PERFORMANCE BASED DESIGN: MAKING THE MOST OF PRE-DESIGN

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1 PERFORMANCE BASED DESIGN: MAKING THE MOST OF PRE-DESIGN Discover how to leverage performance analysis to drive decisions at each stage of the design process.

2 SUSTAINABLE DESIGN BRIEF Performance Based Design: Making the Most of Pre-Design Proposal Bid Preparation / Pre-Design Concept / Schematic Design Design Development Technical Design Documents This is the first in a three-part series on how to leverage performance analysis to drive decisions at each stage of the design process. Performance Based Design is an approach in which performance analysis is used to inform design, rather than in its traditional role as a validation tool. Appropriate analysis can be used to answer relevant questions at every stage of design providing the design team the information they need to address performance in a creative, flexible way. Because it moves some analysis from later stages into the earlier stages of design, Performance Based Design can require additional investments of time and energy up front. However, this extra effort typically means fewer design changes, less rework, and fewer open questions in later stages, ultimately helping the architect deliver a higher performing building at lower design cost. The best opportunity to inform design is before the architect has put pen to paper in the Pre-Design phase of a project. In this stage, performance analysis can be used (1) to identify the best passive design strategies, based upon the climate, context, and building usage; and (2) to explore the implications of the design brief.

3 3 Identify the Best Passive Strategies Typically the first step for a sustainable project is to assess the local climate, with the aim of understanding what passive design strategies might be applicable. Should the architect design for shading and natural ventilation, insulation and thermal mass, or some other combination of elements? How can she best maintain occupant comfort with a minimum of energy use? Understanding the most effective passive design strategies before design begins in earnest allows the architect to incorporate these strategies as fundamental elements of the design perhaps even inspiring some of the major design moves. Fig. 1. A simple box model can be used to explore the implications of climate, site, and use. Physics-based performace analysis can take climate analysis a step further by looking at the best passive strategies not only for a project s climate, but also for the specific site and building type. Because neighboring structures and building use can have a significant impact on performance, analysis that ignores these factors risks pointing the design team in the wrong direction. The additional detail requires little extra time, but provides much more specific and relevant feedback than climate analysis alone. At this stage, the goal is not to analyze a specific design that will come later but rather to understand what passive strategies we should think about as we begin conceptual design. As an example, we analyzed a multi-family residence in Denver, Colorado. We built a simple rectangular box (not yet designed ) with the appropriate internal area and uses, and located this on our site, complete with surrounding buildings (Fig. 1). We Fig. 2. Parametric analysis can show which building elements have the most impact on energy use and utility cost.

4 4 then used parametric analysis to investigate the range of impacts for a number of passive strategies, to see which ones have an outsized effect on performance. We found that the energy use is very sensitive to glazing ratios, natural ventilation, and insulation levels, while orientation, leakage, and shading had less of an impact (Fig. 2). If we look at the impact on utility cost (rather than energy use), we can see that shading has a much greater impact, and insulation much less. This discrepancy exists because air conditioning is powered by higher-cost electricity. These results suggest that we will want to play close attention to the building s facade design, with the aim of creating a facade that will work well with lower glazing ratios (on the order of 30 to 40%) and some amount of shading. We will also want to consider natural ventilation in our design concepts. This may mean orienting the building toward prevailing winds, and creating a building section or floorplate layout that allows for good stack- or cross-ventilation. Our shoebox analysis was also able to indicate the likely drivers of energy use for our project. Specifically, it revealed the following: The building is cooling-dominated. The sample model is driven by cooling for seven months of the year. However, the heating load is still significant. We will want to focus on reducing the cooling load without adding to the heating requirements. The cooling load is dominated by solar gains through the glazing. This helps to show why glazing ratios and shading devices are important. We might also be able to mitigate these loads by specifying better glazing. (Fig. 3) The heating load is dominated by conduction losses through the envelope. We will want to make sure that we have a well-insulated building, and may want to consider a massing with a low surface-area-to-volume ratio (SA:V) in order to minimize the area exposed to the outside. (Fig. 3) These insights allow us to begin the design with the most effective sustainable strategies clearly in mind. Monthly Heat Gains Monthly Heat Losses Fig. 3. Early analysis shows that cooling loads are dominated by solar gain; heating loads by conduction through the envelope.

5 5 Explore Adjusting the Design Brief The design brief and building program define the requirements for a design. Pre-design is the right time to look closely at these requirements to make sure they are correct, and to explore whether they are fixed or flexible. Assumptions about mechanical systems and thermal comfort requirements are particularly important. Do all the spaces need to be heated and cooled? Can the comfort zone be extended in some spaces? Is it possible to eliminate one or more mechanical systems? a move that could save capital cost as well as operational costs. Other relevant investigations at this stage can include: reducing area requirements, adjusting heating and cooling setpoints, and changing the amount of conditioned area. Performance analysis can show which adjustments could have the largest impact, and enables the design team to have an informed conversation with the client about the requirements and potential trade-offs. We used our simple box model from the previous step to investigate the potential for eliminating mechanical cooling systems entirely. Our initial results showed that a combination of shading, natural ventilation, thermal mass, and insulation could keep air temperatures within a comfortable range for the large majority of the year, and could keep temperatures below 28 C (82 F) for all occupied hours (Fig. 4). We can use this information to discuss the possibility of an expanded comfort zone with our client. It also reinforces the passive analysis from the previous step, highlighting the importance of key design strategies such as natural ventilation and shading Occupied Hours < >28 ( C) < >82 ( F) Temperature Fig. 4. Projected air temperatures over the course of a year with passive strategies implemented. Passive design alone can maintain comfortable conditions for the majority of occupied hours.

6 6 How Sefaira Can Help Sefaira makes sustainability analysis a seamless, integral part of the design process. It is specifically tailored to help architects investigate the factors at play in the early stages of design, including the passive design strategies explored above. This type of analysis enables architects to discover the most important sustainable strategies early in design, and evaluate design options before the design is locked down. About Sefaira Sefaira was founded in 2009 with a mission to promote more sustainable buildings by helping the building industry design, build, operate, maintain and transform all facets of the built environment. Sefaira s proprietary cloud-based technology, built upon deep building physics expertise, offers an integrated approach to sustainable design analysis, knowledge management, and decision support. Sefaira helps designers analyze and compare sustainable building strategies for new build or retrofit projects in a fraction of the time and cost previously required. Visit us online at linkedin.com/company/sefaira twitter.com/sefaira Sefaira allows architects to perform more analysis, more frequently, and at lower cost, helping to set projects on the right trajectory and ultimately delivering better-performing, more sustainable buildings.