[esp-r] Re: Setting Shading Coefficient for transparent constructions and double facade

[Jon Hand]

A question about Shading Coefficients in ESP-r....

The short answer is that ESP-r does not use a "shading coefficient"
which is a ratio of a specific glazing product to a 'standard single glazed window' as
used by many engineering software from information supplied by glazing mfg.

Optical properties in ESP-r are calculated via a 3rd part application such as WIS (in Europe)
or Window 5.2 in North America.  Optical properties are angular dependant (5 angles)
and include overall solar band transmission at 5 angles.  For each layer in the transparent
construction there is solar absorption at 5 angles.  The existing ESP-r optics databases
are based on information imported from WIS or Window 5.2 (prj can directly import
reports generated by these applications).

It is difficult to give a full tutorial for WIS or Window 5.2 in an email.  WIS and Window 5.2
take the raw data for each of the layers of glass and produce the kinds of information
used by ESP-r.

The optical properties in ESP-r are used by the calculation engine to figure out
how much of the radiation arriving at the outer surface is absorbed in each layer of the
transparent construction at each timestep an how much is transmitted into the
room.

SEPARATE calculations for SHADING tell the simulator whether it
is necessary to modify the solar radiation arriving at surfaces of a building facade
and the INSOLATION calculations tell the simulator how to distribute the
solar radiation which has already passed through a transparent construction.

The question seems to be asking about the relationship between shading and insolation
calculations and optical properties.  The calculation of optics is a separate calculation
and is used whether or not there is any shading or insolation calculated.

If, as an example there are 100W of direct radiation available and there is 25%
shading at a specific hour of the day then 75W arrives at the outside transparent
layer.  If the optical properties of the glass control how much of the arriving energy
passes through the glass or is absorbed in the glass.  If 40W of radiation finally
emerges from the transparent construction and enters the room the insolation
calculations might put 10% of 40W onto the 2nd
surface of the room and 20% to the 3rd surface and 70% to the 4th surface
of the zone.

In ESP-r (as in every other simulation tool that I know of) the calculation of insolation
is used to predict where solar radiation will fall within a zone from glazing that is facing the
outside.  Insolation calculations are not designed to calculate the path
of radiation arriving from an adjacent zone (such as a double skinned facade).  This
is why you get no 'option' for insolation calculation in the office room - there is no
external facade.

It would be wonderful if insolation were calculated between zones. That would require a significant coding
effort.  Currently, the radiation arriving in adjacent rooms (e.g. the occupied rooms in a double
skin facade) get diffusely distributed radiation based on what arrived at the
transparent partition and the optical properties of the partition.

There is a 'trick' that can be used if the outer room is VERY THIN.  The
trick is not easy to explain in an email.

Regards, Jon Hand

________________________________________
From: esp-r-bounces at lists.strath.ac.uk [esp-r-bounces at lists.strath.ac.uk] On Behalf Of lzyhust [lzyhust at 163.com]
Sent: 03 January 2010 11:31
To: esp-r
Subject: [esp-r] Setting Shading Coefficient for transparent constructions and double facade

    There is optics for transparent glass in the databbase. Then how to change the Sc for the transparent construction ?And how to do if there are three layers for transparent constructions, and each layer has a Shading Coefficient.

    For constrcut a double facade building, how to define the the inner glass in Shading&insolation>

[cid:bef70e$12e125f3f48135$Coremail$lzyhust at 163.com]
I have established a double facade model(see the picture). It shows no selected source When i try to compute the shading or insolation for the inner glass.

Many thanks,
Teresa