Lighting Calculations and RCR (Room Cavity Ratio)

[Anonymous]

Is there any way to go into the program files and change this variable? 

Revit is assuming that all Rooms/Spaces are to figure the RCR based off the multiple of 2.5 which is stated by the ies for irregular rooms, all square or rectangular rooms are to use a 5 for this multiple. Most lighting calculation software out uses 5 for this multiple. These variables drastically effect lighting calculations.

RCR = 2.5 * RCH * P / A: Is shown by the help menu.

Zonal Cavity Method (determining cavity ratios)

Room Cavity Ratio (for regular rooms shaped like a square or rectangle) = [5 x Room Cavity Depth x (Room Length + Room Width)] ÷ (Room Length x Room Width)

Room Cavity Ratio (for irregular-shaped rooms) = (2.5 x Room Cavity Depth x Perimeter) ÷ Area in Square Feet

Ceiling Cavity Ratio = [5 x Ceiling Cavity Depth x (Room Length x Room Width)] ÷ (Room Length x Room Width)

Floor Cavity Ratio = [5 x Floor Cavity Depth x (Room Length x Room Width)] ÷ Room Length x Room Width

[sfidler]

Take a step back and look at the two versions of the formula.  The version for rectangular rooms is just a simplification of the version that takes the perimeter of an irregular room.

Using the perimeter version:

Room Cavity Ratio (for irregular-shaped rooms) = (2.5 x Room Cavity Depth x Perimeter) ÷ Area in Square Feet

RCR = (2.5 * Cavity Depth * Perimeter) / Area

Perimeter of a rectangle = Length + Length + Width + Width = 2 * Length  + 2 * Width = 2(Length + Width)

Substitute into the original equation:

RCR = (2.5 * Room Cavity Depth * 2(Length + Width))/Area

Move the 2 over:

RCR = (2.5 * 2 * Room Cavity Depth * (Length + Width))/Area

RCR = (5 * Room Cavity Depth * (Length + Width))/Area

Substitute Length * Width for Area, and we have the version of the equation for rectangular rooms:

RCR = (5 * Room Cavity Depth * (Length + Width))/(Length * Width)