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How fit is your building?

From CAD User AEC Magazine Vol 22 No 7 - JULY/AUGUST 2009

Autodesk's Ecotect Analysis gives architects the tools to perform Whole Building Performance Analysis to check whether their designs are resource-efficient, as David Chadwick explains.

How on earth can you tell if a building is 'fit’ or not? What the heck is “building performance”? And who really cares whether a building is working to its optimum?

A couple of years ago, such questions would not even have been contemplated. A building was a building. It did, or it didn't look nice, housed the requisite number of people or offices, and allowed its occupants to live or work in reasonable comfort - or not, as the case might have been. My, how things have changed! We are now faced with an environmental crisis, which is forcing us to re-evaluate our use of building materials and methods. Added to that we have an energy crisis, which means that we have to make our buildings just as comfortable using less energy resources, and without creating carbon dioxide - which helps to feed the environmental crisis! And now we have an economic crisis,as well, which means that we have to manage building costs more effectively!

And let’s not forget the comfort crisis. We are no longer content to sit shivering in a large draughty hall, or wilt from direct sunlight coursing through acres of glass windows, and we understand the effects that some buildings have on the long-term health of their occupants. Besides having to cope with all of the above, we demand of our architects that they make our environment as pleasant to live in as possible.

So we now have tools that can look at all of the factors that affect the way a building performs; how it is affected by the sun, how heat - natural or manufactured - is transmitted through a building, how shading affects the occupants and its heating requirements, what effect lighting has on comfort (and safety) levels, and how airflow moves throughout a building. And we are being prodded gently along the route towards totally sustainable buildings by various government regulations, initiatives and grand targets for carbon emissions, sustainable construction and so on.

AUTODESK ECOTECT ANALYSIS 2010

To further those ends, Autodesk has now released its new Whole-Building Performance Analysis Tool, Ecotect Analysis 2010. It’s not the first time we have come across the name in CAD User, as we looked at Ecotect in an earlier issue, before the company was acquired by Autodesk. A judicious move by Autodesk, as the need for sustainable, energy efficient buildings overrides any other construction issue, with even clients demanding greener designs, foregoing the pleasures of maximum profit. (Strong cases have been put forward that have equated green design with greater profitability - but that's for another issue!) Actually they are on safer ground, as no longer do architects have to hand out the simulation and analysis of building performance to expensive outside experts, as all testing can now be done with easyto- use software integrated within the design application.

As Pete Baxter, Autodesk's Senior Director for Northern Europe put it, as he announced the latest release, “Autodesk Ecotect Analysis 2010 reduces the overheads usually associated with sustainable design, eliminating the need to outsource the tasks of testing and analysis and enabling collaboration within the extended building design team using Autodesk applications for BIM. In fact, design data can be imported into Ecotect Analysis from any Autodesk application, including Autodesk Revit, Architecture and MEP 2010, using gbXML (green building extensible Markup) format.”

ECOTECT ANALYSIS AND BIM

You do not have to wait until you have completed your design before subjecting it to Ecotect Analysis. That's the wrong way to go about it. Ecotect Analysis is there to help architects make informed design decisions at any stage of a building's design about energy efficiency and sustainable design. Gathering the data is not complicated, either. All energy management relates to the simulation of movement in, out and through rooms within a building. This is governed by materials, surfaces, and the spatial layout of a building . Which surfaces are exposed to the outside, or to direct sunlight, and for how long? What are the size and orientation of windows and doors, and so on?

Calculating a building's thermal properties from its areas and volumes is not new, but before the advent of 3D modelling and BIM, it was conducted by engineers extracting, and collating the data from 2D building plans and elevations - a time-intensive task only attempted on completion of the design Now much of the data is already available within Revit and other building models and can be used, repeatedly, from the very start of the design process, using the results to confirm, or modify the efficiency of the design.

START AT THE BEGINNING

How early can you invoke Ecotect? You can get useful info from the earliest models, such as a massing model in Revit, exported as DXFs, which just contain the external geometry of building forms, which can then be used to conduct overshadowing, incident radiation and urban-scale simulations. For simplicity and speed, each storey of a building can be defined as a single space, and whole ribbons of glass modelled for windows, reducing simulation times, but providing enough accuracy to analyse the energy impact of different glazing schemes.

More detailed thermal analysis will require more complete models with floors, ceilings to rooms and roofs, although skylights and windows, which contribute significantly to HVAC energy use, can be inserted quickly - and then resized, removed, or optimised to fine tune the simulations.

Following the process from a sustainability angle focusses the mind wonderfully. You wouldn't leave gaps between the walls and the roof if you were going to insulate your home, therefore it is essential that all such factors within Ecotect Analysis are subject to the same scrutiny. It is imperative to have a computable Revit model for sustainability analyses.

Having said that, it is important to kept the design as simple as possible, modelling only major spaces, and combining smaller spaces that are important to the design: washrooms, stairwells, elevator shafts etc. Too much data and you introduce unwanted errors, and slow down the simulation process .

ADDING ROOMS AND SPACES

Some new concepts have been introduced to Revit for the benefit of Ecotect Analysis. In order to export a Revit model to the simulation software using gbXML, room objects must be defined, with rooms properly positioned in the model and high enough to touch bounding surfaces (ceilings). It's a simple process. Select the room object from the Home tab, and click the area in a plan view of the model where you want it placed. Revit will then highlight the bounding walls that make up the new rooms boundaries, which will then be combined in the model under New Construction. Ensure it's height is correct by stipulating the level above your current level as the room wall height, so that it (parametrically) retains its connection even following room height changes. Failure to follow this and other similar rules will mean that the whole object will not be exported to the gbXML file - and the simulation will not work. Interstitial areas - such as plenums and foyers, can't be exported as gbXML objects, and must have room objects created within them for the purposes of Ecotect Analysis.

Revit MEP 2010 doesn't concern itself with rooms but with spaces and HVAC zones, which must be similarly identified. Adding and managing space and zone objects are much the same as adding rooms in Revit.

GREEN BUILDING ANALYSIS

If you subscribe to Autodesk Ecotect Analysis, you also get access to Green Building Studio - a web-based service that provides fast and accurate whole building energy, water and carbon emission analysis, helping architects evaluate the carbon footprint of a building. The service can be accessed directly from the Revit Architecture design environment.

Based on the building's size, type, and location (driving electricity and water usage costs) Green Building Studio determines the appropriate material, construction, system and equipment defaults by using regional building standards and codes to make intelligent assumptions. Drop down menus allow architects to change settings and to define aspects of a design, building orientation, u-values for window glazing and HVAC specifications. This is combined with hourly and historic weather data, and emission data from power plants - coming up within minutes with a building's carbon emissions, viewable in the web browser, including energy and cost summaries. The user can then explore design alternatives to improve the efficiency of the design, which is where we came in.www.autodesk.com

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