CFD Q&A with IES

Computational Fluid Dynamics is a complex area of analysis seeing increased use on innovative projects, as recognized in a recent edition of Architectural Record. I've done my own studies in the past but have had some lingering questions which Dr. Liam Harrison from IES has been kind enough to answer.

Q> I have some questions about the CFD analysis process and wonder if there is reference material anywhere.

At the moment there is only the Microflo manual which can be found in the Help menu of the VE. We are currently putting together some tutorials but they have to wait for some slack periods in our project work to be completed.

Q> I can find wind data from the energy plus web page (tmy2, tmy3), are there better sources that you use?

We tend to use the energy plus data ourselves. Sometimes we use data taken on the site of a proposed development but this is rare as they tend to put the anemometers on top of a building so it is difficult to back out the localized wind effects caused by the buildings and they rarely have a whole years worth of data.

Q> From this wind data I can find the prevailing wind speed and direction which would be measured generally from 10 meters off of the ground. Is this right, 10 meters?

Yes, the standard height to measure wind speed and direction at a weather station is 10m above ground level. At this height the effects of vegetation, buildings and other obstructions on the wind speed and direction is limited. Also the data is usually taken in open areas such as airports to further limit the effect of obstructions.

I have tried to find a statement on the energy plus web page that all the data is taken at 10m height but can't find one so perhaps you will want to check for yourself to make sure.

Q> If my analysis grids extends 10 M then this weather station reading should indicate appropriate values to use in my study?

Microflo asks for the wind speed at 10M height and the terrain type and then produces a wind boundary profile on the inflow boundary of the CFD model equal to the equation from the ASHRAE Handbook - Fundamentals [2005] (section 16.3 “Airflow around Buildings”) - see Appendix D in the Microflo manual.

Q> If my grid extends 100 M for a tall building then I should use the wind profile power law (http://en.wikipedia.org/wiki/Wind_profile_power_law) to adjust for the height?

No, give Microflo the wind speed at 10M and the terrain type. Microflo will then automatically vary the wind speed over the inflow boundary using the ASHRAE handbook equation.

Q> Using the wind profile power law I’ll assume a neutral stability condition and use: “α is approximately 1/7, or 0.143.” Right?

Microflo will use a different value depending on the terrain type. See Appendix D in the Microflo manual.

Q> For an urban site the value of α might not be 1/7, but I don’t want to try to figure out the log wind profile (http://en.wikipedia.org/wiki/Log_wind_profile) unless I have to. Do the IES analysis settings take into account if the site is rural or urban?

Yes Microflo can take terrain type into account - the user can specify "Country," "Suburban," and "City" in Settings>>CFD_Settings.

Q> Finally, I’ve reduced the full analysis grid size to keep the number of cells under 500,000. Are there rules of thumb you use for spacing above or around a site?

The academic studies on CFD for the built environment gives the following recommendations:
The inlet, the lateral and the top boundary should be 5H away from the building, where H is the building height. For buildings with an extension in lateral direction much larger than the height, the blockage ratio should be below 3%. The outflow boundary should be positioned at least 15H behind the building to allow for flow development. For the same reason this outflow length should also be applied for an urban area with many buildings, where H is to be replaced by Hmax, the height of the tallest building. To prevent an artificial acceleration of the flow over the tallest building, the top of the computational domain should be also at least 5Hmax away from this building. For the blockage ratio the limit of 3% is recommended, although there are no results on whether it is better to include more of the surrounding buildings in the model and reduce the distance of the lateral boundaries from the built area.

In a Microflo model the recommendation above will be difficult to follow as it will tend to produce very large mesh sizes if you resolve the flow around the buildings. You need to have a fine mesh in areas where the air velocity gradient is greatest, i.e. around the buildings. In area where the velocity gradient is small you can have larger cells, i.e. near the boundaries of the computational domain. E.g. this can be achieved by:

1. going into "Grid" mode at (1) in image below
2. click into a region in the mesh, at (3) in image
3. click "Edit mesh region" at (2)
4. select a power law to vary the mesh and make it coarser at the boundaries and finer at the building

Even using this technique it will be difficult to resolve the flow near the buildings and have a domain as large as the recommendations so you may have to be pragmatic and forgo some of the computational domain in order to have enough cells near to the buildings. The only way to prove if having a smaller domain and more resolution near the building is better than the reverse situation is to do grid dependence studies where you change the grid to find the point where the solution changes insignificantly between meshes. In general though it is more important to resolve the flow near to the buildings, although this can make to solution less stable and harder to obtain a converged solution (nobody said CFD was easy).

