What style of energy modeling is right for a project?

By Kim Shinn and Kjell Anderson, AIA, October 24, 2018.

How a new ASHRAE standard can help you improve a project’s cost-effectiveness and energy use.

A decade ago, energy modeling became popular as part of LEED and energy code compliance. But ‘compliance’ modeling, as it is known, often isn’t very effective at reducing energy use and controlling cost. Why? Because it usually happens after the design is mostly complete. But several styles of early energy modeling are growing in popularity, proving to be more effective than predecessors.

Compliance versus early energy modeling
Compliance modeling occurs late in the design development and construction documents phases. Early energy modeling is used to inform fundamental design team decisions about passive and active building design and needs to take place in the concept or schematic design phases.

Most architects don’t realize how much their early design massing and fenestration choices affect the ultimate size and cost of mechanical systems. Early energy modeling allows us to understand the most cost-effective, creative way to use our design talents to reduce the size and cost of mechanical systems, which help us reduce energy use and costs. Without early modeling, we have limited data to recommend strategies that may actually meet client goals.

A common language: ASHRAE Standard 209
As firms become more familiar with energy modeling, we need a more nuanced understanding of the different scopes that architects, engineers, and owners might want on a given project. To help our entire industry, ASHRAE put together a 20-page, easy-to-use framework. Energy modeling concepts and approaches in this framework are not new, but the new standard applies a common language that is easy to understand and communicate across the project team and to describe scope within contracts and expectations for coordination

Many architects have never cracked open an ASHRAE publication, but Standard 209 is surprisingly accessible. It includes definitions and concise descriptions of 11 different energy modeling scopes, referred to as ‘cycles.’ Seven of these cycles describe design-phase modeling, each with specific goals coordinated in the typical design process. The standard also outlines three additional modeling cycles for construction and operation phases, including a design and post-occupancy performance comparison. These features help owners and modelers understand the impact of design phase modeling assumptions and inform future modeling choices.

ASHRAE particularly emphasizes the importance of early energy modeling in the first four cycles, focusing on aspects like climate analysis and evaluating passive design techniques. Architects can make the biggest impact by making choices and recommendations based on the early cycles.

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