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Green Building Simulation
Jeremy Faludi, 11 Oct 07
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What if architects could make CAD models of their buildings that would automatically tell them how much energy structures would use at what times of day and year; where sunlight streams into rooms, and how bright it is; and how much air conditioning they need? Well, they can, within limits.

Simulation and modeling is one of the keys to a sustainable future. Otherwise progress can only happen by trial and error, which on the architectural scale is a horribly slow process. Simulating a building's energy use is a hard problem, requiring not only a model of the building and the materials that make it up (including insulation, windows, foundation, etc.) but also a model of the building's location, with the path of the sun through the year and weather data that is accurate and detailed, including humidity, wind, simple daytime-nighttime temperatures, and a host of other information. And of course, the challenges are compounded when you want to make a simulation that will work in any part of the world.

For almost fifteen years now, researchers like those at Lawrence Berkeley National Lab have been working on green building simulation systems. They are far more accurate and easy to use than they were, but the pace of change has not been fast--in fact, their state-of-the-art analysis tool, EnergyPlus, is still written in Fortran, and has no graphical interface. However, several other programs have been written that create interfaces to EnergyPlus. LBL's software is open-source, and they have a great network of developers throughout the country, but the project has never gotten as much budget as it should. LBL also helped develop Radiance, a tool that quantitatively renders daylight in building models to provide not just pretty pictures but luminance numbers so you can determine how much artificial lighting you need in a room (or how much you need to change the room to eliminate the need for artificial light).

The leader of the building simulation industry now may be a relative newcomer, Square One research. their program Ecotect is a whole-building simulator that "combines an interactive building design interface and 3D modeller with a wide range of environmental analysis tools for a detailed assessment of solar, thermal, lighting, shadows & shading design, energy & building regulations, acoustics, air flow, cost & resource performance of buildings at any scale." (And don't worry, you don't have to use their CAD engine, you can import from AutoCAD.)

There are other tools out there, as well. IES's "virtual environment" software can act as a plugin to AutoCAD's Revit, calculating heating and cooling loads from within Revit. Green Building Studio has gotten a lot of press for their eponymous web-based program, which is one of the many interfaces to EnergyPlus (or the older DOE-2 analysis engine). It also helps suggest (read: advertises) materials from manufacturers; this got it dubbed "a Google for green building products" by C|Net, though they may not be familiar with Building Green's GreenSpec directory. Green Building Studio does appear to be a great tool, though, with helpful features like telling you how easy it would be to make your building carbon neutral. Architects at HOK have brief but good summaries of some programs on their blog. If you really want to dive into the field, the DOE's Energy Efficiency and Renewable Energy division has an enormous directory of building analysis software, with scores of programs covering everything from whole-building analysis to fenestration, life-cycle analysis, hydronic heating, and multi-building analysis. Perhaps Google's SketchUp people should make an integrated analysis program. That would elevate SketchUp from a toy to an industry-leading tool, and would let the folks at claim a big impact--after all, the building industry is the single largest energy-user (and thus carbon emitter) in the world.

Simulating a building before it's built is only half the battle. Once the building exists and people are using it, it should be measured to check that it is performing as expected. This is called commissioning, and is crucial to the green building industry. Thousands of buildings around the world perform poorly without anyone knowing -- they just pay the energy bills and get on with their work. But when you monitor a building's performance, you can keep it in peak shape, like an Olympic athlete, to keep its occupants in comfort at minimal expense and environmental impact. Data from commissioning can also feed back into simulation programs, to make their models more accurate and complete.

Image courtesy HOK, from IES.

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I agree that SketchUp would be a good place for such simulation data, particularly since many architects seem to be using it for early-concept work where the greatest opportunity for influencing the design exists. There is actually an EnergyPlus plug-in for SketchUp in the works; it was supposed to be available by now, but I don't see it mentioned on the EnergyPlus site yet. You can see the concept outlined in this NREL presentation:

The one big hurdle for simulating energy data in SketchUp is probably the lack of detail in the model. You don't need to give the walls thickness, much less assign materials to them, so the energy simulation would have to rely on many assumptions. Still, it could give plenty of feedback on orientation, shading, and basic massing.

