Solar Protection Parameters

[jdelgado]

Hello,

I would like to know the exact meaning of the following parameter in Solar Protecion Menu:

"Solar Exposure for Sunscreen Device (1=Full Exposure; 0=Total shading)"

On the other hand, WUFI Wiki presents other description in the same menu, that is (see enclosure document):

"Reduction Factor of Solar Radiation (b-value)", with the following explanation:
"A reduction factor of the solar radiation (b-value): If the device holds off 30 percent of impacting radiation, the b-value consequently is 0,7."

Are these the same parameters?
What shall we consider for it?

For instance, with an example, for an uncolored double glass with a SHGC value of 0.75 and a plastic shutter with an additional thermal resistance of 0.20, which values shall we consider for "Solar Exposure for Sunscreen Device (1=Full Exposure; 0=Total shading)" ?

Shall we "subtract" (as the WUFI WIKI explanation refers) the "SHGC glass" value and the "SHGC total" (glass+protection device), so we have the "SHGC device",
or shall we "multiply" these factors?

Thank you in advance
Sílvia
Francisca

FEUP - PORTO

[mpazold]

Ok this parameter got a lot of renaming in different Software versions... But it's the same. Maybe the best explanation: it's a factor multiplied with the incident solar radiation.

if you have 500 W/m² Incident solar Radiation and a solar exposure 0.3 then, past the shading device, if it is active, its 150 W/m². If the factor is 1.0 -> 500 W/m². With the factor 0.0 -> 0 W/m².

Following this, if you hold off 30 percent of solar radiation (500W/m²) you hold off 30% * 500 W/m² = 150 W/m² and the rest 350 W/m² pass, so the factor (the solar exposure) is 0.7 = 350 W/m².

Additional, regarding a SHGC value of the glass, if ti is 0.75 -> it's the next factor: 350 W/m² (past the shading device) * 0.75 = 262,5 W/m².

You named a plastic shutter with a "thermal resistance" of 0.2. You mean 0.2 m²K/W? the "thermal resistance supplement" is the next value below the solar exposure factor. it's not considered for the solar radiation. It's added to the thermal resistance (the Uw-Value) of the Window to calculate the transmission heat flow depending on different indoor<>outdoor temperature diffreence, if the sunscreen device is active.

So i'm not sure, but if you have a "SHGC glass", describing the fenestration system, with an opened shading device, and a "SHGC total", the same fenestration system with an closed shading device, the solar exposure factor of the shading device is "SHGC total" divided by "SHGC glass". Regarding this for the solar gains via the fenestration system:

opened shading device: e.g. 500 W/m² * 0.75 (SHGC glass) = 375 W/m²

closed shading device: 500 W/m² * 0.20 (SHGC total, glass + shading device) = 100 W/m²
with the exposure factor to regard it in WUFI Plus: 500 W/m² * 0.75 (SHGC glass, parameter for the window) * (0,2 / 0,75 = exposure factor) = 100 W/m²

[jdelgado]

Hello,

Thank you very much for your answer.

We think we understood everything.

But just to confirm our idea, could you please confirm:

1. When you say:
Following this, if you hold off 30 percent of solar radiation (500W/m²) you hold off 30% * 500 W/m² = 150 W/m² and the rest 350 W/m² pass, so the factor (the solar exposure) is 0.7 = 350 W/m².
You mean that the "reduction factor of solar radiation (b-value)" is also= 0.7 (equal to "solar exposure" because they are the same), correct?

2. You have used the value of 0.20 to the "SHGC total, glass+shading device" in your example. Is it a coincidence? Because we understood that it has nothing to do with the "additional thermal resistance" we mentioned in our example (that we shall add to Uw and has nothing to do with the SHGC factors...) Right?
We became confused because you use the same value..

Thank you once again for this last clarification.

Sílvia
Francisca

[mpazold]

Hello Sílvia Francisca,

1. yes. they are the same. A factor multiplied with the incident solar radiation.

2. yes, it is like an coincidence. In my example i used the 0,2 as SHGC total (gals + protection). In your question you used 0,2 for "thermal resistance" of the plastic shutter. I tried to explain that the thermal resistance isn't used for the solar heat gains via the fenestration (radiation), just for the thermal transmittance regarding the temperature difference across the fenestration (transmission).

[jdelgado]

Hello again,

We still have some doubts about “solar protection” and “window parameters” now with the 3.0.3 WUFIPlus version. We would be very thankful if you could clarify us about these issues.

Please consider:
Double Glass - DG
SESD - “Solar Exposure for Sunscreen Device”
RFSR – “Reduction Factor of Solar Radiation”
Uwdn – average Uw (day)/Un (night).
Uwdn means consider an unique value for U considering we close shutters everyday at night for sleep. In this case, additional “thermal resistance” of solar protection shall be “0”, correct?

