Nearly two decades after the 2030 Challenge was issued by Architecture 2030, approximately 40% of all U.S. architecture firms have signed up. In 2019, LSW Architects added its name to the list of signatories in pursuit of designing healthy, responsible and carbon-neutral buildings. This commitment has led to a multi-year effort to alter current design and construction practices and realize significant reductions in the use of natural resources, non-renewable energy sources and waste production, while promoting regeneration of natural resources.
Stepping back, the 2030 Challenge has led to an industry-wide shift in focus towards energy performance and Energy Use Intensity (EUI) in buildings. Overall, this push for large reductions in energy consumption has been centered around efficiency and replacing non-renewable energy sources with renewable options. What this means for most buildings is a close look at the two major systems responsible for more than half of all US-based household energy consumption: heating and cooling. Obviously, the mechanical systems for both are great places to start thinking about a major reduction in energy consumption and CO2 emissions – both of which play a key role in meeting the Paris Climate Agreement’s 1.5’C carbon budget. However, greater efficiency and renewable energy aren’t the only options available to us.
At a design level, Passive Design strategies can bolster an energy-efficient building by allowing nature to do some of the hard work with us. For anyone new to Passive Design strategies or those who are curious about learning more, we wanted to break down the definition, pros and practical details that help explain how this design approach provides big impacts at little to no cost in pursuit of the 2030 Challenge.
Eco-Conscious and Energy-Conscious
Passive Design strategies approach the 2030 Challenge from an energy elimination and load reduction framework rather than an energy efficiency framework. The intent is to reduce the need to use energy through formal design decisions.
Passive Design strategies work with the local climate and surrounding environment to maintain a comfortable indoor environment. A passively designed building aims to eliminate or reduce the need for heating and cooling from “active” systems, like an air conditioning unit, and instead, work with the physics of conduction, convection, radiation and evaporation.
Design strategies focus on daylighting, natural ventilation, thermal mass and the building’s orientation, and are thoughtfully deployed to naturally achieve thermal comfort. Thermal comfort is closely related to passive design and is evaluated based on the combination of humidity, air speed, air temperature, radiant temperature, metabolic rate and clothing insulation.
Nested in Global Culture and History
Passive design isn’t a novel approach in architecture. Before mechanical heating and cooling systems were commonly utilized in the built environment, buildings and homes had to mediate the natural environment through building form and by responding to the surrounding context. This early typology of climate-responsive architecture typically falls within the realm of vernacular architecture.
"Vernacular architecture is defined as being constructed from local materials to suit its native setting, indigenous climate, and specific local needs." American Institute of Architects
Vernacular architecture is closely related to its context and is strongly influenced by the surrounding climate and culture. From Igloos in the arctic to Queenslanders down-under in Australia, vernacular architecture had to meet the thermal comfort needs of occupants through passive heating, passive cooling and natural ventilation strategies. The igloo, for example, capitalizes on the low surface area to volume ratio of spheres to reduce heat loss from the interior space. The thick snowpack also works as an excellent insulator to keep the heat from escaping through the walls. Additionally, the entrance of an igloo is constructed with a tunnel that dips down and then ramps up into the space. This key design feature places the sleeping area up high to benefit from the physics principle that lighter, warmer air rises while cool air sinks. Within an igloo, hot air fills the top of the dome while the shape and materiality of the structure keeps the heat inside the space - no fancy technology needed!
Passive heating, or passive solar heating, means trapping heat from the sun inside your home and using thermal mass, heat flow and insulation effectively to store, distribute and retain the heat. This means relying on greenhouse principles to trap solar radiation. Heat is gained when shortwave radiation from the sun passes through glass, where it is absorbed by building elements and furnishings and re-radiated as longwave radiation. Longwave radiation cannot pass back through glass as easily as shortwave radiation, so the temperature inside the room increases. This is what makes the combination of direct gain glazing and thermal mass (masonry floors, walls or ceilings) so effective.
Thoughtfully placed glazing can keep a space warm during the day while materials with high mass absorb, store and release heat during the nighttime hours. In the Northern Hemisphere, passive heating strategies are most often deployed on the South side of a building or space to benefit directly from the sun’s position. Sunspaces, thermal mass walls and floors and skylights are excellent passive heating strategies to consider from the start of design.
On the other hand, passive cooling means using strategies to reduce heat gain and increase heat loss. Passive cooling strategies are intricately connected to passive ventilation. Passive cooling is different from passive heating in that the natural environment does not ubiquitously provide a source of “cold energy” in the same way that the sun provides heat energy. Remember, heat is a form of energy - thermal energy and temperature is a measurement of the kinetic energy (including thermal energy) within an object. Consequently, there are a lot more ways to heat an object than there are to cool an object. The first law of thermodynamics states that energy cannot be created or destroyed. So, in passive cooling you cannot “destroy” the heat energy, you must use it or avoid it in the first place. Evaporative cooling is an excellent example of cooling. When a liquid gets enough energy to become a gas, it goes through a phase transition which takes energy – thus leaving the liquid with lower energy and a colder temperature.
Ventilation strategies do not inherently change the temperature of a space. They just help circulate air and create perceived thermal comfort. Natural ventilation uses natural forces such as buoyancy and wind to drive air through space and can be used for both ventilation and cooling.
With passive cooling, building envelopes are designed to minimize daytime heat gain, maximize night-time heat loss and encourage ventilation when available. Some strategies include:
- Earth coupling or earth sheltering
- Evaporative cooling tower
- Solar shading
- Vegetative buffers
- Cross ventilation
- Stack ventilation
- Nighttime cooling
Critical to Long-Term Climate Impact
Passive design is crucial to architecture’s role in addressing global climate change. Architecture can be a positive force or a negative force in the efforts against global warming. A passively designed building can eliminate the need for human-made energy to heat, cool and illuminate interior spaces. For hundreds of thousands of years, people all over the world used formal, natural strategies to mitigate and manage the climate around them. Today, we often default to the energy-intensive technologies available to us because of their convenience and our changing threshold for thermal comfort. However, if we are going to hit the 2030 Challenge target of net-zero energy buildings by 2030, architecture will need to rely on passive systems and intuitive, climate-responsive design.
LSW recently began a six-part, in-house sustainability training series to increase baseline literacy and promote designer confidence surrounding major sustainability topics. One of these training courses was focused on passive design strategies. This blog post was adapted from the session on Passive Design Strategies.
If you are interested in learning more about this topic, please reach out to Courtney Jones (email@example.com)