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Performance Modeling in Building Design and Its Importance

April 20th, 2023 | 10 min. read

Performance Modeling in Building Design and Its Importance

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Over 30 years, construction and design costs only make up 2% of the total cost of building ownership. The other 98% includes the cost of utilities, maintenance, and personnel. 

Throughout the design process, your architect should find ways to improve performance and reduce these long-term expenses. One of the most effective tools at an architect’s disposal is performance modeling—the process of running a design through software to simulate building performance. 

Performance modeling can occur throughout the design process and inform decisions at all levels of a project. This article will discuss how an architect can use performance modeling throughout the architectural process, how it impacts design decisions and its importance. 

The Performance Modeling Process  

1. Testing Surface Area Volume

Performance modeling starts with testing high-level concepts known as “white box” or “shoebox models.” In the modeling software, your architect will analyze options for the building’s general shape or “massing.” 

This process provides two vital pieces of information. First, it helps your architect determine the most effective way to place the building on the site relative to the sun—the building’s solar orientation. Second, it shows the most efficient building proportions.   

The goal is to optimize the Surface Area Volume (SAV), the surface area (or building envelope) needed to create the building’s volume. Some shapes can create more volume with less surface area. For example, a cube requires less surface area to achieve the same amount of volume as a rectangular shape. 

Buildings with a large SAV have more surface area to diffuse energy, making them less efficient. An efficient building provides the desired volume with the least amount of surface. 

Lowering the SAV can reduce the size of the mechanical system since buildings with a larger SAV need to make up for heating and cooling lost through the envelope. It can also result in less exterior material, lower construction costs, and reduced maintenance.   

Many factors influence a building’s shape—including its program, site considerations, and zoning regulations. Performance modeling helps your architect find the most efficient option within the project’s constraints. 

2. Testing Window-to-Wall Ratio

Along with SAV, an architect can use performance modeling to determine the most efficient Window-to-Wall Ratio (WWR). 

WWR is the percentage of glazed surfaces (windows) compared to unglazed surfaces (walls). Although buildings lose energy through glazing, it’s necessary for daylighting and occupant well-being. The goal is to maximize daylighting without sacrificing energy efficiency. 

As WWR increases, the mechanical system size often needs to increase to compensate for lost energy. Your architect may need to account for this lost energy by redistributing windows or reorganizing interior spaces.  

The WWR only specifies the percentage of windows—not their placement. When determining window placement, your architect will consider the needs of occupants, their thermal comfort, and glare issues.

window to wall ratio on a building in Iowa City

WWR shows to percentage of windows compared to unglazed surfaces.

They should also consider the site’s characteristics. For example, Northwestern winds are a common feature of Midwestern winters. Limiting  Northwestern glazing and openings helps preserve efficiency and thermal comfort during cold months. 

In the earliest stages of the design process, solar orientation, SAV, and WWR are all in play. These factors have the greatest impact on building performance and the long-term cost of ownership. By testing options, your architect can find a solution that provides a pleasant occupant experience while maintaining efficiency.   

3. Testing Mechanical System Options 

In addition to solar orientation, SAV, and WWR, the mechanical system greatly affects energy efficiency and operating costs. Early modeling helps your architect understand the size of the mechanical system. As you progress through the architectural process, your architect can use performance modeling to test different mechanical system options. 

There are many types of mechanical systems, including: 

  • Variable Air Volume (VAV) rooftop units 
  • Boiler/chiller systems 
  • Variant Refrigerant Flow (VRF) systems 
  • Air source heat pumps 
  • Ground-source heat pumps 

Each option has an initial cost and a life cycle cost. Along with performance modeling, your architect should perform a life cycle cost analysis to help you understand the cost of utilities, maintenance, and replacements. 

Ideally, you will find an option that fits your initial budget and lowers the long-term costs of ownership. 

4. Fine-Tuning Building Systems 

As you progress through the design process, your architect can use performance modeling to fine-tune design decisions and maximize efficiency. Modeling can help with decisions related to all building systems, including: 

  • Types of glass 
  • Quantity of insulation 
  • HVAC zones 
  • Door selection 
  • Power and light controls 

Nearly every design decision has a performance implication. For example, improved window glazing can result in long-term energy savings.  

One way to measure the return on this investment is through payback periods—the number of years required for the energy savings to pay for the improvements. While glazing just above code requirements has a payback period of approximately 17 years, slightly higher-performative glazing has a payback period of just nine years.  

Investing in better glazing can also improve thermal comfort, especially for occupants sitting near windows. Comfortable occupants are less likely to adjust the thermostat, resulting in more energy savings.  

Building performance and occupant comfort are interconnected. Ideally, both these factors will stay in play during the design process.  

The Importance of Performance Modeling 

Performance modeling is one of the most important tools at an architect’s disposal. Rather than assume the best practices for improving performance, your architect can test ideas and back up decisions with data. 

Optimizing the solar orientation, SAV, and WWR provides a solid foundation that can be fine-tuned throughout the design process. 

If you are considering renewable energy sources like solar power, performance modeling sets you up for success. You may be able to hit your energy target with a smaller solar array because the building already performs optimally. 

Performance modeling should not add to the cost of a building project. Ideally, this research is part of the design process and included in the architectural fee. 

However, this research does not always occur, especially when the fee cannot account for the time and effort it takes. Investing in your architect can lead to solutions that improve efficiency and reduce the long-term costs of ownership. 

Learn More About Sustainable Design 

Improving performance is one of the most important aspects of any building project. Performance modeling allows your architect to test ideas and vet decisions at each stage of the design process—from high-level decisions like solar orientation, SAV, and WWR to more detailed decisions like HVAC zones. 

This type of research is one of the benefits of investing in architectural services. Your architect should help you improve efficiency, lower your operating costs, and achieve long-term value.

Performance modeling is most effective when the building receives a third-party inspection from a commissioning agent. Commissioning agents review construction documents and construction work to ensure the building operates as intended. 

Learn more by reading about commissioning and its benefits