Energy Modeling the ASHRAE 209 Way: Throughout Design and Beyond
July 2, 2018
Building energy modeling has become more common over the last decade or so, and it’s a standard practice for projects pursuing LEED certification. But there’s a problem: the later the team waits to start modeling the building, the more potential energy-saving opportunities have been missed along the way.
“Often building energy modeling is used near the end of the design process to justify points in incentive programs such as LEED,” said Jason Glazer, P.E., president and principal engineer at GARD Analytics, in an email to BuildingGreen. “But the real strength of building energy modeling is to provide input to design decisions throughout the entire design process.”
Introducing ASHRAE 209
Glazer is chair of the committee that developed ASHRAE 209, a new standard that lays out guidelines for an approach to modeling that informs the design rather than merely capturing the design’s energy implications after the fact. The standard includes but goes far beyond what we might think of as “early energy modeling”—an increasingly common practice used to analyze the energy-efficiency implications of different building orientations, massing, and other very early design decisions.
ASHRAE 209, formally known as Energy Simulation Aided Design for Buildings Except Low Rise Residential Buildings, advocates for modeling throughout design and even offers guidance for modeling after construction. “Buildings that were designed with the aid of building energy modeling throughout the design process are much more likely to be highly energy efficient,” claimed Glazer.
The standard explains how to best use energy modeling during 11 “modeling cycles,” listed here by design phase:
- Conceptual design—Simple box modeling (1) and conceptual design modeling (2)
- Schematic design—Load reduction modeling (3) and HVAC system selection (4)
- Design development—Design refinement (5) and design integration and optimization (6)
- Construction documents—Energy-simulation-aided value engineering (7)
- Construction and operations—As-designed performance (8), change orders (9), and as-built energy performance (10)
- Post-occupancy—Post-occupancy energy performance comparison (11)
Of all these, only “load reduction modeling” during schematic design and any one other design-phase modeling cycle is required for a project to comply with the standard.
Getting beyond guesses
Glazer described some of the decisions that design-phase energy modeling can help with: “Does a window overhang make more sense than higher-efficiency windows? What about when daylighting controls are being used? How about when coupled with a light shelf? These are tough questions,” he said, “and the answers can only be guesses when building energy modeling is not being used.”
Although architects may have gotten used to the idea of using software tools to do early energy modeling, ASHRAE 209 does not necessarily advocate that approach. “Architects can certainly use building energy modeling, and there are some tools designed specifically for them,” said Glazer, “but to truly take advantage of building energy modeling, a lot of specialized knowledge is needed.” Although an architect’s own early models may be informative, the new standard requires the modeler to be certified in the practice.
But isn’t that going to be costly?
Glazer says it’s not. “Owners realize that having a building energy modeler on the team from the start provides valuable insights into optimizing the design and yet is not costing much more than having them involved at just the end to do the LEED modeling,” he said.
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