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3.4.3 - Interior Lighting #807

Open GoogleCodeExporter opened 9 years ago

GoogleCodeExporter commented 9 years ago 
What 90.1 PRM Section(s) are relevant to this issue?
Interior Lighting

Explanation of issue:
Question on how all lighting fractions are calculated.
In the PRM we document the 'Space Fraction' and the 'Radiative Fraction'. On 
the basis of this, we can calculate the 'Return Air Fraction' and the 'Radiant 
Fraction'
Return Air Fraction = 1 – Space Fraction
Fraction Radiant = Space Fraction X Radiative Fraction

How is the visible fraction calculated? Is there a default that is used based 
on luminaire type? Since we do not know the value for fraction convected 
either, the equation in the IO reference wouldn't work

Fraction Convected = 1- (Return Air Fraction + Fraction Radiant + Fraction 
Visible)

Proposed resolution:

Original issue reported on code.google.com by supriya....@pnnl.gov on 10 Oct 2014 at 10:51

GoogleCodeExporter commented 9 years ago 
The ASHRAE HOF, from which the values provided in the ACM and PRM are derived, 
does not distinguish between the short wave and long wave portions of the 
radiant fraction. 

In the CBECC ->> E+ implementation, we have assigned 100% of the radiant 
fraction to the long wave E+ Property (Field:Fraction Radiant), and left the 
short wave portion (Field:Fraction Visible) unspecified.  I assume unspecified 
translates to 0, but should confirm with the OS team.

The IO ref provides some sample values for the split between the long and short 
wave portions of the radiant fraction, and in all cases the short wave portion 
is less than half of the long wave portion.  In addition, the only difference 
in implementation is that for the long wave portion, the heat absorbed by room 
surfaces in calculated as the long wave radiation x the THERMAL absorptance of 
the room materials, while for the short wave portion, the heat absorbed is the 
short wave radiation x the SOLAR absorptance of the room materials.  For most 
materials, these values are close - i.e. for Gypsum board - THERMAL = 0.9 and 
SOLAR = 0.7.

Original comment by lu...@360-analytics.com on 15 Oct 2014 at 4:58