No it's not easy but it doable, even for architects. Just be sure if you are working in a program other than IES that you know how to adjust the wind speed based on terrain type and the height of your grid.

Design Analysis Workflow

The most appropriate workflow for early analysis is to began designing within the BIM application. At this stage you can utilize the geometry for massing and orientation analysis, while also setting up thermal zones to began the process of energy modeling. But perhaps most crucial to this process is the guarantee that your model always contains the latest information, so that any change to the design can instantly be evaluated.
Our first example (above) shows how a mass in Revit can be used to define the building elements. After manipulating the mass you hit "remake" and all of the building elements will adjust to define the new shape. This process optimizes every benefit of Building Information Modeling while enabling us to reduce our building geometry to a basic form with which we can conduct multiple types of environmental analysis.

Incident solar radiation studies allow us to optimize our massing and orientation, and to prioritize which surfaces will need treatment as a project moves forward. Radiation levels are shown on the north facing surfaces (top) and on the southwest surfaces displayed with vector spikes (above).

If it is the case that 3D design information is consistently generated in non-BIM modeling platforms, we can still utilize this data so long as certain modeling standards are employed. In almost every 3D platform there is an opportunity to model with solids rather than surface geometry. When creating solids, or masses which can behave as solids, you set yourself up for four opportunities:

1. Orientation and facades studies. Subdivide your model into surfaces, thoughtfully, then import it into Ecotect.
2. Coordination. After linking the data into a BIM platform the solids can be sectioned and measured to produce your document set.
3. Area schedules. Instantly.
4. Energy modeling. Rooms/spaces/zones are used within the BIM platform to set up in-depth energy modeling. This can be conducted by the architect but preferably it is done by an experienced engineer.

The simple model shown above was used for facade analysis, plan and section views, area schedules, and an iterative energy model.

In our second example we took a simple tower shape and modified things (twisted it). For a full update after this modification there will be a few more steps than just hitting "remake," but within this process rests infinitely more potential than that where the model is only used to judge aesthetics. I must note here that all of these opportunities were available in the first example but with an improved workflow.

Twisted shape in plan, section, elevation and axonometric.

Modeling solids, analyzing surfaces

The processes described above are those which I have had the most success with, but I am always happy to hear of other experiences.

Understanding Virtual Enviornment

IES Virtual Environment is a comprehensive energy modeling and environmental analysis tool which can simulate just about everything happening to your building. Past use of Virtual Environment existed mostly outside of the architects' realm, however IES has done much recently to integrate their tools into the architectural process with push-button toolkits.

The strength of the toolkit is that it can be embedded into architectural design programs (Revit & Sketchup so far) and with a modified workflow one is capable of achieving truly integrated and iterative analysis.

The toolkit performs a series of independent analysis which makes it less comprehensive than the full Virtual Environment. The full suite contains an array of modules, each performing different tasks that are capable of feeding back into the main energy model. For example, if your project will utilize daylight harvesting you would first run daylight simulations and then link these results back into the thermal simulation module where you can see the energy impact from reduced cooling loads and electricity use. The process is similar for natural ventilation and solar shading analysis where separate modules link their results to the main thermal simulation engine. Even HVAC systems design can feed into the central energy model for collaborative A/E BIM analysis in a central model.

It is not immediately apparent where Virtual Environment falls in the traditional A/E firm structure and project workflow. What is apparent is that the ultimate success of its use requires a process shift in either the way the architect designs and delivers, or in the roles assigned to the mechanical and energy engineers (US in particular). Either way there must be time, budget, and client expectations to ensure that this level of collaboration succeeds.

Understanding Ecotect

Ecotect is a studio companion that enables designers to better understand the relationship between buildings and their environment. As a visualization tool Ecotect interactively displays sun and shadows, solar rays, sun path diagrams and much more.






As an analysis program there are 3 common methods for calculating and visualizing data:

• Analysis Grid (of points)


• Analysis Surfaces


• Thermal Analysis of Zones

Analysis Grid

The Analysis Grid is a single 3-Dimensional grid able to collect data over points in space. The analysis grid is used for analysis where the collected values are not interested in surface area or the sun angle. Common analysis here includes internal daylight levels, external sunlight hours, airflow and others. All of the solar related functions can be done within the program itself but for advanced daylighting and CFD airflow Ecotect links up to other programs, many of which are free to use.

