ESP-r: Shading and Insolation
Current capabilities
ESP-r has the following capabilities with respect to
shading and insolation calculations:
- Calculation of shading for direct radiation on each surface resulting from multiple
shading blocks. Values are stored in a zone shading/insolation file:
each hour of one representative day per month.
The method uses ray projection
from the sun onto a grid of points (typcially 20x20) on each analysed surface and detects
if any defined obstruction block intercepts the ray.
- Calculations according to ASHRAE for overhangs and fins.
- Viewing of shading patterns as a grid of points projected onto
a surface at different times and/or days.
- Insolation calculations can be done for zones in conjunction with or
instead of a shading analyis (if there are no obstruction blocks associated
with a particular zone).
-
Insolation predictions can be undertaken for zones of arbitrary geometric
complexity (i.e. concave, convex, and with internal floating surfaces) and
predictions are resolved to a percentage distribution for each glazing source.
Primary routines
- esruish - code for the module ish that calculates shading
and insolation.
Primary variables
- PSO(I,J) in COMMON/DATA1/ - contains the shading coefficients for
surface I and hour J.
- PINSST(I,J,K) in COMMON/STINS/ - proportion insolated from source I
at hour J to insolated surface K, for the receiving surface.
Issues arising
Planned improvements:
- Direct import from WIS will allow more shading systems to be modelled.
- Saving the specified shading directives (which surfaces to include) so
that recalculation can be automated.
- Creation of an ASCII version of the shading file.
Other possible improvements identified are:
- Automatically accounting for self-shading by adjacent zones. At present
the user must define adjacent zones as shading blocks if they shade the
modelled zone.
- Calculation of shading/insolation distribution at each timestep.
- A test, using Radiance to carry out insolation calculations indicates that
it is possible to do this with minimal overhead for the case of direct
solar and which substantial overhead for the case of diffuse radiation.
Such a method would be generic and could take into account the full range
of geometric entities (e.g. ground surfaces).
- Improvements to the algorithm for projecting obstruction blocks onto a face.
- Ability to seasonally adapt the definition of obstructions - to, for example,
represent changes in trees.
- Diffuse shading is not currently taken into account. It is planned to
allow each surface to have viewfactors to sky/buildings/ground with
shading factors for each based on data at 2 levels:
- "typical" figures for building and ground reflectance with user override;
- import of more accurate values from Radiance.
The viewfactors could also be used for external longwave calculations.