[esp-r] Re: View factors using Raytracing

[Jon Hand]

The method used is not MonteCarlo.  It is a mix of analytical techniques (e.g. detection of
rectangular enclosures) and the grinding of points on surfaces and then geometric checks
to see what 'other-points-in-the-zone' can be seen from each grid point.  It works for
zone enclosures of arbitrary complexity (i.e. the polygons forming the room can  be
of arbitrary complexity) with or without internal mass surface pairs.  I have tested it
with rooms approaching 90 surfaces and with polygons up to 48 edges. In most situations
we find the calculated view factors are quite accurate.  And yes the method is
rather fast on modern computers.

Also the method allows for people to include MRT radiant sensors within zones
and the viewfactors between such bodies and the room surfaces to be calculated.
This allows position specific comfort to be assessed.

The only tweaks needed might be in the case of frames with small dimensions where
the density of the grid would need to be increased.

The original work was done more than a decade ago but there should be a 
publication in the ESRU web pages which describes the numerical approach
in detail.  There are also comments within the code.

You could also have a look at the following web site for more information on
ESP-r facilities:
http://contrasting.no-ip.org/ESP-r_tour/Index.html

and the following web site for a comparison with other simulation tools:
http://contrasting.no-ip.org/Contrast/Index.html

________________________________________
From: esp-r-bounces at lists.strath.ac.uk [esp-r-bounces at lists.strath.ac.uk] on behalf of Raghuram Kalyanam [kalyanam at rhrk.uni-kl.de]
Sent: 24 May 2017 08:54
To: esp-r at lists.strath.ac.uk
Subject: [esp-r]  View factors using Raytracing

Hi Everyone,

I have quick question about how view factors are calculated using raytracing technique. Also raytracing normally takes lot of time, but in ESP-r it seems it is quite fast. Does this raytracing technique do the Montecarlo simulations like in Radiance or is it a different kind of raytracing?

I would be great if someone could throw some light on this, or any references i can go through.


Best Regards,
Raghu


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