Daylight factor calculator

[jeds]

Anyone know of a calculator for Average Daylight Factor. I've got the formula but some Excel wiz kid must have made up a spread sheet for it somewhere.

 

[stevehuws]

What's the formula? I could probably incorporate it into excel.

 

[jeds]

The formula is DF = MWuT/A(1-R^2 )

Where:

W = total glazed area
A = total of room surfaces
R = reflectance of room surfaces (default is 0.5)
M = correction for dirt factor (1.0 for normal accessible windows)
T = glass transmission factor (0.6 for low-e double glazing)
u = angle of visible sky (default is 65°)

I've tried to work up a spreadsheet but I keep getting weird results and I can't work out where I'm going wrong. It's giving me daylight factors of 0.7 to 0.8 for fairly standard window sizes. The minimum specified by code for sustainable homes is 1.5% for living and bedrooms which means I'd have to double the size of the room windows to comply. Which doesn't sound right to me.

 

[stevehuws]

I've had a go, but with no test data to put in I'm not sure it works as it should.

Here's the link (google spreadsheet).

Could you give me some units and test data?

 

[theoldun]

John, This subject is not our field, but we came across this link a while ago.
It's in old money but have shuffti. If it is not what you are seeking, sorry.
oldun


Daylight Factor Calculation Tool Version 1.01
File Format: Microsoft Excel - View as HTML
The spreadsheet tool uses fundamental algorithms and has been bench tested against ... To see grid points with similar daylight factor values, press the “Do ...
www.msbg.umn.edu/downloads_v2_1/5IEQ_App-I-3_V2-1.xls - Similar

 

[jeds]

Steve, spot on. Using a random example your sheet gets a factor of 1.26 where mine gets 0.7...odd

Looking at your spreadsheet formula I can see that I had a pair of brackets in the wrong place.

Thanks for that. I owe you one.

 

[jeds]

oldun. Thanks for the link. As you can see, thanks to stevehuws, I think I'm sorted now.

 

[stevehuws]

No worries, glad I could help.

 

[nico8188]

Dear Sir,

I am looking for the formula to calculate the daylight factor (not the average one but the real one). If I go to the link and I download the sheet it doesn't work... :/ could you help me please?

Do you steal have it?

Best regards.

Nicolas

oldun. Thanks for the link. As you can see, thanks to stevehuws, I think I'm sorted now.

 

[cslev]

I've had a go, but with no test data to put in I'm not sure it works as it should.

Here's the link (google spreadsheet).

Could you give me some units and test data?

 

[cslev]

Hi, is this link to the wrong google doc? This spreadsheet doesn't contain avg daylight factor formula.....
Thanks