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Effective Shading Coefficients in Ecotect

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Message 1 of 15
archmghasemzadeh
3302 Views, 14 Replies

Effective Shading Coefficients in Ecotect

For calculating shading , I want to know what is the result exactly? The result just show the percentage of shade in surface or the rate of direct and diffuse radiation also is considered?

 

What is Effective Shading Coefficients exactly?

Which parameters are concerned in Effective Shading Coefficients exactly?

 

For setting the overshadowing mask in calculated data , which parameters are counted in overshadowing percentage? And which parameters in stress direct and diffuse?

Thanks

14 REPLIES 14
Message 2 of 15

I also would to like to know this.

In my simulations, the effective shading coefficient seems to be the opposite of the real shading percentage.

For example: My surface is a rooftop with almost no shadings. My Avg. SC is 92.6%, my maximum SC is 58.3% and the minimum is 100%.

Can I always consider the opposite values (7.4%, 41.7% and 0%) for the shading percentages of each month?

Thanks!

 

Clarissa

Message 3 of 15
Pennetier1
in reply to: clarissa.zomer

Hello Clarissa, 

Sorry for the late reply... I am going through old unanswered posts to help users.

 

There might be a confusion between % shading and shading coefficient.  

Shading coefficient is generally used to describe the shading potential of certain objectc, typically glazing and shading devices, or a combination of both.

Thus, a shading coefficient of 100% means there is very little shading potential, whil a low shading coefficient indicates a high shading potential.

For your roof example, which does not receive much shading, a SC of 92.6% looks reasonable.

These SC figures are typically not used for opaque objects; for your example, % shading would be a more appropriate metrics.

 

I hope this helps.

Cheers,

Olivier A. PENNETIER

SYMPHYSIS

www.symphysis.net

Message 4 of 15
rafael.herrero
in reply to: Pennetier1

Hello Mr. PENNETIER

 

The % shading that did you mention is from Solar Exposure or Solar Access Analsysis? Besides, the %shading is the same as Fshad?

 

Thank you for your help.

 

Rafael Herrero.

Message 5 of 15
Pennetier1
in reply to: rafael.herrero

Hello Rafael,

 

The % shading mentioned in the posts above are those calculated by the Sun-path calculations in the Calculate menu > Sun-path Diagram, after selecting an object in your model and running the shading calculations.  You have to look at the Tabular display setting to see the shading % table.

 

I do not understand what you mean by Fshad. Do you want to explain?

 

Cheers,

Olivier A. PENNETIER

SYMPHYSIS

www.symphysis.net

Message 6 of 15
rafael.herrero
in reply to: Pennetier1

Hi PENNETIER,

 

First of all , I would like thank you for your fast reply. 

 

The Fshad comes from the expression below to calculate the Eincident radiation I got from Ecotect Forum.

 

"These factors affect the beam normal (Ebeam) and diffuse sky (Ediffuse) radiation differently, such that:

 

Eincident = [(Ebeam x cos(A) x Fshad) + (Ediffuse x Fsky)] x ExposedArea"

 

I notice previously that the tabular display shows the % shading, but only for the current date. Because that, I use the Shading Coefficients  button which it is possible to calculate average overshadowing for each month.  However did you mention in a post that Shading Coefficients are typically not used for opaque objects. 

 

In fact, if you look the pdf attached,  I'm trying to compare the ECOTECT %near shading results with another simulation softwares using the same solar base, but my results are confuse. It's possible that I need to use de Fshad mentioned above for this comparison.

 

Thank you with you could help me.

 

Rafael Herrero.

 

 

 

 

 

 

Message 7 of 15
Pennetier1
in reply to: rafael.herrero

Hello Rafael, 

 

Correct, Shading coefficients are typically used for glazing material such as windows, and it defines the ratio of solar radiation that goes through the window, compared to a single pane 3 mm thick glass window which has a SC of 1.0 (100%).  Thus, a window with a SC of 50% would let half (50%) of the solar radiation pass through the glazing than a single pane glass window.  Note however that this SC is now more commonly replaced by the Solar Heat Gain Coefficient (SHGC), which is equal to 0.87 * SC.

 

Now, for a complete system, such as a wall object behind a shading device, there are no such thing as a shading coefficient, but rather an effective shading coefficient, which is also the ratio of solar radiation that is allowed on the surface, compared to the solar radiation that would pass through that single pane 3 mm thick window.

