ARTICLES
Below are a series of articles relating to various aspects of building performance analysis and simulation. Articles are typically longer and more in-depth than blog posts, and focus on the definition or explanation of specific concepts. I also use them to explain issues or misconceptions that may have arisen, to clarify terms that may have caused confusion, or to step through lengthy processes not covered in any of the technical documentation. Some of the earlier articles in the list began their life as part of the Natural Frequency Journal, but now live on here.
Site Analysis Metrics
Site analysis is an important tool for building designers to help guide the form and orientation of their designs to take optimum advantage of whatever amenity and resources are availabe. As the design develops, site analysis becomes even more important as a means of demonstrating compliance with building codes and meeting the energy efficiency and sustainability criteria set by clients and/or regulatory bodies. As with most building performance analysis though, there is no single metric that will solve all your design problems. Instead, you typically have to compare multiple metrics on each design iteration and try to make the best set of compromises for both your building and the impacts it will have on those that surround it. The aim of this article is to outline the range of site analysis metrics that can be computed and to loosely group them based on their input requirements.
Solar Position
The position of the Sun in the sky varies continually throughout the day and also changes signficantly over the course of a year. It is also very location-dependant, so it is critical that you know the latitude and longitude of your development site before you begin any calculations. Despite our fundamental physical understanding of solar position as a result of experiencing it every day, calculating it at any specific date and time is by no means a trivial exercise. The tilted rotation of the Earth and its elliptical orbit around the Sun add significant complexity to the equations required. Add the fact that one day isn't actually the time required for a full rotation of the Earth around its axis and that 365 days isn't actually the time required for a full orbit around the Sun, and we're in for some real fun and games.
Sky Distribution
This article discusses the processes involved in determining the luminous distribution of daylight and solar radiation over the skydome in order to accurately account for the effects of shading and reflections in and around a building site. It looks at the mathematical models used and their implementation, as well as some of the issues associated with aggregating multiple skies over longer periods.
Significant Latitudes
This article discusses a range of latitude lines on the Earth's surface that have some solar significance. Latitude refers to one of the angular components that define a geographic location, more specifically to imaginary lines that run around the Earth parallel to the line of the Equator and vary from -90° at the South Pole to 90° at the North Pole, passing through 0° at the Equator. As the Earth's axis is tilted relative to the Sun, the amount of available solar radiation varies throughout the year giving us the four seasons. This seasonal variation is marked by solar-related minima and maxima that occur at particular latitudes.
Significant Days of the Year
This article discusses those days within the year that have some solar significance. Known as Solstices and Equinoxes, these days are defined by the cyclical nature of available solar radiation and mark the changing of the seasons. Understanding seasonal variations in temperature, daylight and solar radiation throughout the year is an important part of the building design process.
Significant Times of Day
Over the course of any 24 hour day, the world transitions from the darkness of night to the brightness of day, and then back again. As the Sun arcs its way through the sky during that process, it crosses a number of thresholds and reaches certain maxima that have long influenced man's activities, even today. This article discusses those particular times of day that have some solar significance, which include different stages of twilight, sunrise and sunset, as well as local and solar noon.
Dynamic Daylight Simulation
This article presents the methodology used in the initial versions of the web-based dynamic daylight simulation tools and compares the results with those from Radiance using the exact same model. It is intended as a detailed supplement to a research paper with a similar title submitted to the PLEA 2017 Conference in Edinburgh, providing additional explanatory material, information and results to support the arguments made in the original paper.
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.
Introducing Scripts in ECOTECT
Scripts have been available in ECOTECT from very early on in its development and are probably one of its most under-utilised features. Anyone can write and run a script in ECOTECT and they can be used to add new functionality, automate complex tasks, initialise or standardise a model to your firm's requirements, generate summary data, export to another application, etc. Pretty well anything you can imagine. This article is a brief description of what a script is and what it contains.
Behaviour of Light
Understanding the behaviour of light within materials and spaces is a key skill for any competent architect or building designer. Without this knowledge, a huge amount of the amenity available from natural light and solar control is at risk of being under-utilised or worse, seriously compromised. The concepts themselves, though many, are relatively straightforward. However, once you understand them, you will very likely use them everyday in your design work and specification writing.
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 aperture 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.
Building Analysis: Work Smart, Not Hard
The most efficient approach when undertaking any form of work is to minimise your own effort whilst maximising the potential benefits and/or impacts that may flow from it. This should also be true of simulation and analysis work. This article discusses ways you can approach a project to achieve this, presenting a simple example to illustrate this idea in practice.