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Formulas!

PostPosted: Wed Jul 06, 2011 8:00 am
by James
Anyone have any good knowledge on this?

I am going to attempt to make a formula within revit for average daylight calculation.

Re: Formulas!

PostPosted: Wed Jul 06, 2011 10:55 am
by Revit Zone
This is an area of revit I have been meaning to develop for some time.

The basics are quite simple. All you need to do is create parameters to hold the values you need and also create parmeters to hold the answers. Then just use standard "programming" operators (ie +. -. *, /, =) to perform the forumala. When you come to create your "answer" parameter- just choose "forumla" instead of an absolute value.

I don't mind taking a look at this with you, if you want to keep this thread going- we can share some knowledge here, that may be usedful to others?

Cheers,
Ian

Re: Formulas!

PostPosted: Wed Jul 06, 2011 12:44 pm
by James
that sounds great, I have roughly worked out how to pull the information from the model but im already hitting a problem

W = glazing - see problem below
A = thought of using a formula for either ceiling area and room area, or room area *2 then for the walls using the perimeter from room area * storey height
R = constant for most cases
T = constant for most cases
u = constant for most cases
M = constant

note about constants, they can just be changed on the fly, or within a parameter for the window family.


Glazing!

It seems that Revit is taking the area for glass/glazing from all sides, so it is well over.


This is the equation


DF = MWuT/A(1 – R2)


Where:

W = total glazed area of windows or roof lights
A = total area of all the room surfaces (ceiling, floor, walls and windows)
R = area-weighted average reflectance of the room surfaces
M = a correction factor for dirt
T = glass transmission factor
u = angle of visible sky

Guide values for a typical dwelling with light-coloured walls are as follows (for more accurate values, refer to CIBSE Lighting Guide 10):

R = 0.5
M = 1.0 (vertical glazing that can be cleaned easily)
0.8 (sloping glazing)
0.7 (horizontal glazing)

T = 0.7 (double glazing)
0.6 (double glazing with low emissivity coating)
0.6 (triple glazing)


u = 65˚ (vertical glazing)

Re: Formulas!

PostPosted: Wed Jul 06, 2011 1:29 pm
by Revit Zone
How are you getting the area of glazing, James? (are you taking a "material take-off" from the glass?)

What if you just took the width and height of the window and then deducted the frame area- using the parameters from the window family?

Cheers,
Ian

Re: Formulas!

PostPosted: Wed Jul 06, 2011 1:32 pm
by James
yeah, I was using material take off for Glass. Which is taking all faces for it. This is where i thought of painting one side of the glass and using this for the area.

Could look at deducting the frame from the window and getting it that way, but im unsure if Revit is using the same method for the frame material.

Must be an easy way of doing it! :)

Re: Formulas!

PostPosted: Wed Jul 06, 2011 1:52 pm
by Revit Zone
W=width of window opening
H=Height of window opening
FW=Frame width (when viewing "face on")

Area of glass=(w x H)-(2*(W-(2xFW)*FW))-(2*(H*FW))

Or something like that!

Does this help????

Cheers,
Ian

Re: Formulas!

PostPosted: Wed Jul 06, 2011 2:55 pm
by James
wow :D

will give it a try, but the frame varies whether its opening or fixed.

Re: Formulas!

PostPosted: Mon Aug 22, 2011 3:13 pm
by Revit Zone
Hi James :)

How did you get on with this one????