For example, if a wall behind a shading device (or any other type of obstruction) receives the same amount of solar radiation that would pass through a window with a SC of 0.5, then this wall object would have an effective shading coefficient of 0.5.

 

Note that Shading Coefficient (or effective SC), is not similar to shading %.  The higher the SC, the more solar radiation is allowed on the surface (as it nears the value of 1.0, equal to clear glass), whereas the higher the shading %, the less solar radiation is allowed on the surface.

You can perhaps think of the % shading as the inverse of the effective shading coefficient, so that Shading % = 1 - SC.

You can export the shading % for each segments of the skydome when going to the Shading button > Export shading data.  You can then open this file in a text editor and can be used with other simulation tools.

 

I hope that helps.

Let me know if you have more questions on this topic, otherwise please accept as a solution so that others can benefit from this information.

Cheers,

 

Olivier A. PENNETIER

SYMPHYSIS

www.symphysis.net

Message 8 of 15
rafael.herrero
in reply to: Pennetier1

Hello PENNETIER,

 

Thank you for your explanation about the SC. Because of that, I noticed that % shading displayed in Shading Coefficient button in Sun-Path Diagram, Solar Exposure calculation and Solar Access Analysis are different from % shading presented in PVSYST, that is called FShdGI (Near shadings factor on global) and is calculated by GlobShd/GlobHrz. Then, 1-FshdGI results the %shading in the surface during each month. Notice that, It was considered the energy (kWh/m2) or (Wh) that reaches the surface from sunrise to sunset.

 

In ECOTECT the Avg. SHADE results compare the Percentage Exposure and Percentage Shaded, without taken into account if the energy is the sunrise and sunset are less than 9h or 12h. Because of that, the %shading results in ecotect shown higher values when compared to PVSYST and other PV softwares.

 

Considering thatt PV softwares considered the Fshad using the Energy that reaches the surface. Using the Solar Exposure (Avg. Daily - Sunpath) from ECOTECT, I calculated the Energy (Wh) incident in the surface with and without building shading. After that, I calculated the difference:

 (Wh_shade -Wh_no_shade) / (Wh_no_shade). Using this process, the results appears to be similar to other PV simulation softwares.

 

I'm not sure if I'm correct, but after hundred of simulations in ECOTECT I have observed these behavior. Above the comparison:

 

I will try to simulate again and compare to confirm my results.

 

See you.
Rafael Herrero.

Message 9 of 15
Pennetier1
in reply to: rafael.herrero

Hi Rafael, 

 

I have used Ecotect for PV system outputs as well, and it provides adequate results when I use a photovoltaic efficiency of 10%.

 

I am not sure if you are familiar with the solar collector feature of Ecotect so here are the steps:

 

1. Create you solar collector, such as a solar photovoltaic panel; make sure its surface normal points upward.

2. Assign it a Solar Collector material under the SOLAR COLLECTOR material element.

3. Under the material properties, I assign an electrical efficacy of 10% - this will depend on your particular panel and all the losses (wire loss, panel efficiency, inverter loss etc...).

4. Go to the Analysis page > Resource Consumption.

5. Select Hourly Solar Collection in the drop down menu and click calculate.  This will give you the monthly electrical output, based on the calculated incident solar radiation (from the solar exposure) * the panel's efficiency.

6. You can also switch of the "Show cumulative Graph" option; if you add an APPLIANCE object in your model, you can also use the Load Matching feature; this works well when a schedule is applied to the appliance object.

 

I do not understand what you mean by "if the energy is the sunrise and sunset are less than 9h or 12h"

 

Cheers,

Olivier A. PENNETIER

SYMPHYSIS

www.symphysis.net

Message 10 of 15
clarissa.zomer
in reply to: Pennetier1

Hi Pennetier1,

 

With your answer here, I better understood about the question I had made before.

 

"You can perhaps think of the % shading as the inverse of the effective shading coefficient, so that Shading % = 1 - SC."

 

Thanks for your reply!

 

Best regards,

 

Clarissa

Message 11 of 15
rafael.herrero
in reply to: Pennetier1

Hi Pennetier 1,

 

Sorry for the lately reply and thank you very much for your last post about the photovoltaic efficiency, material properties and Analysis page > Resource Consumption. Until that moment, I didn't know in which analysis the % effciency of solar collector material is considered. Now, make sense the steps that you mentioned.

