple concrete (cement, sand, small stones, and water)?

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Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Roof PV

Post by Tim »

Hi,

Well, you may doublecheck that with the values of those materials (average them again and compare). I would have thought that it would be the simple concrete.

Best regards,
Tim

abcd
Posts: 35
Joined: Wed Jun 03, 2020 11:43 am

Re: Roof PV

Post by abcd »

Thank you for your advice and support. :)

abcd
Posts: 35
Joined: Wed Jun 03, 2020 11:43 am

Re: Roof PV

Post by abcd »

Hi Tim,
Please advise,
To make a special roof, we create it from "Database manager --> Walls" .
But the different layers are vertical, unlike the roof layers which must be horizontal.

Please advise,

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Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Roof PV

Post by Tim »

Hi,

That is irrelevant. It will of course be handled as a roof in the simulation.

Best regards,
Tim

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