No matter how the term is defined, setting and achieving a goal of net zero energy (NZE) use in buildings is audacious. Yet, market and regulatory trends are poised today to take us incrementally in that direction. And, while there is reason to be optimistic that new technologies will be developed to make NZE more attainable for a larger portion of the building stock, arguably the most rational and moral choice we have is not to wait, but to approach each new building project with a mindset of NZE.

A growing number of completed research studies along with experience gained by industry professionals from an increasing number of actual projects bring a more comprehensive understanding of what a NZE approach looks like, whether from the perspective of designer, constructor, owner or occupant. Each player needs to understand and invest in an integrated, interdependent and on-going process. Within this process, the engineer has opportunity to bring significant, critical valueadd.

As one example, mechanical engineers have traditionally been hired to provide energy modeling services, whether on the frontend to help inform design, or as a way of documenting predicted performance compared to a fictitious baseline building. A NZE methodology will require multiple "living" energy models that accurately predict actual future performance. These include whole building energy models, but also focus on individual pieces of equipment or systems. And, the models need to be informed by correct assumptions about the building's actual construction, occupancy and operation.

In a NZE project those "occupancy and operation" assumptions go from being something our industry often simply obtains from an ASHRAE Standard for purposes of sizing HVAC equipment or for incorporation into traditional energy models, to something that itself requires a highly detailed model. The NZE project team has presumably designed and constructed a highly thermally efficient building envelope with the most energy efficient equipment and systems and appropriate renewable energy resources. Now they must also consider finding ways to model the remaining big slices of the energy pie, ones that, given human behavior is at play, arguably carry the most uncertainty. Plug loads, for example, make modeling seemingly "simple" NZE residential projects potentially as challenging as any other building type.