Solar Availability in Cities
Analysing solar and daylight availability in dense urban environment is quite a complex process and depends on dynamic overshadowing inter-relationships between buildings and other site obstructions. Accurately quantifying the effects of shading and overshadowing is key to the prediction of building performance metrics such as solar gains, daylight access and thermal behaviour, as well as the potential benefits of photovoltaics and other renewable energy sources. Not to mention increasingly stringent legislation on solar-access and rights-to-light. All this means that the use simulation tools to predict these complex effects are becoming increasingly necessary, as is the ability to visualise and convey this information obviously and effectively. The first part of this article deals with the means of mapping solar radiation and other metrics on buildings surfaces, whilst the second deals with calculating the full spatial variation in solar availability over the entire un-built volume of a site using an analysis grid.
Comparing Solar Position Data
I have had a couple of occasions recently where I needed to directly compare different solar position algorithms, as well as predicted versus recorded position data. This sounds pretty simple, but there are actually some interesting little quirks where even datasets that are so close as to be virtually identical will still throw up spuriously large differences in individual values. I thought these might be worth documenting and discussing.
ECOTECT and the Average Energy Year
When you perform solar and thermal calculations in Ecotect, it does not do these for any specific year, but rather a standard 'average' energy year. This is true of nearly all thermal and energy analysis tools. Even the weather files used for solar and energy analysis are usually averaged to better represent long-term conditions. This article explains the basic assumptions behind the 'average' energy year and why this approach is more appropriate than using any particular year.
Are Highly Efficient Buildings Sustainable?
Many recent regulations and energy codes focus almost exclusively on energy efficiency during the operational life of a building. In our struggle to adapt to these changes and still appear 'modern', architects and designers are increasingly looking to energy-intensive materials and high-tech solutions, often ignoring many of the wider impacts of their projects. This article questions the true sustainability of these kinds of buildings and suggests that there are better ways to achieve the efficiencies we need.
Fitting a Spatial Analysis Grid
Many people have questioned why the analysis grid produced by the 'Auto-Fit Grid' function in Ecotect leaves a gap around the edges of a room rather than covering the full extents of its floor area. There is a very good reason for this and, as it touches on some more general analysis concepts, is deserving of some detailed explanation.
Averaging Solar Radiation
For the most part, the mathematics of solar radiation is pretty straightforward. However, there are a couple of situations that are less intuitive than they first appear. This is definitely true in the calculation of average hourly incident solar radiation (insolation).
Why Shading Calculations Take so Long
Calculating detailed solar shading and overshadowing is a problem for most building analysis tools, ECOTECT included. It is important to a whole range of building performance criteria, from thermal and daylighting analysis through to solar access and rights-to-light. However, doing it fully and properly can take a frustratingly long time. This article explains exactly what is happening during these calculations and offers tips on how to optimise the process and make best use of your existing shading data.
Solar Shading Potential
Not all parts of a solar shading device are equally effective or even necessary. Techniques have been developed in ECOTECT to visually map variations in effectiveness over the actual geometry of a modelled shading device. These same techniques can be used during the design process to map shading potential over a proposed device or even to determine the best location for shading. This article explains the concepts behind these techniques and how they may be best applied.
RADIANCE and Daylight Factors
The freely available RADIANCE software is one of only a few lighting analysis tools able to accurately calculate illuminance levels on surfaces within a building model. This article explains how illuminance levels can be used to generate daylight factors in RADIANCE and presents a number of ways of doing this, including using ECOTECT as a modelling interface. It also shows how both illuminance levels and daylight factors calculated in RADIANCE can be read back and displayed interactively within your ECOTECT model.
An Optimised Shading Example
A number of people have recently requested information on how to complete an overshadowing exercise I set some Masters students at a couple of different Universities. As a result, I have added some more descriptive text and reformatted the original answer sheet to describe both the exercise problem and an example method that can be used to generate the answer.
CAD Geometry vs Performance Analysis
With an increasing regulatory emphasis on energy efficiency and building performance analysis within the design process, the need for a smooth and hassle-free conversion from CAD tool to analysis engine is becoming critical. This article considers the issues associated with such a transition, looking in detail at the kind of information required by different performance analysis / simulation tools and what is actually available in a typical CAD drawing. It looks at the various options available, including the growing influence of Industry Foundation Classes (IFCs) and gbXML, and what their impacts might be.
The Thermal Effects of Solar Gain
In many building regulations and simplified analysis methods, solar effects on buildings are characterised only by the exposed apperture area and the average solar transmittance of the glazing used. However, the true impact of solar radiation on the internal conditions within a space are often much more complex than this simple relationship would suggest. To explain the problem, this article tracks solar radiation as it enters through a window and looks at the various factors that govern its resultant effects.
Making a Thermal Comparison
One of the first things many people say when introduced to analytical software is: "OK, but just how accurate is it?". The accuracy of analysis software is important, but in the case of a thermal analysis tool this is not a simple question to answer. This article discusses the many issues you must first consider before comparing measured thermal values against simulation results, not just in ECOTECT but in any thermal analysis tool. It also makes the case for concentrating on relative accuracy in simulation rather than absolute accuracy.
Domes and Solar Radiation
Domed roofs have great structural advantages, but also some significant thermal advantages due to their response to incident solar radiation. This article presents a quick outline of this response when compared to flat or inclined roofs and why it may be desirable.
Thermal Modelling - the ECOTECT Way
For ECOTECT to properly 'understand' a thermal analysis model, it requires that you adhere to some specific conventions when constructing it. A lot of work has been done to ensure that you can effectively model most building situations and that the same model can be both analysed in ECOTECT and properly exported to other tools such as EnergyPlus and ESP-r. This article outlines the important elements you must remember when creating thermal models and explains a few shortcuts you can take when modelling multi-storey, multi-zone and earth-bermed buildings.