Questions:
• Is there anyway to introduce this mean value Uwdn in WUFIPlus? We can assume Uw as =Uwdn?
• Is this still possible if we define “schedule” to “SPD activation mode”? As the Uwdn changes also with SPD schedule…
• Isn’t it possible to select both “schedule” and “reduce overheating”. How do I tell WUFI I want to close shutters some hours (at night for instance) and at the same time to “reduce overheating”?
• SESD=RFSR correct? (as you mentioned in previous message, correct?)


Considering 3 scenarios, to evaluate the impact of changing window parameters and SPD characteristics on heating energy consumption, with the following data:

a) No SPD + DG: Uw=3.3 ; Uwdn= 3.3; SHGC glass=0.75 ; SHGC total=0.75
b) Internal SPD + DG: Uw=3.3 ; Uwdn= 2.8; SHGC glass=0.75 ; SHGC total=0.25
c) External SPD + DG: Uw=3.3 ; Uwdn= 2.5; SHGC glass=0.75 ; SHGC total=0.04

I also want to consider shutters closed every night, all year, and closing to reduce overheating.

How shall I introduce these same parameters on WUFIPlus:


a) No SPD + DG: Window Parameters: Uw=3.3; SHGC glass=0.75 ; Solar protections: SPSD=0.75; Thermal resistance=0 ?
b) Internal SPD + DG: Window Parameters: Uw=3.3 (or Uwdn= 2.? SHGC glass=0.75 ; Solar protections: SPSD=0.25/0.75=0.33; Thermal resistance=0.30 (or=0) ?
c) External SPD + DG: Window Parameters: Uw=3.3 (or Uwdn= 2.5)? SHGC glass=0.75 ; Solar protections: SPSD=0.04/0.75=0.05; Thermal resistance=0.22 (or=0) ?

Do you think this is this correct? Would you introduce the information in any possible better way?

Hope I made myself clear.

Thank you very much in advance.

Sílvia Magalhães
FEUP, Oporto

[Manfred Kehrer]

Silvia,
first I would recommend you to create your own profile in the WUFI Forum. Let me know if I can assist with that.
And please say hello to João
Manfred

[jdelgado]

Hello Manfred

Thank you for your quick answer.
In fact, i tried once to create my own account and i had problems with it, so I simply start using João' account who kindly allows us to do that.
But, as you mentioned it, i tried now again to create one, and it simply worked, so i will just copy this last message to a new topic and start using my own account.

Thank you for the reminder

Your greetings to João will be sent. Thank you

Sílvia Magalhães

[silmag]

I don´t think i need to copy for a new topic but just follow this one...

So, can someone help me with these questions?

Thank you very much,
Sílvia Magalhães

[mpazold]

Regarding the "solar exposure for sunscreen device" shading:
I think in most cases there should be a hint beside the factor. But i agree, it is confusing. I thought you talked about the reduction factor for constant shading input in the Component -> Surface -> thermal properties tab.

In the newest Version, the hourly definable schedule named "Reduction factor" was renamed to "Opening factor" to make it clear. This factor is the opposite (more or less). 1 means the shading device is closed, 0 means it is open. 0,5 means it is partly closed.

Following this, e.g. if you have an "solar exposure for sunscreen device" (1=no shading, 0=total shading) input = 0,5 :

If the schedule says = 0, there would be no shading due to the sunscreen device (it is open).

if the schedule says 0,5 the device is partly closed (50%) result in an overall shading factor for the device = 0,75 the calculation is like: 1 - ((1 - "solar exposure for sunscreen device") * "Closing factor")

if it is fully closed, the schedule input should be 1, then the result is the solar exposure = 0,5.


Regarding our questions:
If you count the thermal resistance of the shading device to the Uw input, as an average Uwdn (if i get you right), then of cause, the thermal resistance of the shading device should be 0. Then the overall thermal resistance of the transparent component is not influenced by the shading device.
Then might set for Uw the average Uwdn.
If you set the schedule for the SPD (sunscreen protection device), the thermal resistance of the device is regarded and the Uw-Value adjusted with it, if the device is closed (opening factor 1).
Actually it is not possible to set an predefined schedule for the sunscreen device in addition to reduce overheating.
SESD is not RFSR or with the new name the “Opening factor” (see above).
Considering the 3 scenarios:
a) No SPD + DG: if there is no solar protection device you should use “no solar protection” device
b) If you want to regard reduce overheating, I would set the average Uw day/night as Uw Value as window parameter (in that case, for the shading device thermal resistance = 0). But I would also do some simulations with the thermal resistance of the shading device, to a clue about the error you might get if you average the U value for the window. But there is a bug since 3.0.1.0 and still in the actual release version 3.1.0.3: this thermal resistance of the shading device is not regarded; this will be fixed with the next release). With an solar exposure for sunscreen device = 0,33 the “SHGCtotal” result in 0,75 * 0,3333 = 0,25.
c) For the thermal resistance see b) for the solar exposure I would say 0,0533.
Best regards,
Matthias