LEED Energy Model & Design: Part One, The Freeform Method

With the April launch of LEED v 3.0 the US Green Building Council has made a huge shift in their priorities concerning energy consumption. EA Credit 1, Optimized Energy Performance has always been the biggest potential point getter with 10 available, yet it is often underutilized.
Recognizing the neglect of energy credits for other low-hanging-fruit, the USGBC has raised the stakes in version 3.0 so that EA credit 1 will now allow 19 possible points for NC and Schools, and up to 21 points for Core and Shell. In a similar move the second largest point getter is now EA credit 2, Onsite Renewables with up to 7 points available. This priority shift towards Energy is in line with many other countries, including the EU, who almost solely focus on energy issues as many other areas of focus in LEED are better accounted for already in their local building codes (daylighting, site selection, public transportation, and many more).

The purpose of increasing the importance on energy is to ensure that energy issues becomes design issue. The current mainstream approach is to hold off on a LEED energy analysis until the beginning of Design Development, which keeps the energy analysis budget down. At this stage if a scheme doesn't meet the performance prerequisites, the client and the mechanical engineer/energy modeler began a process small tweaks with glass types, lighting and HVAC systems etc, to try to achieve the needed improvements. When you wait until this stage to evaluate options you're limited in the ability to make improvements, and you are really just buying a few extra percentage points through better materials or more efficient mechanical systems. So where is the architect in this process? Because of the blatant ineffectiveness of this approach everyone knew that something would have to change, and thankfully it will with LEED v 3.0.

Finally we have incentive to use energy analysis to shape our designs and influence our strategies, but how exactly is this done? How can we evaluate very simple schemes and extract information that shapes the development of our design? A current approach used in decision-making (rather than validation) is to run a simulation of a current scheme and then modify specific properties, rerun the analysis and see if the overall energy decreases and by how much? This is somewhat affective but unecesarry as it can be done for the most part without modeling, and isn't really used to inform the big moves at the begining. If we set ambitious goals such as zero energy usage or carbon emissions in line with the 2030 challenge, we then have to rely a lot more on modeling, however both of these are typically very difficult to achieve with in mainstream construction and so they're rarely used as goals. The LEED targets are much more commercially attainable.

The ASHRAE approach used by LEED is fairly good ranking method that sets a base value from which we can compare and evaluate our proposed design. The baseline is established by taking our scheme and simplifying it to a base building with strip windows(usually), ASHRAE specified systems, space types, construction types, then simulating energy use without shading, rotating the building every 90 degrees and taking an average of 4 simulations. After a baseline is establish you will model the building as it is designed and compare the % improvement over the baseline. A 10% improvement is the LEED prerequisite, and the points increase from there up to 19 points for a 48% improvement. This method is successful in certain climates, but let's say you have an office tower in a dessert - using using a baseline value of 40% exposed glazing is simply a bad design to begin with. In temperate regions, though, it is a decent method of evaluation that should be exploited for easy LEED points through informed early design decision. In LEED 3.0 it's not only easier to meet the prerequisite, but once you go above a 14% improvement you can rack up points much faster - which should be an incentive for those developers who typically buy points to start buying better designs.

But again, how can we use this process to shape better buildings? This is where I'd like to introduce the Freeform Method, developed to reveal the current gaps in our software capabilities.

Working in a process where clients need to know how many points they can achieve with a given scheme, I've taken the analysis back one step to evaluate how many points are possible given their site, their program requirements, and a conceptual building form. The building form, or massing, is always the first design decision made and the last decision that the architect is willing to change. In masterplanning the building footprints and heights are often set by planners before an architect even has a chance at the design, and after a client has approves a scheme, or even an image of a scheme, it's hard to go back and change the building form that was agreed upon.

By focusing on the form we can quickly evaluate the potential of a scheme by developing an ASHRAE baseline, simulating energy performance and comparing a number of energy conservation methods. This provides the design team with the knowledge that, given their building form, the greatest potential for energy savings can be achieved by optimizing one or more strategies such as daylighting, solar performance, thermal envelope, ventilation, etc... The rules are then set and the architect can design the building with a clear set of priorities and guidelines for energy performance. Other tools are then used to optimize specific design strategies (see earlier post). Not shown in the process map are the loops for alternate building forms, but you can imagine that coming from the same program requirements multiple forms can be compared equally. You could also include varying levels of each strategy, for example basic passive solar strategies are free but less effective than active strategies such as sun-tracking shades, electrochromic glazing, etc, where the solar performance is truly optimized but at an additional cost.

For this analysis process to be successful the simulation criteria all needs to be automated, the results must be trusted by engineers, and it must be done using simple forms generated or imported through a BIM exchange via .IFC or .XML. If any time is spent on remodeling, reassigning data, or reconfiguring the analysis models, the whole process is liable to fail due to resourcing and time constraints. Efforts in software development are crucial for the mainstream adoption of any improved design methods; when architects encounter information and responsibilities that are new that they don't fully understand, they often divert the responsibility elsewhere and continue their traditional method of working. But if the assessment of LEED energy points and potential was easily understandable at the beginning of design, better decisions could be made with confidence.

Currently there are no tools where such a method is automated, or even where BIM data can easily be reused for LEED energy analysis. However there are many new developments in the works and by the end of 2009 we should have at least three tools capable of BIM to LEED energy analysis. My next post on this topic will be an overview of the different tools and a timeline of when you can expect them to easily handle LEED energy modeling requirements. I'll also talk about which optimization features each program has to aid in the Freeform Method. Any comments on this method are appreciated, and don't just tell me, tell software developers what we need from their tools.