Solar radiation at facades
Site impacts
Solar radiation arriving at the site is then perturbed by interactions with solar obstructions. Users can create combinations of these primitive shapes to represent the neighbourhood of the target building - the level of detail is up to the user. This is a planning issue which could be guided by the types of performance of interest in the project.
Although we can observe reflections from other buildings in the neighbourhood the default treatment in ESP-r is to ignore this. Other buildings are also likely to be static and not change over the period of an assessment and the underlying data structure is consistent with this. Although it might be possible to add schedules to the definition of obstructions, this has not yet been implemented.
We might observe that entities close to facades can influence the microclimate:
Facade-attached rolling shutters are ubiquitous in some regions and embody quite complex thermophysical interactions which are a challenge to represent. Convenient abstractions tend to miss out on important factors - for example representing them as an air space in a construction prevents the low level of ventilation that is likely to occur. More empirical evidence is needed to arrive at a robust approach.
Geometric considerations
The default representations of glazing, fames and facade elements is as polygons with no geometric depth. For a thin facade this is not an issue, however many facades have considerable depth and we may need to adopt alternative approaches to the design of our models and the resolution of assessments to cope with this. Each approach has drawbacks and opportunities:
We can observe slightly specular surface finishes in buildings, however simulation treats reflections as diffuse. This introduces an uncertainty in the distribution of sunlight. Traditionally we ignore this for thermal assessments but may include this in visual studies.
Spandrel panels with non-opaque glass in front of a air space are probably best represented a small zones. This is difficult to scale so the next best approach would be as an air space in a construction.
Blinds embedded within glazing products are actually much simpler to represent than blinds inside the room because the mixing of air near the blinds and the difference in air temperature near blinds is difficult to approximate.
Site considerations
Solar radiation reflected from the ground is often much more complex than the average reflection included in simulation models. Concrete walkways and paved parking areas are rather different from areas of grass. And such features are not evenly distributed around a building. ESP-r does not support such diversity - perhaps it should.
Diffuse solar radiation from the sky vault is reduced to account for diffuse shading from site objects. In urban locations this can be significant.
Some projects would be expected to have complex patterns of shade and shadow on facades from leaf patterns or slat-based or perforated shading devices. This requires considerable inputs from the user. It may be worth carrying out virtual tests of models with different approaches in order to determine which approach is appropriate for a given project.
Where the performance implications of adjustable awnings are important the static nature of obstructions requires that separate models be created.
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