Analysis Surfaces

Analysis surfaces are used to calculate and visualize solar issues that are relative to the sun angle. To understand the difference between this and the analysis grid just think that when a surface closer to being perpendicular to the sun it will read higher solar gain values, by contrast points have no area and will all show the same readings for any period of time exposed. Surface solar analysis is very helpful for early massing and orientation studies, as well as facade design.

Thermal Analysis

Ecotect is one of many energy modeling programs, most of which have different calculation methods and intended uses. The strength of Ecotect is with comparative design analysis where you can modify building geometry or attributes and see the relative impact on performance. For more advanced simulations Ecotect can export to other energy modeling programs with varying degrees of successful interoperability.

There are of course more analysis options in Ecotect than those briefly mentioned here, and if you wish to learn more head over to the Ecotect wiki: http://www.squ1.org/

BIM Use:

Ecotect very easily re-uses data from other programs as long as the models are either very simple or easily able to be reduced to the basic elements needed for analysis (see previous blog on this subject). Ecotect is able to import BIM room objects which are converted into zones for thermal and daylighting analysis. A small to moderate amount of manual cleanup is needed at this point in time depending on the BIM authoring tool used to produce the model (Revit, Archicad, etc).

Daylighting Beyond LEED Part 2

Part 2 is the response to the LEED CIR posted in Part 1

First let me explain the title. The words "Beyond LEED" are not meant to criticize the LEED rating system but only to critically evaluate the LEED analysis requirements against more advanced analysis capabilities available. Specifically, the use of dynamic simulations which takes annual weather data into account may eventually replace static simulations. However, since the majority of this post is about achieving LEED, maybe we should first focus on getting that right. For those going through the process for the first time, the following USGBC clarification points from their CIR ruling may be helpful.

Ruling
The applicant has submitted a multi-point question regarding guidance related to the use of analysis software for the documentation of the daylight distribution. The ruling is provided in order of the questions asked.

1. While there are no specific defaults that have been established by any modeling protocols for daylight simulation, it is reasonable to assume reflectance values similar to those used for calculating lighting fixture coefficients. For example, typical reflectance values could be 50% for walls, 20% for the floor and 80% for the ceiling. If known, actual values must be used.

2. Only the analysis grid is required. There is no need to model the actual work plane.

3. While this CIR cannot provide any specific rules for selection of the sky model to be used, both methodologies are acceptable as long as the applicant submits a narrative explaining the methodology in the submittal.

4. See item 5 below

5.
a. The assumption made is correct. All area above the threshold can be counted, as long as these areas separately defined.
b. Software analysis from grid points is acceptable, as long as the grid points do not fall in walls, columns and other elements that may return a null value and skew results. Adjustments and additional post processing calculations may be necessary to exclude these instances. Secondly, various simulation programs draw foot-candle or daylight factor iso-contours. This is the best way to understand which areas of a space meet or exceed the threshold. Again, adjustments may be necessary.

While this ruling provides guidance to the applicant, it should be noted that there are no set modeling guidelines available for daylight analysis. For the purposes of this credit, it is expected that the person(s) responsible for the analysis have enough experience to make the most appropriate determination of the daylight analysis methodology.

SketchUp Virtual Environment

The green software industry moves forward yet again with the recent announcement of an IES plug-in for Google SketchUp. Similar to the Revit Architecture plug-in IES now offers their VE-Ware, their sustainability toolkit and a direct link into Virtual Environment, one of the most robust, engineering grade analysis programs in the industry.

At the basic level this means that with a free version of SketchUp and a free VE-Ware plug-in, anyone across the globe can design a building or a home and evaluate the energy performance while tracking carbon emissions against the 2030 challenge. For those like myself who are passionate about change, we warmly welcome the opening up of the competition to any clever person owning a computer.

At the professional level this opens up these free tools to those modeling accurately in any non-BIM tools which can be exported into SketchUp (Rhino, 3DS Max, etc.). In essence, any firm using Revit in conjunction with other design tools now has the ability to track carbon at every stage of every project…with a free plug-in.

Sketchup Model...

