An integral part of performance based design is energy modeling. Depending on the design stage, the type of energy modeling used depends on the design decisions you are making and the information available to the designer. For instance, at massing stage, you are using energy modeling to evaluate best form and orientation, and at detailed design stage, you are perhaps using energy modeling to do informed value engineering. However, getting started on using energy modeling for performance based design can sometimes seem a bit daunting. Especially given some of the “prevailing wisdom” around risks associated with the use of energy modeling, some design teams avoid performance-based design. Let’s take a closer look at some of the common misunderstandings about using energy modeling for performance based design.
Myth #1: Energy modeling by architects will result in an over-designed envelope
Since architects make decisions related to building form and envelope, at first sight this cautionary statement seems reasonable. The narrative states that if architects analyze the building at early stages, when most decisions are related to the envelope, they will invest heavily in the envelope and therefore ignore other vital decisions — e.g. integrating optimum mechanical systems.
Probing deeper here reveals a completely different reality. Energy modeling presents a complete picture about building performance, and at early stage one can make reasonable (even empirical) assumptions about the efficiency of mechanical systems. By modeling early, architects can learn of diminishing returns of investing in the envelope. On the contrary, the risk of not modeling can be significant. An example here is if the architect assumes that higher insulation is always better, and therefore end up creating an envelope that exacerbates risk of overheating based on this rule of thumb.
Myth #2: Benefits predicted by early stage energy models are within “margin of error”
No statement does more disservice to performance-based design than this one. So it is well worth dissecting.
Let’s first consider margin of error. Margin of error of energy models is defined as the % difference between predicted and actual building performance. This margin of error is indeed very high, and is mainly attributed to differences in nominal and actual operational specifications of the building (schedule, occupancy, controls, etc.), as well as weather differences, and to some extent it is influenced by the construction itself.
Skeptics use this margin of error argument to suggest that the physics based energy analysis is unpredictably different from actual performance when it comes to building performance. The reality is that energy models are numerical solutions for mathematical equations which represent the physics of actual phenomena. This implies that there is a high degree of fidelity between energy models and actual phenomena, especially when the right equations and operational assumptions are chosen. The margin of error creeps in from areas where we don’t yet do a great job of choosing the right assumptions. In fact, the large margin of error is a case for better software and more rather than less modeling — both empirical as well as physics based.
By feeding real life information into the design process, and by using software that allows you to quickly study sensitivity of your design strategies to operational assumptions, you can use performance design to make much better design decisions. For instance, in Sefaira, we allow and encourage the use of diversity factors and schedules to understand the sensitivity of your building design to various operational realities. Further, energy modeling should be continuous and be done at all stages of design – not just at early stages.
Myth #3: Early stage analysis is poor predictor of operational energy use
This is absolutely correct, and early stage modeling shouldn’t be used to predict operational energy use. Fundamentally, there is nothing wrong with this statement. The problem with this statement is what it decides not to say. Early stage analysis is essential to understanding the relative impact of each design decision on the building’s predicted performance, so that you can make the right early stage decisions about forms, façade design and glazing ratios. This is the real benefit of early stage analysis, and indeed a benefit that ultimately leads to better design outcomes.
Myth #4: Architects can harm the design by doing more performance based decision making
Performance based criteria is one of the multiple criteria architects use to make decisions. Architects can only harm the design if performance based information is presented in terms they don’t understand, and leads them down the wrong path. This places the burden on software providers to raise the quality of information presented to make it meaningful for architects, so that users are empowered to make wise decisions. If there is risk to providing the wrong information, the answer obviously isn’t to conceal all information, but to work tirelessly on making the information and the tools better for designer. That is our mission at Sefaira.
Myth #5: Building consultants need to be part of every design decision when doing performance based design
Building consultants are experts in building physics and bring tremendous value to design teams. However, the practicalities of building design make it impossible to rely on building consultants for every design decision. Once again, if software providers improve the quality of their software, it will make performance based design more accessible to design teams, and allow building consultants to provide even greater value to design teams in a collaborative manner.
At Sefaira, we continue to believe that the burden remains on the industry to enable and inform architects about the importance of energy modeling for performance based design, and build software that makes is intuitive for them to integrate sustainability in the design process.