Posted by: Ethan Goldman on 11 Oct 07

I find it interesting that you don't see a link here to BIM (Building Information Modeling) applications and integration of such Building Performance Analysis capabilities.

I understand the thought process of focusing on SketchUp, as conceptual design tool, but ultimately the BIM will hold the detailed design data for true validation of design decisions before the actual building is constructed.

Posted by: Kyle Bernhardt on 12 Oct 07

I personally have used Ecotect and other simulation software. I find that the margin of error on them is often so great that it is hard to base any decisions upon there results. They are also limited to very simple geometry which is clearly a problem for architects. Then again an accurate programme that uses the real geometry is very time consuming.

I think the best solution would be a little widget like a speedometer (greenometer) on the side of a cad programme, that gave real time feed back about the environmental impact of what you are drawing.

Posted by: Daniel Davis on 12 Oct 07

SketchUp is not open source, K-3D is, but neither talk directly to Ecotect, which uses external simulators such as EnergyPlus for number crunching anyway.

A direct link from K-3D to EnergyPlus would be ideal.

Radiance is a very acurate tool however it does not let you work with some aspects of optics that are relevant to sophisticated passive daylight systems. Although it is not advertised as such I find that the Maxwell renderer (commercial software with free demo) to be as accurate as radiance, easier to use and in may ways much more powerful. A FOSS equivalent of Maxwell that hooks directly into EnergyPlus would be ideal.

At the moment if you want to design and simulate some fancy optics that controls sunlight entry into a building and then calculate the impact of this light on the comfort of the building, taking into account thermal mass, you are going to need to use a handful of programs and a lot of black magic.

Giving the impact a complete, fully integrated and FOSS, tool-set would have on global energy efficiency, governments should make funding it a priority. They should also provide the CPU power required to run such simulations, on the agreement that the end designs be fully documented and placed into the public domain.

Fat chance that it will happen though as most public servants and their mates in the green movement are self serving political creatures who will realize that you only need so many house designs per region before most people will not need their help any more because they can access an off the shelf design that is worlds best practice in terms of renewability and energy efficiency.

Posted by: DSMatthews on 12 Oct 07

Which would you say is the most "kid friendly"?

Posted by: martie on 14 Oct 07

Which would you say is the most "kid friendly"?

Kid friendly mearning something a child could understand... what makes a building green?

Posted by: martie on 14 Oct 07

Which would you say is the most "kid friendly"?

Kid friendly mearning something a child could understand... what makes a building green?

Posted by: martie on 14 Oct 07

BIM is the reason energy analysis tools can exist, and ArchiCAD by Graphisoft is a leader in this regard - fully compatible with energy analysis, structural and MEP applications.

Posted by: Agent Design on 18 Oct 07

BIM is the reason energy analysis tools can exist, and ArchiCAD by Graphisoft is a leader in this regard - fully compatible with energy analysis, structural and MEP applications.

Posted by: Agent Design on 18 Oct 07

BIM is the reason energy analysis tools can exist, and ArchiCAD by Graphisoft is a leader in this regard - fully compatible with energy analysis, structural and MEP applications.

Posted by: Agent Design on 18 Oct 07

We're currently working on a Green Building Studio - Sketchup Plugin. For more info and a video demo see

Posted by: malcolm on 22 Oct 07

Great article. Glad to see you ended with a discussion on commissioning as this is an oft-overlooked piece of the sustainability puzzle. I'm a building envelope specialist in Toronto, Canada and manager of sustainable design services for a local engineering firm and have presented a conference paper on the concept of building envelope commissioning as a way to improved durability and reduce construction defects.

As part of our sustainability service, I'm interested in finding more resources for Ecotect. The online wiki is incomplete and the software has no manual. Does anyone have info on where to find better tutorials for Ecotect?


Posted by: Scott Armstrong on 22 Oct 07



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