IES import

As a personal opinion, for those who have been following earlier blogs I can say that IES has taken the lead among energy modeling tools. http://greenbimnetwork.blogspot.com/2008/06/engineer-takes-lead.html “But perhaps more importantly this software will be able to reuse architectural design models, architectural construction models, and will promote interoperability by cleanly exchanging data between all design and analysis platforms.” While IES is not yet fully interoperable with all platforms, they have swung the door wide open.

Daylighting Beyond LEED Part 1

I've recently submitted a Credit Interpretation Request to the USGBC from which I hope they will clear up some ambiguous requirements with credit EQ 8.1 - Daylight & Views - Option 2. To assist I've attached some images that help visualize the different sky conditions primarily used by daylight simulation tools. It will also help to have your LEED NC 2.2 reference manual with you as you read through the CIR.


"LEED reference material does not give clear guidance on how to use analysis software for documentation, and we are simply asking for general clarification regarding technical requirements. The numbers below correspond to the analysis steps in the reference manual.
From EQ 8.1 Option 2—Daylight Simulation Model:

1. Regarding materials, a problem comes up when we have a core and shell project where the reflectance values of internal materials are unknown. Could there be suggested default values to use in this instance?

2. The analysis grid 30” off of the ground is reasonable but the reference manual does not describe placing an actual work plane in the analysis model. Without an actual work plane there can be instances where a floor-to-ceiling glazing allows light to bounce further into back than if the spaces were filled with furniture or desks. A recently published book on the subject states “Since Option 2 LEED-NC Version 2.2 requires 25 foot-candles of daylight in 75% of regularly occupied areas at the workplane level…the simulation models should have the workplanes incorporated…” The image in this book shows a modeled workplane in the middle of the space with the caption “A model used for qualifying for the LEED daylighting credit.” Nowhere in LEED literature have I found an indication that we should model the plane, though doing so will affect the results.

3. “Clear sky conditions at 12:00 noon on the equinox (March 21/September 21)” is thought not to be technical enough by many experts. Perhaps LEED should cite using CIE Clear Sky as one option, or the Perez All-Weather Sky Model as another option, but with either it needs to specify how the location is defined:

• If we use a CIE Clear Sky (static simulation) option we must find “design sky illuminance” values. There are many ways to find this value but we should have a clear indication of an accepted source(s).


• If we use the Perez Model (static simulation) we incorporate actual weather data and our calculations are potentially more accurate. But with a static simulation we only calculate for 1 specific day and that day could be cloudy, so how could we approach this credit if we want our results based on weather data? Do we want our results based on weather data?
  It’s our opinion that analysis tools are sophisticated enough that LEED should require dynamic simulations which calculate annual daylight autonomy values from weather data.

4. Item 4 proves misleading when you get to 5.

5. This allows us to include the percentage of the floor area above the threshold even if the entire room is not above, contrary to item 4. This misunderstanding has generated multiple CIRs already, none of which explain it clearly. Am I right to assume that all area above the threshold can be counted, as long as we define these areas separately? Option 3 is more clear about this issue.

Item 5 also brings up a question of how to calculate the floor area from a grid of points. Some software programs do this for you but only after interpolating the values between points using contour lines. It should be explained how to derive compliant area based on point readings, and perhaps we should be warned that points falling within walls or columns will read “0” which throws off the data (your example image, Figure 2 on page 384 of LEED-NC 2.2 shows a reading of “0” for a point falls inside a column). Option 3—Daylight Measurement is also unclear about how to translate points into area, could you please be more specific?"

MEP to Set Modeling Standards

• If you say that you are using BIM because you care about sustainability, you could end up misleading people, including yourself.
• If you say that you are using BIM so you can conduct Building Performance Analysis, this could be an accurate statement but only if you know exactly where you are going with it.
• Do you know exactly where you are going with it?

Architects are mostly lost when it comes to understanding an energy model, while MEP engineers get lost trying to wrap their head around BIM. The use of the MEP or any consultant's model for 3D design coordination has only seceded (in my experience) when the model is used to generate drawings and therefore remains up-to-date. An up-to date model is a rare occurrences with today's MEP engineers, where they may produce design coordination models but these are one-offs that don't really assist in the coordination. The fabrication models which comes along later follow much clearer standards, which is what you would expect for information that is used to directly build off of.

Until the MEP engineers can become disciplined in their modeling habits and finally shed the tradition of drafting their deliverables, they risk loosing their design coordination responsibilities and fees to fabricators who are becoming more sophisticated about spatial design. This might not be so bad when you think about it. If the MEP engineer lightens it's design coordination load they can then invest more efforts into energy and environmental expertise, where the industry needs them to lead anyway. So how can they start to position themselves as BIM energy leaders?