 

Regarding your doubt. I tried to say about the irradiance ( kWh/m2) during the first hours of day (7:00 or 6:30) has less energy than 9 o'clock in the sunrise and in sunset, on noon (12:00 o'clock) has higher energy than 16:00 in the evening. Because of irradiance, depending the hour when incident surface is covered by shading, the %shading factor is less or more. Considering the explanation, I would like to know if the ECOTEC analysis considered the irradiance to present the %shade?

 

I do not understant what you mean by "if you add an APPLIANCE object in your model, you can also use the Load Matching feature; this works well when a schedule is applied to the appliance object".

 

 

Thank you for your support.

 

Rafael Herrero.

 

 

 

Message 12 of 15
Pennetier1
in reply to: rafael.herrero

Hello Rafael, 

 

If I understand your question, you are asking if Ecotect accounts for the shading impact even when the solar angle is low (as in the early morning or late afternoon)?  The answer to that is yes.

Ecotect creates a shading mask for each object of your model.  This shading mask is similar to what Ecotect does when calculating shading in the Sun Path Diagram under Calculate menu > Sun-Path Diagram.

If you use the Solar Exposure feature under the Analysis tab, you can see the variation in incident radiation from nearby shading, even in the early morning and late afternoon.  Make sure you un-check the "Direct Light Only" option, so that Ecotect accounts for the diffused radiation that typically prevails around sunrise and sunset.

 

Load Matching: you can add an APPLIANCE object in your model. You can use the button on the left that resemble a computer.  APPLIANCE objects simulate any equipment in your model.  This object can simulate a single equipment (like a fridge for example), or that can represent multiple equipment (such as a room full of computers), depending on your settings of the appliance (as defined in its material properties).

Once Ecotect sees an appliance object in the model, with a defined energy consumption and heat output (also set in its properties), it can calculate if the energy produced by any SOLAR COLLECTOR element in the model can match the electrical load (consumption) of your APPLIANCE element.

Have a look at the APPLIANCE section in the help file for more detail on how to create APPLIANCE object and assign schedules to them.

 

I hope that clarifies things a bit.

Let me know if you have more questions on this topic, otherwise please accept as a solution so that others can benefit from this information.

Cheers,

 

 

Olivier A. PENNETIER

SYMPHYSIS

www.symphysis.net

Message 13 of 15
rafael.herrero
in reply to: Pennetier1

Hi Pennetier,

 

Sorry for lately reply. I spend some time to understand all the concepts did you describe in your last post and doing many simulations to got the correct results. I would like to thank you for all information and support during this time.

 

 

I have one more question to understand how ECOTEC calculated the %Shade. 

 

 As you can see in Attached orthogonal projection. I would like to know if the shading in the sunrise (before 7pm) which is behine the plane of photovoltaic sections is added to the % shade? In other words, even despite the suns comes up, but is behine the incident plane, ECOTEC sums this shading period in the %shade resulted in Solar Exposure Analyse and in Sun-Path Diagram in Effective Shading Coefficients?

 

Best Regards.

 

Rafael Herrero.

 

 

 

 

Message 14 of 15
Pennetier1
in reply to: rafael.herrero

Hi Rafael, 

 

The shading calculations are done for the particular object that is selected in the Sun-Path Diagram, and more specifically for the center of the geometrical object.  So yes, the shading that occurs on your object before 7 am is actual shade on your surface, OR, I suspect that the sun is located behind your surface at that time of the day and year, and thus does not contribute any direct radiation.  It is true that it will also mean that any indirect solar radiation that would contribute to the object during these early times when the sun is blocked - but there is still some light - is not accounted for, but these are typically very minimal compared to the direct solar radiation.

You can always check how much direct or indirect (or both) solar radiation is incident on your object after the over-shading calculations by selecting the appropriate option under the "Calculate Data" drop down menu of the Shading Calculation settings.

 

The image below shows shading on the object (the shading occurs when the sun is behind the object), and its diffused solar radiation results.

 

shading-diffused radiation.gif

 

I hope it makes some sense.

Cheers,

Olivier A. PENNETIER

SYMPHYSIS

www.symphysis.net

Message 15 of 15
rafael.herrero
in reply to: Pennetier1

Hi Pennetier,

 

That is exactly my doubt and yes, the sun is located behind my surface in the first hours during the year.

 

Thank your you fastly reply and .gif sample.

 

Best Regards

Rafael Herrero.

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