Written by Kathy Berg, Partner at ZGF Architects.
As the need to combat climate change intensifies, desire for sustainable structures drives architecture toward deep efficiency. Our clients are increasingly interested in exploring net zero energy and the number of realized projects across the industry is growing.
And yet achieving NZE is still complex and difficult to achieve. The technology, systems, materials, and solutions that work for one project do not work seamlessly for another – requiring designers to pursue net zero with a flexible approach.
Chief among the issues that affect the design of a project targeting NZE are climate, user behavior, and jurisdictional constraints. Each project must consider how these factors interrelate to make the building operationally successful and create champions for more NZE buildings to follow.
Designers are tasked with providing occupants with a comfortable interior while minimizing energy use with systems that depend on the outside environment. Passive heating and cooling strategies must adapt to the local climate and HVAC and renewable energy systems must be tailored to optimize performance for that area.
At the Rocky Mountain Institute (RMI) Innovation Center in Basalt, Colorado, designers were challenged to meet the organization’s goal: creating the most efficient building within a 100-year structure possible while crafting a beautiful and high-performance workplace. Given its high altitude and location in one of the coldest U.S. climates, this was no small task. Coupled with 40° daily temperature swings and limited winter solar capacity due to the average 86” annual snowfall, standard design process was set aside in favor of an entirely new approach.
Nineteen different envelope studies of orientation, massing and thermal insulation resulted in the elimination of mechanical cooling and central heating systems. Even without traditional HVAC, the building prioritizes occupant comfort through a of passive strategies that provide optimal air speed and radiant surfaces and integrating a high-performance envelope with heat recovery ventilation. Notably, the project exceeds energy projections, generating 146% more energy annually than it used in the first year, and boasting a 99th percentile occupant satisfaction rating in thermal and visual comfort.
At the Conrad N. Hilton Foundation Headquarters, the culture of the staff needed to be transitioned from one of controlling a building to a culture of living “within” a building. This included everything from giving up the “suit and tie culture” in favor of dressing seasonally appropriate, to understanding that the building is healthier due to the 100% utilization of outside air. To ensure the building met its mission over its lifespan, users were asked to adjust their daily routine – including operating windows, wearing a sweater during colder months, and/or shutting off a computer at the end of the day. Even with the building systems operating largely as expected, the building fell short of its net zero energy goal after opening. The major culprit? A decorative fountain in the landscape that was not calculated as part of the project’s energy budget.
With each jurisdiction governed by unique regulations, NZE projects present a nuanced set of challenges for designers to navigate.
For the PAE Living Building, the first Living Building in Portland, Oregon, designers needed to be agile in their response to city regulations and forge new pathways for future NZE projects in Portland. While most NZE projects utilize the rooftop for solar panels, the City of Portland requires 60% green roof coverage to reduce storm water runoff, reduce the heat island effect, and create green space habitat within an urban center for wildlife. In order to have enough onsite area to meet Living Building Challenge NZE requirements, the rooftop received a waiver from the city by proving it met the intent of the ecoroof by collecting all storm water in a building cistern for water reuse. Designers proved the full roof coverage of PV panels has no effect on heat island as it absorbs the energy that would otherwise turn to heat. Lastly, the project team provided planting on the building facade and street level to mitigate the loss of green habitat on the roof, additionally purchasing habitat land within the city limits to preserve the land indefinitely.
What it takes to go net zero is dynamic. From climate to user behavior to jurisdictional constraints, each NZE structure presents a set of unique challenges that, when solved, create a pathway. The clearer the pathways become to achieving NZE, the more likely others are to follow.