One way is by teaching themselves how to use Revit for energy calculations.

Earth Rangers Centre, MCW Consultants

In the example shown here MCW Consultants chose to build their energy model first in Revit to then export into IES. At a time when other engineering firms are gaining experience by simply modelling within IES, MCW has gone a step further to understand just how a revit model needs to be built in order for a successful gbxml export...knowledge that can also be applied to Ecotect, Green Building Studio, Loadsoft or any software able to import a gbxml file format.

This level of experience should not merely be shared with the architect, but the combined Architect/MEP team should go so far as to agree upon modelling protocol before any modelling commences (day one is often the point of no return to change modelling habits).

If you find yourself saying that you are using Revit to create high performance buildings, first you must make sure that your MEP engineers are using your model, but in addition they must tell you ahead of time how you need to give it to them.

Next the contractor will shake everything up with modelling standards focused on scheduling, phasing, and clash detection. For now let's get this one worked out.

Autodesk Ecotect

Autodesk takes a giant leap forward in the green software industry with the aquisition of Square One Research LTD including substantially all of the assets related to of the Ecotect software tools for conceptual building performance analysis.

Available for Free Now!

"Square One Research and Autodesk share a commitment to using technology to make the design and construction of sustainable, high-performance buildings easier and more efficient," said Dr. Andrew J. Marsh, Co-Founder and Head of Research & Development, Square One Research. "We are pleased to join Autodesk and look forward to helping develop and deliver simple and effective building performance analysis to architects and engineers around the world."

Autodesk announced simultaneously that it had acquired substantially all assets related to Green Building Studio, Inc., the intent of which they had announced in February of this year.

What the Square One acquisition should mean:

• Improved gbxml workflow
• Improved IFC workflow
• Improved geometry workflow from Revit and other Autodesk applications
• Development of LEED toolkit within Ecotect
• Supported use of Ecotect in conjunction with other energy modelling software
• Improved transfer of metadata for more iterative analysis opportunities
• The View Cube and Steering Wheel now found in all other Autodesk products will be replaced by the Ecotect right mouse orbit and the F5-F8 standard views (please not the other way around)

See related story...

The Engineer Takes the Lead

In this follow up to the "Chicken or Egg" blog I'm attempting to clarify the process, still misunderstood by many.

First it needs to be recognized when designing high performance buildings that we are too limited if we rely on a single energy model which simply calculates overall loads. The concept of multiple models appears inefficient and a departure from what we want out of BIM, but is a reality that can be efficient with a clear stream of data with a clean file exchange.

If we look at the current process we see that engineers are building multiple energy models to fulfill two requirements:

1. Peak loads to size equipment


2. Overall energy consumption for compliance with local code

   

Diagram representing Zone calculations for energy modeling.

What hasn't yet worked well are the efforts made to integrate energy models into the design process. Most efforts in the US to improve this process focus on reassigning the task of energy modeling to the architects who are more able to do it early while (whilst) the results can influence the design. Later in the process the engineer will take charge of the energy model, in theory. Engineers are very excited about the potential to spend less time modeling geometry, but still argue that they need to be brought into the process earlier as they don't particularly trust the architect to do this alone, and will often remodel everything again the traditional way just to validate their results.

The US approach has greatest potential for small offices where the architect often performs tasks without the help of consultants and can now achieve more information than they could previously. Medium and large design firms prefer to rely on consultants for most everything which requires advanced knowledge and skills. To build and understanding an energy model requires advanced abilities--to convey the results effectively, but also to trust them in the first place.

Diagram representing Geometry calculations for environmental analysis

Due to tougher energy regulations Europe and the UK have had more experience and have seen a slightly different process evolve. UK engineers have a greater involvement earlier in the project where they actually use their knowledge and experiences to bully architects into making better design decisions. Architecture firms often bring trusted engineers into sustainability charrettes, or "surgeries," where they will critically evaluate designs for multiple projects that they are not working on. When their involvement begins on a project there is immediately a back and forth between their energy model and architectural analysis models that are focused on specific tasks.

By assigning tasks to the architect the engineer can set the parameters for high performance design that allow the architect to creatively explore and evaluate multiple options. These tasks could be minimizing solar radiation during peak hours, redesigning inefficient shading devices, redesigning the forms or the facade to allow more daylight into spaces, and other ways to reduce loads that the architect can measure without a full energy model. To visual this more clearly I've created a project timeline.

