High-Performance Building Retrofit

High-performance retrofit transforming a former shopping mall to new office space

Elizabeth Ratner from Little Diversified Architectural Consulting was recently a panelist on our September webinar hosted by Architectural Record. During the session, she used a (currently in-progress) retrofit project to illustrate her firm’s approach to Performance-Based Design. Specifically, she described how her team has kept the project on track to meet the ambitious Architecture 2030 Challenge, and how they presented analyses to inform design decisions that could save the client millions of dollars over the life of the building.

Here, we recap her presentation to illustrate a tactical approach that your project teams can readily adopt today to benefit from Performance-Based Design.

The Approach

Elizabeth Ratner leads the Center for Building Performance (CBP) at Little. The CBP’s purpose is to optimize environments for occupants and owners by ensuring increased occupant wellbeing, targeting a neutral capital investment, and reducing future operating costs.

Center for Building Performance at LITTLE

The CBP turns this mission into action by clarifying performance goals, defining performance-based design constraints, and supplying supporting analysis to the project team.

Thus, Little’s replicable approach to Performance-Based Design is fairly straightforward:

  1. Define the project’s performance goals;
  1. Provide designers with clear performance-based constraints, supplementing their progress with additional performance analysis and input as required; and
  1. Report progress toward, and achievement of, performance goals.

The following shows this approach in action, using a real-world, in-progress retrofit project seeking high-performance in the areas of energy use, daylighting, and cost.

The Project: Existing Building Conversion

The Little design team is working to convert a former shopping mall into an office building while meeting the Architecture 2030 Challenge. The image below illustrates the limits of the conversion: part of the shopping mall was converted several years ago, and this particular project is focused on the portion in green–a structure roughly 1,000 feet long and 300 feet deep. The scope of work extends from the building skin through to building interiors.

High-Performance Building Retrofit Scope of Work

As of this writing, the project is in the later stages of schematic design; however, to ensure successful pursuit of project performance goals, building performance was considered from day one. This began with setting appropriate performance goals.

Defining Performance Goals

The client’s aggressive goal of meeting the Architecture 2030 Challenge required a 70% reduction in Annual Energy Use per square foot, or Energy Use Intensity (EUI), compared to a regional average for office buildings.

Ratner’s CBP group used the Energy Star Target Finder to determine the target EUI for this project was 29.1 kBTU/ft2.

Such an aggressive goal would require all designers to work within reasonable and strategic bounds, and would also require performance analysis to be conducted frequently as the design evolved.

Performance-Based Constraints

With a specific performance-goal in hand (an EUI less than or equal to 29.1 kBTU/ft2) the CBP group set about defining design constraints to support their designers.

They began by blocking-in a viable design approach: Using a very simple Revit study model, they applied various potential design conditions informed by past experience and best practice. (For example, Ratner and her team added vertical glazing to the study model to create a 30% WWR and added skylights to cover 3% of the roof.)

Next, using Sefaira Systems and their Revit study model, Ratner’s team worked with the mechanical and electrical engineers to test various mechanical, lighting power density and skin options until they found a reasonable combination that achieved an EUI of 29.

The result of this effort was a clear skeleton solution providing performance-based constraints to bound the design team’s approach. The image below shows how the CBP communicated this design guidance to the designers, and, in turn, to the contractors who would need to understand the project’s goals and basic approach.

Performance-Based Design Guidance

In addition to the above architectural diagram, the team also produced the following energy profile (below). This energy budget–how energy would be used given the building’s assumed materials, construction, usage and systems, was intentionally not aggressive with plug loads at this stage: the team hadn’t yet reached that level of analysis with the owner, and, potential savings related to these loads served as a helpful buffer for the design team.

Energy Budget for Performance-Based Design

Supplemental Analysis

At this stage, the designers were well-armed to explore architectural facade treatments, fenestration changes, and internal space planning. As they did so, Ratner’s team continued to provide support, both regarding client requests and additional performance considerations.

HVAC Comparisons

With design work in progress, the client wanted to know whether the assumed HVAC system–underfloor air with a central plant and ice storage–should be replaced by a rooftop direct exchange system. Ratner’s team used the original study model, and input from the engineer and contractor to compare one system versus another from both an energy-use and cost standpoint:

Performance-Based Design Comparison

The Rooftop DX system would not support the EUI goal, and would incur a cost premium of several million dollars over 50 years.

The results were clear: the assumed system outperformed the rooftop direct exchange equipment, both from an energy and cost standpoint. Not only was the specific conclusion from this analysis valuable, so too was the speed and efficiency with which Ratner’s team delivered it:

“If we take more than a few days to turn around this kind of analysis when the client is only looking for a high-level comparison, ambiguity begins to erode a team’s commitment to aggressive goals.” Elizabeth Ratner, Center for Building Performance, Little

Daylighting Analysis

The original skeleton solution and energy budget assumed successful daylight harvesting to offset Lighting Power Density. What’s more, the project team recognized that adding views to the interior of this very deep building would be critical. As the design team refined their architectural approach, Ratner’s team conducted Daylighting Analysis in parallel to the designers’ work.

Daylighting Analysis per LEEDv4 metrics

The image above shows just one of many options the CBP considered for vertical glazing on the southeast side, which encloses an expanse of open office. It resulted in 31% of the floor area being either fully daylit or overlit per LEED standards.

The team conducted similar analyses on the northwest entry facade, where the designers desired a highly transparent aesthetic and a 20’ deep concourse allowed for the resulting overlit space.

Daylighting Performance

The final task was assessing roof glazing opportunities. The team tested a number of skylight options, with the goal of reducing overlit areas and concentrating them within circulation zones (see below).

Daylight Harvesting to offset Lighting Power Density

The Daylighting Analysis showed an estimated 85% of floor area receiving adequate natural light. The resulting potential to offset Lighting Power Density was in keeping with the initial energy budget’s expectations.

Reporting Progress and Achievement

You’ve seen the images the team used to communicate constraints and impacts of design decisions. Those same outputs can be used to communicate to all project stakeholders, including the client, how well the project is proceeding towards goals. Frequent assessment and communication is key to delivering high-performance designs.

The project team at Little is currently moving through the later stages of schematic design and into design development, all the while conducting and communicating further iterations of energy use impacts, lifecycle cost, and daylighting analysis. Beginning with specific goals, and ending with clear communication has ensured this project, and the project team, are on track to success with Performance-Based Design.

The Takeaway

Performance-Based Design is an approach to design, and as such, may require your design teams to change their current approach to consider new performance-based constraints. But as you can see, it’s imminently doable.

As long as clear goals are established, the pursuit of performance is intentionally supported, and progress is assessed and communicated often, your teams can begin delivering high-performance design solutions today.

Daylight Harvesting to offset Lighting Power Density

About Little and the Center for Building Performance

Little is an international architectural, engineering and consulting specialties firm with six offices. They strive to create a better future for people through breakthrough ideas and results beyond architecture. Elizabeth Ratner directs the Center for Building Performance (CBP) at Little. The CBP works to optimize environments for occupants and owners by ensuring increased occupant wellbeing, targeting a neutral capital investment, and reducing future operating costs.

Center for Building Performance at LITTLE

The Center bridges architecture and engineering in a very intentional way: it adds value by providing high-quality, quantitative feedback to architects in early design and tracking the progress of a project toward its goals throughout the design process.