This timeline is front loaded in that Pre-Design makes up about one third of the analysis effort, Concept and Schematic phases combined are the next third, and there is even an analysis phase during Due Diligence. The first two project phases belong to what some buildingSMART experts describe as the Building Investigation Modeling phase, while the Due Diligence here is a new concept for most that will prove to be invaluable to the process. We are all familiar with architectural due diligence relating to local codes and site history and the term "environmental due diligence" referring to site investigation for pollution hazards. But to commit to high performance design we need a broader background check and an understanding that sunlight, wind, water, and daylight are not just opportunities but are also hazards if not fully understood. Before a single line is drawn, collaborative due diligence should help us understand when we will have heating loads, cooling loads, peak values, daylight opportunities/constraints, wind opportunities/constraints, on-site renewable opportunities and more. This information can be gathered from many different sources, but when related to energy performance the MEP engineers should be utilized to set design guidelines from their knowledge of building type and location, or from a basic energy model. Before the designer draws a single line they should have a clear direction of what not to do and where their opportunities lie.

There are many reputable software packages that are able to calculate total energy loads, fewer that are trusted or able to design equipment around peak loads. The software that ultimately will excel in energy modeling will be one that is accepted by local building codes across the globe. But perhaps more importantly this software will be able to reuse architectural design models, architectural construction models, and will promote interoperability by cleanly exchanging data between all design and analysis platforms.

When it comes to environmental analysis for evaluating specific issues early in design there is currently no software comparable to Ecotect in either function or interoperability. But Ecotect is particularly easy to support philosophically because of its commitment to interoperability, which is imperative for our industry to move forward.

First Pass - Chicken or Egg?

It is well known in the industry that energy analysis used to improve design has the greatest impact at the very earliest stages of a project.
One must add to this that the costs associated with making changes is least also at the earliest stages of the project. *

But the effort to push energy analysis to the front of the project has run into a couple of hurdles:

1) The analysis software in use may not be fully integrated with the design tools, which are often still a pencil and paper. The good news here is that the software industry is working very hard to improve interoperability all of the time.

2) The other hurdle is the amount of assumptions needed to begin an energy model. The accuracy of the simulation is improved by reducing assumptions, by designing the building in detail much earlier. By the time your details are defined your project is usually far enough along that the scheme can't change and the analysis can only have a minimal impact on the design process. **

Another Approach:
We try to avoid these problems associated with assumptions by focusing on the variables we have the greatest control over that enter into the building energy equation.

Thermal balance occurs when the sum of all the different types of heat flow into and out of a building is zero. That is, the building is losing as much heat as it gains so it can be said to be in equilibrium.
Thus:

Qc - Conduction Gains
Qv - Ventilation Gains
Qs - Solar Gains
Qi - Internal Gains
Qe - Evaporative Loss

To remain in thermal equilibrium our HVAC system kicks in gear and is inversely equal to the sum of the gains.

For our projects in hot climates we only have two gains which significantly impact design that we are able to modify during an investigation modelling period. Qs which includes solar heat gain through windows is often our greatest load. The other big one is the heat from lights (Qi) for spaces not utilizing daylighting. ***

Its very easy for us to take a project in a hot climate, forget about all of these other building assumptions and just start working to minimize solar heat gain through windows while maintaining adequate daylight. Later, when we have enough building assumptions to produce an accurate energy model, our design will be in much better shape than if we had held off on the analysis.

But in a hot climate it can become more complicated when taking into account peak loads. The largest cooling loads generally occur late in summer in the afternoon, and the strategy to minimize peak loads sometime works against the strategy to minimize total gains. Knowing closely when the peak occurs can influence wall orientation, shading strategies and daylighting strategies on the west facade. One should rely on a full thermal model to get as close as you can to the time of the peak load to effectively work to reduce it. ***

Even more complicated than this are buildings with both heating and cooling loads for which we will try to minimize solar gains in one season while maximizing them in another (while ensuring that our solar design decisions work with our daylighting strategy). ****

If the designer can utilize solar analysis during the concept stage the building will be much improved by the time accurate energy modeling can enter the process. But to accurately design for solar optimization in moderate and cold climates they must make assumptions about the hours of the day and the months of the year for which there will be heating and cooling loads.

To find the heating and cooling range we probably need one of three things:
1) Expert guidance from a local engineer.
2)"Target Finder" type information that includes monthly loads for heating and cooling.
3) Perhaps a first pass at an energy model before there even is a design. The Egg before the Chicken. A first pass can be done with any reliable analysis software, verified by an engineer familiar with both the software and the building type and location. This analysis could be done using simple boxes, but it would be great to see the architect and engineer jointly develop generic building "type" models, easily dropped into any climate for the first pass at understanding basic loads associated with type and location.


There is a quote about knowing your enemy, but I'd rather focus on enlightened designing, utilizing both technology and one's conscience to design and produce buildings that really work well. To this effect how can we improve upon our process?

Image Reference:
* ASHRAEs 2003 Green Guide with vertical axis notes added for clarity by Alex Hirsig**

**Hirsig, Alex. "Design by Simulation: Building Performance Modeling by Architects in the Conceptual Design Process." Masters Thesis, Design Studies: Design and Technology Concentration, Harvard Universtiy Graduate School of Design, 2008

***The ASHRAE Guide for Buildings in Hot and Humid Climates, 2008

**** Bedington Zero by Bill Dunster Architects

Change The World 2008

Change the World 2008:
Harnessing BIM Technology and Integrated Project Delivery for Sustainable Design

Change The World 2008

A pre-convention to the AIA National Convention next week in Boston will be taking place on the 13th and 14th. I'll be blogging LIVE about the sessions I attend, so stop by and throw in your 2 cents if you have a chance.

Glass Boxes in Hot Climates

"Don't expect comfort inside glass boxes in hot climates" are words from The ASHRAE Guide for Buildings in Hot and Humid Climates. Shading the roof and other badly oriented surfaces is imperative, but you have to address the fact that heat is rapidly entering the space due to the high thermal conductance of glass. The obvious recommendation is to increase the percentage of solid to glass surfaces.

But once you've blocked the direct solar, how much glass is still too much for conduction gains...

Background: Introduction

Green BIM Network is a collaborative movement in the building industry which started as a simple workshop in Washington DC where Architects and Engineers can pool their expertise and ingenuity to pioneer environmental and performance analysis integrated with Building Information Modelling. This blog page will be a recorded document of all efforts either locally or across the web. Postings will be divided into one of five categories:

• Background Information / Editorials
• Forums / Open Ended Problems
• Case Studies /Solution
• Controversies / Challenging Debates
• News / Current Events

Welcome to our forum, please contribute where you are able.

Lighting vs Energy Model

I'm just going to throw this out there; someone needs to own every analysis model and develop a method for keeping it current.
Working with Revit, my belief is that the Architect should own the daylighting model which can be exported either through room objects or BIM geometry. Room objects are the best candidate in that they often describe only those areas that need to be analyzed.
IES daylighting Image courtesy of RTKL











The energy model intended for thermal analysis is best created in Revit MEP using space objects. Space object can be placed into a linked Revit file in Revit MEP, but the must follow the room bounding rules set by the Revit architecture model. To get around this, spaces can be grouped together into zones for analysis, and a sliver tolerance can be adjusted so that leftover gaps don't require space definitions. We now just need to test how effective zones are and if there is an additional performance drain by having many small spaces which the energy modeller would not normally define (this will come in a separate post).

Added Later:

After some discussions I'm rethinking the concept that the Architect always owns the daylighting model. The architect needs to start a daylighting model to reveal problems while they can still be solved schematically. The big danger in Daylighting analysis, as described to me by Chris Chatto of ZGF Architects, is that the end result needs to be a value, either a 2% daylight factor or the 25 footcandle (269 lux) requirement for LEED EQ 8.1. In this case the analysis iterations are not intended to improve a design but to achieve levels above a defined value.



Without carefully defining all of the input parameters such as glass transparency, reflectance of materials, sky condition and others, one could seemingly prove that a design is adequate when in reality it is not.




This level of daylight understanding is not always present in every architecture office and so a level of collaboration becomes necessary. Who actually "owns" this model may end up an irrelevant question, but before deciding a model exchange strategy you have to know exact procedures and what to expect.




Ecotect to IES Exchange

I've mostly been using Ecotect as a design analysis tool, and since the engineers I work with are mostly using IES for lighting calculations I've had to find a clean way to exchange information between the BIM model, the design analysis and the engineering analysis tools (this process will come in a later post).